Nonaqueous electrolyte solution and nonaqueous electrolyte secondary battery

Abstract

A nonaqueous electrolyte solution according to the present disclosure contains: a nonaqueous solvent; an electrolyte that is dissolved in the nonaqueous solvent; and particles of a material that has a composition represented by M1αM2βM3γO3. Here, M1 is at least one element that is selected from the group consisting of Sr, Ca, and Ba, M2 is at least one element that is selected from the group consisting of Zr and Ti, M3 is at least one element that is selected from alkaline earth metal elements, and that is different from M1, and 0.5 ≤ α ≤ 1.5, 0.5 ≤ β ≤ 1.5, and 0 ≤ γ < 1.5 are satisfied.

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] 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] The present disclosure provides a nonaqueous electrolyte suitable for improving the cycle characteristics of a battery.

[0005] The non-aqueous electrolyte solution of the present disclosure includes a non-aqueous solvent, an electrolyte dissolved in the non-aqueous solvent, and particles of a material having a composition represented by the following formula (1): α M2 β M3 γ O3... Formula (1) wherein M1 is at least one selected from the group consisting of Sr, Ca, and Ba, M2 is at least one selected from the group consisting of Zr and Ti, M3 is at least one selected from alkaline earth metal elements and is an element different from M1, and 0.5≦α≦1.5, 0.5≦β≦1.5, and 0≦γ<1.5 are satisfied.

[0006] The nonaqueous electrolyte solution of the present disclosure can improve the cycle characteristics of the battery.

[0007] FIG. 1 is a schematic cross-sectional view showing an example of a nonaqueous electrolyte secondary battery according to the second embodiment.

[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 particles of a material having a composition represented by the following formula (1): M1 α M2 β M3 γ O3...Formula (1)

[0010] In formula (1), M1 is at least one selected from the group consisting of Sr, Ca, and Ba, M2 is at least one selected from the group consisting of Zr and Ti, and M3 is at least one selected from alkaline earth metal elements and is an element different from M1. In formula (1), 0.5≦α≦1.5, 0.5≦β≦1.5, and 0≦γ<1.5 are satisfied. The particles are dispersed in a non-aqueous solvent. By using the non-aqueous electrolyte of embodiment 1 in a battery, the cycle characteristics of the battery can be improved, and therefore the output characteristics can be improved.

[0011] It is more preferable that M1 is at least one selected from the group consisting of Sr and Ca. With this configuration, the cycle characteristics and output characteristics of the battery can be further improved, and for example, a battery using such a nonaqueous electrolyte solution can be suitable for discharge at a large current value.

[0012] Although the mechanism by which the nonaqueous electrolyte of embodiment 1 achieves the above-described effects is not entirely clear, the following mechanism is presumed. As the particles are attracted to the active material particles, the density of Li ions present near the surfaces of the active material particles increases. This improves Li ion conductivity, thereby reducing the transport resistance between Li ions and anions in the electrode. Furthermore, the presence of the particles in the nonaqueous solvent changes the bond (coordination state) between the Li ions and the nonaqueous solvent molecules to a special state, reducing the migration resistance of Li ions when they are inserted into or extracted from the active material. As a result, the cycle characteristics and output characteristics of a battery using the nonaqueous electrolyte of embodiment 1 are improved compared to a battery using a nonaqueous electrolyte that does not contain the particles.

[0013] 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.

[0014] In the present disclosure, "having fluidity at 25°C" means having a viscosity of 20,000 mPa·s or less at 25°C.

[0015] 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.

[0016] The particles may be insoluble in the non-aqueous solvent. The non-aqueous electrolyte solution in embodiment 1 may contain particles of a material having a composition represented by formula (1) above that is insoluble in the non-aqueous solvent. The non-aqueous electrolyte solution in embodiment 1 may be a non-aqueous colloidal solution in which the particles are dispersed.

