JP2002056893A - Nonaqueous electrolyte battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve safety of a battery while maintaining battery performance in the case of using organic electrolyte, even when solid high polymer electrolyte is used and to realize high capacity of the battery by improving a utilization rate of an active material. SOLUTION: In this nonaqueous electrolyte battery, porous solid high polymer electrolyte provided with a high polymer shown in the following formula for instance, is provided within the battery: -(CH2-CH2-O)x-(CH2-C(CH2Cl)H-O)y-.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

2. Description of the Related Art Currently, commercially available lithium ion secondary batteries use a composite oxide active material of a transition metal such as lithium cobalt oxide for a positive electrode, a carbon-based active material such as graphite for a negative electrode, and use polyethylene or polypropylene. The positive and negative electrodes face each other with a porous separator interposed therebetween. Then, various carbonates such as ethylene carbonate, ethyl methyl carbonate, dimethyl carbonate and diethyl carbonate are added to LiPF6, LPF
A non-aqueous solution in which a lithium salt such as iBF4 is dissolved is used as an electrolyte.

The positive and negative electrodes of a lithium ion secondary battery are kneaded with active material particles, a polymer as a binder, and a conductive agent such as acetylene black when the active material has insufficient electron conductivity. The object is applied to the current collector and pressed to produce. The positive / negative electrode fabricated in this way has pores in the gaps between the active material particles, and by impregnating the pores with an electrolyte, a lithium ion transfer path necessary for the electrode reaction is secured, and the battery performance is improved. Can be obtained.

[0004] Non-aqueous electrolyte batteries such as the above-mentioned lithium ion battery and lithium battery using metal lithium for the negative electrode are different from lead-acid batteries, nickel-cadmium batteries, nickel-hydrogen batteries, etc., which use an aqueous solution for the electrolyte. Because of the use of flammable organic electrolytes, due to safety issues, it is necessary to limit the utilization rate of the active material, which limits the capacity of the battery, as well as safety valves, protection circuits,
It is necessary to provide various safety elements such as a PTC element, and there is a problem that the cost increases.

Therefore, it has been attempted to improve the safety of a battery by using a solid polymer electrolyte having a lower chemical reactivity in place of the organic electrolyte, and to omit the safety element. Also, application of solid polymer electrolytes has been attempted for the purpose of flexibility of battery shape, simplification of manufacturing process, reduction of manufacturing cost, and the like.

As the polymer electrolyte, many studies have been made on complexes of polyethers such as polyethylene oxide and polypropylene oxide with alkali metal salts. However, polyether is difficult to obtain high ionic conductivity while maintaining sufficient mechanical strength, and since conductivity is greatly affected by temperature, sufficient conductivity cannot be obtained at room temperature. , Comb-type polymers having polyethers in side chains, copolymers of polyether chains and other monomers, polysiloxanes or polyphosphazenes having polyethers in side chains, cross-linked polyethers, etc. have been attempted. .

Further, Japanese Patent Application Laid-Open No. 9-324114, Japanese Patent Application Laid-Open No. 11-7980, or Japanese Patent Application Laid-Open No. 11-399
In Japanese Patent Publication No. 40, etc., a polymer solid electrolyte mainly composed of glycidyl ether and ethylene oxide is proposed, but the charge / discharge characteristics when applied to a lithium battery, particularly high-rate discharge characteristics, are not sufficient.

Further, it has been attempted to produce a gel-like solid electrolyte by impregnating a polymer with an electrolytic solution and to apply it to a non-aqueous electrolyte battery. Polymers used in the gel solid electrolyte include polyacrylonitrile, polyvinylidene fluoride, polyvinyl chloride, polyvinyl sulfone, polyvinyl pyrrolidinone, and the like. Attempts have also been made to reduce the crystallinity of the polymer by using a copolymer of vinylidene fluoride and hexafluoropropylene, to facilitate impregnation with an electrolytic solution, and to improve the electrical conductivity.

