JP6924264B2 - Semi-solid electrolyte, semi-solid electrolyte, semi-solid electrolyte layer and secondary battery - Google Patents

Description

The present invention relates to a semi-solid electrolyte, a semi-solid electrolyte, a semi-solid electrolyte layer and a secondary battery.

As an electrolyte of a secondary battery, a method of mixing inorganic fine particles with an ionic liquid to thicken, gel, or solidify the liquid is known. As a technique relating to an electrolyte, Non-Patent Document 1 discloses an electrolyte prepared by mixing grime with an imide salt and nanosilica.

scientific reports, DOI: 10.1038 / srep08869

Many conventional lithium ion secondary battery, includes laden organic electrolyte solution LiPF ₆ and LiBF _4, PF ₆ ^- and BF ₄ ^- a part of the anions of the film on a metal electrode collector It is formed and suppresses the elution of the electrode current collector. On the other hand, Non-Patent Document 1 applies Liimide salt instead of _{LiPF 6} or LiBF ₄ from the viewpoint of ionic conductivity and atmospheric compatibility, and does not include _{LiPF 6} or LiBF _4. Therefore, the elution of the metal in the current collector is likely to proceed, and the eluted metal may hinder Li conduction in the lithium ion secondary battery and reduce the battery performance.
An object of the present invention is to suppress elution of an electrode current collector.

The features of the present invention for solving the above problems are as follows, for example.

A mixed solvent comprising a semisolid electrolyte solvent and an electrolyte salt, and comprises a first additive, the anion of the first additive is BF ₄ ^- or PF ₆ ^- a is the formula weight of the cation of the first additive Semi-solid electrolyte that is 100 or more.
This specification includes the disclosure content of Japanese Patent Application No. 2017-144079, which is the basis of the priority of the present application.

According to the present invention, elution of the electrode current collector can be suppressed. Issues, configurations and effects other than those described above will be clarified by the following description of the embodiments.

It is an external view of a secondary battery. It is sectional drawing of a secondary battery. It is a table which shows the result of an Example and a comparative example. It is a graph which shows the charge / discharge cycle test result.

Hereinafter, embodiments of the present invention will be described with reference to the drawings and the like. The following description shows specific examples of the contents of the present invention, and the present invention is not limited to these explanations, and various works by those skilled in the art will be made within the scope of the technical ideas disclosed in the present specification. It can be changed and modified. Further, in all the drawings for explaining the present invention, those having the same function may be designated by the same reference numerals, and the repeated description thereof may be omitted.

The "~" described in the present specification is used to mean that the numerical values described before and after it are included as the lower limit value and the upper limit value. In the numerical range described stepwise in the present specification, the upper limit value or the lower limit value described in one numerical range may be replaced with the upper limit value or the lower limit value described in another stepwise. The upper or lower limit of the numerical range described herein may be replaced with the values shown in the examples.

In this specification, a lithium ion secondary battery will be described as an example of the secondary battery. A lithium ion secondary battery is an electrochemical device that stores or makes available electrical energy by storing and releasing lithium ions into electrodes in an electrolyte. This is called by another name of a lithium ion battery, a non-aqueous electrolyte secondary battery, and a non-aqueous electrolyte secondary battery, and all of the batteries are the subject of the present invention. The technical idea of the present invention can also be applied to a sodium ion secondary battery, a magnesium ion secondary battery, a calcium ion secondary battery, a zinc secondary battery, an aluminum ion secondary battery and the like.

FIG. 1 is an external view of a secondary battery according to an embodiment of the present invention. FIG. 2 is a cross-sectional view of a secondary battery according to an embodiment of the present invention. 1 and 2 are laminated secondary batteries, and the secondary battery 1000 has a positive electrode 100, a negative electrode 200, an exterior body 500, and a semi-solid electrolyte layer 300. The exterior body 500 accommodates a semi-solid electrolyte layer 300, a positive electrode 100, and a negative electrode 200. The material of the exterior body 500 can be selected from materials having corrosion resistance to non-aqueous electrolytes such as aluminum, stainless steel, and nickel-plated steel. The present invention can also be applied to a rechargeable secondary battery.

In the secondary battery 1000, an electrode body 400 composed of a positive electrode 100, a semi-solid electrolyte layer 300, and a negative electrode 200 is laminated. The positive electrode 100 or the negative electrode 200 may be referred to as an electrode or an electrode for a secondary battery. The positive electrode 100, the negative electrode 200, or the semi-solid electrolyte layer 300 may be referred to as a secondary battery sheet. An electrode having a semi-solid electrolyte layer 300 and a positive electrode 100 or a negative electrode 200 having an integral structure may be referred to as an electrode for a secondary battery with a semi-solid electrolyte layer.

The positive electrode 100 has a positive electrode current collector 120 and a positive electrode mixture layer 110. Positive electrode mixture layers 110 are formed on both sides of the positive electrode current collector 120. The negative electrode 200 has a negative electrode current collector 220 and a negative electrode mixture layer 210. Negative electrode mixture layers 210 are formed on both sides of the negative electrode current collector 220. The positive electrode mixture layer 110 or the negative electrode mixture layer 210 may be referred to as an electrode mixture layer, and the positive electrode current collector 120 or the negative electrode current collector 220 may be referred to as an electrode current collector.

