JP2009181874A - Lithium ion secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method of an all-solid lithium ion secondary battery in which, when a current collector is fixed on a solid electrode, the current collector is adhered to the electrode sufficiently and is not likely to peel off even after a battery manufacturing is completed. <P>SOLUTION: The lithium ion secondary battery is provided with a positive electrode and a negative electrode on both sides of a solid electrolyte and current collectors provided on the outer sides of the positive electrode and the negative electrode respectively, and at least one current collector is made of a material containing a viscoelastic body. The current collector is a composite material made of a conductive inorganic material and a resin. The current collector may be laminated by coating a slurry containing a current collector material, and may be laminated by pasting green sheets made by drying the slurry containing the current collector material. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an all solid lithium ion secondary battery.

  Conventionally, as an electrolyte in a lithium ion secondary battery, an electrolyte obtained by impregnating a microporous membrane called a separator with a non-aqueous electrolyte solution has been used. An all-solid battery using an inorganic solid electrolyte as an electrolyte instead of such a liquid-based electrolyte has been proposed. All solid state batteries are excellent in safety because they do not use flammable organic solvents such as electrolytes and therefore do not leak or ignite. However, in the case of an all-solid-state battery, since all of the positive electrode, the electrolyte, and the negative electrode are solid, there is a problem that the contact interface is difficult to take and the interface resistance is increased. In this case, since the lithium ion conductivity at the electrode-electrolyte interface is not sufficiently high, it has not been put into practical use yet.

  As a method for efficiently producing such an all-solid battery, a solid electrolyte, a positive electrode, and a negative electrode are each prepared as a green sheet from a slurry containing a powder having a specific composition as a main component. It is conceivable to obtain a laminate for a lithium ion secondary battery by bonding together a green sheet for a battery and a green sheet for a negative electrode.

  In this case, the solid electrolyte, the positive electrode, and the negative electrode are baked together with the green sheets bonded together, or the solid electrolyte, the positive electrode, and the negative electrode are individually baked, and the baked solid electrolyte, positive electrode, An all-solid laminate for a lithium ion secondary battery can be prepared by laminating the negative electrode to form a laminate.

  A conventional lithium ion secondary battery has a positive electrode current collector formed by attaching an aluminum foil to a positive electrode of a laminate composed of a solid electrolyte, a positive electrode and a negative electrode, and a negative electrode current collector formed by attaching a copper foil to the negative electrode. However, in the case of an all-solid laminate as described above, the problem is that metal foils such as aluminum foil and copper foil are difficult to adhere to and adhere to the fired positive electrode and the fired negative electrode. However, it is difficult to avoid the formation of a minute gap between the metal foil and the laminate, so that the electronic conductivity is inferior, and the metal foil is easily peeled off due to the expansion and contraction of the laminate accompanying charging / discharging of the battery. There is a problem that a long battery cannot be maintained for a long time.

  Also, the positive electrode and negative electrode formed by firing a green sheet on the solid electrolyte obtained by grinding and polishing a solid electrolyte obtained by grinding and polishing a powder that has been molded, pressed and sintered, and then polished. Similarly, when an all-solid battery is used, there is a problem that a current collector made of a metal foil is difficult to adhere.

  The present invention has been considered in view of the problems in realizing the above all-solid-state battery, and the current is collected on a solid electrode such as an electrode formed with a green sheet and fired from the green sheet. An object of the present invention is to provide an all-solid-state lithium ion secondary battery in which a current collector adheres well to an electrode when the body is attached and there is no possibility of peeling after the battery is produced.

In order to achieve the above object of the present invention, the present inventor has conducted research and experiment,
When at least one of the current collectors is formed of a material containing a viscoelastic body, and the material containing the viscoelastic body is preferably composed of a composite material of a conductive inorganic material and a resin, the current collector can be satisfactorily used as an electrode. The present inventors have found that there is no risk of adhesion and peeling even after the battery is produced.

