JPH11354155A - Non-aqueous electrolyte secondary battery - Google Patents

Abstract

(57) [Problem] In a battery using an electrolytic solution in which a salt containing fluorine such as LiPF6 is dissolved, hydrogen fluoride (HF) generated by thermal decomposition of the salt when used or left at high temperatures is used. In addition, there has been a problem that the surface of the current collector metal of the electrode is oxidized to lower the current collecting property, and the battery characteristics are deteriorated. An electrolytic solution contains a lithium imide salt or a salt containing fluorine and a lithium imide salt to suppress generation of hydrogen fluoride.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a non-aqueous electrolyte secondary battery.

[0002]

2. Description of the Related Art In recent years, electronic devices such as a portable radio telephone, a portable personal computer, and a portable video camera have been developed, and various electronic devices have been reduced in size to be portable. Along with this, a battery having a high energy density and a light weight is also adopted as a built-in battery. A typical battery that satisfies such requirements is an active material such as lithium metal or lithium alloy, and a lithium ion as a host material (here, the host material refers to a material that can occlude and release lithium ions). LiClO4, LiPF
This is a lithium secondary battery using an aprotic organic solvent in which a lithium salt such as No. 6 is dissolved as an electrolyte.

A lithium secondary battery has a negative electrode plate in which the above-mentioned negative electrode material is held on a negative electrode current collector as a support, and a reversible electrochemical reaction with lithium ions, such as a lithium nickel composite oxide. A positive electrode plate holding the positive electrode active material to be supported on a positive electrode current collector as a support, and a separator that holds an electrolyte and intervenes between the negative electrode plate and the positive electrode plate to prevent a short circuit between the two electrodes. I have. In the case of a strip-shaped or cylindrical battery, the positive electrode plate, the separator and the negative electrode plate are each formed by sequentially laminating thin sheets or foils, or spirally winding and then wrapped in a battery container. Is stored in. Conventionally, as the current collector of the electrode plate,
Since it is necessary to have its own conductivity, a metal foil such as copper or aluminum has been used.

[0004] Further, in the case of a device using a battery as a power source, not limited to a lithium-based secondary battery, the demand for weight reduction and safety of the whole device is not exhausted. In addition, users who prefer battery performance that is higher than existing products, lighter, and safer. In order to achieve the object, a positive electrode current collector composed of an electrically insulating thin film such as a resin, a conductive thin film provided on one surface of the electric insulating thin film, and a positive electrode mixture layer provided on the positive electrode current collector A negative electrode current collector comprising a conductive thin film provided on the other surface of the electrically insulating thin film; a negative electrode material mixture layer provided on the negative electrode current collector; and at least one of a positive electrode material mixture layer and a negative electrode material mixture layer One of the present inventors has already proposed a non-aqueous electrolyte secondary battery characterized by comprising an electrolyte membrane in contact with an electrolyte membrane (Japanese Patent Application No. 10-100038).

[0005]

In this proposed battery, when a conventional electrolytic solution in which only a salt of LiPF6 is dissolved is used, when the battery is used or left at a high temperature, the LiP
Hydrogen fluoride (HF) generated by thermal decomposition of F6 oxidizes the surface of the current collector metal, lowering the current collecting property and increasing the internal resistance of the battery. Further, there is a problem that the metal layer is peeled off from the resin layer by hydrogen fluoride (HF) and the film is broken to lower the current collecting property. Therefore, use of the battery at a high temperature is not preferable. As a result, it is currently unsuitable to use these batteries in devices that get hot, such as portable personal computers with tremendous production. When the battery is used or left at a high temperature, Li
Even when a fluorine-containing salt such as LiBF4 and LiAsF6 other than PF6 is present, hydrogen fluoride (H
F) was generated and had the same problem as in the case of LiPF6.

Accordingly, the present invention has been made in view of the above-mentioned problems, and has been made to withstand use at high temperatures, and to be lightweight.
An object is to provide a safe non-aqueous electrolyte secondary battery.

