JP2000067851A - Method for manufacturing lithium secondary battery and lithium secondary battery - Google Patents

Abstract

(57) [Problem] To provide a lithium secondary battery excellent in productivity and excellent in battery characteristics. SOLUTION: The positive electrode and / or the negative electrode contain an active material capable of inserting and extracting lithium ions, a nonaqueous electrolyte and a gel electrolyte containing a gel polymer for gelling the electrolyte. A method for manufacturing a lithium secondary battery, comprising the following steps (1) to (3) in the method for manufacturing a secondary battery. (1) a step of forming an active material layer containing a positive electrode or negative electrode active material and a gel polymer on a current collector as a layer having voids; (2) an electrolytic solution or a gel polymer and / or gel height; A step of filling the gap with an electrolytic solution in which a precursor capable of producing a molecule is dissolved, and (3) a step of forming a positive electrode and / or a negative electrode by subjecting the solution to a gelling treatment.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a lithium secondary battery. More specifically, a lithium secondary battery using a gel electrolyte in place of the electrolyte, with a high energy density,
The present invention relates to a lithium secondary battery having excellent battery characteristics and productivity.

[0002]

2. Description of the Related Art In recent years, various devices such as a camera-integrated VTR device, an audio device, a portable computer, and a cellular phone have been reduced in size and weight, and there has been a demand for higher performance of a battery as a power supply for these devices. Is growing. In particular, in order to cope with the miniaturization of the device main body, miniaturization of the battery and simultaneous securing of the capacity, that is, high energy density are required. In particular, expectations are high for a secondary battery that can be used repeatedly by charging. On the other hand, lithium secondary batteries are being actively developed because they can realize a high energy density.

A lithium secondary battery is composed of a positive electrode and a negative electrode capable of inserting and extracting lithium ions, and a non-aqueous electrolyte mainly comprising a lithium salt and a non-aqueous solvent. The reason for using a non-aqueous electrolyte is that lithium has such a high reactivity that water cannot be stably present with respect to water, which is a main component of the electrolyte of the conventional battery. However, non-aqueous electrolytes are mostly organic compound liquids and often have flammability and odor. Therefore, batteries using non-aqueous electrolytes have a risk of leakage or ignition. For this reason, in recent years, in order to improve safety, a battery in which a nonaqueous electrolyte is replaced with a gel electrolyte has been developed.

In the case of a gel electrolyte, a non-aqueous electrolyte is contained in, for example, a polymer, and many of its characteristics such as ionic conductivity maintain the same performance as the electrolyte while maintaining the same performance.
Fluidity is extremely reduced and has shape retention. Also, the volatilization rate is suppressed. Therefore, the risk of liquid leakage and ignition can be reduced. In particular, in a secondary battery using lithium metal, heat generation and ignition caused by internal short circuit due to lithium dendrite deposition that occurs when using a conventional electrolyte are problematic, but dendritic deposition is suppressed in a gel electrolyte. It was reported that practical application was desired.

Further, as described above, a lithium secondary battery using a gel electrolyte containing an electrolyte in a polymer,
Since the liquid leakage is suppressed, there is no need to use a heavy and bulky container such as a metal can used in the liquid system, and there is an advantage that it can be lighter and simpler than the liquid system. Generally, a lithium secondary battery composed of a gel electrolyte is a mixture containing a positive electrode active material or a negative electrode active material, an electrolyte, a conductive material, a gel-forming polymer, and the like on a current collector such as an aluminum plate or a copper plate. (Electrode paint) is applied to form a positive electrode and a negative electrode, and an electrolyte layer made of a gel electrolyte is sandwiched between them to form a laminated structure of a positive electrode, an electrolyte layer, and a negative electrode. Specifically, the following method is known.

For example, in the method described in US Pat. No. 5,453,335, a mixture of an active material, a polymerizable monomer and an electrolytic solution (coating material for an electrode) is applied to a current collector.
Thereafter, the electrolytic solution is converted into a gel electrolyte by polymerization of the monomer to form a positive electrode and a negative electrode, and a polymerizable monomer and a mixture of the electrolytic solution are applied on the positive electrode and the negative electrode,
Thereafter, a gel electrolyte layer is formed by polymerization of the monomer.

In the method described in US Pat. No. 5,609,974, a high-temperature kneading substance (electrode paint) of an active material, a polymer, and an electrolytic solution is applied onto a current collector and cooled. An electrode is formed in such a manner that the polymer-electrolyte solution is converted into a gel electrolyte. Then, the gel electrolyte on the electrode is prepared by using the method described in the above U.S. Patent Specification or by laminating an electrolyte membrane separately prepared from a mixture of a polymerizable monomer and an electrolyte. use.

[0008]

The method for producing a positive electrode or a negative electrode having a gel electrolyte as described above has some restrictions in production. First, as described above, the presence of water is a problem in a lithium secondary battery, and pp.
It is necessary that the water content is controlled to the order of m. However, in the above-mentioned production method, since the electrolyte is already contained from the kneading stage, the water must be controlled in all the steps of dispersion and application. This is achieved by installing a dispersing machine and a coating machine in a room (dry room) where dehumidification is controlled, but this requires a considerably large dry room and increases costs.
Also, the longer the process, the higher the possibility of absorbing moisture even in a dry room.

