WO2019021522A1 - Semisolid electrolyte solution, semisolid electrolyte, semisolid electrolyte layer, and secondary battery - Google Patents

Abstract

In the present invention, elution of an electrode current collector is suppressed. The present invention provides a semisolid electrolyte solution, a semisolid electrolyte, a semisolid electrolyte layer, and a secondary battery in which there are contained: a mixed solvent that contains a semisolid electrolyte solvent and an electrolyte salt; as well as a first additive. The anion of the first additive is BF4 – or PF6 –, and the formula weight of the cation of the first additive is at least 100. Preferably, the present invention provides a semisolid electrolyte solution, a semisolid electrolyte, a semisolid electrolyte layer, and a secondary battery for which the amount of the first additive added to the mixed solvent is 1 to 20 wt% , and the first additive is NBu4PF6. It is thereby possible to suppress elution of the electrode current collector.

Description

Semisolid Electrolyte, Semisolid Electrolyte, Semisolid Electrolyte Layer, and Secondary Battery

The present invention relates to a semisolid electrolyte, a semisolid electrolyte, a semisolid electrolyte layer, and a secondary battery.

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

scientific reports, DOI: 10.1038 / srep08869

Many common lithium ion secondary batteries contain an organic electrolyte containing LiPF ₆ or LiBF ₄ and some of the PF ₆ ^- and BF ₄ ^- anions have a coating formed on a metallic electrode current collector. It forms and suppresses the elution of an electrode collector. On the other hand, Non-Patent Document 1, the ion conductivity, has been applied LiPF ₆ and LiBF ₄ rather than Li imide salt in terms of atmospheric compatible, it does not contain LiPF ₆ and LiBF _4. Therefore, the elution of the metal in the current collector tends to proceed, and the eluted metal may inhibit the Li conduction in the lithium ion secondary battery, which may lower the battery performance.
An object of the present invention is to suppress the elution of an electrode current collector.

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

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 solution that is over 100.
The present specification includes the disclosure content of Japanese Patent Application No. 201-144079 based on which the priority of the present application is based.

According to the present invention, the elution of the electrode current collector can be suppressed. Problems, configurations, and effects other than those described above will be apparent from the description of the embodiments below.

It is an external view of a secondary battery. It is a sectional view of a rechargeable battery. It is a table | surface which shows the result of an Example and a comparative example. It is a graph which shows a charging / discharging cycle test result.

Hereinafter, embodiments of the present invention will be described using the drawings and the like. The following description shows specific examples of the content of the present invention, and the present invention is not limited to these descriptions, and various modifications by those skilled in the art can be made within the scope of the technical idea disclosed herein. Changes and modifications are possible. Moreover, in all the drawings for explaining the present invention, what has the same function may attach the same numerals, and may omit explanation of the repetition.

As used herein, “to” is used in the sense of including the numerical values described before and after it as the lower limit value and the upper limit value. In the numerical ranges that are described stepwise in the present specification, the upper limit or the lower limit described in one numerical range may be replaced with the upper limit or the lower limit described in another stepwise. The upper limit value or the lower limit value of the numerical range described herein may be replaced with the value shown in the examples.

In the present specification, a lithium ion secondary battery will be described as an example of a secondary battery. A lithium ion secondary battery is an electrochemical device capable of storing or utilizing electrical energy by insertion and extraction of lithium ions to an electrode 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 any battery is an object of the present invention. The technical concept of the present invention is also applicable to sodium ion secondary batteries, magnesium ion secondary batteries, calcium ion secondary batteries, zinc secondary batteries, aluminum ion secondary batteries 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. FIGS. 1 and 2 illustrate a stacked secondary battery, and the secondary battery 1000 includes a positive electrode 100, a negative electrode 200, an outer package 500, and a semisolid electrolyte layer 300. The exterior body 500 accommodates the semi-solid electrolyte layer 300, the positive electrode 100, and the negative electrode 200. The material of the exterior body 500 can be selected from materials having corrosion resistance to the non-aqueous electrolyte, such as aluminum, stainless steel, nickel plated steel, and the like. The present invention is also applicable to a wound secondary battery.

