Non-aqueous electrolytic solution and non-aqueous electrolyte secondary battery

Abstract

A non-aqueous electrolytic solution according to the present disclosure includes a non-aqueous solvent, an electrolyte dissolved in the non-aqueous solvent, and fluoride particles insoluble in the non-aqueous solvent. The fluoride particles include Li, M1, and F, and M1 is at least one selected from the group consisting of Al, Ti, Nb, Ta, and Zr. The fluoride particles may further contain M2, and M2 is at least one selected from the group consisting of Be, Mg, Ca, Sr, Ba, Sc, Y, Ga, In, Sn, and Fe.

Description

Nonaqueous electrolyte and nonaqueous electrolyte secondary battery

[0001] The present disclosure relates to a non-aqueous electrolyte solution and a non-aqueous electrolyte secondary battery.

[0002] As known to those skilled in the art, conventional battery electrolytes contain various components. For example, Patent Document 1 discloses that a non-aqueous electrolyte secondary battery containing vinylene carbonate as a non-aqueous solvent has good cycle characteristics.

[0003] Japanese Patent Application Laid-Open No. 2005-268230

[0004] In non-aqueous electrolyte secondary batteries, one of the causes of battery performance degradation is decomposition of the electrolyte solution and / or side reactions of the electrolyte solution. The present disclosure provides a technique for suppressing the degradation of battery performance due to the decomposition of the electrolyte solution and / or side reactions of the electrolyte solution.

[0005] The present disclosure provides a non-aqueous electrolyte solution comprising: a non-aqueous solvent; an electrolyte dissolved in the non-aqueous solvent; and fluoride particles insoluble in the non-aqueous solvent, wherein the fluoride particles contain Li, M1, and F, and M1 is at least one selected from the group consisting of Al, Ti, Nb, Ta, and Zr.

[0006] The nonaqueous electrolyte solution of the present disclosure can suppress deterioration of battery performance due to decomposition and / or side reactions.

[0007] Fig. 1 is a schematic cross-sectional view showing an example of a nonaqueous electrolyte secondary battery according to Embodiment 2. Fig. 2 is a schematic view of a pressure molding die used for measuring ionic conductivity.

[0008] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. The present disclosure is not limited to the following embodiments.

[0009] (Embodiment 1) The nonaqueous electrolyte solution in Embodiment 1 includes a nonaqueous solvent, an electrolyte dissolved in the nonaqueous solvent, and fluoride particles insoluble in the nonaqueous solvent. The fluoride particles include Li, M1, and F. M1 is at least one selected from the group consisting of Al, Ti, Nb, Ta, and Zr. By using the nonaqueous electrolyte solution in Embodiment 1 in a battery, it is possible to suppress deterioration of battery performance due to decomposition and / or side reactions of the nonaqueous electrolyte solution.

[0010] Although the mechanism by which the nonaqueous electrolyte solution of embodiment 1 exhibits the above-described effects is not entirely clear, the following mechanism is presumed. That is, the fluoride particles are attracted to the active material particles, suppressing decomposition of the nonaqueous solvent on the surfaces of the active material particles. Because the fluoride particles are dispersed in the nonaqueous electrolyte solution, even if new surfaces are formed by repeated charge and discharge of the active material particles, the fluoride particles can act on the new surfaces. As a result, the effects of the fluoride particles are sustained. For example, compared to active material particles that are pre-coated with fluoride particles, the effects of the fluoride particles are expected to be sustained for a longer period with the nonaqueous electrolyte solution of the present disclosure.

[0011] The non-aqueous electrolyte solution in the first embodiment is, for example, liquid at 25°C. The liquid state includes a sol. The non-aqueous electrolyte solution in the first embodiment can have fluidity at 25°C.

[0012] In the present disclosure, "having fluidity at 25°C" means having a viscosity of 20,000 mPa·s or less at 25°C.

[0013] The viscosity of the nonaqueous electrolyte solution in Embodiment 1 at 25° C. may be 5000 mPa·s or less, 3000 mPa·s or less, or 1000 mPa·s or less. The viscosity can be measured using a rheometer.

[0014] The non-aqueous electrolyte in the first embodiment may be a non-aqueous colloidal solution in which fluoride particles are dispersed.

[0015] In the present disclosure, "fluoride particles insoluble in non-aqueous solvents" refers to fluoride particles that require 100 mL or more of non-aqueous solvent to dissolve 1 g of the particles at 25°C. That is, the solubility of the fluoride particles in 100 mL of non-aqueous solvent is 1 g or less. Here, "solubility" means that the permeability of the solution obtained when the fluoride particles are dissolved in the non-aqueous solvent in a container does not change from the permeability of the solvent, i.e., the solution is not cloudy and no precipitate is observed on the bottom of the container after standing for 24 hours. For example, electrolyte salts such as LiPF6 and LiBF6 are sufficiently soluble in non-aqueous solvents, and therefore are not included in the fluoride particles in the present disclosure.

[0016] The fluoride particles may be composed of Li, M1, and F. With this configuration, the above-described effects of the fluoride particles can be sufficiently obtained.

[0017] "Fluoride particles comprised of Li, M1, and F" means that the molar ratio (i.e., molar fraction) of the total amount of substance of Li, M1, and F to the total amount of substance of all elements constituting the fluoride particles is 90% or more. As an example, the molar ratio may be 95% or more. The fluoride particles may not contain any intentionally added elements other than Li, M1, and F.

