JP2020053171A - Non-aqueous electrolyte, non-volatile electrolyte, and secondary battery - Google Patents

Abstract

To provide a non-aqueous electrolyte that improves battery safety.SOLUTION: There is provided a non-aqueous electrolyte with a volatilization temperature of 80°C or higher, and log (O/Li) which is the logarithm of the ratio of the amount of oxygen contained in the non-aqueous electrolyte to the amount of lithium contained in the non-aqueous electrolyte is 0.87 to 2.05.SELECTED DRAWING: None

Description

  The present invention relates to a non-aqueous electrolyte, a nonvolatile electrolyte, and a secondary battery.

As a technique relating to a non-aqueous electrolyte, Patent Document 1 discloses the following content. A hetero element-containing organic solvent containing a specific organic solvent having a relative dielectric constant of 10 or less and / or a dipole moment of 5 D or less, and a metal salt having lithium as a cation and having a chemical structure represented by the following general formula (1) as an anion , At a molar ratio of 3 to 5, and in the powder X-ray diffraction measurement, 1.10 ≦ (integrated intensity of peak derived from (003) plane I (003)) / derived from ((104) plane) Satisfies the integrated intensity I (104)) <2.0 of the peak to be obtained, or the general formula Li _a (Ni _x Co _y M _z ) O _b (1.05 ≦ a ≦ 1.20, 0.15 ≦ x ≦ 0.55, 0.25 ≦ y ≦ 0.75, 0.01 ≦ z ≦ 0.29, x + y + z = 1, 1.7 ≦ b ≦ 2.3, M is Mn, Zr, Mg, Ti, Al , W, Si, Mo, Fe, B, Zn, Cu) A lithium ion secondary battery comprising a lithium metal composite oxide having a layered rock salt structure represented by the formula:

International Publication No. WO 2016/143295

  In Patent Literature 1, there is no description or suggestion regarding the temperature at which the electrolytic solution volatilizes. Therefore, the electrolytic solution may volatilize depending on the use conditions of the battery, and the safety of the battery may be reduced.

  The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a non-aqueous electrolyte, a non-aqueous electrolyte having the non-aqueous electrolyte, and a secondary battery which improve the safety of the battery.

In order to solve the above problems, the present invention has, for example, the following configuration.
A non-aqueous electrolyte having a volatilization temperature of 80 ° C. or higher, and log (O / Li), which is a logarithm of the ratio of the amount of oxygen contained in the non-aqueous electrolyte to the amount of lithium contained in the non-aqueous electrolyte, is 0.87 to 2.05 non-aqueous electrolyte.

ADVANTAGE OF THE INVENTION According to this invention, the nonaqueous electrolyte which improves the safety | security of a battery, the non-volatile electrolyte which has a nonaqueous electrolyte, and a secondary battery can be provided.
Problems, configurations, and effects other than those described above will be apparent from the following description of the embodiments.

1 is a schematic cross-sectional view illustrating a configuration of a secondary battery according to one embodiment of the present invention. Regarding the contents of Table 1-2, Table 2-2, Table 3-2, and Table 4-2, the logarithm log (ion conductivity) of the ionic conductivity of the non-aqueous electrolyte is expressed as log (O / Li). It is the figure which plotted. In the figure, the horizontal axis indicates log (O / Li), and the vertical axis indicates log (ion conductivity) (S / cm). It is the figure which plotted the volatilization temperature of the nonaqueous electrolyte with respect to log (O / Li) about the content of Table 1-2, Table 2-2, Table 3-2, and Table 4-2. In the figure, the horizontal axis indicates log (O / Li), and the vertical axis indicates volatilization temperature (° C.). It is the figure which plotted the volatilization temperature of the non-volatile electrolyte with respect to log (O / Li) about the content of Table 1-2, Table 2-2, Table 3-2, and Table 4-2. In the figure, the horizontal axis indicates log (O / Li), and the vertical axis indicates volatilization temperature (° C.).

Hereinafter, embodiments of the present invention will be described with reference to the drawings and the like. The following description shows specific examples of the content of the present invention, and the present invention is not limited to these descriptions, and various modifications by those skilled in the art within the technical idea disclosed in the present specification. Changes and modifications are possible. In all the drawings for describing the present invention, components having the same function are denoted by the same reference numerals, and repeated description thereof may be omitted.
The term “to” described in this specification is used to mean that the numerical values described before and after it are used as a lower limit and an upper limit. In the numerical ranges described stepwise in this specification, the upper limit or lower limit described in one numerical range may be replaced with the upper limit or lower limit described in another step. The upper limit or lower limit of the numerical range described in this specification may be replaced with the value shown in the examples.

