JP2017183151A - Power storage device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a power storage device which can suppress the reduction in capacity owing to the repetition of charge and discharge at a low temperature.SOLUTION: In a power storage device, at least one electrode of positive and negative electrodes has an active material layer including a particulate active material and a cellulose derivative (e.g. carboxymethyl cellulose or hydroxyethyl cellulose). The active material has an average particle diameter D50 of 1 to smaller than 5 μm. In the power storage device, the cellulose derivative is 0.6-1.8 in degree of etherification, or the surface roughness Ra of one face of the active material layer is 0.15-1.20 μm.SELECTED DRAWING: None

Description

  The present invention relates to a power storage device such as a lithium ion secondary battery.

  Conventionally, a lithium secondary battery including a positive electrode capable of inserting and extracting lithium, a negative electrode capable of inserting and extracting lithium, and an electrolyte is known. As this type of battery, a battery in which an active material layer of a negative electrode includes an active material and carboxymethyl cellulose is known (for example, Patent Document 1).

  In the active material of the battery described in Patent Document 1, a dispersion obtained by dispersing 100 g of active material powder in 200 g of water together with 2 g of carboxymethylcellulose is measured according to the degree of dispersion according to JIS K5400 grain gauge method. The particle diameter at which grains begin to appear is 50 μm or less. That is, in the battery described in Patent Document 1, an active material (active material that does not include relatively large particles) in which the particle diameter at which the above-described grains begin to appear is 50 μm or less is employed for the negative electrode.

  By the way, in the battery of patent document 1, a capacity | capacitance may fall by repeating charging / discharging at low temperature.

Japanese Patent No. 4765253

  This embodiment makes it a subject to provide the electrical storage element which can suppress that a capacity | capacitance falls by repeating charging / discharging at low temperature.

  The electricity storage device of the present embodiment includes a positive electrode and a negative electrode as electrodes, and at least one of the electrodes is an electrode base material, an active material layer containing a particulate active material and a cellulose derivative, and the electrode base material The active material layer has an average particle diameter D50 of 1 μm or more and less than 5 μm, and the surface roughness of one surface of the active material layer that does not overlap the electrode substrate Ra is 0.15 μm or more and 1.20 μm or less. According to the electricity storage device having the above configuration, it is possible to suppress a decrease in capacity due to repeated charge and discharge at a low temperature.

  The electricity storage device of this embodiment includes a positive electrode and a negative electrode as electrodes, and at least one of the electrodes has an active material layer containing a particulate active material and a cellulose derivative, and an average particle diameter D50 of the active material. Is 1 μm or more and less than 5 μm, and the degree of etherification of the cellulose derivative is 0.6 or more and 1.8 or less. According to the electricity storage device having the above configuration, it is possible to suppress a decrease in capacity due to repeated charge and discharge at a low temperature.

In the above power storage element, the density of the active material layer may be 0.6 g / cm ³ or more and 1.5 g / cm ³ or less. With such a configuration, it is possible to more sufficiently suppress a decrease in capacity due to repeated charging and discharging at a low temperature.

In the above electricity storage element, the basis weight of the active material layer may be 0.3 g / 100 cm ² or more and 1.0 g / 100 cm ² or less. With such a configuration, it is possible to more sufficiently suppress a decrease in capacity due to repeated charging and discharging at a low temperature.

  In the above electricity storage element, any one of the above electrodes may be a negative electrode.

  According to this embodiment, it can suppress that a capacity | capacitance falls by charging / discharging being repeated at low temperature.

FIG. 1 is a perspective view of a power storage device according to this embodiment. FIG. 2 is a front view of the energy storage device according to the embodiment. 3 is a cross-sectional view taken along line III-III in FIG. 4 is a cross-sectional view taken along the line IV-IV in FIG. FIG. 5 is a perspective view of a state in which a part of the energy storage device according to the embodiment is assembled, and is a perspective view of a state in which a liquid filling tap, an electrode body, a current collector, and an external terminal are assembled to a lid plate. is there. FIG. 6 is a view for explaining the configuration of the electrode body of the energy storage device according to the embodiment. FIG. 7 is a cross-sectional view of the superimposed positive electrode, negative electrode, and separator (cross section VII-VII in FIG. 6). FIG. 8 is a perspective view of a power storage device including the power storage element according to the embodiment.

  Hereinafter, an embodiment of a power storage device according to the present invention will be described with reference to FIGS. Examples of power storage elements include secondary batteries and capacitors. In the present embodiment, a chargeable / dischargeable secondary battery will be described as an example of a power storage element. In addition, the name of each component (each component) of this embodiment is a thing in this embodiment, and may differ from the name of each component (each component) in background art.

  The electricity storage device 1 of the present embodiment is a nonaqueous electrolyte secondary battery. More specifically, the electricity storage element 1 is a lithium ion secondary battery that utilizes electron movement that occurs in association with movement of lithium ions. This type of power storage element 1 supplies electric energy. The electric storage element 1 is used singly or in plural. Specifically, the storage element 1 is used as a single unit when the required output and the required voltage are small. On the other hand, power storage element 1 is used in power storage device 100 in combination with other power storage elements 1 when at least one of a required output and a required voltage is large. In the power storage device 100, the power storage element 1 used in the power storage device 100 supplies electric energy.

