WO2018230238A1

WO2018230238A1 - Semisolid electrolyte, electrode, electrode having semisolid electrolyte layer, and secondary battery

Info

Publication number: WO2018230238A1
Application number: PCT/JP2018/018977
Authority: WO
Inventors: 篤宇根本; 克上田; 敦史飯島; 明秀田中; 純川治; 奥村　壮文
Original assignee: 株式会社日立製作所
Priority date: 2017-06-15
Filing date: 2018-05-16
Publication date: 2018-12-20
Also published as: JPWO2018230238A1; KR20190119654A; KR102272029B1; CN110521049B; CN110521049A; JP6875522B2

Abstract

The purpose of the present invention is to prolong the life of a secondary battery. This semisolid electrolyte includes: a semisolid electrolytic solution that includes a semisolid electrolytic solvent and a negative electrode interface additive; and particles, wherein the weight ratio of the negative electrode interface additive with respect to the sum of the weight of the semisolid electrolyte and the weight of a negative electrode to be applied is 0.6-11.7%. The weight ratio of the negative electrode interface additive to be applied with respect to the sum of the weight of the semisolid electrolyte and the weight of the negative electrode is preferably 1.7-5.8% by weight. In the secondary battery which includes the semisolid electrolyte, the capacity maintenance rate of the secondary battery after a prescribed number of cycles is preferably higher than that of a secondary battery not including the negative electrode interface additive.

Description

Semi-solid electrolyte, electrode, electrode with semi-solid electrolyte layer, and secondary battery

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

As a conventional non-aqueous electrolyte secondary battery, Patent Document 1 discloses a positive electrode containing a positive electrode active material capable of inserting or removing anions, a negative electrode containing a negative electrode active material capable of inserting or removing cations, A non-aqueous electrolyte storage element comprising a non-aqueous electrolyte obtained by dissolving an electrolyte salt in an aqueous solvent, wherein the non-aqueous solvent comprises 85.0-99.9% by weight of chain carbonate with respect to the total amount of the non-aqueous solvent. And non-aqueous electrolyte, wherein the cyclic carbonate contains at least fluorinated cyclic carbonate, and the concentration of the electrolyte salt in the non-aqueous electrolyte is 2 mol / L or more A power storage element is disclosed.

JP 2016-058252 A

In the method of Patent Document 1, since the amount of fluorinated cyclic carbonate is regulated with respect to the weight of the non-aqueous solvent, it is difficult to improve the life of the secondary battery.

The present invention aims to improve the life of a secondary battery.

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

A semi-solid electrolyte containing a semi-solid electrolyte solvent and a negative electrode interface additive, and a semi-solid electrolyte containing particles, wherein the weight of the negative electrode interface additive is 0.6% relative to the sum of the weight of the semi-solid electrolyte and the negative electrode applied Semi-solid electrolyte that is ~ 11.7%.

This specification includes the disclosure of Japanese Patent Application No. 2017-117337, which is the basis of the priority of the present application.

The lifetime of the secondary battery can be improved by the present invention. Problems, configurations, and effects other than those described above will be clarified by the following description of embodiments.

It is an external view of a secondary battery. It is sectional drawing of a secondary battery. It is a table | surface which shows the result of an Example and a comparative example. It is a related figure of a deterioration coefficient and negative electrode interface additive weight ratio. It is a relationship diagram of negative electrode interface additive weight ratio and initial discharge capacity. It is a related figure of initial discharge capacity and negative electrode bulk density. It is a related figure of negative electrode bulk density and negative electrode interface additive weight ratio.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. The following description shows specific examples of the contents of the present invention, and the present invention is not limited to these descriptions. Various modifications by those skilled in the art are within the scope of the technical idea disclosed in this specification. Changes and modifications are possible. In all the drawings for explaining the present invention, components having the same function are denoted by the same reference numerals, and repeated description thereof may be omitted.

"~" Described in this specification is used to mean that the numerical values described before and after it are included as a lower limit value and an upper limit value. In the numerical ranges described stepwise in this 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 manner. The upper limit value or the lower limit value of the numerical ranges described in this specification may be replaced with the values shown in the examples.

In this specification, a lithium ion secondary battery will be described as an example of the secondary battery. A lithium ion secondary battery is an electrochemical device that can store or use electrical energy by occlusion / release of lithium ions to and from an electrode in a nonaqueous electrolyte. This is called by another name of a lithium ion battery, a non-aqueous electrolyte secondary battery, and a non-aqueous electrolyte secondary battery, and any battery is a subject of the present invention. The technical idea of the present invention can be applied to sodium ion secondary batteries, magnesium ion secondary batteries, aluminum ion secondary batteries and the like in addition to lithium ion secondary batteries.