The positive electrode current collector 120 has a positive electrode tab portion 130. The negative electrode current collector 220 has a negative electrode tab portion 230. The positive electrode tab portion 130 or the negative electrode tab portion 230 may be referred to as an electrode tab portion. The electrode mixture layer is not formed on the electrode tab portion. However, the electrode mixture layer may be formed on the electrode tab portion as long as the performance of the secondary battery 1000 is not adversely affected. The positive electrode tab portion 130 and the negative electrode tab portion 230 project to the outside of the exterior body 500, and the plurality of protruding positive electrode tab portions 130 and the plurality of negative electrode tab portions 230 are bonded to each other by, for example, ultrasonic bonding. Then, a parallel connection is formed in the secondary battery 1000. The present invention can also be applied to a bipolar type secondary battery in which an electrical series connection is formed in the secondary battery 1000.

The positive electrode mixture layer 110 has a positive electrode active material, a positive electrode conductive agent, and a positive electrode binder. The negative electrode mixture layer 210 has a negative electrode active material, a negative electrode conductive agent, and a negative electrode binder. The semi-solid electrolyte layer 300 has a semi-solid electrolyte binder and a semi-solid electrolyte. The semi-solid electrolyte has particles and a semi-solid electrolyte. The positive electrode active material or the negative electrode active material may be referred to as an electrode active material, the positive electrode conductive agent or the negative electrode conductive agent may be referred to as an electrode conductive agent, and the positive electrode binder or the negative electrode binder may be referred to as an electrode binder.

The pores of the electrode mixture layer may be filled with a semi-solid electrolytic solution. In this case, the semi-solid electrolyte is injected into the secondary battery 1000 from one vacant side of the exterior body 500 or the liquid injection hole, and the pores of the electrode mixture layer are filled with the semi-solid electrolyte. In this case, the particles contained in the semi-solid electrolyte are not required, and the particles such as the electrode active material and the electrode conductive agent in the electrode mixture layer function as particles, and these particles hold the semi-solid electrolyte. As another method of filling the pores of the electrode mixture layer with the semi-solid electrolyte, a slurry in which the semi-solid electrolyte, the electrode active material, the electrode conductive agent, and the electrode binder are mixed is prepared, and the prepared slurry is used as the electrode current collector. There is a method of applying together on top.

A separator such as a microporous membrane may be used for the semi-solid electrolyte layer 300. As the separator, polyolefins such as polyethylene and polypropylene, glass fibers, and the like can be used. When a microporous film is used for the separator, the semi-solid electrolyte is applied to the semi-solid electrolyte layer 300 by injecting the semi-solid electrolyte into the secondary battery 1000 through an empty side of the exterior body 500 or the liquid injection hole. It is filled.

The semi-solid electrolyte may be contained in only one or two or more of the positive electrode 100, the negative electrode 200, or the semi-solid electrolyte layer 300.

<Electrode conductive agent>
The electrode conductive agent improves the conductivity of the electrode mixture layer. As the electrode conductive agent, Ketjen black, acetylene black, graphite and the like are preferably used, but the present invention is not limited thereto.

<Electrode binder>
The electrode binder binds the electrode active material and the electrode conductive agent in the electrode. Electrode binders include, but are not limited to, styrene-butadiene rubber, carboxymethyl cellulose, polyvinylidene fluoride (PVDF) and mixtures thereof.

<Positive electrode active material>
In the positive electrode active material showing a noble potential, lithium ions are desorbed in the charging process, and lithium ions desorbed from the negative electrode active material in the negative electrode mixture layer are inserted in the discharging process. A lithium composite oxide containing a transition metal is desirable as a material for the positive electrode active material, and specific examples thereof include LiMO ₂ , Li [LiM] O ₂ , LiM ₂ O ₄ , LiMPO ₄ , LiMVO _x , and LiMBO _{3 having an excess composition of Li.} , Li ₂ MSiO ₄ (provided that at least one type of M = Co, Ni, Mn, Fe, Cr, Zn, Ta, Al, Mg, Cu, Cd, Mo, Nb, W, Ru, etc. is included). .. Further, a part of oxygen in these materials may be replaced with another element such as fluorine. In addition, sulfur, chalcogenides such as _{TiS 2} , MoS ₂ , Mo ₆ S ₈ , and TiSe ₂ , vanadium oxides such as _{V 2} O ₅ , halides such as _{FeF 3, and Fe (MoO 4} ) ₃ , which constitutes polyanions, Examples include, but are not limited to, quinone-based organic crystals such as Fe ₂ (SO ₄ ) ₃ and Li ₃ Fe ₂ (PO ₄ ) _3. Further, the amounts of lithium and anions in the chemical composition may deviate from the above constant ratio composition.

<Positive current collector 120>
As the positive electrode current collector 120, an aluminum foil having a thickness of 1 μm to 100 μm, or an aluminum perforated foil having a thickness of 10 μm to 100 μm and a hole diameter of 0.1 mm to 10 mm, an expanded metal, a foamed metal plate, or the like is used. In addition to aluminum, stainless steel and titanium can also be used as the material. Any positive electrode current collector 120 can be used without being limited by the material, shape, manufacturing method, and the like.

