WO2021225065A1

WO2021225065A1 - Non-aqueous electrolytic solution, semi-solid electrolyte layer, sheet for secondary battery, and secondary battery

Info

Publication number: WO2021225065A1
Application number: PCT/JP2021/015591
Authority: WO
Inventors: 篤宇根本; 祥晃熊代; 栄二關; 和英上野; 薫獨古; 正義渡邉
Original assignee: 株式会社日立製作所; 国立大学法人横浜国立大学
Priority date: 2020-05-08
Filing date: 2021-04-15
Publication date: 2021-11-11
Also published as: JP2021177470A; CN115461907A; JP7553044B2

Abstract

The purpose of the present invention is to provide a non-aqueous electrolytic solution with which the discharge capacity retention of a secondary battery operated at a relatively high temperature can be maintained at a high level.　The non-aqueous electrolytic solution contains an electrolyte salt and an organic solvent, wherein the organic solvent includes a main solvent, which is at least one selected from the group consisting of sulfolane and derivatives thereof, and a low viscosity organic solvent, the concentration of the electrolyte salt in the main solvent is 1.06-3.46 mol/L, and the dielectric constant of the organic solvent is 63 or less.

Description

Non-aqueous electrolyte solution, semi-solid electrolyte layer, secondary battery sheet and secondary battery

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

As a prior art relating to a non-aqueous electrolyte solution used in various secondary batteries, Patent Document 1 describes a non-aqueous solvent, an electrolyte salt, and an overcharge control agent that causes an oxidation-reduction reaction at a predetermined potential, and has high thermal stability. , A heat-stable salt that stably remains in the non-aqueous electrolyte solution, a protective film-forming agent that forms a protective film on the positive and negative electrodes to suppress the decomposition of the overcharge control agent, or a complex that forms a complex with the transition metal. Liquid or gel-like non-aqueous electrolytes containing at least one of the forming agents are disclosed.

Japanese Unexamined Patent Publication No. 2012-256502

The electrolytic solution in the lithium ion secondary battery of Patent Document 1 is insufficient to maintain a high discharge capacity retention rate of the secondary battery when the secondary battery is operated at a relatively high temperature, and is still improved. There was room for.

An object of the present invention is to provide a non-aqueous electrolytic solution capable of maintaining a high discharge capacity retention rate of a secondary battery when the secondary battery is operated at a relatively high temperature. Another object of the present invention is to provide a semi-solid electrolyte layer using the non-aqueous electrolyte solution, a sheet for a secondary battery, and a secondary battery.

In order to solve the above problems, the non-aqueous electrolyte solution of the present invention contains an electrolyte salt and an organic solvent, and the organic solvent is at least one main solvent and a low-viscosity organic solvent selected from the group consisting of sulfolanes and derivatives thereof. The concentration of the electrolyte salt with respect to the main solvent is 1.06 mol / L to 3.46 mol / L, and the relative permittivity of the organic solvent is 63 or less.
This specification includes the disclosure of Japanese Patent Application No. 2020-082631, which is the basis of the priority of the present application.

The non-aqueous electrolyte solution of the present invention provides a non-aqueous electrolyte solution capable of maintaining a high discharge capacity retention rate of the secondary battery when the secondary battery is operated at a relatively high temperature. Issues, configurations and effects other than those described above will be clarified by the following description of the embodiments.

It is sectional drawing which shows one Embodiment of the secondary battery of this invention. It is a graph which shows the relationship between the lithium salt concentration (mol / L) with respect to the main solvent and the discharge capacity retention rate (%) at 45 degreeC in Examples and Comparative Examples. It is a graph which shows the relationship between the relative permittivity of an organic solvent (mixed solvent) in an Example and a comparative example, and a discharge capacity retention rate (%) at 45 degreeC.

Hereinafter, embodiments of the present invention will be described with reference to 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. 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.

"-" Described in this specification is used to mean that the numerical values described before and after it are used as the lower limit value and the upper limit value. When the upper limit value or the lower limit value is 0, the upper limit value or the lower limit value is not included. 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 limit value or the lower limit value of the numerical range described in the present specification may be replaced with the value shown in the examples.

As an 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 stores or makes available electrical energy by storing and releasing lithium ions into 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 any of these batteries is 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.

When selecting a material from the material group illustrated below, the material may be selected alone or in combination within a range not inconsistent with the contents disclosed in the present specification. In addition, materials other than the material group illustrated below may be selected as long as they do not contradict the contents disclosed in the present specification.

FIG. 1 is a cross-sectional view of a lithium ion secondary battery according to an embodiment of the present invention. FIG. 1 shows a laminated lithium ion secondary battery, in which the lithium ion secondary battery 1000 has a positive electrode 100, a negative electrode 200, an exterior body 500, and an insulating layer 300. The exterior body 500 houses the insulating layer 300, the positive electrode 100, and the negative electrode 200. The exterior body 500 is selected from a group of materials having corrosion resistance to a non-aqueous electrolytic solution such as aluminum, stainless steel, and nickel-plated steel. The lithium ion secondary battery may also have a winding type configuration.