In the secondary battery 1000, an electrode assembly 400 including the positive electrode 100, the semi-solid electrolyte layer 300, and the negative electrode 200 is stacked. 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 semisolid electrolyte layer 300 may be referred to as a secondary battery sheet. What the semisolid electrolyte layer 300 and the positive electrode 100 or the negative electrode 200 have an integral structure may be called an electrode for a secondary battery with a semisolid electrolyte layer.

The positive electrode 100 has a positive electrode current collector 120 and a positive electrode mixture layer 110. The positive electrode mixture layer 110 is formed on both sides of the positive electrode current collector 120. The negative electrode 200 includes a negative electrode current collector 220 and a negative electrode mixture layer 210. A negative electrode mixture layer 210 is 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. An 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 protrude to the outside of the exterior body 500, and a plurality of protruding positive electrode tab portions 130 and a plurality of negative electrode tab portions 230 are joined by ultrasonic bonding, for example. Then, parallel connection is formed in the secondary battery 1000. The present invention can also be applied to a bipolar secondary battery in which electrical series connection is configured in the secondary battery 1000.

The positive electrode mixture layer 110 includes a positive electrode active material, a positive electrode conductive agent, and a positive electrode binder. The negative electrode mixture layer 210 includes a negative electrode active material, a negative electrode conductive agent, and a negative electrode binder. The semisolid electrolyte layer 300 has a semisolid electrolyte binder and a semisolid electrolyte. A semi-solid electrolyte comprises 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 electrolyte. In this case, a semi-solid electrolyte is injected into the secondary battery 1000 from one open side of the outer package 500 or a liquid injection hole, and the pores of the electrode mixture layer are filled with the semi-solid electrolyte. In this case, particles contained in the semi-solid electrolyte are not required, and particles such as the electrode active material and the electrode conductive agent in the electrode mixture layer function as particles, and the particles hold the semi-solid electrolyte. As another method of filling the pores of the electrode mixture layer with the semi-solid electrolytic solution, a slurry is prepared by mixing a semi-solid electrolyte, an electrode active material, an electrode conductive agent, and an electrode binder, and the prepared slurry is used as an electrode current collector. There is a method of applying together on top.

The semi-solid electrolyte layer 300 may use a separator such as a microporous film. As a separator, polyolefin such as polyethylene and polypropylene and glass fiber can be used. When a microporous film is used for the separator, the semi-solid electrolyte solution is injected into the semi-solid electrolyte layer 300 by injecting the semi-solid electrolyte solution into the secondary battery 1000 from one open side of the outer package 500 or the injection hole. Be filled.

A semisolid electrolyte may be contained in any one or two or more of the positive electrode 100, the negative electrode 200, or the semisolid 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 suitably used, but it is not limited thereto.

<Electrode binder>
The electrode binder binds an electrode active material, an electrode conductive agent, and the like in the electrode. The electrode binder may include, but is not limited to, styrene-butadiene rubber, carboxymethylcellulose, polyvinylidene fluoride (PVDF), and mixtures thereof.

<Positive electrode active material>
In the positive electrode active material exhibiting 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 of the positive electrode active material, and specific examples thereof include LiMO ₂ , Li excess composition Li [LiM] O ₂ , LiM ₂ O ₄ , LiMPO ₄ , LiMVO _x , LiMBO ₃ And Li ₂ MSiO ₄ (wherein, at least one or more of M Co Co, Ni, Mn, Fe, Cr, Zn, Ta, Al, Mg, Cu, Cd, Mo, Nb, W, Ru, etc.) can be mentioned. . In addition, a part of oxygen in these materials may be replaced with another element such as fluorine. Further, chalcogenides such as sulfur, 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 constituting a polyanion such as _{Fe 2 (SO 4) 3,} Li 3 Fe 2 (PO 4) 3, but such quinone organic crystals, but is not limited thereto. Furthermore, the amounts of lithium and anion in the chemical composition may be deviated from the above-mentioned stoichiometric composition.

<Positive Electrode 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 foam metal plate or the like is used. Besides aluminum, stainless steel, titanium and the like can also be applied. Any positive electrode current collector 120 can be used without limitation to the material, shape, manufacturing method, and the like.

