JPH1092470A - Lithium ion battery and manufacture of it - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the danger of fire generation by spirally winding first and second copper foil-like collectors each in which a positive electrode and a negative electrode are formed on the front surface so that the positive electrode faces the negative electrode, impregnating organic solvent and gelling agent between the positive electrodes and the negative electrodes, and diffusing electrolyte into gel. SOLUTION: A positive electrode in which LiCoO2 is applied to aluminum foil, and a negative electrode in which graphite is applied to copper foil are spirally wound through a separator composed of a porous polyethylene layer. Solution formed by dissolving polystyrene monomer, divinylbenzene, benzene peroxide in tetrahydrofuran is impregnated into a part between the positive electrode and the negative electrode, and polymerization reaction is performed. Solution formed by dissolving LiPF6 in mixed liquid of ethylene carbonate and dimethoxy ethane and is added and swelled into gel-like electrolyte. Therefore, there is no possibility that organic solvent is allowed to flow to the outside of a container even if the battery is broken, and the danger of fire can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a lithium ion battery and a method for producing the same, and more particularly to a lithium ion battery using a novel electrolyte having excellent safety and durability, and a method for producing the same.

[0002]

2. Description of the Related Art Because of its high energy density, lithium ion batteries are widely used as power sources for portable electronic devices, and are also being developed as power sources for electric vehicles. In this type of battery, carbon that causes lithium intercalation is used for the negative electrode, and a composite oxide of lithium such as Co, Ni, Mn and the like is used for the positive electrode, and a porous film-shaped The separator is sandwiched, and the three members are immersed in an electrolytic solution in which LiPF ₆ or the like as an electrolyte is dissolved in ethylene carbonate or the like as an organic solvent. However, this battery uses a flammable organic solvent as the electrolyte solvent, and if the battery is damaged or the seal is incomplete,
There is a drawback that the organic solvent flows out of the container and ignites, which may cause a fire.

[0003] Further, as the battery is charged and discharged, the positive electrode material and the negative electrode material slightly change in volume, and as a result, a gap is formed between the two electrodes and the separator is clogged, so that the capacity and internal capacity of the battery are reduced. There was a problem that the resistance deteriorated.

A so-called polymer battery using an ion-conductive polymer sheet as a separator between both electrodes instead of an organic solvent has been developed, but the internal resistance is high due to insufficient contact with the electrode active material. There were drawbacks such as an extra volume of the separator.

[0005]

SUMMARY OF THE INVENTION In view of the above problems, the present invention has a low possibility that an organic solvent will flow out of a container even when a battery is damaged, and therefore has high safety and is accompanied by charge and discharge. It is an object of the present invention to provide a lithium ion battery which has little deterioration and a large volume energy density.

[0006]

According to the present invention, there are provided (1) a positive electrode and a negative electrode which are respectively formed on the surface of a foil-like current collector, and are spirally wound in a state where both are opposed to each other; A method for producing a lithium ion battery in which a liquid comprising an organic solvent and a gelling agent or a raw material thereof is impregnated, gelled, and then an electrolyte containing lithium is diffused in the gel; A negative electrode is formed on the surface of the foil-like current collector, and the two are spirally wound in a state where both are opposed to each other. An electrolyte containing lithium, an organic solvent in which the electrolyte is dissolved, a gelling agent, Alternatively, a method for producing a lithium ion battery in which an electrolyte solution comprising the raw material is impregnated and gelled, and (3) forming a positive electrode and a negative electrode on the surface of a foil-shaped current collector, respectively, Also A gelling agent or a raw material thereof is present in at least a part of a separator interposed between the two electrodes, and the positive electrode and the negative electrode are spirally wound in a state where the positive electrode and the negative electrode are opposed to each other, and an organic solvent is impregnated between the two to form the gel. A method for producing a lithium ion battery in which an agent or a raw material thereof is dissolved, the solution is gelled, and then an electrolyte containing lithium is diffused into the gel; and (4) a positive electrode and a negative electrode each having a foil-like current collector Formed on the surface of the body, and further present a gelling agent or its raw material on at least a part of the separator interposed between those surfaces or both electrodes,
The positive electrode and the negative electrode are spirally wound in a state where they are opposed to each other, and an electrolyte containing lithium and an organic solvent in which the electrolyte is dissolved is impregnated between the two to impregnate the gelling agent or the raw material thereof. A method for producing a lithium ion battery that dissolves and gels the solution, and
(5) forming a positive electrode and a negative electrode respectively on the surface of the foil-shaped current collector, and further causing a gel comprising an organic solvent and a polymer to be present on at least a part of the surface or a separator interposed between both electrodes; A method of manufacturing a lithium ion battery in which a positive electrode and a negative electrode are spirally wound in a state where they are opposed to each other, and an electrolyte containing lithium is impregnated between the two; and (6) the positive electrode and the negative electrode are each formed of a foil-like current collector. A gel formed of an organic solvent, a polymer, and an electrolyte containing lithium is present on at least a part of the separator formed on the surface or between the electrodes or between the electrodes, and the positive electrode and the negative electrode are opposed to each other. And (7) forming a positive electrode and a negative electrode on the surface of a foil-shaped current collector, respectively. Are spirally wound in a state where they face each other, and a gel electrolyte formed by a thermal polymerization reaction is interposed between the two, and an electrolyte containing lithium and a solution of the electrolyte are contained in the gel electrolyte. A lithium ion battery impregnated with an organic solvent.

