JP2001345121A - Nonaqueous electrolyte secondary battery and method of manufacturing it - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of manufacturing a nonaqueous electrolyte secondary battery using a gelled polymer solid electrolyte, with high charging/ discharging cycle characteristics, high productivity, and high production yield. SOLUTION: In the method of manufacturing a nonaqueous electrolyte secondary battery having an electrode group formed by integratedly winding a positive electrode and a negative electrode through a separator, a pregel solution comprising a polymerizable compound of an oligomer having high molecular weight and the nonaqueous electrolyte is impregnated into the electrode group, the electrode group and the pregel solution are closely contacted by applying pressure, the electrode group containing the pregel solution is put into an outer case, the outer case is sealed under a reduced pressure atmosphere, and then the pregel solution is polymerized and cured.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-aqueous electrolyte secondary battery having a gel polymer solid electrolyte and a method for producing the same.

[0002]

2. Description of the Related Art Conventionally, non-aqueous electrolytes have been used as electrolytes for lithium ion secondary batteries, but batteries using polymer solid electrolytes instead of such liquid electrolytes have been actively developed. . A battery using a polymer solid electrolyte has a feature that the electrolyte is not liquid, so that there is no fear of liquid leakage and the battery can be easily miniaturized. But,
The solid electrolyte has a problem that it has poor ionic conductivity as compared with the liquid electrolyte and has poor contact with the active material, so that sufficient battery performance cannot be obtained. Therefore, in recent years, as a means for solving such a problem, a gel polymer solid electrolyte of a type in which a liquid electrolyte is retained in a polymer has been developed and put into practical use. A gel polymer solid electrolyte is a gel in which a liquid electrolyte is held in a polymer network structure, and contains a liquid electrolyte as compared with a conventional solid electrolyte, so that ion conductivity and contact with an active material are improved. In addition, it has a feature that liquid leakage hardly occurs as compared with a liquid electrolyte.

A gel polymer solid electrolyte battery is generally manufactured by the following method.

[0004] A pregel solution comprising an electrolytic solution containing a lithium salt and an organic high molecular compound which becomes a polymer after polymerization, called an oligomer, and a polymerizable compound is applied to the surface of the positive electrode or the negative electrode. First, by heating or irradiating ultraviolet rays, the oligomer and the polymerizable compound in the pregel solution are polymerized and cured to form a gel polymer solid electrolyte membrane on the electrode surface, and then the positive electrode and the negative electrode face each other. In this case, the power generator is firstly bonded and then polymerized and cured to form a gelled polymer solid electrolyte between the positive and negative electrodes. Then, it is stored in an exterior body.

[0005] However, the above-mentioned conventional methods have problems that productivity and yield are poor, and that discharge capacity and cycle characteristics are not sufficient. Specifically, when a certain pressure is applied during the manufacturing process, the gel polymer solid electrolyte is broken, and a short circuit inside the battery occurs. If the concentration of the organic polymer solid electrolyte with respect to the non-aqueous electrolyte or the thickness of the gel polymer solid electrolyte layer is increased in order to increase the mechanical strength, the ion conductivity becomes poor, and the discharge capacity and cycle characteristics become poor.

Therefore, a method of interposing a porous film between the positive electrode and the negative electrode has been proposed. In this case, in order to obtain sufficient ion conductivity, a gel-like polymer solid electrolyte is held on the porous film. And the number of steps increases. In addition, it is difficult to apply a pre-gel solution to the porous electrode surface having pores or irregularities and to penetrate the electrode, and it is susceptible to external environmental factors (such as humidity and oxygen concentration) during the manufacturing process. This is also a cause of insufficient battery characteristics.