A positive electrode slurry obtained by mixing a positive electrode active material, a positive electrode conductive agent, a positive electrode binder and an organic solvent is attached to the positive electrode current collector 120 by a doctor blade method, dipping method or spray method, and then the organic solvent is dried. The positive electrode 100 can be manufactured by pressure molding according to. The plurality of positive electrode mixture layers 110 may be stacked on the positive electrode current collector 120 by performing application to drying a plurality of times. The thickness of the positive electrode mixture layer 110 is desirably equal to or more than the average particle diameter of the positive electrode active material. When the thickness of the positive electrode mixture layer 110 is smaller than the average particle diameter of the positive electrode active material, the electron conductivity between adjacent positive electrode active materials may be deteriorated.

<Anode 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 charge process. As a material of the negative electrode active material exhibiting a slight potential, for example, carbon-based materials (eg, graphite, graphitizable carbon materials, amorphous carbon materials, organic crystals, activated carbon, etc.), conductive polymer materials (eg, polyacene) , Polyparaphenylene, polyaniline, polyacetylene, lithium complex oxide (eg, lithium titanate: Li ₄ Ti ₅ O ₁₂ , Li ₂ TiO _4, etc.), metallic lithium, metal alloyed with lithium (eg, aluminum, silicon) And tin and the like) or oxides thereof can be used, but the invention is not limited thereto.

<Anode Current Collector 220>
As the negative electrode current collector 220, a copper foil having a thickness of 1 μm to 100 μm, a perforated copper foil having a thickness of 1 μm to 100 μm and a hole diameter of 0.1 mm to 10 mm, an expanded metal, a foam metal plate or the like is used. Besides copper, stainless steel, titanium, nickel and the like can also be applied. Any negative electrode current collector 220 can be used without limitation to the material, shape, manufacturing method, and the like.

<Electrode>
An electrode mixture layer is formed by adhering an electrode slurry obtained by mixing 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, dipping method, or spray method. Be done. Thereafter, the electrode mixture layer is dried in order to remove the organic solvent, and the electrode mixture layer is pressure-formed by a roll press to produce an electrode. The electrode slurry may include a semi-solid electrolyte or a semi-solid electrolyte. A plurality of electrode mixture layers may be stacked on the electrode current collector by performing application to drying a plurality of times. The thickness of the electrode mixture layer is desirably equal to or more than the average particle diameter of the electrode active material. When the thickness of the electrode mixture layer is small, the electron conductivity between adjacent electrode active materials may be deteriorated. When the electrode active material powder contains coarse particles having an average particle diameter equal to or larger than the thickness of the electrode mixture layer, the coarse particles are removed in advance by sieve classification, air flow classification, etc., and particles smaller than the thickness of the electrode mixture layer It is desirable to

<Particle>
The particles are preferably insulating particles and insoluble in a semisolid electrolytic solution containing an organic solvent or an ionic liquid, from the viewpoint of electrochemical stability. 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, zirconia (ZrO ₂ ) particles and the like can be preferably used. A solid electrolyte may be used as the particles. Examples of solid electrolytes include particles of inorganic solid electrolytes such as oxide-based solid electrolytes such as Li-La-Zr-O and sulfide-based solid electrolytes such as Li ₁₀ Ge ₂ PS ₁₂ .

The average particle diameter of the primary particles of the particles is preferably 1 nm to 10 μm because the amount of the semi-solid electrolyte held is proportional to the specific surface area of the particles. If the mean particle size of the primary particles of the particles is large, the particles may not hold a sufficient amount of the semi-solid electrolyte properly, which may make it difficult to form a semi-solid electrolyte. In addition, when the average particle size of the primary particles of the particles is small, the surface-to-surface force between the particles is increased, the particles are easily aggregated, and the formation of the semisolid electrolyte may be difficult. The average particle diameter of the primary particles of the particles is more preferably 1 nm to 50 nm, and further preferably 1 nm to 10 nm. The average particle diameter of the primary particles of the particles can be measured 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, an optional low viscosity organic solvent, an electrolyte salt, a first additive, and an optional second additive. Semi-solid electrolyte solvents have ether solvents that exhibit properties similar to ionic liquids or ionic liquids. The ionic liquid or ether solvent may be referred to as a main solvent. An ionic liquid is a compound which dissociates into a cation and an anion at normal temperature, and maintains the 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 preferably has low volatility, specifically, one having a vapor pressure of 150 Pa or less at room temperature, from the viewpoint of the stability in the air and the 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 electrolyte is small, the ion conduction path inside the electrode mixture layer may not be sufficiently formed, and the rate characteristics may be degraded. In addition to the possibility that the semi-solid electrolyte may leak out of the electrode mixture layer when the content of the semi-solid electrolyte is large, the active material is insufficient and the energy density is lowered.