[0007]

SUMMARY OF THE INVENTION The present invention provides an electric insulating thin film, a positive electrode current collector comprising a conductive thin film provided on one side of the electric insulating thin film, and a positive electrode current collector provided on the positive electrode current collector. Non-aqueous solution using an electrode plate comprising: a negative electrode current collector comprising a conductive material layer provided on the other surface of the electrically insulating thin film; and a negative electrode mixture layer provided on the negative electrode current collector. In the electrolyte secondary battery, the electrolyte solution contains a lithium imide salt, or contains a lithium imide salt and a salt containing fluorine other than the lithium imide salt. Further, in the electrolyte solution in which the lithium imide salt is dissolved, the weight ratio of the lithium imide salt to the total weight of the salts contained in the electrolyte solution is 5 wt%.
It is preferable that it is above.

Here, the lithium imide salt is generally a compound represented by the following chemical formula.

[0009]

Embedded image

Embedded image

Embedded image In the above chemical formula, R1 and R2 may be the same or different, and both are-(CF2) n-C
F3 [n ≧ 3]. A typical compound is LiN (SO2CF2CF3) 2.

In the present invention, in the case of a spiral electrode plate, the current collector may be thin because the wound electrode plate has an electrically insulating thin film as a core. And since the electrically insulating thin film is not metal, even if a thin film current collector is provided on both surfaces, the overall mass is lighter than the current collector made of metal foil of the same thickness,
Suitable for high energy density batteries. Further, in the conventional battery, since the positive electrode, the negative electrode, and the separator are configured separately from each other, the positions of the respective poles are shifted with respect to the counter electrode during lamination or winding, and the reaction area is reduced. In contrast to the possibility that the separator may move and cause a short circuit, the battery according to the present invention utilizes substantially both sides of a single electrically insulating thin film, and has a positive electrode, Since the negative electrode is supported on the other surface, there is an advantage that the positions of the positive electrode and the negative electrode do not shift.

The above-mentioned electrically insulating thin film may be substantially a single one. Therefore, usually one sheet, but two sheets
Also included are those in which the sheets are closely attached and integrated. If it is one sheet from the beginning, the step of integrating can be omitted. on the other hand,
In the case of a configuration in which two sheets are closely adhered, the current collector and mixture layer of the positive electrode and those of the negative electrode are fixed to only one surface of each electrically insulating thin film, and the two electrically insulating thin films are formed in a later step. They can be integrated by bringing them into close contact with each other. Therefore, when the mixture layer is applied, the variation in the thickness of one mixture layer does not affect the accuracy of the other layer. As the material of the electrically insulating thin film, it is preferable to use a thermoplastic resin such as polyethylene (PE), polyethylene terephthalate (PET), or polypropylene (PP) as a main component. Most thermoplastic resins have a thermal deformation temperature lower than the ignition point of the organic electrolyte, so even if heat is generated by short-circuiting, the resin film thermally contracts before the organic electrolyte such as the organic electrolyte or polymer electrolyte ignites. This is because the short-circuit point is eliminated and the current is quickly cut off. Accordingly, particularly preferred electrically insulating thin films are those having a heat distortion temperature lower than the ignition point of the organic electrolyte of the battery in which the current collector is used. As a method for measuring the ignition point, there are known two methods, a constant-speed heating method and a constant-temperature heating method. If you are not sure which one is more realistic, it is safer to choose a lower measurement.

The conductive thin film constituting the current collector includes a rolled foil in addition to a thin film formed by plating, vapor deposition, sputtering, or the like. Aluminum can also be used as the conductive thin film material serving as the current collector of the positive electrode. Aluminum is excellent in corrosion resistance and does not dissolve in the electrolyte even during charging when the positive electrode has a high potential. Rolled foil is easily available in the case of aluminum, but another form uses an aluminum vapor-deposited resin film in which an electrically insulating thin film and a metal thin film serving as a current collector of a positive electrode are integrated. You may. It is also possible to use an aluminum alloy instead of aluminum.