  As shown in FIGS. 1 to 7, the storage element 1 includes an electrode body 2 including a positive electrode 11 and a negative electrode 12, a case 3 that houses the electrode body 2, and an external terminal 7 that is disposed outside the case 3. And an external terminal 7 that is electrically connected to the electrode body 2. In addition to the electrode body 2, the case 3, and the external terminal 7, the power storage element 1 includes a current collector 5 that electrically connects the electrode body 2 and the external terminal 7.

  The electrode body 2 is formed by winding a laminated body 22 in which the positive electrode 11 and the negative electrode 12 are laminated with the separator 4 being insulated from each other.

  The positive electrode 11 includes a metal foil 111 (positive electrode base material) and an active material layer 112 that is superimposed on the surface of the metal foil 111 and contains an active material. In the present embodiment, the active material layer 112 overlaps both surfaces of the metal foil 111. The thickness of the positive electrode 11 is usually 40 μm or more and 150 μm or less.

  The metal foil 111 has a strip shape. The metal foil 111 of the positive electrode 11 of this embodiment is, for example, an aluminum foil. The positive electrode 11 has an uncovered portion (a portion where the positive electrode active material layer is not formed) 115 of the positive electrode active material layer 112 at one edge portion in the width direction, which is the short direction of the band shape.

The positive electrode active material layer 112 includes a particulate active material, a particulate conductive aid, and a binder. The thickness of the positive electrode active material layer 112 (for one layer) is usually 12 μm or more and 70 μm or less. The basis weight of the positive electrode active material layer 112 (for one layer) is 7.6 mg / cm ² or more and 16.5 mg / cm ² or less. The density of the positive electrode active material layer 112 is 1.7 g / cm ³ or more and 3.0 g / cm ³ or less. The basis weight and density are for one layer arranged so as to cover one surface of the metal foil 111. The density of the positive electrode active material layer 112 is determined by cutting the positive electrode 11 into a predetermined size, measuring the mass and thickness, and then peeling the positive electrode active material layer 112 from the metal foil 111. Is measured, and the mass and thickness of the metal foil 111 are subtracted from the mass and thickness of the electrode plate, respectively.

  The active material of the positive electrode 11 is a compound that can occlude and release lithium ions. The average particle diameter D50 of the active material of the positive electrode 11 is usually 3 μm or more and 8 μm or less. The average particle diameter D50 of the active material is an average particle diameter (also referred to as a median diameter) in which a volume cumulative distribution is drawn from the smaller diameter side in the particle size distribution of the particle diameter and the volume cumulative frequency is 50%. The average particle diameter D50 is obtained by measurement using a laser diffraction / scattering particle size distribution measuring apparatus. The measurement conditions will be described in detail in the examples. In addition, when measuring the average particle diameter D50 of the active material of the manufactured battery, for example, after discharging the battery, the battery is disassembled in a dry atmosphere. Next, the active material layer is taken out, washed with dimethyl carbonate and crushed, followed by vacuum drying for 2 hours or more. Then, it can measure using a particle size distribution measuring apparatus.

The active material of the positive electrode 11 is, for example, a lithium metal oxide. Specifically, the active material of the positive electrode, for _example, Li p _MeO t (Me represents one or more transition metal) complex oxide represented by _{(Li p Co s O 2,} Li p Ni q O _{2, Li p Mn r O 4} , Li p Ni q Co s Mn r O 2 , etc.), _{or, Li p Me u (XO v} ) w (Me represents one or more transition metals, X is e.g. P, Si, B, a polyanion compounds represented by the representative of the _{V) (Li p Fe u PO} 4, Li p Mn u PO 4, Li p Mn u SiO 4, Li p Co u PO 4 F , etc.).

In this embodiment, the active material of the positive electrode _{11, Li p Ni q Mn r Co} s O lithium-metal composite oxide represented by the chemical composition of the _t (where a 0 <p ≦ 1.3, q + r + s = 1 0 ≦ q ≦ 1, 0 ≦ r ≦ 1, 0 ≦ s ≦ 1, and 1.7 ≦ t ≦ 2.3. Note that 0 <q <1, 0 <r <1, and 0 <s <1.

Additional such _{Li p Ni q Mn r Co s} O lithium-metal composite oxide represented by the chemical composition of the _t, for _{example, LiNi 1/3 Co 1/3 Mn 1/3 O} 2, LiNi 1/6 Co 1 _{/ 6} Mn _2/3 O ₂ , LiCoO ₂ and the like.

  Examples of the binder used for the positive electrode active material layer 112 include polyvinylidene fluoride (PVdF), a copolymer of ethylene and vinyl alcohol, polymethyl methacrylate, polyethylene oxide, polypropylene oxide, polyvinyl alcohol, polyacrylic acid, and polymethacrylic acid. Acid, styrene butadiene rubber (SBR). The binder of this embodiment is polyvinylidene fluoride.

  The conductive additive of the positive electrode active material layer 112 is a carbonaceous material containing 98% by mass or more of carbon. Examples of the carbonaceous material include ketjen black (registered trademark), acetylene black, and graphite. The positive electrode active material layer 112 of this embodiment has acetylene black as a conductive additive.