The present invention that achieves the above object has the following configuration.
Configuration 1
In a lithium ion secondary battery including a positive electrode and a negative electrode on both sides of a solid electrolyte, and a current collector on each of the positive electrode and the negative electrode, at least one of the current collectors includes a viscoelastic body. Lithium ion secondary battery.
Configuration 2
2. The lithium ion secondary battery according to Configuration 1, wherein the current collector is a composite material of a conductive inorganic material and a resin.
Configuration 3
The lithium ion secondary battery according to claim 1, wherein the current collector is porous.
Configuration 4
The lithium ion secondary battery according to any one of claims 1 to 3, wherein the viscoelastic body has a hardness of less than 90 according to a JIS K 6253 type A durometer hardness test.
Configuration 5
The lithium ion secondary battery according to Configuration 2, wherein the conductive inorganic material of the composite material includes a carbon material.
Configuration 6
The lithium ion secondary battery according to Configuration 2, wherein the conductive inorganic material of the composite material contains a metal powder.
Configuration 7
The lithium ion secondary battery according to Configuration 2, wherein the conductive inorganic material of the composite material includes a metal oxide.
Configuration 8
The lithium ion secondary battery according to any one of configurations 5 to 7, wherein the conductive inorganic material of the composite material includes a fibrous substance.
Configuration 9
The solid electrolyte is Li _{1 + x + z} M _x (Ge _1−y Ti _y ) _2−x Si _z P _3−z O ₁₂ (where 0 ≦ x ≦ 0.8, 0 ≦ y ≦ 1.0, 0 ≦ z ≦ 0.6, one or more selected from M = Al and Ga). The lithium ion secondary battery according to any one of Configurations 1 to 8, wherein

  According to the present invention, in a lithium ion secondary battery including a positive electrode and a negative electrode on both sides of a solid electrolyte, and a current collector on each of the positive electrode and the negative electrode, at least one of the current collectors includes a viscoelastic body. By including, the adhesion between the current collector and the electrode is improved, and a small gap is hardly generated between the current collector and the electrode, so that high electron conductivity can be obtained. Also, in the completed battery, the current collector has sufficient elasticity, so that the current collector is not likely to peel from the electrode even if the laminate is repeatedly expanded and contracted due to charging / discharging of the battery. A long battery can be maintained for a long time.

  According to the present invention, since the current collector is a composite material of a conductive inorganic material and a resin, the slurry containing the current collector material is applied onto the electrode or the slurry containing the current collector material is dried. A battery can be produced by a simple method by laminating the laminated green sheets on the electrodes.

  Further, according to the present invention, since the current collector material is porous, this hole has an effect of imparting cushioning properties to the current collector material and increasing the elasticity of the current collector material.

  According to the present invention, since the conductive inorganic material contains a fibrous substance, the fibrous substance has an effect of imparting cushioning properties to the current collector material and increasing the elasticity of the current collector material.

Hereinafter, embodiments of the present invention will be described in detail.
The laminated body to which the current collector is attached in the lithium ion secondary battery to which the present invention is applied includes an inorganic powder having lithium ion conductivity, an inorganic powder that exhibits lithium ion conductivity by heat treatment, or both A negative electrode obtained by heat-treating a positive electrode obtained by heat-treating a green sheet containing a positive electrode active material on both sides of a solid electrolyte obtained by heat-treating the green sheet containing Alternatively, the solid electrolyte green sheet, the positive electrode green sheet, and the negative electrode green sheet made of such inorganic powders may be bonded together and then fired at one time. However, the present invention is not limited to this. Molded, pressed and sintered products that have been ground and polished, and glass ceramic bulk materials It can be applied to a positive electrode obtained by heat-treating a green sheet containing a positive electrode active material on both sides of a solid electrolyte obtained by cutting and polishing, and a negative electrode obtained by heat-treating a green sheet containing a negative electrode active material. it can.

  The solid electrolyte is preferably obtained by firing an inorganic powder having lithium ion conductivity or a green sheet containing inorganic powder exhibiting lithium ion conductivity or both by heat treatment.

  If there are pores inside the solid electrolyte, there is no ion conduction path in that portion, so the ionic conductivity of the solid electrolyte itself is low. When used as a battery, the higher the conductivity, the faster the lithium ion transfer speed, and thus a high output battery can be obtained. Accordingly, the porosity in the solid electrolyte is preferably low, and is preferably 20 vol% or less. In order to make the porosity 20 vol% or less, the solid electrolyte is preferably a green sheet.

  In the present specification, the “green sheet” refers to a green body of glass powder and crystal (ceramics, glass ceramics) molded into a thin plate, and includes glass powder, crystal (ceramics or glass ceramics) powder, organic A mixed slurry of a binder, a plasticizer, a solvent and the like is formed into a thin plate shape by a doctor blade, a calendar method or the like.

  In addition, since the green sheet is formed to have a uniform thickness, the green sheet is uniformly heated at the time of firing. Therefore, the sintering proceeds uniformly in the material, and as a result, the porosity is 20 vol% or less. A very small number of thin plate-like solid electrolytes can be obtained. Therefore, the change in the thickness of the green sheet before firing is preferably in the range of + 10% to −10% with respect to the average value of the thickness distribution of the green sheet before firing. Furthermore, by thoroughly mixing the raw materials, the composition of the green sheet is made uniform, and it is pressed by a roll press, uniaxial, isotropic pressure, etc. before firing, and is densified, so that it has a dense and porosity after firing. A small amount of solid electrolyte can be obtained, whereby a high output solid electrolyte with high ionic conductivity can be obtained. Therefore, it is desirable to mix the raw materials for at least 1 hour, for example, with a ball mill.