The ionic liquid is composed of cations and anions. The ionic liquid is classified into imidazolium type, ammonium type, pyrrolidinium type, piperidinium type, pyridinium type, morpholinium type, phosphonium type, sulfonium type and the like according to the cationic species. Examples of the cation constituting the imidazolium-based ionic liquid include alkylimidazolium cations such as 1-ethyl-3-methylimidazolium and 1-butyl-3-methylimidazolium (BMI). Examples of the cation constituting the ammonium-based ionic liquid include N, N, N-, in addition to N, N-diethyl-N-methyl-N- (2-methoxyethyl) ammonium (DEME) and tetraamyl ammonium. There is an alkyl ammonium cation such as trimethyl-N-propyl ammonium. Examples of the cation constituting the pyrrolidinium-based ionic liquid include alkyl pyrrolidinium cations such as N-methyl-N-propyl pyrrolidinium (Py13) and 1-butyl-1-methyl pyrrolidinium. Examples of the cation 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 cation constituting the pyridinium-based ionic liquid include alkyl pyridinium cations such as 1-butyl pyridinium and 1-butyl-4-methyl pyridinium. Examples of the cation constituting the morpholinium-based ionic liquid include alkyl morpholinium such as 4-ethyl-4-methyl morpholinium. Examples of the cation constituting the phosphonium-based ionic liquid include alkyl phosphonium cations such as tetrabutyl phosphonium and tributyl methyl phosphonium. Examples of the cation constituting the sulfonium-based ionic liquid include alkylsulfonium cations such as trimethylsulfonium and tributylsulfonium. As the anion to be paired with these cations, for example, bis (trifluoromethanesulfonyl) imide (TFSI), bis (fluorosulfonyl) imide, tetrafluoroborate (BF ₄ ), hexafluorophosphate (PF ₆ ), bis (penta) Fluoroethanesulfonyl) imide (BETI), trifluoromethanesulfonate (triflate), acetate, dimethyl phosphate, dicyanamide, trifluoro (trifluoromethyl) borate and the like. You may use these ionic liquids individually or in combination of multiple.

As electrolyte salt used with an ionic liquid, what can be disperse | distributed to a solvent uniformly can be used. Lithium having a cation 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 include, but are not limited to, sulfonyl) imide (LiBETI), lithium tetrafluoroborate (LiBF ₄ ), lithium hexafluorophosphate (LiPF ₆ ), lithium triflate and the like. These electrolyte salts may be used alone or in combination of two or more.

The ether-based solvent constitutes a solvated ionic liquid with the electrolyte salt. As ether-based solvents, symmetric glycol represented by the known exhibit similar properties to the ionic liquid glyme _{(RO (CH 2 CH 2 O} ) n -R '(R, R' is a saturated hydrocarbon, n represents an integer) Generic term for ether can be used. From the viewpoint of ion conductivity, tetraglyme (tetraethylene dimethyl glycol, G4), triglyme (triethylene glycol dimethyl ether, G3), pentag lime (pentaethylene glycol dimethyl ether, G5), hexaglyme (hexaethylene glycol dimethyl ether, G6) It can be used preferably. In addition, as ether solvents, crown ethers (general name of 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 not limited thereto. These ether solvents may be used alone or in combination of two or more. It is preferable to use tetraglyme and triglyme in that they can form a complex structure with the electrolyte salt.

As electrolyte salt used with an ether type solvent, although lithium salts, such as LiFSI, LiTFSI, LiBETI, can be utilized, it is not restricted to this. A mixture of an ether solvent and an electrolyte salt may be used alone or in combination as a mixed solvent containing a semisolid electrolyte solvent and an electrolyte salt.

Although the weight ratio of the main solvent in the semi-solid electrolyte is not particularly limited, the weight ratio of the main solvent to the total of the solvents in the semi-solid electrolyte is 30% to 70% from the viewpoint of battery stability and high-speed charge and discharge. In particular, the content is preferably 40% to 60%, and more preferably 45% to 55%.