In the lithium ion secondary battery 1000, an electrode body 400 composed of a positive electrode 100, an insulating layer 300, and a negative electrode 200 is laminated to form an electrode group. Hereinafter, the positive electrode 100 or the negative electrode 200 may be referred to as an electrode. Further, a sheet in which the positive electrode 100 and / or the negative electrode 200 and the insulating layer 300 are laminated may be referred to as a secondary battery sheet. When the insulating layer 300 and the electrodes are integrated, 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. 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 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 referred to as an electrode tab. No electrode mixture layer is formed on the electrode tab. However, the electrode mixture layer may be formed on the electrode tab as long as the performance of the lithium ion secondary battery 1000 is not adversely affected. The positive electrode tab 130 and the negative electrode tab 230 project to the outside of the exterior body 500, and the plurality of protruding positive electrode tabs 130 and the plurality of negative electrode tabs 230 are bonded to each other by, for example, ultrasonic bonding, thereby forming lithium ions. A parallel connection is formed within the secondary battery 1000. The lithium ion secondary battery according to the present invention may also have a bipolar configuration having an electrical series connection inside the secondary battery.

The positive electrode mixture layer 110 contains a positive electrode active material, a positive electrode conductive agent, and a positive electrode binder. The negative electrode mixture layer 210 contains a negative electrode active material, a negative electrode conductive agent, and a negative electrode binder. 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.

<Electrode conductive agent>
The electrode conductive agent improves the conductivity of the electrode mixture layer. As the electrode conductive agent, it can be appropriately selected and used from a material group such as Ketjen black, acetylene black, and graphite.

<Electrode binder>
The electrode binder binds the electrode active material, the electrode conductive agent, and the like in the electrode. As the electrode binder, a copolymer (P (P)) of styrene-butadiene rubber (SBR), carboxymethyl cellulose (CMC), polyvinylidene fluoride (PVDF), vinylidene fluoride (VDF) and hexafluoropropylene (HFP). It can be appropriately selected and used from a material group such as VdF-HFP)).

<Positive electrode active material>
Lithium ions are desorbed from the positive electrode active material showing a noble potential in the charging process, and lithium ions desorbed from the negative electrode active material are inserted in the discharging process. As the positive electrode active material, a lithium composite oxide having a transition metal is desirable. Specifically, LiMO ₂ , Li excess composition 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 and the like). Further, a part of oxygen in these materials may be replaced with another element such as fluorine. Further, 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} , and Fe (MoO _{4) constituting polyanions.} ) ₃ , Fe ₂ (SO ₄ ) ₃ , Li ₃ Fe ₂ (PO ₄ ) _3, etc., can contain at least one selected from the material group such as quinone-based organic crystals and oxygen.

<Positive current collector 120>
The positive electrode current collector 120 includes an aluminum foil having a thickness of 1 μm to 100 μm, 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, and stainless steel. It can be appropriately selected and used from a material group such as a material such as titanium.

<Negative electrode active material>
In the negative electrode active material showing a low potential, 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. Examples of the negative electrode active material include carbon-based materials (graphite, easily graphitized carbon material, amorphous carbon material, organic crystals, activated carbon, etc.), conductive polymer materials (polyacene, polyparaphenylene, polyaniline, polyacetylene, etc.), and lithium. Composite oxides (lithium titanate: Li ₄ Ti ₅ O ₁₂ , Li ₂ TiO _4, etc.), metallic lithium, metals alloying with lithium (having at least one type of aluminum, silicon, tin, etc.) and oxides thereof. It can be appropriately selected and used from the material group such as.

<Negative electrode current collector 220>
The negative electrode current collector 220 includes 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, stainless steel, titanium, nickel, etc. It can be appropriately selected and used from the material group of.

<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 a solvent, to an electrode current collector by a coating method such as a doctor blade method, a dipping method, or a spray method. NS. The solvent is selected from a group of materials such as N-methylpyrrolidone (NMP) and water. Then, 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 solution, the content of the non-aqueous electrolyte solution in the electrode mixture layer is preferably 20% by volume to 40% by volume. When the content of the non-aqueous electrolyte 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 non-aqueous electrolyte solution is high, the non-aqueous electrolyte solution may leak from the electrode mixture layer, and the relative amount of the electrode active material becomes insufficient to increase the energy density. May lead to a decline.