Second, the positive and negative electrode films before the gelation is completed are still soft, and problems such as desorption of the active material occur after coating on the current collector until the gelation is completed. There is a problem that the production line is easily polluted. In addition, if a gelation process is added in-line, the line will become longer,
This leads to higher costs. Particularly problematic are the filling amount of the active material and the viscosity of the paint. In the above-mentioned conventional method, the paint before application becomes the composition of the positive electrode and the negative electrode almost as they are, but if the ratio of the active material in the paint is increased by increasing the capacity, the viscosity increases and the dispersion application becomes difficult. . Therefore, the filling amount of the active material cannot be increased, and the high capacity of the lithium-based active material cannot be effectively used. This problem becomes a problem particularly when a gel electrolyte using a chain-like high molecular weight polymer is used. In a gel electrolyte using a chain polymer, the gel structure is maintained by entanglement of the polymer, and a good gel is obtained without low molecular weight components.

On the other hand, in the method described in US Pat. No. 5,609,974, since the polymer-electrolyte is a gel electrolyte having no fluidity at room temperature, the polymer-electrolyte cannot be dispersed or coated unless heated to a high temperature. I can not get the nature. Therefore, the active material, polymer, and electrolyte are kneaded at a high temperature exceeding 90 ° C.
Coated. Attaching such a heating facility to a dispersing machine or a coating machine causes an increase in cost. In addition, when exposed to a high temperature for a long time, volatilization and reaction of a solvent, particularly decomposition of a lithium salt are apt to occur, which is not preferable.

Further, in the charge / discharge process, the active material expands and contracts with the insertion and extraction of lithium ions. In particular, a carbon-based negative electrode active material such as graphite repeatedly expands and contracts by about 10% as an interlayer distance when inserting and extracting lithium ions in a charge and discharge process. On the other hand, US Pat.
In the case of a negative electrode using a gel electrolyte as described in 453335 and US Pat. No. 5,609,974, the gel electrolyte is structurally weak and cannot withstand the expansion and contraction of the active material in the electrode. There is a problem that the electrode structure including the electrolyte is easily broken, ion conduction and electron conduction are deteriorated, and cycle characteristics are poor. In particular, in the battery described in US Pat. No. 5,609,974, the polymer gels are not bonded to each other, and the gel structure is maintained by entanglement of the polymer chains. In such a structure, the entangled chains gradually slide under a long or repeated stress, and the structure cannot be maintained. In order to strengthen the structure, the concentration of the polymer may be increased, but this causes an immediate rise in concentration, which is difficult in the process and cannot be realized. As disclosed in U.S. Pat. No. 5,453,335, in the method of polymerizing a polymer from a monomer on a current collector, the polymerization in the electrode does not proceed sufficiently, so that a polymer network is not formed and the structure is maintained. Not.

[0012]

DISCLOSURE OF THE INVENTION The present invention has been made in view of the above circumstances, and as a result of intensive studies to obtain a lithium secondary battery that suppresses problems such as liquid leakage using a gel electrolyte, By performing the formation of the positive electrode and / or the negative electrode stepwise by a specific method, it is possible to increase the volume fraction of the active material in the electrode in the lithium secondary battery using the polymer gel electrolyte, The production process has been simplified to dramatically improve productivity. As a result, a lithium secondary battery having high energy density, excellent battery characteristics, and suppressing problems such as liquid leakage can be obtained at low cost.

That is, the gist of the present invention is that a positive electrode and / or a negative electrode comprises an active material capable of inserting and extracting lithium ions, a non-aqueous electrolyte, and a gel polymer for gelling the electrolyte. A method for producing a lithium secondary battery containing a lithium electrolyte, comprising the following steps (1) to (3). (1) a step of forming an active material layer containing a positive electrode or negative electrode active material and a gel polymer on a current collector as a layer having voids; (2) an electrolytic solution or a gel polymer and / or gel height; A step of filling the gap with an electrolytic solution in which a precursor capable of producing a molecule is dissolved, and (3) a step of forming a positive electrode and / or a negative electrode by subjecting the solution to a gelling treatment.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION The lithium secondary battery of the present invention has a positive electrode and / or a negative electrode containing an active material, a gel polymer for gelling an electrolytic solution, and a non-aqueous electrolytic solution. Also,
In the present invention, the positive electrode and / or the negative electrode are manufactured by forming an active material containing an active material and a gel polymer, and then impregnating with an electrolytic solution. First, the active material layer will be described.

The active material layer is formed by forming an active material and a binder resin so as to have appropriate voids on the current collector. The size of the void is usually 0.5 μm as the average void diameter.
Or more, preferably 0.8 μm or more.
μm or less, preferably 2 μm or less. The volume ratio occupied by the voids is usually 10% or more, preferably 30% or more, and usually 90% or less, preferably 60% or less. The compounding amount of the binder resin is preferably 0.1 to 30 parts by weight, more preferably 1 to 15 parts by weight, based on 100 parts by weight of the active material. If the amount of the binder resin is too small, a strong active material layer is not formed, and the active material is likely to be detached during the process. If the amount of the binder resin is too large, the amount of voids in the active material layer may decrease, which may hinder impregnation of the electrolyte later. As a part or all of the binder resin, a gel polymer that gels the electrolytic solution is used.