  The negative electrode 12 includes a metal foil 121 (negative electrode base material) and a negative electrode active material layer 122 formed on the metal foil 121. In the present embodiment, the negative electrode active material layer 122 is overlaid on both surfaces of the metal foil 121. The metal foil 121 has a strip shape. The metal foil 121 of the negative electrode of this embodiment is, for example, a copper foil. The negative electrode 12 has an uncoated portion 125 of the negative electrode active material layer 122 (a portion where the negative electrode active material layer is not formed) at one end edge in the width direction, which is the short direction of the belt shape. The thickness of the negative electrode 12 is usually 40 μm or more and 150 μm or less.

  The negative electrode active material layer 122 includes a particulate active material and a binder. The negative electrode active material layer 122 is disposed so as to face the positive electrode 11 with the separator 4 interposed therebetween. The width of the negative electrode active material layer 122 is larger than the width of the positive electrode active material layer 112.

  The surface roughness Ra of one surface of the negative electrode active material layer 122 that does not overlap the metal foil 121 is usually 0.15 μm or more and 1.20 μm or less. The surface roughness Ra may be 0.26 μm or more, or 0.36 μm or more. The surface roughness Ra may be 0.45 μm or less, or 0.39 μm or less. The surface roughness Ra is an arithmetic average roughness measured using a laser microscope (measuring instrument) and determined according to the method described in JIS B0601-2001. The surface roughness Ra can be adjusted, for example, by changing the degree of etherification of the cellulose derivative. Specifically, the surface roughness Ra can be reduced by reducing the degree of etherification of the cellulose derivative. Moreover, as a method of adjusting surface roughness Ra, the method of changing the solid content ratio of the mixture when kneading the mixture (after-mentioned) for forming the negative electrode active material layer 122 is mentioned. Specifically, the surface roughness Ra can be reduced by increasing the solid content ratio.

  In the negative electrode active material layer 122, the ratio of the binder may be 5% by mass or more and 10% by mass or less with respect to the total mass of the negative electrode active material and the binder.

  The active material of the negative electrode 12 can contribute to the electrode reaction of the charge reaction and the discharge reaction in the negative electrode 12. For example, the active material of the negative electrode 12 has an alloying reaction with carbon materials such as graphite and amorphous carbon (non-graphitizable carbon and graphitizable carbon), or lithium ions such as silicon (Si) and tin (Sn). The resulting material. The active material of the negative electrode of this embodiment is amorphous carbon. More specifically, the negative electrode active material is non-graphitizable carbon.

  The average particle diameter D50 of the active material of the negative electrode 12 is 1 μm or more and less than 5 μm. The average particle diameter D50 may be 1.5 μm or more and 4.0 μm or less. The average particle diameter D50 of the active material of the negative electrode 12 is measured in the same manner as the average particle diameter D50 of the active material of the positive electrode 11 as described above.

The thickness of the negative electrode active material layer 122 (for one layer) is usually 10 μm or more and 50 μm or less. The basis weight (one layer) of the negative electrode active material layer 122 is usually 0.3 g / 100 cm ² or more and 1.0 g / 100 cm ² or less. The basis weight (for one layer) may be 0.35 g / 100 cm ² or more. The basis weight (for one layer) may be 0.4 g / 100 cm ² or less. The density (one layer) of the negative electrode active material layer 122 is usually 0.6 g / cm ³ or more and 1.5 g / cm ³ or less. The density (for one layer) may be 0.97 g / cm ³ or more and 1.11 g / cm ³ or less.

  The binder used for the negative electrode active material layer is the same as the binder used for the positive electrode active material layer. The binder of this embodiment is styrene butadiene rubber (SBR).

  The negative electrode active material layer 122 includes a cellulose derivative. The cellulose derivative is obtained by reacting a part of the hydroxy group of cellulose with a compound having a hydrophilic group. The hydrophilic group introduced into the cellulose derivative is bonded to carbon constituting cellulose by an ether bond. An index representing the number of reactions between the compound having a hydrophilic group and the hydroxy group of cellulose is, for example, the degree of etherification described below.

  Cellulose derivatives are, for example, carboxymethylcellulose (including salts), hydroxyethylcellulose, and hydroxypropylmethylcellulose. The cellulose derivative of this embodiment is carboxymethyl cellulose. Carboxymethyl cellulose may be in a salt state.

  The degree of etherification of the cellulose derivative is usually 0.6 or more and 1.8 or less. It may be 0.8 or more and 1.5 or less. The degree of etherification of the cellulose derivative is one of the water solubility indicators of the cellulose derivative. The greater the degree of etherification of the cellulose derivative, the easier it is for the cellulose derivative to dissolve in water. On the other hand, the smaller the degree of etherification of the cellulose derivative, the more difficult the cellulose derivative dissolves in water. In the cellulose derivative, a part of the hydroxy group of cellulose insoluble in water is replaced with an ether bond. Not all cellulose derivatives are soluble in water. When the cellulose derivative is allowed to coexist with water, an insoluble material that is not dissolved in water and is agglomerated is generated. Thereby, when the mixture (after-mentioned) for forming the negative electrode active material layer 122 contains water as a solvent, a part of cellulose derivative does not melt | dissolve in a mixture. Therefore, the negative electrode active material layer 122 has a massive insoluble material having a particle size of 10 μm or more and 200 μm or less.