[0018] However, fluoride particles may contain unavoidable contaminant elements, such as hydrogen, oxygen, and nitrogen, which may be contained in the raw material powder of the fluoride particles or may be present in the atmosphere used to produce and store the fluoride particles.

[0019] M1 may be Al. This configuration can fully achieve the above-described effects of the fluoride particles. In addition, the fluoride particles can be imparted with lithium ion conductivity.

[0020] The fluoride particles may be composed of Li, Al, and F. With this configuration, the above-described effects of the fluoride particles can be sufficiently obtained, and raw material costs can also be reduced.

[0021] M1 may be Ti and Al. With this configuration, the above-described effects of the fluoride particles can be sufficiently obtained.

[0022] The fluoride particles may be composed of Li, Ti, Al, and F. With this configuration, the above-described effects of the fluoride particles can be fully obtained. In addition, the fluoride particles can be imparted with lithium ion conductivity. Raw material costs can also be reduced.

[0023] M1 may be Zr or Al. This configuration can fully achieve the above-described effects of the fluoride particles. In addition, the fluoride particles can be imparted with lithium ion conductivity.

[0024] The fluoride particles may be composed of Li, Zr, Al, and F. With this configuration, the above-described effects of the fluoride particles can be sufficiently obtained. In addition, the fluoride particles can be imparted with lithium ion conductivity. Raw material costs can also be reduced.

[0025] The fluoride particles may have a composition represented by the following formula (1): x satisfies 0<x≦1.2, and n is the weighted average valence of the elements contained in M. M is at least one selected from the group consisting of Al, Ti, and Zr.

[0026] Li 6-nx M x F6...(1)

[0027] The fluoride particles may further contain M2, where M2 is at least one selected from the group consisting of Be, Mg, Ca, Sr, Ba, Sc, Y, Ga, In, Sn, and Fe. With this configuration, the above-described effects of the fluoride particles can be sufficiently obtained.

[0028] The fluoride particles may be composed of Li, M1, M2, and F. With this configuration, the above-described effects of the fluoride particles can be fully obtained. In addition, lithium ion conductivity can be imparted to the fluoride particles. Raw material costs can also be reduced.

[0029] "Fluoride particles consisting of Li, M1, M2, and F" means that the molar ratio (i.e., molar fraction) of the total amount of substance of Li, M1, M2, and F to the total amount of substance of all elements constituting the fluoride particles is 90% or more. As an example, the molar ratio may be 95% or more. The fluoride particles may not intentionally contain raw material elements other than Li, M1, M2, and F.

[0030] M1 may be Ti, and M2 may be Fe. With this configuration, the above-described effects of the fluoride particles can be sufficiently obtained.

[0031] The fluoride particles may be composed of Li, Ti, Fe, and F. With this configuration, the above-described effects of the fluoride particles can be fully obtained. In addition, the fluoride particles can be imparted with lithium ion conductivity. Raw material costs can also be reduced.

[0032] The fluoride particles may have a composition represented by the following formula (2). M1 is at least one selected from the group consisting of Ti, Nb, Ta, and Zr. M2 is at least one selected from the group consisting of Be, Mg, Ca, Sr, Ba, Sc, Y, Ga, In, Sn, and Fe. d represents the valence of M1. e represents the valence of M2. Formula (2) satisfies 0≦a<1.33, 0≦b<2, and 0≦c<2, except for the case where a, b, and c are all zero. With this configuration, the above-mentioned effects of the fluoride particles can be sufficiently obtained.

[0033] Li4-3a-db-ecAl a M1 b M2 c F... (2)

[0034] The fluoride particles may have lithium ion conductivity. Specifically, the fluoride particles may be a fluoride solid electrolyte having lithium ion conductivity. When the fluoride particles have lithium ion conductivity, the nonaqueous electrolyte solution of embodiment 1 can be suitably used in a lithium ion secondary battery. When the fluoride particles have lithium ion conductivity, an increase in resistance when the fluoride particles adhere to an active material is suppressed.

[0035] The lithium ion conductivity of the fluoride particles is, for example, 1.0 × 10 -5 mS / cm or more. With this configuration, an increase in resistance when the fluoride particles adhere to the active material is suppressed. The upper limit of the lithium ion conductivity is not particularly limited. The upper limit of the lithium ion conductivity of the fluoride particles is, for example, 1.0 mS / cm.

[0036] The anion contained in the fluoride particles may be only F. In this case, the fluoride particles can have excellent oxidation resistance.

[0037] The fluoride particles may not contain sulfur, except in cases where sulfur is inevitably mixed in. With this configuration, it is possible to prevent the generation of hydrogen sulfide gas.

[0038] The shape of the fluoride particles is not particularly limited, and may be needle-like, scale-like, spherical, or oval-spherical.

[0039] The fluoride particles may be crystalline, amorphous, or may have both phases.

[0040] The method for producing the fluoride particles is not particularly limited. For example, a plurality of types of raw material powders may be mixed in a ratio corresponding to a target composition. The raw material powders may be fluorides.

[0041] For example, if the target composition is Li 2.7 Ti 0.3 Al 0.7 In the case of F, the raw material powders are mixed with LiF, TiF, and AlF in a molar ratio of about 2.7:0.3:0.7. The raw material powders may be mixed in a pre-adjusted molar ratio to offset compositional changes that may occur during the synthesis process.

