JP6885802B2 - Secondary battery - Google Patents

Description

The homogeneity of the present invention relates to a product, a method, or a manufacturing method. Alternatively, the present invention relates to a process, machine, manufacture, or composition (composition of matter). One aspect of the present invention relates to a semiconductor device, a display device, a light emitting device, a power storage device, a lighting device or an electronic device, or a method for manufacturing the same. In particular, the present invention relates to a positive electrode active material that can be used for a secondary battery, a secondary battery, and an electronic device having the secondary battery.

In addition, in this specification, a power storage device refers to an element having a power storage function and a device in general. For example, it includes a storage battery (also referred to as a secondary battery) such as a lithium ion secondary battery, a lithium ion capacitor, an electric double layer capacitor, and the like.

Further, in the present specification, the electronic device refers to all devices having a power storage device, and an electro-optical device having a power storage device, an information terminal device having a power storage device, and the like are all electronic devices.

In recent years, various power storage devices such as lithium ion secondary batteries, lithium ion capacitors, and air batteries have been actively developed. Lithium-ion secondary batteries, which have particularly high output and high energy density, are mobile information terminals such as mobile phones, smartphones, tablets, or notebook computers, portable music players, digital cameras, medical devices, or hybrid vehicles (HEVs). Demand for next-generation clean energy vehicles such as electric vehicles (EVs) or plug-in hybrid vehicles (PHEVs) is expanding rapidly with the development of the semiconductor industry, and modern information is available as a source of rechargeable energy. It has become indispensable to the computerized society.

The characteristics required for a lithium-ion secondary battery include further increase in energy density, improvement in cycle characteristics, safety in various operating environments, and improvement in long-term reliability.

Therefore, improvement of the positive electrode active material is being studied with the aim of improving the cycle characteristics and increasing the capacity of the lithium ion secondary battery. (Patent Document 1 and Patent Document 2)

Japanese Unexamined Patent Publication No. 2012-018914 JP 2015-201432

The lithium ion secondary battery and the positive electrode active material layer used therein have room for improvement in various aspects such as charge / discharge characteristics, cycle characteristics, reliability, safety, or cost.

Lithium-ion secondary batteries are required to have a high energy density that further increases the discharge capacity (which can be said to be the volume capacity density) per unit volume of the positive electrode plate. A high electrode density is required for a positive electrode for obtaining a lithium ion secondary battery having a high energy density. Further, when the average particle size of the positive electrode active material is large, a high electrode density can be obtained. Further, in order to obtain a high electrode density, press working may be performed. The high electrode density is indexed by the tap density and compression density of the active material, and the compression density is particularly highly correlated with the electrode density. In the present specification, the true density is a value obtained by dividing the mass by the volume of the object itself excluding the surface of the object and the pores inside, and the tap density is a value obtained by filling a container with powder, vibrating it, and filling it. It is the bulk density measured in the above, and may be less than the true density.

On the other hand, when the electrode density is increased by pressing, the battery capacity in the charge / discharge cycle tends to decrease.

One aspect of the present invention is to provide a secondary battery having a positive electrode active material layer having a high electrode density.

Alternatively, one aspect of the present invention is to provide a secondary battery in which a decrease in battery capacity during a charge / discharge cycle is suppressed. Alternatively, one aspect of the present invention is to provide a high-capacity secondary battery. Alternatively, one aspect of the present invention is to provide a secondary battery having excellent charge / discharge characteristics. Alternatively, one aspect of the present invention is to provide a secondary battery having high safety or reliability.

Alternatively, one aspect of the present invention is to provide a novel secondary battery or a method for producing the same.

The description of these issues does not prevent the existence of other issues. It should be noted that one aspect of the present invention does not need to solve all of these problems. It is possible to extract problems other than these from the description, drawings, and claims.

In order to achieve the above object, one aspect of the present invention is a carbon material having a small specific surface area as a conductive auxiliary agent to be mixed with a positive electrode active material containing lithium, specifically, a fiber such as a carbon fiber ^{having a specific surface area of less than 60 m 2 / g.} A similar material (for example, carbon nanotube (also called CNT)) is used. Since the specific surface area is ^{as small as less than 60 m 2} / g, there is little aggregation and friction with itself and the active material is also small, so that a uniform high electrode density can be obtained after press working. Further, in addition to carbon fibers (specific surface area of ^{less than 60 m 2} / g), carbon black having a specific surface area of 60 m ² / g or more may be mixed as a conductive auxiliary agent. Carbon fiber can disperse pressure and improve strength. Since the conductive path can be efficiently formed even with a small amount of carbon fiber, it is not necessary to reduce the amount of the active material supported, which is particularly preferable.

Further, the carbon fiber having a specific surface area of ^{less than 60 m 2} / g is a structure that maintains the shape of the positive electrode active material layer, and also functions as a cushioning material in the pressing process. The electrode density of the positive electrode active material layer is 4.0 g / cm by applying a slurry in which a positive electrode active material and ^{a carbon fiber having a specific surface area of less than 60 m 2 / g are mixed and firing, and then pressing at a pressure of 1050 kN / m or more.} It can be ^{3 or more.}

Further, by pressing at a pressure of 1450 kN / m or more, the electrode density of the positive electrode active material layer can be set ^{to 4.3 g / cm 3 or more.}

On the other hand, when only fine particles such as carbon black, typically acetylene black, are used as the conductive auxiliary agent, agglomeration of the fine particles occurs and a uniform electrode density can be obtained even when pressed with a high pressing pressure. Have difficulty. The fine particles have a large specific surface area of 60 m ² / g or more and a large friction. Therefore. If the friction is large, it will be less likely to be clogged when pressed. Therefore, it is preferable to use a carbon material having a ^{specific surface area of less than 60 m 2} / g and at least a hollow as the conductive auxiliary agent. Since it is a hollow carbon material, it also functions as a cushioning material in a high pressing process of 1050 kN / m or more, and it is possible to reduce the occurrence of cracks in the active material particles. The hollow material is not limited to carbon fibers, and a plurality of types of single-walled carbon nanotubes (SWNTs) and multi-walled carbon nanotubes (MWNTs) can be used as carbon nanotubes.

Further, another aspect of the present invention is a secondary battery having the positive electrode active material or a positive electrode having a conductive auxiliary agent in contact with the positive electrode active material and a negative electrode. The positive electrode is produced by applying an active material solution containing a conductive auxiliary agent or a binder to one or both sides of a metal foil that functions as a positive electrode current collector, drying the metal leaf, and then pressing the metal leaf to increase the electrode density. .. The electrode density is the achieved density when the linear pressure under the press pressure is the same. The linear pressure is an index indicating the forming pressure per unit length in the width direction of the roll to be pressed.

Further, as the secondary battery, various shapes can be used according to the device to be used, and examples thereof include a cylindrical shape, a square shape, a coin shape, a laminated type (flat plate) shape and the like.

The electrode density of the positive electrode active material layer can be adjusted to 4.0 g / cm ³ or more by mixing the positive electrode active material and ^{carbon fibers having a specific surface area of less than 60 m 2 / g and pressing at a pressure of 1050 kN / m or more.} It is possible to suppress the decrease in the charge / discharge cycle at the 100th charge / discharge cycle to less than 15% in the measurement of the charge / discharge cycle.

High-density filling with a positive electrode active material layer having an electrode density of 4.0 g / cm ³ or more, preferably 4.3 g / cm ³ or more is possible, and the battery capacity per unit volume is increased, resulting in a high capacity. A secondary battery can be realized.

Alternatively, it is possible to realize a secondary battery in which a decrease in battery capacity in the charge / discharge cycle is suppressed. Alternatively, one aspect of the present invention can realize a secondary battery with high safety or reliability.

It is a figure explaining the peripheral part of the positive electrode active material which shows one aspect of this invention. The figure explaining the sol-gel method. The figure explaining the charging method of a secondary battery. The figure explaining the charging method of a secondary battery. The figure explaining the discharge method of a secondary battery. The figure explaining an example of an electronic device. The figure explaining an example of an electronic device. The figure explaining an example of an electronic device. Cross-sectional SEM photograph. The graph which shows the relationship between the electrode density and the press pressure. Data showing charge / discharge cycle characteristics.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. However, the present invention is not limited to the following description, and it is easily understood by those skilled in the art that the form and details thereof can be changed in various ways. Further, the present invention is not construed as being limited to the description contents of the embodiments shown below.

In each of the figures described in the present specification, the size and thickness of each component such as the positive electrode, the negative electrode, the active material layer, the separator, and the exterior body are exaggerated individually for the purpose of clarifying the explanation. In some cases. Therefore, each component is not necessarily limited to its size, nor is it limited to the relative size between the components.

(Embodiment 1)
First, the positive electrode active material 100a and its surroundings, which is one aspect of the present invention, will be described with reference to FIG. In FIG. 1, three positive electrode active materials 100a, 100b, and 100c are shown, and carbon fibers 131a, 131b and a binder 130 are shown between them.

The carbon fibers 131a and 131b are hollow carbon materials, which function as a conductive auxiliary agent and also as a cushioning material. In addition, since the specific surface area is smaller than that of AB (acetylene black), which is one of the carbon materials, there is less aggregation and less friction with itself and the active material, so that a uniform density can be obtained after press working. .. In particular, even when the press pressure is as high as 1050 kN / m or more, it functions as a cushioning material, so that a high-density electrode can be obtained. The carbon fiber 131a shown in FIG. 1 has a fiber length of 1 μm or more and 20 μm or less, and a fiber diameter of 70 nm or more. The carbon fiber 131a may have a finer fiber diameter of 10 nm or more and 40 nm or less, or may have a fiber length of 100 μm or more. The carbon fiber 131b shows a cross section in the length direction, and the carbon fiber 131a is cut in the cross section, and a circular diameter is shown.

The structure will be described by taking one positive electrode active material 100a as an example. The positive electrode active material 100a has a first region 101 inside, and has a second region 102 and a third region 103 on the surface layer portion. As shown in FIG. 1, the second region 102 does not have to cover all of the first region 101. Similarly, the third region 103 may not cover all of the second region 102. Further, a third region 103 may exist in contact with the first region 101.