  In this specification, a lithium ion secondary battery will be described as an example of a secondary battery. A lithium ion secondary battery is an electrochemical device that stores or uses electric energy by inserting and extracting lithium ions into and from an electrode in an electrolyte. This is referred to by another name such as a lithium ion battery, a non-aqueous electrolyte secondary battery, and a non-aqueous electrolyte secondary battery, and any of the batteries is an object of the present invention. The technical idea of the present invention can 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 exemplified below, the material may be selected alone, or may be selected in combination of two or more, within a range not inconsistent with the content disclosed in the present specification. Alternatively, a material other than the material group exemplified below may be selected within a range not inconsistent with the content disclosed in the present specification.

  FIG. 1 is a schematic sectional view illustrating the configuration of a secondary battery according to one embodiment of the present invention. FIG. 1 illustrates a stacked secondary battery. As shown in FIG. 1, the secondary battery 1000 has a positive electrode 100, a negative electrode 200, a package 500, and an insulating layer 300. The outer package 500 contains the insulating layer 300, the positive electrode 100, and the negative electrode 200. The exterior body 500 may be formed of any material selected from a group of materials having corrosion resistance to a non-aqueous electrolyte, such as aluminum, stainless steel, and nickel-plated steel. The present invention can also be applied to a wound secondary battery.

An electrode body 400 composed of a positive electrode 100, an insulating layer 300, and a negative electrode 200 is stacked in a secondary battery 1000. It is preferable that the insulating layer 300 has a nonvolatile electrolyte layer having a nonvolatile electrolyte as described later. That is, in the present embodiment, the secondary battery 1000 may include the positive electrode 100, the negative electrode 200, and the non-volatile electrolyte layer having a non-volatile electrolyte described below formed between the positive electrode 100 and the negative electrode 200. preferable.
The positive electrode 100 or the negative electrode 200 may be called an electrode. The positive electrode 100, the negative electrode 200, or the insulating layer 300 may be referred to as a secondary battery sheet.

  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 surfaces of 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 surfaces of 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, an electrode mixture layer may be formed on the electrode tab within a range that does not adversely affect the performance of the secondary battery 1000. The positive electrode tab 130 and the negative electrode tab 230 protrude outside the exterior body 500. Then, the plurality of protruding positive electrode tabs 130 and the plurality of negative electrode tabs 230 are connected to each other by, for example, ultrasonic bonding, so that a parallel connection is formed in the secondary battery 1000. The present invention can be applied to a bipolar secondary battery in which an electric series connection is formed in the secondary battery 1000.

  The positive electrode mixture layer 110 has a positive electrode active material, a positive electrode conductive agent, and a positive electrode binder. The negative electrode mixture layer 210 includes 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. The electrode conductive agent is selected from a material group such as Ketjen black, acetylene black, and graphite. As the electrode conductive agent, a particulate agent can be suitably used.

<Electrode binder>
The electrode binder binds an electrode active material and an electrode conductive agent in the electrode. The electrode binder is selected from a group of materials such as, for example, styrene-butadiene rubber, carboxymethylcellulose, polyvinylidene fluoride (PVDF), and the like.

<Positive electrode active material>
In the positive electrode active material having a noble potential, lithium ions are desorbed in a charging process, and lithium ions desorbed from the negative electrode active material in the negative electrode mixture layer 210 are inserted in a discharging process. As the positive electrode active material, a lithium composite oxide having a transition metal is desirable. As the positive electrode active material, for example, LiMO ₂ , Li [LiM] O ₂ having a Li excess composition, LiM ₂ O ₄ , LiMPO ₄ , LiMVO _x , LiMBO ₃ , Li ₂ MSiO ₄ (where M = Co, Ni, Mn , Fe, Cr, Zn, Ta, Al, Mg, Cu, Cd, Mo, Nb, W, Ru, etc. x is the concentration of oxygen contained in the compound, and is an integer of 0 or more. Can be taken.). The element ratio may deviate from the stoichiometric composition. As the positive electrode active material, a material which is selected from the above-described material group and formed into particles can be suitably used.

<Positive electrode current collector 120>
The positive electrode current collector 120 is selected from a material group such as an aluminum foil having a thickness of 1 to 100 μm and a perforated aluminum foil having a thickness of 10 to 100 μm and a hole diameter of 0.1 to 10 mm.

<Negative electrode active material>
In the negative electrode active material having a low potential, lithium ions are desorbed in a discharging process, and lithium ions desorbed from the positive electrode active material in the positive electrode mixture layer 110 are inserted in a charging process. The negative electrode active material includes, for example, a carbon-based material (graphite, easily graphitized carbon material, amorphous carbon material, organic crystal, activated carbon, and the like), silicon, a silicon-containing compound, and a conductive polymer material (polyacene, polyparaphenylene, Polyaniline, polyacetylene, etc.), lithium composite oxide (lithium titanate: Li ₄ Ti ₅ O ₁₂ , Li ₂ TiO _4, etc.), metallic lithium, at least one kind of metal alloying with lithium (aluminum, silicon, tin, etc.) ) And oxides thereof. The element ratio may deviate from the stoichiometric composition. As the negative electrode active material, a material which is selected from the above-described material group and formed into a particle shape can be suitably used.

