TW202429740A - Electrolyte composition and secondary battery - Google Patents

Abstract

The subject of the present invention is to provide an electrolyte composition and a secondary battery capable of reducing the migration of an electrolyte. The solution of the present invention is an electrolyte composition comprising a solid electrolyte having lithium ion conductivity, an electrolyte solution in which a lithium salt is dissolved, and a granular polymer dispersed in the electrolyte. A secondary battery comprises a positive electrode, an electrolyte layer, and a negative electrode in sequence, and at least one of the positive electrode, the electrolyte layer, and the negative electrode is composed of an electrolyte composition comprising a solid electrolyte having lithium ion conductivity, an electrolyte solution in which a lithium salt is dissolved, and a granular polymer dispersed in the electrolyte.

Description

Electrolyte composition and secondary battery

The present invention relates to an electrolyte composition and a secondary battery.

As a prior art related to a secondary battery including a solid electrolyte having lithium ion conductivity, Patent Document 1 discloses a technology for improving ion conductivity by further including an electrolyte solution in which a lithium salt is dissolved and the electrolyte solution exists at the grain boundaries of the solid electrolyte. [Prior Art Document] [Patent Document]

[Patent Document 1] Japanese Patent No. 6682708

[Problems to be solved by the invention]

In the prior art, if an external force is applied to the secondary battery or the temperature around the secondary battery rises, the electrolyte will move and it will be easy to produce a small amount of electrolyte between the solid electrolyte. If a small amount of electrolyte is produced, there is a risk that the contact area between the solid electrolyte and the electrolyte will decrease, and the internal resistance of the secondary battery will increase.

The present invention is completed to solve this problem, and its purpose is to provide an electrolyte composition and a secondary battery that can reduce the movement of electrolyte. [Means for solving the problem]

To achieve this object, the electrolyte composition of the present invention comprises a solid electrolyte having lithium ion conductivity, an electrolyte solution in which a lithium salt is dissolved, and a granular polymer dispersed in the electrolyte solution.

The secondary battery of the present invention comprises a positive electrode, an electrolyte layer and a negative electrode in sequence, and at least one of the positive electrode, the electrolyte layer and the negative electrode is composed of an electrolyte composition comprising a solid electrolyte having lithium ion conductivity, an electrolyte solution in which a lithium salt is dissolved, and a granular polymer dispersed in the electrolyte solution. [Effect of the invention]

The electrolyte composition of the present invention can reduce the migration of the electrolyte because the granular polymer is dispersed in the electrolyte. The secondary battery containing the electrolyte composition can reduce the increase of the internal resistance because the polymer reduces the migration of the electrolyte.

[Form used to implement the invention]

The preferred embodiments of the present invention are described below with reference to the attached drawings. FIG1 is a schematic cross-sectional view of a secondary battery 10 in an embodiment. The secondary battery 10 in this embodiment is a lithium ion solid-state battery in which the power generation element is composed of a solid. The so-called power generation element is composed of a solid means that the skeleton of the power generation element is composed of a solid, for example, the skeleton is not excluded from being impregnated with a liquid.

As shown in FIG1 , the secondary battery 10 sequentially includes a positive electrode 11, an electrolyte layer 14, and a negative electrode 15. The positive electrode 11, the electrolyte layer 14, and the negative electrode 15 are accommodated in an outer casing (not shown).

The positive electrode 11 is formed by stacking a collector layer 12 and a composite layer 13. The collector layer 12 is a conductive member. Examples of the material of the collector layer 12 include metals selected from Ni, Ti, Fe and Al, alloys containing two or more of these elements, stainless steel and carbon materials.

The composite layer 13 is composed of an electrolyte composition (described later). The electrolyte composition includes a solid electrolyte 18 and an active material 19. In order to reduce the electrical resistance of the composite layer 13, a conductive additive may be included in the composite layer 13. Examples of the conductive additive include carbon black, acetylene black, Ketjen black, carbon fiber, Ni, Pt, and Ag.