Further, the thickness of the second region 102 and the third region 103 may vary from place to place.

Further, the third region 103 may exist inside the positive electrode active material 100a. For example, when the first region 101 is polycrystalline, the third region 103 may exist in the vicinity of the grain boundary. Further, the third region 103 may be present in the portion of the positive electrode active material 100a having a crystal defect, the crack portion, and the vicinity thereof. In FIG. 1, a part of the grain boundary is shown by a dotted line. In the present specification and the like, the crystal defect means a defect that can be observed in a TEM image or the like, that is, a structure or cavity in which another element is contained in the crystal.

Similarly, as shown in FIG. 1, the second region 102 may exist inside the positive electrode active material 100a. For example, when the first region 101 is polycrystalline, the second region 102 may exist in the vicinity of the grain boundary. Further, the second region 102 may be present in the portion of the positive electrode active material 100a having a crystal defect, the crack portion, and the vicinity thereof. Further, the third region 103 and the second region 102 inside the positive electrode active material 100a may overlap.

<First area 101>
The first region 101 has a composite oxide of lithium and a first transition metal. Further, the first region 101 may be said to have lithium, a first transition metal, and oxygen.

The composite oxide of lithium and the first transition metal preferably has a layered rock salt type crystal structure.

As the first transition metal, only cobalt may be used, two kinds of cobalt and manganese may be used as the first transition metal, and three kinds of cobalt, manganese and nickel may be used.

That is, the first region can have lithium cobalt oxide, lithium manganate, lithium nickel oxide, lithium cobalt oxide in which a part of cobalt is replaced with manganese, lithium nickel-manganese-lithium cobalt oxide, and the like. Further, the first region 101 may have a metal other than the transition metal such as aluminum in addition to the transition metal.

The first region 101 functions as a region particularly contributing to the charge / discharge reaction in the positive electrode active material 100. In order to increase the capacity when the positive electrode active material 100 is used in the secondary battery, it is preferable that the first region 101 has a larger volume than the second region and the third region.

A material having a layered rock salt type crystal structure has features such as a high discharge capacity and low resistance because lithium can be diffused two-dimensionally, and is preferable as the first region 101. Further, when the first region 101 has a layered rock salt type crystal structure, segregation of a typical element such as magnesium, which will be described later, is unexpectedly likely to occur.

The first region 101 may be a single crystal or a polycrystal. For example, the first region 101 may be a polycrystal having an average crystallite size of 280 nm or more and 630 nm or less. In the case of polycrystal, grain boundaries may be observed by TEM or the like. The average crystal grain size can be calculated from the half width of XRD.

Since polycrystals have a clear crystal structure, a two-dimensional diffusion path for lithium ions is sufficiently secured. In addition, it is preferable as the first region 101 because it is easier to produce than a single crystal.

Further, not all of the first region 101 need to have a layered rock salt type crystal structure. For example, a part of the first region 101 may be amorphous or may have another crystal structure.

<Second area 102>
The second region 102 has an oxide of the second transition metal. It may be said that the second region 102 has a second transition metal and oxygen.

As the second transition metal, it is preferable to use a metal having an indefinite specificity. It may be said that the second region 102 preferably has an indefinite ratio compound. For example, at least one of titanium, vanadium, manganese, iron, chromium, niobium, cobalt, zinc, zirconium, nickel and the like can be used as the second transition metal. However, the second transition metal is preferably an element different from that of the first transition metal.

In the present specification and the like, a metal having an indefinite ratio means a metal having a plurality of valences. The non-stoichiometric compound refers to a compound of a metal having a plurality of valences and other elements.

The second region 102 preferably has a rock salt type crystal structure.

The second area 102 functions as a buffer area connecting the first area 101 and the third area 103, which will be described later. The interatomic distance of the non-stoichiometric compound can be changed by changing the valence of the metal contained in the non-stoichiometric compound. In addition, non-stoichiometric compounds often form cation or anion deficiencies and dislocations (so-called magnetic phases). Therefore, the second region 102 can be used as a buffer region to absorb the strain generated between the first region 101 and the third region 103.

Further, the second region 102 may have lithium in addition to the second transition metal and oxygen. For example, it may have lithium titanate, lithium manganate, and the like. Further, the second region 102 may have a typical element possessed by the third region 103, which will be described later. It is preferable that the second region 102 contains an element contained in the first region 101 including lithium and an element contained in the third region 103 as the buffer region.

That is, the second region 102 can have lithium titanate, titanium oxide, vanadium oxide, manganese oxide, iron oxide, copper oxide, chromium oxide, niobium oxide, cobalt oxide, zinc oxide and the like.

Further, the second region 102 may have a first transition metal. For example, the second transition metal may be present in a part of the first transition metal site of the composite oxide having the first transition metal.

Further, the second region 102 may have fluorine.

The second region 102 preferably has a rock salt type crystal structure, but not all of the second region 102 need to have a rock salt type crystal structure. For example, the second region 102 may have other crystal structures such as a spinel type crystal structure, an olivine type crystal structure, a corundum type crystal structure, and a rutile type crystal structure.

Further, as long as the structure in which 6 oxygen atoms are adjacent to the cation is maintained, the crystal structure may be distorted. In addition, a part of the second region 102 may have a cation deficiency.

Further, a part of the second region 102 may be amorphous.

If the second region 102 is too thin, the function as a buffer region deteriorates, but if it becomes too thick, the capacity may decrease. Therefore, the second region 102 preferably exists up to 20 nm, more preferably 10 nm in the depth direction from the surface of the positive electrode active material 100. The second transition metal may also have a concentration gradient.

<Third area 103>
The third region 103 has a compound of a main group element. A compound of a main group element is a compound having a constant specificity. As the compound of the main group element, for example, at least one of magnesium oxide, calcium oxide, beryllium oxide, lithium fluoride, and sodium fluoride can be used.

The third region 103 is a region that comes into contact with the electrolytic solution when the positive electrode active material 100 is used in the secondary battery. Therefore, the material used for the third region 103 is preferably a material that has little electrochemical change in the process of charging and discharging and is not easily deteriorated by contact with the electrolytic solution. A compound of a typical element that is electrochemically stable because it is a non-stoichiometric compound is preferable as the third region 103. By having the third region 103 on the surface layer portion of the positive electrode active material 100, the stability in charging and discharging of the secondary battery can be improved. Here, the high stability of the secondary battery means that, for example, the crystal structure of the composite oxide containing lithium and the first transition metal contained in the first region 101 is more stable. Alternatively, it means that the change in the capacity of the secondary battery is small even if charging and discharging are repeated. Alternatively, it means that the change in the valence of the metal of the positive electrode active material 100 is suppressed even after repeated charging and discharging.

Further, the third region 103 may have fluorine. When the third region 103 has fluorine, some of the anions in the compound of the main group element may be substituted with fluorine.

By partially substituting the anions in the compound of the main group element with fluorine, for example, the diffusibility of lithium can be enhanced. Therefore, even if the third region 103 exists, it is difficult to prevent charging / discharging. Further, the presence of fluorine on the surface layer of the positive electrode active material particles may improve the corrosion resistance to hydrofluoric acid generated by the decomposition of the electrolytic solution.

Further, the third region 103 may have lithium, a first transition metal and a second transition metal.

Further, the compound of the main group element contained in the third region 103 preferably has a rock salt type crystal structure. When the third region 103 has a rock salt-type crystal structure, the orientation of the crystal tends to match that of the second region 102. When the crystal orientations of the first region 101, the second region 102, and the third region 103 are substantially the same, the second region 102 and the third region 103 can function as a more stable coating layer.

However, not all of the third region 103 need to have a rock salt type crystal structure. For example, the third region 103 may have other crystal structures such as a spinel type crystal structure, an olivine type crystal structure, a corundum type crystal structure, and a rutile type crystal structure.

Further, as long as the structure in which six oxygens are adjacent to the cation is maintained, the crystal structure may be distorted. In addition, a part of the third region 103 may have a cation deficiency.

Further, a part of the third region 103 may be amorphous.

If the third region 103 is too thin, the function of improving stability in charging / discharging is deteriorated, but if it is too thick, the capacity is lowered. Therefore, the thickness of the third region is preferably 0.5 nm or more and 50 nm or less, and more preferably 0.5 nm or more and 2 nm or less.

When the third region 103 has fluorine, it is preferable that the fluorine exists in a bonded state other than _{magnesium fluoride (MgF 2} ), lithium fluoride (LiF), and cobalt fluoride (CoF _2). Specifically, when the vicinity of the surface of the positive electrode active material 100 is analyzed by XPS, the peak position of the binding energy of fluorine is preferably 682 eV or more and 685 eV or less, and more preferably about 684.3 eV. This is the binding energy that does not match any _{of MgF 2} , LiF, and CoF _2.

In the present specification and the like, the peak position of the binding energy of a certain element in XPS analysis means the value of the binding energy at which the intensity of the energy spectrum is maximized in the range corresponding to the binding energy of the element. To do.

In general, the positive electrode active material has side reactions such as elution of the first transition metal such as manganese, cobalt, and nickel into the electrolytic solution, oxygen release, and instability of the crystal structure as the charge and discharge are repeated. Occurs, and deterioration progresses. However, the cathode active material 100, which is one aspect of the present invention, has both a second region 102 that functions as a buffer region and a third region 103 that is electrochemically stable. Therefore, it is possible to effectively suppress the elution of the first transition metal and make the crystal structure of the composite oxide containing lithium and the transition metal contained in the first region 101 more stable. Therefore, the cycle characteristics of the secondary battery having the positive electrode active material 100 can be significantly improved. Further, when charging / discharging is performed at a voltage exceeding 4.3 V (vs. LiLi +), particularly a high voltage of 4.5 V (vs. LiLi +) or more, the configuration of one aspect of the present invention exerts a remarkable effect. ..

[Particle size]
If the particle sizes of the positive electrode active materials 100a, 100b, and 100c are too large, it becomes difficult to diffuse lithium, and if they are too small, it becomes difficult to maintain the crystal structure described later. Therefore, D50 (also referred to as median diameter) is preferably 5 μm or more and 100 μm or less, and more preferably 10 μm or more and 70 μm or less.