A positive electrode slurry in which a positive electrode active material, a positive electrode conductive agent, a positive electrode binder, and an organic solvent are mixed is attached to the positive electrode current collector 120 by a doctor blade method, a dipping method, a spray method, or the like, and then the organic solvent is dried and rolled. The positive electrode 100 can be manufactured by pressure molding. A plurality of positive electrode mixture layers 110 may be laminated on the positive electrode current collector 120 by performing the process from application to drying a plurality of times. It is desirable that the thickness of the positive electrode mixture layer 110 is equal to or larger than the average particle size of the positive electrode active material. If the thickness of the positive electrode mixture layer 110 is made smaller than the average particle size of the positive electrode active material, the electron conductivity between adjacent positive electrode active materials may deteriorate.

<Negative electrode active material>
In the negative electrode active material, lithium ions are desorbed in the discharge process, and lithium ions desorbed from the positive electrode active material in the positive electrode mixture layer 110 are inserted in the charging process. As the material of the negative electrode active material showing a low potential, for example, a carbon-based material (for example, graphite, easily graphitized carbon material, amorphous carbon material, organic crystal, activated carbon, etc.), a conductive polymer material (for example, polyacene). , Polyparaphenylene, polyaniline, polyacetylene), lithium composite oxides (eg lithium titanate: Li ₄ Ti ₅ O ₁₂ and Li ₂ TiO ₄ ), metallic lithium, metals alloying with lithium (eg aluminum, silicon) , Tin and the like (including at least one kind) and oxides thereof can be used, but the present invention is not limited to this.

<Negative electrode current collector 220>
As the negative electrode current collector 220, a copper foil having a thickness of 1 μm to 100 μm, a copper perforated foil having a thickness of 1 μm to 100 μm and a pore diameter of 0.1 mm to 10 mm, an expanded metal, a foamed metal plate, or the like is used. In addition to copper, stainless steel, titanium, nickel, etc. can also be applied. Any negative electrode current collector 220 can be used without being limited by the material, shape, manufacturing method, and the like.

<Electrode>
An electrode mixture layer is prepared by adhering an electrode slurry, which is a mixture of an electrode active material, an electrode conductive agent, an electrode binder, and an organic solvent, to an electrode current collector by a coating method such as a doctor blade method, a dipping method, or a spray method. Will be done. Then, the electrode mixture layer is dried in order to remove the organic solvent, and the electrode mixture layer is pressure-molded by a roll press to prepare an electrode. The electrode slurry may contain a semi-solid electrolyte or a semi-solid electrolyte. A plurality of electrode mixture layers may be laminated on the electrode current collector by performing the process from application to drying a plurality of times. The thickness of the electrode mixture layer is preferably equal to or greater than the average particle size of the electrode active material. If the thickness of the electrode mixture layer is small, the electron conductivity between adjacent electrode active materials may deteriorate. If the electrode active material powder contains coarse particles having an average particle size equal to or larger than the thickness of the electrode mixture layer, the coarse particles are removed in advance by sieving classification, wind flow classification, etc., and particles having a thickness equal to or less than the thickness of the electrode mixture layer. Is desirable.

<Particles>
From the viewpoint of electrochemical stability, the particles are preferably insulating particles and are insoluble in a semi-solid electrolytic solution containing an organic solvent or an ionic liquid. As the particles, for example, _{oxide inorganic particles such as silica (SiO 2} ) particles, γ-alumina (Al ₂ O ₃ ) particles, ceria (CeO ₂ ) particles, and zirconia (ZrO ₂ ) particles can be preferably used. A solid electrolyte may be used as the particles. Examples of the solid electrolyte include particles of an oxide-based solid electrolyte such as Li-La-Zr-O and an inorganic solid electrolyte particle such as a sulfide-based solid electrolyte such as _{Li 10} Ge ₂ PS _12.

Since the holding amount of the semi-solid electrolytic solution is considered to be proportional to the specific surface area of the particles, the average particle size of the primary particles of the particles is preferably 1 nm to 10 μm. If the average particle size of the primary particles of the particles is large, the particles may not be able to properly hold a sufficient amount of the semi-solid electrolyte, and it may be difficult to form the semi-solid electrolyte. Further, when the average particle size of the primary particles of the particles is small, the intersurface force between the particles becomes large and the particles tend to aggregate with each other, which may make it difficult to form a semi-solid electrolyte. The average particle size of the primary particles of the particles is more preferably 1 nm to 50 nm, further preferably 1 nm to 10 nm. The average particle size of the primary particles of the particles can be measured by using a known particle size distribution measuring device using a laser scattering method.

<Semi-solid electrolyte>
The semi-solid electrolyte has a semi-solid electrolyte solvent, any low viscosity organic solvent, an electrolyte salt, a first additive, and any second additive. The semi-solid electrolyte solvent has an ionic liquid or an ether solvent having properties similar to those of an ionic liquid. An ionic liquid or an ether solvent may be referred to as a main solvent. An ionic liquid is a compound that dissociates into a cation and an anion at room temperature and maintains a liquid state. The ionic liquid may be referred to as an ionic liquid, a low melting point molten salt or a room temperature molten salt. The semi-solid electrolyte solvent is preferably low in volatility, specifically, having a vapor pressure of 150 Pa or less at room temperature from the viewpoint of stability in the atmosphere and heat resistance in the secondary battery.