<Negative electrode current collector 220>
The negative electrode current collector 220 is selected from a material group such as a copper foil having a thickness of 1 to 100 μm and a copper perforated foil having a thickness of 1 to 100 μm and a hole diameter of 0.1 to 10 mm.

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

  When the electrode has a non-volatile electrolyte, a non-aqueous electrolyte is injected into the secondary battery 1000 from a vacant side or liquid injection hole of the outer package 500, and the pores of the electrode mixture layer are filled with the non-aqueous electrolyte. You may. As a result, the particles such as the electrode active material and the electrode conductive agent in the electrode mixture layer function as the support particles without the need for the support particles contained in the nonvolatile electrolyte, and these particles hold the nonaqueous electrolyte. I do. As another method of filling the pores of the electrode mixture layer with the non-aqueous electrolyte, a slurry is prepared by mixing a non-aqueous electrolyte, an electrode active material, an electrode conductive agent, and an electrode binder, and the adjusted slurry is subjected to electrode current collection. There is a method of applying together on the body.

  It is desirable that the thickness of the electrode mixture layer be equal to or larger than the average particle size of the electrode active material. When the thickness of the electrode mixture layer is set in this manner, the electron conductivity between adjacent electrode active materials can be improved. If the electrode active material powder contains coarse particles having an average particle size greater than the thickness of the electrode mixture layer, the coarse particles are removed in advance by sieving, airflow classification, etc. It is desirable that

<Insulating 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 functions as an electron insulator, and prevents a short circuit between the positive electrode 100 and the negative electrode 200. The insulating layer 300 has a separator or a nonvolatile electrolyte layer. As the insulating layer 300, a separator and a nonvolatile electrolyte layer may be used in combination. In the present embodiment, it is preferable to use the nonvolatile electrolyte layer alone as the insulating layer 300 or to use the separator and the nonvolatile electrolyte layer together.

<Separator>
A porous sheet can be used as the separator. The porous sheet is selected from, for example, a material group of cellulose, denatured cellulose (such as carboxymethylcellulose (CMC) and hydroxypropylcellulose (HPC)), and polyolefin (such as polypropylene (PP) and propylene copolymer). Those formed in an arbitrary shape can be used. By making the separator larger in area than the positive electrode 100 or the negative electrode 200, short circuit between the positive electrode 100 and the negative electrode 200 can be prevented.

  As the separator, for example, a separator formed by applying a separator-forming mixture having separator particles, a separator binder, and a solvent to the electrode mixture layer can be used. As the separator, for example, a separator formed by applying a mixture for forming a separator to the porous sheet can be used.

The separator particles are selected from a material group such as, for example, γ-alumina (Al ₂ O ₃ ), silica (SiO ₂ ), and zirconia (ZrO ₂ ). The average particle diameter of the separator particles is desirably, for example, 1/100 to 1/2 of the thickness of the separator.

  The separator binder is selected from a material group such as polyethylene (PE), PP, polytetrafluoroethylene (PTFE), PVDF, styrene butadiene rubber (SBR), polyalginic acid, and polyacrylic acid.

  When a separator is used as the insulating layer 300, the separator is filled with the nonaqueous electrolyte by injecting the nonaqueous electrolyte into the secondary battery 1000 from one open side or the injection hole of the outer package 500.

<Nonvolatile electrolyte layer>
The nonvolatile electrolyte layer has a nonvolatile electrolyte binder and a nonvolatile electrolyte. The non-volatile electrolyte has a carrier particle and a non-aqueous electrolyte.
The non-volatile electrolyte has pores formed by the aggregate of the supporting particles, and the non-aqueous electrolyte is held therein. By holding the non-aqueous electrolyte in the nonvolatile electrolyte, the nonvolatile electrolyte allows lithium ions to permeate. When a non-aqueous electrolyte is used as the insulating layer 300 and the electrode mixture layer is filled with a non-aqueous electrolyte, it is not necessary to inject the non-aqueous electrolyte into the secondary battery 1000. For example, when the insulating layer 300 has a separator, a nonaqueous electrolyte may be injected into the secondary battery 1000 from one of the open sides or the injection hole of the outer package 500.

  Examples of the method for forming the nonvolatile electrolyte layer include a method in which the nonvolatile electrolyte powder is compression-molded into a pellet shape using a molding die or the like, a method in which a nonvolatile electrolyte binder is added to and mixed with the nonvolatile electrolyte powder, and a method in which a sheet is formed. is there. By adding and mixing the powder of the nonvolatile electrolyte binder to the nonvolatile electrolyte, a highly flexible sheet-like nonvolatile electrolyte layer can be produced. In addition, a solution of a binder obtained by dissolving a nonvolatile electrolyte binder in a dispersion solvent is added to and mixed with the nonvolatile electrolyte, the mixture is applied on a substrate such as an electrode, and the dispersion solvent is distilled off by drying. Then, a nonvolatile electrolyte layer may be formed.