Examples of the active material 19 include metal oxides containing transition metals. Examples of the metal oxides containing transition metals include oxides containing Li and one or more elements selected from Mn, Co, Ni, Fe, Cr, and V. Examples of the metal oxides containing transition metals include LiCoO ₂ , LiNi _0.8 Co _0.15 Al _0.05 O ₂ , LiMn ₂ O ₄ , LiNiVO ₄ , LiNi _0.5 Mn _1.5 O ₄ , LiNi _1/3 Mn _1/3 Co _1/3 O ₄ , and LiFePO ₄ .

For the purpose of suppressing the reaction between the active material 19 and the solid electrolyte 18, a coating layer can be provided _on the surface of the active material 19. Examples of the coating layer include _{Al2O3 , ZrO2} , _LiNbO3 , _{Li4Ti5O12 , LiTaO3 , LiNbO3 , LiAlO2 , Li2ZrO3 , Li2WO4 , Li2TiO3} , _{Li2B4O7 , Li3PO4} , and _{Li2MoO4 .}

The negative electrode 15 is formed by overlapping the collector layer 16 and the composite layer 17. The collector layer 16 is a conductive member. Examples of the material of the collector layer 16 include metals selected from Ni, Ti, Fe, Cu and Si, alloys containing two or more of these elements, stainless steel and carbon materials.

The composite layer 17 is composed of an electrolyte composition (described later). The electrolyte composition includes a solid electrolyte 18 and an active material 20. In order to reduce the electrical resistance of the composite layer 17, a conductive additive may be included in the composite layer 17. Examples of the conductive additive include carbon black, acetylene black, Ketjen black, carbon fiber, Ni, Pt, and Ag.

Examples of the active material 20 include Li, Li-Al alloy, Li ₄ Ti ₅ O ₁₂ , graphite, In, Sn, Si, Si-Li alloy, and SiO.

FIG2 is a partial cross-sectional view of the electrolyte layer 14, which is an enlarged view of the portion shown in II of FIG1. The electrolyte layer 14 is composed of an electrolyte composition. The electrolyte composition includes a solid electrolyte 18, an electrolyte 21 in which a lithium salt is dissolved, and a granular polymer 22 dispersed in the electrolyte 21. The electrolyte composition of the composite layer 13 constituting the positive electrode 11 and the composite layer 17 constituting the negative electrode 15 also includes the electrolyte 21 and the polymer 22.

The solid electrolyte 18 is a solid material that conducts lithium ions. The solid electrolyte 18 includes one or more selected from oxides, sulfides, hydrides, and organic systems. Oxide-based solid electrolytes 18 are preferred because they do not generate toxic gases when exposed to the atmosphere. The solid electrolyte 18 may also be a complex in which a hydride is bonded to the surface of an oxide, for example.

Examples of the oxide-based solid electrolyte 18 include oxides having a NASICON structure, oxides having a calcite structure, and oxides having a garnet structure. Examples of oxides having a NASICON structure include oxides containing at least Li, M (M is one or more elements selected from Ti, Zr, and Ge), and P, such as Li(Al,Ti) ₂ ( _PO4 ) ₃ and Li(Al,Ge) ₂ ( _PO4 ) ₃ . Examples of oxides having a calcite structure include oxides containing at least _Li , Ti, and La, such as La2 _{/3- xLi3xTiO3} .

The basic composition of the garnet-type oxide is Li ₅ La ₃ M ₂ O ₁₂ (M=Nb, Ta). The solid electrolyte 18 including the garnet-type oxide preferably includes Li, La, Zr and O. The solid electrolyte 18 can be exemplified by Li ₇ La ₃ Zr ₂ O ₁₂ in which the pentavalent M cations of the basic composition are replaced with tetravalent cations.

