JP4318233B2 - Lithium secondary battery and manufacturing method thereof - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a lithium secondary battery. More specifically, the present invention relates to a lithium secondary battery having a high capacity, high energy density, low internal resistance, high productivity, and low cost, and is particularly suitable when a solid or gel electrolyte is used instead of the electrolyte. Next battery.
[0002]
[Prior art]
A lithium secondary battery is generally composed of a positive electrode and a negative electrode capable of occluding and releasing lithium ions, and a non-aqueous electrolyte mainly composed of a lithium salt and a solvent. The positive electrode and the negative electrode are separated by a separator made of a porous film, and are ionically bonded by a non-aqueous electrolyte solution that fills the pores of the porous film. However, most of the solvents used in the electrolytic solution are organic compound liquids, and are often flammable and odorous. A battery using a non-aqueous electrolytic solution has a risk of leakage or ignition. For this reason, in recent years, in order to improve safety, a battery that replaces a non-aqueous electrolyte with a gel electrolyte has been developed. In gel electrolytes, non-aqueous electrolytes are held in, for example, polymers, and many of their properties, such as ionic conductivity, maintain the performance of the electrolyte, but the fluidity is extremely low and the shape is maintainable, and the volatilization The speed is also suppressed. Therefore, the risk of leakage or ignition can be reduced. In particular, in secondary batteries using lithium metal, heat generation and ignition due to internal short circuit due to lithium dendrite precipitation have been a problem. It was rare.
[0003]
Furthermore, unlike the conventional lithium secondary battery, a gel electrolyte containing an electrolyte in a polymer as described above can be operated without using a separator, unlike the conventional lithium secondary battery. The separator can be omitted and the gel electrolyte layer can be sandwiched between the positive electrode and the negative electrode. Since the battery using such a polymer electrolyte has a low possibility of liquid leakage, there is an advantage that the exterior can be simplified and the weight can be simplified compared to the liquid system. Furthermore, there is a possibility that a card-like thin battery can be realized.
[0004]
[Problems to be solved by the invention]
Gel electrolytes are self-supporting and can replace separators by themselves, but the mechanical strength is never sufficient, and gel electrolytes alone are particularly difficult in severe environments where various stresses are applied. There are problems with insulation.
Thus, attempts have been made to increase the mechanical strength of the gel electrolyte by providing a separator. However, when using such a separator, there are the following manufacturing problems.
[0005]
That is, in general, a lithium secondary battery has a positive electrode, a separator made of a porous film, and a negative electrode in a roll shape. The ends of each roll are bundled and wound while applying tension to the core material, and the winding length is predetermined. When reaching the length, the laminate is cut. Thereafter, an electrolyte is mainly injected from the side surface of the laminate to form an ion mobile phase. In this method, it is necessary to prepare the porous film as a roll, and a winder for the porous film is also required. In addition, electrolyte injection takes a considerable amount of time and increases costs.
[0006]
Another problem when using a separator such as a porous film is that it is difficult to stack the batteries in a flat plate. In the case of flat plate lamination, it is difficult to laminate and assemble while applying tension to the separator. On the other hand, it is not practical to accurately position and stack thin and soft separators by simply holding the ends and preventing wrinkles and the like from approaching. Further, if the separator is made thick so that the wrinkles are not easily moved, the thickness of the electrolyte layer is increased, the resistance is increased, and the capacity is reduced. In particular, when the battery is stored in a case having shape changeability, the battery cannot be pressed down by the case, and therefore, the position of the separator is likely to be shifted when the electrolyte is injected. These problems become more prominent as the planar battery has a larger area. Therefore, it has been difficult to manufacture a thin flat battery using a separator.
[0007]
On the other hand, the battery using the gel electrolyte also has the following problems.
First, there is a problem of resistance at the interface of the gel electrolyte. In the gel electrolyte, the electrolytic solution is held in a polymer network, and macroscopically there is no fluidity of the electrolytic solution. Since the electrolyte layer formed from such a gel electrolyte is self-supporting, the solid surface is bonded to the bonding surface of the electrolyte layer and the electrode, and the adhesion of the gel electrolyte to each other deteriorates. , Ion conductivity is impaired. Such an increase in resistance causes a decrease in capacity, rate characteristics, and cycle characteristics.
[0008]
There are also manufacturing problems. For example, in USP 5,453,335 and USP 5,609,974, an electrode made of an active material, a polymer, and an electrolytic solution is formed, and then a gel electrolyte layer is formed. Such a method has a drawback in that the formation of the gel electrolyte in the electrode and the formation of the gel electrolyte in the electrolyte layer are performed separately, resulting in a long process and cost. Further, since the electrolytic solution is contained from the electrode formation stage, there is a problem that moisture must be managed in all steps of electrode dispersion and coating. This is achieved by installing a disperser and a coating machine in a dehumidified room (dry room). However, this requires a considerably large dry room and is expensive. In addition, the longer the process, the higher the possibility of absorbing moisture even in a dry room.
[0009]
[Means for Solving the Problems]
This invention is made | formed in view of the said actual condition, The objective is to provide the lithium secondary battery excellent in mechanical strength.
Another object of the present invention is to provide a lithium secondary battery having excellent cycle characteristics and capacity.
Furthermore, another object of the present invention is to provide a lithium secondary battery having a small number of manufacturing steps and high productivity. Still another object of the present invention is to provide a lithium secondary battery capable of increasing the area. Still another object of the present invention is to provide a method for producing the lithium secondary battery as described above.
[0010]
  The present inventor has found that the above object can be achieved by providing an intermediate layer having a non-electrically conductive powder and a non-electrically conductive binder between the electrodes, and has completed the present invention.
  That is, the gist of the present invention is (1) a positive electrode, (2) a negative electrode, and (3) an intermediate layer provided between them and containing a non-electrically conductive powder and a non-electrically conductive binder. HaveA lithium secondary battery comprising: (1) a positive electrode and / or (2) an active material layer containing a powdered active material and a binder, and a gel electrolyte formed in the active material layer The intermediate layer of (3) is formed in the skeleton layer containing a non-electrically conductive powder and a non-electrically conductive binder. And the non-electroconductive powder of (3) is selected from silica, titanium oxide, and aluminum oxide, and comprises (1) to (3). The binder is polyvinylidene fluoride, and the gel electrolytes (1) to (3) contain polyacrylonitrile or a polyethylene oxide resin having an acrylic group at the terminal, and are used for the active material layers of the positive electrode and the negative electrode. Thickness is 1 to 300 μm, medium Porosity and thickness of the layer is 1~200μm intermediate layer, i.e., the volume ratio in the intermediate layer of ion transfer phase formed in the void of the skeleton layer, but 30 to 95%It exists in the lithium secondary battery characterized by this.
  Another gist of the present invention includes (1) a positive electrode, (2) a negative electrode, and (3) a non-electrically conductive powder and a non-electrically conductive binder provided between them. The positive electrode and / or the negative electrode includes an active material layer containing a powdery active material and a binder for fixing the active material, and a gel electrolyte formed in the active material layer The intermediate layer is composed of a skeleton layer containing a non-electrically conductive powder and a non-electrically conductive binder, and a gel formed in the skeleton layer. Lithium comprising an ion mobile phase comprising an electrolyte, wherein the ion mobile phase formed in the positive electrode and / or negative electrode and the ion mobile phase formed in the intermediate layer are continuous Secondary batteryWherein the non-electrically conductive powder of (3) is selected from silica, titanium oxide and aluminum oxide, the binder of (1) to (3) is polyvinylidene fluoride, and The gel electrolytes (1) to (3) contain polyacrylonitrile or a polyethylene oxide resin having an acrylic group at the end, and the active material layers of the positive electrode and the negative electrode have a thickness of 1 to 300 μm, and an intermediate layer Lithium secondary battery in which the thickness of the intermediate layer is 1 to 200 μm and the porosity of the intermediate layer, that is, the volume ratio of the ion mobile phase formed in the voids of the skeleton layer in the intermediate layer is 30 to 95%Exist.