<Nonvolatile electrolyte binder>
As the nonvolatile electrolyte binder, a fluorine-based resin is preferably used. The fluorine-based resin is selected from a group of materials such as PTFE and PVDF. These materials may be used alone or in combination. Among them, when PVDF is used, the adhesion between the insulating layer 300 and the electrode current collector is improved, so that the battery performance is improved.

<Nonvolatile electrolyte>
The non-aqueous electrolyte is carried or held by the carrier particles to form a nonvolatile electrolyte. As a method for producing a nonvolatile electrolyte, for example, a non-aqueous electrolyte solution and carrier particles are mixed at a specific volume ratio, an organic solvent such as methanol is added and mixed, and a nonvolatile electrolyte slurry is prepared. The slurry may be spread on a petri dish, and the organic solvent may be distilled off to obtain a nonvolatile electrolyte powder.

<Supported particles>
The supporting particles are preferably insulating particles and insoluble in the non-aqueous electrolyte from the viewpoint of electrochemical stability. The carrier particles are selected from a material group such as SiO ₂ particles, Al ₂ O ₃ particles, ceria (CeO ₂ ) particles, oxide inorganic particles such as ZrO ₂ particles, and solid electrolyte. By using the oxide inorganic particles as the supporting particles, the non-aqueous electrolyte can be held at a high concentration in the nonvolatile electrolyte layer.

  Since the holding amount of the nonaqueous electrolyte is considered to be proportional to the specific surface area of the carrier particles, the average particle size of the primary particles of the carrier particles is preferably, for example, 1 nm to 10 μm. When the average particle size of the primary particles of the carrier particles is in this range, the carrier particles can appropriately hold a sufficient amount of the non-aqueous electrolyte, thereby facilitating the formation of the nonvolatile electrolyte. When the average particle size of the primary particles of the supported particles is in this range, the surface force between the supported particles is appropriately obtained, and the supported particles are less likely to aggregate with each other, so that the formation of the nonvolatile electrolyte is facilitated. The average particle size of the primary particles of the supporting particles is more preferably 1 to 50 nm, and further preferably 1 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 is obtained by dissolving an electrolyte (for example, an electrolyte salt or a solvate electrolyte salt described later) in a non-aqueous solvent. The volatilization temperature of the non-aqueous electrolyte in this embodiment is 80 ° C. or higher. The volatilization temperature of the non-aqueous electrolyte in the present embodiment refers to a temperature at which the non-aqueous electrolyte is heated for a predetermined time and a predetermined amount of the non-aqueous electrolyte is reduced from the start of heating. Depending on the repetitive operation of charging and discharging of the secondary battery having the non-aqueous electrolyte and the place where the secondary battery is installed, the temperature of the secondary battery becomes 60 ° C. or higher. Therefore, depending on the components contained in the non-aqueous electrolyte, such as when the non-aqueous electrolyte contains a flammable organic solvent in a certain amount or more, the non-aqueous electrolyte may volatilize, and the safety of the secondary battery may decrease. . Thus, by setting the volatilization temperature of the non-aqueous electrolyte to 80 ° C. or higher, even if the non-aqueous electrolyte contains a flammable organic solvent, the volatilization of the flammable organic solvent can be suppressed, and the secondary battery Safety can be improved.

  When the volatilization temperature of the non-aqueous electrolyte is 80 ° C. or higher, the number of lithium ion carriers contained in the non-aqueous electrolyte and the interaction between the non-aqueous solvent in the non-aqueous electrolyte and lithium ions cause the non-aqueous electrolyte to The ionic conductivity changes. If the ionic conductivity of the non-aqueous electrolyte is low, the input / output characteristics of the secondary battery 1000 may deteriorate. Therefore, by defining log (O / Li), which is the logarithm of the ratio of the amount of oxygen contained in the non-aqueous electrolyte to the amount of lithium contained in the non-aqueous electrolyte, within a desired range, the ionic conductivity of the non-aqueous electrolyte is regulated. Rate can be improved. Specifically, by setting log (O / Li) to 0.87 to 2.05, the ionic conductivity of the non-aqueous electrolyte can be increased to 0.2 mS / cm (milli-Siemens per centimeter) or more. The volatilization temperature of the water electrolyte can be maintained at 80 ° C. or higher. As a result of various studies, the amount of lithium contained in the non-aqueous electrolyte and the amount of oxygen contained in the non-aqueous electrolyte were determined and managed by calculating the logarithm log (O / Li) of these ratios. It has been found that the ionic conductivity of the electrolytic solution can be suitably controlled. Regarding that the ionic conductivity of the non-aqueous electrolyte can be improved by defining log (O / Li) in a desired range, and that log (O / Li) is specifically set to 0.87 to 2.05. Will be described in the section of Examples. When the log (O / Li) is small, the amount of lithium ion carriers contained in the non-aqueous electrolyte decreases, so that the ionic conductivity of the non-aqueous electrolyte decreases. On the other hand, when log (O / Li) is large, the interaction between the non-aqueous solvent in the non-aqueous electrolyte and the lithium ions becomes strong, and the lithium ions become difficult to move, so that the ionic conductivity of the non-aqueous electrolyte decreases. I do. The log (O / Li) can be measured by quantifying the chemical composition and the mixing ratio by NMR or the like.