  When used as a battery, the thin plate-like solid electrolyte which is a preferred embodiment of the present invention provides a high output battery because the lithium ion has a shorter migration distance, and ensures a large electrode area per unit volume. Therefore, a high capacity battery can be obtained. Therefore, the thickness of the electrolyte layer used as the solid electrolyte is preferably 500 μm or less, more preferably 400 μm or less, and most preferably 300 μm or less.

  The mobility of lithium ions during charging and discharging of a lithium ion secondary battery depends on the lithium ion conductivity and lithium ion transport number of the electrolyte. Therefore, it is preferable to use a substance having high lithium ion conductivity for the solid electrolyte of the present invention.

The ion conductivity after heat treatment of the lithium ion conductive powder or the powder that exhibits lithium ion conductivity by heat treatment is preferably 1 × 10 ⁻⁴ S · cm ⁻¹ or more, and 5 × 10 5. It is more preferably ⁻⁴ S · cm ⁻¹ or more, and most preferably 1 × 10 ⁻³ S · cm ⁻¹ or more.

  The lithium ion conductive inorganic powder used in the present invention is a powder of an inorganic substance containing a lithium ion conductive crystal (ceramic or glass ceramic) powder or a mixture thereof. The inorganic powder that exhibits lithium ion conductivity by heat treatment is glass powder that becomes glass ceramics by heat treatment.

Here, lithium ion conductivity means that the lithium ion conductivity exhibits a value of 1 × 10 ⁻⁸ S · cm ⁻¹ or more at 25 ° C.

  The average particle size of the inorganic powder having lithium ion conductivity or the inorganic powder that exhibits lithium ion conductivity by heat treatment is preferably 3 μm or less and the maximum particle size is preferably 15 μm or less. This makes it possible to obtain a solid electrolyte that is dense and has few vacancies and thus high ionic conductivity.

  In order to obtain high lithium ion conductivity, the lithium ion conductive inorganic powder preferably contains lithium, silicon, phosphorus, and titanium as main components.

  Since a higher conductivity can be obtained by including many of these crystals in the solid electrolyte, it is preferable that 50 wt% or more of lithium ion conductive crystals be included in the solid electrolyte.

  In addition, since lithium ion conductive inorganic powder contained in a molded body for obtaining a solid electrolyte contains a large amount of these crystals, higher conductivity can be obtained. It is preferable to contain lithium ion conductive crystals in an amount of 50 wt% or more.

Here, as a lithium ion conductive crystal that can be used, a crystal that does not include a grain boundary that inhibits ion conduction is advantageous in terms of ion conduction, and LiN, LISICON, La _0.55 Li _0. Crystals having a perovskite structure having lithium ion conductivity such as ₃₅ TiO _3, LiTi ₂ P ₃ O ₁₂ having a NASICON type structure, and glass ceramics on which these crystals are deposited can be used. A preferable lithium ion conductive crystal is Li _{1 + x + z} M _x (Ge _1-y Ti _y ) _2−x Si _z P _3−z O ₁₂ (where 0 ≦ x ≦ 0.8, 0 ≦ y ≦ 1.0). , 0 ≦ z ≦ 0.6, M = one or more selected from Al and Ga). In particular, glass ceramics on which crystals having a NASICON type structure are deposited are more preferable because they have almost no vacancies or crystal grain boundaries that hinder ion conduction, and thus have high ion conductivity and excellent chemical stability.

  Since a high conductivity can be obtained by containing a large amount of this glass ceramic in the solid electrolyte, it is preferable that 80 wt% or more of lithium ion conductive glass ceramic is contained in the solid electrolyte. More preferably, it is 85 wt% or more, and most preferably 90 wt% or more.

  Here, the vacancies and grain boundaries that hinder ion conduction refer to the conductivity of the entire inorganic substance including lithium ion conductive crystals with respect to the conductivity of the lithium ion conductive crystal itself in the inorganic substance. Ion conductivity-inhibiting substances such as vacancies and grain boundaries that decrease to 10 or less.