[0017] In the present disclosure, "particles are insoluble in a non-aqueous solvent" means that 100 mL or more of non-aqueous solvent is required to dissolve 1 g of particles at 25°C. That is, the solubility of the particles in 100 mL of non-aqueous solvent is 1 g or less. Here, "dissolution" means that the permeability of the solution obtained when the particles are dissolved in the non-aqueous solvent in a container does not change from the permeability of the solvent, that is, the solution is not cloudy and no precipitate is observed on the bottom of the container after standing for 24 hours.

[0018] The material may have a perovskite structure, and such a configuration allows the above-described effects of the particles to be fully obtained.

[0019] The material may be a ferroelectric material. That is, the particles may be particles of a ferroelectric material. With this configuration, the above-mentioned effects of the particles can be fully obtained. Specifically, the ferroelectric material particles are attracted to the active material particles, generating polarization charges on the surfaces of the active material particles, which allows the interfacial reaction to proceed smoothly. In addition, the density of Li ions present on the surfaces of the active material particles increases.

[0020] The dielectric constant of the material is, for example, not less than 40. The upper limit of the dielectric constant of the material is not particularly limited, but is, for example, not more than 7000, more preferably not more than 2500, and even more preferably not more than 500. With this configuration, the cycle characteristics and output characteristics of the battery are further improved.

[0021] In formula (1), 0.8≦α≦1.2, 0.8≦β≦1.2, and 0≦γ≦1.0 may be satisfied.

[0022] M3 may be at least one selected from the group consisting of Be, Mg, Ba, and Ra. In formula (1), γ=0 may be satisfied.

[0023] The material may include at least one selected from the group consisting of SrZrO3, CaTiO3, SrTiO3, and BaTiO3. This configuration allows the particles to fully achieve the above-described effects. Furthermore, the particles can be imparted with ferroelectricity.

[0024] More preferably, the material contains at least one selected from the group consisting of SrZrO3, CaTiO3, and SrTiO3. This configuration can further improve the cycle characteristics and output characteristics of the battery, and for example, a battery using such a nonaqueous electrolyte can be suitable for discharge at a large current value.

[0025] The particles may consist essentially of M1, M2, M3, and O. This configuration allows the particles to fully achieve the aforementioned effects. "The particles consist essentially of M1, M2, M3, and O" means that the molar ratio (i.e., molar fraction) of the sum of the amounts of substance of M1, M2, M3, and O to the total amount of substance of all elements constituting the particles is 90% or more. For example, this molar ratio may be 95% or more. The particles may not intentionally contain any raw material elements other than M1, M2, M3, and O. Furthermore, the particles may consist essentially of M1, M2, and O. This configuration allows the particles to fully achieve the aforementioned effects. "The particles consist essentially of M1, M2, and O" means that the molar ratio (i.e., molar fraction) of the sum of the amounts of substance of M1, M2, and O to the total amount of substance of all elements constituting the particles is 90% or more. For example, this molar ratio may be 95% or more. The particles may be those to which no raw material elements other than M1, M2, and O have been intentionally added.

[0026] The shape of the particles is not particularly limited, and may be needle-like, scale-like, spherical, or oval-spherical.

[0027] The particles may be crystalline, amorphous, or may have both phases.

[0028] The particle content in the non-aqueous electrolyte may be 0.1% by volume or more and 50% by volume or less. The particle content in the non-aqueous electrolyte 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 particles and the fluidity of the non-aqueous electrolyte.

[0029] The particle content 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 particle volume is calculated from the specific gravity determined from the particle mass and particle components. The particle components 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 particle content 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.

[0030] The particles may be nanoparticles.

[0031] The average particle diameter of the particles may be 1 nm or more and 90 nm or less. This configuration improves the dispersibility of the particles in the nonaqueous electrolyte solution, thereby enabling increased industrial productivity of the nonaqueous electrolyte solution. The average particle diameter of the particles may be 1 nm or more and 50 nm or less, or 5 nm or more and 30 nm or less. When the average particle diameter of the particles is 90 nm or less, in a battery using the nonaqueous electrolyte solution of the present disclosure, when the nonaqueous electrolyte solution penetrates into the positive electrode active material layer, the particles may penetrate between the positive electrode active material particles arranged inside 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. This can improve the battery characteristics.