  In the present embodiment, log (O / Li) is desirably 0.87 to 1.93. This makes it possible to maintain the ionic conductivity of the non-aqueous electrolyte at 0.2 mS / cm or more and maintain the volatilization temperature of the non-aqueous electrolyte at 90 ° C. or more. Also, it is desirable that log (O / Li) is 1.10 to 1.84. Thereby, the volatilization temperature of the non-aqueous electrolyte can be kept at 95 ° C. or more while the ionic conductivity of the non-aqueous electrolyte is kept at 0.5 mS / cm or more. Also, it is desirable that log (O / Li) is 1.30 to 1.71. Thereby, the volatilization temperature of the non-aqueous electrolyte can be kept at 100 ° C. or more while the ionic conductivity of the non-aqueous electrolyte is kept at 1.1 mS / cm or more.

<Constituent materials of non-aqueous electrolyte>
The non-aqueous electrolyte has a non-aqueous solvent. The non-aqueous solvent has an organic solvent, an ionic liquid, or a mixture (complex) of an ether-based solvent and a solvated electrolyte salt exhibiting properties similar to the ionic liquid. An organic solvent, an ionic liquid or an ether solvent may be referred to as a main solvent. The nonaqueous electrolyte may use these materials alone or in combination.
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.
Non-aqueous solvent, from the viewpoint of stability in the atmosphere and heat resistance in the secondary battery, low volatility, specifically, those having a vapor pressure of 150 Pa or less at room temperature are desirable, but are not limited thereto. Absent.
By using a non-volatile solvent such as an ionic liquid or an ether-based solvent having properties similar to the ionic liquid as the non-aqueous electrolyte, volatilization of the non-aqueous electrolyte from the nonvolatile electrolyte layer can be suppressed.

  The content of the non-aqueous electrolyte in the nonvolatile electrolyte layer is not particularly limited, but is preferably 40 to 90 vol%. When the content of the non-aqueous electrolyte is in this range, the interface resistance between the electrode and the nonvolatile electrolyte layer hardly increases. Further, when the content of the non-aqueous electrolyte is in this range, the non-aqueous electrolyte hardly leaks from the nonvolatile electrolyte layer. When the non-volatile electrolyte layer is formed in a sheet shape, the content of the non-aqueous electrolyte in the non-volatile electrolyte layer is preferably 50 to 80 vol%, more preferably 60 to 80 vol%.

  Although the mixing mass ratio of the main solvent in the nonaqueous electrolyte is not particularly limited, the mass ratio of the main solvent to the total solvent in the nonaqueous electrolyte is 30 to 70 mass% from the viewpoint of battery stability and high-speed charge and discharge. , More preferably 40 to 60% by mass, and even more preferably 45 to 55% by mass.

<Organic solvent>
Examples of the organic solvent include carbonates such as ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC), and γ-butyrolactone. (GBL). By mixing multiple types of organic solvents in the non-aqueous electrolyte, the interaction between lithium ions and the organic solvent is controlled, the ionic conductivity of the non-aqueous electrolyte is increased, and the volatilization temperature of the non-aqueous electrolyte is increased. it can.

  The ionic liquid or an ether-based solvent having properties similar to the ionic liquid may have a low-viscosity organic solvent. The low-viscosity organic solvent lowers the viscosity of the non-aqueous electrolyte and improves the ionic conductivity. When the internal resistance of the non-aqueous electrolyte is large, the internal resistance of the non-aqueous electrolyte can be reduced by adding a low-viscosity organic solvent to increase the ionic conductivity of the non-aqueous electrolyte. The low-viscosity organic solvent is preferably, but not limited to, a solvent having a viscosity of less than 140 Pa · s at 25 ° C. of a mixture of an ether solvent and a solvated electrolyte salt. The low-viscosity organic solvent is selected from a group of materials such as EC, PC, and GBL.

<Ionic liquid>
Ionic liquids are composed of cations and anions. Ionic liquids are classified into imidazolium-based, pyrrolidinium-based, and the like, depending on the type of cation. Examples of the cation constituting the imidazolium-based ionic liquid include an alkyl imidazolium cation such as 1-butyl-3-methylimidazorium (BMI). Examples of the cations constituting the pyrrolidinium-based ionic liquid include alkylpyrrolidinium cations such as N-methyl-N-propylpyrrolidinium (Py13) and 1-butyl-1-methylpyrrolidinium. Examples of the anion to be paired with these cations include bis (trifluoromethanesulfonyl) imide (TFSI), bis (fluorosulfonyl) imide, and tetrafluoroborate (BF ₄ ).