Further, it is also possible to produce a polymer film by drying a latex such as nitrile rubber, styrene-butadiene rubber, polybutadiene, polyvinylpyrrolidone and the like, and to impregnate it with an electrolytic solution to produce a lithium ion conductive polymer film. Attempted.

[0010]

However, in a non-aqueous electrolyte battery using the above-described solid electrolyte instead of the organic electrolyte, the diffusion rate of ions in the solid electrolyte is extremely large as compared with the organic electrolyte. Because of the slowness, the supply of lithium ions required for the electrode reaction is not sufficiently performed, and there has been a problem that sufficient battery performance cannot be obtained when charging and discharging are performed at a high rate or at a low temperature.

The present invention has been made in view of the above problems, and improves the safety of a battery even when a solid polymer electrolyte is used, while maintaining the battery performance when an organic electrolyte is used. As a result, it is possible to increase the capacity of the battery by improving the utilization rate of the active material and to reduce the cost of the battery by omitting the safety element.

[0012]

The non-aqueous electrolyte battery of the present invention comprises at least one selected from the group consisting of
The present invention is characterized in that a porous solid polymer electrolyte having various kinds of polymers is provided in the battery. Where x, y, z, m,
n is a natural number, R, R ₁ and R ₂ each represent an alkyl group having 1 to 12 carbon atoms, and R ₁ = R ₂ or R ₁ ≠ R ₂ .

[0013]

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[0014]

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[0015]

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[0016]

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[0017]

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[0018]

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Further, the above-mentioned porous solid polymer electrolyte comprises:
Positive electrode surface, in positive electrode hole, negative electrode surface, negative electrode hole, positive electrode
It is provided at any one or more locations between the negative electrodes.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION The non-aqueous electrolyte battery according to the present invention comprises a porous polymer electrolyte which swells or wets with an electrolytic solution inside the battery, preferably on the positive electrode surface, in the positive electrode hole, on the negative electrode surface,
It is provided at one or more places between the positive electrode and the negative electrode in the hole of the negative electrode.

The porous polymer electrolyte used in the present invention comprises:
It is provided with at least one polymer selected from the group shown in Chemical formulas 7 to 12. These polymers are
As shown in Chemical formula 12, various functional groups are introduced into the side chain of polyethylene oxide, and polyethylene oxide does not have a side chain when used as a polymer electrolyte by having these side chains. As compared with the case, the ionic conductivity becomes higher, and by using this polymer electrolyte, a non-aqueous electrolyte battery having excellent high-rate discharge characteristics can be obtained.

Since the porous polymer has the property of swelling or wetting with the electrolytic solution, even if the amount of liquid injected into the battery is small, the porous polymer absorbs the electrolytic solution and spreads evenly over the entire electrode. Can be made. Therefore, when the battery holds a smaller amount of electrolyte than the amount of electrolyte sufficient to occupy all the pores such as the pores of the porous polymer electrolyte and the electrodes,
That is, even in the case where a gas portion remains in the pores of the porous polymer electrolyte or in the pores of the electrode, it is possible to obtain sufficient battery performance by spreading the electrolyte over the entire electrode. it can.

In this case, when a safety test such as nail penetration is performed, since a gas serving as a cushion against the pressure rise is present near the electrode, the heat generated in the internal short-circuited portion causes the electrolytic solution in the vicinity to evaporate. Even in such a case, a local pressure rise is greatly reduced, and a reaction which is a starting point of the exothermic chain reaction hardly occurs, thereby improving safety. Therefore, the safety of the battery is improved, and the utilization rate of the restricted active material can be improved, so that the battery can be a high-capacity battery, and various safety elements can be omitted. The cost can be reduced because of the above.

Further, in the present invention, unlike the conventional solid electrolyte battery, since the polymer has pores holding the gas and the free electrolyte, ions diffuse at a high speed in the free electrolyte. Sufficient battery performance is obtained.