When the electrode mixture layer contains a semi-solid electrolyte, the content of the semi-solid electrolyte in the electrode mixture layer is preferably 20% by volume to 40% by volume. When the content of the semi-solid electrolytic solution is small, the ionic conduction path inside the electrode mixture layer may not be sufficiently formed and the rate characteristics may deteriorate. Further, when the content of the semi-solid electrolytic solution is high, the semi-solid electrolytic solution may leak from the electrode mixture layer, and the active material becomes insufficient, resulting in a decrease in energy density.

Ionic liquids are composed of cations and anions. The ionic liquids are classified into imidazolium-based, ammonium-based, pyroridinium-based, piperidinium-based, pyridinium-based, morpholinium-based, phosphonium-based, sulfonium-based, and the like according to the cation species. Examples of the cations constituting the imidazolium-based ionic liquid include alkylimidazolium cations such as 1-ethyl-3-methylimidazolium and 1-butyl-3-methylimidazolium (BMI). The cations that make up the ammonium-based ionic liquid include, for example, N, N-diethyl-N-methyl-N- (2-methoxyethyl) ammonium (DEME), tetraamylammonium, and N, N, N-. There are alkylammonium cations such as trimethyl-N-propylammonium. Examples of the cations constituting the pyrrolidinium-based ionic liquid include alkylpyrrolidinium cations such as N-methyl-N-propylpyrrolidinium (Py13) and 1-butyl-1-methylpyrrolidinium. Examples of the cations constituting the piperidinium-based ionic liquid include alkyl piperidinium cations such as N-methyl-N-propyl piperidinium (PP13) and 1-butyl-1-methyl piperidinium. Examples of the cations constituting the pyridinium-based ionic liquid include alkylpyridinium cations such as 1-butylpyridinium and 1-butyl-4-methylpyridinium. Examples of the cation constituting the morpholinium-based ionic liquid include alkylmorpholinium such as 4-ethyl-4-methylmorpholinium. Examples of the cations constituting the phosphonium-based ionic liquid include alkylphosphonium cations such as tetrabutylphosphonium and tributylmethylphosphonium. Examples of the cations constituting the sulfonium-based ionic liquid include alkylsulfonium cations such as trimethylsulfonium and tributylsulfonium. Examples of anions paired with these cations include bis (trifluoromethanesulfonyl) imide (TFSI), bis (fluorosulfonyl) imide, tetrafluorobolate (BF ₄ ), hexafluorophosphate (PF ₆ ), and bis (penta). Fluoroethanesulfonyl) imide (BETI), trifluoromethanesulfonate (triflate), acetate, dimethylphosphate, dicyanamide, trifluoro (trifluoromethyl) borate and the like. These ionic liquids may be used alone or in combination of two or more.

As the electrolyte salt used together with the ionic liquid, a salt that can be uniformly dispersed in a solvent can be used. The cation consisting of lithium and the above anion can be used as a lithium salt, for example, lithium bis (fluorosulfonyl) imide (LiFSI), lithium bis (trifluoromethanesulfonyl) imide (LiTFSI), lithium bis (pentafluoroethane). Examples thereof include, but are not limited to, sulfonyl) imide (LiBETI), lithium tetrafluoroborate (LiBF ₄ ), lithium hexafluorophosphate (LiPF _{6), and lithium trifurate.} These electrolyte salts may be used alone or in combination of two or more.

The ether solvent constitutes a solvated ionic liquid together with the electrolyte salt. _{As an ether solvent, a symmetric glycol di represented by a known glyme (RO (CH 2} CH ₂ O) _n -R'(R, R'is a saturated hydrocarbon and n is an integer) having properties similar to those of an ionic liquid. A generic term for ether) can be used. From the viewpoint of ionic conductivity, tetraglyme (tetraethylene dimethyl glycol, G4), triglyme (triethylene glycol dimethyl ether, G3), pentaglycol (pentaethylene glycol dimethyl ether, G5), hexaglyme (hexaethylene glycol dimethyl ether, G6) It can be preferably used. Further, as an ether solvent, crown ether ( _{a general term for macrocyclic ethers represented by (-CH 2-} CH _2- O) _n (n is an integer)) can be used. Specifically, 12-crown-4, 15-crown-5, 18-crown-6, dibenzo-18-crown-6 and the like can be preferably used, but the present invention is not limited to this. These ether solvents may be used alone or in combination of two or more. It is preferable to use tetraglyme or triglyme because it can form a complex structure with the electrolyte salt.

Lithium salts such as LiFSI, LiTFSI, and LiBETI can be used as the electrolyte salt used together with the ether solvent, but the electrolyte salt is not limited to this. As the mixed solvent containing the semi-solid electrolyte solvent and the electrolyte salt, a mixture of the ether solvent and the electrolyte salt may be used alone or in combination of two or more.

The weight ratio of the main solvent in the semi-solid electrolyte is not particularly limited, but the weight ratio of the main solvent in the total solvent in the semi-solid electrolyte is 30% to 70% from the viewpoint of battery stability and high-speed charging / discharging. In particular, it is preferably 40% to 60%, and further preferably 45% to 55%.