<Electrolyte salt>
When the non-aqueous solvent has an organic solvent or an ionic liquid, the non-aqueous electrolyte has an electrolyte salt. It is desirable that the electrolyte salt can be uniformly dispersed in the main solvent. As the electrolyte salt, a lithium salt composed of a lithium cation and the above-mentioned anion can be used. Examples of the electrolyte salt include lithium bis (fluorosulfonyl) imide (LiFSI), lithium bis (trifluoromethanesulfonyl) imide (LiTFSI), lithium tetrafluoroborate (LiBF ₄ ), lithium bisoxalate borate (LiBOB), and lithium It is selected from a group of materials such as triflate. By mixing a plurality of types of electrolyte salts with the non-aqueous electrolyte, electrolyte salts having different anions are mixed, and by controlling the interaction between lithium ions and anions, the ionic conductivity of the non-aqueous electrolyte and Can control volatility.

<Ether solvent>
The ether solvent forms a solvated ionic liquid with the solvated electrolyte salt. Ether solvents, for example, glyme showing similar properties to the ionic liquid _{(R-O (CH 2 CH} 2 O) n -R '(R, R' is a saturated hydrocarbon, symmetric n is represented by an integer) Glycol diether). From the viewpoint of ion conductivity, the glyme is preferably, for example, tetraglyme (tetraethylene dimethyl glycol, G4) or triglyme (triethylene glycol dimethyl ether, G3). It is desirable to use tetraglyme or triglyme as the ether-based solvent in that a complex structure can be formed with the solvated electrolyte salt.
Solvated electrolyte salt, for example, LiFSI, LiTFSI, is selected from the group of materials such as LiBF _4.

  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 nonvolatile electrolyte>
As shown in Table 1-1, Li salt 1 (A) was LiTFSI, Li salt 2 (B) was not used, solvent 1 (C) was G4, solvent 2 (D) was PC, and solvent 3 (E) was not used. By mixing, a non-aqueous electrolyte according to Example 1 was prepared. Note that, for the materials used, “LiTFSI”, “G4”, and the like correspond to those exemplified in the description of the embodiments for each material. "-" In Table 1-1 indicates that it is not used. These are the same for Tables 2-1, 3-1 and 4-1.
Then, this mixed solvent and fumed silica nanoparticles having a particle diameter of 7 nm were weighed and mixed so as to have a volume ratio of 80:20 to obtain a powdery nonvolatile electrolyte.

<Preparation of nonvolatile electrolyte layer>
The nonvolatile electrolyte and PTFE were each weighed so as to have a mass ratio of 95: 5, put into a mortar, and mixed uniformly. The mixture was set on a hydraulic press via a PTFE sheet and pressed at 39.2 MPa (400 kgf / cm ² ). Further, the PTFE sheet was rolled by a roll press to have a thickness of 200 μm, and the mixture mass ratio of A, B, C, D, and E was 45.1: 0: 34.9: 20.0: 0 (Table 1). For No. 1, sheet-shaped non-volatile dissolved layers (insulating layers) of “45.1”, “−”, “34.9”, “20.0”, and “−” were obtained, respectively. . This was punched out at a diameter of 16 mm and used as a nonvolatile electrolyte. The mixing mass ratio of the liquid components contained in the nonvolatile electrolyte layer was evaluated by NMR.

<Measurement of log (O / Li)>
From the liquid composition of the non-aqueous electrolyte contained in the nonvolatile electrolyte evaluated by NMR measurement, log (O / Li) was derived from the amount of oxygen contained in the solvent in the non-aqueous electrolyte and the concentration of Li salt (amount of lithium). .

<Measurement of ionic conductivity>
The nonvolatile electrolyte layer was sandwiched between two pieces of metal lithium foil punched out with a diameter of 16 mm and sealed in a CR2032 type coin cell. The impedance was measured at a voltage amplitude of 10 mV by a two-terminal method in a frequency range of 2 MHz to 10 mHz (2 MHz to 10 mHz). The point of intersection with the real axis on the high frequency side was defined as the resistance of the nonvolatile electrolyte layer, and the ionic conductivity (mS / cm) of the nonvolatile electrolyte layer was determined. Then, log {ion conductivity (S / cm)} was derived from the ion conductivity.

<Measurement of volatilization temperature of non-aqueous electrolyte>
The non-aqueous electrolyte used for the preparation of the nonvolatile electrolyte was transferred to an aluminum pan having a diameter of 5.2 mm, and a thermogravimetric / differential thermal analyzer (TG-DTA) was used. The rate of change was measured. The measurement temperature range was from room temperature (25 ° C.) to 350 ° C. The weight immediately before the start of the measurement was taken as 100%, and the temperature at which the weight was reduced by 2%, that is, the temperature at the time when the remaining weight became 98% was taken as the volatile temperature (° C.).