The porous polymer used in the present invention, which swells or wets with an electrolytic solution, acts as a polymer electrolyte in a battery. Thus, ions can move even in the portion of the polymer swollen or wet. Therefore, even if the amount of electrolyte in the pores of the membrane is reduced by using a membrane having a porous polymer electrolyte instead of a conventional polyethylene or polypropylene separator that does not exhibit ion conductivity, the battery It is possible to prevent the performance from lowering, and it is possible to improve the safety of the battery.

Also, ions are sufficiently supplied to the portion of the electrode covered with the polymer, and the ions can move at high speed in the electrolyte in the pores of the polymer electrolyte. The distance from the portion covered with the polymer electrolyte to the pores of the polymer electrolyte is very short. Therefore, even when the diffusion coefficient of the ions in the polymer electrolyte is smaller than that of the electrolyte, the ions are quickly supplied to the electrodes, and sufficient battery performance can be obtained.

When comparing the high molecular weight per unit volume between the electrode and the polymer electrolyte between the positive electrode and the negative electrode, the polymer can be filled only in the pores of the active material in the electrode. -The polymer electrolyte per unit volume of the polymer electrolyte between the negative electrodes is several times higher. Therefore, even when the amount of liquid injected into the battery is small, when a polymer that swells or wets with the electrolyte between the positive and negative electrodes is used, the polymer between the positive and negative electrodes quickly converts the electrolyte. Since the battery can be absorbed and spread over the entire battery, sufficient battery performance can be obtained in a short time after the injection.

Further, by using the positive and negative electrodes provided with the porous polymer electrolyte, the electrolyte can be uniformly distributed in the positive and negative electrodes. Current distribution becomes uniform, charging and discharging at a high rate become possible, and dendritic deposition of alkali metal on the negative electrode during charging can be prevented, so that a safer battery can be obtained.

Further, since the polymer electrolyte has poorer chemical reactivity or a lower chemical reaction rate than the organic electrolyte, the use of a positive / negative electrode provided with a porous polymer electrolyte allows
Oxidation of the electrolytic solution at the positive electrode and reduction of the electrolytic solution at the negative electrode can be suppressed, self-discharge of the battery can be suppressed, and the battery can have a long life.

Further, since the porous polymer electrolyte occupies a certain volume in the positive and negative electrodes, the amount of the electrolyte in and around the pores of the positive and negative electrodes can be reduced, and the electrolyte is vaporized due to a short circuit or the like. The internal pressure rise near the positive and negative electrodes can be suppressed. For this reason, even when the carbon-based negative electrode active material is charged to a higher level, lithium carbide (Li ₂ C ₂ ) is generated by the reaction between lithium and carbon in the negative electrode, and the resulting heat generation and rapid internal pressure of the battery are caused. The rise can be suppressed, and the safety of the battery can be improved.

Further, since the positive electrode holds the polymer electrolyte, the speed of movement of oxygen released from the positive electrode to the negative electrode during abnormal heat generation of the battery can be reduced, and a rapid exothermic reaction between oxygen and the negative electrode can occur. Therefore, the safety of the battery can be improved.

When the porous polymer electrolyte exists between the positive electrode, the negative electrode, and the positive and negative electrodes, the entirety between the positive electrode, the negative electrode, and the positive and negative electrodes has the ability to retain the electrolyte evenly. Therefore, even if the amount of the electrolyte decreases due to the decomposition of the electrolyte at the positive and negative electrodes by repeating the charge and discharge cycle at a high temperature, the electrolytic solution is locally located between the positive electrode, the negative electrode, and the positive and negative electrodes. And a battery with excellent cycle life at high temperatures.

In the battery of the present invention, the solvent of the non-aqueous electrolyte is ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (D
MC), diethyl carbonate (DEC), γ-butyrolactone, sulfolane, dimethyl sulfoxide, acetonitrile, dimethylformamide, dimethylacetamide, 1,2-dimethoxyethane, 1,2-diethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dioxolan, Polar solvents such as methyl acetate,
Alternatively, a mixture thereof may be used.

Further, the salts contained in the non-aqueous electrolyte include LiPF ₆ , LiBF ₄ , LiAsF ₆ , and LiClO.
₄ , LiSCN, LiI, LiCF ₃ SO ₃ , LiCl,
A lithium salt such as LiBr and LiCF ₃ CO ₂ or a mixture thereof may be used.