[0042] The raw material powders may be mixed using a mixing device such as a planetary ball mill. The raw material powders are reacted with each other by mechanochemical milling to obtain a reactant. The reactant may be fired in a vacuum or in an inert atmosphere. Alternatively, the mixture of raw material powders may be fired in a vacuum or in an inert atmosphere to obtain a reactant. The firing is carried out, for example, at a temperature of 100°C or higher and 400°C or lower for one hour or longer. To suppress composition changes that may occur during firing, the raw material powders may be fired in a sealed container such as a quartz tube. Fluoride particles are obtained through these processes.

[0043] The content of the fluoride particles in the non-aqueous electrolyte may be 0.1% by volume or more and 50% by volume or less. The content of the fluoride particles may be 0.1% by volume or more and 10% by volume or less, 0.1% by volume or more and 8% by volume or less, 0.5% by volume or more and 6% by volume or less, 1% by volume or more and 5% by volume or less, or 1% by volume or more and 4% by volume or less. The above configuration can improve the dispersibility of the fluoride particles and the fluidity of the non-aqueous electrolyte.

[0044] The content of fluoride particles in a non-aqueous electrolyte can be determined, for example, by the following method. After measuring the volume of the non-aqueous electrolyte, the non-aqueous electrolyte is filtered to separate the particles. The separated particles are washed with a solvent such as dimethyl carbonate, and the washing solvent is evaporated and dried, after which the mass of the particles is measured. The volume of the particles is calculated from the specific gravity determined from the mass of the particles and their components. The components of the particles can be determined by various analytical methods such as inductively coupled plasma analysis (ICP), X-ray diffraction (XRD), infrared absorption spectroscopy (IR), and nuclear magnetic resonance analysis (NMR). In this way, the content of fluoride particles in the non-aqueous electrolyte can be calculated. The volume of the non-aqueous electrolyte can also be calculated from the composition and mass. The composition of the non-aqueous electrolyte can be measured using a liquid chromatograph, gas chromatograph, etc.

[0045] The fluoride particles may be nanoparticles.

[0046] The average particle diameter of the fluoride particles may be 1 nm or more and 500 nm or less. This configuration improves the dispersibility of the fluoride particles in the nonaqueous electrolyte solution, thereby enabling increased industrial productivity of the nonaqueous electrolyte solution. The average particle diameter of the fluoride particles may be 5 nm or more and 400 nm or less, or 10 nm or more and 300 nm or less. When the average particle diameter of the fluoride particles is 500 nm or less, in a battery using the nonaqueous electrolyte solution of the present disclosure, the fluoride particles may penetrate between the positive electrode active material particles arranged inside the positive electrode active material layer when the nonaqueous electrolyte solution penetrates into the positive electrode active material layer. As a result, oxidative decomposition of the nonaqueous solvent inside the positive electrode active material layer can be suppressed.

[0047] The average particle size of the fluoride particles may be equal to or smaller than the pore size of the separator of a battery using a nonaqueous electrolyte. According to the above configuration, the fluoride particles do not clog the pores of the separator, and therefore circulation of the electrolyte inside the electrode group is not hindered even during charge and discharge.

[0048] In the present disclosure, the average particle size refers to the median diameter (d50). The median diameter is the particle size at which the cumulative volume in the volume-based particle size distribution is 50%. The volume-based particle size distribution can be determined by a laser diffraction scattering method using a commercially available laser diffraction measuring device.

[0049] The electrolyte may include, for example, a lithium salt. Examples of the lithium salt include lithium hexafluorophosphate (LiPF), lithium tetrafluoroborate (LiBF), lithium perchlorate (LiClO), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bisperfluoroethylsulfonylimide (LiN(SO2C2F5)2), LiAsF6, LiCF3SO3, and lithium difluoro(oxalato)borate. The lithium salt may be at least one selected from the above-mentioned substances. The lithium salt may contain fluorine (F). The lithium salt may be LiPF6.

[0050] The concentration of the lithium salt in the nonaqueous electrolyte may be, for example, 0.5 mol / L or more and 2 mol / L or less. By controlling the lithium salt concentration within the above range, an electrolyte having excellent ionic conductivity and appropriate viscosity can be obtained. However, the lithium salt concentration is not limited to the above.

[0051] The non-aqueous solvent is not particularly limited, and for example, a cyclic carbonate, a chain carbonate, a cyclic carboxylic acid ester, or the like may be used.

[0052] Examples of the cyclic carbonate include propylene carbonate (PC) and ethylene carbonate (EC).

[0053] Examples of the chain carbonate ester include diethyl carbonate (DEC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC).

[0054] Examples of the cyclic carboxylic acid ester include γ-butyrolactone (GBL) and γ-valerolactone (GVL).

[0055] The nonaqueous solvent may be used alone or in combination of two or more. The nonaqueous solvent may contain ethylene carbonate. This can increase the solubility of an electrolyte such as a lithium salt in the nonaqueous solvent.

[0056] The nonaqueous electrolyte solution in embodiment 1 may further contain other substances than those described above. For example, the nonaqueous electrolyte solution in embodiment 1 may further contain an additive to improve the dispersibility of the fluoride particles. The additive is, for example, a fluorine-containing solvent. That is, the nonaqueous electrolyte solution in embodiment 1 may further contain a fluorine-containing solvent. With the above configuration, it is possible to reduce aggregation of fluoride particles over time and the resulting sedimentation of the particles.