  Here, the glass ceramic is a material obtained by precipitating a crystal phase in a glass phase by heat-treating glass, and means a material composed of an amorphous solid and a crystal. Glass ceramics is a material in which all of the glass phase is phase-transformed into a crystal phase when there are almost no vacancies between crystal grains or in the crystal, that is, the crystal content (crystallinity) in the material is 100% by mass. Including In general, ceramics and sintered bodies referred to in the production process cannot avoid the presence of pores or crystal grain boundaries between crystal grains, or crystals, and can be distinguished from glass ceramics. In particular, with regard to ionic conduction, in the case of ceramics, due to the presence of vacancies and crystal grain boundaries, the value is considerably lower than the conductivity of the crystal grains themselves. Glass ceramics can suppress a decrease in conductivity between crystals by controlling the crystallization process, and can maintain the same conductivity as crystal grains.

  In addition to glass ceramics, examples of materials that have almost no vacancies or crystal grain boundaries that impede ion conduction include single crystals of the above crystals, but they are difficult to manufacture and expensive, so lithium ion conductive glass ceramics can be used. Most preferably it is used.

  Inorganic powder with lithium ion conductivity to be included in the solid electrolyte layer or inorganic powder that exhibits lithium ion conductivity by heat treatment is obtained by pulverizing lithium ion conductive glass ceramics or its mother glass. It is preferable. The lithium ion conductive inorganic powder is preferably dispersed uniformly in the solid electrolyte from the viewpoint of the ionic conductivity and mechanical strength of the solid electrolyte. In order to improve the dispersibility and to obtain a desired thickness of the solid electrolyte, the average particle size of the inorganic powder is preferably 3 μm or less, more preferably 2 μm or less, and most preferably 1 μm or less. .

What is preferable as the lithium ion conductive glass ceramic is that the mother glass is mol% based on oxide,
Li ₂ O 10~25%, and Al ₂ O ₃ and / or _Ga 2 _O 3 _0.5~15%, and TiO ₂ and / or _GeO 2 25 to 50%, and SiO ₂ 0 to 15%, and P ₂ O ₅ 26-40%
The glass is crystallized by heat treatment, and the main crystal phase at that time is Li _{1 + x + z} M _x (Ge _1-y Ti _y ) _2−x Si _z P _3−z O ₁₂ (However, 0 ≦ x ≦ 0.8, 0 ≦ y ≦ 1.0, 0 ≦ z ≦ 0.6, one or more selected from M = Al and Ga).

  In the case of the above-mentioned system, glass can be easily obtained by casting molten glass, and glass ceramics having the crystal phase obtained by heat-treating this glass have high lithium ion conductivity.

  In addition to the above composition, if the glass ceramic has a similar crystal structure, the range in which the ion conductivity is not lowered in order to lower the melting point or increase the stability of the glass during the production of the glass ceramic. It is also possible to add a small amount of other raw materials.

Examples of the inorganic powder exhibiting lithium ion conductivity by heat treatment include, for example, mol% based on oxide, Li ₂ O 10 to 25%, and Al ₂ O ₃ and / or Ga ₂ O ₃ 0.5. Those containing -15% and TiO ₂ and / or GeO ₂ 25-50%, SiO ₂ 0-15%, and P ₂ O ₅ 26-40% are preferred.

It is desirable that the glass ceramic composition does not contain alkali metals such as Na ₂ O and K ₂ O other than Li ₂ O as much as possible. When these components are present in the glass ceramics, the conductivity of the lithium ions is inhibited by the effect of mixing alkali ions, thereby lowering the conductivity.

  Further, when sulfur is added to the composition of the glass ceramic, the lithium ion conductivity is slightly improved, but the chemical durability and stability are deteriorated.

  It is desirable that the glass ceramic composition does not contain as much as possible components such as Pb, As, Cd, and Hg that may cause harm to the environment and the human body.

  Lithium ion conductive inorganic powder, that is, a crystal powder (ceramics or glass ceramic) having high lithium ion conductivity and chemical stability, or glass powder exhibiting such lithium ion conductivity by heat treatment The powder mixture is mixed using a solvent together with an organic binder and, if necessary, a dispersant, and a green sheet is produced by a simple production method such as a doctor blade method. The produced green sheet is processed into an arbitrary shape, preferably pressed by a roll press, uniaxial, isotropic pressure, etc. and then baked to remove the organic component of the organic binder, thereby forming a thin plate shape or an arbitrary shape. An all-solid electrolyte is obtained.

  As the organic binder used for forming the green sheet, a commercially available binder can be used as a forming aid for a doctor blade. In addition to the doctor blade, a molding aid generally used for rubber press, extrusion molding or the like can be used. Specifically, acrylic resin, ethyl cellulose, polyvinyl butyral, methacrylic resin, urethane resin, butyl methacrylate, vinyl copolymer and the like can be used. In addition to these binders, it is more preferable to add an appropriate amount of a dispersant for enhancing the dispersibility of the particles, a surfactant for improving foam removal during drying, or the like.