In the method (1), there is no need to consider interference with the polymerization reaction caused by the electrolyte, the selection range of the type of gel is relatively wide, and a gel having good characteristics is easily obtained, but the process becomes complicated and It takes a long time to impregnate the electrolyte. In the method (2), the selection range of the gel is narrow, but the production is possible by slightly changing the conventional production process, and the productivity is high. (3)
The methods (4) and (4) are particularly effective when the raw material solution of the gelling agent has a high viscosity, and can produce a gel having a uniform concentration in a short time. In the methods (5) and (6), the distribution of the gel becomes the most uniform, and a battery with less variation in quality can be obtained.

As a method for producing a gel electrolyte, it is desirable to use a thermal polymerization reaction in terms of easiness of the production process and stability of the gel in the event of a product breakage. For example, vinylene is used as a solvent using ethylene carbonate as a solvent. Dissolve carbonate and azobisisobutyronitrile, impregnate and impregnate the wound product of the cathode material, the anode material, and the separator with a reduced pressure, and perform a bulk polymerization reaction at 60 ° C. for 20 hours in a nitrogen atmosphere. . As a result, it is formed so as to fill both the electrodes containing ethylene carbonate and the fine pores of the separator. Thereafter, the electrolyte is immersed in an ethylene carbonate solution in which LiPF ₆ is dissolved and diffused, whereby a gel containing the electrolyte and filled between the two electrodes is obtained. Further, the monomer and the polymerization initiator may be dissolved in a non-aqueous solvent in which an electrolyte is dissolved in advance to cause a reaction.

The gelation reaction by thermal polymerization can be easily controlled by controlling the temperature of the assembled battery. For example, in the case of solution polymerization using a vinyl-type monomer and a vinyl-type macromonomer, the time required for completing the reaction is short. Is as follows. Here, the macromonomer is also called a reactive oligomer, and its molecular weight is several thousand daltons. By designing various chemical structures, it is possible to control the solubility and physical properties of the gel according to the purpose. On the other hand, the gelation reactivity of the macromonomer is almost the same as the reactivity of the monomer, and thermal polymerization is possible. (1) When AIBN is used as an initiator. 50 ° C 74 hours 70 ° C 4.8 hours 100 ° C 7.2 minutes (2) When lauryl peroxide is used as an initiator. 50 ° C. 47.7 hours 70 ° C. 3.5 hours 100 ° C. 3.5 minutes As described above, the time for gelation can be controlled by controlling the temperature, so that optimum conditions for the manufacturing process can be set.

The mechanism of the polymerization reaction used in the present invention comprises a bifunctional monomer and a polyfunctional monomer by an addition polymerization reaction, a polyaddition reaction, a ring-opening polymerization reaction, or a polycondensation reaction. A polymerization reaction caused by formation of a branched or crosslinked polymer can be suitably used.

The polymers constituting the gel in the present invention include polymethyl acrylate, polymethyl methacrylate, polyacrylonitrile, polystyrene, polyvinyl acetate, polyvinyl cinnamate, cyclized rubber, polysilane, polysiloxane, Those containing at least one of epoxidized polybutadiene, polyether, polyurethane, polyester and a copolymer thereof can be suitably used.