[0057] Examples of fluorine-containing solvents include fluorinated cyclic esters and fluorinated ethers. The fluorinated cyclic esters may include fluoroethylene carbonate. The fluorinated ethers may include 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether.

[0058] The nonaqueous electrolyte solution in the first embodiment can be produced, for example, by the following method.

[0059] A lithium salt is dissolved in a non-aqueous solvent. The resulting solution, the fluoride particles, and ZrO balls as a mixing medium are mixed in a ball mill. The mixing medium is removed from the resulting mixture to obtain the non-aqueous electrolyte solution of embodiment 1.

[0060] The method for producing the non-aqueous electrolyte is not limited to the above. For example, fluoride particles may be dispersed in a non-aqueous solvent containing a lithium salt dissolved therein using an ultrasonic homogenizer.

[0061] (Embodiment 2) A nonaqueous electrolyte secondary battery according to Embodiment 2 includes a positive electrode, a negative electrode, and the nonaqueous electrolyte solution according to Embodiment 1. By using the nonaqueous electrolyte solution according to Embodiment 1, the cycle characteristics of the secondary battery can be improved.

[0062] FIG. 1 is a schematic cross-sectional view showing an example of a nonaqueous electrolyte secondary battery according to Embodiment 2. The secondary battery 100 includes a container 1, an electrode group 4, and an electrolyte solution (not shown). The electrolyte solution is the nonaqueous electrolyte solution of Embodiment 1. The electrode group 4 has a wound structure. The electrode group 4 is housed in the container 1. The electrode group 4 includes a positive electrode 5, a negative electrode 6, and a pair of separators 7. The electrode group 4 is impregnated with the electrolyte solution. The opening of the container 1 is closed with a sealing plate 2. The positive electrode 5 includes a positive electrode current collector 5a and a positive electrode active material layer 5b. One end of a positive electrode lead 5c is connected to the positive electrode 5. The other end of the positive electrode lead 5c is connected to the back surface of the sealing plate 2. An insulating packing 3 is disposed around the sealing plate 2. The negative electrode 6 includes a negative electrode current collector 6a and a negative electrode active material layer 6b. One end of the negative electrode lead 6c is connected to the negative electrode 6. The other end of the negative electrode lead 6c is connected to the bottom surface of the container 1. An insulating ring 8 is disposed on each of the upper and lower surfaces of the electrode group 4.

[0063] Each component of the secondary battery 100 will be specifically described below.

[0064] The positive electrode current collector 5a can be a sheet or film made of a metal material such as aluminum, stainless steel, titanium, or an alloy thereof. Aluminum and its alloys are suitable materials for the positive electrode current collector 5a because they are inexpensive and easy to form into thin films. The sheet or film may be porous or non-porous. Examples of the sheet or film include metal foil and metal mesh. A carbon material such as carbon may be applied to the surface of the positive electrode current collector 5a as a conductive auxiliary material.

[0065] The positive electrode active material layer 5b includes a positive electrode active material. The positive electrode active material may be a material capable of absorbing and releasing lithium ions. Examples of the positive electrode active material include lithium-containing transition metal oxides, lithium-containing transition metal phosphates, transition metal fluorides, polyanionic materials, fluorinated polyanionic materials, transition metal sulfides, transition metal oxysulfides, and transition metal oxynitrides. In particular, using a lithium-containing transition metal oxide or a lithium-containing transition metal phosphate as the positive electrode active material can reduce the manufacturing cost of the battery and increase the average discharge voltage. Examples of lithium-containing transition metal oxides include lithium cobalt oxide, lithium nickel cobalt aluminum oxide, lithium nickel cobalt manganese oxide, and lithium nickel manganese oxide. Examples of lithium-containing transition metal phosphates include lithium iron phosphate, lithium vanadium phosphate, lithium cobalt phosphate, and lithium nickel phosphate.

[0066] The positive electrode active material may contain lithium nickel oxide having a layered rock salt crystal structure. The proportion of Ni among metal elements other than Li contained in the lithium nickel oxide may be 50 atomic % or more. The lithium nickel oxide may also contain other transition metals. The lithium nickel oxide is useful for achieving a high operating voltage.

[0067] The lithium nickel oxide may be represented by the following composition formula (3): Element M3 is at least one selected from the group consisting of V, Co, and Mn. Element M4 is at least one selected from the group consisting of Mg, Al, Ca, Ti, Cu, Zn, and Nb. Composition formula (3) satisfies 0.9≦α≦1.10, −0.05≦β≦0.05, 0.5≦x1<1, 0≦x2≦0.5, and 0≦1−x1−x2≦0.5.

[0068] Li α Ni x1 M3 x2 M4 (1-x1-x2) O 2+β ...(3)

[0069] The positive electrode active material layer 5b may contain other materials such as a conductive additive and a binder.

[0070] The conductive additive is used to reduce the resistance of the positive electrode 5. Examples of the conductive additive include a carbon material and a conductive polymer compound. Examples of the carbon material include carbon black, graphite, acetylene black, carbon nanotubes, carbon nanofibers, graphene, fullerene, and graphite oxide. Examples of the conductive polymer compound include polyaniline, polypyrrole, and polythiophene.

[0071] The binder is used to improve the binding property of the material constituting the positive electrode 5. As the binder, polymer materials such as polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, polytetrafluoroethylene, carboxymethyl cellulose, polyacrylic acid, styrene-butadiene copolymer rubber, polypropylene, polyethylene, and polyimide can be used.