In addition to Li, La and Zr, the solid electrolyte 18 can also contain at least one element selected from the group consisting of Mg, Al, Si, Ca, Ti, V, Ga, Sr, Y, Nb, Sn, Sb, Ba, Hf, Ta, W, Bi, Rb and lanthanide elements (except La). Examples include: Li ₆ La ₃ Zr _1.5 W _0.5 O ₁₂ , Li _6.15 La ₃ Zr _1.75 Ta _0.25 Al _0.2 O ₁₂ , Li _6.15 La ₃ Zr _1.75 Ta _0.25 Ga _0.2 O ₁₂ , Li _6.25 La ₃ Zr ₂ Ga _0.25 O ₁₂ , Li _6.4 La ₃ Zr _1.4 Ta _0.6 O ₁₂ , Li _6.5 La ₃ Zr _1.75 Te _0.25 O ₁₂ , Li _6.75 La ₃ Zr _1.75 Nb _0.25 O ₁₂ , Li _6.9 La ₃ Zr _1.675 Ta _0.289 Bi _0.036 O ₁₂ , Li _6.46 Ga _0.23 La ₃ Zr _1.85 Y _0.15 O ₁₂ , Li _6.8 La _2.95 Ca _0.05 Zr _1.75 Nb _0.25 O ₁₂ , Li _7.05 La _3.00 Zr _1.95 Gd _0.05 O ₁₂ , Li _6.20 Ba _0.30 La _2.95 Rb _0.05 Zr ₂ O ₁₂ .

The solid electrolyte 18 is particularly suitable to contain at least one of Mg and element A (A is at least one element selected from the group including Ca, Sr and Ba), and the molar ratio of each element satisfies all of the following (1) to (3); or contains both Mg and element A, and the molar ratio of each element satisfies all of the following (4) to (6). Element A improves the ion conductivity of the solid electrolyte 18, so Sr is preferred. (1) 1.33≦Li/(La+A)≦3 (2) 0≦Mg/(La+A)≦0.5 (3) 0≦A/(La+A)≦0.67 (4) 2.0≦Li/(La+A)≦2.5 (5) 0.01≦Mg/(La+A)≦0.14 (6) 0.04 ≦A/(La+A)≦0.17.

Examples of the sulfide-based solid electrolyte 18 include crystalline thio-LISICON type, Li ₁₀ GeP ₂ S ₁₂ type, thiogermanite type, glass and glass ceramics represented by Li ₇ P ₃ S ₁₁ type and Li ₂ S P ₂ S _5. Examples of the hydride-based solid electrolyte 18 include solid solutions of LiBH ₄ and lithium halide compounds (LiI, LiBr, LiCl) and lithium amide (LiNH ₂ ). Examples of the organic-based solid electrolyte 18 include polyethylene oxide, polypropylene oxide, and polyacrylonitrile.

The electrolyte 21 is a solution in which a lithium salt is dissolved in a solvent. The lithium salt is a compound used to transfer lithium ions between the positive electrode 11 and the negative electrode 15. Examples of the anion of the lithium salt include halogenide ions (I ^- , Cl ^- , Br ^- and the like), SCN ^- , BF ₄ ^- , BF ₃ (CF ₃ ) ^- , BF ₃ (C ₂ F ₅ ) ^- , PF ₆ ^- , ClO ₄ ^- , SbF ₆ ^- , N(SO ₂ F) ₂ ^- , N(SO ₂ CF ₃ ) ₂ ^- , N(SO ₂ C ₂ F ₅ ) ₂ ^- , B(C ₆ H ₅ ) ₄ ^- , B(O ₂ C ₂ H ₄ ) ₂ ^- , C(SO ₂ F) ₃ ^- , C(SO ₂ CF ₃ ) ₃ ^- , CF ₃ COO ^- , CF ₃ SO ₂ O ^- , C ₆ F ₅ SO ₂ O ^- , B(O ₂ C ₂ O ₂ ) ₂ ^- .

N(SO ₂ F) ₂ ^- is sometimes abbreviated as [FSI] ^- , which is called bis(fluorosulfonyl)imide anion; N(SO ₂ CF ₃ ) ₂ ^- is abbreviated as [TFSI] ^- , which is called bis(trifluoromethanesulfonyl)imide anion; B(O ₂ C ₂ O ₂ ) ₂ ^- is abbreviated as [BOB] ^- , which is called bis(oxalatoborate) anion; C(SO ₂ F) ₃ ^- is abbreviated as [f3C] ^- , which is called tris(fluorosulfonyl)carbon anion.