In the present invention, the solubility parameter (δ) between the solvent constituting the gel and the polymer is similar,
Desirable for obtaining a good gel. That is, a combination of a polymer and a solvent having similar or the same solubility parameters has the best function of dissolving the polymer in the solvent, and such a solvent is called a good solvent. Good solvents swell the gel to the maximum. The database of solubility parameters of existing polymers and solvents is almost complete, and a method for estimating δ values of new substances has been established. Therefore, it is possible to search for an organic electrolyte solution that swells the gel to the maximum. The mobility of lithium ions in the swollen gel is almost equal to the value of the organic electrolyte alone. Therefore, the change in ionic conductivity due to the presence of the gel is negligible in the gel / good solvent system. The ratio of the solubility parameter between the polymer constituting the gel and the organic solvent contained therein is preferably in the range of 1: 0.7 to 1: 1.3 in order to obtain a good gel, and furthermore, More preferably, it is in the range of 1: 0.8 to 1: 1.2. Examples of good solvents include polymers having polystyrene (δ = 18.7 MPa ^1/2 ), polymethyl methacrylate (δ = 18.6 MPa ^1/2 ), and polyvinyl acetate (δ = 19.6 MPa ^{1). / 2} )
The good solvent is tetrahydrofuran (δ = 19.4 MP
a ^1/2 ), diethyl carbonate (δ = 18.0 M)
Pa ^1/2 ).

After forming a thin gel on the surface of the electrode in advance,
As a winding method, for example, a mixture of one or more kinds of various acrylate and methacrylate monomers and a vinylene carbonate monomer is used as AIBN.
Is copolymerized using a DMF solvent as an initiator, and the product is precipitated with methanol to obtain a binary or multicomponent copolymer in a solid state. The copolymer is swollen and dispersed in an organic electrolyte to obtain a gel. Under high shear stress, the gel breaks the associated structure and becomes a viscous solution showing good fluidity. This solution is applied on the electrode in a thin layer using a doctor blade. The coating returns to the gel state. By winding the electrode thus formed, a battery having a gel electrolyte can be obtained.

The positive electrode material and the negative electrode material used in the present invention can be appropriately selected according to the required performance of the battery. For example, the positive electrode material mainly contains a transition metal such as Mn, Ni, Fe, etc. A lithium composite metal oxide composed of oxygen and capable of desorbing and occluding lithium during charging and discharging can be used.

[0015]

【Example】

[First Embodiment] LiCoO ₂ is applied to an aluminum foil, and a pressed positive electrode, and graphite is applied to a copper foil and a pressed negative electrode is spirally wound through a porous polyethylene layer. It was attached to a battery can with a cylindrical bottom. Between these two electrodes, a monomer mixture consisting of a methyl methacrylate monomer and a diallyl carbonate monomer of bisphenol A having a weight ratio of 2: 1 was mixed with 1M LiBF ₄
Was dissolved in a mixed organic solvent consisting of propylene carbonate and 1,2 dimethoxyethane in which 12% was dissolved to obtain a 12% by weight solution, and a solution obtained by adding 1.5% by weight of AIBN based on the total weight of the monomers to this solution was added under reduced pressure. Impregnated. This was sealed in a nitrogen gas atmosphere and heated at 75 ° C. for 30 minutes to obtain a lithium ion battery having a gel electrolyte.

[0016]

[Second Embodiment] LiCoO ₂ is applied to an aluminum foil and pressed to form a positive electrode, and graphite is applied to a copper foil to form a pressed negative electrode in a spiral manner through a separator made of a porous polyethylene layer. It was wound and attached to a cylindrical battery can with a bottom. A solution obtained by dissolving 180 g of polystyrene monomer, 5 g of divinylbenzene, and 1.5 g of benzene peroxide in 150 g of tetrahydrofuran was impregnated under reduced pressure between the two electrodes, and then heated at 60 ° C. for 2 hours in a nitrogen atmosphere. A polymerization reaction was performed.
Under a nitrogen atmosphere, a solution of 1 M LiPF ₆ dissolved in a mixture of ethylene carbonate and dimethoxyethane was added to swell the mixture to form a good gel electrolyte, which was then sealed.
A lithium ion battery was obtained.