If it is desired to increase the electron conductivity without impeding the lithium conductivity, there is no problem even if other inorganic powders or organic substances are added. The effect may be obtained by adding a small amount of highly dielectric insulating crystal or glass as the inorganic powder. For example _{BaTiO 3, SrTiO 3, Nb 2} O 5, LaTiO 3 , and the like.

  Since the organic matter is removed during firing, there is no problem even if it is used for adjusting the viscosity of the slurry during molding.

  A simple doctor blade, roll coater or die coater can be used for forming the green sheet. If the viscosity is adjusted, a general-purpose apparatus such as kneading / extrusion can be used, so that various shapes of solid electrolyte can be produced efficiently and inexpensively.

  The solid electrolyte green sheet thus prepared is preferably fired at a temperature of 1200 ° C. or lower.

  The sheet-shaped solid electrolyte obtained by firing can be easily processed into an arbitrary shape because the shape of the formed green sheet can be obtained as it is. Therefore, a thin film, a solid electrolyte of an arbitrary shape, or this solid electrolyte can be used. The used all-solid lithium ion secondary battery can be manufactured.

  Moreover, since the solid electrolyte after firing does not contain organic substances, it has excellent heat resistance and chemical durability, and is less harmful to safety and the environment.

  The volume of the thin plate-like solid electrolyte is preferably 65% by volume or more of the green sheet. As a result, deformation such as shrinkage of the green sheet due to firing can be minimized.

The ion conductivity after heat treatment of the inorganic powder having lithium ion conductivity or the inorganic powder exhibiting lithium ion conductivity by heat treatment is 1 × 10 ⁻⁴ S · cm ⁻¹ or more at room temperature. preferable.

The ion conductivity after heat treatment of an inorganic powder having lithium ion conductivity or an inorganic powder that exhibits lithium ion conductivity by heat treatment, or both, is 5 × 10 ⁻⁵ S ⁻¹ cm or more. It is preferable that

A transition metal compound capable of occluding and releasing Li ions for producing the lithium ion secondary battery of the present invention can be used. For example, manganese, cobalt, nickel, vanadium, niobium, molybdenum, titanium, iron, phosphorus , Transition metal oxides containing at least one selected from aluminum and chromium can be used.
The lower limit of the content of the active material contained in the positive electrode green sheet is preferably 40% by weight or more and more preferably 50% by weight or more because if the amount is small, the battery capacity per unit volume is reduced after firing. Preferably, it is most preferably 60 wt% or more.

  In addition, the content of the active material contained in the positive electrode green sheet is preferably 97 wt%, more preferably 94 wt%, and more preferably 90 wt% or less because if it is too much, the flexibility is lost and handling becomes difficult. Most preferably it is.

  In order to obtain a positive electrode green sheet having the active material content and to prepare a slurry that can be satisfactorily applied, a mixture comprising positive electrode active material powder, inorganic powder, organic binder, plasticizer, solvent, etc. The amount of the positive electrode active material is preferably 10 wt% or more, more preferably 15 wt% or more, and most preferably 20 wt% or more with respect to the amount of slurry.

  In order to prepare a slurry that can be satisfactorily applied, the upper limit value of the content of the active material is preferably 90 wt% or less, more preferably 85 wt% or less with respect to the amount of the mixed slurry. 80 wt% or less is most preferable.

  Moreover, when the electron conductivity of a positive electrode active material is low, electron conductivity can be provided by adding an electron conduction auxiliary agent. As the electron conduction aid, fine particles, fibrous carbon materials and metals can be used. As the metal that can be used, metals such as titanium, nickel, chromium, iron, stainless steel, and aluminum, and noble metals such as platinum, gold, and rhodium can be used.

  Materials such as alloys capable of occluding and releasing Li ions such as aluminum, silicon, and tin, and metal oxides such as titanium, vanadium, chromium, niobium, and silicon can be used.

  The lower limit of the content of the active material contained in the negative electrode green sheet is preferably 40% by weight or more, more preferably 50% by weight or more, since the battery capacity per unit volume decreases if the content is small. Most preferably, it is 60 wt% or more.

  In addition, the lower limit of the content of the active material contained in the negative electrode green sheet is the negative electrode active material powder, inorganic powder, organic binder, plasticizer, The amount of the negative electrode active material is preferably 10 wt% or more, more preferably 15 wt% or more, and most preferably 20 wt% or more with respect to the amount of the mixed slurry composed of a solvent or the like.

  Further, the upper limit of the content of the active material needs to be slurried using a binder or a solvent. Therefore, the upper limit is preferably 90 wt% or less, and preferably 85 wt% or less with respect to the amount of the mixed slurry. More preferably, it is most preferable to set it as 80 wt% or less.