Further, in order to increase the density of the positive electrode active material layer, large particles (the longest part is about 20 μm or more and about 40 μm or less) and small particles (the longest part is about 3 μm) are mixed, and the gaps between the large particles are made small particles. It is also effective to fill with. Therefore, there may be two or more peaks of the particle size distribution.

The particle size of the positive electrode active material is influenced not only by the particle size of the starting material but also by the ratio of lithium contained in the starting material to the first transition metal (hereinafter referred to as Li to the first transition metal ratio). receive.

When the particle size of the starting material is small, it is necessary to grow the particles during firing in order to bring the particle size of the positive electrode active material into the above-mentioned preferable range.

In order to promote grain growth during calcination, it is effective to make the ratio of the starting material Li to the first transition metal metal more than 1, that is, to make lithium slightly excessive. For example, when the ratio of Li to the first transition metal is about 1.06, it is easy to obtain a positive electrode active material having a D50 of 15 μm or more. As will be described later, lithium may be lost to the outside of the system during the process of producing the positive electrode active material. Therefore, the ratio of lithium to the first transition metal in the finished positive electrode active material is the starting material lithium and the first transition metal. It may not match the ratio of transition metals in.

However, if the amount of lithium is excessive in order to keep the particle size within a preferable range, the capacity retention rate when used in a secondary battery may decrease.

However, by providing the second region 102 having the second transition metal on the surface layer portion, the positive electrode active material having a high capacity retention rate while keeping the particle size in a preferable range by controlling the ratio of Li and the first transition metal. Can be produced.

In the case of a positive electrode active material in which a region having a second transition metal is provided on the surface layer portion, the ratio of the starting material Li to the first transition metal is preferably 1.00 or more and 1.07 or less, and 1.03 or more and 1 It is more preferably .06 or less.

[Formation of the second region]
The second region 102 can be formed by coating particles of a composite oxide having lithium and a first transition metal with a material having a second transition metal.

As a method for coating a material having a second transition metal, a liquid phase method such as a sol-gel method, a solid phase method, a sputtering method, a vapor deposition method, a CVD (chemical vapor deposition) method, and a PLD (pulse laser deposition) method are used. ) Laws and other methods can be applied. In the present embodiment, a case where a sol-gel method, which can be expected to have a uniform coating and can be treated at atmospheric pressure, is applied will be described.

<Sol-gel method>
A method of coating a material having a second transition metal by applying the sol-gel method will be described with reference to FIG.

First, the alkoxide of the second transition metal is dissolved in the alcohol.

FIG. 2 (A-1) shows a general formula of the alkoxide of the second transition metal. M2 in the formula of FIG. 2 (A-1) indicates the alkoxide of the second transition metal. R represents an alkyl group having 1 to 18 carbon atoms or an aryl group having a substituted or unsubstituted carbon number of 6 to 13 carbon atoms. Further, although FIG. 2 (A-1) shows a general formula when the second transition metal is tetravalent, one aspect of the present invention is not limited to this. The second transition metal may be divalent, trivalent, pentavalent, hexavalent or heptavalent. In this case, the alkoxide of the second transition metal has an alkoxy group corresponding to the valence of the second transition metal.

FIG. 2 (A-2) shows a general formula of titanium alkoxide used when titanium is applied as the second transition metal. R in FIG. 2 (A-2) represents an alkyl group having 1 to 18 carbon atoms or an aryl group having a substituted or unsubstituted carbon number of 6 to 13 carbon atoms.

For example, as titanium alkoxide, tetramethoxytitanium, tetraethoxytitanium, tetra-n-propoxytitanium, tetra-i-propoxytitanium (tetraisopropyl orthotitanium, titanium (IV) isopropoxide, titanium tetraisopropoxide (IV), TTIP, etc. (Sometimes referred to as), tetra-n-butoxytitanium, tetra-i-butoxytitanium, tetra-sec-butoxytitanium, tetra-t-butoxytitanium and the like can be used.

FIG. 2 (A-3) shows the chemical formula of titanium (IV) isopropoxide (TTIP), which is one of the titanium alkoxides described in the production method described later.

Alcohols are preferable as the solvent for dissolving the alkoxide of the second transition metal, and for example, methanol, ethanol, propanol, 2-propanol, butanol, 2-butanol and the like can be used.

Next, particles of a composite oxide having lithium, transition metal, magnesium and fluorine are mixed with an alcohol solution of the alkoxide of the second transition metal, and the mixture is stirred in an atmosphere containing water vapor.

When _{placed in an atmosphere containing H 2} O, hydrolysis of water and the alkoxide of the second transition metal occurs as shown in FIG. 2 (B). Subsequently, dehydration condensation occurs between the products of FIG. 2 (B) as shown in FIG. 2 (C). By repeating the hydrolysis shown in FIG. 2 (B) and the condensation reaction shown in FIG. 2 (C), a sol of the oxide of the second transition metal is produced. This reaction also occurs on the composite oxide particles 110 as shown in FIGS. 2 (D-1) and 2 (D-2), and a layer containing the second transition metal is formed on the surface of the particles 110.

Then, the particles 110 are collected and the alcohol is vaporized. Details of the manufacturing method will be described later.

In this embodiment, an example of coating a material having a second transition metal before applying particles of a composite oxide having lithium, a first transition metal, a main group element, and fluorine to a positive electrode current collector. However, one aspect of the present invention is not limited to this. A positive electrode active material layer containing particles of lithium, a first transition metal, a typical element, and a composite oxide having fluorine is formed on the positive electrode current collector, and then both the positive electrode current collector and the positive electrode active material layer are formed on the positive electrode current collector. The material having the second transition metal may be coated by immersing it in an alkoxide solution of the second transition metal.

[Segregation of the third region]
The third region 103 can also be formed by a method such as a sputtering method, a solid phase method, a liquid phase method such as a sol-gel method, or the like. In particular, when a typical element source such as magnesium and a fluorine source are mixed with the material of the first region 101 and then heated, the typical element segregates on the surface layer portion of the positive electrode active material particles to form the third region 103. Can be done. Further, when the third region 103 formed in this manner is provided, the positive electrode active materials 100a, 100b, and 100c having excellent cycle characteristics are obtained.

When the third region 103 is formed by heating as described above, the heating is preferably performed after the particles of the composite oxide are coated with the material containing the second transition metal. Surprisingly, even after coating the material containing the second transition metal, typical elements such as magnesium segregate on the surface of the particles when heated.

When the main group element is segregated by heating, when the composite oxide containing lithium and the first transition metal contained in the first region 101 is polycrystalline or crystal defects are present, not only the surface layer portion but also lithium. Main group elements can also segregate near the grain boundaries and crystal defects of the composite oxide containing the first transition metal. The main group elements segregated near the grain boundaries and near the crystal defects can contribute to further stabilizing the crystal structure of the composite oxide containing lithium and the first transition metal contained in the first region 101.

Further, when the composite oxide containing lithium and the first transition metal contained in the first region 101 has a crack portion, a typical element may segregate in the crack portion by heating. Moreover, not only the main group element but also the second transition metal can be segregated. The crack portion is a region in contact with the electrolytic solution as well as the particle surface. Therefore, the main group element and the second transition metal are segregated in the crack portion to generate the third region 103 and the second region 102, so that the region in contact with the electrolytic solution is made into a chemically stable material. Can be done. Therefore, a secondary battery having excellent cycle characteristics can be obtained.

When the ratio of the main group element (T) to fluorine (F) of the starting material is in the range of T: F = 1: x (1.5 ≦ x ≦ 4) (atomic number ratio), the segregation of the main group element is effective. Is preferable because Further, it is more preferable that T: F = 1: 2 (atomic number ratio).

Since the third region 103 formed by segregation is formed by epitaxial growth, the crystal orientations of the second region 102 and the third region 103 may partially match. That is, the second region 102 and the third region 103 may become topotaxi. If the crystal orientations of the second region 102 and the third region 103 are substantially the same, they can function as a better coating layer.

However, it is not necessary that all the typical elements such as magnesium added as a starting material are segregated in the third region 103. For example, the first region 101 may contain a small amount of a typical element such as magnesium.

[Method for producing positive electrode active material]
Next, an example of a method for producing the positive electrode active materials 100a, 100b, and 100c will be described.

<Step 11: Preparation of starting materials>
First, prepare the starting material. From the raw materials prepared in this step, the first region 101 and the third region 103 are finally formed.

A lithium source and a first transition metal source are prepared as raw materials for the lithium and the first transition metal contained in the first region 101. Further, a typical element source is prepared as a raw material for the compound of the typical element contained in the third region 103.

In addition to these, it is preferable to prepare a fluorine source. Fluorine, when added to the raw material, has the effect of promoting the segregation of the main group elements of the third region 103 on the surfaces of the positive electrode active materials 100a, 100b, and 100c in a later step.

As the lithium source, for example, lithium carbonate or lithium fluoride can be used. As the first transition metal source, for example, an oxide of the first transition metal can be used. As a typical element source, for example, an oxide of a typical element contained in the third region, a fluoride of a typical element contained in the third region, or the like can be used.

As the fluorine source, for example, lithium fluoride, fluoride of a typical element having a third region, or the like can be used. That is, lithium fluoride can be used as both a lithium source and a fluorine source.

Fluorine contained in the fluorine source is preferably 1.0 times or more and 4 times or less (atomic number ratio), and 1.5 times or more and 3 times or less (atomic number ratio) of the main group element contained in the main group element source. Is more preferable.

<Step 12: Mixing of starting materials>
Next, the lithium source, the first transition metal source, and the main group element source are mixed. Further, it is preferable to add a fluorine source. For example, a ball mill or a bead mill can be used for mixing.

<Step 13: First heating>
Next, the mixed materials in step 12 are heated. This step may be referred to as firing or first heating. The heating is preferably performed at 800 ° C. or higher and 1100 ° C. or lower, and more preferably 900 ° C. or higher and 1000 ° C. or lower. The heating time is preferably 2 hours or more and 20 hours or less. The firing is preferably performed in a dry atmosphere such as dry air. The dry atmosphere preferably has a dew point of −50 ° C. or lower, more preferably −100 ° C. or lower. In the present embodiment, heating is performed at 1000 ° C. for 10 hours, and dry air having a temperature rise of 200 ° C./h and a dew point of −109 ° C. is flowed at 10 L / min. The heated material is then cooled to room temperature.