  In addition, still another aspect of the present invention covers almost the entire area between the positive electrode and the negative electrode,ReContains a thion ion conductive electrolyteThe middle classAn electrolyte layer is provided, and the positive electrode and / or the negative electrode includes an active material layer containing a powdery active material and a binder for fixing the active material, and a gel electrolyte formed in the active material layer. The electrolyte layer is composed of a skeleton layer containing a non-electrically conductive powder and a non-electrically conductive binder, and a gel electrolyte formed in the skeleton layer. Lithium ion, wherein the ion mobile phase formed in the positive electrode and / or negative electrode and the ion mobile phase formed in the electrolyte layer are continuous. Secondary batteryThe non-electrically conductive powder is selected from silica, titanium oxide and aluminum oxide, and the binder for fixing the active material and the non-electrically conductive binder are both polyvinylidene fluoride. And the gel electrolyte contains polyacrylonitrile or a polyethylene oxide resin having an acrylic group at the end, the thickness of the active material layer of the positive electrode and the negative electrode is 1 to 300 μm, and the thickness of the intermediate layer is 1 to Lithium secondary battery having 200 μm and a porosity of the intermediate layer, that is, a volume ratio in the intermediate layer of the ion mobile phase formed in the void of the skeleton layer, of 30 to 95%Exist.
  The other gist of the present invention is as follows.A method for manufacturing a lithium secondary battery in which an intermediate layer containing a non-electrically conductive powder and a non-electrically conductive binder is formed between a positive electrode and a negative electrode. It includes an intermediate layer forming step of applying and drying a paint containing a conductive powder, a non-electrically conductive binder, and a solvent, and after the intermediate layer forming step, impregnation with an ion mobile phase raw material As an ion mobile phase material for forming a gel electrolyte, (i) containing an electrolytic solution and a gelled polymer, or (ii) using an electrolytic solution and a monomer The positive electrode and / or the negative electrode are composed of an active material layer containing a powdery active material and a binder, and the non-electrically conductive powder of the intermediate layer is made of silica, titanium oxide, and aluminum oxide. The binder and non-electric The conductive binder is polyvinylidene fluoride, and the gel electrolyte contained in the ion mobile phase formed from the ion mobile phase raw material contains polyacrylonitrile or a polyethylene oxide resin having an acrylic group at the end. The thickness of the active material layer of the positive electrode and the negative electrode is 1 to 300 μm, the thickness of the intermediate layer is 1 to 200 μm, and the porosity of the intermediate layer, that is, the intermediate of the ion mobile phase formed in the voids of the skeleton layer Method for manufacturing lithium secondary battery, wherein volume ratio in layer is 30 to 95%Exist.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
The lithium secondary battery of the present invention usually has a positive electrode, a negative electrode and an electrolyte layer provided therebetween, and further has an intermediate layer provided between the positive electrode and the negative electrode. . The intermediate layer is preferably provided in contact with at least one of the positive electrode and the negative electrode, and particularly preferably provided integrally with at least one of the positive electrode and the negative electrode. The term “integral” refers to a state in which the electrode and the intermediate layer are continuous at least partially, and can be manufactured by a manufacturing method as described below.
[0012]
The intermediate layer preferably contains a lithium ion conductive electrolyte so as to function also as an electrolyte. Furthermore, the electrolyte layer provided over almost the entire surface between the electrodes contains a non-electroconductive powder and a non-electrically conductive binder in addition to the lithium ion conductive electrolyte, thereby providing an intermediate layer. It is preferable from the viewpoint of simplification of the manufacturing process and mechanical strength of the battery. In this case, the intermediate layer and the electrolyte layer have substantially the same function and composition.
Hereinafter, first, the electrolyte layer will be described.
[0013]
The electrolyte layer is responsible for the movement of lithium ions between the positive electrode and the negative electrode, and contains a lithium ion conductive electrolyte. In the present invention, any non-aqueous material that is stable with respect to a positive electrode active material, a negative electrode active material, etc., and that can move for lithium ions to perform an electrochemical reaction with the positive electrode active material or the negative electrode active material. Can also be used. In particular, a supporting electrolyte mainly composed of a lithium salt and an electrolytic solution composed of a non-aqueous solvent are preferably used because of excellent characteristics.
As the supporting electrolyte, LiPF₆, LiAsF₆, LiSbF₆, LiBF_FourLiClO_Four, LiI, LiBr, LiCl, LiAlCl, LiHF₂, LiSCN, LiSO_ThreeCF₂And lithium salts such as Of these, LiPF in particular₆LiClO_FourIs preferred.
[0014]
The content in the case of using these supporting electrolytes dissolved in a solvent is generally 0.5 to 2.5 mol / L. The solvent 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-butyllactone, etc. Lactones, sulfur compounds such as sulfolane, nitriles such as acetonitrile, and the like. Moreover, these 1 type, or 2 or more types of mixtures can also be used. Of these, one or more selected from cyclic carbonates such as ethylene carbonate and propylene carbonate, and acyclic carbonates such as dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate are particularly preferable. In addition, those in which some of hydrogen atoms in these molecules are substituted with halogen or the like can be used. Moreover, you may add an additive etc. to these electrolyte solutions. Examples of additives include trifluoropropylene carbonate, vinylidene carbonate, 1,6-Dioxaspiro [4,4] nonane-2,7-dione, 12-crown-4-ether, etc. Can be used for enhancing purposes.
[0015]
In the present invention, a gel electrolyte can also be used as an electrolyte for the purpose of suppressing liquid leakage and improving safety, and is preferable.
The gel electrolyte mainly consists of an electrolytic solution and a polymer, and the electrolytic solution is held in a polymer network and the fluidity as a whole is remarkably lowered. Although characteristics such as ion conductivity are similar to those of ordinary electrolytes, fluidity and volatility are remarkably suppressed and safety is enhanced.
[0016]
The type of polymer is not particularly limited as long as it forms a gel with respect to the electrolyte and is stable as a battery material. However, since the electrolyte used for the lithium battery usually has polarity, a polymer having a certain degree of polarity is preferable. The molecular weight of the polymer is usually in the range of 10,000 to 5,000,000, preferably 100,000 to 1,000,000. If the molecular weight is too low, gel formation is difficult, and if the molecular weight is too high, the viscosity is too high and handling becomes difficult.
The gel electrolyte forming step includes (1) a method of cooling a polymer to room temperature by using an electrolyte containing a polymer that can be gelled by cooling in a heated state, and (2) a monomer. A method of polymerizing the monomer using the electrolytic solution is preferably used.
[0017]
  As a specific example of the polymer used in the method (1) aboveTheRear critronitriLeCan be mentioned. Also, the above polymerーModified products, derivatives, random copolymers, alternating copolymers, graft copolymers, block copolymers and the like can also be used.
[0018]
  In the above method (2), as a suitable polymer formed by polymerization of monomersIncludes a polyethylene oxide resin having an acrylic group at the terminal. HeavyPolymers produced by addition polymerization that can be easily controlled and do not generate by-products during polymerization are preferred. In particular, a polymer produced by addition polymerization of a reactive unsaturated group-containing monomer is excellent in productivity.
[0019]
  And as a reactive unsaturated group containing monomer used in the method of said (2),Is a polyethylene oxide resin having an acrylic group at the end.Can be mentioned.
[0020]
Examples of the method for polymerizing the monomer include methods using heat, ultraviolet rays, electron beams, and the like. From the viewpoint of productivity, a method using ultraviolet rays is preferred. In this case, in order to effectively advance the reaction, a polymerization initiator that reacts with ultraviolet rays can be blended in the electrolytic solution. Examples of the ultraviolet polymerization initiator include benzoin, benzyl, acetophenone, benzophenone, Michler ketone, biacetyl, benzoyl peroxide and the like. These initiators can be used alone or in combination.
[0021]
In the case of thermal polymerization, the structure of the gel can be controlled and the ionic conductivity can be improved by changing the type and amount of the thermal polymerization initiator, the type and amount of the monomer, the number of reactive groups in the monomer, and the like. Furthermore, since the entire reaction proceeds uniformly, a uniform gel is formed. In thermal polymerization, a polymerization initiator can be used for reaction control. As thermal polymerization initiators, 1,1-di (tertiarybutylperoxy) -3,3,5-trimethylcyclohexane, 2,2-bis- [4,4-di (tertiarybutylperoxycyclohexyl) propane ], 1,1-di (tertiary butyl peroxy) -cyclohexane, tertiary butyl peroxy-3,5,5-trimethyl hexanonate, tertiary butyl peroxy-2-ethyl hexanonate, dibenzoyl per Examples include oxides. These initiators can be used alone or in combination.