  Moreover, when the electronic conductivity of a negative electrode active material is low, electron conductivity can be provided by adding an electron conduction support agent. As the electron conduction aid, fine particles, fibrous carbon materials and metals can be used. As the metal that can be used, metals such as titanium, nickel, chromium, iron, stainless steel, and aluminum, and noble metals such as platinum, gold, and rhodium can be used.

  It is preferable to add lithium ion conductive inorganic powder to the positive electrode green sheet and the negative electrode green sheet because ion conduction is imparted. Specifically, the lithium ion conductive glass ceramics can be included. Moreover, it is more preferable to add the same ion conductive inorganic substance contained in the solid electrolyte green sheet. When the same material is included in this way, the ion transfer mechanism included in the electrolyte and the electrode material can be shared, and ion transfer between the electrolyte and the electrode can be performed smoothly. Therefore, a battery with higher output and higher capacity can be provided.

  In the case of the positive electrode green sheet, the lower limit of the content of the lithium ion conductive inorganic powder when mixed with the organic binder needs to be imparted with ion conductivity, so that the positive electrode active material powder, inorganic powder, organic The amount is preferably 1 wt% or more, more preferably 3 wt% or more, and most preferably 5 wt% or more with respect to the amount of the mixed slurry composed of a binder, a plasticizer, a solvent, and the like.

  The lower limit of the content of the lithium ion conductive inorganic powder in the positive electrode green sheet after drying is preferably 3 wt% or more, more preferably 5 wt% or more, for the same reason as described above. Most preferably.

  Further, the upper limit of the content of the lithium ion conductive inorganic powder is set to 50 wt% or less with respect to the amount of the mixed slurry because the amount of the active material contained is small and the battery capacity is reduced when the amount is too large. It is preferably 40 wt% or less, more preferably 30 wt% or less.

  For the same reason as described above, the upper limit of the content of the lithium ion conductive inorganic powder in the positive electrode green sheet after drying is preferably 70 wt% or less, more preferably 60 wt% or less, and 50 wt%. The following is most preferable.

  In the case of the negative electrode green sheet, the lower limit of the content of the lithium ion conductive inorganic powder when mixed with the organic binder needs to be imparted with ionic conductivity, so the negative electrode active material powder, inorganic powder, organic The amount is preferably 1 wt% or more, more preferably 3 wt% or more, and most preferably 5 wt% or more with respect to the amount of the mixed slurry composed of a binder, a plasticizer, a solvent, and the like.

  The lower limit of the content of the lithium ion conductive inorganic powder in the negative electrode green sheet after drying is preferably 3 wt% or more, more preferably 5 wt% or more, for the same reason as above. Most preferably.

  In addition, the upper limit of the content of the lithium ion conductive inorganic powder is too large, the amount of active material contained is small and the battery capacity is reduced, so the sheet shape is maintained. On the other hand, it is preferably 50 wt% or less, more preferably 40 wt% or less, and most preferably 30 wt% or less.

  The upper limit of the content of the lithium ion conductive inorganic powder in the negative electrode green sheet after drying is preferably 70 wt% or less, more preferably 60 wt% or less, for the same reason as described above, and 50 wt%. The following is most preferable.

  The positive electrode green sheet and the negative electrode green sheet can be formed in the same manner as the production of the thin plate-like solid electrolyte green sheet.

  The thin plate-like positive electrode green sheet and the thin plate-like negative electrode green sheet thus prepared are fired at an appropriate firing temperature corresponding to each material. Usually, the proper firing temperature of the positive electrode green sheet and the negative electrode green sheet is in the range of 500 ° C to 1000 ° C.

  The fired solid electrolyte, the positive electrode, and the negative electrode thus prepared are bonded together to form a laminate.

  As another method, it is also possible to prepare a laminate by arranging and laminating a positive electrode green sheet and a negative electrode green sheet on both sides of the solid electrolyte green sheet prepared by the above method and then firing them together.

  A current collector material is laminated on the positive electrode side and the negative electrode side of the laminate composed of the thin plate-shaped solid electrolyte, the positive electrode, and the negative electrode thus prepared, thereby forming a current collector.

  The current collector may be laminated by applying a slurry containing a current collector material, or may be laminated by attaching a green sheet obtained by drying a slurry containing a current collector material.

  The current collector includes a viscoelastic body. If the hardness of the viscoelastic body is 90 or more according to the JIS K6253 type A durometer hardness test, the current collector cannot provide sufficient elasticity. , Peeling from the electrode occurs.