Examples of the lithium salt include at least one selected from the group consisting of LiPF ₆ , LiBF ₄ , Li[FSI], Li[TFSI], Li[f 3 C], Li[BOB], LiClO ₄ , LiBF ₃ (CF ₃ ), LiBF ₃ (C ₂ F ₅ ), LiBF ₃ (C ₃ F ₇ ), LiBF ₃ (C ₄ F ₉ ), LiC(SO ₂ CF ₃ ) ₃ , LiCF ₃ SO ₂ O, LiCF ₃ COO, and LiRCOO (R is an alkyl group having 1 to 4 carbon atoms, a phenyl group, or a naphthyl group).

The solvent of the electrolyte 21 is not particularly limited as long as it is a liquid within the operating temperature range of the secondary battery 10. Examples of the solvent include carbonates, aliphatic carboxylates, phosphates, γ-lactones, ethers, nitriles, cyclobutane sulfonate, dimethyl sulfoxide, fluorocarbon solvents, and ionic liquids. A mixture of these may also be used.

Examples of the carbonate ester include cyclic carbonates such as propylene carbonate, ethyl carbonate, butyl carbonate, vinyl carbonate, vinyl ethyl carbonate, and fluoroethyl carbonate; and chain carbonates such as dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate.

Examples of aliphatic carboxylic acid esters include methyl formate, methyl acetate, and ethyl propionate. Examples of phosphate esters include trimethyl phosphate. Examples of γ-lactones include γ-butyrolactone. Examples of ethers include chain ethers such as 1,2-dialkoxyethane, 1,3-diol Cyclic ethers such as tetrahydrofuran, 2-methyltetrahydrofuran, etc. Nitriles include acetonitrile and propionitrile. Fluorocarbon solvents are compounds and their derivatives in which the hydrogen atom of a hydrocarbon is replaced by a fluorine atom.

An ionic liquid is a compound containing cations and anions, which is liquid at room temperature and pressure. As long as the solvent is an ionic liquid, the flame retardancy of the electrolyte can be improved. The ionic liquid is preferably one containing at least one selected from the group consisting of ammonium, imidazolium, pyrrolidinium and piperidinium as a cationic component.

The anion component of the ion liquid is not particularly limited. Examples ^of the anion component include inorganic anions such as _BF4- ^, N( _SO2F ) _2- ^, and organic anions such as B( _C6H5 ) _4- ^, _{CH3SO3- , CF3SO3-} , ^N ( _SO2CF3 ) _2- ^, and N( _SO2C4F9 ) _2- ^. _It is preferred that the anion component of the ion liquid is the same as the _anion component of the lithium salt because _it is easy to control the coordination ₍ interaction ₎ between the lithium ions and anions contained in the electrolyte 21.

Examples of the ionic liquid include N,N-diethyl-N-methyl-N-(2-methoxyethyl)ammonium-bis(fluorosulfonyl)imide (DEME-FSI), N,N-diethyl-N-methyl-N-(2-methoxyethyl)ammonium-bis(trifluoromethanesulfonyl)imide (DEME-TFSI), 1-ethyl-3-methylimidazolium-bis(fluorosulfonyl)imide (EMI-FSI), 1-ethyl-3-methylimidazolium-bis(fluorosulfonyl)imide (EMI-FSI), Imidazolium-bis(trifluoromethanesulfonyl)imide (EMI-TFSI), N-butyl-N-methylpiperidinium-bis(fluorosulfonyl)imide, N-methyl-N-propylpiperidinium-bis(trifluoromethanesulfonyl)imide, N-methyl-N-propylpiperidinium-bis(fluorosulfonyl)imide (P13-FSI), N-methyl-N-propylpiperidinium-bis(trifluoromethanesulfonyl)imide (P13-TFSI).