[0022]
The ratio of the polymer in the gel electrolyte is usually 0.1 to 80% by weight, preferably 1 to 50% by weight. When the ratio of the polymer is too low, it is difficult to hold the electrolytic solution and leakage occurs, and when it is too high, the ionic conductivity is lowered and the battery characteristics are lowered. Although the ratio of the polymer with respect to a solvent is suitably selected according to molecular weight, it is 0.1-50 weight% normally, Preferably it is 1-30 weight%. When the ratio of the polymer is too small, the gel shape becomes difficult, and the retention of the electrolytic solution tends to be lowered, thereby causing a problem of flow and liquid leakage. When the proportion of the polymer is too large, the viscosity becomes too high and handling becomes difficult, and the ion conductivity is lowered due to the decrease in the concentration of the electrolytic solution, and the battery characteristics such as the rate characteristics tend to be lowered.
[0023]
The gel electrolyte layer can further contain a skeleton polymer that exists in a solid state in the electrolytic solution. The skeleton polymer functions as an electrolyte skeleton in contrast to the above-described polymer for gel formation (hereinafter, sometimes referred to as “gel polymer”). Presence in the solid state means that it is insoluble or only swells in the electrolyte used. The backbone polymer is 0.05 (cal / cc) than the solubility parameter of the solvent in the electrolyte used.^0.5Or more, preferably 0.1 (cal / cc)^0.5Or more, more preferably 0.2 (cal / cc)^0.5Or more, most preferably 0.5 (cal / cc)^0.5It is preferable to use polymers having different solubility parameters.
[0024]
Although the kind of said skeleton polymer changes with electrolyte solutions used, the following polymers are mentioned with respect to the highly polar solvent generally used for a lithium ion battery. That is, an alkane polymer such as polyethylene, polypropylene and poly-1,1-dimethylethylene, an unsaturated polymer such as polybutadiene and polyisoprene, a ring such as polystyrene, polymethylstyrene, polyvinylpyridine, and poly-N-vinylpyrrolidone. Polymers having poly (methyl methacrylate), poly (ethyl methacrylate), poly (butyl methacrylate), poly (methyl acrylate), poly (ethyl acrylate), poly (acrylic acid), poly (methacrylic acid), polyacrylamide and other acrylic derivative polymers, polyvinyl fluoride, poly (fluoride) Fluorine resins such as vinylidene chloride and polytetrafluoroethylene, CN group-containing polymers such as polyacrylonitrile and polyvinylidene cyanide, polyvinyl alcohol polymers such as polyvinyl acetate and polyvinyl alcohol Chromatography, polyvinyl chloride, halogen-containing polymers such as polyvinylidene chloride, silicone-based polymers such as polydimethylsiloxane can be used. Moreover, said polymer mixture, a modified body, a derivative | guide_body, a random copolymer, an alternating copolymer, a graft copolymer, a block copolymer, etc. may be sufficient. The molecular weight of these polymers is usually 10,000 to 3,000,000, preferably 100,000 to 1,000,000. If the molecular weight is too low, the strength may decrease, and if it is too high, the viscosity may increase and formation may be difficult. It is preferable to increase the molecular weight from the viewpoint of securing mechanical strength.
[0025]
In particular, when the electrolytic solution used contains ethylene carbonate or propylene carbonate, it is preferable to use a polymer comprising repeating units of the following formula C and / or formula D as the skeleton polymer. The reason is as follows.
That is, since the gelled polymer and the electrolyte solution may be in a heated state, the electrolyte solution used is an electrolyte solution containing ethylene carbonate or propylene carbonate having a high boiling point for safety in production. And effective in terms of management. And with respect to the electrolyte solution which has polarity and a comparatively high solubility parameter, the skeleton polymer of the following composition can suppress the solubility low, and its effect is high from a viewpoint of skeleton maintenance.
[0026]
[Chemical 1]
C:-(CH₂-CR^FiveR⁶) −
D:-(CH₂-CR^Five= CH₂-CH₂) −
(However, R^FiveIs —H, —F, —Cl or —CH_ThreeGroup, R⁶Are -H, -F, -Cl, -C₆H_FiveRepresents a group. )
[0027]
In the present invention, a solid electrolyte can be used in addition to the liquid or gel electrolyte. The solid electrolyte can be obtained, for example, by mixing a supporting electrolyte used for a gel electrolyte and a polymer.
Next, the intermediate layer will be described. The intermediate layer contains at least a non-electrically conductive powder and a non-electrically conductive binder.
[0028]
  As the non-electrically conductive powder used for the intermediate layer, any powder can be used as long as it is stably present in the battery and is non-electrically conductive. For example, various inorganic powdersBodyCan be used. As inorganic powderThe acidSilicon fluoride, aluminum oxide, titanium oxideEtc.The oxide powder is used. These may be element-substituted, surface-treated, or solid solution as necessary.Yes. MaThe surface of conductive metal such as carbon black, graphite, SnO2, ITO, metal powder, and fine powder of conductive compounds and oxides is surface treated with a non-electrically conductive material to provide electrical insulation. It is also possible to use it. These non-electrically conductive powders may be used in combination. The particle size of these powders is preferably 0.001 to 50 μm. When fine particles of 0.1 μm or less are used, it is preferable that the structure is developed as a secondary structure and the secondary particle diameter is a certain size. Particularly preferably, when the thickness is in the range of 0.1 to 10 μm, the dispersion, the ease of coating, and the control of voids are excellent. The specific surface area of the powder is preferably 0.01 to 300 m @ 2 / g. If it is too low, the stability of the prepared paint will be reduced. If it is too high, the viscosity of the coating will increase, making it difficult to disperse and apply. The shape of the powder is not particularly limited, such as a spherical shape, a needle shape, a rod shape, a conical shape, and a plate shape. Porous powder can also be used.
[0029]
  The non-electrically conductive binder used for the intermediate layer is a material that holds the powder, is non-electrically conductive, and exists stably in the battery.Polyvinylidene fluoride is used. ProtectionExamples of the holding form include those that are chemically bonded, those that are physically bonded, and those that are held by the network structure of the binder.
[0030]
  The intermediate layer preferably has some or all of the functions of the electrolyte layerThe
[0031]
DepartureIn a particularly preferred embodiment in that the light effect is remarkable, the electrolyte layer also serves as an intermediate layer (that is, is the same), and the intermediate layer (= electrolyte layer) contains a gel electrolyte containing a non-aqueous electrolyte.Mu
[0032]
In addition to the gel electrolyte, the intermediate layer can contain a skeleton polymer that exists in a solid state in the electrolytic solution, and is preferable. In this case, the intermediate layer is preferably composed of a skeleton layer containing powder and a skeleton polymer, and an ion mobile phase composed of a gel electrolyte formed in the skeleton layer. In a more preferred embodiment in that the effect of the invention is remarkable, the electrolyte layer also serves as an intermediate layer (that is, is the same), and the intermediate layer includes a skeleton polymer and a gel electrolyte. The binder used for the intermediate layer can be used as the backbone polymer.
When the intermediate layer has a function of part or all of the electrolyte layer, the same electrolyte as that used for the electrolyte layer can be used as the electrolyte of the intermediate layer.
[0033]
  The ratio of the non-electrically conductive powder and the non-electrically conductive binder is preferably 0.01 to 100% by weight, particularly 0.1 to 100% by weight. In particular, when a skeleton polymer is used as the binder, the ratio of the binder to the powder is usually 0.01 to 100% by weight, preferably 0.1 to 30% by weight. This is preferably prepared according to the specific surface area of the powder. When the intermediate layer is composed of a skeleton layer containing a non-electrically conductive powder and a non-electrically conductive binder, and an ion mobile phase formed in the voids of the skeleton layer, the porosity of the intermediate layer, that is, , Volume fraction of ion mobile phase in the intermediate layerIs 30 to 95%. Lowering the porosity improves the mechanical strength, and increasing the porosity improves the ionic conductivity. What is necessary is just to select a preferable value for a porosity according to the objective. The porosity can be controlled by the ratio between the powder and the binder, the calendar process, and the like.
[0034]
  The thickness of the electrolyte layer including the intermediate layerIs 1~ 200 μm. When the thickness is reduced, the capacity of the entire battery is lowered and the insulation between the positive electrode and the negative electrode tends to be lowered. If it is thick, the internal resistance increases, the capacity decreases, and the rate characteristics tend to deteriorate. Next, the electrode will be described. The positive electrode or the negative electrode is preferably composed of an active material layer capable of occluding and releasing lithium ions and an ion mobile phase formed in the active material layer.