[0017]

Third Embodiment LiCoO ₂ was applied to an aluminum foil and pressed to form a positive electrode, graphite was applied to a copper foil and pressed to form a negative electrode, and a separator made of a porous polyethylene layer was charged with 100 g of vinyl acetate. , Vinyl cinnamate 10 g and AIBN 2 g in tetrahydrofuran 1
The solution dissolved in 50 g was impregnated under reduced pressure. Each of them is taken out of the liquid, and is placed in a nitrogen gas atmosphere at 60 °
C for 30 minutes to form a gel. The positive electrode, the separator, and the negative electrode in which the gel thus obtained was filled in the voids were wound and mounted on a bottomed cylindrical battery can. Between the two electrodes, a solution of 1M LiPF ₆ dissolved in a mixture of ethylene carbonate and dimethoxyethane was added under a nitrogen atmosphere and allowed to diffuse into the gel to form a good gel electrolyte, which was then sealed and sealed with a lithium ion battery. I got

[0018]

Fourth Embodiment 100 g of a styrene monomer and 2.5 g of divinylbenzene are mixed with 1 g of an emulsifier and 1 g of potassium persulfate.
And stirred at 60 ° C. for 1 hour to obtain a polystyrene latex. This latex was freeze-dried to a powder, and then dispersed in chloroform or dimethylformamide, which is a good solvent for polystyrene, to obtain a swollen microgel. This microgel was subjected to surface sulfonation (sulfonation degree: 0.1 to 15%) with sulfur trioxide. The microgel was recovered, dispersed in water, completely neutralized with LiOH, and lyophilized to obtain a microgel powder. The surface sulfonated microgel powder thus obtained is swollen with a 1 M solution of LiPF ₆ in ethylene carbonate and methyl ethyl carbonate (volume ratio 1: 3) to form a gel. The gel is applied to the surfaces of the positive electrode, the separator and the negative electrode. It was applied thinly, and each was overlapped and spirally wound, and mounted on a cylindrical battery can with a bottom.
This was sealed in a nitrogen atmosphere to obtain a lithium ion battery.

[0019]

Fifth Embodiment 200 g of methacrylate and 1 g of divinylbenzene were diluted with 1 g of benzoyl peroxide with 300 ml of an organic electrolyte and stirred at 60 ° C. for 3 hours to obtain a polymer solution. This was applied in a thin layer on the surfaces of both electrodes, wound around a porous plastic spacer, and attached to a bottomed cylindrical battery can. This was sealed in a nitrogen atmosphere to obtain a lithium ion battery.

[0020]

[Sixth Embodiment] LiCoO ₂ is applied to an aluminum foil and pressed to form a positive electrode, and graphite is applied to a copper foil and pressed to form a negative electrode through a separator made of a porous polyethylene layer in a spiral manner. It was wound and attached to a cylindrical battery can with a bottom. Between these two electrodes, a mixture of 10 ml of styrene monomer, 10 ml of acrylate or methacrylate monomer and 1 ml of divinylbenzene were added to 100 ml of organic electrolyte, and 60 ml of dicumyl peroxide was added.
The mixed solution was infiltrated. This was heat-treated at 70 ° C. for 3 hours to cause a polymerization reaction. As a result, the permeated solution became a concentrated polymer solution, and the fluidity was significantly reduced.

[0021]

Seventh Embodiment 0.5 g of polyvinyl alcohol is dissolved in 30 ml of hot water and then diluted to 500 ml. To this solution, 15 g of styrene monomer, 2 g of divinylbenzene and 0.2 g of benzoyl peroxide are added. After stirring for 4 hours, latex particles were obtained. The particles were swelled with tetrahydrofuran, dispersed in an organic electrolyte to form a slurry, applied to both surfaces of a lithium ion battery, and wound to form a battery.

[0022]

The batteries prepared in the first to fourth embodiments were subjected to a destructive test (a nail insertion test) in which a nail was inserted from the side of the cylindrical battery. As shown in Table 1, as shown in Table 1, the generation of flame was extremely small or not recognized in the battery made by the method of the present invention. It became a big flame.