On the other hand, a particularly preferred thin film for the current collector of the negative electrode is a vapor-deposited film or a rolled thin film of copper (Cu), a copper-nickel alloy or nickel (Ni), or a combination thereof. Copper is excellent in that it has high conductivity and low cost. However, for copper, 3.1 V vs. Li /
It is experimentally known that melting occurs in a potential region that is more noble than Li +. Therefore, use within the range of 0 V to 3 V is appropriate. On the other hand, nickel is 4.0 ~
4.2V vs. Since it does not dissolve to Li / Li +,
Excellent in wide potential window. In the case of a copper-nickel alloy, it has excellent characteristics of both high electrical conductivity by copper and corrosion resistance of Ni.

In the present invention, the lithium imide salt used as the salt contained in the electrolytic solution does not cause a thermal decomposition reaction up to about 300 ° C., and has a much better thermal stability as compared with the thermal decomposition of LiPF6 from about 45 ° C. ing. Also,
Currently, compared to LiPF6 and the like, lithium imide salt is
Inexpensive LiPF used conventionally because it is expensive
6, LiBF4, LiAsF6, LiCF3CO2, and at least one salt selected from the group of LiCF3SO3 are preferably used as a mixture.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described based on examples with reference to the drawings.

[0016]

Embodiment 1 FIG. 2 shows a cross-sectional structure of a non-aqueous electrolyte secondary battery according to Embodiment 1 of the present invention. In FIG. 2, reference numeral 10 denotes a non-aqueous electrolyte secondary battery, in which a battery power generating element 8 formed by spirally winding a tape-shaped electrode plate is impregnated with an electrolytic solution, and then hermetically sealed in an aluminum case 9.

FIG. 1 shows a cross section of an electrode plate 7 constituting a battery power generating element 8. In FIG.
2 is a positive electrode current collector layer, 3 is an insulator layer, 4 is a negative electrode current collector layer,
Reference numeral 5 denotes a negative electrode mixture layer, and reference numeral 6 denotes an electrolyte layer, which has a configuration in which these are sequentially laminated. The positive electrode mixture layer 1 includes 6 parts by weight of polyvinylidene fluoride as a binder, 3 parts by weight of acetylene black as a conductive agent, and LiCo 0.15 as an active material.
Ni0.82Al0.03O2, 91 parts by weight, N-methylpyrrolidone as a solvent is appropriately added and mixed, and the produced active material paste has a coating weight after drying of 2.44 g / 1.
It was applied on the positive electrode current collector layer 2 so as to have a thickness of 00 cm 2, dried, and press-formed so as to have a thickness of 70 μm. The positive electrode current collector layer 2 was formed by laminating and bonding an aluminum foil having a thickness of 2 μm to the insulator layer 3. Insulator layer 3
A polyethylene terephthalate film having a thickness of 10 μm was used. However, the positive electrode mixture layer 2 was not applied to the lead attachment portion.

The negative electrode mixture layer 5 is prepared by adding N-methylpyrrolidone to a mixture of 92 parts by weight of graphite and 8 parts by weight of polyvinylidene fluoride, adding N-methylpyrrolidone appropriately, and forming a paste. The coating weight is 1.20 g / 100 cm 2. Was applied onto the negative electrode current collector layer 4 and dried, and was press-formed to a thickness of 80 μm. The negative electrode current collector layer 4 has a thickness of 3 μm.
m of copper, nickel is deposited first and then 3 μm
By electroplating copper. However, the negative electrode mixture layer 5 was not applied to the lead attachment portion.

Next, a terminal lead (not shown) was attached to each of the positive and negative electrodes to the current collector of the electrode plate.

Next, a laminate of the electrode plate and the separator was wound to produce a flat electrode body. Further, the positive electrode terminal and the negative electrode terminal are respectively taken out from the positive electrode current collector layer 2 and the negative electrode current collector layer 4 and stored in an aluminum case 9 as shown in FIG. 2, and ethylene carbonate (EC) and diethyl carbonate (DEC) ) In a solvent mixed at a volume ratio of 1: 1 with LiN (SO2CF2CF3).
After impregnating 2.5 g of an electrolyte solution obtained by dissolving 2 in 1 M under vacuum,
The battery according to the present invention having a design capacity of 600 mAh was sealed by sealing the aluminum case 9 and the battery lid by laser welding.
0 were produced.