<Low viscosity organic solvent>
The low viscosity organic solvent lowers the viscosity of the semi-solid electrolyte solvent and improves the ion conductivity. Since the internal resistance of the semisolid electrolyte containing the semisolid electrolyte solvent is large, the internal resistance of the semisolid electrolyte can be lowered by increasing the ion conductivity of the semisolid electrolyte solvent by adding a low viscosity organic solvent . However, since the semi-solid electrolyte solvent is electrochemically unstable, the decomposition reaction is promoted for the cell operation, causing the resistance increase and the capacity decrease of the secondary battery 1000 along with the repeated operation of the secondary battery 1000 there is a possibility. Furthermore, in the secondary battery 1000 using graphite as the negative electrode active material, during the charging reaction, the cation of the semi-solid electrolyte solvent may be inserted into the graphite to destroy the graphite structure and the secondary battery 1000 can not be repeatedly operated. There is.

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

<First additive>
The semi-solid electrolytic solution preferably contains a first additive that forms a film that hardly elutes metal 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 an index indicating that the compound is stable in the atmosphere, the solubility in water and the presence or absence of hydrolysis can be mentioned. When the first additive is solid, it is desirable that its solubility in water be less than 1%. Moreover, the presence or absence of hydrolysis can be evaluated by molecular structure analysis of the sample after mixing with water. Here, not to be hydrolyzed means that 95% of the residue after removing the water after heating the temperature at 100 ° C. or higher after mixing the first additive with moisture or water is the same molecule as the first additive It means that the structure is shown.

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 It 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 is considered to be due to the fact that the B anion of BF ₄ ⁻ or PF ₆ ⁻ reacts with SUS or aluminum of the electrode current collector to form a passive film.

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

As an example of the first additive, quaternary ammonium of tetrabutylammonium hexafluorophosphate (NBu ₄ PF ₆ , cationic amount of about 242), tetrabutylammonium tetrafluoroborate (NBu ₄ BF ₄ , cationic amount of about 242) salt, 1-ethyl-3-methylimidazolium tetrafluoroborate (EMI-BF _4, cation type amounts to about 111), 1-ethyl-3-methylimidazolium hexafluorophosphate (EMI-PF _6, cation type amounts to about 111 ), 1-butyl-3-methylimidazolium tetrafluoroborate (BMI-BF ₄ , cationic weight about 139), 1-butyl-3-methylimidazolium hexafluorophosphate (BMI-PF ₆ , cationic weight about 139) And the like). In particular, the anion is PF ₆ ^- if, it is possible to suppress elution of the positive electrode current collector 120. These first additives may be used alone or in combination.

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 semisolid electrolyte solvent, the optional low viscosity organic solvent and the mixed solvent containing the electrolyte salt. It is ̃10 wt%. When the addition amount of the first additive is small, the effect of suppressing the elution of the electrode current collector is reduced, and the battery capacity is likely to be reduced with charge and discharge. In addition, when the amount of the first additive added is large, the lithium ion conductivity decreases, and furthermore, a large amount of stored energy is consumed for the decomposition of the additive, and as a result, the battery capacity decreases.

<Second additive>
In addition to the first additive, the second additive may be added to the semi-solid electrolyte. The second additive includes 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. Specifically, vinylene carbonate, fluoroethylene carbonate, 1,3-propane sultone, 1-propene 1,3-sultone, ethylene sulfate or derivatives thereof can be mentioned. 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.

The addition amount of the second additive is preferably 0.1 wt% to 10 wt%, more preferably 2 wt%, based on the total weight of the semisolid electrolyte solvent, the optional low viscosity organic solvent and the mixed solvent containing the electrolyte salt. It is ̃4 wt%. If the amount of the second additive is small, the formation of the lithium conductive film may be insufficient, the decomposition of the electrolyte may proceed, and the life characteristics may be degraded. In addition, when the amount of the second additive added is large, the internal resistance of the secondary battery may be increased because the conduction of lithium ions is inhibited.

<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 suitably used. These semisolid electrolyte binders may be used alone or in combination. 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 semisolid electrolyte is constituted by supporting or holding the semisolid 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, a slurry of the semi-solid electrolyte is prepared, and then the slurry is charged. And the organic solvent is distilled off to obtain a semi-solid electrolyte powder, and the like.