[0032] The average particle size of the particles may be equal to or smaller than the pore size of the separator of a battery that uses a nonaqueous electrolyte. With this configuration, the 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.

[0033] 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.

[0034] 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.

[0035] 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.

[0036] 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.

[0037] Examples of the cyclic carbonate include propylene carbonate (PC) and ethylene carbonate (EC).

[0038] Examples of the chain carbonate ester include diethyl carbonate (DEC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC).

[0039] Examples of the cyclic carboxylic acid ester include γ-butyrolactone (GBL) and γ-valerolactone (GVL).

[0040] 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.

[0041] 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 particle dispersibility. 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, particle aggregation over time and the resulting particle sedimentation can be reduced.

[0042] 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.

[0043] The nonaqueous electrolyte solution in the first embodiment can be produced, for example, by the following method.

[0044] A lithium salt is dissolved in a non-aqueous solvent. The resulting solution, the 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.

[0045] The method for producing the non-aqueous electrolyte is not limited to the above, and for example, particles may be dispersed in a non-aqueous solvent in which a lithium salt has been dissolved, using an ultrasonic homogenizer.

[0046] (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 and therefore the output characteristics of the secondary battery can be improved.

[0047] 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.

[0048] Each component of the secondary battery 100 will be specifically described below.

[0049] 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.

[0050] 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.

[0051] 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.

[0052] The lithium nickel oxide may be represented by the following composition formula (2): Element M4 is at least one selected from the group consisting of V, Co, and Mn. Element M5 is at least one selected from the group consisting of Mg, Al, Ca, Ti, Cu, Zn, and Nb. Composition formula (2) satisfies 0.9≦a≦1.10, −0.05≦b≦0.05, 0.5≦x1<1, 0≦x2≦0.5, and 0≦1−x1−x2≦0.5. Li a Ni x1 M4 x2 M5 (1-x1-x2) O 2+b ...(2)

[0053] The positive electrode active material layer 5b may contain other materials such as a conductive additive and a binder.

[0054] 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.

[0055] 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.

[0056] 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.

[0057] 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.

[0058] 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.

[0059] 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.

[0060] 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.

[0061] The average particle size of the particles contained in the electrolyte may be equal to or smaller than the pore size of the separator 7 .

[0062] The separator 7 has lithium ion conductivity. The material of the separator 7 is not particularly limited as long as it allows lithium ions to pass through. 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 can suppress oxidation of the separator 7 and reduce deterioration in the strength of the separator 7.

[0063] 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.

[0064] The electrode group 4 may be wound into a cylindrical shape or an oval shape.

[0065] 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.

[0066] 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.

[0067] (Other Embodiments) (Additional Notes) The above description of the embodiments discloses the following techniques.

[0068] (Technology 1) A non-aqueous electrolyte solution comprising: a non-aqueous solvent; an electrolyte dissolved in the non-aqueous solvent; and particles of a material having a composition represented by the following formula (1): α M2 β M3 γ O3... Formula (1) wherein M1 is at least one selected from the group consisting of Sr, Ca, and Ba, M2 is at least one selected from the group consisting of Zr and Ti, and M3 is at least one selected from alkaline earth metal elements and is an element different from M1, and 0.5≦α≦1.5, 0.5≦β≦1.5, and 0≦γ<1.5 are satisfied.

[0069] The nonaqueous electrolyte solution of the present disclosure can improve the cycle characteristics and output characteristics of the battery.

[0070] (Technology 2) The nonaqueous electrolyte according to Technology 1, wherein the content of the particles in the nonaqueous electrolyte is 0.1% by volume or more and 50% by volume or less. With this configuration, the dispersibility of the particles and the fluidity of the nonaqueous electrolyte can be improved.

[0071] (Technology 3) The nonaqueous electrolyte according to Technology 1 or 2, wherein the material has a perovskite structure.

[0072] (Technology 4) The nonaqueous electrolyte according to any one of Technologies 1 to 3, wherein the material is a ferroelectric material. With this configuration, the above-described effects of the particles can be sufficiently obtained.