FIG. 1 is an external view of a secondary battery according to an embodiment of the present invention. FIG. 2 is a cross-sectional view of a secondary battery according to an embodiment of the present invention. 1 and FIG. 2 are stacked secondary batteries, and the secondary battery 1000 includes a positive electrode 100, a negative electrode 200, an outer package 500, and a semi-solid electrolyte layer 300. FIG. The outer package 500 houses the semi-solid electrolyte layer 300, the positive electrode 100, and the negative electrode 200. The material of the outer package 500 can be selected from materials that are corrosion resistant to the nonaqueous electrolyte, such as aluminum, stainless steel, and nickel-plated steel. The present invention can also be applied to a wound secondary battery.

In the secondary battery 1000, an electrode body 400 including a positive electrode 100, a semi-solid electrolyte layer 300, and a negative electrode 200 is laminated. The positive electrode 100 or the negative electrode 200 may be referred to as an electrode or a secondary battery electrode. The positive electrode 100, the negative electrode 200, or the semi-solid electrolyte layer 300 may be referred to as a secondary battery sheet. A structure in which the semi-solid electrolyte layer 300 and the positive electrode 100 or the negative electrode 200 are integrated may be referred to as an electrode with a semi-solid electrolyte layer. The electrode with a semi-solid electrolyte layer has a semi-solid electrolyte layer containing a semi-solid electrolyte and an electrode, and the electrode is preferably a negative electrode.

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

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

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

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

The semi-solid electrolyte used for forming the semi-solid electrolyte layer 300 includes a semi-solid electrolyte solvent in which an electrolyte salt such as a lithium salt is dissolved in an ether solvent or an ionic liquid, a negative electrode interface additive, and an optional low-viscosity organic solvent. It is a material in which a semi-solid electrolyte and particles such as SiO ₂ are mixed. The semi-solid electrolyte layer 300 serves as a medium for transmitting lithium ions between the positive electrode 100 and the negative electrode 200 and also serves as an electronic insulator, thereby preventing a short circuit between the positive electrode 100 and the negative electrode 200.

A separator such as a microporous membrane may be used for the semisolid electrolyte layer 300. As the separator, polyolefin such as polyethylene or polypropylene, glass fiber, or the like can be used. When a microporous membrane is used for the separator, the semi-solid electrolyte is applied to the semi-solid electrolyte layer 300 by injecting the semi-solid electrolyte into the secondary battery 1000 from the vacant side or the injection hole of the outer package 500. Filled.

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

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

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

<Positive electrode active material>
In the positive electrode active material exhibiting a noble potential, lithium ions are desorbed during the charging process, and lithium ions desorbed from the negative electrode active material in the negative electrode mixture layer are inserted during the discharging process. As a material of the positive electrode active material, a lithium composite oxide containing a transition metal is desirable. Specific examples include LiMO ₂ , Li-rich composition Li [LiM] O ₂ , LiM ₂ O ₄ , LiMPO ₄ , LiMVO _x , LiMBO ₃ , Li ₂ MSiO ₄ (however, M = Co, Ni, Mn, Fe, Cr, Zn, Ta, Al, Mg, Cu, Cd, Mo, Nb, W, Ru, etc. are included) . Further, part of oxygen in these materials may be replaced with other elements such as fluorine. Furthermore, chalcogenides such as sulfur, TiS ₂ , MoS ₂ , Mo ₆ S ₈ and TiSe ₂ , vanadium oxides such as V ₂ O ₅ , halides such as FeF ₃ , Fe (MoO ₄ ) ₃ constituting polyanions, Examples include, but are not limited to, quinone organic crystals such as Fe ₂ (SO ₄ ) ₃ and Li ₃ Fe ₂ (PO ₄ ) ₃ . Furthermore, the amount of lithium or anion in the chemical composition may deviate from the above stoichiometric composition.

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

<Negative electrode active material>
In the negative electrode active material, lithium ions are desorbed in the discharging 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 exhibiting a base potential include carbon materials (eg, graphite, graphitizable carbon material, amorphous carbon material, organic crystal, activated carbon, etc.), conductive polymer materials (eg, polyacene). , Polyparaphenylene, polyaniline, polyacetylene), lithium composite oxides (eg, lithium titanate: Li ₄ Ti ₅ O ₁₂ and Li ₂ TiO ₄ ), metal lithium, metals alloyed with lithium (eg, aluminum, silicon) , Tin or the like) and oxides thereof can be used, but are not limited thereto.

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

<Electrode>
An electrode mixture layer is prepared by adhering an electrode slurry in which an electrode active material, an electrode conductive agent, an electrode binder, and an organic solvent are mixed to an electrode current collector by a doctor blade method, a dipping method, a spray method, or the like. Then, an organic solvent is dried and an electrode is produced by press-molding an electrode mixture layer by a roll press. The electrode slurry may contain a semisolid electrolyte or a semisolid electrolyte. A plurality of electrode mixture layers may be laminated on the electrode current collector by performing a plurality of times from application to drying. The thickness of the electrode mixture layer is preferably equal to or greater than the average particle diameter 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.