By heating in step 13, a composite oxide of lithium and a first transition metal having a layered rock salt type crystal structure can be synthesized. At this point, the main group elements and fluorine contained in the starting material are solid-solved in the composite oxide. However, some of the main group elements may already be unevenly distributed on the surface of the composite oxide.

In addition, particles of a composite oxide containing lithium, cobalt, fluorine, and magnesium that have been synthesized in advance may be used as a starting material. In this case, steps 12 and 13 can be omitted. For example, lithium cobalt oxide particles (trade name: C-20F) manufactured by Nippon Chemical Industrial Co., Ltd. can be used as one of the starting materials. This is a lithium cobalt oxide particle having a particle size of about 20 μm and containing fluorine, magnesium, calcium, sodium, silicon, sulfur, and phosphorus in a region that can be analyzed by XPS from the surface.

<Step 14: Covered with a second transition metal>
Next, the composite oxide of lithium and the first transition metal is cooled to room temperature. Then, the surface of the composite oxide particles of lithium and the first transition metal is coated with a material having the second transition metal. In this production method example, the sol-gel method is applied.

First, the alkoxide of the second transition metal dissolved in alcohol and the composite oxide particles of lithium and the first transition metal are mixed.

For example, when titanium is used as the second transition metal, for example, TTIP can be used as the alkoxide of the second transition metal. Further, as the alcohol, for example, isopropanol can be used.

Next, the mixture is stirred in an atmosphere containing water vapor. Stirring can be done, for example, with a magnetic stirrer. The stirring time may be a time sufficient for water in the atmosphere and TTIP to cause a hydrolysis and polycondensation reaction, for example, under the conditions of 4 hours, 25 ° C., and 90% humidity RH (Relative Humidity). Can be done with.

As described above, by reacting water in the atmosphere with TTIP, the sol-gel reaction can proceed more slowly than when liquid water is added. Further, by reacting titanium alkoxide with water at room temperature, the sol-gel reaction can proceed more slowly than, for example, when heating is performed at a temperature exceeding the boiling point of alcohol as a solvent. By slowly advancing the sol-gel reaction, a coating layer containing titanium having a uniform thickness and good quality can be formed.

The precipitate is recovered from the mixed solution after the above treatment. As a recovery method, filtration, centrifugation, evaporation to dryness, or the like can be applied. In the present embodiment, it is collected by filtration. A paper filter is used for filtration, and the residue is washed with the same alcohol as the solvent in which the titanium alkoxide is dissolved.

Next, the recovered residue is dried. In this embodiment, vacuum drying is performed at 70 ° C. for 1 hour.

<Step 15: Second heating>
Next, the composite oxide particles prepared in step 14 and coated with the material having the second transition metal are heated. This step may be referred to as a second heating. As for the heating time, the holding time within the specified temperature range is preferably 50 hours or less, more preferably 2 hours or more and 10 hours or less, and further preferably 1 hour or more and 3 hours or less. If the heating time is too short, segregation of the main group element may not occur, but if it is too long, the diffusion of the second transition metal may proceed too much and a good second region 102 may not be formed.

The specified temperature is preferably 500 ° C. or higher and 1200 ° C. or lower, and more preferably 800 ° C. or higher and 1000 ° C. or lower. If the specified temperature is too low, segregation of the main group element and the second transition metal may not occur. However, if it is too high, the first transition metal in the composite oxide particles is reduced and the composite oxide particles are decomposed, and the layered structure of lithium and the first transition metal in the composite oxide particles cannot be maintained. , Etc. may occur.

In the present embodiment, the specified temperature is set to 800 ° C. and the temperature is maintained for 2 hours, the temperature rise is 200 ° C./h, and the flow rate of dry air is 10 L / min.

By heating in step 15, the composite oxide of lithium and the first transition metal and the oxide of the second transition metal coated on the composite oxide become topotaxis. That is, the first region 101 and the second region 102 become topotaxi.

Further, by the heating in step 15, the typical element that was solid-solved inside the composite oxide particles of lithium and the first transition metal is unevenly distributed on the surface and solid-solved, that is, segregated to become a compound of the typical element, and the third Region 103 is formed. At this time, the compound of the main group element grows heteroepitaxially from the second region 102. That is, the second region 102 and the third region 103 become topotaxi.

Since the crystal orientations of the second region 102 and the third region 103 are substantially the same and have a stable bond with the first region 101, when the positive electrode active materials 100a, 100b, and 100c are used in the secondary battery, The change in the crystal structure of the first region 101 caused by charging and discharging can be effectively suppressed. Further, even if lithium is released from the first region 101 by charging, the surface layer portion having a stable bond suppresses the separation of the first transition metal such as cobalt and oxygen from the first region 101. can do. Further, the region in contact with the electrolytic solution can be a chemically stable material. Therefore, a secondary battery having excellent cycle characteristics can be obtained.

It should be noted that the first region 101 and the second region 102 may be partially topotoxy, and it is not necessary that all of the first region 101 and the second region 102 are topotaxis. Further, it is sufficient that a part of the second region 102 and the third region 103 is topotaxis, and it is not necessary that all of the second region 102 and the third region 103 are topotaxis.

When the compound of the main group element contained in the third region has oxygen, it is preferable to perform the heating in step 15 in an atmosphere containing oxygen. Heating in an oxygen-containing atmosphere promotes the formation of the third region 103.

In addition, the fluorine contained in the starting material promotes segregation of typical elements.

As described above, in the method for producing a positive electrode active material, which is one aspect of the present invention, the third region 103 is formed by coating the element forming the second region 102 and then heating to form the positive electrode active material. It is possible to form two types of regions on the surfaces of 100a, 100b and 100c. That is, normally, two coating steps are required to provide two types of regions on the surface layer portion, but the method for producing a positive electrode active material, which is one aspect of the present invention, is a single coating step (solgel step). ) Is sufficient, so it is a highly productive manufacturing method.

<Step 16: Cooling>
Next, the particles heated in step 15 are cooled to room temperature. It is preferable to take a long time for lowering the temperature because it is easy to make it topotaxy. For example, the temperature lowering time from the holding temperature to room temperature is preferably the same as or longer than the temperature rising, specifically 10 hours or more and 50 hours or less.

<Step 17: Recovery>
Next, the cooled particles are collected. In addition, it is preferable to sift the particles. In the above steps, positive electrode active materials 100a, 100b, and 100c having a first region 101, a second region 102, and a third region 103 can be produced.

Then, an active material layer containing the obtained positive electrode active materials 100a, 100b, 100c, vapor-grown carbon fibers 131a, 131b, which are conductive auxiliary agents, and a binder 130 is formed on the positive electrode current collector. A positive electrode paste containing positive electrode active materials 100a, 100b, 100c, vapor-grown carbon fibers 131a, 131b, and binder 130 is prepared, applied to a positive electrode current collector, dried, and pressure-molded with a roll or the like. In order to obtain a high-density electrode density, the electrode density can be adjusted to 4.0 g / cm ³ or more by pressing at a pressure of 1050 kN / m or more. FIG. 1 shows an example of a cross section of an active material layer formed on a positive electrode current collector (not shown).

As the binder 130, for example, it is preferable to use a rubber material such as styrene-butadiene rubber (SBR), styrene-isoprene-styrene rubber, acrylonitrile-butadiene rubber, butadiene rubber, or ethylene-propylene-diene copolymer. Further, fluororubber can be used as the binder.

Further, as the binder, for example, it is preferable to use a water-soluble polymer. As the water-soluble polymer, for example, a polysaccharide or the like can be used. As the polysaccharide, cellulose derivatives such as carboxymethyl cellulose (CMC), methyl cellulose, ethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose and regenerated cellulose, starch and the like can be used. Further, it is more preferable to use these water-soluble polymers in combination with the above-mentioned rubber material.

Alternatively, the binder includes polystyrene, methyl polyacrylate, polymethyl methacrylate (PMMA), sodium polyacrylate, polyvinyl alcohol (PVA), polyethylene oxide (PEO), polypropylene oxide, polyimide, polyvinyl chloride, and polytetrafluoro. It is preferable to use materials such as ethylene, polyethylene, polypropylene, polyisobutylene, polyethylene terephthalate, nylon, polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), ethylenepropylene diene polymer, polyvinyl acetate, and nitrocellulose.

The binder may be used in combination of a plurality of the above.

<Positive current collector>
As the positive electrode current collector, a material having high conductivity such as metals such as stainless steel, gold, platinum, aluminum and titanium, and alloys thereof can be used. Further, it is preferable that the material used for the positive electrode current collector does not elute at the potential of the positive electrode. Further, an aluminum alloy to which an element for improving heat resistance such as silicon, titanium, neodymium, scandium, and molybdenum is added can be used. Further, it may be formed of a metal element that reacts with silicon to form VDD. Examples of metal elements that react with silicon to form silicide include zirconium, titanium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, cobalt, nickel and the like. As the current collector, a foil shape, a plate shape (sheet shape), a net shape, a punching metal shape, an expanded metal shape, or the like can be appropriately used. It is preferable to use a current collector having a thickness of 5 μm or more and 30 μm or less.

(Embodiment 2)
In the first embodiment, an example of producing a positive electrode is shown, but in the present embodiment, a secondary battery in which the positive electrode, the negative electrode and the electrolytic solution are wrapped in an exterior body will be described as an example.

[Negative electrode]
The negative electrode has a negative electrode active material layer and a negative electrode current collector. Further, the negative electrode active material layer may have a conductive auxiliary agent and a binder.

<Negative electrode active material>
As the negative electrode active material, for example, an alloy-based material, a carbon-based material, or the like can be used.

