JP7270210B2 - Non-aqueous electrolyte, semi-solid electrolyte layer, sheet for secondary battery and secondary battery - Google Patents

Description

TECHNICAL FIELD The present invention relates to a non-aqueous electrolyte, a semi-solid electrolyte layer, a secondary battery sheet, and a secondary battery.

As a prior art related to non-aqueous electrolyte solutions used in various secondary batteries, Patent Document 1 describes two compounds containing an electrolyte, a non-aqueous solvent, and a predetermined compound having a carbon atom bonded to three oxygen atoms in the molecule. Non-aqueous electrolytes for secondary batteries are disclosed. The non-aqueous solvent can contain a sulfone compound such as sulfolane, and the amount of the sulfone compound is preferably 0.3% by volume or more, more preferably 1 volume in 100% by volume of the non-aqueous solvent. % or more, more preferably 5 volume % or more, preferably 40 volume % or less, more preferably 35 volume % or less, and even more preferably 30 volume % or less.

JP 2018-029034 A

Patent Document 1 does not describe or suggest using sulfolane as a component of the solvated ionic liquid, and in that case, the input/output characteristics of the secondary battery change depending on the content of sulfolane. Therefore, with the technique of Patent Document 1, there is a possibility that sufficient input/output characteristics of the secondary battery cannot be obtained. In particular, when sulfolane is simply contained in the non-aqueous electrolyte, there is a risk that the life of the secondary battery at high temperatures may be shortened or sufficient rate characteristics may not be obtained. do not have.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a non-aqueous electrolytic solution capable of improving the input/output characteristics of a secondary battery, particularly improving the life and rate characteristics at high temperatures. Another object of the present invention is to provide a semi-solid electrolyte layer, a secondary battery sheet, and a secondary battery using the non-aqueous electrolyte.

The present inventors have found that a solvated ionic liquid containing sulfolane and/or a derivative thereof and an electrolyte salt, an optional low-viscosity organic solvent, and a non-aqueous electrolyte containing an optional negative electrode interface stabilizer, the formulation of each component The inventors have found that the above problems can be solved by adjusting the ratio within a predetermined range, and completed the invention.

That is, the non-aqueous electrolyte of the present invention comprises a solvated ionic liquid having sulfolane and/or a derivative thereof and an electrolyte salt, an optional low-viscosity organic solvent, and an optional negative electrode interface stabilizer, The equilibrium vapor pressure of the solvent at room temperature is 1 Pa or more, and the ratio of the number of moles of the solvated ionic liquid to the total number of moles of the solvated ionic liquid and the low-viscosity organic solvent is X, and the solvated ionic liquid When the ratio of the weight of the negative electrode interface stabilizer to the total weight of the low-viscosity organic solvent is Y (%),
Y≤142.86X-11.429
is characterized by satisfying

The non-aqueous electrolyte of the present invention can improve the input/output characteristics of a secondary battery. In addition, it is possible to extend the life of the secondary battery at high temperatures and improve the rate characteristics. Problems, configurations, and effects other than those described above will be clarified by the following description of the embodiments.

1 is a cross-sectional view of a lithium ion secondary battery according to this embodiment; FIG. 4 is a graph showing the relationship between the molar ratio X and the weight ratio Y (%) in Examples and Comparative Examples. 4 is a graph showing changes in 40° C. discharge capacity retention rate with respect to molar ratio X in Examples and Comparative Examples.

Embodiments of the present invention will be described below with reference to 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 within the scope of the technical ideas disclosed in the present specification. Changes and modifications are possible. In addition, in all the drawings for explaining the present invention, parts having the same functions are denoted by the same reference numerals, and repeated explanations thereof may be omitted.

In this specification, "~" is used to mean having the lower and upper limits of the numerical values before and after it. In the numerical ranges described stepwise in this specification, the upper limit value or lower limit value described in one numerical range may be replaced with the upper limit value or lower limit value described in other steps. The upper or lower limits of the numerical ranges described herein may be replaced with the values shown in the examples.

As one embodiment of the secondary battery according to the present invention, a lithium ion secondary battery will be described below as an example. A lithium ion secondary battery is an electrochemical device that can store or utilize electrical energy by intercalating and deintercalating lithium ions to and from electrodes in an electrolyte. Lithium-ion secondary batteries are also called by other names such as lithium-ion batteries, non-aqueous electrolyte secondary batteries, and non-aqueous electrolyte secondary batteries, and all of these batteries are covered by the present invention. The technical idea of the present invention can also be applied to sodium ion secondary batteries, magnesium ion secondary batteries, calcium ion secondary batteries, zinc secondary batteries, aluminum ion secondary batteries and the like.