<Particle>
From the viewpoint of electrochemical stability, the particles are preferably insulative particles and insoluble in a semi-solid electrolytic solution containing an organic solvent or ionic liquid. As the particles, for example, oxide inorganic particles such as silica (SiO ₂ ) particles, γ-alumina (Al ₂ O ₃ ) particles, ceria (CeO ₂ ) particles, zirconia (ZrO ₂ ) particles can be preferably used. A solid electrolyte may be used as the particles. Examples of the solid electrolyte include particles of an inorganic solid electrolyte such as an oxide solid electrolyte or a sulfide solid electrolyte.

Since the amount of semi-solid electrolyte retained is considered to be proportional to the specific surface area of the particles, the average primary particle size of the particles is preferably 1 nm to 10 μm. If the average particle size of the primary particles of the particles is large, the particles may not properly hold a sufficient amount of the semisolid electrolyte, which may make it difficult to form a semisolid electrolyte. Moreover, when the average particle diameter of the primary particle of particle | grains is small, the surface force between particle | grains will become large and particle | grains will aggregate easily, and formation of a semi-solid electrolyte may become difficult. The average primary particle diameter of the particles is more preferably 1 nm to 50 nm, and further preferably 1 nm to 10 nm. The average particle size of the primary particles of the particles can be measured using a known particle size distribution measuring device using a laser scattering method.

<Semi-solid electrolyte>
The semi-solid electrolyte includes a semi-solid electrolyte solvent, an optional low viscosity organic solvent, and a negative electrode interface additive. The semi-solid electrolyte solvent includes an ionic liquid or a mixture of an ether solvent exhibiting similar properties to the ionic liquid and an electrolyte salt. When the semi-solid electrolyte contains a low-viscosity organic solvent, the electrolyte salt may contain a low-viscosity organic solvent instead of the semi-solid electrolyte. Moreover, you may contain in both a semi-solid electrolyte solvent and a low-viscosity organic solvent. An ionic liquid or an ether solvent may be referred to as a main solvent. An ionic liquid is a compound that dissociates into a cation and an anion at room temperature, and maintains a liquid state. The ionic liquid may be referred to as an ionic liquid, a low melting point molten salt or a room temperature molten salt. The semi-solid electrolyte solvent is desirably a low volatility, specifically, a vapor pressure at room temperature of 150 Pa or less from the viewpoint of stability in the air and heat resistance in the secondary battery.

When the electrode mixture layer contains a semisolid electrolyte, the content of the semisolid electrolyte in the electrode mixture layer is preferably 20% by volume to 40% by volume. When the content of the semi-solid electrolytic solution is small, there is a possibility that the ion conduction path inside the electrode mixture layer is not sufficiently formed and the rate characteristic is lowered. Moreover, when there is much content of a semi-solid electrolyte solution, a semi-solid electrolyte solution may leak from an electrode mixture layer.

The ionic liquid is composed of a cation and an anion. Ionic liquids are classified into imidazolium, ammonium, pyrrolidinium, piperidinium, pyridinium, morpholinium, phosphonium, sulfonium, and the like depending on the cation species. Examples of the cation constituting the imidazolium-based ionic liquid include alkyl imidazolium cations such as 1-ethyl-3-methylimidazolium (EMI) and 1-butyl-3-methylimidazolium (BMI). Examples of the cation constituting the ammonium-based ionic liquid include N, N-diethyl-N-methyl-N- (2-methoxyethyl) ammonium (DEME) and tetraamylammonium, as well as N, N, N- There are alkylammonium cations such as trimethyl-N-propylammonium. Examples of the cation constituting the pyrrolidinium-based ionic liquid include alkylpyrrolidinium cations such as N-methyl-N-propylpyrrolidinium (Py13) and 1-butyl-1-methylpyrrolidinium. Examples of the cation constituting the piperidinium-based ionic liquid include alkylpiperidinium cations such as N-methyl-N-propylpiperidinium (PP13) and 1-butyl-1-methylpiperidinium. Examples of the cation constituting the pyridinium-based ionic liquid include alkylpyridinium cations such as 1-butylpyridinium and 1-butyl-4-methylpyridinium. Examples of the cation constituting the morpholinium-based ionic liquid include alkylmorpholinium such as 4-ethyl-4-methylmorpholinium. Examples of cations constituting the phosphonium-based ionic liquid include alkylphosphonium cations such as tetrabutylphosphonium and tributylmethylphosphonium. Examples of the cation constituting the sulfonium-based ionic liquid include alkylsulfonium cations such as trimethylsulfonium and tributylsulfonium. Examples of the anion paired with these cations include bis (trifluoromethanesulfonyl) imide (TFSI), bis (fluorosulfonyl) imide (FSI), tetrafluoroborate (BF ₄ ), hexafluorophosphate (PF ₆ ), There are bis (pentafluoroethanesulfonyl) imide (BETI), trifluoromethanesulfonate (triflate), acetate, dimethyl phosphate, dicyanamide, trifluoro (trifluoromethyl) borate and the like. These ionic liquids may be used alone or in combination.