<Low viscosity organic solvent>
The low viscosity organic solvent reduces the viscosity of the semi-solid electrolyte solvent and improves the ionic conductivity. Since the internal resistance of the semi-solid electrolyte solution containing the semi-solid electrolyte solvent is large, the internal resistance of the semi-solid electrolyte solution can be lowered by adding a low-viscosity organic solvent to increase the ionic conductivity of the semi-solid electrolyte solvent. .. However, since the semi-solid electrolyte solvent is electrochemically unstable, the decomposition reaction is promoted with respect to the battery operation, and the resistance of the secondary battery 1000 increases and the capacity decreases with the repeated operation of the secondary battery 1000. there is a possibility. Further, in the secondary battery 1000 using graphite as the negative electrode active material, there is a possibility that the cation of the semi-solid electrolyte solvent is inserted into the graphite during the charging reaction and destroys the graphite structure, so that the secondary battery 1000 cannot be repeatedly operated. There is.

The low-viscosity organic solvent is preferably a solvent having a viscosity lower than, for example, 140 Pa · s, which is the viscosity of a mixture of an ether solvent and an electrolyte salt at 25 ° C. As low-viscosity organic solvents, propylene carbonate (PC), trimethyl phosphate (TMP), gamma-butyl lactone (GBL), ethylene carbonate (EC), triethyl phosphate (TEP), tris phosphite (2,2,2- Examples thereof include trifluoroethyl) (TFP) and dimethyl methylphosphonate (DMMP). These low-viscosity organic solvents may be used alone or in combination of two or more. The above electrolyte salt may be dissolved in a low-viscosity organic solvent.

<First additive>
It is desirable that the semi-solid electrolyte contains a first additive that forms a film in which the metal does not easily elute even when the positive electrode current collector 120 is exposed to a high electrochemical potential. The first additive, PF ₆ ^- or BF ₄ ^- like include anionic species, and it is desirable to include a cationic species having a strong chemical bond to form a stable compound moisture atmosphere containing.

As one index indicating that the compound is stable in the atmosphere, the solubility in water and the presence or absence of hydrolysis can be mentioned. If the first additive is a solid, it should have a solubility in water of less than 1%. The presence or absence of hydrolysis can be evaluated by molecular structure analysis of the sample after mixing with water. Here, "not hydrolyzed" means that 95% of the residue after the first additive absorbs moisture or is mixed with water and then heated at 100 ° C. or higher to remove water is the same molecule as the first additive. It means that it shows the structure.

The first additive (MR) ⁺ A _n ^- is represented by. (MR) ⁺ A _n ^- is a cation, (MR) is ^+, M is nitrogen (N), boron (B), phosphorus (P), made from any of the sulfur (S), R is a hydrocarbon radical Consists of. Further, (MR) ⁺ A _n ^- anions A _n ^- a is, BF ₄ ^- or PF ₆ ^- is preferably used. The anion of the first additive BF ₄ ^- or PF ₆ ^- is to be in, it can be efficiently suppressed the elution of the positive electrode current collector 120. This, BF ₄ ^- or PF ₆ ^- F anions react with SUS and aluminum electrode current collector is believed to be due to the effect of forming a passive film.

As the first additive that is stable in the atmosphere, it is desirable that the cation species have a large formula amount and that it is a liquid or solid ionic material at room temperature. Specifically, the formula amount of the cation species is preferably 100 or more, more preferably 240 or more. The formula amount of the cation species can be measured by determining the molecular structure by elemental analysis and nuclear magnetic resonance NMR.

As an example of the first additive, tetrabutylammonium hexafluorophosphate (NBu ₄ PF ₆ , cationic formula amount about 242), tetrabutylammonium tetrafluorobolate (NBu ₄ BF ₄ , cationic formula amount about 242) quaternary ammonium Salt, 1-ethyl-3-methylimidazolium tetrafluorobolate (EMI-BF ₄ , cation formula amount about 111), 1-ethyl-3-methylimidazolium hexafluorophosphate (EMI-PF ₆ , cation formula amount about 111) ), 1-Butyl-3-methylimidazolium tetrafluorobolate (BMI-BF ₄ , cation formula amount about 139), 1-butyl-3-methylimidazolium hexafluorophosphate (BMI-PF ₆ , cation formula amount about 139) ) And other imidazolium salts. In particular, if the anion is PF ₆ ⁻ , the elution of the positive electrode current collector 120 can be suppressed. These first additives may be used alone or in combination of two or more.

The amount of the first additive added is preferably 1 wt% to 20 wt%, more preferably 2.5 wt%, based on the total weight of the mixed solvent containing the semi-solid electrolyte solvent, any low-viscosity organic solvent and the electrolyte salt. ~ 10wt%. If the amount of the first additive added is small, the effect of suppressing the elution of the electrode current collector is reduced, and the battery capacity tends to be reduced with charging and discharging. Further, if the amount of the first additive added is large, the lithium ion conductivity is lowered, and a large amount of stored energy is consumed for decomposition of the additive, resulting in a decrease in battery capacity.