In order to contain the non-aqueous electrolytic solution in the electrode mixture layer, the non-aqueous electrolytic solution is injected into the lithium ion secondary battery 1000 through an open side of the exterior body 500 or a liquid injection hole, and the electrode mixture layer is thinned. This can be done by filling the pores with a non-aqueous electrolytic solution. In addition, a slurry in which a non-aqueous electrolyte solution, an electrode active material, an electrode conductive agent, and an electrode binder are mixed is prepared, and the prepared slurry is applied together on the electrode current collector to be applied to the pores of the electrode mixture layer. It may be filled with a water electrolyte. As a result, the supporting particles such as those 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 the supporting particles, and these particles make the non-aqueous electrolyte solution. Can be retained.

It is desirable that the thickness of the electrode mixture layer is 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.

<Insulation layer 300>
The insulating layer 300 serves as a medium for transmitting ions between the positive electrode 100 and the negative electrode 200. The insulating layer 300 also acts as an electron insulator to prevent a short circuit between the positive electrode 100 and the negative electrode 200. The insulating layer 300 can have a semi-solid electrolyte layer. As the insulating layer 300, a separator and a semi-solid electrolyte layer may be used in combination.

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

A separator may be formed by applying a separator forming mixture having 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.

Separator particles are selected from a group of materials such as γ-alumina (Al ₂ O ₃ ), silica (SiO ₂ ), and 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 is appropriately selected from materials such as polyethylene (PE), PP, polytetrafluoroethylene (PTFE), PVDF, P (VdF-HFP), styrene butadiene rubber (SBR), polyargic acid, and polyacrylic acid. Can be used.

When the insulating layer 300 includes a separator, the separator is filled with the non-aqueous electrolytic solution by injecting the non-aqueous electrolytic solution into the lithium ion secondary battery 1000 from the open side of the exterior body 500 or the liquid injection hole. Can be done.

<Semi-solid electrolyte layer>
The semi-solid electrolyte layer has a semi-solid electrolyte binder and a semi-solid electrolyte. The semi-solid electrolyte has supported particles and a non-aqueous electrolyte solution. The semi-solid electrolyte has pores formed by aggregates of supported particles, in which the non-aqueous electrolyte solution is held. By retaining the non-aqueous electrolyte solution in the semi-solid electrolyte, the semi-solid electrolyte allows lithium ions to permeate. When a semi-solid electrolyte layer is used as the insulating layer 300 and the electrode mixture layer is filled with the non-aqueous electrolyte solution, it is not necessary to inject the non-aqueous electrolyte solution into the lithium ion secondary battery 1000.

The semi-solid electrolyte layer can be treated like a solid while containing a liquid component such as a non-aqueous electrolyte solution, and can be a translucent self-supporting membrane. Locally, a liquid component such as a non-aqueous electrolyte solution is responsible for lithium ion conduction, so that it exhibits high ion conductivity. That is, the semi-solid electrolyte layer has the advantages of both the high safety of the solid and the high ionic conduction characteristics of the liquid.

As a method for producing the semi-solid electrolyte layer, there are a method of compression molding the semi-solid electrolyte powder into pellets with a molding die or the like, and a method of adding and mixing the semi-solid electrolyte binder to the semi-solid electrolyte powder to form a sheet. be. By adding and mixing the semi-solid electrolyte binder to the powder of the semi-solid electrolyte, a highly flexible sheet-shaped semi-solid electrolyte layer can be produced. A solution of a binder 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 on a substrate such as an electrode, and the dispersion solvent is distilled off by drying. A semi-solid electrolyte layer may be prepared.

<Supported particles>
From the viewpoint of electrochemical stability, the supported particles are preferably insulating particles and insoluble in a non-aqueous electrolytic solution. The supporting particles can be appropriately selected from a group of materials such as _{SiO 2} particles, Al ₂ O ₃ particles, Celia (CeO ₂ ) particles, _{oxide inorganic particles such as ZrO 2 particles, and a solid electrolyte.} By using the oxide-inorganic particles as the supporting particles, the non-aqueous electrolyte solution can be held at a high concentration in the semi-solid electrolyte layer. Further, since gas is not generated from the oxide inorganic particles, a semi-solid electrolyte layer can be produced by a roll-to-roll process in the atmosphere. The solid electrolyte can be appropriately selected and used from a material group such as an oxide-based solid electrolyte such as Li-La-Zr-O and _{a sulfide-based solid electrolyte such as Li 10} Ge ₂ PS _12.

Since the holding amount of the non-aqueous electrolytic solution is considered to be proportional to the specific surface area of the supported particles, the average particle size of the primary particles of the supported particles is preferably 1 nm to 10 μm. If the average particle size of the primary particles of the supporting particles is large, the supporting particles may not be able to properly hold a sufficient amount of the non-aqueous electrolyte solution, and it may be difficult to form a semi-solid electrolyte. Further, if the average particle size of the primary particles of the supported particles is small, the intersurface force between the supported particles becomes large and the supported 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 supported particles is more preferably in the range of 1 nm to 50 nm, further preferably in the range of 1 nm to 10 nm. The average particle size of the primary particles of the supported particles can be measured using a TEM.