Examples of the compound capable of inserting and extracting lithium ions as a positive electrode active material that can be used for the positive electrode include transition metal oxides, composite oxides of lithium and transition metals, and transition metal sulfides as inorganic compounds. No. Here, Fe, Co, Ni, Mn, or the like is used as the transition metal. Specifically, MnO, V ₂ O ₅ , V ₆ O ₁₃ , Ti
Transition metal oxide powder such as O ₂ , composite oxide powder of lithium and transition metal such as lithium nickelate, lithium cobaltate, lithium manganate, etc., TiS ₂ , FeS, M
transition metal sulfide powders such as oS ₂ and the like. These compounds may be partially substituted with elements in order to improve their properties. Examples of the organic compound include polyaniline, polypyrrole, polyacene, disulfide-based compounds, polysulfide-based compounds, and N-fluoropyridinium salts. As a positive electrode active material,
These inorganic compounds and organic compounds may be used as a mixture.

The particle size of the active material of the positive electrode may be appropriately selected in consideration of the other components of the battery, and is usually 1 to 30 μm, particularly 1 to 10 μm, so that the rate characteristics and the cycle characteristics can be improved. And other battery characteristics are improved. As the negative electrode active material used for the negative electrode capable of inserting and extracting lithium ions, a carbon-based active material such as graphite and coke is preferably used. These carbon-based active materials can be used in the form of a mixture with a metal, a salt thereof, or an oxide, or a coating. Also silicon, tin, zinc, manganese,
Oxides such as iron and nickel, or sulfates, as well as metallic lithium, Li-Al, Li-Bi-Cd, and Li-
A lithium alloy such as Sn—Cd, a lithium transition metal nitride, silicon, or the like can also be used. The particle size of the active material of the negative electrode may be appropriately selected in consideration of the other components of the battery, but is usually 1 to 50 μm, particularly 15 μm.
By setting the thickness to 30 μm, battery characteristics such as initial efficiency, rate characteristics, and cycle characteristics are improved.

As the gel polymer used for the active material layer, any gel polymer can be used as long as it forms a gel with respect to the electrolyte used and is stable as a battery material. For example, ether polymers such as polyethylene oxide and polypropylene oxide, polymers having a ring such as polyvinyl pyridine and poly-N-vinylpyrrolidone, polymethyl methacrylate, polyethyl methacrylate, polybutyl methacrylate, polymethyl acrylate, polymethyl acrylate Acrylic derivative polymers such as ethyl acrylate, polyacrylic acid, polymethacrylic acid, and polyacrylamide; fluorine resins such as polyvinyl fluoride and polyvinylidene fluoride; CN group-containing polymers such as polyacrylonitrile and polyvinylidene cyanide; and polyacetic acid Examples thereof include polyvinyl alcohol polymers such as vinyl and polyvinyl alcohol, and halogen-containing polymers such as polyvinyl chloride and polyvinylidene chloride. Further, polyester, polyamide, polycarbonate, polyimide, polyurethane, polyurea and the like can also be used. Mixtures of the above polymers and the like, denatured products, derivatives, random copolymers, alternating copolymers, graft copolymers, block copolymers, and the like can also be used. When these gel polymers are linear, the increase in viscosity is suppressed, and the effect of the present invention is remarkable. Further, as will be described later, since the electrolyte and the electrolyte used for the lithium battery usually have polarities, it is preferable that the polymer also has a certain degree of polarity. Therefore, preferably, acrylic derivative-based polymers such as polymethyl methacrylate and polymethyl acrylate, ether-based polymers such as polyethylene oxide and polypropylene oxide, and C such as polyacrylonitrile.
It is preferred to use N-group containing polymers, more preferably polyacrylonitrile. In these polymers, as long as the main structure is maintained, a part of the structure may be substituted with another component.

As the binder resin used for the active material layer, the above-mentioned polymer which gels the electrolytic solution, an alkane polymer such as polyethylene, polypropylene, poly-1,1-dimethylethylene, polybutadiene, polyisoprene, etc. Unsaturated polymers, polymers having a ring such as polystyrene and polymethylstyrene, fluorine-based resins such as polytetrafluoroethylene, and conductive polymers such as polyaniline can also be used in combination. Further, a mixture of the above-mentioned polymers and the like, a modified substance, a derivative, a random copolymer, an alternating copolymer, a graft copolymer, a block copolymer, and the like can be used in combination.

The weight average molecular weight of these binder resins is usually from 10,000 to 3,000,000, preferably from 10 to
0000-1,000,000. If it is too low, the strength of the coating film decreases, which is not preferable. If it is too high, the viscosity becomes high and it becomes difficult to form an active material layer.

The active material layer may contain additives, such as a conductive material and a reinforcing material, exhibiting various functions such as a reinforcing material, a powder, and a filler, if necessary. The conductive material is not particularly limited as long as it is capable of imparting conductivity by being mixed in an appropriate amount with the above active material, but is usually carbon powder such as acetylene black, carbon black, graphite, and various metal fibers and foils. And the like. As additives, trifluoropropylene carbonate, vinylene carbonate, 1,
6-Dioxaspiro [4,4] nonane-
2,7-dion, 12-crown-4-ether and the like can be used to increase the stability and life of the battery. As the reinforcing material, various inorganic or organic spherical or fibrous fillers can be used.