<Volatile temperature of non-aqueous electrolyte in nonvolatile electrolyte layer>
Even in a mixed system with a large supporting particle having a large specific surface area that is considered to promote the volatilization of the nonaqueous electrolyte, in order to confirm that the volatilization temperature of the nonaqueous electrolyte does not significantly decrease, The volatilization temperature of the non-aqueous electrolyte was measured. Specifically, the nonvolatile electrolyte layer cut to a diameter of 5 mm was transferred to an aluminum pan having a diameter of 5.2 mm, and the volatilization temperature was measured in the same manner as described above. The temperature at which the weight loss was reduced by 2% in the course of raising the temperature with respect to the weight at room temperature was defined as the volatile temperature (° C.).

<Examples after Example 2>
Example 1 was repeated except that the non-aqueous electrolyte and the like were changed as shown in Table 1-1, Table 2-1, Table 3-1, and Table 4-1.

<Comparative Example 1>
When measuring the ionic conductivity and the volatilization temperature, a 30 μm-thick PP / PE / PP three-layer separator was used instead of the nonvolatile electrolyte, and Li salt 1 (A), solvent 1 (C), solvent Example 2 was repeated except that LiPF ₆ , EC and EMC were used for 2 (D), respectively.

<Comparative example after Comparative example 2>
The procedure was the same as in Example 1 except that the nonaqueous electrolyte and the like were as shown in Table 4-1.

<Results and discussion>
The contents and results of the examples and comparative examples are shown in Tables 1-1 to 4-2. FIGS. 2 to 4 show graphs of Table 1-2, Table 2-2, Table 3-2, and Table 4-2.

  According to Examples and Comparative Examples, the logarithm (σ) of the ionic conductivity of the nonaqueous electrolyte as shown in FIG. 2 and the ratio of the amount of oxygen contained in the nonaqueous electrolyte to the amount of lithium contained in the nonaqueous electrolyte are shown in FIG. A logarithmic log (O / Li) relationship was derived. The relational expression between log (σ) and log (O / Li) was derived as in the following expression (1).

log (σ) = 1.2334 log (O / Li) ³ −7.3723 log (O / Li) ² +13.973 log (O / Li) −11.387 (1)

FIG. 2 shows the logarithm (ion conductivity) of the ionic conductivity of the non-aqueous electrolyte as log (O / O) for the contents of Tables 1-2, 2-2, 3-2, and 4-2. It is the figure plotted with respect to Li).
The curve shown in FIG. 2 is obtained by polynomial approximation of the minimum value of the ionic conductivity at each log (O / Li) among the obtained experimental values. It is larger than the value calculated from the curve. The log (σ) derived from this approximate expression reached a maximum value when log (O / Li) = 1.55. A composition smaller than this value is a region where the mixing ratio of the low-viscosity organic solvent is small, and as log (O / Li) approaches 1.55, that is, as the mixing ratio of the low-viscosity organic solvent increases, In addition, the viscosity of the non-aqueous electrolyte decreased, and the ionic conductivity of the non-aqueous electrolyte increased.

  On the other hand, when log (O / Li) is greater than 1.55, the composition has an excessively low-viscosity organic solvent concentration. As log (O / Li) approached 1.55, the lithium salt concentration in the non-aqueous electrolyte increased, the ion carrier concentration increased, and the ionic conductivity of the non-aqueous electrolyte increased.

  From the above, the balance between the effect of lowering the viscosity of the non-aqueous electrolyte by mixing a low-viscosity organic solvent and the effect of increasing the ion carrier concentration of the non-aqueous electrolyte is optimized, and the ionic conduction of the non-aqueous electrolyte is optimized. The value with the highest rate is log (O / Li) = 1.55. From the relationship between log (σ) and log (O / Li) derived from equation (1), it is possible to determine a composition for obtaining a desired ionic conductivity of the non-aqueous electrolyte.

  FIG. 3 is a diagram in which the volatilization temperature of the nonaqueous electrolyte is plotted against log (O / Li) for the contents of Tables 1-2, 2-2, 3-2, and 4-2. As a result, in the plots except for Comparative Example 1, the volatilization temperature of the non-aqueous electrolyte increased as the log (O / Li) became smaller, that is, as the mixing ratio of the low-viscosity organic solvent became smaller. As the log (O / Li) decreases, the mixing ratio of the low-viscosity organic solvent decreases. That is, it is considered that the increase in the concentration of lithium salt contained in the non-aqueous electrolyte and an increase in the interaction between lithium ions and the solvent molecules are factors that increase the volatilization temperature. Assuming that the volatilization temperature of the non-aqueous electrolyte is T, T and log (O / Li) in the non-aqueous electrolyte satisfy the following relational expression (2). Equation (2) represents the curve (approximate equation) shown in FIG. This equation is obtained by polynomial approximation of the minimum value of the volatilization temperature at each log (O / Li) among the obtained experimental values, and the volatilization temperature of various materials is calculated from this curve. It is larger than the value.