<Second additive>
In addition to the first additive, a second additive may be added to the semi-solid electrolyte. Examples of the second additive include a precursor material for forming a stable lithium conductive film on the active material surfaces of the negative electrode 200 and the positive electrode 100. Specific examples thereof include vinylene carbonate, fluoroethylene carbonate, 1,3-propane sultone, 1-propene 1,3-sultone, ethylene sulfate or derivatives thereof. Since these second additives react at the positive electrode 100, the elution resistance of the electrode current collector is further improved. These second additives may be used alone or in combination of two or more.

The amount of the second additive added is preferably 0.1 wt% to 10 wt%, more preferably 2 wt%, based on the total weight of the mixed solvent containing the semi-solid electrolyte solvent, any low-viscosity organic solvent and the electrolyte salt. ~ 4wt%. If the amount of the second additive added is small, the formation of the lithium conductive film is insufficient, the decomposition of the electrolyte proceeds, and the life characteristics may be deteriorated. Further, if the amount of the second additive added is large, the conduction of lithium ions is hindered, so that the internal resistance of the secondary battery may increase.

<Semi-solid electrolyte binder>
A fluorine-based resin is preferably used as the semi-solid electrolyte binder. As the fluorine-based resin, polyvinylidene fluoride (PVDF) or a copolymer of polyvinylidene fluoride and hexafluoropropylene (P (VDF-HFP)) is preferably used. These semi-solid electrolyte binders may be used alone or in combination of two or more. By using PVDF or P (VDF-HFP), the adhesion between the semi-solid electrolyte layer 300 and the electrode current collector is improved, so that the battery performance is improved.

<Semi-solid electrolyte>
The semi-solid electrolyte is formed by supporting or holding the semi-solid electrolyte on the particles. As a method for producing a semi-solid electrolyte, a semi-solid electrolyte and particles are mixed in a specific volume ratio, an organic solvent such as methanol is added and mixed to prepare a slurry of the semi-solid electrolyte, and then the slurry is chaleted. A method of obtaining a semi-solid electrolyte powder by distilling off an organic solvent can be mentioned.

<Semi-solid electrolyte layer 300>
The semi-solid electrolyte layer 300 serves as a medium for transmitting lithium ions between the positive electrode 100 and the negative electrode 200. The semi-solid electrolyte layer 300 also acts as an electron insulator to prevent a short circuit between the positive electrode 100 and the negative electrode 200.

As a method for producing the semi-solid electrolyte layer 300, a method of compression molding the semi-solid electrolyte powder into pellets with a molding die or the like, a method of adding and mixing the semi-solid electrolyte binder to the semi-solid electrolyte powder, and forming a sheet, etc. There is. By adding and mixing the powder of the semi-solid electrolyte binder to the semi-solid electrolyte, a highly flexible sheet-shaped semi-solid electrolyte layer 300 can be produced. Further, the semi-solid electrolyte layer 300 can be prepared by adding and mixing a solution of a binder in which a semi-solid electrolyte binder is dissolved in a dispersion solvent to the semi-solid electrolyte and distilling off the dispersion solvent. The semi-solid electrolyte layer 300 may be prepared by applying and drying the above-mentioned semi-solid electrolyte to which a solution of a binder is added and mixed on an electrode.

The content of the semi-solid electrolyte in the semi-solid electrolyte layer 300 is preferably 70% by volume to 90% by volume. If the content of the semi-solid electrolyte is small, the interfacial resistance between the electrode and the semi-solid electrolyte layer 300 may increase. Further, when the content of the semi-solid electrolyte is large, the semi-solid electrolyte may leak from the semi-solid electrolyte layer 300.

Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.

<Example 1>
<Preparation of semi-solid electrolyte layer 300>
Lithium bis (trifluoromethanesulfonyl) imide (LiTFSI) as the lithium imide salt (electrolyte salt), tetraglime (G4) as the main solvent, propylene carbonate (PC) as the low-viscosity organic solvent, and a magnetic stirrer in a glass bottle. A mixed solvent was prepared by stirring and dissolving. Tetrabutylammonium hexafluorophosphate (NBu ₄ PF ₆ ) as the first additive and vinylene carbonate (VC) as the second additive were added to a mixed solvent containing LiTFSI, G4, and PC, respectively, and semi-solid electrolyzed. It was made into a liquid.

A mixed solvent to which the first additive and the second additive were added and SiO ₂ nanoparticles (particle size 7 nm) were mixed at a volume fraction of 80:20, methanol was added thereto, and then a magnetic stirrer was used. Stirred for 30 minutes. Then, the obtained mixed solution was spread on a petri dish, and methanol was distilled off to obtain a powdery and semi-solid semi-solid electrolyte. By adding 5% by mass of polytetrafluoroethylene (PTFE) powder to this semi-solid electrolyte and stretching it under pressure while mixing well, a sheet-shaped semi-solid electrolyte layer 300 having a thickness of about 200 μm was obtained. The semi-solid electrolyte contained in the obtained semi-solid electrolyte layer 300 has a mixed molar ratio of LiTFSI, G4, and PC of 1: 1: 4, and the concentration of lithium imide salt in the mixed solvent is 1.5 mol / L. The mixed weight ratio of the complex composed of the main solvent G4 and the lithium imide salt LiTFSI and the low-viscosity solvent PC was 55.5: 44.5. _{The weight ratio of NBu 4} PF ₆ to this mixed solvent was 5 wt%, and the weight ratio of vinylene carbonate (VC) was 3 wt%. This was punched out with a size of 15 mm in outer diameter.