[0035]
As the positive electrode active material used in the positive electrode of the present invention, various organic and inorganic compounds can be used. Examples of the inorganic compound include transition metal oxides, composite oxides of lithium and transition metals, transition metal sulfides, and the like. Here, Fe, Co, Ni, Mn, or the like is used as the transition metal. Specifically, MnO, V₂O_Five, V₆O₁₃TiO₂Transition metal oxide powders such as lithium nickel oxide, lithium cobaltate, lithium manganate and other complex oxide powders of TiS, TiS₂, FeS, MoS₂And transition metal sulfide powders. These compounds may be partially element-substituted in order to improve the characteristics. Examples of the organic compound include polyaniline, polypyrrole, polyacene, disulfide compounds, polysulfide compounds, N-fluoropyridinium salts, and the like. A mixture of these inorganic compounds and organic compounds may be used as the positive electrode active material. The particle size of the active material of these positive electrodes may be appropriately selected depending on the other constituent elements of the battery, but it is usually 1-30 μm, particularly 1-10 μm. This is preferable because the characteristics are improved.
[0036]
Examples of the negative electrode active material used for the negative electrode include carbon-based active materials such as graphite and coke. These carbon-based active materials can be used even in the form of a metal, a salt thereof, a mixture with an oxide, or a coating. Also oxides or sulfates of silicon, tin, zinc, manganese, iron, nickel, etc. Furthermore, lithium metal such as lithium metal, Li—Al, Li—Bi—Cd, Li—Sn—Cd, lithium transition metal nitride, silicon, or the like can be used. The particle size of the negative electrode active material may be selected as appropriate in consideration of the other constituent elements of the battery. Usually, the initial efficiency, rate characteristics, cycle characteristics are set to 1 to 50 μm, particularly 15 to 30 μm. It is preferable because battery characteristics such as are improved.
[0037]
  The active material layer further contains a binder in order to increase the strength of the electrode, further improve the adhesion to the current collector, and fix the active material in the active material layer.TheThe types of binders used arePolyvinylidene fluoride is used.
[0038]
The electrode may contain additives, powders, fillers, and the like that exhibit various functions such as a conductive material and a reinforcing material, as necessary. The conductive material is not particularly limited as long as it is capable of imparting conductivity by mixing an appropriate amount of the above active material. Usually, carbon powder such as acetylene black, carbon black, graphite, and various metal fibers and foils are used. Etc. Additives such as trifluoropropylene carbonate, vinylidene carbonate, catechol carbonate, 1,6-Dioxaspiro [4,4] nonane-2,7-dione, 12-crown-4-ether improve the stability and life of the battery. Can be used for. As the reinforcing material, various inorganic, organic spherical, plate-like, rod-like or fibrous fillers can be used.
[0039]
  The thickness of the active material layer is positive electrode, negative electrode andAlso 1It is in the range of ˜300 μm. If it is thicker than 300 μm, ionic conduction tends to decrease and the rate characteristics tend to deteriorate. When the thickness is less than 1 μm, the ratio of the electrode layer, the current collector and the like in the battery increases, and the capacity of the battery as a whole tends to decrease. In the present invention, a uniform electrolyte layer having a large area can be formed, and the sizes of the positive electrode and the negative electrode can be arbitrarily set. In the present invention, in particular, the area of the positive electrode and / or the negative electrode can be 50 cm @ 2 or more. The size ratio between the positive electrode and the negative electrode is preferably substantially the same. In particular, it is preferable to set the negative electrode slightly larger than the positive electrode because the insulation is enhanced and the generation of dendrites is suppressed. As the ion mobile phase formed in the active material layer, various electrolytes used in the electrolyte layer are used.
[0040]
The active material layer is usually provided on the current collector. In general, a metal foil such as an aluminum foil or a copper foil can be used as the current collector. The thickness is preferably 1 to 30 μm. If it is too thin, the mechanical strength becomes weak, which may cause problems in production. If it is too thick, the capacity of the entire battery may be reduced. It is preferable to roughen the surfaces of these current collectors in advance because 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 wire brush provided with abrasive cloth paper, a grindstone, an emery buff, a steel wire or the like to which abrasive particles are fixed. In addition, another layer may be formed on the current collector surface in order to increase the adhesive strength and conductivity.
[0041]
In a preferred embodiment, the positive electrode and / or the negative electrode is composed of an active material layer containing a powdery active material and a binder, and an ion mobile phase comprising a gel electrolyte formed in the active material layer. The intermediate layer is composed of a skeleton layer containing a non-electrically conductive powder and a non-electrically conductive binder, and an ion mobile phase comprising a gel electrolyte formed in the skeleton layer; and The ion mobile phase in the electrode and the ion mobile phase in the intermediate layer are continuous. With such a configuration, the positive electrode and / or the negative electrode and the intermediate layer can be provided integrally. As a result, the interface resistance can be lowered and the capacity and rate characteristics can be improved. In addition, as will be described later, a battery having such a structure can be easily manufactured by forming an active material layer and a skeleton layer and then simultaneously impregnating each layer with a material that is a material of an ion mobile phase.
[0042]
Also in this embodiment, it is preferable that the electrolyte layer also serves as an intermediate layer (that is, the same). That is, the positive electrode and / or the negative electrode includes a powdery active material and an active material layer containing a binder for fixing the active material, and an ion mobile phase composed of a gel electrolyte formed in the active material layer. The electrolyte layer is composed of a skeleton layer containing a non-electrically conductive powder and a non-electrically conductive binder, and an ion mobile phase composed of a gel electrolyte formed in the skeleton layer. It is preferable that the ion mobile phase formed in the positive electrode and / or the negative electrode and the ion mobile phase formed in the electrolyte layer are continuous.
[0043]
Note that “continuous” can be determined simply because both cannot be peeled off without breaking the gel electrolyte.
Further, it is preferable that the ion mobile phase in the positive electrode and the ion mobile phase in the intermediate layer or the electrolyte layer and the ion mobile phase in the negative electrode are all continuous because the effect of the present invention is great.
[0044]
In the lithium secondary battery of the present invention, the positive electrode, the negative electrode, and the electrolyte layer are preferably laminated in a flat plate and accommodated in a case. When laminated in a flat plate, the effect of the present invention is remarkable. As a case to be used, those having shape changeability are preferable, and the effect of the present invention is also remarkable. The case having shape change means a case having flexibility, flexibility, flexibility, and the like, and examples of the material include plastic, polymer film, metal film, rubber, thin metal plate and the like. Specific examples of the case include a bag made of a polymer film such as a plastic bag, a vacuum packaging bag or vacuum pack made of a polymer film, a vacuum packaging bag or vacuum made of a laminate material of a metal foil and a polymer film. Examples include a pack, a can made of plastic, and a case where the periphery is fixed by welding, bonding, fitting, etc. sandwiched between plastic plates. Among these, a vacuum packaging bag or vacuum pack made of a polymer film or a vacuum packaging bag or vacuum pack made of a laminate material of a metal foil and a polymer film is preferable in terms of airtightness and shape changeability. These cases do not have the same weight and rigidity as metal cans, and have flexibility, flexibility, flexibility, etc., so that there is the freedom of shape that can be bent after storage of the battery and the weight can be reduced. have. Of course, for the convenience of battery installation, etc., it is possible to enclose the battery in a shape-variable case, shape it into a preferred shape, and then store multiple cases in a rigid outer case if necessary. is there.
[0045]
Next, the manufacturing method of the battery of this invention is demonstrated.
In the method of the present invention, an intermediate layer containing a non-electrically conductive powder and a non-electrically conductive binder is formed between the positive electrode and the negative electrode. As a method of forming the intermediate layer, a method of applying and drying a paint containing a non-conductive powder, a non-electric conductive binder, and a solvent is preferable. If the intermediate layer is formed through such an intermediate layer forming step, a battery having excellent mechanical strength can be easily manufactured without taking the troublesome work of installing a separator.
[0046]
The “intermediate layer forming step” does not necessarily require that the intermediate layer be completely formed in this step, but is a name used for convenience.
As described above, the intermediate layer preferably contains a skeleton polymer in addition to the gel electrolyte. In this case, the intermediate layer is preferably formed by applying and drying a paint containing a non-electrically conductive powder, a non-electrically conductive skeleton polymer, and a solvent, and then impregnating the ion mobile phase raw material. Let By including such an impregnation step, an intermediate layer having the above-mentioned preferred structure can be formed.
The raw material of the ion mobile phase may be the same as the composition of the ion mobile phase, or may be the ion mobile phase by performing a predetermined treatment after the impregnation step. Since an ion mobile phase made of a gel electrolyte generally has a high viscosity, it is preferable to employ the following method.