T = −628.27 {log (O / Li)} ³ +262.13 {log (O / Li)} ² −375.04 {log (O / Li)} + 288.83 (2)

  From the equation (2), the composition of the non-aqueous electrolyte that satisfies the predetermined non-aqueous electrolyte volatility temperature can be determined.

  FIG. 4 is a diagram in which the volatilization temperature of the nonvolatile electrolyte is plotted against log (O / Li) for the contents of Tables 1-2, 2-2, 3-2, and 4-2. Assuming that the volatilization temperature of the non-volatile electrolyte is T ', T' and log (O / Li) satisfy the following equation (3). Equation (3) represents the curve (approximation equation) in FIG.

^{T '= - 101.24 {log (} O / Li)} 3 +423.56 {log (O / Li)} 2 -582.51 {log (O / Li)} + 365.7 ... (3)

  Although the volatilization temperature of the non-volatile electrolyte was lower than the volatilization temperature of the non-aqueous electrolyte, the temperature difference in each log (O / Li) derived from equations (1) and (2) was the largest. However, it was about 8 ° C.

  The ionic conductivity of the non-aqueous electrolyte is derived from the relationship between log (σ) and log (O / Li) (formula (1)) and the relationship between T and log (O / Li) (formula (2)). The range of log (O / Li) at which the volatilization temperature of the non-aqueous electrolyte is not less than 0.2 mS / cm and not less than 80 ° C. is 0.87 to 2.05 (the non-aqueous electrolyte in the nonvolatile electrolyte layer has a In this case, it was 0.87 to 2.04).

  The range of log (O / Li) at which the ionic conductivity of the non-aqueous electrolyte is 0.2 mS / cm or more and the volatilization temperature of the non-aqueous electrolyte is 90 ° C. or more is 0.87 to 1.93 ( In the case of the non-aqueous electrolyte in the nonvolatile electrolyte layer, the ratio was 0.87 to 1.95).

  The range of log (O / Li) at which the ionic conductivity of the nonaqueous electrolyte is 0.5 mS / cm or more and the volatilization temperature of the nonaqueous electrolyte is 95 ° C or more is 1.10 to 1.84 (non-volatile). In the case of the non-aqueous electrolyte in the electrolyte layer, it was 1.10 to 1.88).

  The range of log (O / Li) at which the ionic conductivity of the non-aqueous electrolyte is 1.1 mS / cm or more and the volatilization temperature of the non-aqueous electrolyte is 100 ° C. or more is 1.30 to 1.71 (non-volatile). In the case of the non-aqueous electrolyte in the electrolyte layer, it was found to be 1.30 to 1.78).

  As described above, since the nonaqueous electrolyte according to the example satisfying the requirements of the present invention has an ionic conductivity of 0.2 mS / cm or more, the input / output characteristics are deteriorated when used in a secondary battery. Hard to do. In addition, the non-aqueous electrolyte according to the example satisfying the requirements of the present invention has a volatilization temperature of 80 ° C. or higher as described above, so even if the non-aqueous electrolyte contains a flammable organic solvent, The volatilization of the flammable organic solvent can be suppressed, and the safety of the secondary battery can be improved.

  As described above, the non-aqueous electrolyte, the nonvolatile electrolyte, and the secondary battery according to the present invention have been described in detail with reference to the embodiments and the examples. However, the gist of the present invention is not limited thereto, and various modifications may be made. included. For example, the above-described embodiments have been described in detail for easy understanding of the present invention, and are not necessarily limited to those having all the configurations described above. Further, a part of the configuration of one embodiment can be replaced with the configuration of another embodiment, and the configuration of one embodiment can be added to the configuration of another embodiment. Further, for a part of the configuration of each embodiment, it is possible to add, delete, or replace another configuration.

REFERENCE SIGNS LIST 100 positive electrode 110 positive electrode mixture layer 120 positive electrode current collector 130 positive electrode tab 200 negative electrode 210 negative electrode mixture layer 220 negative electrode current collector 230 negative electrode tab 300 insulating layer 400 electrode body 500 exterior body 1000 secondary battery

Claims (6)

A non-aqueous electrolyte having a volatilization temperature of 80 ° C.
A non-aqueous electrolyte having a log (O / Li) of 0.87 to 2.05, which is a logarithm of the ratio of the amount of oxygen contained in the non-aqueous electrolyte to the amount of lithium contained in the non-aqueous electrolyte. In claim 1,
A non-aqueous electrolyte having a log (O / Li) of 0.87 to 1.93. In claim 1,
A non-aqueous electrolyte having a log (O / Li) of 1.10 to 1.84. In claim 1,
A non-aqueous electrolyte having a log (O / Li) of 1.30 to 1.71. Carrying particles,
A non-volatile electrolyte comprising: the non-aqueous electrolyte according to claim 1. A positive electrode,
A negative electrode,
A non-volatile electrolyte layer comprising the non-volatile electrolyte according to claim 5 formed between the positive electrode and the negative electrode.

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