When selecting a material from the material group exemplified below, the material may be selected singly or in combination as long as it is not inconsistent with the content disclosed in this specification. , materials other than those exemplified below may be selected as long as they are consistent with what is disclosed herein.

FIG. 1 is a cross-sectional view of a lithium ion secondary battery according to one embodiment of the present invention. FIG. 1 shows a laminated lithium ion secondary battery, and a lithium ion secondary battery 1000 has a positive electrode 100 , a negative electrode 200 , an exterior body 500 and an insulating layer 300 . The outer package 500 accommodates the insulating layer 300 , the positive electrode 100 and the negative electrode 200 . The exterior body 500 is selected from a group of materials, such as aluminum, stainless steel, and nickel-plated steel, which are corrosion-resistant to the non-aqueous electrolyte. The lithium ion secondary battery can also have a wound configuration.

In the lithium ion secondary battery 1000, an electrode assembly 400 composed of a positive electrode 100, an insulating layer 300 and a negative electrode 200 is stacked to form an electrode group. Below, the positive electrode 100 or the negative electrode 200 may be called an electrode. Moreover, a laminate of the positive electrode 100 and/or the negative electrode 200 and the insulating layer 300 may be referred to as a secondary battery sheet. When the insulating layer 300 and the electrodes are integrally structured, the electrode group can be produced only by laminating the secondary battery sheets.

The positive electrode 100 has a positive electrode current collector 120 and a positive electrode mixture layer 110 . A positive electrode mixture layer 110 is formed on both surfaces 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 . 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 cathode current collector 120 has a cathode tab 130 . The negative electrode current collector 220 has a negative electrode tab 230 . The positive electrode tab 130 or the negative electrode tab 230 may be called an electrode tab. No electrode mixture layer is formed on the electrode tab. However, an electrode material mixture layer may be formed on the electrode tab within a range that does not adversely affect the performance of the lithium ion secondary battery 1000 . The positive electrode tabs 130 and the negative electrode tabs 230 protrude to the outside of the outer package 500, and the plurality of protruding positive electrode tabs 130 and the plurality of negative electrode tabs 230 are bonded together by, for example, ultrasonic bonding, thereby producing lithium ions. A parallel connection is formed within the secondary battery 1000 . The lithium-ion secondary battery according to the present invention can also be configured as a bipolar type with an electrical series connection within the secondary battery.

The positive electrode mixture layer 110 includes a positive electrode active material, a positive electrode conductor, and a positive electrode binder. The negative electrode mixture layer 210 includes a negative electrode active material, a negative electrode conductor, and a negative electrode binder. A positive electrode active material or a negative electrode active material may be referred to as an electrode active material, a positive electrode conductive agent or a negative electrode conductive agent may be referred to as an electrode conductive agent, and a positive electrode binder or a negative electrode binder may be referred to as an electrode binder.

<Electrode Conductive Agent>
The electrode conductive agent improves the conductivity of the electrode mixture layer. As the electrode conductive agent, it is possible to appropriately select and use from a group of materials such as ketjen black, acetylene black, and graphite.

<Electrode binder>
The electrode binder binds the electrode active material, electrode conductive agent, etc. in the electrode. Examples of electrode binders include styrene-butadiene rubber (SBR), carboxymethyl cellulose (CMC), polyvinylidene fluoride (PVDF), and a copolymer of vinylidene fluoride (VDF) and hexafluoropropylene (HFP) (P ( VdF-HFP)), etc. can be appropriately selected and used.

<Positive electrode active material>
In the positive electrode active material exhibiting a noble potential, lithium ions are desorbed during the charging process, and the lithium ions desorbed from the negative electrode active material are inserted during the discharging process. A lithium composite oxide containing a transition metal is desirable as the positive electrode active material. Specifically, LiMO ₂ , Li-excess Li[LiM]O ₂ , LiM ₂ O ₄ , LiMPO ₄ , LiMVO ₄ , LiMBO ₃ , Li ₂ MSiO ₄ (where M is Co, Ni, Mn, Fe , Cr, Zn, Ta, Al, Mg, Cu, Cd, Mo, Nb, W, Ru, etc.). Also, part of oxygen in these materials may be replaced with other elements such as fluorine. Furthermore, the positive electrode active material includes 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 , Fe (MoO ₄ ) ₃ , Fe ₂ (SO ₄ ) ₃ , Li ₃ Fe ₂ (PO ₄ ) ₃ , quinone-based organic crystals, and oxygen.

<Positive electrode current collector 120>
As the positive electrode current collector 120, aluminum foil with a thickness of 1 to 100 μm, perforated aluminum foil with a thickness of 10 to 100 μm and holes with a hole diameter of 0.1 to 10 mm, expanded metal, foamed metal plate, stainless steel, It can be used by appropriately selecting from a group of materials such as titanium.