As the electrolyte salt used with the ionic liquid, one that can be uniformly dispersed in a solvent can be used. Lithium cation and those consisting of the above anions can be used as lithium salts, such as lithium bis (fluorosulfonyl) imide (LiFSI), lithium bis (trifluoromethanesulfonyl) imide (LiTFSI), lithium bis (pentafluoroethane) Examples include, but are not limited to, sulfonyl) imide (LiBETI), lithium tetrafluoroborate (LiBF ₄ ), lithium hexafluorophosphate (LiPF ₆ ), and lithium triflate. These electrolyte salts may be used alone or in combination.

The ether solvent constitutes a solvated ionic liquid together with the electrolyte salt. As an ether solvent, a symmetric glycol diglyceride represented by a known glyme (RO (CH ₂ CH ₂ O) n-R ′ (R and R ′ are saturated hydrocarbons, n is an integer)) showing properties similar to ionic liquids. The generic name of ether) can be used. From the viewpoint of ion conductivity, tetraglyme (tetraethylene dimethyl glycol, G4), triglyme (triethylene glycol dimethyl ether, G3), pentag lime (pentaethylene glycol dimethyl ether, G5), hexaglyme (hexaethylene glycol dimethyl ether, G6) It can be preferably used. In addition, crown ether (a general term for macrocyclic ethers represented by (—CH ₂ —CH ₂ —O) n (n is an integer)) can be used as an ether solvent. Specifically, 12-crown-4, 15-crown-5, 18-crown-6, dibenzo-18-crown-6 and the like can be preferably used, but are not limited thereto. These ether solvents may be used alone or in combination. Tetraglyme and triglyme are preferably used in that they can form a complex structure with the electrolyte salt.

As the electrolyte salt used together with the ether solvent, lithium imide salts such as LiFSI, LiTFSI, and LiBETI can be used, but are not limited thereto. A mixture of an ether solvent and an electrolyte salt may be used alone or in combination.

<Low viscosity organic solvent>
The low viscosity organic solvent lowers the viscosity of the semi-solid electrolyte solvent and improves the ionic conductivity. Since the internal resistance of the semi-solid electrolyte containing the semi-solid electrolyte solvent is large, the internal resistance of the semi-solid electrolyte can be lowered by increasing the ionic conductivity of the semi-solid electrolyte solvent by adding a low viscosity organic solvent. . However, since the semi-solid electrolyte solvent is electrochemically unstable, the decomposition reaction is accelerated with respect to the battery operation, causing the secondary battery 1000 to increase in resistance and decrease in capacity with the repeated operation of the secondary battery 1000. there is a possibility. Furthermore, in the secondary battery 1000 using graphite as the negative electrode active material, the cations of the semi-solid electrolyte solvent are inserted into the graphite during the charging reaction, destroying the graphite structure, and the repetitive operation of the secondary battery 1000 may not be possible. There is.

The low-viscosity organic solvent is desirably a solvent having a viscosity lower than 140 Pa · s, which is a viscosity of a mixture of an ether solvent and an electrolyte salt at 25 ° C., for example. Low-viscosity organic solvents include propylene carbonate (PC), trimethyl phosphate (TMP), gamma butyl lactone (GBL), ethylene carbonate (EC), triethyl phosphate (TEP), tris phosphite (2,2,2- Trifluoroethyl) (TFP), dimethyl methylphosphonate (DMMP), and the like. These low-viscosity organic solvents may be used alone or in combination. The above electrolyte salt may be dissolved in a low viscosity organic solvent. From the viewpoint of the capacity retention rate of the secondary battery 1000, EC is desirable as a low viscosity organic solvent.

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

<Semi-solid electrolyte>
A semi-solid electrolyte is constituted by supporting or holding the semi-solid electrolyte on the particles. As a method for producing a semi-solid electrolyte, a semi-solid electrolyte solution and particles are mixed at a specific volume ratio, an organic solvent such as methanol is added and mixed to prepare a semi-solid electrolyte slurry, and the slurry is then mixed with a petri dish. And a method of obtaining a semi-solid electrolyte powder by distilling off the organic solvent. When semi-solid electrolyte contains low-viscosity organic solvent, considering that low-viscosity organic solvent tends to volatilize, control so that semi-solid electrolyte is finally included in semi-solid electrolyte in the target amount It shall be.

<Semi-solid electrolyte layer 300>
Methods for producing the semi-solid electrolyte layer 300 include a method of compressing a semi-solid electrolyte powder into a pellet using a molding die, a method of adding a semi-solid electrolyte binder to a semi-solid electrolyte powder, and mixing it into a sheet. There is. By adding and mixing semi-solid electrolyte binder powder to the semi-solid electrolyte, a highly flexible sheet-like semi-solid electrolyte layer 300 can be produced. Moreover, the semi-solid electrolyte layer 300 can be produced by adding and mixing a solution of a binder in which a semi-solid electrolyte binder is dissolved in a dispersion solvent to the semi-solid electrolyte and distilling off the dispersion solvent. The semi-solid electrolyte layer 300 may be produced by applying and drying the above-mentioned semi-solid electrolyte with a binder solution added and mixed on the electrode.