The various physical properties and functions of the electrolyte 21 are determined by the types of lithium salt and solvent, and the salt concentration. In order to ensure lithium ion conductivity, the salt concentration (lithium ion concentration) of the electrolyte is, for example, 0.5-5 mol/dm ³ .

In the electrolyte layer 14 (electrolyte composition), the content (volume %) of the electrolyte 21 relative to the total amount of the solid electrolyte 18 and the electrolyte 21 is preferably 50 volume % or less (but 0 volume %). That is, solid electrolyte: electrolyte = (100-X): X, 0 <X ≦ 50. This is because the electrolyte 21 existing between the solid electrolyte 18 and the solid electrolyte 18 ensures ion conductivity and reduces the occurrence of electrolyte 21 seepage.

The content (volume %) of the electrolyte solution 21 is determined by freezing the electrolyte layer 14 or embedding the electrolyte layer 14 in a tetrafunctional epoxy resin or the like and fixing it, and then analyzing a 5000-fold field of view randomly selected from a cross section of the electrolyte layer 14 (a polished surface or a surface obtained by focused ion beam (FIB) irradiation) using a scanning electron microscope (SEM) equipped with an energy dispersive X-ray spectrometer (EDS). The analysis is to identify the distribution of elements or to analyze the contrast of reflected electron images, thereby identifying the area of the solid electrolyte 18 and the area of the electrolyte 21, and taking the ratio of the area in the cross section of the electrolyte layer 14 as the ratio of the volume in the electrolyte layer 14 to obtain the content (volume %) of the electrolyte 21.

The polymer 22 is a granular compound (polymer) dispersed in the electrolyte 21. Examples of the material of the polymer 22 include polyethylene, polypropylene, polyethylene terephthalate, polystyrene, polyamide, polyvinyl alcohol, ethylene vinyl alcohol copolymer, polyvinylidene chloride, polyacrylonitrile, polycarbonate, and polysilicone. The solvent of the electrolyte 21 is selected so as not to dissolve the polymer 22.

The polymer 22 is dispersed in the electrolyte 21 present around the solid electrolyte 18, so the polymer 22 fills a part of the gap between the solid electrolyte 18 and the solid electrolyte 18. As a result, since the structure including the solid electrolyte 18, the electrolyte 21 and the polymer 22 can be easily made dense, the area of the solid electrolyte 18 in contact with the electrolyte 21 can not be reduced. Therefore, the ion conductivity of the electrolyte layer 14 can be ensured. For example, the solid electrolyte 18 of the oxide system usually has a large grain boundary resistance, but by the electrolyte 21 dispersed with the polymer 22 being present between the solid electrolyte 18 and the solid electrolyte 18, the grain boundary resistance can be reduced.

The polymer 22 fills a part of the gap between the solid electrolytes 18 and the solid electrolytes 18, so that the electrolyte 21 existing between the solid electrolytes 18 and the solid electrolytes 18 becomes difficult to move. Since the electrolyte 21 is difficult to move, even if an external force is applied to the electrolyte layer 14 or the temperature around the electrolyte layer 14 rises, it is possible to prevent a small amount of electrolyte 21 from being generated between the solid electrolytes 18, or to prevent the electrolyte 21 from leaking. The contact area between the solid electrolyte 18 and the electrolyte 21 can be prevented from being reduced, so that the internal resistance of the electrolyte layer 14 can be prevented from increasing.

The polymer 22 contained in the composite layers 13 and 17 of the positive electrode 11 and the negative electrode 15 is also dispersed in the electrolyte 21. The polymer 22 exists between the solid electrolyte 18 and the solid electrolyte 18, or between the solid electrolyte 18 and the active materials 19 and 20, or between the active materials 19 and 20 and the active materials 19 and 20. The polymer 22 can reduce the migration of the electrolyte 21, so that the area where the electrolyte 21 contacts the solid electrolyte 18 and the active materials 19 and 20 will not be reduced. This ensures ion conduction between the solid electrolyte 18 and the solid electrolyte 18, ion conduction between the solid electrolyte 18 and the active materials 19 and 20, and ion conduction between the active materials 19 and 20.