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

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

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

EXAMPLES Hereinafter, the present invention will be more specifically described by way of examples, but the present invention is not limited to these examples.

Example 1
<Fabrication of semi-solid electrolyte layer 300>
Using lithium bis (trifluoromethanesulfonyl) imide (LiTFSI) as a lithium imide salt (electrolyte salt), tetraglyme (G4) as a main solvent, propylene carbonate (PC) as a low viscosity organic solvent, using a magnetic stirrer in a glass bottle The mixture was stirred and dissolved to prepare a mixed solvent. Semi-solid electrolysis by adding tetrabutylammonium hexafluorophosphate (NBu ₄ PF ₆ ) as the first additive and vinylene carbonate (VC) as the second additive to the mixed solvent containing LiTFSI, G4 and PC, respectively. It was a liquid.

A mixed solvent to which the first additive and the second additive have been added and SiO ₂ nanoparticles (particle size 7 nm) are mixed at a volume fraction of 80:20, and methanol is added thereto, using a magnet stirrer. The mixture was stirred for 30 minutes. Thereafter, the obtained mixture was spread in a petri dish, and methanol was distilled off to obtain a powdery and semisolid semisolid electrolyte. 5% by mass of polytetrafluoroethylene (PTFE) powder was added to the semi-solid electrolyte, and the mixture was stretched while being mixed well to obtain a sheet-like semi-solid electrolyte layer 300 having a thickness of about 200 μm. The semisolid electrolyte solution contained in the obtained semisolid electrolyte layer 300 has a mixed molar ratio of LiTFSI, G4, PC of 1: 1: 4, and the concentration of lithium imide salt in the mixed solvent is 1.5 mol / L, The mixing weight ratio of the complex consisting of the main solvent G4 and the lithium imide salt LiTFSI to 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%. It was punched out with a size of outer diameter 15 mm.

<Fabrication of Positive Electrode 100>
Mix LiNi _0.33 Mn _0.33 Co _0.33 O _{2 as} a positive electrode active material, polyvinylidene fluoride (PVDF) as a positive electrode binder, acetylene black as a positive electrode conductive agent in a weight ratio of 84: 9: 7, N A slurry-like solution was prepared by adding methyl-2-pyrrolidone and further mixing. The prepared slurry was applied to a positive electrode current collector 120 made of a SUS foil with 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 applied amount of the slurry was adjusted such 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.

<Fabrication of Negative Electrode 200>
Graphite (amorphous coating, average particle diameter 10 μm) as a negative electrode active material, polyvinylidene fluoride (PVDF) as a negative electrode binder, and acetylene black as a negative electrode conductive agent are mixed in a weight ratio of 88: 10: 2, N-methyl A slurry solution was prepared by adding -2-pyrrolidone and further mixing. The prepared slurry was applied to a negative electrode current collector 220 made of SUS foil with a thickness of 10 μm using a doctor blade, and dried at 80 ° C. for 2 hours or more. At this time, the applied amount of the slurry was adjusted such 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.

<Production of Secondary Battery 1000>
The produced 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. Thereafter, the negative electrode 200 is disposed on one side of the semi-solid electrolyte layer 300, and the positive electrode 100 is placed on the other side, placed in a 2032 size coin-type battery cell holder, the semi-solid electrolyte is injected, and sealing is performed by a caulking machine. A battery 1000 was produced.

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 addition amounts of the first additive and the first additive were changed as shown in FIG.

Example 21
Ionic liquid (Py13 TFSI) composed of LiTFSI as lithium imide salt (electrolyte salt), N-methyl-N-propylpyrrolidinium (Py13) as main solvent and bis (trifluoromethanesulfonyl) imide (TFSI), low viscosity solvent LiTFSI and Py13 TFSI were prepared so that the concentration of LiTFSI was 1 mol / L, using PC as Then, PC of the same volume as Py13TFSI was added to prepare a mixed solvent. A semi-solid electrolyte is 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, Py13 TFSI, and PC. did. A semisolid 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 addition amounts of the first additive and the first additive were changed as shown in FIG.

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

<Method of measuring dissolution onset 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 with an electrode area of 1 cm ² was used here, and Li metal was used as a counter electrode to sandwich it to prepare an evaluation cell. There, the potential was swept from a potential range of 3.0 V to 6.0 V at a scanning potential of 10 μV / sec, and the potential at which the oxidation current rose [to Li foil] (V) was measured.