[0072] The negative electrode current collector 6a may be a sheet or film made of a metal material such as stainless steel, nickel, copper, or an alloy thereof. The sheet or film may be porous or non-porous. Examples of the sheet or film include metal foil and metal mesh. A carbon material such as carbon may be applied to the surface of the negative electrode current collector 6a as a conductive auxiliary material.

[0073] The negative electrode active material layer 6b includes a negative electrode active material. The negative electrode active material can be a material capable of absorbing and releasing lithium ions. The negative electrode active material includes, for example, at least one selected from the group consisting of carbon materials and materials capable of forming an alloy with lithium. Examples of carbon materials include graphite. Examples of materials capable of forming an alloy with lithium include silicon, silicon-containing oxides, tin, zinc alloys, bismuth, and germanium. One type selected from these negative electrode active materials may be used, or two or more types may be used in combination.

[0074] The negative electrode active material layer 6b may contain at least one selected from the group consisting of graphite and silicon as the negative electrode active material. The negative electrode active material layer 6b may contain only graphite as the negative electrode active material. Graphite is recommended because it is resistant to deterioration even when repeatedly charged and discharged at a deep depth. Carbon materials other than graphite may also be used as the negative electrode active material. Silicon has a larger capacity than graphite and is therefore advantageous for increasing the capacity of the secondary battery 100.

[0075] The negative electrode active material layer 6b may contain other materials such as a conductive additive, a binder, etc. Materials that can be used as the conductive additive and binder for the positive electrode active material layer 5b can also be used for the negative electrode active material layer 6b.

[0076] The electrolyte is the nonaqueous electrolyte in embodiment 1. The electrolyte is impregnated into the positive electrode 5, the negative electrode 6, and the separator 7. The electrolyte may fill the internal space of the container 1. The electrolyte allows lithium ions to move between the positive electrode 5 and the negative electrode 6.

[0077] The average particle size of the fluoride particles contained in the electrolyte may be equal to or smaller than the pore size of the separator 7 .

[0078] The separator 7 has lithium ion conductivity. The material of the separator 7 is not particularly limited as long as it allows the passage of lithium ions. The material of the separator 7 can be at least one selected from the group consisting of a gel electrolyte, an ion exchange resin membrane, a semipermeable membrane, and a porous membrane. Using these materials for the separator 7 can sufficiently ensure the safety of the secondary battery 100. Examples of gel electrolytes include gel electrolytes containing fluororesins such as PVdF. Examples of ion exchange resin membranes include cation exchange membranes and anion exchange membranes. Examples of porous membranes include porous membranes made of polyolefin resins and porous membranes containing glass paper obtained by weaving glass fibers into a nonwoven fabric. Using the nonaqueous electrolyte of embodiment 1 in the secondary battery 100 suppresses oxidation of the separator 7 and reduces deterioration in the strength of the separator 7.

[0079] The container 1 is made of a metal such as aluminum or stainless steel, and may have a cylindrical shape or a rectangular tube shape.

[0080] The electrode group 4 may be wound into a cylindrical shape or an oval shape.

[0081] The shape of the secondary battery 100 is not particularly limited. In the present disclosure, as an example of the structure of the nonaqueous electrolyte secondary battery according to embodiment 2, the configuration example shown in FIG. 1 is described, i.e., a secondary battery in which an electrode group formed by winding a positive electrode and a negative electrode with a separator interposed therebetween and an electrolyte solution are housed in an exterior body. However, the secondary battery according to the present disclosure is not limited to this configuration example. The secondary battery according to the present disclosure may have any shape, such as a cylindrical shape, a prismatic shape, a coin shape, a button shape, a laminate shape, or the like. Furthermore, as the electrode group in the secondary battery according to the present disclosure, instead of a wound-type electrode group, an electrode group of another shape, such as a stacked-type electrode group formed by stacking a positive electrode and a negative electrode with a separator interposed therebetween, may be used.

[0082] The application of the nonaqueous electrolyte solution of the present disclosure is not limited to the secondary battery 100. In addition to lithium secondary batteries, the nonaqueous electrolyte solution of the present disclosure can be applied to various secondary batteries such as sodium secondary batteries and magnesium secondary batteries.

[0083] (Other Embodiments) (Additional Notes) The above description of the embodiments discloses the following techniques.

[0084] (Technology 1) A non-aqueous electrolyte solution comprising: a non-aqueous solvent; an electrolyte dissolved in the non-aqueous solvent; and fluoride particles insoluble in the non-aqueous solvent, wherein the fluoride particles contain Li, M1, and F, and M1 is at least one selected from the group consisting of Al, Ti, Nb, Ta, and Zr.

[0085] The nonaqueous electrolyte solution of the present disclosure can suppress deterioration of battery performance due to decomposition and / or side reactions.

[0086] (Technology 2) The nonaqueous electrolyte according to Technology 1, wherein M1 is Al.

[0087] (Technology 3) The nonaqueous electrolyte according to Technology 1 or 2, wherein the fluoride particles are composed of Li, Al, and F.

[0088] (Technology 4) The nonaqueous electrolyte according to Technology 1, wherein M1 is Ti and Al.

[0089] (Technology 5) The nonaqueous electrolyte according to Technology 1 or 4, wherein the fluoride particles are composed of Li, Ti, Al, and F.

[0090] (Technology 6) The nonaqueous electrolyte according to Technology 1, wherein M1 is Zr and Al.