<Negative electrode active material>
Lithium ions are desorbed from the negative electrode active material exhibiting a base potential in the discharging process, and the lithium ions desorbed from the positive electrode active material in the positive electrode mixture layer 110 are inserted in the charging process. Examples of negative electrode active materials include carbon materials (graphite, graphitizable carbon materials, amorphous carbon materials, organic crystals, activated carbon, etc.), conductive polymer materials (polyacene, polyparaphenylene, polyaniline, polyacetylene, etc.), lithium Composite oxides (lithium titanate: _Li4Ti5O12 , _Li2TiO4 , etc.), _metallic lithium, metals alloyed with _lithium (having at least one kind of aluminum, silicon, tin, _etc. ) and oxides thereof can be selected from a group of materials such as

<Negative electrode current collector 220>
As the negative electrode current collector 220, copper foil with a thickness of 1 to 100 μm, perforated copper foil with a thickness of 1 to 100 μm and a hole diameter of 0.1 to 10 mm, expanded metal, metal foam plate, stainless steel, titanium, nickel, etc. can be used by appropriately selecting from the group of materials.

<Electrode>
An electrode mixture layer is produced by adhering an electrode slurry obtained by mixing an electrode active material, an electrode conductive agent, an electrode binder, and a solvent to an electrode current collector by a coating method such as a doctor blade method, a dipping method, or a spray method. be. Solvents are selected from the group of materials such as N-methylpyrrolidone (NMP), water, and the like. Thereafter, the electrode mixture layer is dried to remove the solvent, and the electrode mixture layer is pressure-molded by a roll press to produce an electrode.

When the electrode mixture layer contains a non-aqueous electrolyte, the content of the non-aqueous electrolyte in the electrode mixture layer is preferably 20 to 40% by volume. When the content of the non-aqueous electrolyte is small, there is a possibility that the ion conduction path is not sufficiently formed inside the electrode mixture layer and the rate characteristics are deteriorated. In addition, when the content of the non-aqueous electrolyte is large, the non-aqueous electrolyte may leak from the electrode mixture layer, and the relative amount of the electrode active material is insufficient, resulting in a decrease in energy density. may lead to a decline.

In order to contain the non-aqueous electrolyte in the electrode mixture layer, the non-aqueous electrolyte is injected into the lithium ion secondary battery 1000 through one open side of the outer package 500 or the injection hole, and the electrode mixture layer is finely divided. The pores can be filled with a non-aqueous electrolyte. Alternatively, a slurry is prepared by mixing a non-aqueous electrolyte, an electrode active material, an electrode conductive agent, and an electrode binder, and the prepared slurry is applied on an electrode current collector together so that the pores of the electrode mixture layer are non-porous. Aqueous electrolyte may be filled. As a result, the particles of the electrode active material, the electrode conductive agent, etc. in the electrode mixture layer function as supporting particles, and the non-aqueous electrolyte is supported by these particles without requiring the supporting particles contained in the semi-solid electrolyte. can hold.

The thickness of the electrode mixture layer is desirably equal to or greater than the average particle size of the electrode active material. If the thickness of the electrode mixture layer is too small, the electronic 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 greater than the thickness of the electrode mixture layer, the coarse particles are removed in advance by sieve classification, wind classification, or the like, and particles having an average particle size equal to or less than the thickness of the electrode mixture layer are removed. It is desirable to

<Insulating layer 300>
The insulating layer 300 serves as a medium for transferring ions between the positive electrode 100 and the negative electrode 200 . The insulating layer 300 also acts as an insulator for electrons and prevents a short circuit between the positive electrode 100 and the negative electrode 200 . The insulating layer 300 has a semi-solid electrolyte layer. As the insulating layer 300, a separator and a semi-solid electrolyte layer may be used together.

<Separator>
A porous sheet can be used as the separator. The porous sheet is made of cellulose, modified cellulose (carboxymethyl cellulose (CMC), hydroxypropyl cellulose (HPC), etc.), polyolefin (polypropylene (PP), propylene copolymer, etc.), polyester (polyethylene terephthalate (PET), Polyethylene naphthalate (PEN), polybutylene terephthalate (PBT), etc.), polyacrylonitrile (PAN), polyaramid, polyamideimide, polyimide and other resins, glass, and other materials. By making the separator larger in area than the positive electrode 100 or the negative electrode 200, short circuit between the positive electrode 100 and the negative electrode 200 can be prevented.

The separator may be formed by applying a separator-forming mixture containing separator particles, a separator binder and a solvent to the electrode mixture layer. Alternatively, the separator-forming mixture may be applied to the porous sheet.