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

<Negative bulk density>
By setting the negative electrode bulk density (hereinafter also simply referred to as negative electrode density or density) to a predetermined value, the battery capacity of the secondary battery 1000 can be improved. Specifically, (negative electrode bulk density (g / cm ³ )) ≦ −0.05042 (negative electrode interface additive weight ratio (%)) ² +0.4317 (negative electrode interface additive weight ratio (%)) + 0.9032, especially Desirably, (negative electrode bulk density (g / cm ³ )) ≦ −0.076 (weight ratio of negative electrode interface additive (%)) ² +0.571 (weight ratio of negative electrode interface additive (%)) + 0.6251. Here, the weight ratio of the negative electrode interface additive means the weight ratio of the negative electrode interface additive to the sum of the weight of the semisolid electrolyte and the weight of the applied negative electrode (hereinafter the same). The method for measuring the negative electrode bulk density can be obtained by measuring the weight and thickness of the negative electrode mixture layer 210 applied on the current collector foil. Specifically, it can be obtained by dividing the measured weight of the negative electrode mixture layer 210 by the product of the thickness and area of the negative electrode mixture layer 210.

<Negative electrode interface additive>
The negative electrode interface additive forms a passive film on the negative electrode surface and suppresses reductive decomposition of the semi-solid electrolyte. Examples of the negative electrode interface additive include vinylene carbonate (VC), lithium bis (oxalate) borate (LiBOB), fluoroethylene carbonate (FEC), and ethylene sulfite. These negative electrode interface additives may be used alone or in combination.

The semi-solid electrolyte of the present invention comprises a semi-solid electrolyte solvent, an optional low-viscosity organic solvent and a semi-solid electrolyte solution containing a negative electrode interface additive, and particles, with respect to the sum of the weight of the semi-solid electrolyte and the negative electrode applied. It is used by applying to the negative electrode so that the weight of the negative electrode interface additive is 0.6% to 11.7%. By defining the amount of the negative electrode interface additive relative to the sum of the weight of the semisolid electrolyte and the negative electrode, the stability between the semisolid electrolyte and the interface of the negative electrode 200 containing graphite or the like is improved. Specifically, the weight ratio of the negative electrode interface additive to the sum of the weight of the semisolid electrolyte and the applied negative electrode (hereinafter referred to as the negative electrode interface additive weight ratio) is 0.6% to 11.7%, particularly 1.7% to 5.8. % Is desirable. When the weight ratio of the negative electrode interface additive is small, the interface between the semisolid electrolyte that contributes to the stable operation of the secondary battery 1000 and the negative electrode 200 containing graphite may not be formed, which may reduce the life of the secondary battery 1000. . When the weight ratio of the negative electrode interface additive is large, there is a possibility that a decomposition reaction is induced on the surface of the positive electrode 100, thereby reducing the Coulomb efficiency and increasing the battery resistance. The weight ratio of the negative electrode interface additive can be determined by determining the weight of the negative electrode interface additive relative to the sum of the weights of the semisolid electrolytes used for the negative electrode 200 and the semisolid electrolyte layer 300.

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

<Example 1>
<Preparation of semi-solid electrolyte>
Tetraglyme (G4) and lithium bis (trifluoromethanesulfonyl) imide (LiTFSI) were weighed so as to have a molar ratio of 1: 1, charged into a beaker, and mixed until a homogeneous solvent was prepared to produce a lithium glyme complex. . A lithium glyme complex and fumed silica nanoparticles having a particle diameter of 7 nm are weighed so that the volume ratio is 80:20, and further, propylene carbonate (PC) as a low viscosity organic solvent, vinylene carbonate (VC) as a negative electrode interface additive, Methanol was put into a beaker together with a stir bar and stirred at 600 rpm using a stirrer to obtain a uniform mixture. This mixture was put into an eggplant flask and dried for 3 hours at 100 mbar and 60 ° C. using an evaporator. After drying, the powder was passed through a 100 μm mesh sieve to obtain a powdery semi-solid electrolyte.

<Preparation of positive electrode 100>
Polyvinylidene fluoride (PVDF) prepared by dissolving LiNi _0.33 Mn _0.33 Co _0.33 O ₂ as a positive electrode active material, acetylene black as a positive electrode conductive agent, and N-methylpyrrolidone as a positive electrode binder has a weight ratio of 84: 7: 9 Weighed and mixed so that a positive electrode slurry was obtained. This was applied onto a stainless steel foil as the positive electrode current collector 120 and dried at 80 ° C. for 2 hours to remove N-methylpyrrolidone, thereby obtaining a positive electrode sheet. The positive electrode sheet was punched out with a diameter of 13 mm and uniaxially pressed to obtain a positive electrode 100 with a double-side coating amount of 37.5 g / cm ² and a density of 2.5 g / cm ³ .