Therefore, it is preferable that the upper limit of the hardness by the said test is less than 90, More preferably, it is 85 or less, Most preferably, it is 80 or less. As long as the conductive inorganic material and the resin are maintained as a composite material, the lower limit is not limited by the above test.
The current collector is made of a composite material of a conductive inorganic material and a resin.

  Specifically, a conductive inorganic material powder material or fiber material is bound with a binder such as a fluoropolymer such as polytetrafluoroethylene or polyvinylidene fluoride, a polyolefin polymer such as polyethylene or polypropylene, or a synthetic rubber. The configuration is exemplified.

  This composite material is preferably porous in order to impart sufficient cushioning properties to the current collector.

  The conductive inorganic material in the composite material can include a carbon material. For example, carbon nanofibers are suitable as the carbon material.

  The conductive inorganic material in the composite can include a metal powder. As the current collector material for the positive electrode, for example, aluminum powder is suitable. As the negative electrode current collector material, for example, copper powder is suitable.

  The conductive inorganic material in the composite material can include a metal oxide powder. For example, nickel oxide powder is suitable as the positive electrode current collector material. As the negative electrode current collector material, for example, tin oxide powder is suitable.

  The conductive inorganic material in the composite material preferably contains a fibrous substance. Accordingly, this fibrous substance has an effect of imparting cushioning properties to the current collector material and increasing the elasticity of the current collector material.

  The resin in the composite material functions as a binder or solvent for the conductive inorganic material, and one or two or more of these resins are mixed and dissolved to form a liquid, and the conductive inorganic material is added to the solution. Thus, a slurry for forming a current collector is prepared. As this resin, for example, polyvinylidene fluoride is suitable.

  In order to maintain the state of the composite material, the upper limit of the content of the conductive material in the composite material is preferably 98% or less, more preferably 95% or less, and most preferably 92% or less. In order to obtain high conductivity, the lower limit is preferably 30% by weight or more, more preferably 35% by weight or more, and most preferably 40% by weight or more.

  A slurry containing this composite material is applied to the laminate, or a green sheet made from this slurry is attached to the laminate, and a positive electrode lead is connected to the positive electrode side and a negative electrode lead is connected to the negative electrode side to complete a lithium ion secondary battery. To do.

  The upper limit of the thickness of the current collector of the present invention is preferably 40 μm or less, more preferably 35 μm or less, and most preferably 30 μm or less from the viewpoint of easy and dense film formation. Further, the lower limit is preferably 0.5 μm or more, more preferably 1 μm or more, and most preferably 3 μm or more from the viewpoint of suppressing peeling and tearing during charging and discharging.

Production of Oxide Glass Powder H ₃ PO ₄ , Al (PO ₃ ) ₃ , Li ₂ CO ₃ , SiO ₂ , and TiO ₂ are used as raw materials, and these are 35. P ₂ O ₅ in mol% in terms of oxide. 0%, Al ₂ O ₃ 7.5%, Li ₂ O 15.0%, TiO ₂ 38.0%, SiO ₂ 4.5% and so forth were weighed and mixed uniformly. Later, it was put into a platinum pot and heated and melted for 3 hours while stirring at a temperature of 1500 ° C. in an electric furnace to obtain a glass melt. Then, the glass melt was rapidly cooled by dropping it into running water at room temperature while heating from a platinum pipe attached to the pot, to obtain an oxide glass.

When this glass was crystallized in an electric furnace at 1000 ° C. and the lithium ion conductivity was measured, it was 1.3 × 10 ⁻³ Scm ⁻¹ at room temperature. Further, the precipitated crystal phase is Li _{1 + x + y} Al _x Ti _2−x Si _y P _3−y O ₁₂ (0 ≦ x ≦ 0.4, 0 <y ≦ 0.6) by the powder X-ray diffraction method. Phase was confirmed.

  The oxide glass was pulverized with a jet mill, then placed in a ball mill using ethanol as a solvent, and wet pulverized to obtain an oxide glass powder having an average particle size of 0.5 μm and a maximum particle size of 1 μm.

Preparation of Solid Electrolyte Green Sheet An oxide slurry having an average particle size of 0.5 μm was prepared by dispersing and mixing together with an acrylic binder, a dispersant, and an antifoaming agent using water as a solvent. The slurry was depressurized to remove bubbles, and then shaped using a doctor blade and dried to prepare an electrolyte green sheet having a thickness of 30 μm.

Production of Positive Electrode Green Sheet As a positive electrode active material, commercially available lithium manganate (manufactured by Honjo Chemical) was used. Lithium manganate powder ground to an average particle size of 0.9μm and oxide glass with an average particle size of 0.5μm are weighed in a ratio of 75: 25wt%, and dispersed and mixed using an acrylic binder and dispersant as a solvent with water. A positive electrode slurry was prepared. The slurry was decompressed to remove bubbles, and then shaped using a doctor blade and dried to produce a positive electrode green sheet having a thickness of 20 μm.