The electrodes are usually formed on a current collector. Generally, a metal foil such as an aluminum foil or a copper foil is used as the current collector. The thickness is preferably 1-30 μm. If the thickness is too small, the mechanical strength becomes weak, which causes a problem in production. If the thickness is too large, the capacity of the battery as a whole tends to decrease. It is preferable that the surface of the current collector be subjected to a roughening treatment in advance, since the adhesive strength of the active material layer is increased. Examples of the surface roughening method include a mechanical polishing method, an electrolytic polishing method, and a chemical polishing method. Examples of the mechanical polishing method include a method of polishing the surface of the current collector with a polishing cloth paper having abrasive particles fixed thereon, a grindstone, an emery buff, a wire brush provided with a steel wire, or the like. Further, an intermediate layer may be formed on the surface of the current collector to increase the adhesive strength and the conductivity.

Next, the electrolyte will be described. As the electrolytic solution, a solution obtained by dissolving a supporting electrolyte in a non-aqueous solvent can be used.
The supporting electrolyte contained in the electrolytic solution is a non-electrolyte that is stable as an electrolyte with respect to the positive electrode active material and the negative electrode active material and is capable of performing lithium ions for performing an electrochemical reaction with the positive electrode active material or the negative electrode active material. Any water substance can be used. Specifically, L
_{iPF 6, LiAsF 6, LiSbF 6} , LiBF 4,
LiClO ₄ , LiI, LiBr, LiCl, LiAl
Cl, LiHF ₂ , LiSCN, LiSO ₃ CF _{2 and the} like. Among these, LiPF ₆ , LiC
10 ₄ is preferred.

The content of these supporting electrolytes in the electrolytic solution is generally 0.5 to 2.5 mol / L. The electrolytic solution for dissolving these supporting electrolytes is not particularly limited, but a solvent having a relatively high dielectric constant is preferably used. Specifically, cyclic carbonates such as ethylene carbonate and propylene carbonate, acyclic carbonates such as dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate, glymes such as tetrahydrofuran, 2-methyltetrahydrofuran and dimethoxyethane, γ-butyl lactone and the like Lactones, sulfur compounds such as sulfolane, and nitriles such as acetonitrile.
Also, one or a mixture of two or more of these can be used. Among them, cyclic carbonates such as ethylene carbonate and propylene carbonate,
One or more mixed solutions selected from acyclic carbonates such as dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate are preferred. In addition, those in which a part of hydrogen atoms in these molecules are substituted with halogen or the like can also be used. Additives and the like may be added to these electrolytes. As additives, for example, trifluoropropylene carbonate, vinylene carbonate,
1,6-Dioxaspiro [4,4] nonane
-2,7-done, 12-crown-4-ether and the like can be used for the purpose of enhancing the stability, performance and life of the battery.

The electrode contains an active material, a gel polymer, and a non-aqueous electrolyte. The amount of the active material in the electrode is 40% or more for the positive electrode and 33% for the negative electrode. % Is preferable. More preferably, both the positive electrode and the negative electrode are preferably set to 50% or more. On the other hand, these volume fractions are usually 95% for both the positive and negative electrodes.
It is as follows. More preferably, the weight fraction of the active material in the electrode is 70% for the positive electrode and 45% or more for the negative electrode. On the other hand, these weight fractions are usually 95% or less for both the positive electrode and the negative electrode. By satisfying the above requirements, the capacity is increased, the electric conductivity is improved, and the battery characteristics are improved. Further, such a battery can be manufactured by the method of the present invention described later.

The concentration of the gel polymer with respect to the electrolyte in the electrode is usually 1% by weight or more, preferably 7% by weight or more, especially 10% by weight or more, and usually 50% by weight or less, preferably 30% by weight. Or less, particularly preferably 20% by weight or less. If it is too low, the strength of the electrode tends to decrease, and the battery characteristics tend to deteriorate. If it is too high, the ionic conductivity tends to decrease, and the battery characteristics tend to deteriorate.

Next, the lithium secondary battery of the present invention will be described. In the lithium secondary battery of the present invention, the positive electrode and the negative electrode having the above-described configurations are stacked with an electrolyte layer interposed therebetween to form a battery cell. When the battery cells are flat,
It can be made thinner and can be used for a wide range of applications. As the electrolyte layer separating the positive electrode and the negative electrode, a gel electrolyte composed of the above-mentioned gel polymer and an electrolytic solution can be used. The electrolyte layer made of the gel electrolyte may be formed separately and laminated on the positive electrode and the negative electrode, or may be formed directly on the positive electrode and the negative electrode. Further, a reinforcing material or the like may be used in combination. When a porous spacer is used, a filter, a nonwoven fabric, a battery separator, or the like made of various materials can be used. The porosity is preferably in the range of 30-90% by volume, more preferably 50-80% by volume. The battery cells are singly or stacked, and terminals for external connection are attached, and are housed in a case having a variable shape.

The case having a variable shape used in the present invention is a case having flexibility, flexibility, flexibility and the like, and is made of a material such as plastic, polymer film, metal film, rubber, thin metal plate and the like. And those consisting of More specifically, a bag made of a polymer film like a plastic bag, a vacuum packaging bag made of a polymer film, a vacuum pack, a vacuum packaging bag made of a laminated material of a metal foil and a polymer film, a vacuum pack, a plastic And a case which is sandwiched between plastic plates and fixed around by welding, bonding, fitting or the like. Among these, a vacuum packaging bag made of a polymer film, a vacuum pack, a vacuum packaging bag made of a laminated material of a metal foil and a polymer film, a vacuum pack, and the like are particularly preferable in terms of airtightness and shape changeability. Of course, for convenience such as mounting the battery on equipment, it is possible to enclose the battery in a case with variable shape and mold it into a preferred shape, and then store multiple cases in a rigid outer case if necessary. is there.