<Preparation of negative electrode 200>
Graphite was used as the negative electrode active material. The negative electrode conductive agent and the negative electrode binder are the same as those of the positive electrode 100. These were weighed and mixed so that the weight ratio was 88: 2: 10 to obtain a negative electrode slurry. This was applied onto a stainless steel foil as the negative electrode current collector 220 and dried at 80 ° C. for 2 hours to remove N-methylpyrrolidone, thereby obtaining a negative electrode sheet. The negative electrode sheet was punched out with a diameter of 13 mm and uniaxially pressed to obtain a negative electrode 200 with a double-side coating amount of 17 mg / cm ² and a density of 1.6 g / cm ³ . The weight of the obtained negative electrode was measured.

<Preparation of semi-solid electrolyte layer 300>
The semi-solid electrolyte and polytetrafluoroethylene (PTFE) as a binder were weighed to a weight ratio of 95: 5, put into a mortar, and uniformly mixed. This mixture was set in a hydraulic press through a polytetrafluoroethylene sheet and pressed at 400 kgf / cm ² . Further, the sheet was rolled with a roll press machine having a gap set to 500 to produce a sheet-like semi-solid electrolyte layer 300 having a thickness of 200 μm. This was punched out to a diameter of 16 mm and used for the production of the following lithium ion secondary battery. The weight ratio of the lithium glyme complex to PC in the obtained semisolid electrolyte layer 300 was 55.5: 44.5. The weight of VC was 0.6% (negative electrode interface additive weight ratio) with respect to the sum of the weight of the semisolid electrolyte and the weight of the negative electrode 200.

<Production of lithium ion secondary battery>
A positive electrode 100, a negative electrode 200, and a semi-solid electrolyte layer 300 were laminated and sealed in a 2032 type coin cell to obtain a lithium ion secondary battery.

<Examples 2 to 9>
Example 1 was performed except that the weight of VC (weight ratio of negative electrode interface additive) with respect to the sum of the weight of the semisolid electrolyte and the negative electrode 200 was changed as shown in FIG.

<Examples 10 to 11>
Lithium bis (oxalate) borate (LiBOB) was used as the negative electrode interface additive, and the LiBOB weight (negative electrode interface additive weight ratio) relative to the sum of the weight of the semisolid electrolyte and the negative electrode 200 was as shown in FIG. The same as in Example 1.

<Examples 12 to 14>
Example except that fluoroethylene carbonate (FEC) was used as the negative electrode interface additive, and the weight of the FEC relative to the sum of the weight of the semisolid electrolyte and the negative electrode 200 (weight ratio of the negative electrode interface additive) was as shown in FIG. Same as 1.

<Example 15>
Ethylene carbonate (EC) is used as the low viscosity organic solvent, vinylene carbonate (VC) is used as the negative electrode interface additive, and the weight ratio of the lithium glyme complex and EC in the semisolid electrolyte layer 300 is as shown in FIG. Example 1 was repeated except that the weight of VC with respect to the sum of the weight of the solid electrolyte and the weight of the negative electrode 200 was 1.7%.

<Examples 16 to 33>
Example 1 was performed except that the density of the negative electrode 200, the weight of the semisolid electrolyte, and the weight of VC with respect to the sum of the negative electrode 200 (weight ratio of the negative electrode interface additive) were as shown in FIG.

<Comparative Example 1>
Example 1 was repeated except that no negative electrode interface additive was used.

<Comparative Examples 2-3>
Example 1 was performed except that the weight of VC (weight ratio of negative electrode interface additive) with respect to the sum of the weight of the semisolid electrolyte and the negative electrode 200 was changed as shown in FIG.

<Comparative Examples 4 to 9>
The same operation as in Examples 16 to 21 except that the negative electrode interface additive was not used.

<Measurement of discharge capacity>
For the lithium ion secondary batteries of Examples and Comparative Examples, the measurement voltage range is 2.7 V to 4.2 V, the battery is operated in the constant current-constant voltage mode, the discharge is operated in the constant current mode, and the discharge is performed after the first cycle discharge. The capacity (initial discharge capacity) and the discharge capacity after 30 cycle discharge (30 cycle discharge capacity) were measured.

<Discussion>
FIG. 3 shows the measurement results of Examples and Comparative Examples. Figure 3 shows the value obtained by dividing the initial discharge capacity by the 30-cycle discharge capacity (discharge capacity retention rate). It is considered that the initial discharge capacity strongly influences the battery capacity of the secondary battery 1000, and the discharge capacity maintenance ratio strongly influences the life of the secondary battery 1000. Therefore, the battery capacity evaluation standard was that the initial discharge capacity was 105 (mAh / g) or more, and the life evaluation standard was that the discharge capacity retention rate was 65% or more.