<Manufacturing of positive electrode 100>
_{LiNi 0.33} Mn _0.33 Co _0.33 O ₂ as the positive electrode active material, polyvinylidene fluoride (PVDF) as the positive electrode binder, and acetylene black as the positive electrode conductive agent are mixed at a weight ratio of 84: 9: 7, and N -Methyl-2-pyrrolidone was added and further mixed to prepare a slurry-like solution. The prepared slurry was applied to a positive electrode current collector 120 made of SUS foil having a thickness of 10 μm using a doctor blade (positive electrode mixture layer 110), and dried at 80 ° C. for 2 hours or more. At this time, the amount of the slurry applied was adjusted so that the weight of the positive electrode mixture layer 110 per ^{1 cm 2 after drying was 18 mg / cm 2.} The dried electrode was pressurized to a density of 2.5 g / cm ³ and punched out with an outer diameter of 13 mm to obtain a positive electrode 100.

<Manufacturing of negative electrode 200>
Graphite (amorphous coating, average particle size 10 μm) as the negative electrode active material, polyvinylidene fluoride (PVDF) as the negative electrode binder, and acetylene black as the negative electrode conductive agent are mixed at a weight ratio of 88:10: 2 and N-methyl. -2-Pyrrolidone was added and further mixed to prepare a slurry-like solution. The prepared slurry was applied to a negative electrode current collector 220 made of SUS foil having a thickness of 10 μm using a doctor blade, and dried at 80 ° C. for 2 hours or more. At this time, the amount of the slurry applied was adjusted so that the weight of the negative electrode mixture layer 210 per ^{1 cm 2 after drying was 8 mg / cm 2.} The dried electrode was pressurized to a density of 1.5 g / cm ³ and punched out with an outer diameter of 13 mm to obtain a negative electrode 200.

<Manufacturing of secondary battery 1000>
The prepared positive electrode 100, negative electrode 200, and semi-solid electrolyte layer 300 were dried at 100 ° C. for 2 hours or more, and then transferred into a glove box filled with argon. After that, the negative electrode 200 is placed on one side of the semi-solid electrolyte layer 300, and the positive electrode 100 is placed on the other side. A battery 1000 was manufactured.

<Examples 2 to 20>
A semi-solid electrolyte layer and a secondary battery were produced in the same manner as in Example 1 except that the first additive and the amount of the first additive added were as shown in FIG.

<Example 21>
LiTFSI as lithiumimide salt (electrolyte salt), ionic liquid (Py13TFSI) composed of N-methyl-N-propylpyrrolidinium (Py13) and bis (trifluoromethanesulfonyl) imide (TFSI) as main solvent, low-viscosity solvent LiTFSI and Py13TFSI were prepared so that the concentration of LiTFSI was 1 mol / L. Then, the same volume of PC as Py13TFSI was added to prepare a mixed solvent. _{A semi-solid electrolyte was prepared by adding 5 wt% of NBu 4} PF ₆ as the first additive and 3 wt% of vinylene carbonate (VC) as the second additive to a mixed solvent containing LiTFSI, Py13TFSI, and PC. bottom. A semi-solid electrolyte layer and a secondary battery were produced in the same manner as in Example 10 except for the above.

<Comparative Examples 1 to 6>
A semi-solid electrolyte layer and a secondary battery were produced in the same manner as in Example 1 except that the first additive and the amount of the first additive added were as shown in FIG.

<Evaluation of ionic conductivity>
It was sandwiched between both sides of the semi-solid electrolyte layer 300 with SUS foil having an outer diameter of 13 mm, and this was incorporated into a 2032 coin cell. Ion conductivity was evaluated by AC impedance measurement.

<Measurement method of dissolution start potential of positive electrode current collector 120>
The liquid component applied to the semi-solid electrolyte layer 300 was contained in a porous resin sheet, ^{and Al or SUS having an electrode area of 1 cm 2} and Li metal as a counter electrode were sandwiched therein to prepare an evaluation cell. Then, at a scanning potential of 10 μV / sec, the potential was swept from the potential range of 3.0 V to 6.0 V, and the potential at which the oxidation current rises [against Li foil] (V) was measured.

<Evaluation of initial battery capacity>
The measurement was performed at 50 ° C. using a secondary battery 1000. It was charged at a constant current-constant potential (CC-CV) at a 1C rate using a Solartron 1480 Potentiostat. Then, after resting in the open circuit state for 1 hour, a constant current was discharged at a 1C rate. The upper limit voltage was 4.2V and the lower limit voltage was 2.7V. The battery capacity was converted to the value per positive electrode weight used.

<Evaluation of cycle characteristics>
After performing the initial charge / discharge in the previous procedure, the charge / discharge cycle is repeated 100 times at a rate of 1C, and the discharge capacity after 100 cycles is evaluated again from the ratio with the initial discharge capacity. , The capacity retention rate was calculated. After charging and discharging, the secondary battery 1000 was inactive for 1 hour in an open circuit state.

<Results and consideration of results>
FIG. 3 shows the results of Examples and Comparative Examples. The dissolution start potential of the positive electrode current collector 120 in the examples was higher than the dissolution start potential of the positive electrode current collector 120 in the comparative example, and the elution of the electrode current collector could be suppressed in the example.