[0091] (Technology 7) The nonaqueous electrolyte according to Technology 1 or 6, wherein the fluoride particles are composed of Li, Zr, Al, and F.

[0092] (Technology 8) The nonaqueous electrolyte solution according to Technology 1, wherein the fluoride particles further contain M2, and the M2 is at least one selected from the group consisting of Be, Mg, Ca, Sr, Ba, Sc, Y, Ga, In, Sn, and Fe.

[0093] (Technology 9) The nonaqueous electrolyte according to Technology 8, wherein M1 is Ti and M2 is Fe.

[0094] (Technology 10) The nonaqueous electrolyte according to Technology 8 or 9, wherein the fluoride particles are composed of Li, Ti, Fe, and F.

[0095] According to the configurations of Techniques 2 to 10, the above-described effects of the fluoride particles can be sufficiently obtained, and lithium ion conductivity can be imparted to the fluoride particles.

[0096] (Technology 11) The nonaqueous electrolyte solution according to any one of Technologies 1 to 10, wherein a content of the fluoride particles in the nonaqueous electrolyte solution is 0.1 volume % or more and 50 volume % or less. With this configuration, the dispersibility of the fluoride particles and the fluidity of the nonaqueous electrolyte solution can be improved.

[0097] (Technology 12) A non-aqueous electrolyte solution comprising: a non-aqueous solvent; an electrolyte dissolved in the non-aqueous solvent; and fluoride particles insoluble in the non-aqueous solvent, wherein the fluoride particles have lithium ion conductivity.

[0098] When the fluoride particles have lithium ion conductivity, the nonaqueous electrolyte solution of the present disclosure can be suitably used in a lithium ion secondary battery. The lithium ion conductivity of the fluoride particles suppresses an increase in resistance when the fluoride particles adhere to an active material.

[0099] (Technology 13) The fluoride particles have a composition represented by the following formula (2), where M1 is at least one selected from the group consisting of Ti, Nb, Ta, and Zr, M2 is at least one selected from the group consisting of Be, Mg, Ca, Sr, Ba, Sc, Y, Ga, In, Sn, and Fe, d represents the valence of M1, e represents the valence of M2, and 0≦a<1.33, 0≦b<2, and 0≦c<2 are satisfied, except when all of a, b, and c are zero. This configuration allows the above-mentioned effects of the fluoride particles to be fully obtained. Furthermore, lithium ion conductivity can be imparted to the fluoride particles. Li4-3a-db-ecAl a M1 b M2 c F... (2)

[0100] (Technology 14) The lithium ion conductivity of the fluoride particles is 1.0 × 10 -5 14. The nonaqueous electrolyte solution according to claim 12, wherein the electrolytic solution has a conductivity of at least mS / cm. 15. According to this configuration, an increase in resistance when the fluoride particles adhere to the active material is suppressed.

[0101] (Technology 15) The nonaqueous electrolyte solution according to any one of Techniques 12 to 14, wherein a content of the fluoride particles in the nonaqueous electrolyte solution is 0.1 volume % or more and 50 volume % or less. With this configuration, the dispersibility of the fluoride particles and the fluidity of the nonaqueous electrolyte solution can be improved.

[0102] (Technology 16) A non-aqueous electrolyte secondary battery comprising: a positive electrode; a negative electrode; and the non-aqueous electrolyte solution according to any one of Technologies 1 to 15.

[0103] The nonaqueous electrolyte solution of the present disclosure is suitable for nonaqueous electrolyte secondary batteries.

[0104] (Technology 17) The nonaqueous electrolyte secondary battery according to Technology 16, wherein the positive electrode contains lithium nickel manganese oxide. The nonaqueous electrolyte of the present disclosure is particularly useful for high-voltage type lithium ion secondary batteries.

[0105] [Example 1] (Preparation of Fluoride Particles: LTAF) In an argon atmosphere having a dew point of -60°C or less, raw material powders of LiF, TiF, and AlF were weighed out in a molar ratio of LiF:TiF:AlF = 2.7:0.3:0.7. These were pulverized and mixed in a mortar to obtain a mixture. Thereafter, the mixture was milled using a φ5 mm zirconia ball and a planetary ball mill (manufactured by Fritsch, Model P-7) at 500 rpm for 12 hours. As a result, Li 2.7 Ti 0.3 Al 0.7 Fluoride particles having the composition F6(LTAF) were obtained.

[0106] (Measurement of ionic conductivity) Fig. 2 is a schematic diagram showing a pressure molding die used to measure the ionic conductivity of fluoride particles. The pressure molding die 300 included an upper punch 301, a frame 302, and a lower punch 303. The upper punch 301 and the lower punch 303 were made of stainless steel. The frame 302 was made of polycarbonate.

[0107] The fluoride particles 101 were filled into the pressure molding die 300 in a dry atmosphere having a dew point of −60° C. or less. A pressure of 400 MPa was applied to the fluoride particles 101 using an upper punch 301 and a lower punch 303.

[0108] While pressure was still applied, the upper punch 301 and the lower punch 303 were connected to a potentiostat (Princeton Applied Research, VersaSTAT4) equipped with a frequency response analyzer. The upper punch 301 was connected to a working electrode and a potential measurement terminal. The lower punch 303 was connected to a counter electrode and a reference electrode. The impedance of the fluoride particles was measured by electrochemical impedance measurement at 25°C and -40°C.