Further, as a positive electrode material capable of inserting and extracting an alkali metal, as an inorganic compound, a composition formula Li _x MO ₂ ,
Or Li _y M ₂ O ₄ (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, LiCo
O ₂ , LiNiO ₂ , LiMn ₂ O ₄ , Li ₂ Mn ₂ O ₄ ,
MnO ₂ , FeOOH, FeO ₂ , V ₂ O ₅ , V ₆ O ₁₃ ,
TiO ₂ , TiS ₂ , nickel oxyhydroxide and the like can be mentioned. Examples of the organic compound include a conductive organic polymer such as polyaniline. Furthermore, regardless of an inorganic compound or an organic compound, the above-mentioned various active materials may be mixed and used.

Further, as a compound as a negative electrode material, A
Alloys of lithium with l, Si, Pb, Sn, Zn, Cd, etc., transition metal composite oxides such as LiFe ₂ O ₃ , Mo
Transition metal oxides such as O ₂ and tin oxide, graphite,
A carbonaceous material such as carbon, lithium nitride such as Li ₅ (Li ₃ N) can be used, or a metal lithium foil and a mixture thereof may be used.

[0037]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a preferred embodiment of the present invention will be described.

[Example 1] Nickel oxyhydroxide 70w
t%, acetylene black 6wt%, PVdF9wt
% And 15 wt% of NMP were applied on an aluminum foil having a width of 20 mm, a length of 480 mm and a thickness of 20 μm, and dried at 100 ° C. to evaporate NMP. This operation was performed on both sides of the aluminum foil to produce a positive electrode having an active material layer on both sides.

The negative electrode was manufactured by pressing a metal lithium foil having a thickness of 20 μm on both sides of a copper foil having a thickness of 14 μm as a current collector.

Next, a porous lithium ion conductive polymer film used as a film for preventing short circuit between the positive electrode and the negative electrode was manufactured by a wet method as follows. A solid polymer powder having a molecular weight of about 1,500,000 represented by Chemical Formula 8 (provided that R
= CH ₃ ) was dissolved in 88 g of dioxane to prepare a paste. This paste was applied on polyethylene coated silica gel by the doctor blade method,
By immersing in water and replacing dioxane with water, a polymer membrane having a porosity of about 80% and a thickness of about 25 μm having communication holes was produced.

The porous polymer membrane thus prepared,
A positive electrode and a negative electrode are stacked and wound, and a height of 47.0 mm and a width of 2
The battery was inserted into a 2.2 mm, 6.4 mm thick stainless steel case to assemble a prismatic battery. Inside the battery, ethylene carbonate (EC) and diethyl carbonate (DEC) were mixed at a volume ratio of 1: 1 and mixed at 1 mol / l.
Of LiPF6 was added by vacuum injection,
The battery (A) of the present invention having a nominal capacity of 400 mAh was manufactured by swelling the porous polymer membrane between the positive electrode and the negative electrode with an electrolytic solution to obtain a porous polymer electrolyte.

Comparative Example 1 As a short-circuit preventing film between a positive electrode and a negative electrode, a polymer film having no holes was manufactured as follows. A paste was prepared by dissolving 12 g of a solid polymer powder having a molecular weight of about 1,500,000 shown in Chemical formula 8 in 88 g of dioxane. This paste was applied on a polyethylene-coated silica paper by a doctor blade method and then dried to produce a polymer film having a thickness of about 25 μm and having no holes.

Except for using the polymer membrane having no pores, the same procedure as in (A) of the present invention was carried out, and the nominal capacity was 40%.
A comparative battery (B) using a conventionally known solid polymer electrolyte of about 0 mAh was manufactured.

[Comparative Example 2] A nominal capacity of about 400 mAh was obtained in the same manner as in (A) according to the present invention, except that a polyethylene separator having a porosity of 40% was used as a short-circuit preventing film between the positive electrode and the negative electrode. A comparative battery (C) using no conventionally known solid polymer electrolyte was manufactured. The porosity of the films shown in Examples and Comparative Examples is a value calculated from the weight and size of the film and the true specific gravity of the material of the film.