The degree of etherification of the cellulose derivative is obtained, for example, by the following measurement method. Cellulose derivatives of 0.5 to 0.7 g are weighed, wrapped in filter paper and incinerated in a crucible. After cooling, the ashed product is transferred to a 500 mL beaker, about 250 mL of water is added, and 35 mL of 0.05 mol / L sulfuric acid aqueous solution is added, and the mixture is boiled for 30 minutes. After cooling, phenolphthalein indicator is added, excess acid is back titrated with 0.1 mol / L potassium hydroxide aqueous solution, and the degree of etherification is calculated by the following formula.
A = {(af−bf ¹ ) / weighed amount [g]} − alkalinity (or + acidity)
Degree of etherification = (162 × A) / (10,000-80 × A)
A: mL of 0.05 mol / L sulfuric acid consumed by bound alkali in 1 g of cellulose derivative
a: Use mL of 0.05 mol / L sulfuric acid
f: titer of 0.05 mol / L sulfuric acid b: titration mL of 0.1 mol / L potassium hydroxide
f ¹ : 0.1 mol / L potassium hydroxide titer

  The molecular weight of the cellulose derivative is usually 200,000 or more and 1.4 million or less.

  The negative electrode active material layer 122 may further include a conductive additive such as ketjen black (registered trademark), acetylene black, or graphite.

  In the electrode body 2 of the present embodiment, the positive electrode 11 and the negative electrode 12 configured as described above are wound in a state where they are insulated by the separator 4. That is, in the electrode body 2 of the present embodiment, the stacked body 22 of the positive electrode 11, the negative electrode 12, and the separator 4 is wound. The separator 4 is a member having insulating properties. The separator 4 is disposed between the positive electrode 11 and the negative electrode 12. Thereby, in the electrode body 2 (specifically, the laminated body 22), the positive electrode 11 and the negative electrode 12 are insulated from each other. The separator 4 holds the electrolytic solution in the case 3. Thereby, at the time of charging / discharging of the electrical storage element 1, lithium ion moves between the positive electrode 11 and the negative electrode 12 which are laminated | stacked alternately on both sides of the separator 4. FIG.

  The separator 4 has a strip shape. The separator 4 has a porous separator base material. The separator 4 of this embodiment has only a separator base material. The separator 4 is disposed between the positive electrode 11 and the negative electrode 12 in order to prevent a short circuit between the positive electrode 11 and the negative electrode 12.

  The separator substrate is configured to be porous by, for example, a woven fabric, a nonwoven fabric, or a porous film. Examples of the material for the separator substrate include polymer compounds, glass, and ceramics. Examples of the polymer compound include polyesters such as polyacrylonitrile (PAN), polyamide (PA), and polyethylene terephthalate (PET), polyolefins (PO) such as polypropylene (PP) and polyethylene (PE), and cellulose. .

  The width of the separator 4 (the dimension of the strip shape in the short direction) is slightly larger than the width of the negative electrode active material layer 122. The separator 4 is disposed between the positive electrode 11 and the negative electrode 12 that are stacked in a state of being displaced in the width direction so that the positive electrode active material layer 112 and the negative electrode active material layer 122 overlap. At this time, as shown in FIG. 6, the non-covered portion 115 of the positive electrode 11 and the non-covered portion 125 of the negative electrode 12 do not overlap. That is, the uncovered portion 115 of the positive electrode 11 protrudes in the width direction from the region where the positive electrode 11 and the negative electrode 12 overlap, and the non-covered portion 125 of the negative electrode 12 extends from the region where the positive electrode 11 and the negative electrode 12 overlap in the width direction ( It protrudes in a direction opposite to the protruding direction of the non-covering portion 115 of the positive electrode 11. The electrode body 2 is formed by winding the stacked positive electrode 11, negative electrode 12, and separator 4, that is, the stacked body 22. The portion where only the uncovered portion 115 of the positive electrode 11 or the uncovered portion 125 of the negative electrode 12 is stacked constitutes the uncoated stacked portion 26 in the electrode body 2.

  The uncoated laminated portion 26 is a portion that is electrically connected to the current collector 5 in the electrode body 2. The uncoated laminated portion 26 has two parts (divided uncoated laminated portions divided by sandwiching the hollow portion 27 (see FIG. 6) between the wound positive electrode 11, the negative electrode 12, and the separator 4 in the winding center direction. ) 261.

  The uncoated laminated portion 26 configured as described above is provided on each electrode of the electrode body 2. That is, the non-coated laminated portion 26 in which only the non-coated portion 115 of the positive electrode 11 is laminated constitutes the non-coated laminated portion of the positive electrode 11 in the electrode body 2, and the non-coated laminated layer in which only the non-coated portion 125 of the negative electrode 12 is laminated. The portion 26 constitutes an uncoated laminated portion of the negative electrode 12 in the electrode body 2.