Next, a method for manufacturing a lithium secondary battery according to the present invention will be described. In the present invention, first, the active material layer is formed as a layer having voids. As an example of a method for forming the active material layer, a powdery active material and a binder solution containing a gel polymer are mixed and dispersed and coated with a ball mill, a sand mill, a twin-screw kneader, or the like. And drying. Here, all of dispersion, coating and drying can be performed in a normal atmosphere.
As the solvent used at this time, various inorganic and organic solvents such as N-methylpyrrolidone can be used.

In the above-described method of forming an active material layer by applying and drying a coating material containing an active material and a gel polymer, if a gel polymer is a linear polymer, low viscosity Paint is obtained, which is preferable. Alternatively, the active material layer can be formed by a method of pressing or spraying the current collector on a current collector in a state where the active material is mixed with a binder resin and heated to be softened.

Further, an active material layer can be formed by applying and drying a paint containing an active material and a precursor capable of forming a gel polymer. The precursor capable of producing a gel polymer is not particularly limited as long as it can generate a gel polymer by a predetermined treatment and reaction, and examples thereof include monomers and oligomers that are raw materials of the gel polymer. Preferably it is a monomer. In this case, preferred monomers are those that carry out addition polymerization in which no by-product is generated by the polymerization reaction. In particular, a monomer having a reactive unsaturated group is preferable because of its excellent productivity.

Examples of the monomer having a reactive unsaturated group include acrylic acid, methyl acrylate, ethyl acrylate, ethoxyethyl acrylate, methoxyethyl acrylate, ethoxyethoxyethyl acrylate, polyethylene glycol monoacrylate, ethoxyethyl methacrylate, and methoxyethyl. Methacrylate, ethoxyethoxyethyl methacrylate, polyethylene glycol monomethacrylate, N, N-diethylaminoethyl acrylate, N, N-dimethylaminoethyl acrylate, glycidyl acrylate, allyl acrylate, acrylonitrile, N-vinylpyrrolidone, diethylene glycol diacrylate, triethylene glycol diacrylate Acrylate, tetraethylene glycol diacrylate, polyethylene Glycol diacrylate, diethylene glycol dimethacrylate, triethylene glycol dimethacrylate, tetraethylene glycol dimethacrylate, can be used such as polyethylene glycol dimethacrylate, reactive, polar, may be used in alone or in combination, it is most preferable because such safety.

When precursors are used, they are usually made into gel polymers by impregnation with an electrolytic solution by means such as polymerization. As a method of polymerizing these monomers,
Examples of the method include heat, ultraviolet rays, and electron beams. A polymerization initiator can also be used to make the reaction proceed effectively. The active material layer may be subjected to a calendering treatment as necessary to consolidate the active material layer so as to increase the filling amount of the active material in the electrode.

Next, the active material layer is impregnated with the electrolytic solution to fill the voids in the active material layer with the electrolytic solution. As a method of impregnating the electrolytic solution, a method of applying the electrolytic solution on the active material layer can be adopted. In order to increase the efficiency and speed of impregnation, operations such as press-fitting and vacuum impregnation may be performed. In particular, when the electrolytic solution dissolves a high-concentration polymer, it is preferable to perform an operation such as vacuum impregnation because the viscosity is high. It is preferable that the electrolyte solution completely fills the voids in the active material layer. However, even if voids that are insufficiently impregnated with the electrolyte solution remain, there is no significant problem in battery characteristics. In the case where voids are generated to the extent that the battery characteristics deteriorate, it is preferable to employ the above-described technique for increasing the impregnation efficiency.

The electrolyte to be impregnated may be used alone or may be an electrolyte containing a gel polymer or a precursor of a gel polymer. In this case, the same gel polymer as described above can be used as the gel polymer and its precursor contained in the electrolytic solution. Of course, the gel polymer and its precursor used in forming the active material layer and the gel polymer and its precursor contained in the electrolytic solution may be the same or different.

When a gel polymer is contained, its concentration is usually 0.1-20% by weight, preferably 1-10% by weight. When a gel polymer is contained, the concentration is preferably such that the electrolyte does not gel. Of course, heat may be applied to lower the viscosity. When containing a gel polymer precursor, since it generally has a lower viscosity than containing the gel polymer itself, its concentration has a greater degree of freedom,
Usually, any amount can be contained.

After the impregnation, the gel polymer in the active material layer and, if necessary, the gel polymer or gel precursor in the electrolytic solution and the electrolytic solution are subjected to a gelling treatment to form a gel electrolyte. That is,
The electrolyte is retained in the gel polymer network to form a gel with reduced fluidity. The method of the gelation treatment is not particularly limited, and may be left alone if a gel is formed.However, it is usually a method of further cooling after heating,
A method of irradiating energy rays such as ultraviolet rays can be used.

Between the step of forming the active material and the step of impregnating the electrolytic solution, or between the step of impregnating the electrolytic solution and the step of performing the gelling treatment, the positive electrode and the negative electrode are laminated via a spacer. Preferably, a step is provided. With such a configuration, it is possible to perform the impregnation of the electrolytic solution at one time or to perform the gelling process at one time. The method of the present invention can be employed for the production of one of the positive electrode and the negative electrode, but it is preferable to employ the method for both electrodes because the effect of the invention becomes larger. In the case of only one electrode, of course, for the other electrode, various conventionally known materials and manufacturing methods can be adopted.