[0021]

Example 2 1M [LiN (SO2CF2)
CF3) 2,95 wt% + LiPF6.5 wt%] /
Except that EC + DEC (volume ratio 1: 1) was used, 100 batteries of the present invention were manufactured in the same manner as in Example 1.

[0022]

Embodiment 3 1M [LiN (SO2CF2)
CF3) 2,80 wt% + LiPF6,20 wt%]
Example 1 except that / EC + DEC (volume ratio 1: 1) was used.
100 batteries of the present invention similar to the above were produced.

[0023]

EXAMPLE 1M [LiN (SO2CF2C)
F3) 2,50 wt% + LiPF6,50 wt%] /
Except that EC + DEC (volume ratio 1: 1) was used, 100 batteries of the present invention were manufactured in the same manner as in Example 1.

[0024]

Embodiment 5 1M [LiN (SO2CF2)
CF3) 2,20wt% + LiPF6,80wt%]
Example 1 except that / EC + DEC (volume ratio 1: 1) was used.
100 batteries of the present invention similar to the above were produced.

[0025]

Embodiment 6 1 M [LiN (SO2CF2)
CF3) 2,10 wt% + LiPF6, 90 wt%]
Example 1 except that / EC + DEC (volume ratio 1: 1) was used.
100 batteries of the present invention similar to the above were produced.

[0026]

Embodiment 7 1M [LiN (SO2CF2)
CF3) 2,5 wt% + LiPF6,95 wt%] /
Except that EC + DEC (volume ratio 1: 1) was used, 100 batteries of the present invention were manufactured in the same manner as in Example 1.

[0027]

[Comparative Example] 1M LiPF6 / EC + DE as electrolyte
Except for using C (1: 1 by volume), 100 conventional batteries were manufactured in the same manner as in Example 1.

After leaving the battery according to the present invention obtained in Examples 1 to 7 and the conventional battery of Comparative Example for several hours,
The battery was charged at a constant current and a constant voltage up to 4.1 V with a current of 0.5 C for 3 hours to obtain a fully charged state. Then at 85 ° C for 30
Left at high temperature for days. Table 1 shows the measured battery capacity and internal resistance after being left at high temperature.
The numerical values in Table 1 are average values of 100 batteries.

[0029]

[Table 1] From Table 1, it can be seen that the lithium imide salt Li
By adding N (SO2CF2CF3) 2 in a small amount of 5 wt% with respect to the total weight of the salt contained in the electrolytic solution, the increase in internal resistance after standing was significantly reduced, while the decrease in discharge capacity after standing was small.

From the above results, in the battery according to the present invention, the lithium imide salt LiN (SO
By adding 2CF2CF3) 2 in a small amount of about 5 wt% with respect to the total weight of the salt contained in the electrolytic solution,
It became clear that a battery exhibiting excellent characteristics even after storage at high temperature was obtained. The reason is that the presence of the lithium imide salt in the electrolytic solution suppresses the decomposition reaction of the salt containing fluorine coexisting in the electrolytic solution, thereby suppressing the generation of hydrogen fluoride (HF) inside the battery. However, its reaction mechanism is not clear at present.

In the examples, LiN (SO2CF2CF3) 2 was used as the lithium imide salt, but LiN (SO2
CF3) 2, LiN (COCF3) 2, LiN (COC
Compounds such as F2CF3) 2 can be used. The salt mixed with the lithium imide salt is LiPF6
, But is not limited to this.
BF4, LiAsF6, LiCF3CO2 and LiC
A salt such as F3SO3 or a mixture thereof may be used.