  The case 3 includes a case main body 31 having an opening and a cover plate 32 that closes (closes) the opening of the case main body 31. The case 3 houses the electrolytic solution in the internal space together with the electrode body 2 and the current collector 5. Case 3 is formed of a metal having resistance to the electrolytic solution. The case 3 is made of an aluminum-based metal material such as aluminum or an aluminum alloy, for example. The case 3 may be formed of a metal material such as stainless steel and nickel, or a composite material obtained by bonding a resin such as nylon to aluminum.

The electrolytic solution is a non-aqueous electrolytic solution. The electrolytic solution is obtained by dissolving an electrolyte salt in an organic solvent. Examples of the organic solvent include cyclic carbonates such as propylene carbonate and ethylene carbonate, and chain carbonates such as dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate. The electrolyte salt is LiClO ₄ , LiBF ₄ , LiPF ₆ or the like. The electrolytic solution of this embodiment is obtained by dissolving 0.5 to 1.5 mol / L LiPF ₆ in a mixed solvent in which propylene carbonate, dimethyl carbonate, and ethyl methyl carbonate are mixed at a predetermined ratio.

  The case 3 is formed by joining the peripheral edge of the opening of the case main body 31 and the peripheral edge of the rectangular lid plate 32 in an overlapping state. The case 3 has an internal space defined by the case main body 31 and the lid plate 32. In this embodiment, the opening peripheral part of the case main body 31 and the peripheral part of the cover plate 32 are joined by welding.

  In the following, as shown in FIG. 1, the long side direction of the cover plate 32 is the X-axis direction, the short side direction of the cover plate 32 is the Y-axis direction, and the normal direction of the cover plate 32 is the Z-axis direction. The case body 31 has a rectangular tube shape (that is, a bottomed rectangular tube shape) in which one end in the opening direction (Z-axis direction) is closed. The lid plate 32 is a plate-like member that closes the opening of the case body 31.

  The cover plate 32 has a gas discharge valve 321 that can discharge the gas in the case 3 to the outside. The gas discharge valve 321 discharges gas from the inside of the case 3 to the outside when the internal pressure of the case 3 rises to a predetermined pressure. The gas discharge valve 321 is provided at the center of the lid plate 32 in the X-axis direction.

  The case 3 is provided with a liquid injection hole for injecting an electrolytic solution. The liquid injection hole communicates the inside and the outside of the case 3. The liquid injection hole is provided in the lid plate 32. The liquid injection hole is sealed (closed) by a liquid injection stopper 326. The liquid filling tap 326 is fixed to the case 3 (the cover plate 32 in the example of the present embodiment) by welding.

  The external terminal 7 is a part that is electrically connected to the external terminal 7 of another power storage element 1 or an external device. The external terminal 7 is formed of a conductive member. For example, the external terminal 7 is formed of a highly weldable metal material such as an aluminum-based metal material such as aluminum or aluminum alloy, or a copper-based metal material such as copper or copper alloy.

  The external terminal 7 has a surface 71 to which a bus bar or the like can be welded. The surface 71 is a flat surface. The external terminal 7 has a plate shape extending along the lid plate 32. Specifically, the external terminal 7 has a rectangular plate shape when viewed in the Z-axis direction.

  The current collector 5 is disposed in the case 3 and is directly or indirectly connected to the electrode body 2 so as to be energized. The current collector 5 of the present embodiment is connected to the electrode body 2 through the clip member 50 so as to be energized. That is, the electrical storage element 1 includes a clip member 50 that connects the electrode body 2 and the current collector 5 so as to allow energization.

  The current collector 5 is formed of a conductive member. As shown in FIG. 3, the current collector 5 is disposed along the inner surface of the case 3. The current collector 5 is disposed on each of the positive electrode 11 and the negative electrode 12 of the power storage element 1. In the power storage device 1 of the present embodiment, the case 3 is arranged in the uncoated stacked portion 26 of the positive electrode 11 and the uncoated stacked portion 26 of the negative electrode 12 in the electrode body 2.

  The current collector 5 of the positive electrode 11 and the current collector 5 of the negative electrode 12 are formed of different materials. Specifically, the current collector 5 of the positive electrode 11 is formed of, for example, aluminum or an aluminum alloy, and the current collector 5 of the negative electrode 12 is formed of, for example, copper or a copper alloy.

  In the electricity storage device 1 of the present embodiment, the electrode body 2 (specifically, the electrode body 2 and the current collector 5) housed in a bag-like insulating cover 6 that insulates the electrode body 2 and the case 3 is the case 3. Housed inside.

  Next, the manufacturing method of the electrical storage element 1 of the said embodiment is demonstrated.

  In the manufacturing method of the electrical storage element 1, first, the mixture containing an active material is apply | coated to metal foil (electrode base material), an active material layer is formed, and an electrode (the positive electrode 11 and the negative electrode 12) is produced. Next, the positive electrode 11, the separator 4, and the negative electrode 12 are overlapped to form the electrode body 2. Subsequently, the electrode body 2 is put in the case 3 and the electrolytic solution is put in the case 3 to assemble the power storage element 1.