The separator particles are selected from a group of materials such as gamma-alumina (Al ₂ O ₃ ), silica (SiO ₂ ), zirconia (ZrO ₂ ). The average particle size of the separator particles is preferably 1/100 to 1/2 of the thickness of the separator. The separator binder can be selected from a group of materials such as polyethylene (PE), PP, polytetrafluoroethylene (PTFE), PVDF, P (VdF-HFP), styrene-butadiene rubber (SBR), polyalginic acid, polyacrylic acid. can.

When the insulating layer 300 includes a separator, the non-aqueous electrolyte is injected into the lithium ion secondary battery 1000 through one open side of the outer package 500 or the injection hole, thereby filling the separator with the non-aqueous electrolyte. can be done.

<Semisolid electrolyte layer>
The semi-solid electrolyte layer has a semi-solid electrolyte binder and a semi-solid electrolyte. A semi-solid electrolyte has support particles and a non-aqueous electrolyte. A semi-solid electrolyte has pores formed by aggregates of support particles, in which a non-aqueous electrolyte is retained. By retaining the non-aqueous electrolyte in the semi-solid electrolyte, the semi-solid electrolyte is permeable to lithium ions. When a semi-solid electrolyte layer is used as the insulating layer 300 and the electrode mixture layer is filled with a non-aqueous electrolyte, injection of the non-aqueous electrolyte into the lithium ion secondary battery 1000 becomes unnecessary. If the insulating layer 300 has a separator or the like, the nonaqueous electrolyte may be injected into the lithium ion secondary battery 1000 through one open side of the outer package 500 or through an injection hole.

The semi-solid electrolyte layer can be a translucent self-supporting film that can be handled like a solid while containing a liquid component such as a non-aqueous electrolyte. Locally, a liquid component such as a non-aqueous electrolyte is responsible for lithium ion conduction, so that high ion conductivity is exhibited. That is, the semi-solid electrolyte layer has both advantages of the high safety of solids and the high ionic conductivity of liquids.

As a method of manufacturing the semi-solid electrolyte layer, there is a method of compressing the semi-solid electrolyte powder into a pellet shape using a molding die or the like, and a method of adding and mixing a semi-solid electrolyte binder to the semi-solid electrolyte powder to form a sheet. be. By adding and mixing the semi-solid electrolyte powder with the semi-solid electrolyte binder, a highly flexible sheet-like semi-solid electrolyte layer can be produced. A binder solution in which a semi-solid electrolyte binder is dissolved in a dispersion solvent is added to and mixed with the semi-solid electrolyte, the mixture is applied to a substrate such as an electrode, and the dispersion solvent is distilled off by drying. A semi-solid electrolyte layer may be produced.

<Carried particles>
From the viewpoint of electrochemical stability, the carrier particles are preferably insulating particles that are insoluble in the non-aqueous electrolyte. The support particles are selected from a group of materials such as SiO ₂ particles, Al ₂ O ₃ particles, ceria (CeO ₂ ) particles, oxide inorganic particles such as ZrO ₂ particles, solid electrolytes and the like. By using inorganic oxide particles as the support particles, the non-aqueous electrolyte can be retained at a high concentration in the semi-solid electrolyte layer. Moreover, since no gas is generated from the oxide inorganic particles, the semi-solid electrolyte layer can be produced by a roll-to-roll process in the atmosphere. The solid electrolyte is appropriately selected from a group of materials such _as oxide _- based solid electrolytes such as Li--La--Zr--O and sulfide-based solid electrolytes such as _{Li.sub.10Ge.sub.2PS.sub.12} .

Since the amount of non-aqueous electrolyte retained is considered to be proportional to the specific surface area of the support particles, the average particle size of the primary particles of the support particles is preferably 1 nm to 10 μm. If the average particle size of the primary particles of the support particles is large, the support particles may not be able to properly hold a sufficient amount of the non-aqueous electrolyte, making it difficult to form a semi-solid electrolyte. In addition, when the average particle size of the primary particles of the support particles is small, the surface-to-surface force between the support particles increases, and the support particles tend to agglomerate, which may make it difficult to form a semi-solid electrolyte. The average particle size of the primary particles of the support particles is more preferably in the range of 1 to 50 nm, and even more preferably in the range of 1 to 10 nm. The average particle size of the primary particles of the support particles can be measured using TEM.

<Non-aqueous electrolyte>
The non-aqueous electrolyte has a non-aqueous solvent. Non-aqueous solvents include solvated ionic liquids, any low viscosity organic solvent, and any negative electrode interfacial stabilizer. In the following description, the solvated ionic liquid may be referred to as the main solvent. Components contained in the non-aqueous electrolyte can be measured by NMR or the like.