[0073] (Technology 5) The nonaqueous electrolyte solution according to any one of Technologies 1 to 4, wherein the material has a relative dielectric constant of 40 or more and 7000 or less. With this configuration, the cycle characteristics and output characteristics of the battery can be further improved.

[0074] (Technology 6) The nonaqueous electrolyte according to any one of Technologies 1 to 5, wherein the material includes at least one selected from the group consisting of SrZrO3, CaTiO3, SrTiO3, and BaTiO3. With this configuration, the above-described effects of the particles can be sufficiently obtained.

[0075] (Technology 7) The nonaqueous electrolyte solution according to any one of Technology 1 to Technology 6, wherein M1 is at least one selected from the group consisting of Sr and Ca. This configuration can further improve the cycle characteristics and output characteristics of the battery. For example, a battery using the nonaqueous electrolyte solution of Technology 7 can be suitable for discharge at a high current value.

[0076] (Technology 8) The nonaqueous electrolyte according to any one of Technology 1 to Technology 7, wherein the material includes at least one selected from the group consisting of SrZrO3, CaTiO3, and SrTiO3. This configuration can further improve the cycle characteristics and output characteristics of the battery. For example, a battery using the nonaqueous electrolyte of Technology 8 can be suitable for discharge at a high current value.

[0077] (Technology 9) The nonaqueous electrolyte solution according to any one of Technologies 1 to 8, wherein the particles have an average particle size of 1 nm or more and 90 nm or less. With this configuration, the dispersibility of the particles in the nonaqueous electrolyte solution is improved, and the industrial productivity of the nonaqueous electrolyte solution can be increased.

[0078] (Technology 10) The nonaqueous electrolyte according to any one of Technologies 1 to 9, further comprising a fluorine-containing solvent. Such a configuration improves the dispersibility of particles in the nonaqueous electrolyte, making it possible to increase the industrial productivity of the nonaqueous electrolyte.

[0079] (Technology 11) The nonaqueous electrolyte according to Technology 10, wherein the fluorine-containing solvent comprises at least one selected from the group consisting of fluoroethylene carbonate and 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether.

[0080] (Technology 12) 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 11.

[0081] The nonaqueous electrolyte solution of the present disclosure is suitable for nonaqueous electrolyte secondary batteries.

[0082] [Sample 1] Ethylene carbonate (EC), fluoroethylene carbonate (FEC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) were used as non-aqueous solvents. EC, FEC, DMC, and 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 resulting non-aqueous solvent to a concentration of 1.35 mol / L to obtain a solution. The resulting solution, ZrO2 balls (particle diameter 0.5 mm) as mixing media, and SrZrO3 particles (average particle diameter 200 nm) were placed in a planetary ball mill container and sealed in a dry atmosphere. The amount of SrZrO3 particles was adjusted so that the content in the non-aqueous electrolyte was 4% by volume. The container was mixed at 300 rpm for 3 hours using a planetary ball mill. The average particle size of the SrZrO3 particles after mixing was 30 nm or less. The supernatant liquid of the resulting mixture was sucked up with a dropper to remove the ZrO2 balls, yielding a nonaqueous electrolyte solution of Sample 1. 4 volume % of SrZrO3 particles were dispersed in the nonaqueous electrolyte solution of Sample 1. The nonaqueous electrolyte solution of Sample 1 had fluidity at 25°C. The SrZrO3 particles used had a relative dielectric constant of 54 at 1 GHz. The relative dielectric constant was measured using a perturbation cavity resonance method.

[0083] [Sample 2] A nonaqueous electrolyte solution of Sample 2 was obtained in the same manner as Sample 1, except that CaTiO particles (average particle diameter 200 nm) were used instead of SrZrO particles. The average particle diameter of the CaTiO particles in the nonaqueous electrolyte solution of Sample 2 was 30 nm or less. The nonaqueous electrolyte solution of Sample 2 had fluidity at 25°C. The relative dielectric constant of the CaTiO particles used at 1 GHz was 272.