  In producing the electrode (positive electrode 11), the positive electrode active material layer 112 is formed by applying a mixture containing an active material, a binder, and a solvent to both surfaces of the metal foil. The basis weight of the positive electrode active material layer 112 can be adjusted by adjusting the coating amount of the mixture. As a coating method for forming the positive electrode active material layer 112, a general method is employed. The applied positive electrode active material layer 112 is roll-pressed at a predetermined pressure. The density of the positive electrode active material layer 112 can be adjusted by adjusting the pressing pressure. The negative electrode 12 is produced in the same manner. In preparation of the negative electrode, a mixture is prepared by mixing an active material, a binder, a cellulose derivative (thickening agent), and a solvent (water).

  In the formation of the electrode body 2, the electrode body 2 is formed by winding a laminate 22 in which the separator 4 is sandwiched between the positive electrode 11 and the negative electrode 12. Specifically, the positive electrode 11, the separator 4, and the negative electrode 12 are overlapped so that the positive electrode active material layer 112 and the negative electrode active material layer 122 face each other through the separator 4, thereby forming the laminate 22. The laminated body 22 is wound to form the electrode body 2.

  In assembling the electricity storage element 1, the electrode body 2 is inserted into the case body 31 of the case 3, the opening of the case body 31 is closed with the cover plate 32, and the electrolytic solution is injected into the case 3. When closing the opening of the case main body 31 with the cover plate 32, the electrode body 2 is inserted into the case main body 31, the positive electrode 11 and the one external terminal 7 are electrically connected, and the negative electrode 12 and the other external terminal 7 are connected to each other. In the conductive state, the opening of the case body 31 is closed with the lid plate 32. When the electrolytic solution is injected into the case 3, the electrolytic solution is injected into the case 3 from the injection hole of the cover plate 32 of the case 3.

  In the electricity storage device 1 of the present embodiment configured as described above, the negative electrode 12 has a negative electrode active material layer 122 containing a particulate active material and a cellulose derivative. The average particle diameter D50 of the active material is 1 μm or more and less than 5 μm, and the degree of etherification of the cellulose derivative is 0.6 or more and 1.8 or less. In the above electricity storage device 1, since the degree of etherification of the cellulose derivative is 0.6 or more and 1.8 or less, the negative electrode active material layer 122 has an insoluble material having a particle size of 10 μm or more and 200 μm or less. Specifically, the negative electrode active material layer 122 is formed by applying a mixture of an active material, a cellulose derivative, and water to the metal foil 121. As described above, a part of the cellulose derivative does not dissolve in water and generates a lump insoluble matter. Therefore, the negative electrode active material layer 122 includes an insoluble matter having a particle size of 10 μm or more and 200 μm or less. Such insoluble matter is larger than the active material having an average particle diameter D50 of 1 μm or more and less than 5 μm. Thereby, it is considered that the active material is filled between the insoluble materials. In a state where the space between the insoluble materials is filled with the active material, the conductivity between the active materials is relatively good. Therefore, since the electrical conductivity between the active materials is relatively good, it is possible to suppress a decrease in the battery capacity even when charging and discharging are repeated at a low temperature. Thereby, it can suppress that the capacity | capacitance of a battery falls by repeating charging / discharging at low temperature.

  In the power storage device 1 described above, the surface roughness Ra of one surface of the negative electrode active material layer 122 that does not overlap the metal foil 121 is 0.15 μm or more and 1.20 μm or less. The surface roughness Ra is 0.15 μm or more and 1.20 μm or less because the negative electrode active material layer 122 contains an insoluble material derived from a cellulose derivative having an appropriate size as described above. That is, the surface roughness Ra is 0.15 μm or more and 1.20 μm or less because the negative electrode active material layer 122 contains an insoluble material having an appropriate size and larger than the active material. To do. It is considered that an insoluble matter having a moderate size derived from the cellulose derivative is contained in the negative electrode active material layer 122, so that the active material is appropriately filled between the insoluble matters. In such a state, even if charging / discharging is repeated at a low temperature, the conductivity between the active materials is relatively good. Therefore, it can suppress that the capacity | capacitance of a battery falls by repeating charging / discharging at low temperature.

  In the above electricity storage device 1, the surface roughness Ra of the negative electrode active material layer 122 may be not less than 0.365 μm and not more than 0.450 μm. When the insoluble matter derived from cellulose contained in the negative electrode active material layer 122 has an appropriate size, the surface roughness Ra becomes 0.365 μm or more and 0.450 μm or less. Thereby, it will be in the state with which the active material was appropriately filled between insoluble matters. Therefore, it is possible to further suppress the occurrence of current unevenness when charging / discharging at a high rate is repeated. Therefore, it is possible to further suppress the increase in battery resistance and the decrease in input / output performance.

In the above electricity storage device 1, the thickness of the negative electrode active material layer 122 (for one layer) is usually 10 μm or more and 50 μm or less. The basis weight (one layer) of the negative electrode active material layer 122 is usually 0.3 g / 100 cm ² or more and 1.0 g / 100 cm ² or less. The density (one layer) of the negative electrode active material layer 122 is usually 0.6 g / cm ³ or more and 1.5 g / cm ³ or less. Thereby, it can suppress more reliably that the capacity | capacitance of a battery falls by repeating charging / discharging at low temperature.