[0047]
(1) A method of forming a gel electrolyte by using an ion mobile phase raw material containing an electrolytic solution and a gelled polymer, performing impregnation in a heated state, and cooling the impregnation step. In this method, the ion mobile phase material has a low viscosity like a solution in a heated state, and is in a gel state at room temperature.
(2) A method of forming a gel electrolyte by containing an electrolytic solution and a monomer as an ion mobile phase raw material, and polymerizing the monomer after the impregnation step. In this method, the monomer is selected so that the ion mobile phase raw material is gelled by polymerization.
[0048]
In a more preferred method, (1) an active material layer forming step of forming an active material layer containing a positive electrode active material or a negative electrode active material and a binder on a current collector; and (2) directly on the active material layer. An intermediate layer forming step of forming a layer containing a non-electrically conductive powder and a non-electrically conductive binder preferably or indirectly, and (3) an active material layer forming step and an intermediate After the layer formation step, an impregnation step of impregnating the ion mobile phase raw material is included. In this method, since the ion mobile phase is impregnated after the active material layer, the skeleton layer, and the like are formed, each ion mobile phase is continuous, and the positive electrode and / or the negative electrode and the intermediate layer are integrated. It becomes possible to provide. In such a method, the skeleton layer is preferably formed by the step (2), but it is not always necessary, and it may be a gel precursor, for example.
[0049]
In particular, from the viewpoint of ease of production, it is preferable to form the layers in the steps (1) and (2) by applying and drying a paint containing the respective raw materials. The coating in the active material forming step (1) and the coating in the intermediate layer forming step (2) can be performed sequentially or simultaneously. It is also possible to dry after applying sequentially or simultaneously. In the case of this method, the number of coating or drying steps can be reduced. Prior to coating, it can be formed into a dispersion paint by a ball mill, a sand mill, a twin-screw kneader or the like. As the solvent to be used, various inorganic solvents and organic solvents that are generally used such as N-methylpyrrolidone can be used as long as they dissolve the binder to be used.
[0050]
In addition, as a method for forming the skeleton layer or the like or the active material layer, a method in which the mixture having each composition is softened by heating or being sprayed can be employed.
In the coating / drying method and the pressure bonding or spraying method, the weight ratio of the skeleton polymer to the powder in the intermediate layer may be appropriately selected depending on the specific surface area of the powder, but is usually 0.01 to 100%, preferably 0.1 to 30%. If the amount of the skeleton polymer is too large, the amount of voids in the intermediate layer may be reduced, and impregnation with the ion mobile phase raw material may be difficult.
[0051]
Furthermore, after the active material layer is formed, an intermediate layer forming step can be performed after a calendar process is applied. In this case, since the filling rate (volume ratio of the ion mobile phase) of the active material layer can be controlled by the calendering conditions, the degree of freedom of the amount of components in the active material layer is increased. In addition, since the flatness of the active material layer is increased, workability in the case of stacking the batteries in a flat plate is improved.
[0052]
As a method for impregnating the ion mobile phase material, it is usually sufficient to leave it for a predetermined time after application, but operations such as press-fitting and vacuum impregnation may be performed in order to increase the efficiency and speed of impregnation. It is preferable that the ion mobile phase completely fills the voids in the layer, but even if a certain amount of voids remain, there is no significant hindrance to battery characteristics. When troubles occur, the above-described impregnation methods such as press-fitting and vacuum impregnation can be employed.
[0053]
【Example】
Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples. However, the present invention is not limited to the examples shown below as long as the gist thereof is not exceeded. The raw materials used in both Examples and Comparative Examples were vacuum-dried at 240 ° C. for 24 hours before use. The binder and supporting electrolyte were dried at 110 ° C. for 4 hours. The monomer was used after dehydration treatment with molecular sieve. The electrolyte used was previously dehydrated for lithium batteries.
[0054]
First, a positive electrode paint and a negative electrode paint were prepared according to the following composition.
The following were used as raw materials for the positive electrode paint and the negative electrode paint.
Cathode active material LiCoO₂Powder (Nippon Chemical Co., Ltd.)
Conductive material Acetylene Black (manufactured by Denki Kagaku Kogyo)
Negative electrode active material SFG15: Graphite (manufactured by TIMCAL)
Binder Polyvinylidene fluoride (Kureha Chemical)
Solvent N-methylpyrrolidone (Mitsubishi Chemical)
(Positive electrode coating composition)
LiCoO₂                    90.0 parts
Acetylene black 5.0 parts
Polyvinylidene fluoride 5.0 parts
N-methylpyrrolidone 100.0 parts
(Negative electrode coating composition)
SFG15 90.0 parts
Polyvinylidene fluoride 10.0 parts
N-methylpyrrolidone 150.0 parts
[0055]
The above materials were each kneaded and dispersed in a sand mill for 1 hour to form a paint. The positive electrode coating material was applied onto an aluminum foil having a thickness of 20 μm using a doctor blade and dried at 120 ° C. to obtain a layer having a positive electrode active material having voids. The negative electrode paint was formed in the same manner on a 20 μm thick copper foil. The amount of voids in each layer after the calendar process was about 30% by volume for the positive electrode and about 40% by volume for the negative electrode, as measured by thickness and weight. All the steps up to here were performed in a normal environment.
[0056]
Next, the following coating materials A to C were prepared for the intermediate layer.
Paint A composition
Silica (Japan Aerosil Manufacturing OX-50) 100 parts
50 parts of polyvinylidene fluoride
850 parts of N-methylpyrrolidone
Paint B composition
100 parts of titanium oxide (FTL-300 manufactured by Ishihara Sangyo)
Polyvinylidene fluoride 3 parts
240 parts of N-methylpyrrolidone
Paint C composition
100 parts of aluminum oxide (AA-10, manufactured by Sumitomo Chemical)
Polyvinylidene fluoride 2 parts
100 parts of N-methylpyrrolidone
Each paint was dispersed in a sand mill for 10 minutes.
[0057]
referenceExample 1
The coating material A was apply | coated using the doctor blade on the positive electrode active material layer provided on the electrical power collector, and it dried at 120 degreeC, and formed the frame | skeleton layer which has a space | gap. All processes up to this point were performed in a normal environment. Thereafter, the coating film was re-dried at 120 ° C. in a dry room and punched into a predetermined shape. The size of the electrode was set as small as 4 square centimeters in consideration of difficulty in laminating the porous film. An electrolyte solution having the following composition was applied and impregnated on the sheet thus obtained and the negative electrode active material layer, respectively.
[0058]
By impregnating the electrolyte solution in the voids of the skeleton layer, it acts as an electrolyte layer having ion conductivity. A positive electrode and a negative electrode were laminated with the electrolyte layer on the inside, terminals were attached, and sealed in a vacuum pack to make a lithium secondary battery for evaluation.
[0059]
  Example1
  referenceIn Example 1, paint A was changed to paint B. The thickness of the skeleton layer after drying at 120 ° C. was about 40 microns, and the porosity was 75 to 85% by volume. All the steps up to here were performed in a normal environment. Thereafter, the coating film was re-dried at 120 ° C. in a dry room and punched into a predetermined shape. Further, the composition of the liquid to be impregnated was changed as follows.
(Impregnating liquid composition)
PC 40.8 parts EC 40.8 parts LiClO4 10.4 parts Polyacrylonitrile 8.0 parts (however, polyacrylonitrile: molecular weight 150,000, manufactured by Aldrich).
[0060]
  The above impregnation solution was dissolved at 110 ° C. to obtain a uniform solution. This solution was heated to 110 ° C. and applied to a positive electrode active material layer, a skeleton layer, and a negative electrode active material layer having voids with a doctor blade and impregnated. Thereafter, it was cooled at 0 ° C., and the impregnated impregnating solution was gelled to form a gel electrolyte in the voids in the active material layer and the skeleton layer, thereby obtaining a positive electrode having a negative electrode and an electrolyte layer thereon. . Other than thatreferenceA battery was formed with Example 1.
[0061]
  Example2
  referenceIn Example 1, the composition of the liquid to be impregnated was changed as follows.
(Impregnating liquid composition)
  PC 40.8 parts
  EC 40.8 parts
  LiClO_Four           10.4 parts
  8.0 parts of polyacrylonitrile
(However, polyacrylonitrile: molecular weight 150,000, manufactured by Aldrich).