As the negative electrode active material, an element capable of performing a charge / discharge reaction by an alloying / dealloying reaction with lithium can be used. For example, a material containing at least one of silicon, tin, gallium, aluminum, germanium, lead, antimony, bismuth, silver, zinc, cadmium, indium and the like can be used. Such elements have a larger capacity than carbon, and silicon in particular has a high theoretical capacity of 4200 mAh / g. Therefore, it is preferable to use silicon as the negative electrode active material. Moreover, you may use the compound which has these elements. For example, SiO, Mg ₂ Si, Mg ₂ Ge, SnO, SnO ₂ , Mg ₂ Sn, SnS ₂ , V ₂ Sn ₃ , FeSn ₂ , CoSn ₂ , Ni ₃ Sn ₂ , Cu ₆ Sn ₅ , Ag ₃ Sn, Ag. _{There are 3} Sb, Ni ₂ MnSb, CeSb ₃ , LaSn ₃ , La ₃ Co ₂ Sn ₇ , CoSb ₃ , InSb, SbSn and the like. Here, an element capable of performing a charge / discharge reaction by an alloying / dealloying reaction with lithium, a compound having the element, and the like may be referred to as an alloy-based material.

In the present specification and the like, SiO refers to, for example, silicon monoxide. Alternatively, SiO can also be expressed _{as SiO x.} Here, x preferably has a value in the vicinity of 1. For example, x is preferably 0.2 or more and 1.5 or less, and more preferably 0.3 or more and 1.2 or less.

As the carbon-based material, graphite, easily graphitizable carbon (soft carbon), non-graphitizable carbon (hard carbon), carbon nanotubes, graphene, carbon black and the like may be used.

Examples of graphite include artificial graphite and natural graphite. Examples of the artificial graphite include mesocarbon microbeads (MCMB), coke-based artificial graphite, pitch-based artificial graphite and the like. Here, as the artificial graphite, spheroidal graphite having a spherical shape can be used. For example, MCMB may have a spherical shape, which is preferable. In addition, MCMB is relatively easy to reduce its surface area and may be preferable. Examples of natural graphite include scaly graphite and spheroidized natural graphite.

Graphite exhibits a potential as low as lithium metal when lithium ions are inserted into graphite (during the formation of a lithium-graphite intercalation compound) (0.05 V or more and 0.3 V or less vs. Li ^/ Li +). As a result, the lithium ion secondary battery can exhibit a high operating voltage. Further, graphite is preferable because it has advantages such as relatively high capacity per unit volume, relatively small volume expansion, low cost, and high safety as compared with lithium metal.

Further, as the negative electrode active material, titanium dioxide (TiO ₂ ), lithium titanium oxide (Li ₄ Ti ₅ O ₁₂ ), lithium-graphite interlayer compound (Li _x C ₆ ), niobium pentoxide (Nb ₂ O ₅ ), oxidation. Oxides such as tungsten (WO ₂ ) and molybdenum oxide (MoO ₂ ) can be used.

_{Further, as the negative electrode active material, Li 3-x} M _x N (M = Co, Ni, Cu) having _{a Li 3} N type structure, which is a compound nitride of lithium and a transition metal, can be used. For example, Li _2.6 Co _0.4 N ₃ shows a large charge / discharge capacity (900 mAh / g, 1890 mAh / cm ³ ) and is preferable.

When a double nitride of lithium and a transition metal is used, lithium ions are contained in the negative electrode active material, so that it can be combined with materials such as _{V 2} O ₅ and Cr ₃ O _{8 which do not contain lithium ions as the positive electrode active material, which is preferable.} .. Even when a material containing lithium ions is used as the positive electrode active material, a double nitride of lithium and a transition metal can be used as the negative electrode active material by desorbing the lithium ions contained in the positive electrode active material in advance.

Further, a material that causes a conversion reaction can also be used as the negative electrode active material. For example, a transition metal oxide that does not form an alloy with lithium, such as cobalt oxide (CoO), nickel oxide (NiO), and iron oxide (FeO), may be used as the negative electrode active material. Materials that cause a conversion reaction include oxides such as Fe ₂ O ₃ , CuO, Cu ₂ O, RuO ₂ , Cr ₂ O ₃ , sulfides such as CoS _0.89 , NiS, and CuS, and Zn ₃ N _2. , Cu ₃ N, Ge ₃ N _{4 and} other nitrides, NiP ₂ , FeP ₂ and CoP _{3 and} other phosphates, and FeF ₃ and BiF _{3 and} other fluorides.

As the conductive auxiliary agent and the binder that the negative electrode active material layer can have, the same material as the conductive auxiliary agent and the binder that the positive electrode active material layer can have can be used.

<Negative electrode current collector>
The same material as the positive electrode current collector can be used for the negative electrode current collector. The negative electrode current collector preferably uses a material that does not alloy with carrier ions such as lithium.

[Electrolytic solution]
The electrolytic solution has a solvent and an electrolyte. The solvent of the electrolytic solution is preferably an aproton organic solvent, for example, ethylene carbonate (EC), fluoroethylene carbonate (FEC), propylene carbonate (PC), butylene carbonate, chloroethylene carbonate, vinylene carbonate, γ-butyrolactone, γ-Valerolactone, dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), methyl formate, methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, 1, One of 3-dioxane, 1,4-dioxane, dimethoxyethane (DME), dimethyl sulfoxide, diethyl ether, methyl diglime, acetonitrile, benzonitrile, tetrahydrofuran, sulfolane, sulton, etc., or two or more of them. It can be used in any combination and ratio.

Further, by using one or more flame-retardant and volatile ionic liquids (normal temperature molten salt) as the solvent of the electrolytic solution, the internal temperature rises due to an internal short circuit of the secondary battery, overcharging, or the like. However, it is possible to prevent the secondary battery from exploding or catching fire. Ionic liquids consist of cations and anions, including organic cations and anions. Examples of the organic cation used in the electrolytic solution include aliphatic onium cations such as quaternary ammonium cations, tertiary sulfonium cations, and quaternary phosphonium cations, and aromatic cations such as imidazolium cations and pyridinium cations. Further, as anions used in the electrolytic solution, monovalent amide anion, monovalent methide anion, fluorosulfonic anion, perfluoroalkyl sulfonic acid anion, tetrafluoroborate anion, perfluoroalkyl borate anion, hexafluorophosphate anion. , Or perfluoroalkyl phosphate anion and the like.

As the electrolytes dissolved in the above solvent, for example _{LiPF 6, LiClO 4, LiAsF 6} , LiBF 4, LiAlCl 4, LiSCN, LiBr, LiI, Li 2 SO 4, Li 2 B 10 Cl 10, Li 2 B 12 Cl ₁₂ , LiCF ₃ SO ₃ , LiC ₄ F ₉ SO ₃ , LiC (CF ₃ SO ₂ ) ₃ , LiC (C ₂ F ₅ SO ₂ ) ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₄ F ₉₎ Lithium salts such as SO ₂ ) (CF ₃ SO ₂ ) and LiN (C ₂ F ₅ SO ₂ ) ₂ can be used alone, or two or more of them can be used in any combination and ratio.

As the electrolytic solution used for the secondary battery, it is preferable to use a highly purified electrolytic solution having a small content of elements other than granular dust and constituent elements of the electrolytic solution (hereinafter, also simply referred to as “impurities”). Specifically, the weight ratio of impurities to the electrolytic solution is preferably 1% or less, preferably 0.1% or less, and more preferably 0.01% or less.

Further, even if an additive such as vinylene carbonate, propane sultone (PS), tert-butylbenzene (TBB), fluoroethylene carbonate (FEC), LiBOB, or a dinitrile compound such as succinonitrile or adiponitrile is added to the electrolytic solution, it may be added. Good. The concentration of the material to be added may be, for example, 0.1 wt% or more and 5 wt% or less with respect to the entire solvent.

Alternatively, a polymer gel electrolyte obtained by swelling the polymer with an electrolytic solution may be used.

By using the polymer gel electrolyte, the safety against liquid leakage and the like is enhanced. In addition, the secondary battery can be made thinner and lighter.

As the gelled polymer, silicone gel, acrylic gel, acrylonitrile gel, polyethylene oxide gel, polypropylene oxide gel, fluoropolymer gel and the like can be used.

As the polymer, for example, a polymer having a polyalkylene oxide structure such as polyethylene oxide (PEO), PVDF, polyacrylonitrile, etc., and a copolymer containing them can be used. For example, PVDF-HFP, which is a copolymer of PVDF and hexafluoropropylene (HFP), can be used. Further, the polymer to be formed may have a porous shape.

Further, instead of the electrolytic solution, a solid electrolyte having an inorganic material such as a sulfide type or an oxide type, or a solid electrolyte having a polymer material such as PEO (polyethylene oxide) type can be used. When a solid electrolyte is used, it is not necessary to install a separator or a spacer. In addition, since the entire battery can be solidified, there is no risk of liquid leakage and safety is dramatically improved.

[Separator]
Further, the secondary battery preferably has a separator. As the separator, for example, paper, non-woven fabric, glass fiber, ceramics, or one formed of nylon (polyamide), vinylon (polyvinyl alcohol-based fiber), polyester, acrylic, polyolefin, synthetic fiber using polyurethane, etc. shall be used. Can be done. It is preferable that the separator is processed into an envelope shape and arranged so as to wrap either the positive electrode or the negative electrode.

The separator may have a multi-layer structure. For example, an organic material film such as polypropylene or polyethylene can be coated with a ceramic material, a fluorine material, a polyamide material, or a mixture thereof. As the ceramic material, for example, aluminum oxide particles, silicon oxide particles and the like can be used. As the fluorine-based material, for example, PVDF, polytetrafluoroethylene and the like can be used. As the polyamide-based material, for example, nylon, aramid (meth-based aramid, para-based aramid) and the like can be used.

Since the oxidation resistance is improved by coating with a ceramic material, deterioration of the separator during high voltage charging / discharging can be suppressed, and the reliability of the secondary battery can be improved. Further, when a fluorine-based material is coated, the separator and the electrode are easily brought into close contact with each other, and the output characteristics can be improved. Coating a polyamide-based material, particularly aramid, improves heat resistance and thus can improve the safety of the secondary battery.