<Non-aqueous electrolyte>
The non-aqueous electrolyte solution contains a main solvent, a low-viscosity organic solvent having a relative permittivity different from that of the main solvent, an electrolyte salt, and an optional negative electrode interface stabilizer. The main solvent has a high relative permittivity and has the effect of increasing the concentration of lithium ions by dissociating the lithium salt. The main solvent is at least one selected from the group consisting of sulfolanes and derivatives thereof (also referred to as "sulfolanes and / or derivatives thereof"). Therefore, the main solvent may contain two or more kinds, for example, two kinds, three kinds, or four kinds of solvents selected from the group consisting of sulfolane and its derivatives. Sulfolanes and / or derivatives thereof, together with electrolyte salts, constitute solvated ionic liquids. In the following description, sulfolane and / or its derivative may be referred to as a main solvent. The components contained in the non-aqueous electrolytic solution can be measured by NMR or the like. The relative permittivity of the main solvent and the low-viscosity organic solvent can be measured by a relative permittivity measuring device.

The content of the non-aqueous electrolyte solution in the semi-solid electrolyte layer is not particularly limited, but is preferably 40% by volume to 90% by volume. If the content of the non-aqueous electrolyte solution is small, the interfacial resistance between the electrode and the semi-solid electrolyte layer may increase. Further, when the content of the non-aqueous electrolyte solution is large, the non-aqueous electrolyte solution may leak from the semi-solid electrolyte layer. When the semi-solid electrolyte layer is in the form of a sheet, the content of the non-aqueous electrolyte solution in the semi-solid electrolyte layer is preferably 50% by volume to 80% by volume, more preferably 60% by volume to 80% by volume. When a semi-solid electrolyte layer is formed by applying a mixture of a semi-solid electrolyte and a solution of a semi-solid electrolyte binder in a dispersion solvent on an electrode, the content of the non-aqueous electrolyte solution in the semi-solid electrolyte layer is It is preferably 40% by volume to 60% by volume.

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

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

Examples of the sulfolane derivative include those in which the hydrogen atom bonded to the carbon atom constituting the sulfolane ring is replaced with a fluorine atom, an alkyl group or the like. As a specific example, it can be appropriately selected and used from a material group such as fluorosulfolane, difluorosulfolane, and methylsulfolane.

<Electrolyte salt>
As the electrolyte salt, one that can be uniformly dispersed in a low-viscosity organic solvent is desirable, and when the cation is lithium, various lithium salts can be used. As electrolyte salts, lithium tetrafluoroborate (LiBF ₄ ), lithium bis (trifluoromethanesulfonyl) imide (LiTFSI), lithium bis (fluorosulfonyl) imide (LiFSI), LiClO ₄ , lithium bis (fluorosulfonyl) amide (LiFSA) , Lithium bis (trifluoromethanesulfonyl) amide (LiTFSA), a mixture of two or more of them, and the like, a material satisfying the above conditions can be appropriately selected and used. It is desirable to use _{LiBF 4} as the electrolyte salt. LiBF ₄ is stable with respect to a negative electrode active material such as graphite, and can increase the capacity of a secondary battery.

The solvated ionic liquid having a sulfolane and / or a derivative thereof and an electrolyte salt can be integrally described as an apparent composition. For example, a solvated ionic liquid composed of sulfolane and LiTFSI is expressed as Li (SL) _x TFSI (x = 2 to 6) as an apparent composition, and the number of moles is calculated as a single substance having this composition.

The concentration of the electrolyte salt with respect to the main solvent is preferably 1.06 mol / L to 3.46 mol / L. If the concentration is too high, the viscosity tends to increase, the resistance increases, and the capacity tends to decrease. If the concentration is too low, the solvent tends to be unstable and the life characteristics tend to deteriorate.

<Low viscosity organic solvent>
The low-viscosity organic solvent is an organic solvent having a relative permittivity different from that of the main solvent and having a lower viscosity than the solvated ionic liquid. Therefore, by mixing the low-viscosity organic solvent and the solvated ionic liquid, the viscosity of the solvated ionic liquid can be lowered and the ionic conductivity can be improved. When the internal resistance of the non-aqueous electrolytic solution is large, the internal resistance of the non-aqueous electrolytic solution can be reduced by adding a low-viscosity organic solvent to increase the ionic conductivity of the non-aqueous electrolytic solution.

Examples of the low-viscosity solvent include cyclic carbonate esters such as ethylene carbonate (EC), propylene carbonate (PC), 1,2-butylene carbonate (BC), and fluoroethylene carbonate (FEC), methyl ethyl carbonate (EMC), and carbonic acid. Acyclic esters such as dimethyl (DMC) and diethyl carbonate (DEC), trimethyl phosphate (TMP), triethyl phosphate (TEP), tris phosphite (2,2,2-trifluoroethyl) (TFP), methylphosphon It can be appropriately selected and used from a material group such as a phosphate ester such as dimethyl acid (DMMP), a lactone such as γ-butyrolactone (GBL), and a mixture of two or more thereof.