[0084] [Sample 3] A nonaqueous electrolyte solution of Sample 3 was obtained in the same manner as Sample 1, except that SrTiO particles (average particle diameter 200 nm) were used instead of SrZrO particles. The average particle diameter of the SrTiO particles in the nonaqueous electrolyte solution of Sample 3 was 30 nm or less. The nonaqueous electrolyte solution of Sample 3 had fluidity at 25°C. The relative dielectric constant of the SrTiO particles used at 1 GHz was 436.

[0085] [Sample 4] A nonaqueous electrolyte solution of Sample 4 was obtained in the same manner as Sample 1, except that BaTiO particles (average particle diameter 200 nm) were used instead of SrZrO particles. The average particle diameter of the BaTiO particles in the nonaqueous electrolyte solution of Sample 4 was 30 nm or less. The relative dielectric constant of the BaTiO particles used at 1 GHz was 2000.

[0086] [Sample 5] BaTi instead of SrZrO3 particles 0.8 Zr 0.2 The non-aqueous electrolyte solution of Sample 5 was obtained in the same manner as Sample 1, except that O particles (average particle diameter: 200 nm) were used. 0.8 Zr 0.2 The average particle size of the O3 particles was 30 nm or less. 0.8 Zr 0.2 The relative dielectric constant of the O3 particles at 1 GHz was 543.

[0087] [Sample 6] Except for not dispersing particles in the non-aqueous solvent, the non-aqueous electrolyte solution of Sample 6 was prepared in the same manner as Sample 1. That is, the non-aqueous electrolyte solution of Sample 6 was a solution obtained by dissolving LiPF6 at a concentration of 1.35 mol / L in a non-aqueous solvent in which EC, FEC, DMC, and EMC were mixed in a volume ratio of EC:FEC:DMC:EMC = 10:10:75:5.

[0088] [Preparation of Evaluation Cells] Evaluation cells using the nonaqueous electrolyte solutions of Samples 1 to 6 were prepared according to the following procedure.

[0089] (Half cell) LiNi 0.8 Co 0.15 Al0.05 A positive electrode slurry was prepared by adding N-methyl-2-pyrrolidone (NMP) to a positive electrode active material (NCA) having a composition of O, acetylene black (AB), and polyvinylidene fluoride (PVDF), and stirring the mixture. The mass ratio of these materials in the positive electrode active material layer was positive electrode active material:AB:PVDF=96:2:2.

[0090] 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.

[0091] 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 each of the nonaqueous electrolytes of Samples 1 to 6. A polyethylene separator (Celgard, #2320) was used as the separator. The half-cells were used to evaluate output characteristics.

[0092] (Full Cell) A positive electrode was obtained in the same manner as above.

[0093] An appropriate amount of water was added to the negative electrode mixture and mixed to obtain a negative electrode slurry. The negative electrode mixture was a mixture of a negative electrode active material, a binder, and a conductive agent. Graphite (average particle size (D50) 25 μm) was used as the negative electrode active material. Sodium polyacrylate (PAA-Na), a sodium salt of CMC (CMC-Na), and styrene butadiene rubber (SBR) were used as the binder. The contents of PAA-Na, CMC-Na, and SBR in the negative electrode mixture were each 1% by mass. Next, the negative electrode slurry was applied to the surface of copper foil, the coating film was dried, and then rolled to form a negative electrode mixture layer (thickness 80 μm, density 1.6 g / cm 3 ) was formed to obtain a negative electrode.

[0094] A cylindrical full cell was fabricated using a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte. A polyethylene separator (Celgard, #2320) was used as the separator. The full cell was used for a cycle test.

[0095] [Evaluation of Output Characteristics] The output characteristics of the evaluation cells, which were half cells of Samples 1 to 6, were evaluated according to the following procedure.