Each of the battery A of the present invention and the comparative batteries B and C was prepared in a quantity of five, and discharged at 25 ° C. in the first cycle at a current of 0.2, 0.5, 1 and 2 CA at 2.0 V. Until discharge. Then, at a current of 1 CA, 4.1
V, followed by charging at a constant voltage of 4.1 V for 2 hours, and then discharging and discharging under the same conditions as in the first cycle.
The cycle was repeated. Table 1 shows a comparison of the discharge capacity at the first cycle and the sixth cycle. In addition, the discharge capacity of Table 1 is an average value of 5 cells of each battery.

[0046]

[Table 1]

The discharge capacity of the battery A using the porous solid polymer electrolyte membrane of the present invention has the same discharge characteristics as that of the conventional battery C without using the solid polymer electrolyte. It was found that the discharge performance at a particularly high rate was improved as compared with the battery B using the electrolyte. Similar results were obtained after a lapse of the cycle.

Further, the following safety comparison test was performed using one battery of the present invention A and one battery of the comparative battery C. At room temperature, the battery was charged to 4.5 V with a current of 1 CA, and then charged at a constant voltage of 4.5 V for 2 hours.
A nail having a diameter of m was pierced by piercing the battery. Table 2 shows the results.

[0049]

[Table 2]

From the results shown in Table 2, the battery A according to the present invention has
It was found that the battery was more excellent in safety than the conventionally known battery C.

In the above embodiment, the polymer shown in Chemical Formula 8 was used as the polymer of the polymer electrolyte. However, the effect of the present invention is not limited to this. The derivatives may be used alone or as a mixture.

In the above embodiment, dioxane was used as the solvent for dissolving the solid polymer powder. However, any solvent having the property of dissolving the solid polymer may be used. For example, acetonitrile , Tetrahydrofuran (THF) or NMP can be used.

In the battery of the above embodiment, the porous solid polymer electrolyte membrane is used for the separator portion. However, at least one of the surfaces of the electrode plates in the holes of the positive electrode and the negative electrode. The porous solid polymer electrolyte may be disposed on the surface, or may be disposed in any combination.

Further, in the battery of the above embodiment, the method of making the porous polymer electrolyte porous by the wet method has been described, but the method of making the polymer porous is not limited to this, and the foaming agent may be used. , A method of adhering a powder, a method of depositing a solid in a polymer, and the like, and a hole may be physically formed with a laser or a fine needle.

[0055]

As described above, the non-aqueous electrolyte battery according to the present invention is characterized in that the solid polymer electrolyte used in the battery is made porous so that the conventional solid polymer electrolyte having no pores can be used. Since the charge / discharge performance can be improved as compared with the used battery, and a battery with higher safety than a conventionally known battery using no solid polymer electrolyte can be provided, the industrial value thereof is extremely large.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5H029 AJ03 AJ12 AK02 AK03 AK05 AK16 AK18 AL01 AL02 AL03 AL07 AL08 AL12 AM02 AM03 AM04 AM05 AM07 AM16 DJ14 EJ14 HJ02

Claims (2)

[Claims] 1. A non-aqueous electrolyte battery comprising a porous solid polymer electrolyte including at least one polymer selected from the group consisting of Chemical Formulas 1 to 6 in the battery. Here, x, y, z, m and n are natural numbers, R, R ₁ and R ₂ are alkyl groups having 1 to 12 carbon atoms, and R ₁ = R ₂ or R ₁ ≠ R ₂ . Embedded image Embedded image Embedded image Embedded image Embedded image Embedded image 2. The method according to claim 1, wherein the porous solid polymer electrolyte is provided on any one or more of the positive electrode surface, the positive electrode hole, the negative electrode surface, the negative electrode hole, and between the positive electrode and the negative electrode. The non-aqueous electrolyte battery according to claim 1.