In the examples, a mixed solution of ethylene carbonate (EC) and diethyl carbonate (DEC) is used as a solvent for the electrolytic solution. However, the present invention is not limited to this. Polar solvents such as carbonate, γ-butyrolactone, sulfolane, dimethyl sulfoxide, acetonitrile, dimethylformamide, dimethylacetamide, 1,2-dimethoxyethane, 1,2-diethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dioxolane, and methyl acetate; Alternatively, a mixture thereof may be used. In the examples, the non-aqueous electrolyte was used as the electrolyte to be used, but the electrolyte used in the battery according to the present invention is not limited to these, and a lithium ion conductive polymer solid electrolyte membrane was used. In such a case, the electrolyte contained in the lithium ion conductive polymer solid electrolyte may be different from the electrolyte contained in the pores of the electrode.

Further, in the above embodiment, the compound capable of inserting and extracting lithium as the positive electrode material is LiCo.
Although 0.15Ni0.82Al0.03O2 is used, the cathode material is not limited to this. In addition, as the inorganic compound, a composition formula LixMO2 or LiyM2O4 (where M is a transition metal, 0 ≦ x ≦
1, 0 ≦ y ≦ 2), a composite oxide, an oxide having tunnel-like vacancies, and a metal chalcogenide having a layered structure can be used. As a specific example, LiC
oO2, LiNiO2, LiMn2O4, Li2Mn
2O4, MnO2, FeO2, V2O5, V6O1
3, TiO2, TiS2, and the like. Examples of the organic compound include a conductive polymer such as polyaniline. Further, the above-mentioned various active materials may be mixed and used regardless of an inorganic compound or an organic compound.

Further, in the above embodiment, graphite is used as a compound as a negative electrode material. In addition, alloys of lithium with Al, Si, Pb, Sn, Zn, Cd, etc., WO2, MoO2, etc. Carbonaceous materials such as transition metal oxides, graphite, and carbon; Li5 (Li3
N) or a lithium metal foil such as N), or a mixture thereof.

[0035]

According to the non-aqueous electrolyte secondary battery of the present invention, the generation of hydrogen fluoride (HF) inside the battery is suppressed even when the battery is left at a high temperature, and the surface of the current collector metal Is not oxidized by hydrogen fluoride (HF). As a result, the increase in internal resistance of the battery is extremely small,
As can be seen from the fact that the decrease in the discharge capacity can be reduced, it is possible to provide a non-aqueous electrolyte battery excellent in energy density per volume and extremely light without significantly reducing the performance of the battery. Thus, the battery according to the present invention can extend the usable temperature range to a high temperature range. Therefore, the present invention is not only industrially and commercially valuable, but also very useful for users because it can be used at high temperatures.

[Brief description of the drawings]

FIG. 1 is a diagram showing a cross section of an electrode plate constituting a power generation element of a nonaqueous electrolyte secondary battery of Example 1.

FIG. 2 is a view showing a cross-sectional structure of a non-aqueous electrolyte secondary battery of Example 1.

[Description of Signs] 1 Positive electrode mixture layer 2 Positive electrode current collector layer 3 Electric insulating film 4 Negative current collector layer 5 Negative electrode mixture layer 6 Electrolyte layer 7 Electrode plate 10 Non-aqueous electrolyte secondary battery

Claims (3)

[Claims] An electric insulating thin film, a positive electrode current collector comprising a conductive thin film provided on one side of the electric insulating thin film, a positive electrode mixture layer provided on the positive electrode current collector, and an electric insulating thin film A negative electrode current collector made of a conductive thin film provided on the other surface, and an electrode plate having a negative electrode mixture layer provided on the negative electrode current collector,
A non-aqueous electrolyte secondary battery, wherein the electrolyte contains a lithium imide salt. 2. The non-aqueous electrolyte secondary battery according to claim 1, wherein the electrolyte contains a salt containing fluorine other than a lithium imide salt. 3. The non-aqueous electrolyte secondary battery according to claim 1, wherein the ratio of the weight of the lithium imide salt to the total weight of the salts contained in the electrolyte is 5 wt% or more.