[0096] An initial charge / discharge process was performed before the output characteristic evaluation. Specifically, the evaluation cell was subjected to constant current charging at a current value of 0.2 C until the voltage reached 4.4 V, and constant voltage charging at a voltage of 4.4 V until the current value reached 0.02 C. After a 20-minute pause, constant current discharging was performed at a current value of 0.1 C until the voltage reached 2.5 V. After a 20-minute pause, constant current charging was performed at a current value of 0.2 C until the voltage reached 4.4 V, and constant voltage charging was performed at a voltage of 4.4 V until the current value reached 0.02 C. After a 20-minute pause, constant current discharging was performed at a current value of 0.2 C until the voltage reached 2.5 V. After a 20-minute pause, constant current charging was performed again at a current value of 0.2 C until the voltage reached 4.4 V, and constant voltage charging was performed at a voltage of 4.4 V until the current value reached 0.02 C. After a 20-minute rest, constant current discharge was performed at a current value of 0.2 C until the voltage reached 2.5 V. The initial charge / discharge treatment was performed at an ambient temperature of 25°C.

[0097] The evaluation cell, which had undergone the above charge / discharge process, was then placed under an ambient temperature of 45°C. Constant-current charging was performed at a current of 0.2C until the voltage reached 4.4V, followed by constant-voltage charging at 4.4V until the current reached 0.02C. After a 20-minute pause, constant-current discharging was performed at a current of 2C until the voltage reached 2.5V. Constant-current discharging was then performed at a current of 1C until the voltage reached 2.5V. Constant-current discharging was then performed at a current of 0.5C until the voltage reached 2.5V. Constant-current discharging was then performed at a current of 0.2C until the voltage reached 2.5V. The discharge capacity at 2C discharge and the discharge capacity at 0.2C discharge were measured. The discharge capacity at 0.2C discharge refers to the discharge capacity measured throughout the entire discharge process during the output characteristic evaluation. The results of the output characteristic evaluation are shown in Table 1.

[0098] [Cycle Test I] Cycle test I was carried out on the evaluation cells, which were full cells of samples 1 to 6, according to the following procedure.

[0099] An initial charge / discharge treatment was performed before the cycle test. Specifically, the evaluation cell was subjected to constant current charging at a current value of 0.1 C until the voltage reached 4.3 V, and constant voltage charging at a voltage of 4.3 V until the current value reached 0.02 C. After a 20-minute pause, constant current discharging was performed at a current value of 0.1 C until the voltage reached 2.5 V. After a 20-minute pause, constant current charging was performed at a current value of 0.2 C until the voltage reached 4.3 V, and constant voltage charging was performed at a voltage of 4.3 V until the current value reached 0.02 C. After a 20-minute pause, constant current discharging was performed at a current value of 0.2 C until the voltage reached 2.5 V. After a 20-minute pause, constant current charging was performed again at a current value of 0.2 C until the voltage reached 4.3 V, and constant voltage charging was performed at a voltage of 4.3 V until the current value reached 0.02 C. After a 20-minute rest, constant current discharge was performed at a current value of 0.2 C until the voltage reached 2.5 V. The initial charge / discharge treatment was performed at an ambient temperature of 25°C.

[0100] The evaluation cells that had undergone the above charge / discharge treatment were then placed under an ambient temperature of 45°C. These cells were then subjected to constant current charging at a current value of 0.2C until the voltage reached 4.3V, and constant voltage charging at a voltage of 4.3V until the current value reached 0.02C. After a 20-minute break, constant current discharging was performed at a current value of 0.2C until the voltage reached 2.5V. The above charge / discharge cycle was counted as one cycle, and this cycle was repeated 100 times to evaluate the capacity retention rate. The evaluation results of the capacity retention rate from Cycle Test I are shown in Table 1.

[0101] In Table 1, the "2C / 0.2C" item in the output characteristics section represents the ratio of the discharge capacity at 2C discharge to the discharge capacity at 0.2C discharge in the output characteristics evaluation test. This value can be considered an index of the output characteristics of the evaluation cell. In Table 1, the "50 cyc / 1 cyc" item represents the ratio of the discharge capacity at the 50th cycle to the discharge capacity at the first cycle of each evaluation cell in Cycle Test I. The "100 cyc / 1 cyc" item represents the ratio of the discharge capacity at the 100th cycle to the discharge capacity at the first cycle of each evaluation cell in Cycle Test I.