JP-A-11-210438 and JP-A-11-283673 propose a method in which a pregel solution is injected into a power generator housed in an exterior body, and the exterior body is heated and polymerized. However, the viscosity of the pregel solution has a great effect on the configuration in which the liquid is injected into the power generator housed in the outer package and is heated and polymerized. If the viscosity is high, the permeability to the positive electrode active material, the negative electrode active material, and the separator deteriorates, resulting in a non-uniform gel-like polymer solid electrolyte membrane, and a sufficient discharge capacity cannot be obtained. It is effective to reduce the molecular weight of the oligomer in order to lower the viscosity, but then the oligomer is polymerized.
The mechanical strength of the cured polymer is reduced, and it is difficult to obtain a battery having good charge / discharge cycle characteristics.
When the concentration with respect to the electrolytic solution is increased, the injectability and permeability deteriorate, and when the concentration is decreased, the presence of the electrolytic solution which is phase-separated after polymerization and curing of the pregel is concerned. As described above, the conventional method has problems that productivity and yield are poor, and discharge capacity and cycle characteristics are not sufficient.

[0008]

SUMMARY OF THE INVENTION The present invention solves such a conventional problem and provides a non-aqueous electrolyte secondary battery using a gel polymer solid electrolyte and having a high production yield and a high production yield. The purpose is to do so.

[0009]

Means for Solving the Problems In order to solve the above problems, a nonaqueous electrolyte secondary battery of the present invention has a nonaqueous electrolyte having a group of electrode plates in which a positive electrode and a negative electrode are laminated or wound with a separator interposed therebetween. In a water electrolyte secondary battery, having a gel polymer solid electrolyte made by holding a non-aqueous electrolyte in a polymer between the separator and the positive electrode and between the separator and the negative electrode as a lithium ion conductive medium, and The polymer is obtained by polymerizing and curing an oligomer having a number average molecular weight of 200,000 or more. As described above, the separator is interposed between the positive electrode and the negative electrode in addition to the solid electrolyte, and by using a high molecular weight oligomer, the separator and the mechanical strength can be maintained even when a certain pressure is applied to the gel polymer solid electrolyte. Since a polymer having excellent heat resistance is interposed, a short circuit inside the battery can be prevented, and the charge / discharge cycle characteristics are good. In addition, even when the concentration of the oligomer with respect to the electrolytic solution is reduced, the high molecular weight oligomer does not have the electrolytic solution that is phase-separated after polymerization and curing, so that sufficient mechanical strength can be obtained.

Further, the method of manufacturing a non-aqueous electrolyte secondary battery having an electrode group in which a positive electrode and a negative electrode are laminated or wound via a separator according to the present invention is provided. A step of impregnating and impregnating a pregel solution comprising a water electrolyte and a polymerizable compound, a step of further applying external pressure to bring the electrode group and the pregel solution into close contact with each other, and attaching the electrode group containing the pregel solution to an exterior body. After the insertion and sealing under a reduced pressure atmosphere, the oligomer and the polymerizable compound are polymerized and cured to form a polymer and simultaneously form a gel polymer electrolyte. First, a step of impregnating and infiltrating a pregel solution into the integrated electrode plate group is provided, and a high molecular weight oligomer is sufficiently penetrated into the separator and the active material layers of the positive electrode and the negative electrode. In addition, since the electrode group containing the pregel solution is subjected to external pressure to increase the adhesion and then polymerized and cured, the contact resistance at the interface between the active material layers of the positive electrode and the negative electrode and the gel polymer solid electrolyte is small,
Good ion conductivity. Further, according to the present invention, the electrode plate group containing the pregel solution is housed in the outer package and sealed under a reduced pressure atmosphere before the polymerization and curing, so that an oxygen shielding atmosphere is provided, and the polymerization and curing reaction can be surely promoted.

In particular, the number average molecular weight of the oligomer is preferably 200,000 or more.

Therefore, according to the present invention, it is possible to provide a non-aqueous electrolyte secondary battery having good productivity and yield, high capacity and good cycle characteristics.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION The non-aqueous electrolyte secondary battery of the present invention
A positive electrode and a negative electrode are laminated via a separator, and a positive electrode and a negative electrode are laminated or wound and integrated, and an electrode plate group, and a polymer is used to hold a non-aqueous electrolyte between the separator and the positive electrode and between the separator and the negative electrode. And a polymer obtained by polymerizing and curing an oligomer having a number average molecular weight of 200,000 or more as a polymer.

Particularly, the amount of the oligomer is preferably 5,000,000 or less.