For example, a mixed material of aluminum oxide and aramid may be coated on both sides of a polypropylene film. Further, the surface of the polypropylene film in contact with the positive electrode may be coated with a mixed material of aluminum oxide and aramid, and the surface in contact with the negative electrode may be coated with a fluorine-based material.

When a separator having a multi-layer structure is used, the safety of the secondary battery can be maintained even if the thickness of the entire separator is thin, so that the capacity per volume of the secondary battery can be increased.

[Exterior body]
As the exterior body of the secondary battery, for example, a metal material such as aluminum or a resin material can be used. Moreover, a film-like exterior body can also be used. As the film, for example, a metal thin film having excellent flexibility such as aluminum, stainless steel, copper, and nickel is provided on a film made of a material such as polyethylene, polypropylene, polycarbonate, ionomer, and polyamide, and an exterior is further formed on the metal thin film. A film having a three-layer structure provided with an insulating synthetic resin film such as a polyamide resin or a polyester resin can be used as the outer surface of the body.

A secondary battery is assembled using the negative electrode, the negative electrode active material, the negative electrode current collector, the electrolytic solution, the separator, and the exterior body shown above, and the positive electrode, the positive electrode active material, and the positive electrode current collector shown in the first embodiment. be able to. For example, if the exterior body is a metal can and a circular one is used, a coin-type (single-layer flat type) secondary battery can be produced by a known production method.

Further, if a metal can having a hollow cylindrical exterior body is used, a cylindrical secondary battery can be manufactured by a known manufacturing method.

Further, by storing the above-mentioned wound body in a space formed by laminating a film-like exterior body and a film having a recess by thermocompression bonding or the like, a laminated type secondary battery can be produced by a known manufacturing method. Can be made.

[Charging / discharging method]
The secondary battery can be charged and discharged as follows, for example.

≪CC charging≫
First, CC charging will be described as one of the charging methods. CC charging is a charging method in which a constant current is passed through a secondary battery during the entire charging period, and charging is stopped when a predetermined voltage is reached. It is assumed that the secondary battery is an equivalent circuit of the internal resistance R and the secondary battery capacity C as shown in FIG. 3 (A). In this case, the secondary battery voltage V _B is the sum of the voltage V _C applied to the voltage V _R and the secondary battery capacity C according to the internal resistance R.

During CC charging, as shown in FIG. 3A, the switch is turned on and a constant current I flows through the secondary battery. During this time, since a current I is constant, the Ohm's law V R _{= R} × I, a voltage V _R is also constant according to the internal resistance R. On the other hand, the voltage V _C applied to the secondary battery capacity C increases with time. Therefore, the secondary battery voltage V _B rises with the passage of time.

Then, when the secondary battery voltage V _B reaches a predetermined voltage, for example, 4.3 V, charging is stopped. When the CC charging is stopped, as shown in FIG. 3B, the switch is turned off and the current I = 0. Therefore, the voltage _{V R} applied to the internal resistance R becomes 0V. _{Therefore, the secondary battery voltage V B} drops by the amount that the voltage drop in the internal resistance R disappears.

FIG. 3 (C) shows an example of the _{secondary battery voltage V B} and the charging current during CC charging and after CC charging is stopped. It is shown that the secondary battery voltage V _B , which had been rising during CC charging, decreased slightly after CC charging was stopped.

≪CCCV charging≫
Next, CCCV charging, which is a charging method different from the above, will be described. CCCV charging is a charging method in which first charging is performed to a predetermined voltage by CC charging, and then charging is performed until the current flowing by CV (constant voltage) charging decreases, specifically, until the final current value is reached. ..

During CC charging, as shown in FIG. 4A, the constant current power supply switch is turned on, the constant voltage power supply switch is turned off, and a constant current I flows through the secondary battery. During this time, since a current I is constant, the Ohm's law V R _{= R} × I, a voltage V _R is also constant according to the internal resistance R. On the other hand, the voltage V _C applied to the secondary battery capacity C increases with time. Therefore, the secondary battery voltage V _B rises with the passage of time.

Then, when the secondary battery voltage V _B reaches a predetermined voltage, for example, 4.3 V, the CC charge is switched to the CV charge. During CV charging, as shown in FIG. 4B, the constant voltage power supply switch is turned on, the constant current power supply switch is turned off, and the secondary battery voltage V _B becomes constant. On the other hand, the voltage V _C applied to the secondary battery capacity C increases with time. Because it is _{V B = V R + V C} , the voltage _{V R} applied to the internal resistance R becomes smaller with time. According voltage V _R becomes smaller according to the internal resistance R, by Ohm's law of V R _{= R} × I, also decreases the current I flowing through the secondary battery.

Then, when the current I flowing through the secondary battery reaches a predetermined current, for example, a current equivalent to 0.01C, charging is stopped. When the CCCV charging is stopped, as shown in FIG. 4C, all the switches are turned off and the current I = 0. Therefore, the voltage _{V R} applied to the internal resistance R becomes 0V. However, since the voltage V _R applied to the internal resistance R by CV charging is sufficiently small, even run out of the voltage drop at the internal resistance R, the secondary battery voltage V _B is hardly lowered.

FIG. 4 (D) shows an example of the _{secondary battery voltage V B} and the charging current during the CCCV charging and after the CCCV charging is stopped. It is shown that the _{secondary battery voltage V B} hardly drops even when the CCCV charging is stopped.

≪CC discharge≫
Next, CC discharge, which is one of the discharge methods, will be described. CC discharge is a discharge method in which a constant current is passed from a secondary battery during the entire discharge period, _{and the discharge is stopped when the secondary battery voltage V B} reaches a predetermined voltage, for example, 2.5 V.

An example of the secondary battery voltage V _{B and the discharge current during CC discharge is shown in FIG.} It is shown that the secondary battery voltage V _{B drops as the discharge progresses.}

Next, the discharge rate and the charge rate will be described. The discharge rate is a relative ratio of the current at the time of discharge to the battery capacity, and is expressed in the unit C. In a battery having a rated capacity of X (Ah), the current corresponding to 1C is X (A). When discharged with a current of 2X (A), it is said to be discharged at 2C, and when discharged with a current of X / 5 (A), it is said to be discharged at 0.2C. The charging rate is also the same. When charged with a current of 2X (A), it is said to be charged with 2C, and when charged with a current of X / 5 (A), it is charged with 0.2C. It is said that

(Embodiment 3)
In the present embodiment, an example of mounting the secondary battery, which is one aspect of the present invention, in an electronic device will be described.

By using the secondary battery of one aspect of the present invention as the secondary battery in the daily electronic device, a product having a long life can be provided. For example, daily electronic devices include electric toothbrushes, electric shavers, electric beauty devices, etc., and the secondary batteries of these products are compact and lightweight with a stick-shaped shape in consideration of user-friendliness. Moreover, a large-capacity secondary battery is desired.

6 (A) and 6 (B) show an example of a tablet terminal that can be folded in half. The tablet terminal 9600 shown in FIGS. 6A and 6B has a housing 9630a, a housing 9630b, a movable portion 9640 connecting the housing 9630a and the housing 9630b, a display unit 9631a, and a display unit 9631b. It has a display unit 9631, a display mode changeover switch 9626, a power supply switch 9627, a power saving mode changeover switch 9625, a fastener 9629, and an operation switch 9628. By using a flexible panel for the display unit 9631, a tablet terminal having a wider display unit can be obtained. FIG. 6A shows a state in which the tablet terminal 9600 is open, and FIG. 6B shows a state in which the tablet terminal 9600 is closed.

Further, the tablet terminal 9600 has a power storage body 9635 inside the housing 9630a and the housing 9630b. The power storage body 9635 passes through the movable portion 9640 and is provided over the housing 9630a and the housing 9630b.

A part of the display unit 9631a can be a touch panel area 9632a, and data can be input by touching the displayed operation key 9638. The display unit 9631a shows, for example, a configuration in which half of the area has a display-only function and the other half of the area has a touch panel function, but the configuration is not limited to this. The entire area of the display unit 9631a may have a touch panel function. For example, the entire surface of the display unit 9631a can be displayed as a keyboard button to form a touch panel, and the display unit 9631b can be used as a display screen.

Further, in the display unit 9631b as well, a part of the display unit 9631b can be a touch panel area 9632b, similarly to the display unit 9631a. Further, the keyboard button can be displayed on the display unit 9631b by touching the position where the keyboard display switching button 9639 on the touch panel is displayed with a finger or a stylus.

Further, touch input can be simultaneously performed on the touch panel area 9632a and the touch panel area 9632b.

Further, the display mode changeover switch 9626 can switch the display direction such as vertical display or horizontal display, and can select switching between black and white display and color display. The power saving mode changeover switch 9625 can optimize the brightness of the display according to the amount of external light during use detected by the optical sensor built in the tablet terminal 9600. The tablet terminal may incorporate not only an optical sensor but also another detection device such as a gyro, an acceleration sensor, or other sensor for detecting inclination.

Further, FIG. 6A shows an example in which the display areas of the display unit 9631b and the display unit 9631a are the same, but the display area is not particularly limited, and one size and the other size may be different, and the display quality is also good. It may be different. For example, one may be a display panel capable of displaying a higher definition than the other.

FIG. 6B shows a closed state, and the tablet terminal has a charge / discharge control circuit 9634 including a housing 9630, a solar cell 9633, and a DCDC converter 9636. Further, as the power storage body 9635, the power storage body according to one aspect of the present invention is used.

Since the tablet terminal 9600 can be folded in two, it can be folded so that the housing 9630a and the housing 9630b overlap each other when not in use. By folding, the display unit 9631a and the display unit 9631b can be protected, so that the durability of the tablet terminal 9600 can be improved. Further, since the power storage body 9635 using the secondary battery of one aspect of the present invention has a high capacity and good cycle characteristics, it is possible to provide a tablet terminal 9600 that can be used for a long time over a long period of time.

In addition to this, the tablet-type terminal shown in FIGS. 6 (A) and 6 (B) has a function of displaying various information (still images, moving images, text images, etc.), a calendar, a date, a time, and the like. It can have a function of displaying on a display unit, a touch input function of performing a touch input operation or editing information displayed on the display unit, a function of controlling processing by various software (programs), and the like.