[0023]

[Table 1]

As is clear from the above description, according to the present invention, after the wound product of both electrodes is impregnated with the electrolytic solution, the electrolytic solution is made into a gel state or the surface of both electrodes contains the electrolytic solution. Excellent safety because there is almost no outflow of electrolyte when the battery container is damaged by winding the gel in the presence of the gel or impregnating the gel in the wound product of both electrodes with the electrolyte. In addition, a lithium-ion battery with less deterioration due to charge and discharge can be obtained, which is extremely useful in industry.

Claims (11)

[Claims] A positive electrode and a negative electrode are respectively formed on the surface of a foil-shaped current collector, and spirally wound in a state where both are opposed to each other, and an organic solvent, a gelling agent or a raw material thereof are interposed therebetween. A method for producing a lithium-ion battery, comprising: impregnating a solution consisting of: and then gelling the solution, and then diffusing an electrolyte containing lithium into the gel. 2. A positive electrode and a negative electrode are respectively formed on the surface of a foil-shaped current collector, spirally wound in a state where both are opposed to each other, and an electrolyte containing lithium and an electrolyte dissolved between the two. A method for producing a lithium ion battery, comprising impregnating an electrolytic solution comprising an organic solvent and a gelling agent or a raw material thereof and gelling the same. 3. The method according to claim 1, wherein the positive electrode and the negative electrode are formed on the surface of a foil-shaped current collector, and a gelling agent or a raw material thereof is present on at least a part of the surface or a separator interposed between the electrodes. The positive electrode and the negative electrode are spirally wound in a state where they face each other, and the gelling agent or the raw material is dissolved by impregnating an organic solvent between the two,
A method for producing a lithium ion battery, comprising: gelling the solution; and then diffusing an electrolyte containing lithium into the gel. 4. A positive electrode and a negative electrode are formed on the surface of a foil-shaped current collector, and a gelling agent or its raw material is present on at least a part of the surface or at least a part of a separator interposed between both electrodes. The positive electrode and the negative electrode are spirally wound in a state where they are opposed to each other, and an electrolyte containing an electrolyte containing lithium and an organic solvent in which the electrolyte is dissolved is impregnated between the two to dissolve the gelling agent or its raw material. And a method for producing a lithium ion battery, wherein the solution is gelled. 5. A positive electrode and a negative electrode are formed on the surface of a foil-shaped current collector, and a gel comprising an organic solvent and a polymer is present on at least a part of the surface or a separator interposed between the electrodes. A method of manufacturing a lithium ion battery, comprising: spirally winding the positive electrode and the negative electrode so as to face each other, and impregnating an electrolyte containing lithium therebetween. 6. A positive electrode and a negative electrode are respectively formed on the surface of a foil-like current collector, and at least a part of a separator interposed between the surfaces or both electrodes contains an organic solvent, a polymer, and lithium. A method for producing a lithium-ion battery, comprising: a gel comprising an electrolyte; and spirally winding the positive electrode and the negative electrode in a state of facing each other. 7. The method for producing a lithium ion battery according to claim 1, wherein gelation occurs by a thermal polymerization reaction. 8. The gelation is caused by the formation of a branched or crosslinked polymer composed of a bifunctional monomer and a polyfunctional monomer by any of an addition polymerization reaction, a polyaddition reaction, a ring-opening polymerization reaction and a polycondensation reaction. Claims 1 to 6
The method for producing a lithium ion battery according to any one of the above. 9. The polymer constituting the gel is polymethyl acrylate, polymethyl methacrylate, polyacrylonitrile, polystyrene, polyvinyl acetate, polyvinyl cinnamate, cyclized rubber, polysilane, polysiloxane, epoxidized polybutadiene, poly The method for producing a lithium ion battery according to any one of claims 1 to 6, comprising at least one of ether, polyurethane, polyester, and a copolymer thereof. 10. The method according to claim 1, wherein the ratio of the solubility parameter between the polymer constituting the gel and the organic solvent contained therein is in the range of 1: 0.7 to 1: 1.3.
The method for producing a lithium ion battery according to any one of the above. 11. A positive electrode and a negative electrode are respectively formed on the surface of a foil-shaped current collector, and are wound spirally in a state where both are opposed to each other, and a gel electrolyte formed by a thermal polymerization reaction therebetween. A lithium-ion battery, wherein a liquid is interposed, and the gel electrolyte is impregnated with an electrolyte containing lithium and an organic solvent in which the electrolyte is dissolved.