When the non-aqueous electrolyte solution contains one or more main solvents and one or more low-viscosity organic solvents, the relative dielectric constant Z of the mixed solvent (main solvent + low-viscosity organic solvent) is the relative dielectric of the i-th main solvent. the rate p _i, the molar ratio of the main solvent of the i in a mixed solvent q _i, the relative dielectric constant of the low viscosity organic solvent p _'i of the _i, moles of low viscosity organic solvent of the i in a mixed solvent when the ratio was q _'i,

(In the formula, n is the number of types of the main solvent contained in the mixed solvent, and m is the number of types of the low-viscosity organic solvent contained in the mixed solvent.)
It can be represented by, and Z is preferably 63 or less.

For example, when the non-aqueous electrolyte solution contains one kind of main solvent and one kind of low-viscosity organic solvent, the relative dielectric constant Z of the mixed solvent (main solvent + low-viscosity organic solvent) is the relative dielectric constant of the main solvent. When the molar ratio of the main solvent in the mixed solvent is q, the specific dielectric constant of the low-viscosity organic solvent is p', and the molar ratio of the low-viscosity organic solvent in the mixed solvent is q',
Z = p × q + p'× q'・・・ Equation (2)
It can be represented by, and Z is preferably 63 or less.

By adding a low-viscosity organic solvent having a low relative permittivity to the solvated ionic liquid, the viscosity of the solvated ionic liquid can be reduced. On the other hand, if a low-viscosity organic solvent is added too much to the solvated ionic liquid, the degree of dissociation of the lithium salt is lowered and high-quality SEI (Solid Electrolyte Interphase) cannot be formed, and the temperature is high (45 ° C.). Life characteristics are reduced. Therefore, by setting Z to 63 or less, it is possible to suppress a decrease in the dissociation degree of the lithium salt while reducing the viscosity of the solvated ionic liquid, and it is possible to improve the life characteristics at a high temperature (45 ° C.). can. The method for measuring the molar ratio of the main solvent in the mixed solvent and the molar ratio of the low-viscosity organic solvent in the mixed solvent can be measured by NMR.

<Negative electrode interface stabilizer>
Since the non-aqueous electrolyte solution contains the negative electrode interface stabilizer, the rate characteristics of the secondary battery can be improved and the battery life can be improved. The negative electrode interface stabilizer can be appropriately selected from a group of materials such as vinylene carbonate (VC) and fluoroethylene carbonate (FEC).

<Corrosion inhibitor>
The non-aqueous electrolyte solution may contain a corrosion inhibitor, if necessary. The corrosion inhibitor 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. As the corrosion inhibitor, a material _{containing an anionic species such as PF 6} or BF ₄ and containing a cation species having a strong chemical bond for forming a stable compound in a water-containing atmosphere is desirable.

As one index showing that the compound is stable in the atmosphere, the solubility in water and the presence or absence of hydrolysis can be mentioned. When the corrosion inhibitor is a solid, it is desirable that the solubility in water is less than 1%. In addition, 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 after the corrosion inhibitor absorbs moisture or mixes with water, it is heated at 100 ° C. or higher to remove water, and 95% of the residue has the same molecular structure as the original corrosion inhibitor. Means showing.

Corrosion ^{inhibitor, (M-R) + An} - denoted. ^(M-R) + An ^- cation is ^{(M-R) +.} M is selected from nitrogen (N), boron (B), phosphorus (P) or sulfur (S). R is composed of a hydrocarbon group.

^(M-R) + An ^- of the anion An ^- is. An ^- The, BF ₄ ^- or PF ₆ ^- it is preferably used. The anions of corrosion inhibitor 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.

Corrosion inhibitors are quaternary ammonium salts such as tetrabutylammonium hexafluorophosphate (TBAPF ₆ ) and tetrabutylammonium tetrafluorobolate (TBABF ₄ ), 1-ethyl-3-methylimidazolium tetrafluorobolate (EMI-BF _4). ), 1-Ethyl-3-methylimidazolium hexafluorophosphate (EMI-PF ₆ ), 1-butyl-3-methylimidazolium tetrafluorobolate (BMI-BF ₄ ), 1-butyl-3-methylimidazolium hexa. It can be appropriately selected and used from a material group such as an imidazolium salt such as fluorophosphate (BMI-PF _6). In particular, when 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 preferably 0.5% by weight to 20% by weight, more preferably 1% by weight to 10% by weight, based on the total weight of the non-aqueous electrolyte solution. 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 be reduced with charging and discharging. In addition, if the content of the corrosion inhibitor is high, the lithium ion conductivity is lowered, and a large amount of stored energy is consumed to decompose the corrosion inhibitor, which may result in a decrease in battery capacity. be.