  In addition, the electrical storage element of this invention is not limited to the said embodiment, Of course, a various change can be added in the range which does not deviate from the summary of this invention. For example, the configuration of another embodiment can be added to the configuration of a certain embodiment, and a part of the configuration of a certain embodiment can be replaced with the configuration of another embodiment. Furthermore, a part of the configuration of an embodiment can be deleted.

  In the above embodiment, the negative electrode having a negative electrode active material layer containing a cellulose derivative has been described in detail. However, in the present invention, the positive electrode may have a positive electrode active material layer containing a cellulose derivative.

  In the above embodiment, the positive electrode in which the active material layer containing the active material is in direct contact with the metal foil has been described in detail. However, in the present invention, the positive electrode is a conductive layer containing a binder and a conductive auxiliary agent, and the active material layer And a conductive layer disposed between the metal foil and the metal foil.

  In the above embodiment, the electrodes in which the active material layers are disposed on both sides of the metal foil of each electrode have been described. However, in the electricity storage device of the present invention, the positive electrode 11 or the negative electrode 12 has the active material layer on one side of the metal foil. It may be provided only on the side.

  In the said embodiment, although the electrical storage element 1 provided with the electrode body 2 by which the laminated body 22 was wound was demonstrated in detail, the electrical storage element of this invention may be provided with the laminated body 22 which is not wound. Specifically, the storage element may include an electrode body in which a positive electrode, a separator, a negative electrode, and a separator each formed in a rectangular shape are stacked a plurality of times in this order.

  In the above embodiment, the case where the power storage element 1 is used as a chargeable / dischargeable non-aqueous electrolyte secondary battery (for example, a lithium ion secondary battery) has been described. However, the type and size (capacity) of the power storage element 1 are arbitrary. is there. Moreover, although the lithium ion secondary battery was demonstrated as an example of the electrical storage element 1 in the said embodiment, it is not limited to this. For example, the present invention can be applied to various secondary batteries, and other power storage elements such as electric double layer capacitors.

  The power storage element 1 (for example, a battery) may be used in a power storage device 100 as shown in FIG. 8 (a battery module when the power storage element is a battery). The power storage device 100 includes at least two power storage elements 1 and a bus bar member 91 that electrically connects two (different) power storage elements 1 to each other. In this case, the technique of the present invention may be applied to at least one power storage element.

  A nonaqueous electrolyte secondary battery (lithium ion secondary battery) was produced as shown below.

(Test Example 1)
(1) Preparation of positive electrode N-methyl-2-pyrrolidone (NMP), a conductive additive (acetylene black), a binder (PVdF), and an active material (LiNi _1/3 Co _1/3 Mn _1/3 ) as a solvent A mixture for positive electrode was prepared by mixing and kneading the aggregated particles in which the primary particles of O ₂ ) coagulated with each other. The blending amounts of the conductive assistant, binder, and active material were 4.5% by mass, 4.5% by mass, and 91% by mass, respectively. The prepared positive electrode mixture was applied to both surfaces of an aluminum foil (15 μm thickness) so that the application amount (weight per unit area) after drying was 8.61 mg / cm ² . After drying, a roll press was performed. Thereafter, it was vacuum dried to remove moisture and the like. The thickness of the active material layer (for one layer) was 32 μm. The density of the active material layer was 2.69 g / cm ³ .

(2) Production of negative electrode As the active material, particulate amorphous carbon (non-graphitizable carbon) was used. As the binder, styrene butadiene rubber was used. As the cellulose derivative, carboxymethyl cellulose Na salt (product name “2200” manufactured by Daicel Corporation) was used. The negative electrode mixture was prepared by mixing and kneading water, a binder, a cellulose derivative, and an active material as a solvent. The cellulose derivative was blended so as to be 1.0% by mass, the binder was blended so as to be 2.0% by mass, and the active material was blended so as to be 97.0% by mass. The prepared negative electrode mixture was applied to both sides of a copper foil (thickness: 10 μm) so that the coating amount (weight per unit area) after drying was 3.8 mg / cm ² . After drying, roll pressing was performed and vacuum drying was performed to remove moisture and the like. The thickness of the active material layer (for one layer) was 39 μm. The density of the active material layer was 0.974 g / cm ³ . The density of the active material layer is determined by cutting the negative electrode into a predetermined size, measuring the mass and thickness, peeling the active material layer from the metal foil, measuring the mass and thickness of the metal foil, The measurement was performed by subtracting the mass and thickness of the metal foil from the mass and thickness, respectively.

(3) Separator A polyethylene microporous film having a thickness of 22 μm was used as a separator. The air permeability of the polyethylene microporous membrane was 100 seconds / 100 cc.

(4) Preparation of electrolytic solution As the electrolytic solution, one prepared by the following method was used. As a non-aqueous solvent, propylene carbonate, dimethyl carbonate, and ethyl methyl carbonate were mixed in a volume of 1 part by volume, and LiPF ₆ was dissolved in this non-aqueous solvent so that the salt concentration was 1 mol / L. An electrolyte solution was prepared.