In the secondary battery 10 that stores energy by inserting and removing lithium ions from the active materials 19 and 20, the volume of the active materials 19 and 20 changes with charge and discharge. The polymer 22 exists between the solid electrolyte 18 and the active materials 19 and 20, or between the active materials 19 and 20 and the active materials 19 and 20. Therefore, the polymer 22 buffers the volume change of the active materials 19 and 20 accompanying charge and discharge, reduces the damage of the active materials 19 and 20, and can maintain the structure of the composite layers 13 and 17.

FIG3(a) is a cross-sectional view of a polymer 22, and FIG3(b) is a cross-sectional view of another polymer 22. The so-called "polymer 22 is granular" means that most polymers 22 have a cross-sectional view close to a sphere. In order to confirm that the polymer 22 is spherical, first, an image of the polymer 22 appearing on a cross-sectional view perpendicular to the interface between the positive electrode 11 (see FIG1) and the electrolyte layer 14 and the interface between the negative electrode 15 and the electrolyte layer 14 is obtained using SEM. The range of the image is set to a square range of 100 μm in length and 100 μm in width on the object observed by SEM.

When the thickness of the electrolyte layer 14 is less than 100 μm and a square range of 100 μm in length and 100 μm in width cannot be set on the electrolyte layer 14, the square range can be enlarged not only to the electrolyte layer 14 but also to the composite layers 13 and 17 including the polymer 22. In addition, when an image of a cross section of any one of the electrolyte layer 14, the composite layer 13, and 17 is obtained, if the thickness of the electrolyte layer 14, the composite layer 13, and 17 is less than 100 μm, the short side of the range to obtain the image is set to the maximum in the thickness direction of the object, and the long side is set along the interface of the object so that the area becomes 10000 ^μm2 . In this way, an image of a range of ¹⁰⁰⁰⁰ μm2 on the object is obtained.

After obtaining the cross-sectional image, as shown in FIG3(a) and FIG3(b), the circle 24 with the smallest area among the circles that touch the outer shape 23 of the polymer 22 from the outside and the circle 25 with the largest area among the circles that touch the outer shape 23 from the inside are obtained for each polymer 22 through image processing. The diameter Do of the circle 24 and the diameter Di of the circle 25 are obtained. When the number of polymers 22 in the image that satisfy the condition (Do-Di)/2＜Di accounts for more than 80% of the total number of polymers 22 in the image, it can be said that most of the polymers 22 have a cross-section close to a sphere, and therefore the polymer 22 is called spherical.

The specific energy of the polymer 22 can be analyzed by Fourier transform infrared spectroscopy (FTIR) or microscopic infrared spectroscopy combining a microscope and FTIR. Alternatively, the polymer 22 can be removed from the object and analyzed. It can also be analyzed using a nuclear magnetic resonance device (NMR).

The particle size of the polymer 22 refers to the diameter of a circle having an area equivalent to the area of each particle of the polymer 22 obtained by analyzing the image of the polymer 22 appearing in the cross section (equivalent circle diameter). The particle size of the solid electrolyte 18 refers to the equivalent circle diameter of the solid electrolyte 18 obtained by analyzing the image of the solid electrolyte 18 appearing in the cross section. The maximum value of the particle size of the polymer 22 is smaller than the maximum value of the particle size of the solid electrolyte 18. This can make the effect of the polymer 22 of reducing the migration of the electrolyte 21 more effective.

The polymer 22 is preferably mixed at a ratio of 5-30 vol% relative to the solid electrolyte 18. This is because the polymer 22 between the solid electrolyte 18 and the solid electrolyte 18, the polymer 22 between the solid electrolyte 18 and the active substances 19 and 20, and the polymer 22 between the active substances 19 and 20 will not excessively hinder ion conduction, while ensuring a dense structure including the solid electrolyte 18, the electrolyte 21 and the polymer 22.