[0062]
  The above impregnation solution was dissolved at 110 ° C. to obtain a uniform solution. With this solution heated to 110 ° C., the positive electrode active material layer, the skeleton layer, and the negative electrode active material layer were applied and impregnated with a doctor blade. Thereafter, it was cooled at 0 ° C., and the impregnated impregnating solution was gelled to form a gel electrolyte in the voids in the active material layer and the skeleton layer, thereby obtaining a positive electrode having a negative electrode and an electrolyte layer thereon. . Other than thatreferenceExample 1 andIn the same wayA battery was formed.
[0063]
  Example3
referenceIn Example 1, the composition of the liquid to be impregnated was changed as follows.
(Impregnating liquid composition)
  40 PCs
  EC 40 parts
  LiClO_Four               10 copies
  Photomer 4050 6 parts
  Photomer 4158 3 parts
  Trignox21 1 part
  (However, Photomer 4050, Photomer 4158: Polyethylene oxide resin having an acrylic group at the end (manufactured by Henkel), Trignox 21: Thermal crosslinking initiator (manufactured by Ciba Geigy).
[0064]
  The above impregnating solution was applied to the positive electrode active material layer, the skeleton layer, and the negative electrode active material layer with a doctor blade and impregnated. The solution had a low viscosity and the impregnation was completed rapidly. Thereafter, the impregnated electrolytic solution was gelled by curing at 90 ° C. for 30 minutes to obtain a negative electrode having an ion mobile phase made of a gel electrolyte and a positive electrode having an electrolyte layer thereon. Other than thatreferenceA battery was formed as in Example 1.
[0065]
  Example4
  referenceIn Example 1, paint A was changed to paint C. The thickness of the skeleton layer after drying at 120 ° C. was about 70 microns, and the porosity was about 80% by volume. All the steps up to here were performed in a normal environment. Thereafter, the coating film was re-dried at 120 ° C. in a dry room and punched into a predetermined shape. Also, the coating material C was applied on the negative electrode active material layer and dried at 120 ° C. to form a skeleton layer on the negative electrode. The thickness of this skeleton layer was about 10 microns, and the average porosity was 60% by volume. The composition of the impregnation liquid into the positive electrode active material layer having a skeleton layer, the gelation method, and the composition / gelation method of the impregnation liquid into the negative electrode active material layer having a skeleton layer are:referenceExample1It is the same. Other than thatreferenceA battery was formed as in Example 1.
[0066]
  Example5
  referenceIn Example 1, paint A was changed to paint B. The thickness of the skeleton layer after drying at 120 ° C. was about 40 microns, and the porosity was 75 to 85% by volume. Also, the coating material C was applied on the negative electrode active material layer and dried at 120 ° C. to form a skeleton layer on the negative electrode. The thickness of this skeleton layer was about 10 microns, and the average porosity was 60% by volume. All the steps up to here were performed in a normal environment. Thereafter, the coating film was re-dried at 120 ° C. in a dry room and punched into a predetermined shape.referenceExample1The same impregnating solution as used in the above was applied to each sheet on the positive electrode side and the negative electrode side while being heated to 110 ° C., and impregnated into the voids in the active material layer and the skeleton layer. When the impregnating solution is in a solution state, the positive electrode side and the negative electrode side are laminated, and then cooled at 0 ° C. to gel the impregnated electrolytic solution, into the voids in the active material layer and the skeleton layer, A gel electrolyte integrated with the positive electrode, the electrolyte layer, and the negative electrode was formed. Other than thatreferenceA battery was formed as in Example 1.
[0067]
  Comparative Example 1
  referenceIn Example 1, the formation of the intermediate layer was omitted, and two separators having a thickness of 25 microns were provided in the electrolyte layer. That is, after impregnating the positive electrode, the negative electrode, and the separator with the electrolytic solution, the separator was spread, positioned, and laminated on the flat plate. Other than thatreferenceA battery was prepared in the same manner as in Example 1.
[0068]
  Comparative Example 2
  referenceIn Example 1, the formation of the intermediate layer was omitted, and a non-woven fabric having a thickness of 60 microns was provided in the electrolyte layer. That is, after impregnating the electrolytic solution into the positive electrode, the negative electrode, and the nonwoven fabric, the nonwoven fabric was positioned and laminated on the flat plate. Other than thatreferenceA battery was prepared in the same manner as in Example 1.
[0069]
  Comparative Example 3
  Example1In Example 1, the positive electrode active material layer and the negative electrode active material layer in which the formation of the skeleton layer was omitted1The same impregnating solution as used in the above was applied in a heated state at 110 ° C., impregnated, and then cooled at 0 ° C. to form a gel electrolyte in the electrode. Then on the positive and negative electrodes, the examples3An electrolyte layer having a thickness of 60 microns was formed by applying a solution obtained by replacing the cross-linking initiator of the electrolyte stock solution used in the above with Darocur 1173 (UV cross-linking initiator, manufactured by Ciba Geigy) and irradiating with UV light. Thereafter, the positive electrode and the negative electrode were laminated with the electrolyte layer side inside. Other than thatreferenceA battery was prepared in the same manner as in Example 1.
[0070]
  Comparative Example 4
  Example1In Example 1, the positive electrode active material layer and the negative electrode active material layer in which the formation of the skeleton layer was omitted1The same impregnating solution as used in 1 was applied while being heated to 110 ° C. and impregnated. Furthermore, a void in the nonwoven fabric was filled with the impregnating liquid by immersing a nonwoven fabric having a thickness of 60 microns in the liquid. Then, the positive electrode, the nonwoven fabric, and the negative electrode were laminated with the impregnating solution in a solution state. Thereafter, it was cooled at 0 ° C., and the impregnated electrolyte was gelled to obtain a battery in which the positive electrode, the electrolyte layer, and the gel electrolyte in the negative electrode were integrated. Other than thatreferenceA battery was prepared in the same manner as in Example 1.
[0071]
Reference example
In order to evaluate the intermediate layer alone, each of the paints A to C was applied onto an aluminum foil having a thickness of 20 μm using a doctor blade, and dried at 120 ° C. to form a layer having voids on the aluminum foil. . While measuring the weight and thickness of the coating film excluding the substrate, LiClO_FourIs impregnated in an air gap in a solution of propylene carbonate: ethylene carbonate = (1: 1) at a concentration of 1 mol / L, and an aluminum foil of the same shape is used as a counter electrode to measure the impedance in the coating film. The ionic conductivity of was measured. For comparison, the ionic conductivity was also measured when a commercially available separator and nonwoven fabric were used.
[0072]
Table 1 shows the results of the reference examples. The thickness was measured with a micrometer. The porosity was calculated from the measurement of thickness and weight using the true specific gravity of the material. Catalog values were adopted for porous films. The sheet resistance was measured as a sheet resistance by a resistance meter having four probe electrodes. The porous film was measured on an aluminum foil. The ionic conductivity was calculated from the conductivity at a frequency of 100 KHz by measuring the AC conductivity using an impedance analyzer.
[0073]
  Table-2 and Table-3 show examples.Reference examplesAnd the result of a comparative example is shown. The electrolyte layer structure is the part separating the positive electrode and the negative electrode.Reference examplesIn the intermediate layer, the comparative example is a porous film. The capacity of the battery is 0.046 / cm2 current density (corresponding to a rate of about C / 24) and charged at a constant current condition up to 4.05V, then a voltage of 4.05V is constant voltage up to 0.0046 / cm2 The capacity that can be taken out when the battery charged by charging was discharged at a current density of 0.046 cm @ 2 at a constant current condition up to 2.7 V was calculated as the capacity per unit volume of the positive electrode excluding the current collector. The cycle characteristics are as follows. A battery charged by charging at a constant current condition of up to 0.005 V / cm2 at a current density of 0.55/cm@2 and then charged at a voltage of 4.05 V to a current density of 0.0011/cm@2 The cycle of discharging at a constant current condition up to 2.7 V at a current density of .55 / cm @ 2 was repeated, and the capacity retention rate after 20 cycles was indicated in%. Table 3 also shows the number of gelation steps and the number of gel electrolyte interfaces. The number of steps in which gelation is performed indicates the total number of times that the steps required for forming the gel electrolyte are performed for the positive electrode, the negative electrode, and the electrolyte layer. The number of interfaces of the gel electrolyte indicates the total number of interfaces formed by bonding gel electrolytes such as a bonded surface.