[0109] In the Cole-Cole plot obtained by the impedance measurement, the real value of the impedance at the measurement point where the absolute value of the phase of the complex impedance was smallest was regarded as the resistance value to ionic conduction of the fluoride particles. Using this resistance value, the ionic conductivity was calculated based on the following formula (A). The results are shown in Table 1.

[0110] σ = (R SE × S / t) -1 ...(A)

[0111] In formula (A), σ represents ionic conductivity. S represents the contact area between the fluoride particles and the upper part of the punch 301. S is equal to the cross-sectional area of ​​the hollow part of the frame mold 302 in FIG. 2. R SE represents the resistance value of the fluoride particle in the impedance measurement. t represents the thickness of the fluoride particle. t represents the thickness of the layer of the fluoride particle 101 in FIG. 2 .

[0112] (Preparation of Non-Aqueous Electrolyte) Ethylene carbonate (EC), fluoroethylene carbonate (FEC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) were mixed in a volume ratio of EC:FEC:DMC:EMC = 10:10:75:5 to prepare a non-aqueous solvent. LiPF6 was dissolved in the obtained non-aqueous solvent to a concentration of 1.35 mol / L to obtain a solution. The solution and fluoride particles were mixed so that the content of the fluoride particles in the non-aqueous electrolyte was 4 volume %, to obtain the non-aqueous electrolyte of Example 1. The non-aqueous electrolyte of Example 1 had fluidity at 25°C.

[0113] [Example 2] (Preparation of Fluoride Particles: LAF) In an argon atmosphere having a dew point of -60°C or less, raw material powders of LiF and AlF were weighed out in a molar ratio of LiF:AlF = 3:1. Except for this point, synthesis was carried out in the same manner as in Example 1 to obtain fluoride particles of Example 2. The fluoride particles of Example 2 had a composition represented by LiAlF (LAF).

[0114] [Example 3] (Preparation of Fluoride Particles: LZAF) In an argon atmosphere having a dew point of -60°C or less, raw material powders of LiF, ZrF4, and AlF3 were weighed out in a molar ratio of LiF:ZrF4:AlF3 = 2.8:0.2:0.8. Except for this point, synthesis was carried out in the same manner as in Example 1 to obtain fluoride particles of Example 3. The fluoride particles of Example 3 were prepared by LiF, ZrF4, and AlF3. 2.8 Zr 0.2 Al 0.8 F6(LZAF).

[0115] [Example 4] (Preparation of Fluoride Particles: LTFF) The raw material powders LiF, TiF, and FeF were weighed out in a molar ratio of LiF:TiF:FeF = 2.7:0.3:0.7. Except for this point, synthesis was carried out in the same manner as in Example 1 to obtain fluoride particles of Example 4. The fluoride particles of Example 4 were prepared by the following method. 2.7 Ti 0.3 Fe 0.7 F6 (LTFF).

[0116] The ionic conductivity of the fluoride particles of Examples 2 to 4 was measured in the same manner as in Example 1. The results are shown in Table 1.

[0117] Non-aqueous electrolyte solutions of Examples 2 to 4 were prepared in the same manner as in Example 1, except that the fluoride particles of Examples 2 to 4 were used instead of the fluoride particles of Example 1.

[0118] Comparative Example 1 A non-aqueous electrolyte solution of Comparative Example 1 was prepared in the same manner as in Example 1, except that the fluoride particles were not dispersed in the non-aqueous solvent.

[0119] [Preparation of Test Cells] Test cells using the nonaqueous electrolyte solutions of Examples 1 to 4 and Comparative Example 1 were prepared according to the following procedure.

[0120] LiNi 0.8 Mn 0.2 A positive electrode slurry was prepared by adding N-methyl-2-pyrrolidone (NMP) to a positive electrode active material having a composition of O, acetylene black (AB), carbon nanotubes (CNT), and PVDF, and stirring the mixture. The mass ratio of these materials in the positive electrode active material layer was positive electrode active material:AB:CNT:PVDF=100:0.75:0.4:0.9.

[0121] The positive electrode slurry was applied to the surface of an aluminum foil (1.45 cm x 1.45 cm), the coating was dried, and then rolled to form a positive electrode active material layer. In this way, a positive electrode was obtained.

[0122] Laminate half cells were fabricated using a positive electrode, a Li metal foil (2 cm × 2 cm, 200 μm thick) as a counter electrode, a separator, and the nonaqueous electrolyte solutions of Examples 1 to 4 and Comparative Example 1. A polyethylene separator (#2320, manufactured by Celgard) was used as the separator.

[0123] [Trickle Charge Test at 55° C.] A trickle charge test at 55° C. was carried out on the evaluation cells of Examples 1 to 4 and Comparative Example 1 according to the following procedure.

[0124] An initial charge / discharge process was performed before the trickle charge test. Specifically, constant current charging was performed at a current value of 0.2 C until the voltage reached 4.5 V, and constant voltage charging was performed at a voltage of 4.5 V until the current value reached 0.02 C. After a 20-minute break, constant current discharging was performed at a current value of 0.2 C until the voltage reached 2.5 V. The initial charge / discharge process was performed at an ambient temperature of 25°C.