The material of polymer 22 is preferably polysilicone. This is because it has excellent heat resistance and chemical stability and a wide potential window. Polysilicone is a general term for polymers of organic silicon compounds with -Si(R ¹ R ² )-O- as the skeleton, formed by organic groups bonded to siloxane bonds (Si-O). The organic groups R ¹ R ² can be exemplified by functional groups such as methyl, vinyl, phenyl, alkoxy, and hydroxyl. Polysilicone can be classified into polysilicone rubber and polysilicone resin according to its structure and properties.

Silicone rubber has the characteristics of containing many organic groups and having rubber elasticity. A typical example is a structure formed by cross-linking dimethyl polysiloxane. Silicone rubber exhibits rubber elasticity in the range of -50°C to 250°C. The linear structure formed by cross-linking dimethyl polysiloxane can be exemplified by a block of linear polyorganosiloxane represented by -(R ³ ₂ SiO) _a -.

^R3 is selected from the following monovalent organic groups or monovalent organic groups formed by replacing a part of hydrogen atoms bonded to such carbon atoms with halogen atoms, and the monovalent organic groups are selected from alkyl groups such as methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, decyl, dodecyl, tetradecyl, hexadecyl, octadecyl, etc.; cycloalkyl groups such as cyclopentyl, cyclohexyl, cyclooctyl, etc.; aryl groups such as phenyl, tolyl, etc., and one or more monovalent organic groups containing 1 to 20 carbon atoms. In order to ensure the smoothness of the surface, a can be 5 to 5000, preferably 10 to 1000.

Polysilicone has many three-dimensional network structures with R ³ SiO _3/2 and R ³ ₂ SiO _2/2 as constituent units. R ³ is the above-mentioned organic group. Polysilicone has excellent heat resistance and does not swell in many solvents.

Examples of polymer 22 include those made entirely of silicone rubber, those made entirely of silicone resin, and composites of silicone rubber and silicone resin. Examples of composites include those in which the surface of silicone rubber is covered with silicone resin. Polymer 22 is preferably one having silicone resin on the surface. This is because, compared with a polymer having silicone rubber on the surface, the dispersibility is good and the potential window is further widened. Examples of polymer 22 having silicone resin on the surface include those made entirely of silicone resin and those in which the surface of silicone rubber is covered with silicone resin. The composite in which the surface of the silicone rubber is covered with the silicone resin is better because the silicone rubber shows elasticity.

The electrolyte layer 14 and the composite layers 13 and 17 may contain a binder. The binder is used to bond the solid electrolyte 18 and the active substances 19 and 20. The binder and the electrolyte 21 may exist separately, or the binder and the electrolyte 21 may exist mixedly to form a gel. The binder is not particularly limited, but preferably has a potential window wider than the potential window of the electrolyte 21. An example of the binder is polyvinylidene fluoride-hexafluoropropylene copolymer. A solvent for dissolving the binder may be contained in the electrolyte layer 14 and the composite layers 13 and 17. An example of the solvent is carbonate, acetonitrile, and 1,2-dimethoxyethane.

When the binder is included, the polymer 22 is preferably mixed at a ratio of 5-30 vol% relative to the binder. This is because the polymer 22 does not interfere with the adhesion of the binder and the elasticity of the electrolyte layer 14 and the composite layers 13 and 17 is ensured. The content (volume %) of the binder can be specified by the ratio of the area of the binder to the area of the cross section of the electrolyte layer 14 and the composite layers 13 and 17. The area of the binder can be obtained by image analysis using SEM-EDS analysis.

The secondary battery 10 is manufactured, for example, as follows. A solution containing a binder is mixed with an electrolyte 21 containing a lithium salt dissolved in a solvent and a solid electrolyte 18 to prepare a slurry. After forming a thin strip, it is dried to obtain a green sheet (electrolyte sheet) for the electrolyte layer 14.