An ionic liquid is a compound that dissociates into cations and anions at room temperature and maintains a liquid state. Ionic liquids are sometimes referred to as ionic liquids, low-melting-point molten salts, or normal-temperature molten salts. The non-aqueous solvent preferably has low volatility from the viewpoint of stability in the atmosphere and heat resistance in the secondary battery, and specifically has a vapor pressure of 150 Pa or less at room temperature. Not limited. When the non-aqueous electrolyte contains the hardly volatile solvated ionic liquid, volatilization of the non-aqueous electrolyte from the semi-solid electrolyte layer can be suppressed.

The content of the non-aqueous electrolyte in the semi-solid electrolyte layer is not particularly limited, but is desirably 40 to 90% by volume. If the content of the non-aqueous electrolyte is small, the interfacial resistance between the electrode and the semi-solid electrolyte layer may increase. Moreover, when the content of the non-aqueous electrolyte is large, there is a possibility that the non-aqueous electrolyte may leak out of the semi-solid electrolyte layer. When the semisolid electrolyte layer is sheet-like, the content of the non-aqueous electrolyte in the semisolid electrolyte layer is desirably 50 to 80% by volume, more preferably 60 to 80% by volume. When the semi-solid electrolyte layer is formed by applying a mixture of the semi-solid electrolyte and a solution in which the semi-solid electrolyte binder is dissolved in the dispersion solvent on the electrode, the content of the non-aqueous electrolyte in the semi-solid electrolyte layer is It is desirable to be 40 to 60% by volume.

The weight ratio of the main solvent in the non-aqueous electrolyte is not particularly limited, but from the viewpoint of the stability of the lithium ion secondary battery and to enable high-speed charging and discharging, the weight ratio of the main solvent in the non-aqueous electrolyte is is preferably 30 to 70% by weight, particularly 40 to 60% by weight, more preferably 45 to 55% by weight.

<Solvation ionic liquid>
A solvated ionic liquid comprises sulfolane and/or its derivatives and an electrolyte salt. When a solvated ionic liquid containing sulfolane and/or a derivative thereof is used, the sulfolane and/or derivative thereof and lithium ions form a unique coordination structure, so that the transport rate of lithium ions in the semi-solid electrolyte layer is increased. Become. Therefore, unlike the solvated ionic liquid having an ether solvent and an electrolyte salt, in which the input/output characteristics of the secondary battery deteriorate as the viscosity increases, the solvated ionic liquid can be used even if the viscosity of the solvated ionic liquid is increased. It is possible to suppress deterioration in input/output characteristics of the secondary battery.

Examples of sulfolane derivatives include those in which hydrogen atoms bonded to carbon atoms constituting the sulfolane ring are substituted with fluorine atoms, alkyl groups, or the like. Specific examples include fluorosulfolane, difluorosulfolane, methylsulfolane, and the like. Any one of these may be used alone, or a plurality of them may be used in combination.

As the electrolyte salt, one that can be uniformly dispersed in a low-viscosity organic solvent is desirable, and various lithium salts whose cation is lithium can be used. Examples include lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(pentafluoroethanesulfonyl)imide (LiBETI), lithium tetrafluoroborate ( _LiBF4 ), lithium hexa Fluorophosphate (LiPF ₆ ), lithium triflate and the like can be mentioned. Any one of these may be used alone, or two or more of them may be used in combination.

A solvated ionic liquid containing sulfolane and/or a derivative thereof and an electrolyte salt can be integrally described as an apparent composition. For example, a solvated ionic liquid consisting of sulfolane and LiTFSI is expressed as Li(SL) _x TFSI (x=2 to 3) as an apparent composition, and the number of moles is calculated as a single substance having this composition.

The mixing ratio of sulfolane and/or its derivative to the electrolyte salt is not particularly limited, but the molar ratio of (sulfolane and/or its derivative)/electrolyte salt is within the range of 1.0 to 3.5. Preferably.

<Low viscosity organic solvent>
A low-viscosity organic solvent lowers the viscosity of the non-aqueous electrolyte and improves the ionic conductivity. When the internal resistance of the non-aqueous electrolyte is high, the internal resistance of the non-aqueous electrolyte can be lowered by adding a low-viscosity organic solvent to increase the ionic conductivity of the non-aqueous electrolyte.

The equilibrium vapor pressure of the low-viscosity organic solvent at room temperature (25° C.) is desirably 1 Pa or more. As a result, volatilization of the low-viscosity organic solvent is suppressed, safety is improved, and the life of the lithium-ion secondary battery 1000 during high-temperature operation is improved. The equilibrium vapor pressure can be evaluated using a vapor pressure measuring device or the like.