The lithium secondary battery of the present invention and the method of manufacturing the same have the following effects. That is, in the present invention, the components constituting the electrode are supplied onto the current collector at least twice. As a result, effects in the process such as a decrease in the viscosity of the paint in each process and easiness of water management can be obtained, and an effect of improving characteristics such as an increase in capacity due to the possibility of increasing the active material can be obtained.

In the present invention, at the stage of forming the active material layer, the polymer that gels the electrolyte contained in the active material layer acts as a binder at this stage. Since this step can be subjected to moisture removal by a drying step or the like later, it is possible to perform the treatment in a normal atmosphere without the need for moisture control. Therefore, the dispersing machine,
It is not necessary to install the coating machine in the dry room, and the equipment can be simplified. In the case of adopting the step of forming a dispersion paint, the solvent used is dried and removed, so that any kind and amount can be used according to the purpose. For example, it is possible to reduce the viscosity of the paint by selecting a solvent having high solubility in the polymer or by using a large amount of the solvent. When the polymer is polymerized on the current collector from the precursor, there are few restrictions on the polymerization conditions.Therefore, by controlling the composition, temperature, etc., the polymerization should proceed sufficiently to form a strong active material layer. Becomes possible.

Next, the active material layer is impregnated with an electrolytic solution. In the present invention, since part or all of the gel polymer has already been supplied into the active material layer, the electrolytic solution is required to satisfy the required composition. A small amount or unnecessary polymer is contained and supplied. Therefore, the viscosity of the electrolytic solution can be reduced, and the workability is improved. Subsequently, a gelation treatment is performed. In this step,
It is presumed that the gel polymer supplied first and the electrolyte supplied later are united to form a gel electrolyte.
Therefore, in the battery of the present invention, the electrolyte is held in the gel electrolyte, and problems such as liquid leakage are suppressed.

When the positive electrode and the negative electrode are laminated via a spacer and then subjected to a gelling treatment, the formed gel electrolyte is integrated with the positive electrode, the negative electrode and the electrolyte layer, so that the internal resistance is reduced. And the like can be realized, and the battery characteristics can be improved.

According to the method of the present invention, since the active material is firmly held by a sufficient amount of polymer, problems such as desorption of the active material hardly occur. Further, the deterioration of the cycle characteristics due to the structural destruction of the electrode, unlike the lithium secondary battery using the conventional gel electrolyte, is unlikely to occur. In addition, since the active material is held on the current collector by a polymer and the electrolyte is held as a gel electrolyte, it is not necessary to enclose it in a metal can as in a conventional lithium secondary battery. It operates simply by being housed in a case with a variable shape. Of course, there is no problem if it is formed into a winding type and a cylindrical type, and there is no problem even if a part of the flat plate is curved.

[0044]

EXAMPLES The present invention will be described more specifically with reference to examples and comparative examples below, but the present invention is not limited to the following examples unless it exceeds the gist thereof. The raw materials used in the examples and comparative examples are as follows: before use, the powder is vacuum-dried at 240 ° C. for 24 hours, the resin and the supporting electrolyte are dried at 110 ° C. for 4 hours, and the monomer is dehydrated with molecular sieve Used. The electrolyte used was one that was previously dehydrated for a lithium battery. Also,
Hereinafter, “parts” means “parts by weight”.

Example 1 First, a paint for a positive electrode active material layer and a paint for a negative electrode active material layer were prepared according to the following compositions. The following were used as raw materials for the positive electrode paint and the negative electrode paint.

[0046]

[Table 1] Positive electrode active material LiCoO ₂ powder Conductive material Acetylene black Negative electrode active material Graphite Polymer Polyacrylonitrile Solvent N-methylpyrrolidone

[0047]

[Table 2] (Coating composition of positive electrode active material layer) LiCoO ₂ 90.0 parts Acetylene black 5.0 parts Polyacrylonitrile 5.0 parts N-methylpyrrolidone 100.0 parts

[0048]

[Table 3] (Negative electrode active material layer coating composition) Graphite 90.0 parts Polyacrylonitrile 10.0 parts N-methylpyrrolidone 150.0 parts

Each of the above materials was kneaded and dispersed in a sand mill for 0.5 hour to form a coating. The coating material for the positive electrode active material layer was applied on an aluminum foil having a thickness of 20 μm using a doctor blade so that the film thickness became 100 μm, and dried to obtain a positive electrode active material layer. Thereafter, it was subjected to a calendar process. (The final film thickness is about 70-90 μm). The coating material for the negative electrode active material layer was applied on a copper foil having a thickness of 20 μm using a doctor blade so that the film thickness became 100 μm, and dried. Thereafter, it was subjected to a calendar process. (Final film thickness is 60-90μ)
m). All the steps up to this point were performed in a normal environment. Thereafter, the coating film was dried again at 120 ° C. and punched into a predetermined shape to obtain a sheet provided with a positive electrode / negative electrode active material layer on a current collector. Next, an impregnating liquid having the following materials and composition was produced.