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

<Evaluation of cycle characteristics>
After performing the initial charge and discharge according to the previous procedure, repeat the charge and discharge cycle 100 times at 1 C rate for the amount of current at the time of charge and discharge, and evaluate the discharge capacity after 100 cycles again, from the ratio to the initial discharge capacity The capacity retention rate was calculated. In addition, after charging and discharging, the secondary battery 1000 was rested for one hour in an open circuit state.

<Result and Result Discussion>
The result of an Example and a comparative example is shown in FIG. The dissolution onset potential of the positive electrode current collector 120 in the example is higher than the dissolution onset potential of the positive electrode current collector 120 in the comparative example, and the elution of the electrode current collector was able to be suppressed in the example.

In Comparative Examples 3 to ₆ in which highly hydrolyzable LiPF ₆ and LiBF ₄ were used as the first additive, the capacity retention rate was as low as 30% although it improved. This is considered to be because the first additive was decomposed and consumed by the water contained in the produced electrode and was not appropriately used for film formation on the positive electrode current collector 120.

On the other hand, in Examples 1 to ₄ using the low hydrolyzable NBu ₄ PF ₆ and NBu ₄ BF ₄ as the first additive, the capacity retention ratio is improved to 68% or more, and the SEM after disassembly analysis In EDX analysis, detection of the metal component resulting from the dissolution of the positive electrode current collector 120 was not confirmed. Further, the dissolution onset potential of the positive electrode current collector 120 was greatly 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 the case of NBu ₄ PF ₆ . Furthermore, the ion conductivity tends to be higher than that of NBu ₄ PF ₆ , which is a desirable result in terms of charge and discharge rate.

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

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

Examples 15 to 17 are different from Example 10 in the type of the low viscosity organic solvent. 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 ion conductivity of Example 2 is high and the first time discharge capacity is increasing. Therefore, it was found that when PC is used as the low viscosity organic solvent, the initial discharge capacity is increased.

Examples 18 to 20 are different from Example 10 in the type of the second additive. The capacity 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 has higher ion conductivity than the complex of G4 and LiTFSI in Example 10, and the initial discharge capacity has increased.

The charge / discharge cycle test results of Example 1 and Comparative Example 1 are shown in FIG. In Comparative Example 1 in which the liquid component did not contain the first additive, the capacity dropped sharply during 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 is clearly eluted, and from SEM-EDX (scanning electron microscope-energy dispersive X-ray spectroscopy), the eluted metal component is on the negative electrode 200 side It was confirmed that it was concentrated. This tendency was the same as in Comparative Example 2.

100 positive electrode
110 Positive mix layer
120 Positive current collector
130 Positive electrode tab part
200 negative electrode
210 Negative electrode mixture layer
220 negative electrode current collector
230 Negative electrode tab part
300 Semisolid Electrolyte Layer
400 electrode body
500 exterior body
1000 Secondary Battery All publications, patents and patent applications cited herein are incorporated herein by reference in their entirety.

Claims (7)

A mixed solvent comprising a semisolid electrolyte solvent and an electrolyte salt, and a first additive,
Anion of the first additive is BF ₄ ^- or PF ₆ ^- is and,
Semi-solid electrolytic solution wherein the formula weight of the cation of the first additive is 100 or more. In the semi-solid electrolyte according to claim 1,
The semi-solid electrolytic solution, wherein the addition amount of the first additive to the mixed solvent is 1 wt% to 20 wt%. In the semi-solid electrolyte according to claim 1,
Semi-solid electrolytic solution in which the mixed solvent further contains a low viscosity organic solvent. In the semi-solid electrolyte according to claim 1,
Semi-solid electrolyte containing a second additive. A semi-solid electrolyte comprising the semi-solid electrolyte according to claim 1 and particles. A semisolid electrolyte layer comprising the semisolid electrolyte according to claim 5 and a semisolid electrolyte binder. A positive electrode current collector and a positive electrode including a positive electrode mixture layer formed on the positive electrode current collector;
A negative electrode current collector and a negative electrode including a negative electrode mixture layer formed on the negative electrode current collector;
A semi-solid electrolyte layer according to claim 6, and a secondary battery.

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