As the separator, for example, a polyolefin-based polymer such as polypropylene or polyethylene can be used. The positive electrode and the negative electrode can be manufactured by applying a mixture layer containing a conductive agent, a binder, and the like to the surface of the current collector on a positive electrode material or a negative electrode material capable of electrochemically and reversibly absorbing and releasing lithium ions. . The electrode plate group can be produced, for example, by stacking and stacking a sheet-shaped positive electrode, a separator, and a negative electrode, or by winding the stacked one in an elliptical or circular shape. As the positive electrode material, preferably, Li _x Co
Lithium-containing transition metal oxides such as O ₂ , Li _x NiO ₂ , Li _x MnO _2, or those obtained by dissolving other metals in these are used. As the negative electrode material, preferably, natural graphite, artificial graphite, amorphous carbon, amorphous carbon, Sn or Si
An intermetallic compound, alloy or oxide having lithium as a constituent element, a composite nitride of lithium and cobalt, or the like is used.

The gel-like solid electrolyte is present between the separator and the positive electrode and between the separator and the negative electrode, and is held by a polymer that holds the non-aqueous electrolyte. The gelling method will be described later.

Examples of the polymer for holding the non-aqueous electrolyte and the oligomer for forming the same include polyethylene oxide, polypropylene oxide, polyphosphazene, polyaziridine, polyethylene sulfide, polyvinyl alcohol, polyvinylidene fluoride, and polyhexafluoropropylene. , Polyacrylonitrile, polyacryl methacrylate and their derivatives, mixtures,
Complexes and the like can be used. Particularly, polyethylene oxide, polypropylene oxide and derivatives thereof are preferable.

This oligomer needs to have a number average molecular weight of 200,000 or more. If the molecular weight is smaller than 200,000, the mechanical strength of the polymer formed in the battery is inferior, and the effects of the present invention such as prevention of short circuit inside the battery and improvement of charge / discharge cycle characteristics cannot be obtained. Also, it seems that the number average molecular weight is preferably 5,000,000 or less.
If it is larger than 5 million, the viscosity of the pregel solution increases,
This is because it becomes difficult to impregnate and permeate the pores of the electrode plate group and the separator.

As the non-aqueous electrolyte, those which are usually used for non-aqueous electrolyte secondary batteries can be used. Preferably, ethylene carbonate, propylene carbonate,
Examples thereof include those obtained by dissolving LiPF ₆ or LiBF ₄ as a supporting electrolyte in a mixed organic solvent of a cyclic carbonate such as vinylene carbonate and a chain carbonate such as dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate.

The weight ratio of the oligomer to the non-aqueous electrolyte is desirably 1:99 to 10:90. If the amount of the oligomer is too small, the amount of the nonaqueous electrolyte released without gelation increases, and the advantage of the battery using the polymer is lost. Conversely, if the amount is too large, the lithium ion conductivity decreases.

The above non-aqueous electrolyte secondary battery can be manufactured by a manufacturing method having the following steps. A step of impregnating and penetrating a pregel solution comprising an oligomer having a high number average molecular weight, a non-aqueous electrolyte and a polymerizable compound into an electrode group obtained by laminating or winding a positive electrode and a negative electrode via a separator, and further applying external pressure The step of bringing the electrode group and the pregel solution into close contact with each other, and inserting the electrode group containing the pregel solution into the outer package, sealing the mixture under reduced pressure, and then polymerizing the oligomer and the polymerizable compound.
This is a step of curing and simultaneously forming a polymer as well as a gel polymer electrolyte.

The electrode group in the step (1) does not need to be a true cylindrical shape, and may be a prismatic shape such as a long cylinder or a rectangle having an elliptical cross section. As the oligomer and the non-aqueous electrolyte having a large number average molecular weight, those described above can be used. Further, as the polymerizable compound, an organic peroxide such as t-hexylperoxypiparate, t-butylperoxynodecanoate or the like can be used. Examples of the method of impregnating and permeating the pregel solution include a method of immersing the electrode group in a container containing the pregel solution, and a method of pressurizing and injecting the pregel solution into the electrode group. The molecular weight of the oligomer is 2
When the molecular weight is more than 100,000, the effect of the present invention is large,
If it exceeds 10,000, impregnation / penetration becomes difficult.