[0125] Next, the evaluation cell was placed in a thermostatic chamber at 55°C and constant current charging was performed at a current value of 0.2C until the voltage reached 4.5V. After a 20-minute pause, a trickle charge test was started at 55°C. Specifically, constant current charging was performed at a current value of 0.2C until the voltage reached 4.5V. After reaching 4.5V, constant voltage charging was performed at 4.5V for a total of 6 hours. After a 20-minute pause, trickle charging was performed using the same procedure. This operation was repeated 12 times, for a total of 72 hours of trickle charging. The integrated capacity from the 12-hour point to the 72-hour point was calculated as the "excess charge capacity." The results are shown in Table 1.

[0126]

[0127] The excess charge capacity measured in the 55°C trickle charge test represents the capacity lost due to decomposition and / or side reactions of the non-aqueous electrolyte under high-temperature, high-voltage conditions. That is, a large excess charge capacity indicates that the non-aqueous electrolyte is prone to decomposition and / or side reactions. A small excess charge capacity indicates that the non-aqueous electrolyte is less likely to decompose and / or side reactions.

[0128] As shown in Table 1, the excess charge capacities of the batteries of Examples 1 to 4, which used non-aqueous electrolyte solutions containing fluoride particles, were lower than the excess charge capacity of the battery of Comparative Example 1, which used non-aqueous electrolyte solutions not containing fluoride particles. This result suggests that the inclusion of fluoride particles in the non-aqueous electrolyte solution improved the electrochemical stability of the non-aqueous electrolyte solution against high temperatures and high voltages.

[0129] The excess charge capacities were particularly small in Examples 1 and 3. From these results, it can be said that the fluoride particles containing Li, Al, M', and F have the effect of improving the electrochemical stability of the non-aqueous electrolyte. M' is at least one selected from the group consisting of Ti, Nb, Ta, and Zr.

[0130] Although the correlation between ionic conductivity and excess charge capacity is not necessarily clear, examples using fluoride particles with high ionic conductivity tended to exhibit low excess charge capacity.

[0131] The nonaqueous electrolyte solution of the present disclosure is particularly useful for high-voltage lithium-ion secondary batteries. One of the positive electrode active materials used in such lithium-ion secondary batteries is the lithium nickel manganese oxide used in the examples.

[0132] The technology of the present disclosure is useful for, for example, lithium ion secondary batteries.

Claims

1. A non-aqueous electrolyte solution comprising: a non-aqueous solvent; an electrolyte dissolved in the non-aqueous solvent; and fluoride particles insoluble in the non-aqueous solvent, wherein the fluoride particles contain Li, M1, and F, and M1 is at least one selected from the group consisting of Al, Ti, Nb, Ta, and Zr.

2. The nonaqueous electrolyte according to claim 1, wherein M1 is Al.

3. The nonaqueous electrolyte according to claim 1, wherein the fluoride particles are composed of Li, Al, and F.

4. The nonaqueous electrolyte according to claim 1, wherein M1 is Ti and Al.

5. The nonaqueous electrolyte according to claim 1, wherein the fluoride particles are composed of Li, Ti, Al, and F.

6. The nonaqueous electrolyte according to claim 1, wherein M1 is Zr and Al.

7. The nonaqueous electrolyte according to claim 1, wherein the fluoride particles are composed of Li, Zr, Al, and F.

8. The nonaqueous electrolyte solution according to claim 1, wherein the fluoride particles further contain M2, and M2 is at least one selected from the group consisting of Be, Mg, Ca, Sr, Ba, Sc, Y, Ga, In, Sn, and Fe.

9. The nonaqueous electrolyte according to claim 8, wherein M1 is Ti and M2 is Fe.

10. The nonaqueous electrolyte according to claim 8, wherein the fluoride particles are composed of Li, Ti, Fe, and F.

11. The non-aqueous electrolyte according to claim 1, wherein the content of the fluoride particles in the non-aqueous electrolyte is 0.1% by volume or more and 50% by volume or less.

12. A non-aqueous electrolyte solution comprising: a non-aqueous solvent; an electrolyte dissolved in the non-aqueous solvent; and fluoride particles insoluble in the non-aqueous solvent, wherein the fluoride particles have lithium ion conductivity.

13. The fluoride particles have a composition represented by the following formula (2): Li4-3a-db-ecAl a M1 b M2 c F... (2) The nonaqueous electrolyte solution according to claim 12, wherein M1 is at least one selected from the group consisting of Ti, Nb, Ta, and Zr, M2 is at least one selected from the group consisting of Be, Mg, Ca, Sr, Ba, Sc, Y, Ga, In, Sn, and Fe, d represents a valence of M1, and e represents a valence of M2, satisfying 0≦a<1.33, 0≦b<2, and 0≦c<2, except when all of a, b, and c are zero.

14. The lithium ion conductivity of the fluoride particles is 1.0 × 10 -5 The nonaqueous electrolyte solution according to claim 12, having a conductivity of at least mS / cm.

15. The non-aqueous electrolyte according to claim 12, wherein the content of the fluoride particles in the non-aqueous electrolyte is 0.1% by volume or more and 50% by volume or less.

16. A non-aqueous electrolyte secondary battery comprising: a positive electrode; a negative electrode; and the non-aqueous electrolyte solution according to claim 1.

17. The nonaqueous electrolyte secondary battery according to claim 16, wherein the positive electrode comprises lithium nickel manganese oxide.

18. A non-aqueous electrolyte secondary battery comprising: a positive electrode; a negative electrode; and the non-aqueous electrolyte solution according to claim 12.

19. The nonaqueous electrolyte secondary battery according to claim 18, wherein the positive electrode comprises lithium nickel manganese oxide.

Images