[0074]
  As shown in Table 1, the intermediate layer formed of the non-electrically conductive powder and the non-electrically conductive binder has voids equivalent to the porous film. There is no problem with the electrical insulation, and the ionic conductivity is equal to or higher than that of the porous film. For this reason, it is thought that it functions without a problem as a layer which separates a positive electrode and a negative electrode. In fact, as shown in Table 2, in a battery using an electrolytic solution, a battery having a high capacity and no problem in cycle characteristics can be obtained as compared with the case where a porous film is used. The reason why the capacity of the comparative example is low is presumed to be that the resistance between the electrode and the porous film easily floats due to the electrolytic solution and the resistance increases in the case of a flat plate laminated battery that is not pressed by a metal can. ExampleReference examplesThen, since the structure is integrated with the electrode, such a problem hardly occurs. Further, in Comparative Examples 1 and 2, in consideration of workability, an electrode with an extremely small size of 4 square centimeters was used. It took a lot of time and great care to impregnate the porous film with electrolyte, laminate the electrode with the porous film, and position it.referenceIn Example 1, the assembly was completed simply by impregnation and lamination of the positive electrode and the negative electrode.
[0075]
  Also in the battery using the gel electrolyte shown in Table 3,1-5This battery has no problem in battery characteristics as compared with Comparative Examples 3 and 4, and is rather excellent in characteristics in many cases. Example1-4As shown in Comparative Example 3, the number of gelation steps is small in the process, and the equipment can be simplified. In addition, the reduction of moisture by reducing the process, the reduction of capital investment, and the improvement of productivity are realized. it can. The gel electrolyte stock solution only needs to be applied twice on the positive electrode side and the negative electrode side, and it is not necessary to reapply for the electrolyte or impregnate the porous film separately. Further, since there are few interfaces, no extra resistance is generated, and the cycle characteristics are excellent as compared with Comparative Example 3 having a large number of interfaces. An embodiment in which a gel electrolyte is integrated5In comparison with Comparative Example 4, Example5There is no problem in terms of battery characteristics and the capacity is exceeded. The number of steps of gelation is the same on the process, but the example5In contrast, the gel electrolyte stock solution only needs to be applied twice on the positive electrode side and the negative electrode side, whereas in Comparative Example 4, it is necessary to impregnate the nonwoven fabric separately, transport it, and laminate it, which takes extra time. . In Comparative Example 4, the positioning of the nonwoven fabric was necessary.5Then, only a positive electrode and a negative electrode are laminated, and the process becomes simple.
[0076]
【The invention's effect】
According to the present invention, since the layer containing the non-electrically conductive powder and the non-electrically conductive binder is formed between the positive electrode and the negative electrode, at least a part of the electrolyte layer is a non-electrically conductive powder. And will be reinforced by a non-electrically conductive binder. The structure formed by the powder and the binder is excellent in mechanical strength, as can be seen from the fact that the powder is used as a reinforcing agent for the polymer film. Therefore, the overall mechanical strength of the electrolyte layer is increased. In particular, since powders have various materials, shapes, and particle sizes, various properties such as mechanical strength and pore structure can be controlled by selecting the type.
[0077]
Further, when the intermediate layer is integrally formed on at least one of the positive electrode and the negative electrode, this layer can act as an electrolyte layer having electrical insulation and ion conductivity separating the positive electrode and the negative electrode. That is, at least a part of the electrolyte layer is integrally formed on the positive electrode or the negative electrode. For this reason, it is not necessary to prepare a separate separator or an assembly facility therefor. A battery can be assembled by simply stacking a positive electrode and a negative electrode, at least one of which has an intermediate layer thereon, and the device is simplified. It also eliminates the need for positioning a thin and cumbersome separator. This is very advantageous because the process is facilitated when the battery is stacked on a large area flat plate or when the thickness of the electrolyte layer is reduced to increase the capacity.
[0078]
In particular, in the case of a lithium secondary battery using a gel electrolyte, the effect of reinforcing the gel strength is great, and the risk of short-circuiting can be reduced. In the method of forming an electrolyte layer by applying the electrolyte layer as a gel electrolyte stock solution on the electrode and gelling as seen in US Pat. Nos. 5,453,335 and 5,609,974, non-electric conduction By dispersing the conductive powder in the stock solution, the formed electrolyte layer is reinforced with the powder component, and the mechanical strength is remarkably increased. Further, by dispersing the powder in the stock solution, the viscosity of the stock solution is increased moderately, and the flow on the electrode is suppressed to facilitate the formation of the electrolyte layer. This is extremely effective because it is a viscosity control method that does not involve the phenomenon of pulling the yarn, unlike the thickening by addition of a polymer.
[0079]
Further, the method of impregnating the ion mobile phase material after forming the active material layer and the skeleton layer is excellent in the following points. First, since the active material layer and the powder layer formed on the active material layer are formed in a state that does not include an electrolyte solution, moisture can be easily removed by a drying process or the like. Therefore, it is not necessary to manage moisture, and the production can be performed in a normal atmosphere. Therefore, it is not necessary to install both the disperser and the coating machine in the dry room, and the equipment can be simplified. As a method for forming these layers, a method can be used in which an active material or a powder and a binder are dispersed in a suitable solution together with a suitable solution, and after application, the coating is dried. And productivity is extremely high. Further, by adding a calendering process to the coating film, it is possible to consolidate the coating film to increase the filling amount of the active material, and to control the filling rate of the powder in the intermediate layer. In addition, since the rigidity of the entire coating film including the current collector is increased and the flatness of the coating film is increased, workability in the case of stacking the batteries in a flat plate is improved. Further, in the film formation by coating, the thickness can be about 1 micron. This reduces the internal resistance of the battery and contributes to an increase in capacity. In addition, there are no process difficulties associated with this thinning. For example, if it is attempted to realize a thickness of 50 microns or less with a porous film, the film cannot be handled well because elongation, cutting, kinking, and the like of the film occur due to strength problems. In particular, when laminating flat plates, it is extremely difficult to widen a porous film having a thickness of 50 microns or less so as not to have wrinkles, and it is almost impossible to increase the area. In addition, the technique of using a gel electrolyte alone as an electrolyte layer has a problem in film thickness uniformity and a problem in the mechanical strength of the electrolyte layer. In the method of the present invention, there is no area limitation, and an electrolyte layer having a thin, uniform and excellent mechanical strength is formed without difficulty in the process on an electrode of “roll width of application” × “any length”. Is possible. As an example, an active material layer and a skeleton layer can be formed on a 90 cm wide roll by the method of the present invention and cut into a length of 180 cm to make a battery of one tatami mat. In application, it is not difficult to form a uniform layer having a thickness of 20 microns even for this area, and an electrolyte layer having a thickness of 20 microns can be formed. It is difficult to spread a 20-micron-thick porous film neatly and adhere to an electrode at the stage where the area is about 50 square centimeters. Of course, the above-described effects are also exhibited when an electrolyte electrolyte is used as the ion mobile phase.
[0080]
Furthermore, the gel electrolyte existing in the positive electrode, the negative electrode, and the electrolyte layer may be formed by applying an ion mobile phase raw material on the active material layer and the skeleton layer, filling the voids, and then forming the gel electrolyte. . Since the step of forming the gel electrolyte can be reduced once for each of the positive electrode side and the negative electrode side, the step is simplified. In the method as shown in USP 5,453,335, 5,609,974, the gelation process is required three times to four times with the positive electrode side, the negative electrode side, and the electrolyte layer. The effect of simplification is great. Especially when the gel electrolyte is formed by polymerizing the monomer, or when it is formed by impregnation in a heated state and cooling it, it takes time in minutes to form the gel electrolyte. The effect on productivity and cost reduction by omitting the process is great.
[0081]
Furthermore, in the present invention, at least a part of the gel electrolyte in the electrolyte layer and the gel electrolyte in the electrode can be formed as a continuous body. Gel-like electrolyte that is in close contact with the continuum is a problem when using a gel-like electrolyte that is completely ion-moved and has a shape-maintaining property, such as poor bonding at the interface between the electrolyte layer and the positive and negative electrodes Extra interface resistance due to can be reduced. For this reason, the internal resistance of the battery can be lowered, and the capacity and rate characteristics are improved. In particular, the gel electrolyte (positive electrode, negative electrode, intermediate layer or electrolyte layer) inside the battery is formed as a continuous body. In this case, ion migration is completely ensured, and internal resistance is reduced, capacity and rate characteristics are improved. The effect of is great.