The number of donors in the low-viscosity organic solvent is desirably 12 or more. As a result, the interaction between the low-viscosity organic solvent and lithium ions is strengthened, and the low-viscosity organic solvent is less likely to volatilize. The number of donors can be evaluated by NMR or the like.

As low-viscosity organic solvents having an equilibrium vapor pressure of 1 Pa or more at room temperature (25°C) and a donor number of 12 or more, propylene carbonate (PC), butylene carbonate (BC), ethylene carbonate (EC), trimethyl phosphate (TMP ), triethyl phosphate (TEP), tris(2,2,2-trifluoroethyl) phosphite (TFP), γ-butyrolactone (GBL), dimethyl methylphosphonate (DMMP), and the like.

<Negative electrode interface stabilizer>
By including the negative electrode interface stabilizer in the non-aqueous electrolyte, it is possible to improve the rate characteristics and the battery life of the secondary battery. The negative electrode interface stabilizer can be used by appropriately selecting from a material group such as vinylene carbonate (VC) and fluoroethylene carbonate (FEC).

<Input/output characteristics>
The ratio of the number of moles of the solvated ionic liquid (A) to the total number of moles of the solvated ionic liquid (A) and the low-viscosity organic solvent (B) is X (A / (A + B)), and the solvated ionic liquid (A) When the ratio of the weight of the negative electrode interface stabilizer (C) to the total weight of the low-viscosity organic solvent (B) is Y (C/(A+B)) (%),
Y≤142.86X-11.429
It is desirable to satisfy The values of X and Y can be measured by NMR.

As the weight of the negative electrode interface stabilizer increases, the transport rate of lithium ions increases, and the coordination structure between sulfolane and/or its derivatives and lithium ions is disturbed. may be inhibited. Therefore, in order to improve the input/output characteristics of the lithium ion secondary battery 1000, it is desirable that the weight of the negative electrode interface stabilizer be small.

<Life characteristics>
Regarding the ratio X of the number of moles of the solvated ionic liquid to the total number of moles of the solvated ionic liquid and the low-viscosity organic solvent, it is desirable to satisfy 0.35≦X<1. More preferably, 0.39≦X≦0.93, and still more preferably 0.45≦X≦0.87. By making X equal to or higher than the lower limit of the above range, excessive addition of the low-viscosity organic solvent is suppressed, reductive decomposition on the surface of the negative electrode active material contained in the negative electrode 200 is suppressed, and reduction in the life of the lithium ion secondary battery 1000 is suppressed. can do. In addition, by setting X to be equal to or less than the upper limit of the above range, the ion transport resistance is lowered, reversible exchange of lithium ions between the positive and negative electrodes is promoted, and lithium ion secondary battery 1000 is repeatedly operated. A decrease in the capacity of the ion secondary battery 1000 can be suppressed, and a decrease in the life of the lithium ion secondary battery 1000 can be suppressed.

<Corrosion inhibitor>
The non-aqueous electrolyte may contain a corrosion inhibitor as needed. The corrosion inhibitor forms a film in which the metal does not easily dissolve even when the positive electrode current collector 120 is exposed to a high electrochemical potential. As corrosion inhibitors, materials containing anionic species such as _PF6 and _BF4 and containing cationic species with strong chemical bonds to form compounds that are stable in moist atmospheres are desirable.

As one index indicating that a compound is stable in the atmosphere, the solubility in water and the presence or absence of hydrolysis can be cited. If the corrosion inhibitor is a solid, it should have a water solubility of less than 1%. In addition, the presence or absence of hydrolysis can be evaluated by molecular structure analysis of the sample mixed with water. Here, "do not hydrolyze" means that after the corrosion inhibitor absorbs moisture or is miscible with water, the water is removed by heating at 100° C. or higher, and 95% of the residue has the same molecular structure as the original corrosion inhibitor. means showing

Corrosion inhibitors are represented as (MR) ⁺ An ^- . The cation of (MR) ⁺ An ^- is (MR) ⁺ . M is selected from nitrogen (N), boron (B), phosphorus (P) or sulfur (S). R is composed of hydrocarbon groups.

The anion of (MR) ⁺ An ^- is An ^- . An ^- is preferably BF ₄ ^- or PF ₆ ^- . By using BF ₄ ⁻ or PF ₆ ⁻ as the anion of the corrosion inhibitor, the elution of the positive electrode current collector 120 can be efficiently suppressed. This is probably because the F anions of BF ₄ ^- and PF ₆ ^- react with SUS and aluminum of the electrode current collector to form a passive film.