<Semi-solid electrolyte binder>
As the semi-solid electrolyte binder, a fluorine-based resin is preferably used. The fluorine-based resin can be appropriately selected and used from a material group such as PTFE, PVDF, and P (VdF-HFP). By using PVDF or P (VdF-HFP), the adhesion between the insulating layer 300 and the electrode current collector is improved, so that the battery performance is improved.

<Semi-solid electrolyte>
A semi-solid electrolyte is formed by supporting or holding the non-aqueous electrolyte solution on the supporting particles. As a method for producing a semi-solid electrolyte, a non-aqueous electrolyte solution and a supporting particle 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 thereof include a method of spreading it on a chalet or the like and distilling off an organic solvent to obtain a powder of a semi-solid electrolyte.

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>
<Preparation of non-aqueous electrolyte solution>
Lithium bis (trifluoromethanesulfonyl) amide (LiTFSA), which is a lithium salt (Li salt), is used as an electrolyte salt, sulfolane (SL) is used as a main solvent, propylene carbonate (PC) is used as a low-viscosity solvent, and a graphite film is formed as a negative electrode interface stabilizer. Vinylene carbonate (VC), which is a material, and tetrabutylammonium hexafluorophosphate (TBA-PF ₆ ), which is an Al current collector foil suppression additive as a corrosion inhibitor, are weighed and mixed to prepare a non-aqueous electrolyte solution. Made. The components contained in the prepared non-aqueous electrolytic solution were quantified by NMR. As a result, the molar ratio of the main solvent (SL) to the low-viscosity solvent (PC) was 65.4: 34.6, and the lithium salt concentration was 2.37 mol / L.

<Preparation of positive electrode>
_LiNi 1/3 _Co 1/3 _Mn 1/3 _{O 2} based oxide as a positive electrode active material, acetylene black as a cathode electrical conductor, the PVDF dissolved in N- methylpyrrolidone as a positive electrode binder, the weight ratio of the solids 94 Each was weighed so as to have a ratio of: 4: 2, and these were uniformly mixed in a kneader. The obtained mixture was slurried by adding NMP to adjust the solid content concentration. Next, the slurry whose concentration was adjusted was applied to both sides of the aluminum foil, which is the positive electrode current collecting foil, with a tabletop coater, and passed through a drying furnace at 120 ° C. to obtain a positive electrode. The total amount of the positive electrode mixture (positive electrode active material + positive electrode conductive agent + positive electrode binder) was 30.1 mg / cm ^{2 on} both sides. The electrode density of the obtained positive electrode was adjusted to ^{3.15 g / cm 3 by a roll press.}

<Manufacturing of negative electrode>
Graphite as the negative electrode active material and styrene-butadiene rubber and carboxylmethyl cellulose as the negative electrode binder were weighed so that the weight ratio of the solid content was 98: 1: 1, and these were uniformly mixed by a kneader. The obtained mixture was slurried by adding water to adjust the solid content concentration. Next, the slurry whose concentration was adjusted was applied to both sides of the copper foil, which is the negative electrode current collecting foil, with a tabletop coater, and passed through a drying furnace at 100 ° C. to obtain a negative electrode. The amount of the negative electrode mixture (negative electrode active material + negative electrode binder) applied was 18.1 mg / cm ^{2 in} total on both sides. The electrode density of the obtained negative electrode was adjusted to ^{1.55 g / cm 3 by a roll press.}

<Formation of separator>
The separator was formed by applying a non-volatile electrolyte to the surface of the electrode mixture layer. _{First, SiO 2} having an average particle size of 1 μm as the supporting particles and vinylidene fluoride-hexafluoropropylene copolymer (P (VdF-HFP)) as the binder have a weight ratio of 89.3: 10.7. Each was weighed so as to be, and these were uniformly mixed in a kneader. The obtained mixture was slurried by adding NMP to adjust the solid content concentration. Next, the slurry having the adjusted concentration was applied to both the positive electrode and the negative electrode with a tabletop coater and passed through a drying oven at 100 ° C. to obtain a positive electrode and a negative electrode having a non-volatile electrolyte layer formed therein.

<Making secondary batteries>
<Assembly>
The prepared positive electrode and negative electrode were punched with an air punching machine so that the positive electrode mixture layer had a size of 45 mm × 70 mm and the negative electrode mixture layer had a size of 47 mm × 74 mm, and tab portions were formed on the positive electrode and the negative electrode. Then, the positive electrode and the negative electrode were dried at 100 ° C. for 2 hours to remove NMP in the electrodes. The dried positive electrode was sandwiched between microporous films made of resin having a thickness of 30 μm and a three-layer structure of PP / PE / PP, and three sides other than the side on which the tab portion was formed were heat-welded.