[0050]

[Table 4]

[0051]

(Table 5) (impregnating liquid composition) PC 44.1 parts EC 44.1 parts LiClO ₄ 7.7 parts Polyacrylonitrile 4.0 parts

The above impregnating solution was dissolved at 90 ° C. to obtain a uniform solution. As can be seen in Table 2, this was a low viscosity liquid at 40 ° C and a lower viscosity liquid at 90 ° C. Upon cooling to 0 ° C., a white gel electrolyte was formed. This solution was applied to each of the positive electrode and negative electrode active material layers while being heated to 90 ° C., and was impregnated into voids in the active material layers. Then put a cover film made of polypropylene,
The whole electrode was kept in a 90 ° C. oven for 10 minutes, and then cooled at 0 ° C. to gel the whole electrode. Further, a liquid having the following composition was applied on the positive electrode and the negative electrode as an electrolyte layer, and a 60 μm-thick gel electrolyte layer was formed on each of them by irradiating ultraviolet rays.

[0053]

(Table 6) (Electrolyte solution composition) PC 83 parts LiClO ₄ 7 parts Photomer 4050 6.7 parts Photomer 4158 3.3 parts Darocure 1173 0.5 parts

However, Photomer 4050 and P
Photomer 4158 is a polyethylene oxide resin having an acrylic group at the terminal (manufactured by Henkel), and Darocure 1173 is a crosslinking initiator (manufactured by Ciba Geigy). Thereafter, a positive electrode and a negative electrode were laminated with the electrolyte layer inside, terminals were attached, and the battery was sealed in a vacuum pack to prepare a lithium secondary battery and evaluated.

Example 2 The composition of the impregnating liquid was changed as follows.

[0056]

(Table 7) (impregnating liquid composition) PC 43.2 parts EC 43.2 parts LiClO ₄ 7.6 parts Polyacrylonitrile 6.0 parts

The above impregnating solution was dissolved at 110 ° C. to obtain a uniform solution. This solution forms a gel electrolyte at normal temperature,
At 0 ° C., the liquid was slightly viscous. Add this solution to 9
The solution was applied to the positive electrode / negative electrode active material layer while being heated to 0 ° C., and was impregnated into voids in the active material layer. Other steps were the same as in Example 1 to prepare a battery.

Example 3 The composition of the impregnating liquid was changed as follows.

[0059]

(Table 8) (impregnating liquid composition) PC 46.0 parts EC 46.0 parts LiClO ₄ 8.0 parts

The above impregnating solution was dissolved at room temperature to obtain a uniform solution. This solution was applied to the positive electrode / negative electrode active material layer and impregnated into the voids in the active material layer. Other steps were the same as in Example 1 to prepare a battery.

Example 4 In the same manner as in Example 1, the impregnating liquid was heated and heated at 90 ° C. to apply and impregnate the active material layers of the positive electrode and the negative electrode, and the impregnating liquid was further immersed in a nonwoven fabric having a thickness of 60 μm. Thereafter, a positive electrode, a nonwoven fabric, and a negative electrode were laminated. Thereafter, the entire laminate was covered with a cover film made of polypropylene, and the entire electrode was kept in an oven at 90 ° C. for 10 minutes, and then cooled at 0 ° C. to gel the entire electrode and electrolyte layer. Next, electrodes were attached and sealed in a vacuum pack to prepare a lithium secondary battery and evaluated.

Comparative Example 1 A positive electrode and a negative electrode were kneaded integrally with an active material and a gel electrolyte component.
It was prepared by a method of applying. All steps after kneading were performed in a dry room.

[0063]

(Table 9) (Positive electrode coating composition) LiCoO ₂ 51.0 parts Acetylene black 5.0 parts Polyacrylonitrile 2.5 parts LiClO ₄ 3.5 parts PC 19.0 parts EC 19.0 parts

[0064]

(Table 10) (Negative electrode coating composition) MBC (Coke: manufactured by Mitsubishi Chemical Corporation) 45.0 parts Acetylene black 5.0 parts Polyacrylonitrile 3.0 parts LiClO ₄ 4.2 parts PC 21.4 parts EC 21.4 parts

The above materials are kneaded for 8 hours at 90 ° C.
Dispersion treatment was performed to make paint. The paste for a negative electrode using the same graphite as in Example 1 as an active material for a negative electrode was too high in viscosity to be dispersed. The coating material for the positive electrode was applied on a 20-μm-thick aluminum foil using a doctor blade while heating at 90 ° C. so that the film thickness became 100 μm, and then cooled to obtain a positive electrode composed of a gel electrolyte. The coating material for the negative electrode was heated to 90 ° C. using a doctor blade on a copper foil having a thickness of 20 μm, and the thickness was 75 μm.
And then cooled to obtain a negative electrode comprising a gel electrolyte. Thereafter, the positive electrode and the negative electrode were punched into a predetermined shape. The electrolyte layer was composed of P in the composition of the electrolyte layer in Example 1.
5 parts of C were 1,6-Dioxaspiro [4,4]
nonane-2,7-done (hereinafter "spir
o) and polymerized by ultraviolet rays separately from the electrodes to form a gel electrolyte layer having a thickness of 120 μm. Thereafter, a positive electrode, an electrolyte layer, and a negative electrode were laminated, terminals were provided, and the resultant was sealed in a vacuum pack to prepare a lithium secondary battery, which was evaluated.

Comparative Example 2 A positive electrode and a negative electrode were kneaded integrally with an active material and a gel electrolyte component.
It was prepared by a method of applying. All steps after kneading were performed in a dry room.