Corrosion inhibitors include quaternary ammonium salts such as tetrabutylammonium hexafluorophosphate (TBAPF ₆ ), tetrabutylammonium tetrafluoroborate (TBABF ₄ ), 1-ethyl-3-methylimidazolium tetrafluoroborate (EMI-BF ₄ ), 1-ethyl-3-methylimidazolium hexafluorophosphate (EMI-PF ₆ ), 1-butyl-3-methylimidazolium tetrafluoroborate (BMI-BF ₄ ), 1-butyl-3-methylimidazolium It is selected from the group of imidazolium salt materials such as hexafluorophosphate (BMI-PF ₆ ). In particular, if the anion is PF ₆ ⁻ , the elution of the positive electrode current collector 120 can be suitably suppressed.

The content of the corrosion inhibitor is desirably 0.5 to 20% by weight, more preferably 1 to 10% by weight, based on the total weight of the non-aqueous electrolyte. If the content of the corrosion inhibitor is small, the effect of suppressing the elution of the electrode current collector is reduced, and the battery capacity may decrease with charging and discharging. In addition, if the corrosion inhibitor content is high, the lithium ion conductivity will decrease, and a large amount of stored energy will be consumed to decompose the corrosion inhibitor, resulting in a decrease in battery capacity. be.

<Semi-solid electrolyte binder>
A fluorine-based resin is preferably used as the semi-solid electrolyte binder. The fluorine-based resin is selected from a group of materials such as PTFE, PVDF and P(VdF-HFP). These materials may be used singly or in combination. By using PVDF or P (VdF-HFP), the adhesion between the insulating layer 300 and the electrode current collector is improved, so the battery performance is improved.

<Semisolid electrolyte>
A semi-solid electrolyte is formed by carrying or holding the non-aqueous electrolyte on the carrier particles. As a method for producing a semi-solid electrolyte, a non-aqueous electrolyte and supporting particles are mixed in a specific volume ratio, an organic solvent such as methanol is added and mixed to prepare a semi-solid electrolyte slurry, and then the slurry is prepared. Examples include a method of obtaining semi-solid electrolyte powder by spreading on a Petri dish or the like and distilling off the organic solvent.

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

(Example 1)
(1) Production of lithium ion secondary battery <Production of semi-solid electrolyte layer>
LiBF ₄ and sulfolane (SL) as electrolyte salts, and TBAPF ₆ as a corrosion inhibitor were weighed and mixed to obtain a non-aqueous electrolyte. This non-aqueous electrolyte and fumed silica nanoparticles with a particle size of 7 nm were weighed and mixed at a volume ratio of 80:20 to obtain a powdery semi-solid electrolyte.

The semi-solid electrolyte powder and the semi-solid electrolyte binder PTFE were weighed so that the weight ratio was 95:5, put into a mortar, and uniformly mixed. This mixture was set in a hydraulic press via a PTFE sheet and pressed to a thickness of 200 μm to obtain an insulating layer 300 (semi-solid electrolyte layer). When the mixing ratio of the liquid components contained in the semi-solid electrolyte layer was evaluated by NMR, the molar ratio of SL and _LiBF4 was 2:1, and the solvated ionic liquid Li(SL) _2BF4 composed of electrolyte salt and sulfolane _was obtained. The weight ratio of TBAPF ₆ to was 2.5%. This semi-solid electrolyte layer was punched out with a diameter of 16 mm.

<Positive electrode 100>
Li (Ni, Co, Mn) O ₂ -based oxide as a positive electrode active material, acetylene black as a positive electrode conductive agent, and PVDF as a positive electrode binder dissolved in N-methylpyrrolidone are mixed in a kneader at a predetermined ratio. and uniformly mixed. NMP was added to this mixture to obtain a slurry. The positive electrode 100 was obtained by applying the slurry onto an Al foil as the positive electrode current collector 120 using a desktop coater and drying it at 120°C. This positive electrode 100 was pressed with a predetermined pressure and cut to a diameter of 13 mm.

<Negative Electrode 200>
Graphite as a negative electrode active material and SBR and CMC as negative electrode binders were uniformly mixed at a predetermined ratio using a kneader. Water was added to this mixture to obtain a slurry. The negative electrode 200 was obtained by applying the slurry onto a Cu foil as the negative electrode current collector 220 using a desk coater and drying it at 100°C. This negative electrode 200 was pressed with a predetermined pressure and cut to a diameter of 13 mm.

<Lithium ion secondary battery 1000>
After the semi-solid electrolyte layer was sandwiched between the positive electrode 100 and the negative electrode 200 and enclosed in a CR2032 type coin cell, the composition of the final non-aqueous electrolyte in the semi-solid electrolyte layer, the positive electrode 100, and the negative electrode 200 was as shown in Table 1. A lithium ion secondary battery 1000 was produced by pouring a non-aqueous electrolyte into a CR2032 type coin cell so as to obtain the content.