Regardless of the composition of the negative electrode interface additive, the discharge capacity retention rate was a desirable value for any of the examples. In particular, when the weight ratio of the negative electrode interface additive was 1.7% to 5.8%, the low-viscosity solvent was the same, and the 30-cycle discharge capacity was larger than that of the comparative example not including the negative electrode interface additive.

Regardless of the negative electrode bulk density, the example in which the negative electrode interface additive was added had a larger initial discharge capacity than the comparative example in which the negative electrode interface additive was not added.

FIG. 4 shows a relationship diagram between the deterioration coefficient and the negative electrode interface additive weight ratio. The discharge capacity retention rate was plotted against the cycle number 1/2, and the slope was obtained by linear approximation and defined as the degradation coefficient. The deterioration coefficient always takes a negative value, and the smaller the absolute value is, the higher the capacity retention rate is. As shown in FIG. 4, when the deterioration coefficient was plotted against the negative electrode interface additive weight ratio and the relationship between the two was fitted by the least square method, (deterioration coefficient) = − 0.1375 (negative electrode interface additive weight ratio) ² +2.0857 (weight ratio of negative electrode interface additive) -7.5141 From this relationship, it was found that the absolute value of the deterioration coefficient is smaller than that of Comparative Example 1 that does not include the negative electrode interface additive, and the weight ratio of the negative electrode interface additive is 15.2% or less. Note that the deterioration coefficient of the secondary battery 1000 not including the negative electrode interface additive is −7.5141, and the discharge capacity retention rate after 100 cycles is expected to be 24.9%. The deterioration factor is -5 (discharge capacity maintenance rate after 100 cycles is 50%) because the negative electrode interface additive weight ratio is 1.3% to 13.9%, and the deterioration factor is -3 (after 100 cycles). The reason why the discharge capacity retention ratio was 70%) was that the weight ratio of the negative electrode interface additive was 2.6% to 12.6%.

<The negative electrode interface additive is VC>
In a secondary battery in which the main solvent is G4, the low-viscosity organic solvent is PC, and the negative electrode interface additive is VC, the weight ratio of the negative electrode interface additive to the sum of the weight of the semisolid electrolyte and the negative electrode 200 is 0.6% to 11.7% In (Examples 1 to 9), compared with Comparative Example 1 that does not include the negative electrode interface additive, and Comparative Examples 2 and 3 in which the weight ratio of the negative electrode interface additive is 14.6% or more, the 30-cycle discharge capacity was large. When the weight ratio of the negative electrode interface additive was 0.6% to 5.8% (Examples 1 to 7), the 30-cycle discharge capacity was larger than those of Comparative Examples 1, 2 and 3. Furthermore, when the weight ratio of the negative electrode interface additive was 1.7% to 5.8% (Examples 3 to 7), the discharge capacity was as high as 130 mAh / g or more during the battery operation at least 30 times.

When the weight ratio of the negative electrode interface additive is small, the interface between the semi-solid electrolyte and the negative electrode 200 is not sufficiently stabilized, and the initial discharge capacity is reduced due to partial progress of co-insertion and reductive decomposition of the lithium glyme complex. It is possible. On the other hand, when the weight ratio of the negative electrode interface additive is large, it is considered that VC gradually decomposes on the surface of the positive electrode 100 with the cycle operation to induce high resistance, thereby reducing the discharge capacity.

In Example 15 where the low-viscosity organic solvent is EC, the initial discharge capacity and 30-cycle discharge capacity were large by setting the weight ratio of the negative electrode interface additive to 1.7%.

<The negative electrode interface additive is LiBOB>
In Examples 10 and 11 in which the negative electrode interface additive was LiBOB, the maximum value of the negative electrode interface additive weight ratio was 1.7%. This is because when the weight ratio is larger than this, the introduced LiBOB may not be completely dissolved in the mixed solvent. By setting the weight ratio of the negative electrode interface additive to 0.6% to 1.7%, the initial discharge capacity and the 30-cycle discharge capacity were larger than those of Comparative Example 1 not including LiBOB.

<Negative electrode interface additive is FEC>
In Examples 12 to 14 in which the negative electrode interface additive was FEC, the initial discharge capacity was larger than that of Comparative Example 1 containing no FEC, and the 30 cycle discharge capacity was 100 mAh / g or more.

When the weight ratio of the negative electrode interface additive was 1.7%, 3.5% and 5.8%, the discharge capacity retention rate decreased monotonously to 97%, 88% and 85%, respectively. This has the effect of partially stabilizing the interface between the graphite-containing negative electrode 200 and the semisolid electrolyte in the composition range where the weight ratio of the negative electrode interface additive is 1.7% or more, but it is in excess of the optimum weight ratio. It can be considered that the FEC decomposition reaction occurred at the interface between the positive electrode 100 and the semisolid electrolyte with repeated battery operation, and this caused high resistance.