Electric power can be supplied to a touch panel, a display unit, a video signal processing unit, or the like by a solar cell 9633 mounted on the surface of a tablet terminal. The solar cell 9633 can be provided on one side or both sides of the housing 9630, and can be configured to efficiently charge the power storage body 9635. As the storage body 9635, if a lithium ion battery is used, there is an advantage that the size can be reduced.

Further, the configuration and operation of the charge / discharge control circuit 9634 shown in FIG. 6B will be described by showing a block diagram in FIG. 6C. FIG. 6C shows the solar cell 9633, the storage body 9635, the DCDC converter 9636, the converter 9637, the switches SW1 to SW3, and the display unit 9631, and shows the storage body 9635, the DCDC converter 9636, the converter 9637, the switch SW1 to The SW3 is a portion corresponding to the charge / discharge control circuit 9634 shown in FIG. 6 (B).

First, an example of operation when power is generated by the solar cell 9633 by external light will be described. The electric power generated by the solar cell is stepped up or down by the DCDC converter 9636 so as to be a voltage for charging the storage body 9635. Then, when the electric power from the solar cell 9633 is used for the operation of the display unit 9631, the switch SW1 is turned on, and the converter 9637 boosts or lowers the voltage required for the display unit 9631. Further, when the display is not performed on the display unit 9631, the SW1 may be turned off and the SW2 may be turned on to charge the power storage body 9635.

The solar cell 9633 is shown as an example of the power generation means, but is not particularly limited, and the storage body 9635 is charged by another power generation means such as a piezoelectric element (piezo element) or a thermoelectric conversion element (Peltier element). It may be. For example, a non-contact power transmission module that wirelessly (non-contactly) transmits and receives power for charging, or a configuration in which other charging means are combined may be used.

FIG. 7 shows an example of another electronic device. In FIG. 7, the display device 8000 is an example of an electronic device using the secondary battery 8004 according to one aspect of the present invention. Specifically, the display device 8000 corresponds to a display device for receiving TV broadcasts, and includes a housing 8001, a display unit 8002, a speaker unit 8003, a secondary battery 8004, and the like. The secondary battery 8004 according to one aspect of the present invention is provided inside the housing 8001. The display device 8000 can be supplied with electric power from a commercial power source, or can use the electric power stored in the secondary battery 8004. Therefore, even when the power cannot be supplied from the commercial power supply due to a power failure or the like, the display device 8000 can be used by using the secondary battery 8004 according to one aspect of the present invention as an uninterruptible power supply.

The display unit 8002 includes a light emitting device having a light emitting element such as a liquid crystal display device and an organic EL element in each pixel, an electrophoresis display device, a DMD (Digital Micromirror Device), a PDP (Plasma Display Panel), and a FED (Field Emission Display). ), Etc., a semiconductor display device can be used.

The display device includes all information display devices such as those for receiving TV broadcasts, those for personal computers, and those for displaying advertisements.

In FIG. 7, the stationary lighting device 8100 is an example of an electronic device using the secondary battery 8103 according to one aspect of the present invention. Specifically, the lighting device 8100 includes a housing 8101, a light source 8102, a secondary battery 8103, and the like. FIG. 7 illustrates a case where the secondary battery 8103 is provided inside the ceiling 8104 in which the housing 8101 and the light source 8102 are installed, but the secondary battery 8103 is provided inside the housing 8101. It may have been done. The lighting device 8100 can be supplied with electric power from a commercial power source, or can use the electric power stored in the secondary battery 8103. Therefore, even when the power cannot be supplied from the commercial power supply due to a power failure or the like, the lighting device 8100 can be used by using the secondary battery 8103 according to one aspect of the present invention as an uninterruptible power supply.

Although FIG. 7 illustrates a stationary lighting device 8100 provided on the ceiling 8104, the secondary battery according to one aspect of the present invention includes, for example, a side wall 8105, a floor 8106, a window 8107, etc., other than the ceiling 8104. It can be used for a stationary lighting device provided in the above, or it can be used for a desktop lighting device or the like.

Further, as the light source 8102, an artificial light source that artificially obtains light by using electric power can be used. Specifically, incandescent lamps, discharge lamps such as fluorescent lamps, and light emitting elements such as LEDs and organic EL elements are examples of the artificial light sources.

In FIG. 7, the air conditioner having the indoor unit 8200 and the outdoor unit 8204 is an example of an electronic device using the secondary battery 8203 according to one aspect of the present invention. Specifically, the indoor unit 8200 has a housing 8201, an air outlet 8202, a secondary battery 8203, and the like. Although FIG. 7 illustrates the case where the secondary battery 8203 is provided in the indoor unit 8200, the secondary battery 8203 may be provided in the outdoor unit 8204. Alternatively, the secondary battery 8203 may be provided in both the indoor unit 8200 and the outdoor unit 8204. The air conditioner can be supplied with electric power from a commercial power source, or can use the electric power stored in the secondary battery 8203. In particular, when the secondary battery 8203 is provided in both the indoor unit 8200 and the outdoor unit 8204, the secondary battery 8203 according to one aspect of the present invention is provided even when power cannot be supplied from a commercial power source due to a power failure or the like. The air conditioner can be used by using the power supply as an uninterruptible power supply.

Although FIG. 7 illustrates a separate type air conditioner composed of an indoor unit and an outdoor unit, the integrated air conditioner having the functions of the indoor unit and the outdoor unit in one housing may be used. , A secondary battery according to one aspect of the present invention can also be used.

In FIG. 7, the electric refrigerator / freezer 8300 is an example of an electronic device using the secondary battery 8304 according to one aspect of the present invention. Specifically, the electric freezer / refrigerator 8300 has a housing 8301, a refrigerator door 8302, a freezer door 8303, a secondary battery 8304, and the like. In FIG. 7, the secondary battery 8304 is provided inside the housing 8301. The electric refrigerator-freezer 8300 can be supplied with electric power from a commercial power source, or can use the electric power stored in the secondary battery 8304. Therefore, even when the power cannot be supplied from the commercial power source due to a power failure or the like, the electric refrigerator-freezer 8300 can be used by using the secondary battery 8304 according to one aspect of the present invention as an uninterruptible power supply.

Among the above-mentioned electronic devices, high-frequency heating devices such as microwave ovens and electronic devices such as electric rice cookers require high electric power in a short time. Therefore, by using the secondary battery according to one aspect of the present invention as an auxiliary power source for assisting the electric power that cannot be covered by the commercial power source, it is possible to prevent the breaker of the commercial power source from being tripped when the electronic device is used. ..

In addition, during times when electronic devices are not used, especially during times when the ratio of the amount of power actually used (called the power usage rate) to the total amount of power that can be supplied by the source of commercial power is low. By storing the electric power in the next battery, it is possible to suppress the increase in the electric power usage rate other than the above time zone. For example, in the case of the electric refrigerator-freezer 8300, electric power is stored in the secondary battery 8304 at night when the temperature is low and the refrigerator door 8302 and the freezer door 8303 are not opened and closed. Then, in the daytime when the temperature rises and the refrigerating room door 8302 and the freezing room door 8303 are opened and closed, the power usage rate in the daytime can be suppressed low by using the secondary battery 8304 as an auxiliary power source.

According to one aspect of the present invention, the cycle characteristics of the secondary battery can be improved and the reliability can be improved. Further, according to one aspect of the present invention, it is possible to obtain a high-capacity secondary battery, thereby improving the characteristics of the secondary battery, and thus reducing the size and weight of the secondary battery itself. it can. Therefore, by mounting the secondary battery, which is one aspect of the present invention, in the electronic device described in the present embodiment, it is possible to obtain an electronic device having a longer life and a lighter weight. This embodiment can be implemented in combination with other embodiments as appropriate.

(Embodiment 4)
In the present embodiment, an example in which a secondary battery, which is one aspect of the present invention, is mounted on a vehicle is shown.

When a secondary battery is mounted on a vehicle, a next-generation clean energy vehicle such as a hybrid electric vehicle (HEV), an electric vehicle (EV), or a plug-in hybrid vehicle (PHEV) can be realized.

FIG. 8 illustrates a vehicle using a secondary battery, which is one aspect of the present invention. The automobile 8400 shown in FIG. 8A is an electric vehicle that uses an electric motor as a power source for traveling. Alternatively, it is a hybrid vehicle in which an electric motor and an engine can be appropriately selected and used as a power source for driving. By using one aspect of the present invention, a vehicle having a long cruising range can be realized. In addition, the automobile 8400 has a secondary battery. As the secondary battery, a plurality of secondary battery modules may be used side by side with respect to the floor portion in the vehicle. Further, a battery pack in which a plurality of secondary batteries are combined may be installed on the floor portion in the vehicle. The secondary battery can not only drive the electric motor 8406, but also supply electric power to a light emitting device such as a headlight 8401 and a room light (not shown).

In addition, the secondary battery can supply electric power to display devices such as a speedometer and a tachometer included in the automobile 8400. In addition, the secondary battery can supply electric power to a semiconductor device such as a navigation system included in the automobile 8400.

The automobile 8500 shown in FIG. 8B can charge the secondary battery of the automobile 8500 by receiving electric power from an external charging facility by a plug-in method, a non-contact power supply method, or the like. FIG. 8B shows a state in which the secondary battery 8024 mounted on the automobile 8500 is being charged from the ground-mounted charging device 8021 via the cable 8022. When charging, the charging method, connector specifications, etc. may be appropriately performed by a predetermined method such as CHAdeMO (registered trademark) or combo. The charging device 8021 may be a charging station provided in a commercial facility or a household power source. For example, the plug-in technology can charge the secondary battery 8024 mounted on the automobile 8500 by supplying electric power from the outside. Charging can be performed by converting AC power into DC power via a conversion device such as an ACDC converter.

Further, although not shown, it is also possible to mount the power receiving device on the vehicle and supply electric power from the ground power transmission device in a non-contact manner to charge the vehicle. In the case of this non-contact power supply system, by incorporating a power transmission device on the road or the outer wall, it is possible to charge the battery not only while the vehicle is stopped but also while the vehicle is running. Further, the non-contact power feeding method may be used to transmit and receive electric power between vehicles. Further, a solar cell may be provided on the exterior of the vehicle to charge the secondary battery when the vehicle is stopped or running. An electromagnetic induction method or a magnetic field resonance method can be used for such non-contact power supply.