(5) Arrangement of electrode body in case A battery was manufactured by a general method using the positive electrode, the negative electrode, the electrolytic solution, the separator, and the case.
First, a sheet-like material in which a separator was disposed between the positive electrode and the negative electrode and laminated was wound. Next, the wound electrode body was placed in the case body of an aluminum square battery case as a case. Subsequently, the positive electrode and the negative electrode were electrically connected to the two external terminals, respectively. Further, a lid plate was attached to the case body. The above electrolytic solution was injected into the case from a liquid injection port formed on the cover plate of the case. Finally, the case was sealed by sealing the liquid injection port of the case.

-About the average particle diameter D50 of the active material of a positive electrode and a negative electrode Each active material layer of the positive electrode and the negative electrode was taken out from the once manufactured battery. The active material layer was washed with dimethyl carbonate, crushed, and then pretreated by vacuum drying for 2 hours or more. A laser diffraction particle size distribution measuring device (“SALD2200” manufactured by Shimadzu Corporation) was used as a measuring device, and a dedicated application software DMSver2 was used as measurement control software. As a specific measurement method, a scattering-type measurement mode is adopted, and a wet cell in which a dispersion liquid in which a measurement sample (active material) is dispersed is placed in an ultrasonic environment for 2 minutes, and then irradiated with laser light. The scattered light distribution was obtained from the measurement sample. Then, the scattered light distribution is approximated by a lognormal distribution, and in the particle size distribution (horizontal axis, σ), the particle size corresponding to a cumulative degree of 50% (D50) is set in a range where the minimum is set to 0.021 μm and the maximum is set to 2000 μm. The average particle size was taken. In addition, the dispersion contains a surfactant and SN Dispersant 7347-C (product name) or Triton X-100 (product name) as a dispersant. A few drops of dispersant were added to the dispersion.

-About surface roughness Ra of a negative electrode active material layer The negative electrode active material layer was taken out from the once manufactured battery, and the same pretreatment as the above was performed. A laser microscope (“VK-8510” manufactured by Keyence Corporation) was used as a measurement device, and VK-H1W was used as software. As a specific measurement method, the magnification of the lens was set to 100 times, and the measurement sample was placed on a measurement table so as to be smooth, and then irradiated with laser light to obtain a color image of the measurement sample surface. And surface roughness Ra was computed with the software from the color image of the surface.

(Test Examples 2 to 11)
A lithium ion secondary battery was produced in the same manner as in Test Example 1 except that cellulose derivatives having the degree of etherification shown in Table 1 were used.

<Evaluation of capacity maintenance rate after repeated charge and discharge (cycle test)>
Charge to 4.2V at a constant current of 5A at 25 ° C, then charge for a total of 3 hours at a constant voltage of 4.2V, then measure the initial discharge capacity by discharging at a constant current of 5A and a final voltage of 2.4V. did. Regarding the battery after the capacity check test, the state of charge (SOC) of the battery is adjusted to 85% by charging 85% of the discharge capacity obtained in the capacity check test, and then held at −30 ° C. for 4 hours. Thereafter, a cycle of charging and discharging at a constant current of 40 A for 10 seconds and resting for 280 seconds was repeated 10,000 times. After carrying out the cycle, the capacity was confirmed, and the capacity retention rate before and after the cycle was calculated.

  In the battery having the predetermined configuration of the present embodiment, the capacity maintenance rate after the repeated charge / discharge test (cycle test) was high.

1: Power storage element (non-aqueous electrolyte secondary battery),
2: Electrode body,
26: Uncoated laminated part,
3: Case, 31: Case body, 32: Cover plate,
4: Separator,
5: current collector, 50: clip member,
6: Insulation cover
7: External terminal, 71: Surface,
11: positive electrode,
111: Metal foil of positive electrode (positive electrode base material), 112: Positive electrode active material layer,
12: negative electrode,
121: negative electrode metal foil (negative electrode substrate), 122: negative electrode active material layer,
91: Bus bar member,
100: Power storage device.

Claims (5)

A positive electrode and a negative electrode are provided as electrodes,
At least one of the electrodes has an electrode substrate, an active material layer containing a particulate active material and a cellulose derivative, and an active material layer overlaid on the electrode substrate,
The average particle diameter D50 of the active material is 1 μm or more and less than 5 μm,
The electric storage element, wherein a surface roughness Ra of one surface of the active material layer that does not overlap the electrode base material is 0.15 μm or more and 1.20 μm or less. A positive electrode and a negative electrode are provided as electrodes,
At least one of the electrodes has an active material layer containing a particulate active material and a cellulose derivative,
The average particle diameter D50 of the active material is 1 μm or more and less than 5 μm,
The electricity storage element whose etherification degree of the said cellulose derivative is 0.6-1.8. The power storage element according to claim 1, wherein the active material layer has a density of 0.6 g / cm ³ or more and 1.5 g / cm ³ or less. 4. The power storage device according to claim 1, wherein a basis weight of the active material layer is 0.3 g / 100 cm ² or more and 1.0 g / 100 cm ² or less.   The power storage element according to claim 1, wherein the one of the electrodes is a negative electrode.