As a method of applying an external pressure in the step, there is a method of applying a pressure using a cylinder, a roller or the like. As a result, the permeability of the pregel solution is improved, and the adhesion between the electrode group and the pregel solution is improved. As a result, the contact resistance between the gelled polymer solid electrolyte formed in a later step and the electrode plate is reduced, and the ion conductivity is improved. Is good.

The sealing under the reduced pressure atmosphere in the step of
For the following reasons. In other words, the presence of oxygen during polymerization / curing causes a radical reaction of the polymerizable compound in the pregel solution due to the presence of oxygen, and sufficient crosslinking cannot be performed. Is required. If the battery is sealed (sealing step) under a reduced pressure atmosphere, it becomes an oxygen-blocking atmosphere and can be degassed, so that it is not necessary to introduce an inert gas atmosphere as equipment in the polymerization / curing manufacturing process. And sufficient crosslinking can be performed. Further, since degassing is performed, a gel-like solid polymer film containing no air bubbles is formed. In addition, as a method of polymerization and curing, heating, electron beam irradiation, ultraviolet irradiation and the like can be mentioned.

[0025]

Embodiments of the present invention will be described below with reference to the drawings.

(Experiment 1) FIG. 1 is an external view of a battery according to a first embodiment of the present invention, and FIG. 2 is a sectional view showing a structure according to the first embodiment of the present invention. In FIG. 2, 1
Denotes a positive electrode current collector, 2 denotes a negative electrode current collector, 3 denotes a separator containing a gel polymer solid electrolyte, and 4 denotes a laminate outer package. 5 is a positive electrode active material layer, and 6 is a negative electrode active material layer.
7 is a positive electrode lead plate, and 8 is a negative electrode lead plate.

The battery having the above structure will be described in detail below.

First, LiCoO ₂ as a positive electrode active material, a conductive agent (acetylene black) and a binder (PVDF) are kneaded with a N-methyl-2-pyrrolidone solution in a weight ratio of 90: 7: 3, and a die coater is used. It was applied on an aluminum foil (20 μm) as a current collector to obtain a positive electrode raw material. Thereafter, the roll was dried and rolled using a roll press, cut out to a predetermined size, and a positive electrode lead plate (made of aluminum) was welded to one end of an aluminum foil as a current collector. At this time, the thickness of one side of the active material layer was 60 μm, and the electrode area was 36 cm ² .

Next, an N-methyl-2-pyrrolidone solution was kneaded with natural graphite and a binder (PVDF) as a negative electrode active material in a weight ratio of 97: 3, and the mixture was coated on a copper foil (10 μm) as a current collector.
Was coated using a die coater to obtain a negative electrode raw material. Thereafter, the roll was dried and rolled using a roll press, cut out to a predetermined size, and a negative electrode lead plate (made of copper) was welded to one end of a copper foil as a current collector. At this time, the thickness of one side of the active material layer was 76 μm, and the electrode area was 66 cm ² .

The positive electrode and the negative electrode were made of polyethylene (10
μm) to form an integrated electrode plate group. The electrode group thus obtained was immersed in a pregel solution, and the vacuum pressure was 1.3 × 10 ^−3.
After impregnation under a reduced pressure atmosphere of Pa, the electrode plate group containing the pregel solution was pressed with a cylinder at a pressure of 5 kgf / cm ² and brought into close contact. Next, the positive electrode lead plate and the negative electrode lead plate were inserted into the concave portions of the laminate exterior body so as to protrude, and the protruding lead side portions and both ends in the longitudinal direction were sealed (heat-welded). Thereafter, the other side facing the protruding lead portion was sealed and sealed under a reduced pressure atmosphere of a vacuum pressure of 1.3 × 10 ⁻³ Pa. Thereafter, the mixture was heated at 80 ° C. for 1 hour to be polymerized and cured.