A positive electrode covered with a microporous film and a punched negative electrode were laminated in the order of negative electrode / positive electrode / negative electrode, and then a 50 μm-thick PTFE sheet was placed on the negative electrode. Each tab portion provided on the positive electrode and the negative electrode, an aluminum positive electrode terminal, and a nickel negative electrode terminal were welded by ultrasonic welding, respectively. The obtained electrode body is sandwiched between laminate films, one side for liquid injection is left, and three sides including the side on which the tab portion is formed are heat-sealed at 200 ° C. by a laminate sealing device for 20 hours at 50 ° C. It was vacuum dried. Next, after injecting a non-aqueous electrolytic solution from one side for liquid injection, one side for liquid injection was vacuum-sealed to obtain a secondary battery.

<Measurement of discharge capacity>
(1) Measurement of initial discharge capacity The prepared secondary battery is held at 25 ° C., charged with a constant current (CC) up to an upper limit voltage of 4.2 V at a charging rate of 0.05 C, and then the voltage is maintained at 4.2 V. , Constant voltage (CV) charging was performed until the current value decreased to 0.005C. Then, a constant current discharge was performed at a discharge rate of 0.05 C to a lower limit voltage of 2.7 V, and the initial discharge capacity of the secondary battery was measured.

(2) Cycle test at 45 ° C. After measuring the initial discharge capacity, the temperature of the secondary battery was raised to 45 ° C., and charging / discharging at 0.3 C was repeated for 100 cycles.

(3) Measurement of discharge capacity after cycle test The temperature of the secondary battery after the cycle test is lowered to 25 ° C, the temperature is maintained, CC charging is performed to the upper limit voltage of 4.2 V at a charging rate of 0.05 C, and then the voltage is applied. Was CV charged until the current value decreased to 0.005 C while maintaining the voltage at 4.2 V. Then, CC discharge was performed at a discharge rate of 0.05 C to a lower limit voltage of 2.7 V, and the discharge capacity of the secondary battery after the cycle test was measured.

(4) Calculation of 45 ° C discharge capacity retention rate The 45 ° C discharge capacity retention rate obtained from the ratio of the discharge capacity after the cycle test measured in (3) to the initial discharge capacity measured in (1) is evaluated as 100 cycle life. bottom.
45 ° C. Discharge capacity retention rate (%) (100 cycle life) = (Discharge capacity after cycle test / Initial discharge capacity) x 100 ... Equation (3)

<Examples 2 to 12, Comparative Examples 1 to 2>
A secondary battery was produced in the same manner as in Example 1 except that the composition of the non-aqueous electrolyte solution was changed as shown in Table 1, and the components contained in the non-aqueous electrolyte solution were quantified and the discharge capacity was measured.

Table 1 shows the composition of the secondary batteries of Examples 1 to 12 and Comparative Examples 1 and 2 and the 45 ° C. discharge capacity retention rate. FIG. 2 shows the relationship between the lithium salt concentration (mol / L) with respect to the main solvent in Examples and Comparative Examples and the discharge capacity retention rate (%) at 45 ° C., and FIG. 3 shows the relationship between the mixed solvents in Examples and Comparative Examples. The relationship between the relative permittivity and the discharge capacity retention rate (%) at 45 ° C. is shown.

<Results and discussion>
In FIG. 2, the 45 ° C. discharge capacity retention rate of the secondary battery was plotted against the lithium salt concentration. As shown in FIG. 2, when the lithium salt concentration is smaller than 2.21 mol / L, the 45 ° C. discharge capacity retention rate becomes small, and when the lithium salt concentration is 2.21 mol / L or more, the 45 ° C. discharge capacity is reduced. The maintenance rate has increased. This result is considered to be due to the fact that by mixing a low-viscosity organic solvent with low viscosity and a solvated ionic liquid, the viscosity of the non-aqueous electrolyte solution decreased and the ionic conductivity of the non-aqueous electrolyte solution increased. .. When the lithium salt concentration was higher than 2.21 mol / L, the lower the concentration, the higher the 45 ° C. discharge capacity retention rate tended to be. It is considered that this is because the lower the concentration, the more the solvent is coordinated to the lithium ions and stabilized.