Production of Negative Electrode Green Sheet Commercially available (Ishihara Sangyo) lithium titanate was used after annealing at 500 ° C. as a negative electrode active material. Negative electrode slurry by weighing lithium titanate powder with an average particle size of 5 μm and oxide glass with an average particle size of 0.5 μm at a ratio of 80:20 wt%, and dispersing and mixing with an acrylic binder and dispersant in water as a solvent. Was prepared. The slurry was decompressed to remove bubbles, and then shaped and dried using a continuous roll coater to prepare a negative electrode green sheet having a thickness of 25 μm.

Production of electrode / electrolyte laminate The positive electrode produced in the above was cut into 20 mm squares, and the negative electrode green sheet was cut into 25 mm squares. Two electrolyte green sheets were superposed and bonded together by a heated roll press. The laminated green sheet laminate was cut to 25 mm. Each of the cut green sheets was pressed at room temperature using CIP (cold isostatic pressing) to be densified. The produced laminate was sandwiched between alumina setters and heated to 400 ° C. in an electric furnace to remove organic substances such as binder and dispersant in the laminate. Thereafter, the temperature was rapidly raised to 900 ° C., held for 5 minutes, and cooled to prepare a laminated sintered body of the positive electrode, the electrolyte, and the negative electrode.

Production of an all-solid-state lithium ion secondary battery On the positive electrode side of the laminate produced above, a slurry made of aluminum powder (average particle size 1 μm) and polyvinylidene fluoride (Pvdf) and N-methylpyrrolidone (NMP) as a binder After coating, NMP was volatilized and removed at 100 ° C. to form a positive electrode current collector. The thickness of the positive electrode current collector was 5 μm. Moreover, the porosity after NMP volatilization was 18%.

  Thereafter, a slurry composed of carbon powder (average particle size 1.5 μm) and Pvdf and NMP as a binder was applied to the negative electrode side, and NMP was volatilized and removed at 100 ° C. to form a negative electrode current collector. The thickness of the negative electrode current collector was 7 μm. The porosity after NMP volatilization was 15%.

  The laminated sintered body provided with the current collector was sealed in a stainless steel container composed of a container and a lid so that the positive electrode current collector was in close contact with the container and the negative electrode current collector. The container and the lid are electrically insulated.

Cycle test The battery produced above was charged and discharged 20 times at 60 ° C. and 1 / 6C. The discharge capacity after 20 cycles was 80% of the initial discharge capacity.

Comparative example

  A laminated sintered body was produced in the same manner as in Example 1. An aluminum thin film was formed on the positive electrode and a copper thin film was formed on the negative electrode by vapor deposition. After this was sealed in the same stainless steel container as in Example 1, 20 charge / discharge tests were conducted at 60 ° C. and 1/6. However, the 5th cycle was 10% of the initial discharge capacity, and the 6th cycle and thereafter. The charge / discharge capacity was almost zero. When the container was disassembled after the test, chips and cracks were observed on the positive electrode side of the sintered body.

Claims (9)

  In a lithium ion secondary battery including a positive electrode and a negative electrode on both sides of a solid electrolyte, and a current collector on each of the positive electrode and the negative electrode, at least one of the current collectors includes a viscoelastic body. Lithium ion secondary battery.   2. The lithium ion secondary battery according to claim 1, wherein the current collector is a composite material of a conductive inorganic material and a resin.   The lithium ion secondary battery according to claim 1, wherein the current collector is porous.   The lithium ion secondary battery according to any one of claims 1 to 3, wherein the viscoelastic body has a hardness of less than 90 according to a JIS K 6253 type A durometer hardness test.   The lithium ion secondary battery according to claim 2, wherein the conductive inorganic material of the composite material includes a carbon material.   The lithium ion secondary battery according to claim 2, wherein the conductive inorganic material of the composite material contains a metal powder.   The lithium ion secondary battery according to claim 2, wherein the conductive inorganic material of the composite material contains a metal oxide.   The lithium ion secondary battery according to claim 5, wherein the conductive inorganic material of the composite material includes a fibrous substance. The solid electrolyte is Li _{1 + x + z} M _x (Ge _1−y Ti _y ) _2−x Si _z P _3−z O ₁₂ (where 0 ≦ x ≦ 0.8, 0 ≦ y ≦ 1.0, 0 ≦ z ≦ The lithium ion secondary battery according to claim 1, wherein the lithium ion secondary battery includes one or more crystals selected from 0.6, M = Al, and Ga.