Further, FIG. 8C is an example of a two-wheeled vehicle using the secondary battery of one aspect of the present invention. The scooter 8600 shown in FIG. 8C includes a secondary battery 8602, a side mirror 8601, and a turn signal 8603. The secondary battery 8602 can supply electricity to the turn signal 8603.

Further, in the scooter 8600 shown in FIG. 8C, the secondary battery 8602 can be stored in the storage under the seat 8604. The secondary battery 8602 can be stored in the under-seat storage 8604 even if the under-seat storage 8604 is small. The secondary battery 8602 is removable, and when charging, the secondary battery 8602 may be carried indoors, charged, and stored before traveling.

According to one aspect of the present invention, the cycle characteristics of the secondary battery are improved, and the capacity of the secondary battery can be increased. Therefore, the secondary battery itself can be made smaller and lighter. If the secondary battery itself can be made smaller and lighter, it will contribute to the weight reduction of the vehicle, and thus the cruising range can be improved. Further, the secondary battery mounted on the vehicle can also be used as a power supply source other than the vehicle.

This embodiment can be implemented in combination with other embodiments as appropriate.

In this embodiment, the result of producing a positive electrode containing the positive electrode active material, which is one aspect of the present invention, and observing the cross section around the positive electrode active material will be described. In addition, the result of evaluating the characteristics of the secondary battery using the positive electrode containing the positive electrode active material will be described.

[Preparation of positive electrode active material]
≪Sample 01≫
In this example, the positive electrode active material of the sample has lithium cobalt oxide as a composite oxide of lithium possessed by the first region and the first transition metal, and the second transition metal possessed by the second region. As an oxide of the above, lithium titanate was prepared, and as an oxide of a main group element possessed by the third region, magnesium oxide was prepared.

In this example, lithium cobalt oxide particles (manufactured by Nippon Chemical Industrial Co., Ltd., trade name: C-20F) were used as a starting material. Therefore, in this embodiment, steps 12 and 13 described in the first embodiment are omitted. The lithium cobalt oxide particles have a particle size of about 20 μm and contain fluorine, magnesium, calcium, sodium, silicon, sulfur, and phosphorus in a region that can be analyzed by XPS.

Next, as step 14, lithium cobalt oxide particles containing magnesium and fluorine were coated with a material containing titanium by a sol-gel method. Specifically, TTIP was dissolved in isopropanol to prepare an isopropanol solution of TTIP. Then, lithium cobalt oxide particles were mixed with the solution. The TTIP was mixed with lithium cobalt oxide containing magnesium and fluorine so as to be 0.04 ml / g.

The mixture was stirred with a magnetic stirrer for 4 hours at 25 ° C. and 90% humidity RH. By this treatment, hydrolysis and polycondensation reaction were caused by TTIP with water in the atmosphere, and a layer containing titanium was formed on the surface of lithium cobalt oxide particles having magnesium and fluorine.

The mixed solution after the above treatment was centrifuged, the supernatant of the solvent was removed, and the residue was recovered. The centrifugation condition was 3000 rpm for 1 minute.

The recovered residue was vacuum dried at 70 ° C. for 1 hour.

Next, the lithium cobalt oxide particles coated with a material having titanium were heated. Using a muffle furnace, the flow rate of oxygen was set to 10 L / min, and heating was performed at 800 ° C. (heating temperature 200 ° C./hour) and holding time of 2 hours.

The heated particles were then cooled to room temperature. The temperature lowering time from the holding temperature to room temperature was 10 to 15 hours. Then, crushing treatment was performed. The crushing treatment was carried out by sieving, and a sieve having an opening of 53 μm was used.

Finally, the cooled particles were collected to obtain the positive electrode active material of Sample 01.

[Making secondary batteries]
A CR2032 type (diameter 20 mm, height 3.2 mm) coin-type secondary battery was produced using the positive electrode active material of the sample 01 produced above.

For the positive electrode, a slurry in which a positive electrode active material (LCO), carbon nanotubes (VGCF (registered trademark)), and polyvinylidene fluoride (PVDF) are mixed at LCO: carbon nanotubes: PVDF = 96: 2: 2 (weight ratio). Was applied to the current collector (aluminum foil). Cross-sectional SEM photographs are shown in FIGS. 9 (A) and 9 (B). For sample 01, three identical samples were prepared, and the press pressures were 210 kN / m, 713 kN / m, 1216 kN / m, and 1467 kN / m, respectively, and the electrode density was measured. The press temperature was 120 ° C. In this embodiment, an example in which the weight ratio of the positive electrode active material, the carbon fiber, and polyvinylidene fluoride is 96: 2: 2 is shown in the positive electrode, but the weight ratio is not particularly limited, and for example, the weight ratio is 95: 3. : May be 2.

The results of measuring the electrode density are shown in Table 1.

As shown in Table 1, the electrode density of the positive electrode active material layer obtained under the two conditions of 1216 kN / m and 1467 kN / m was 4.6 g / cm ³ .

Typical values of the vapor-grown carbon fiber (VGCF (registered trademark): Vapor-Grown Carbon Fiber) used are fiber diameter 150 nm, fiber length 10 μm or more and 20 μm or less, true density 2.1 g / cm ³ , specific surface area 13 m ² /. g. The fiber diameter refers to the diameter of a perfect circle circumscribing the cut surface, with the cross section in the direction perpendicular to the fiber axis as the cut surface from the image taken two-dimensionally by observing with SEM. .. Further, the true density refers to a density in which only the volume occupied by the substance itself is used as the volume for density calculation. The specific surface area is the surface area per unit mass or the surface area per unit volume of the object.

Lithium metal was used as the counter electrode.

1 mol / L lithium hexafluorophosphate (LiPF ₆ ) was used as the electrolyte contained in the electrolytic solution, and ethylene carbonate (EC) and diethyl carbonate (DEC) were used as the electrolytic solution in EC: DEC = 3: 7 ( Volume ratio) and vinylene carbonate (VC) mixed in an amount of 2% by weight were used. Polyporopylene was used as the separator.

As the positive electrode can and the negative electrode can, those made of stainless steel (SUS) were used.

For comparison, sample 02 using AB instead of carbon nanotube (VGCF) was prepared, three samples were prepared in the same process, and the press pressure was no press (0 kN / m), 210 kN / m, and so on. The conditions were set to 713 kN / m, 1216 kN / m, and 1467 kN / m, respectively. ^{4.0 g / cm 3} was obtained only under one condition of 1467 kN / m. From these results, when only AB is used, the electrode density can be obtained so that the electrode density ^{exceeds 4.0 g / cm 3} and the electrode density is 4.2 g / cm ³ or more with good uniformity even when the press pressure is increased. Is difficult.

Further, FIG. 10 shows the result of creating a graph with the average value of the electrode densities. The vertical axis shows the electrode density and the horizontal axis shows the press pressure.

[Evaluation of cycle characteristics]
Next, the charge / discharge characteristics of the secondary battery of the sample 01 (press pressure condition: 1467 kN / m sample) prepared above were evaluated. The measurement temperature was 45 ° C. Charging was 4.55V (CCCV, 1C, cutoff current 0.05C), and discharging was 3V (CC, 1C), each of which was charged and discharged for 100 cycles. The rest time of the cycle test of sample 01 was set to 1 minute. The current value of 1C here was 160 mAh / g per weight of the positive electrode active material.

FIG. 11 shows the cycle test result of sample 01. A cycle test was conducted with a rest time of 1 minute, and the initial discharge capacity was 211.6 mAh / g, and the discharge capacity after 100 cycles was 186.9 mAh / g. As shown in FIG. 11, the capacity retention rate of the charge / discharge cycle at the 100th charge / discharge cycle could be suppressed to 88.3%, which was good. As for the charge / discharge characteristics of the sample 01, good charge / discharge characteristics having a wide plateau are obtained.

100a: Positive electrode active material 100b: Positive electrode active material 100c: Positive electrode active material 130: Binder 131a, 131b: Carbon fiber

Claims (5)

It has a positive electrode and a negative electrode,
The positive electrode has a positive electrode active material and a conductive auxiliary agent.
The positive electrode active material has lithium, cobalt, oxygen, titanium, magnesium, and fluorine.
The conductive auxiliary agent is a secondary battery having carbon fibers having a specific surface area of less than ^{60 m 2 / g and carbon black.} It has a positive electrode and a negative electrode,
The positive electrode has a positive electrode active material and a conductive auxiliary agent.
The positive electrode active material has lithium, cobalt, oxygen, titanium, magnesium, and fluorine.
The conductive auxiliary agent has carbon fibers having a specific surface area of less than ^{60 m 2 / g and carbon black.}
A secondary battery in which the average value of the electrode densities of the positive electrodes is 4.0 g / cm ^{3 or more.} It has a positive electrode and a negative electrode,
The positive electrode has a positive electrode active material and a conductive auxiliary agent.
The positive electrode active material has lithium, cobalt, oxygen, titanium, magnesium, and fluorine.
The conductive auxiliary agent has carbon fibers having a specific surface area of less than ^{60 m 2 / g and carbon black.}
A secondary battery in which the rate of decrease in the charge / discharge cycle at the 100th time is less than 15% in the measurement of the charge / discharge cycle. It has a positive electrode and a negative electrode,
The positive electrode has a positive electrode active material and a conductive auxiliary agent.
The positive electrode active material has lithium, cobalt, oxygen, titanium, magnesium, and fluorine.
The conductive auxiliary agent has carbon fibers having a specific surface area of less than ^{60 m 2 / g and carbon black.}
The average value of the electrode density of the positive electrode is 4.0 g / cm ³ or more.
A secondary battery in which the rate of decrease in the charge / discharge cycle at the 100th time is less than 15% in the measurement of the charge / discharge cycle. In any one of claims 1 to 4,
A secondary battery in which the carbon fibers are carbon nanotubes.

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