_{In Comparative Examples 3 to 6} in which _{LiPF 6 and LiBF 4} having high hydrolyzability were used as the first additives, the volume retention rate was as low as 30% although it was improved. It is considered that this is because the first additive was decomposed and consumed by the water contained in the produced electrode and was not appropriately used for forming the film on the positive electrode current collector 120.

_{On the other hand, in Examples 1 to 4 in which NBu 4} PF ₆ and NBu ₄ BF 4 having low hydrolyzability were used as the first additive, the volume retention rate was improved to 68% or more, and the SEM after dismantling analysis was performed. -EDX analysis did not confirm the detection of metal components due to the dissolution of the positive electrode current collector 120. In addition, the dissolution start potential of the positive electrode current collector 120 was significantly improved from 4.2 V in Comparative Example 1 and Comparative Example 2 to 4.7 to 4.8 V. This, PF ₆ used in the first additive ^- to not BF ₄ ^- anions, presumably because contributed to the film formation reaction in the electrode current collector surface.

In Examples 5 to 8 in which _{EMI-PF 6} and BMI-PF ₆ were used as the first additive, the capacity retention rate after the cycle test was also high, as in _{NBu 4} PF _6. Furthermore, the ionic conductivity _{tends to be higher than that of NBu 4} PF ₆ , which is a desirable result from the viewpoint of charge / discharge rate.

In Example 2 and Examples 9 to 13, NBu ₄ PF ₆ was applied as the first additive, and the amount of the additive was changed from 1 wt% to 20 wt%. The volume retention rate was improved with respect to all the addition amounts as compared with Comparative Example 2, and especially when the addition amount was in the range of 2.5 wt% to 10 wt%, the decrease in ionic conduction due to the application of the first additive was small. Furthermore, the capacity retention rate was also high.

Example 14 is a modification of Example 2 in which the type of lithium imide salt is changed. Even when lithium bis (fluorosulfonyl) imide (LiFSI), which is the same lithium imide salt, was used, the capacity retention rate was high as in the case of LiTFSI.

In Examples 15 to 17, the type of low-viscosity organic solvent was changed from that in Example 10. The capacity retention rate was high regardless of the presence or absence of the low-viscosity organic solvent and regardless of the type of the low-viscosity organic solvent. On the other hand, when Example 2, Example 16 and Example 17 are compared, the ionic conductivity of Example 2 is high and the initial discharge capacity is increased. Therefore, it was found that the initial discharge capacity increased when PC was used as the low-viscosity organic solvent.

In Examples 18 to 20, the type of the second additive is changed from that in Example 10. The volume retention rate was high regardless of the type of the second additive.

Even when an ionic liquid is used as the low volatility liquid as in Example 21, the capacity retention rate is high. It is considered that Py13TFSI in Example 21 had higher ionic conductivity than the complex of G4 and LiTFSI in Example 10 and the initial discharge capacity was increased.

FIG. 4 shows the charge / discharge cycle test results of Example 1 and Comparative Example 1. In Comparative Example 1 in which the first additive was not contained in the liquid component, the capacity decreased sharply in the middle of the cycle as shown in FIG. 4, and the discharge capacity after 100 cycles was almost zero. As a result of disassembly analysis after the test, SUS, which is the positive electrode current collector 120, was clearly eluted, and the eluted metal component was transferred to the negative electrode 200 side from SEM-EDX (scanning electron microscope-energy dispersive X-ray spectroscopy). It was confirmed that it was concentrated. This tendency was the same in Comparative Example 2.

100 positive electrode
110 Positive electrode mixture layer
120 Positive electrode current collector
130 Positive electrode tab
200 negative electrode
210 Negative electrode mixture layer
220 Negative electrode current collector
230 Negative electrode tab
300 semi-solid electrolyte layer
400 electrode body
500 exterior
1000 Rechargeable Batteries All publications, patents and patent applications cited herein are incorporated herein by reference in their entirety.

Claims (6)

Contains a mixed solvent containing a semi-solid electrolyte solvent and an electrolyte salt, as well as the first additive.
The group in which the first additive comprises tetrabutylammonium hexafluorophosphate, tetrabutylammonium tetrafluoroborate, 1-ethyl-3-methylimidazolium hexafluorophosphate and 1-butyl-3-methylimidazolium hexafluorophosphate. a semi-solid electrolyte is one selected from,
With particles
Semi-solid electrolyte containing . Semi solid electrolyte according to claim 1 amount of the first additive to prior Symbol mixed solvent is 1 wt% 20 wt%. Semi solid electrolyte according to claim 1 wherein the mixed solvent further containing a low viscosity organic solvent. The semi-solid electrolyte, a semi-solid electrolyte according to claim 1 comprising a second additive. A semi-solid electrolyte layer having the semi-solid electrolyte and the semi-solid electrolyte binder according to claim 1. A positive electrode including a positive electrode current collector and a positive electrode mixture layer formed on the positive electrode current collector, and a positive electrode.
A negative electrode containing a negative electrode current collector and a negative electrode mixture layer formed on the negative electrode current collector, and a negative electrode.
A secondary battery having the semi-solid electrolyte layer according to claim 5.

Images