The pregel solution has a concentration of LiBF ₄ of 1.2 mol / l as a supporting electrolyte in an organic solvent in which ethylene carbonate (EC) and ethyl methyl carbonate (EMC) are mixed at a volume ratio of 1: 3. Polyethylene oxide (molecular weight 1000)
２００2,000,000) in a weight ratio of 97: 3, and then a polymerizable compound (t-hexylperoxypiparate) was added in an amount of 0.3% by weight based on the mixed solution. Was. A non-aqueous electrolyte secondary battery was manufactured as described above. The theoretical capacity of the battery was 100 mAh. In addition, polyethylene oxide has a molecular weight of 1,000, 10,000, and 20.
The batteries of 10,000, 500,000, 1,000,000 and 2,000,000 were used, and the batteries were designated as batteries A to F, respectively.

(Experiment 2) Next, in order to examine the relationship between the weight ratio of the oligomer and the non-aqueous electrolyte, the molecular weight of polyethylene oxide was set to 1,000,000, and the weight ratio of the non-aqueous electrolyte to the polyethylene oxide was calculated. 99.5-85:
Non-aqueous electrolyte batteries were prepared in the same manner as in Experiment 1, except that the batteries were changed to 0.5 to 15, and batteries GL were obtained.

(Experiment 3) First, an integrated electrode group was produced in the same manner as in Experiment 1. After accommodating the thus obtained electrode plate group in an outer package, ethylene carbonate (EC) and ethyl methyl carbonate (EM) were used as a pregel solution.
C) as a supporting electrolyte in an organic solvent mixed with a volume ratio of 1: 3, LiBF ₄ adjusted to a concentration of 1.2 mol / l, and polyethylene oxide (molecular weight 1).
) Were mixed at a weight ratio of 90:10, and then a polymerizable compound (t-hexylperoxypiparate) was added in an amount of 0.5 part by weight based on the mixed solution. Thereafter, in the same manner as in Experiment 1, the solution was injected, sealed, polymerized and cured to produce a non-aqueous electrolyte secondary battery. This was designated as Battery M.

Each of the batteries A to M produced above was evaluated by the following method, and was evaluated as shown in Table 1 or Table 2.
Shows the evaluation results.

(1) Electrolyte Retentivity of Gel Polymer Solid Electrolyte The battery after polymerization and curing was disassembled, and the presence or absence of a phase-separated electrolyte was visually observed. In the evaluation, the leakage of the electrolyte was regarded as defective, and the defective rate was determined.

(2) Uniformity of the gelled polymer solid electrolyte in the electrode plate group The integrated electrode plate group after polymerization and curing is disassembled, and the gelled polymer solid electrolyte membrane of the electrode plate and the separator is visually observed. did. In the evaluation, those with opaque parts in the separator were regarded as defective,
The defect rate was determined.

(3) Cycle Characteristics For each of the manufactured batteries, 0.7 C at room temperature (25 ° C.) was used.
In a cycle test in which the battery is charged at a constant current of 4.2 V and a constant voltage of 4.2 V and then discharged to 3 V at a constant current of 1 C, the discharge capacity at the first cycle (hereinafter referred to as the initial discharge capacity) is 100
The discharge capacity at the cycle was measured. In the evaluation, the discharge capacity value per unit area of the electrode and the ratio of the discharge capacity at the 100th cycle to the initial discharge capacity were obtained.

[0038]

[Table 1]

[0039]

[Table 2]

The following can be understood from the evaluation results shown in Tables 1 and 2.

First, in the battery M of the comparative example, when liquid is injected into the electrode group housed in the outer package, the permeability is poor, and the uniformity defective rate of the gel polymer solid electrolyte membrane increases. Further, when examining the molecular weight of the organic polymer solid electrolyte, the batteries A and B of the comparative examples have low viscosity because of their small molecular weight, and have good permeability even when injected into the electrode group housed in the outer package. Although the percentage of poor uniformity was low, the phase-separated electrolytic solution was present, and the initial discharge capacity was large, but the cycle capacity was significantly deteriorated. In the batteries C to F of the examples, since the molecular weight of the organic polymer solid electrolyte is large, even if the concentration of the organic polymer solid electrolyte with respect to the electrolyte is reduced, there is no phase-separated electrolyte. Although the viscosity is higher than that of the battery A and the battery B, the electrode group is impregnated in the pregel solution, and furthermore, an external pressure is applied so as to be in close contact with each other. Although the initial discharge capacity is smaller than those of the batteries A and B, a battery with less charge / discharge cycle deterioration can be obtained.