From FIG. 2, the 45 ° C. discharge capacity retention rate Y of the secondary battery is represented by the following formula (4) according to the lithium salt concentration X in the range of the lithium salt concentration of 0.8 mol / L to 3.8 mol / L. It was confirmed that it would be done.
Y = -4.0167X ² + 18.13X + 73.574 ... Equation (4)

According to the formula (4), the range of the lithium salt concentration X at which the 45 ° C. discharge capacity retention rate is larger than the 45 ° C. discharge capacity retention rate (87.7%) of Comparative Example 1 (lithium salt concentration X = 1) is , 1.06 mol / L to 3.46 mol / L. The range of the lithium salt concentration X at which the 45 ° C. discharge capacity retention rate of the secondary battery was 89.5% or more was 1.25 mol / L to 3.26 mol / L. The range of the lithium salt concentration X at which the 45 ° C. discharge capacity retention rate of the secondary battery is 90% or more was 1.32 mol / L to 3.18 mol / L. Further, the range of the lithium salt concentration X at which the 45 ° C. discharge capacity retention rate of the secondary battery is 92% or more was 1.64 mol / L to 2.86 mol / L. Therefore, the range of the lithium salt concentration X is 1.06 mol / L to 3.46 mol / L, preferably 1.25 mol / L to 3.26 mol / L, and more preferably 1.32 mol / L to 3.18 mol / L. Is.

In FIG. 3, the 45 ° C. discharge capacity retention rate of the secondary battery was plotted against the relative permittivity of the mixed solvent in the non-aqueous electrolyte solution. As shown in FIG. 3, in a composition having a relative permittivity smaller than about 31.5, the larger the relative permittivity, the larger the 45 ° C. discharge capacity retention rate. On the other hand, in a composition having a relative permittivity larger than about 31.5, the smaller the relative permittivity, the larger the 45 ° C. discharge capacity retention rate. It is considered that the higher the relative permittivity that affects the dissociation of the electrolyte salt, the more remarkable the reduction decomposition of the solvent on the graphite surface when the electrolyte salt is added at a high concentration, and the smaller the discharge capacity retention rate at 45 ° C. Be done.

Here, the relative permittivity of the main solvent is A, the molar ratio of the main solvent in the mixed solvent is M, the relative permittivity of the low-viscosity organic solvent is B, and the molar ratio of the low-viscosity organic solvent in the mixed solvent is When N is set, the relative permittivity T of the mixed solvent can be defined by the following formula (5).
T = A × M + B × N ・・・ Equation (5)

Therefore, from FIG. 3, it was confirmed that the 45 ° C. discharge capacity retention rate Y of the secondary battery is represented by the following formula (6) by the relative permittivity T of the mixed solvent.
Y = -0.0065T ² + 0.41T + 88 ... Equation (6)

According to the formula (6), the range of the relative permittivity T of the mixed solvent in which the 45 ° C. discharge capacity retention rate is larger than the 45 ° C. discharge capacity retention rate (87.7%) of the secondary battery of Comparative Example 1 is It was 63 or less. The range of the relative permittivity T of the mixed solvent in which the 45 ° C. discharge capacity retention rate Z of the secondary battery was 89.5% or more was 3.9 to 59. Further, the range of the relative permittivity T of the mixed solvent at which the 45 ° C. discharge capacity retention rate of the secondary battery is 90% or more was 5.5 to 58. Further, the range of the relative permittivity T of the mixed solvent at which the 45 ° C. discharge capacity retention rate of the secondary battery is 92% or more was 12.5 to 51.0. Therefore, the range of the relative permittivity T of the mixed solvent is 63 or less, preferably 3.9 to 59, and more preferably 5.5 to 58.

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 Insulation layer 400 Electrode body 500 Exterior body 1000 Lithium ion secondary battery Cited herein. All published publications, patents and patent applications are incorporated herein by reference in their entirety.

Claims

A non-aqueous electrolyte solution containing an electrolyte salt and an organic solvent.
The organic solvent comprises at least one main solvent selected from the group consisting of sulfolanes and derivatives thereof, and a low viscosity organic solvent.
A non-aqueous electrolyte solution in which the concentration of the electrolyte salt with respect to the main solvent is 1.06 mol / L to 3.46 mol / L, and the relative permittivity of the organic solvent is 63 or less.
Low-viscosity organic solvents include ethylene carbonate, propylene carbonate, 1,2-butylene carbonate, fluoroethylene carbonate, methyl ethyl carbonate, dimethyl carbonate, diethyl carbonate, trimethyl phosphate, triethyl phosphate, tris phosphite (2,2). The non-aqueous electrolyte solution according to claim 1, which comprises at least one selected from the group consisting of 2-trifluoroethyl), dimethyl methylphosphonate and γ-butyrolactone.
The non-aqueous electrolyte solution according to claim 1, wherein the electrolyte salt contains at least one selected from the group consisting of lithium tetrafluoroborate and lithium bis (trifluoromethanesulfonyl) amide.
A semi-solid electrolyte layer containing the non-aqueous electrolyte solution, supporting particles and a semi-solid electrolyte binder according to claim 1.
A secondary battery sheet in which a positive electrode and / or a negative electrode and the semi-solid electrolyte layer according to claim 4 are laminated.
With the positive electrode
With the negative electrode
The semi-solid electrolyte layer according to claim 4, which is arranged between the positive electrode and the negative electrode.
Rechargeable battery with.