[0082]
When the gel electrolyte is formed by polymerizing a monomer, the liquid containing the monomer has a low viscosity and is easily impregnated. In particular, when coating is performed on the active material layer or the skeleton layer, the impregnation is rapidly completed because the impregnation only needs to proceed by the thickness of the active material layer or the thickness of the skeleton layer (usually 1 mm or less). Further, when the gel electrolyte is formed by impregnating an electrolyte component mainly composed of an electrolyte solution and a polymer in a heated state and then cooling, the impregnation is performed according to an application method. Since it only needs to proceed by the thickness of the skeleton layer added thereto, the impregnation of the polymer gel electrolyte in the form of a solution having a high viscosity even when heated to form a solution sufficiently proceeds.
[0083]
In the present invention, since the influence of the interface of the gel electrolyte is suppressed and the internal resistance is low, in order to improve the interface contact, the battery stacked in a case with high rigidity is pressed down, There is no need to put pressure on the battery. Therefore, even if the positive electrode, the electrolyte layer, and the negative electrode are laminated in a flat plate and housed in a case having shape changeability, the operation can be performed without any problem. For this reason, it is possible to make it thin and bend it, and it is possible to increase the shape freedom of the battery without impairing the battery characteristics.
[0084]
[Table 1]

Claims (12)

 (1) A lithium secondary battery having a positive electrode, (2) a negative electrode, and (3) an intermediate layer containing non-electrically conductive powder and a non-electrically conductive binder provided between them. And (1) a positive electrode and / or (2) a negative electrode comprising an active material layer containing a powdery active material and a binder, and an ion mobile phase comprising a gel electrolyte formed in the active material layer The intermediate layer of (3) includes a skeleton layer containing a non-electrically conductive powder and a non-electrically conductive binder, and a gel electrolyte formed in the skeleton layer. And the non-electrically conductive powder of (3) is selected from silica, titanium oxide and aluminum oxide, and the binders of (1) to (3) are polyfluorinated. The gel electrolyte of vinylidene and (1) to (3) is polyacrylonitrile or Includes a polyethylene oxide resin having an acrylic group at the end, the thickness of the active material layer of the positive electrode and the negative electrode is 1 to 300 μm, the thickness of the intermediate layer is 1 to 200 μm, and the porosity of the intermediate layer, That is, the lithium secondary battery characterized in that the volume ratio in the intermediate layer of the ion mobile phase formed in the voids of the skeleton layer is 30 to 95%.  The lithium secondary battery according to claim 1, wherein the positive electrode and / or the negative electrode and the intermediate layer are in contact with each other.  The lithium secondary battery according to claim 2, wherein the positive electrode and / or the negative electrode and the intermediate layer are integrally provided.  The lithium secondary battery according to claim 1, wherein the intermediate layer further contains a lithium ion conductive electrolyte. The lithium secondary battery according to claim 4, wherein the intermediate layer includes a gel electrolyte containing a nonaqueous electrolytic solution.  (1) a positive electrode, (2) a negative electrode, and (3) an intermediate layer containing a non-electrically conductive powder and a non-electrically conductive binder provided between them, The negative electrode is composed of a powdery active material and an active material layer containing a binder for fixing the active material, and an ion mobile phase made of a gel electrolyte formed in the active material layer, The intermediate layer is composed of a skeleton layer containing a non-electrically conductive powder and a non-electrically conductive binder, and an ion mobile phase comprising a gel electrolyte formed in the skeleton layer. A lithium secondary battery characterized in that an ion mobile phase formed in the positive electrode and / or negative electrode and an ion mobile phase formed in the intermediate layer are continuous, (3) The non-electrically conductive powder is selected from silica, titanium oxide and aluminum oxide The binders of (1) to (3) are polyvinylidene fluoride and the gel electrolyte of (1) to (3) contains polyacrylonitrile or a polyethylene oxide resin having an acrylic group at the end The active material layer thickness of the positive electrode and the negative electrode is 1 to 300 μm, the thickness of the intermediate layer is 1 to 200 μm, and the porosity of the intermediate layer, that is, the ions formed in the voids of the skeleton layer The lithium secondary battery whose volume ratio in the intermediate | middle layer of a mobile phase is 30 to 95%.  An electrolyte layer, which is an intermediate layer containing a lithium ion conductive electrolyte, is provided over almost the entire area between the positive electrode and the negative electrode, and the positive electrode and / or the negative electrode includes a powdery active material and an active layer. An active material layer containing a binder for fixing a substance and an ion mobile phase made of a gel electrolyte formed in the active material layer, the electrolyte layer comprising a non-electrically conductive powder and Ion migration formed in the positive electrode and / or negative electrode, comprising a skeletal layer containing a non-electrically conductive binder and an ion mobile phase comprising a gel electrolyte formed in the skeleton layer A lithium secondary battery characterized in that a phase and an ion mobile phase formed in the electrolyte layer are continuous, wherein the non-electrically conductive powder is selected from silica, titanium oxide and aluminum oxide Active material Both the fixing binder and the non-electrically conductive binder are polyvinylidene fluoride, and the gel electrolyte contains polyacrylonitrile or a polyethylene oxide resin having an acrylic group at the terminal, a positive electrode, a negative electrode The thickness of the active material layer is 1 to 300 μm, the thickness of the intermediate layer is 1 to 200 μm, and the porosity of the intermediate layer, that is, the volume ratio of the ion mobile phase formed in the voids of the skeleton layer in the intermediate layer , 30 to 95% lithium secondary battery. A method for manufacturing a lithium secondary battery in which an intermediate layer containing a non-electrically conductive powder and a non-electrically conductive binder is formed between a positive electrode and a negative electrode. It includes an intermediate layer forming step of applying and drying a paint containing a conductive powder, a non-electrically conductive binder, and a solvent, and after the intermediate layer forming step, impregnation with an ion mobile phase raw material As an ion mobile phase material for forming a gel electrolyte, (i) one containing an electrolytic solution and a gelled polymer, or (ii) one containing an electrolytic solution and a monomer is used. The positive electrode and / or the negative electrode are composed of an active material layer containing a powdery active material and a binder, and the non-electrically conductive powder of the intermediate layer is made of silica, titanium oxide, and aluminum oxide. The binder and non-electric The conductive binder is polyvinylidene fluoride, and the gel electrolyte contained in the ion mobile phase formed from the ion mobile phase raw material contains polyacrylonitrile or a polyethylene oxide resin having an acrylic group at the end. The thickness of the active material layer of the positive electrode and the negative electrode is 1 to 300 μm, the thickness of the intermediate layer is 1 to 200 μm, and the porosity of the intermediate layer, that is, the intermediate of the ion mobile phase formed in the voids of the skeleton layer The manufacturing method of a lithium secondary battery whose volume ratio in a layer is 30 to 95%. (1) an active material layer forming step of forming an active material layer containing a positive electrode active material or a negative electrode active material and a binder on a current collector; (2) directly or indirectly on the active material layer; An intermediate layer forming step for forming a layer containing an electrically conductive powder and a non-electrically conductive binder, and (3) impregnation with an ion mobile phase raw material after the active material layer forming step and the intermediate layer forming step The method for producing a lithium secondary battery according to claim 8 , comprising an impregnation step.
As an ion mobile phase raw material for forming a gel electrolyte, (i) one containing an electrolytic solution and a gelled polymer or (ii) one containing an electrolytic solution and a monomer is used.
The non-electrically conductive powder is selected from silica, titanium oxide and aluminum oxide, and the binder and the non-electrically conductive binder are polyvinylidene fluoride and formed from the ion mobile phase raw material. The gel electrolyte contained in the ion mobile phase contains polyacrylonitrile or a polyethylene oxide resin having an acrylic group at the terminal, the thickness of the active material layer of the positive electrode and the negative electrode is 1 to 300 μm, and the thickness of the intermediate layer Is a method for producing a lithium secondary battery, in which the porosity of the intermediate layer is 30 to 95%, that is, the volume ratio of the ion mobile phase formed in the void of the skeleton layer in the intermediate layer.  The method for producing a lithium secondary battery according to claim 9, wherein the layers in the steps (1) and (2) are formed by applying and drying a paint containing each raw material.  The ion mobile phase raw material contains an electrolyte solution and a monomer, and after the impregnation step, the monomer is polymerized to form a gel electrolyte containing a polyethylene oxide resin having an acrylic group at the terminal. The manufacturing method of the lithium secondary battery as described in one. 9. The ion mobile phase raw material contains an electrolytic solution and a gelled polymer, and the impregnation is performed in a heated state, and after the impregnation step, the gel electrolyte containing polyacrylonitrile is formed by cooling it. method for producing a lithium secondary battery according to any one of 9.