The electrolyte 21 and the solid electrolyte 18 are mixed with the active material 19, and further mixed with the solution containing the binder and the polymer 22 to prepare a slurry. After the thin strip is formed on the collector layer 12, it is dried to obtain a green sheet (positive electrode sheet) for the positive electrode 11.

The electrolyte 21 and the solid electrolyte 18 are mixed with the active material 20, and further mixed with the solution containing the binder and the polymer 22 to prepare a slurry. After the thin strip is formed on the collector layer 16, it is dried to obtain a green sheet (negative electrode sheet) for the negative electrode 15.

After the electrolyte sheet, the positive electrode sheet and the negative electrode sheet are cut into predetermined shapes, the positive electrode sheet, the electrolyte sheet and the negative electrode sheet are stacked in sequence and pressed together to form an integrated structure. The terminals (not shown) are connected to the collector layers 12 and 16 respectively and sealed in an outer shell (not shown), and a secondary battery 10 including a positive electrode 11, an electrolyte layer 14 and a negative electrode 15 in sequence can be obtained. The secondary battery 10 can reduce the increase of internal resistance because the polymer 22 contained in the positive electrode 11, the electrolyte layer 14 and the negative electrode 15 reduces the movement of the electrolyte 21.

As mentioned above, the present invention has been described based on the embodiments, but the present invention is not limited to the above embodiments, and it can be easily inferred that various improvements and modifications are possible within the scope of the gist of the present invention.

In the embodiment, the secondary battery 10 is described as having a positive electrode 11 with a composite layer 13 provided on one side of a collector layer 12 and a negative electrode 15 with a composite layer 17 provided on one side of a collector layer 16, but the present invention is not necessarily limited to this. For example, in a secondary battery having electrode layers (so-called bipolar electrodes) with composite layers 13 and 17 provided on both sides of a collector layer 12, each element in the embodiment can be applied. If the bipolar electrodes and the electrolyte layer 14 are alternately stacked and housed in an outer case (not shown), a so-called bipolar structure secondary battery can be obtained.

In the embodiment, the case where the composite layers 13, 17 and the electrolyte layer 14 are all made of the electrolyte composition has been described, but the present invention is not necessarily limited to this. The secondary battery only needs to be one in which at least one of the composite layers 13, 17 and the electrolyte layer 14 is made of the electrolyte composition.

In the embodiment, a lithium ion battery (secondary battery) including an electrolyte composition is exemplified and a secondary battery 10 having an electrode layer (a positive electrode 11 and a negative electrode 15) and an electrolyte layer 14 is described, but the present invention is not necessarily limited thereto. Other secondary batteries include lithium sulfur batteries, lithium oxygen batteries, lithium air batteries, and other secondary batteries, primary batteries, and electrolytic capacitors.

10: Secondary battery 11: Positive electrode 14: Electrolyte layer 15: Negative electrode 18: Solid electrolyte 21: Electrolyte 22: Polymer

FIG1 is a cross-sectional view of a secondary battery in an embodiment. FIG2 is a partial cross-sectional view of an electrolyte layer in which the portion shown in II of FIG1 is enlarged. FIG3 (a) is a cross-sectional view of a polymer, and (b) is a cross-sectional view of another polymer.

10: Secondary battery

11: Positive pole

12: Collector layer

13: Composite layer

14: Electrolyte layer

15: Negative

16: Collector layer

17: Composite layer

18: Solid electrolyte

19: Active substances

20: Active substances

Claims (4)

An electrolyte composition includes a solid electrolyte having lithium ion conductivity and an electrolyte solution in which a lithium salt is dissolved, and includes a granular polymer dispersed in the electrolyte solution. The electrolyte composition of claim 1, wherein the polymer is polysilicon. The electrolyte composition of claim 2, wherein the polymer has a polysilicone resin on its surface. A secondary battery comprises a positive electrode, an electrolyte layer and a negative electrode in sequence, wherein at least one of the positive electrode, the electrolyte layer and the negative electrode is composed of the electrolyte composition of any one of claims 1 to 3.