[0067]

[Table 11]

[0068]

(Table 12) (Negative electrode coating composition) Graphite 45.0 parts Photomer 4050 2.5 parts Photomer 4158 2.5 parts EEEA 2.0 parts spiro 3.0 parts PC 45.0 parts

Each of the above materials was kneaded and dispersed in a ball mill for 8 hours to form a coating. Thereafter, 0.5 part of Trignox42 (manufactured by Ciba-Geigy), which is a heat-reactive crosslinking initiator, was added, and a positive electrode paint was applied on a 20-μm-thick aluminum foil using a doctor blade to a thickness of 100 μm. The mixture was cured in a 90 ° C. oven for 30 minutes to obtain a positive electrode made of a gel electrolyte. The negative electrode paint has a thickness of 2
Using a doctor blade on a 0 μm copper foil,
After coating to a thickness of μm, the coating was cured in a 90 ° C. oven for 30 minutes to obtain a negative electrode comprising a gel electrolyte. Thereafter, the positive electrode and the negative electrode were punched into a predetermined shape. The following steps were performed to produce a battery in the same manner as in Comparative Example 1.

The paint prepared according to the above-mentioned formula is as follows:
Tables 1 to 4 show various characteristics of the electrode and the battery. The viscosity of the paint was measured at a constant temperature using an E-type viscometer. The active material and the polymer fraction in the electrode were calculated from the measured values of the thickness and weight of the electrode. When the capacity of the battery is charged at a constant current of C / 24 to 4.1 V and then discharged at a constant voltage of 4.1 V to C / 240, the battery is discharged to 2.7 V at a current of C / 24. The capacity that can be taken out was calculated as the capacity per unit weight of the positive electrode excluding the current collector.
The rate characteristics are as follows: The capacity that can be taken out when discharging under a constant current condition with a current amount of C / 2 between 4.1 V and 2.7 V is C / 24
And expressed as a percentage of the capacity that can be taken out when discharged under constant current conditions. Cycle characteristics are 4.1V-2.7
When charge / discharge was repeated between the upper limit voltage and the lower limit voltage of V, the capacity retention rate during 20 cycles was expressed as a percentage of the capacity at the end to the time at the start.

As shown in Table 1, according to the present invention, the active material fraction at the paint stage can be kept low.
Further, a solvent having high solubility can be selected as a solvent to be used. Therefore, the viscosity of the paint is extremely lower than that of the comparative example, and various steps of liquid preparation, dispersion, liquid sending, and application become remarkably easy. As shown in Table 2, in the present invention, the viscosity of the electrolyte solution supplied later is also at most 1000 cps, and particularly in Examples 1, 2, 4, and 5 where the content of the polymer is low, several hundreds at room temperature. It is easy to prepare, apply and impregnate with cps.
In the comparative example, an electrode paint exceeding 100,000 cps must be dispersed and applied. In the comparative example 1, the process is not easy, for example, heating to near 100 ° C. As shown in Table 3, the electrode obtained by the present invention can increase the active material filling amount and the polymer content as compared with the comparative example. As shown in Table-4, batteries made using these electrodes are excellent in capacity, rate, and cycle characteristics. Comparative Example 1,
In the case of No. 2, since the filling amount of the active material cannot be increased, the capacity is inferior. Further, since the fraction of the polymer is low, the strength of the coating film is poor, and the cycle characteristics are poor.

[0072]

The lithium secondary battery of the present invention is a lithium secondary battery using a gel electrolyte which has high energy density, excellent battery characteristics, and suppresses problems such as liquid leakage. By performing the supply in two stages, the productivity is dramatically improved and the battery characteristics are improved.

[0073]

[Table 13] Note 1) The value in parentheses in the viscosity data is the measurement temperature (° C).

[0074]

[Table 14]

[0075]

[Table 15]

[0076]

[Table 16]

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Claims (7)

[Claims] A positive electrode and / or a negative electrode contains an active material capable of inserting and extracting lithium ions, and a gel electrolyte containing a non-aqueous electrolyte and a gel polymer for gelling the electrolyte. A method for producing a lithium secondary battery, comprising the following steps (1) to (3). (1) a step of forming an active material layer containing a positive electrode or negative electrode active material and a gel polymer on a current collector as a layer having voids; (2) an electrolytic solution or a gel polymer and / or gel height; A step of filling the gap with an electrolytic solution in which a precursor capable of producing a molecule is dissolved, and (3) a step of forming a positive electrode and / or a negative electrode by subjecting the solution to a gelling treatment. 2. A step of laminating a positive electrode and a negative electrode via a porous spacer between step (1) and step (2) or between step (2) and step (3). A method for manufacturing a lithium secondary battery according to claim 1. 3. The active material layer is formed by applying and drying a coating material containing a positive electrode or a negative electrode active material and a gel polymer and / or a precursor capable of forming a gel polymer. Or the method for producing a lithium secondary battery according to 2. 4. A lithium secondary battery in which a positive electrode contains an active material capable of inserting and extracting lithium ions, and a gel electrolyte containing a non-aqueous electrolyte and a gel polymer for gelling the electrolyte. , Wherein the volume fraction of the active material in the positive electrode is 40% or more. 5. A lithium secondary battery in which a negative electrode contains an active material capable of inserting and extracting lithium ions, and a gel electrolyte containing a non-aqueous electrolyte and a gel polymer for gelling the electrolyte. , Wherein the volume fraction of the active material in the negative electrode is 33% or more. 6. The lithium secondary battery according to claim 4, wherein the concentration of the gel polymer with respect to the electrolyte in the electrode is 7% by weight or more. 7. The lithium secondary battery according to claim 4, wherein the gel polymer is a linear polymer.