In examining the concentration of the oligomer in the electrolytic solution, when the concentration of the oligomer is increased, the presence of the phase-separated electrolytic solution is reduced, but the viscosity is high, and the gel-like polymer solid electrolyte membrane has a high viscosity. The rate of defective uniformity increases. It can be said that the charge / discharge reaction becomes non-uniform.
On the other hand, when the concentration of the oligomer is reduced, the presence of a phase-separated electrolyte solution is confirmed.

[0043]

As is apparent from the above results, the present invention uses an oligomer having a large molecular weight, so that even if the concentration of the oligomer in the electrolyte is reduced, there is no electrolyte separated from the electrolyte and the integrated electrode plate is used. The group is impregnated with the pregel solution, and furthermore, an external pressure is applied to make the electrode group and the pregel solution adhere to each other, so that a uniform gel-like solid polymer electrolyte can penetrate into the separator and the active material layer. In addition, polymerization
By sealing the electrode group containing the pregel solution under a reduced-pressure atmosphere before curing, an oxygen-blocking atmosphere is provided, and the polymerization curing reaction can be surely promoted. As described above, the present invention has good productivity and production yield, and can realize excellent cycle characteristics.

[Brief description of the drawings]

FIG. 1 is an external view of a nonaqueous electrolyte secondary battery according to an embodiment of the present invention.

FIG. 2 is a sectional structural view showing a configuration taken along line AA ′ of FIG. 1;

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 positive electrode current collector 2 negative electrode current collector 3 separator including gelled polymer solid electrolyte membrane 4 laminate outer package 5 positive electrode active material 6 negative electrode active material 7 positive electrode lead plate 8 negative electrode lead plate

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Hideyuki Ueda 1006 Kazuma Kadoma, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (72) Inventor Toru 1006 Okadoma Kadoma, Osaka Prefecture Matsushita Electric Industrial F Terms (reference) 5H029 AJ03 AJ05 AJ11 AJ14 AJ15 AK03 AL07 AM00 AM03 AM05 AM07 AM16 BJ02 BJ04 BJ12 BJ14 CJ03 CJ06 CJ07 CJ11 CJ23 CJ28 HJ01 HJ11

Claims (5)

[Claims] 1. A non-aqueous electrolyte secondary battery having an electrode group in which a positive electrode and a negative electrode are laminated or wound with a separator interposed therebetween, wherein a non-aqueous electrolyte between the separator and the positive electrode and between the separator and the negative electrode It has a gelled polymer solid electrolyte in which a non-aqueous electrolyte is held between polymers as a lithium ion conductive medium, and the polymer is obtained by polymerizing and curing an oligomer having a number average molecular weight of 200,000 or more. A non-aqueous electrolyte secondary battery, comprising: 2. The non-aqueous electrolyte secondary battery according to claim 1, wherein the weight ratio of the polymer to the non-aqueous electrolyte is 1:99 to 10:90. 3. A method for producing a non-aqueous electrolyte secondary battery having an electrode group in which a positive electrode and a negative electrode are laminated or wound via a separator, wherein the integrated electrode group includes an oligomer and a non-aqueous electrolyte. And a step of impregnating and permeating a pregel solution comprising a polymerizable compound, and a step of further applying external pressure to bring the electrode group and the pregel solution into close contact with each other, and inserting the electrode group containing the pregel solution into an exterior body and reducing the pressure. A process for polymerizing and curing the oligomer and the polymerizable compound after sealing in an atmosphere to form a polymer and a gel polymer solid electrolyte at the same time as a polymer, the method comprising the steps of: . 4. The method for producing a non-aqueous electrolyte secondary battery according to claim 3, wherein the number average molecular weight of the oligomer is 200,000 or more. 5. The method according to claim 3, wherein the weight ratio of the oligomer to the non-aqueous electrolyte is 1:99 to 10:90.