(2) Characteristic evaluation of lithium ion secondary battery <Evaluation method of output characteristics>
In the first cycle charging, the lithium ion secondary battery 1000 was charged at 0.05C in a constant current mode to 4.2V. held at potential. The discharge in the first cycle was performed at 0.05 C in a constant current mode until the voltage reached 2.7 V, and the discharge capacity of the lithium ion secondary battery 1000 was measured. After that, the second cycle charging was performed in the same manner as the first cycle charging. In the second cycle, the discharge was performed in constant current mode at 0.5 C until the voltage reached 2.7 V, and the discharge capacity of the lithium ion secondary battery 1000 was measured. Table 1 shows the ratio of the capacity at 0.5C in the second cycle to the discharge capacity at 0.05C in the first cycle as "Q_0.5/Q_0.05". All the above measurements were made at 25°C.

<Method for evaluating life characteristics>
The charging/discharging of the first cycle was performed in the same manner as the charging/discharging of the first cycle in the method for evaluating output characteristics. In the second cycle charging, constant current charging was performed at 40° C. at 0.3C to 4.2V, and then the constant potential was maintained until the current value reached 0.03C. In the discharge of the second cycle, constant current discharge was performed at 0.3 C until reaching 2.7V. This was repeated 20 times, and the ratio of the discharge capacity at the 20th cycle to the discharge capacity at the 2nd cycle was defined as the discharge capacity retention rate (%). Table 1 shows the measurement results.

(Examples 2 to 44 and Comparative Examples 1 to 6)
A lithium ion secondary battery was produced in the same manner as in Example 1, except that the composition of the non-aqueous electrolyte was adjusted as shown in Table 1, and the capacity ratio "Q_0.5/Q_0.05" and the discharge capacity retention rate (%) was measured. Table 1 shows the measurement results.

(3) Results and Discussion FIG. 2 is a graph showing the relationship between the molar ratio X and the weight ratio Y (%) in Examples and Comparative Examples. Moreover, FIG. 3 is a graph showing changes in the 40° C. discharge capacity retention rate with respect to the molar ratio X in Examples and Comparative Examples.

As shown in Table 1 and FIG. 2, in all examples, that is, in the range satisfying Y≦142.86X−11.429, the capacitance ratio “Q_0.5/Q_0.05” indicating the input/output characteristics is 40%. That was it. On the other hand, in Comparative Examples 1 to 6, the capacity ratio was below 40%. Moreover, in all the examples in which the discharge capacity retention rate was measured, that is, in the range satisfying 0.35≦X<1, the discharge capacity retention rate indicating life characteristics was 75% or more. In particular, it was 85% or more in the examples satisfying 0.39≦X≦0.93, and 90% or more in the examples satisfying 0.45≦X≦0.87.

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 Insulating layer 400 Electrode body 500 Exterior body 1000 Lithium ion secondary battery

Claims (6)

A solvated ionic liquid having sulfolane and/or a derivative thereof and an electrolyte salt, a low -viscosity organic solvent, and a negative electrode interface stabilizer,
the low-viscosity organic solvent is propylene carbonate, butylene carbonate, ethylene carbonate, trimethyl phosphate, triethyl phosphate, tris(2,2,2-trifluoroethyl) phosphite, γ-butyrolactone or dimethyl methylphosphonate;
the negative electrode interface stabilizer is vinylene carbonate or fluoroethylene carbonate,
The low-viscosity organic solvent has an equilibrium vapor pressure of 1 Pa or more at room temperature,
Let X be the ratio of the number of moles of the solvated ionic liquid to the total number of moles of the solvated ionic liquid and the low-viscosity organic solvent,
When the ratio of the weight of the negative electrode interface stabilizer to the total weight of the solvated ionic liquid and the low-viscosity organic solvent is Y (%),
0.35≦X<1
Y≧3
Y≤142.86X-11.429
Non-aqueous electrolyte that satisfies 0.39≤X≤0.93
The non-aqueous electrolytic solution according to claim 1. 0.45≤X≤0.87
The non-aqueous electrolytic solution according to claim 1. A semi-solid electrolyte layer comprising the non-aqueous electrolyte according to any one of claims 1 to 3 , support particles, and a semi-solid electrolyte binder. A secondary battery sheet comprising a positive electrode and/or a negative electrode and the semi-solid electrolyte layer according to claim 4 laminated together. a positive electrode;
a negative electrode;
The semi-solid electrolyte layer according to claim 4 arranged between the positive electrode and the negative electrode;
A secondary battery.

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