<Negative electrode interface additive weight ratio and negative electrode bulk density>
When the electrode coating amount is constant, the battery capacity depends not only on the negative electrode interface additive weight ratio but also on the negative electrode bulk density. This is because when the negative electrode bulk density is small, the negative electrode 200 becomes thick and the resistance of the secondary battery may increase. Also, when the negative electrode bulk density is large, the gap inside the electrode becomes small, and the negative electrode interface additive does not reach the vicinity of the electrode current collector during the initial charge, so that the decomposition reaction of the semi-solid electrolyte is induced. This is because the resistance of the secondary battery may increase.

FIG. 5 shows the relationship between the initial discharge capacity and the negative electrode interface additive weight ratio, with the negative electrode bulk density being constant (1.12 to 1.77 g / cm ³ ) for Examples 16 to 33 and Comparative Examples 4 to 9. In this case, the initial discharge capacity was approximated by a quadratic function depending on the negative electrode interface additive weight ratio. On the other hand, the constant term of the approximate curve depended on the negative electrode bulk density.

FIG. 6 shows the relationship between the negative electrode bulk density and the initial discharge capacity for Examples 16 to 33 and Comparative Examples 4 to 9, with the negative electrode interface additive weight ratio being constant (0 to 5.8%). In this case, the initial discharge capacity was approximated by a straight line having a negative slope with respect to the negative electrode bulk density. The magnitude of the slope of the straight line was dependent on the weight ratio of the negative electrode interface additive. These results in FIGS. 5 and 6 indicate that both the negative electrode bulk density and the negative electrode interface additive contribute as parameters of the initial discharge capacity.

The relationship between the negative electrode bulk density and the negative electrode interface additive weight ratio required to obtain a certain initial discharge capacity Q was determined from the approximate curves and approximate lines obtained from FIGS. 5 and 6, and is shown in FIG. Regardless of the negative electrode bulk density, the initial discharge capacity Q was increased by adding the negative electrode interface additive. In the region indicated by (negative electrode bulk density (g / cm ³ )) ≦ −0.05042 (negative electrode interface additive weight ratio (%)) ² +0.4317 (negative electrode interface additive weight ratio (%)) + 0.9032 The initial discharge capacity Q was 120 mAh / g or more. Further, in the region indicated by (negative electrode bulk density (g / cm ³ )) ≦ −0.076 (negative electrode interface additive weight ratio (%)) ² +0.571 (negative electrode interface additive weight ratio (%)) + 0.6251 The initial discharge capacity Q was 130 mAh / g or more.

100 positive electrode
110 Positive electrode mixture layer
120 Positive electrode current collector
130 Positive electrode tab
200 Negative electrode
210 Negative electrode mixture layer
220 Negative electrode current collector
230 Negative electrode tab
300 Semi-solid electrolyte layer
400 electrode body
500 exterior body
1000 Secondary battery

All publications, patents and patent applications cited in this specification are incorporated herein by reference in their entirety.

Claims

A semi-solid electrolyte solution comprising a semi-solid electrolyte solvent and a negative electrode interface additive, and a semi-solid electrolyte comprising particles,
A semi-solid electrolyte in which the weight ratio of the negative electrode interface additive to the sum of the weight of the semi-solid electrolyte and the weight of the applied negative electrode is 0.6% to 11.7%.
The semi-solid electrolyte of claim 1,
A semi-solid electrolyte in which the weight ratio of the negative electrode interface additive to the sum of the weight of the semi-solid electrolyte and the weight of the applied negative electrode is 1.7% to 5.8%.
The semi-solid electrolyte of claim 1,
The negative electrode interface additive is a semi-solid electrolyte that is vinylene carbonate (VC).
The semi-solid electrolyte of claim 1,
The semi-solid electrolyte is a semi-solid electrolyte further comprising a low viscosity organic solvent.
An electrode having a semi-solid electrolyte layer containing the semi-solid electrolyte of claim 1.
An electrode with a semi-solid electrolyte layer comprising a semi-solid electrolyte layer containing the semi-solid electrolyte according to claim 1 and an electrode.
The electrode with a semi-solid electrolyte layer according to claim 6,
The electrode is a negative electrode;
An electrode with a semi-solid electrolyte layer that satisfies the following.
(Negative electrode bulk density (g / cm 3 )) ≦ −0.05042 (weight ratio of the negative electrode interface additive to the sum of the weight of the semisolid electrolyte and the negative electrode (%)) 2 +0.4317 (of the semisolid electrolyte Weight ratio of the negative electrode interface additive to the sum of weight and negative electrode weight (%)) + 0.9032
A secondary battery having a semi-solid electrolyte layer comprising the semi-solid electrolyte of claim 1,
A secondary battery in which a capacity retention rate of the secondary battery after a predetermined cycle is larger than a capacity retention ratio of the secondary battery when the negative electrode interface additive is not included.