[0102] The capacity retention rates at 50 cycles and 100 cycles of the evaluation cells of Samples 1 to 5 were both higher than that of Sample 6. Therefore, the nonaqueous electrolytes of Samples 1 to 5 improved the cycle characteristics of the battery. Furthermore, the output characteristics of the evaluation cells of Samples 1 to 5 were higher than that of Sample 6. Therefore, the nonaqueous electrolytes used in each of Samples 1 to 5 can improve the output characteristics of the battery and improve the cycle characteristics of the battery.

[0103] [Cycle Test II] Cycle test II was carried out on the evaluation cells, which were full cells of samples 1 to 6, according to the following procedure.

[0104] An initial charge / discharge treatment was performed before the cycle test. Specifically, the evaluation cell was subjected to constant current charging at a current value of 0.1 C until the voltage reached 4.3 V, and constant voltage charging at a voltage of 4.3 V until the current value reached 0.02 C. After a 20-minute pause, constant current discharging was performed at a current value of 0.1 C until the voltage reached 2.5 V. After a 20-minute pause, constant current charging was performed at a current value of 0.2 C until the voltage reached 4.3 V, and constant voltage charging was performed at a voltage of 4.3 V until the current value reached 0.02 C. After a 20-minute pause, constant current discharging was performed at a current value of 0.2 C until the voltage reached 2.5 V. After a 20-minute pause, constant current charging was performed again at a current value of 0.2 C until the voltage reached 4.3 V, and constant voltage charging was performed at a voltage of 4.3 V until the current value reached 0.02 C. After a 20-minute rest, constant current discharge was performed at a current value of 0.2 C until the voltage reached 2.5 V. The initial charge / discharge treatment was performed at an ambient temperature of 25°C.

[0105] The evaluation cells that had undergone the above charge / discharge treatment were then placed under an ambient temperature of 45°C. These cells were then subjected to constant current charging at a current value of 0.3C until the voltage reached 4.3V, and constant voltage charging at a voltage of 4.3V until the current value reached 0.02C. After a 20-minute break, constant current discharging was performed at a current value of 0.3C until the voltage reached 2.5V. The above charge / discharge cycle was counted as one cycle, and this cycle was repeated 100 times to evaluate the capacity retention rate. The evaluation results of the capacity retention rate from Cycle Test II are shown in Table 2.

[0106] In Table 2, the item "50 cyc / 1 cyc" indicates the ratio of the discharge capacity at the 50th cycle to the discharge capacity at the 1st cycle of each evaluation cell in Cycle Test II. The item "100 cyc / 1 cyc" indicates the ratio of the discharge capacity at the 100th cycle to the discharge capacity at the 1st cycle of each evaluation cell in Cycle Test II.

[0107]

[0108] The capacity retention rates at 50 cycles and 100 cycles in Cycle Test II for the evaluation cells of Samples 1 to 3 were all higher than those for Samples 4 to 6. Therefore, it is considered that the batteries using the nonaqueous electrolytes of Samples 1 to 3 are more suitable for discharge at a larger current value than the batteries using the nonaqueous electrolytes of Samples 4 and 5.

[0109] It is presumed that the above-mentioned effect was particularly exhibited by the non-aqueous electrolytes of Samples 1 to 3, which contain particles of ferroelectric material. On the other hand, the capacity retention rates at 50 cycles and 100 cycles in Cycle Test II for the evaluation cells of Samples 4 and 5 were both lower than those of Samples 1 to 3 and 6. It is known that there is a correlation between crystallinity and ferroelectricity in particles, and it is thought that the nanoparticles were not sufficiently sintered to have high crystallinity in order to reduce their particle size. As a result, when discharging the battery at a large current value, the BaTiO3 and BaTiO3 used in the non-aqueous electrolytes of Samples 4 and 5 0.8 Zr 0.2 It is presumed that the above results were due to the fact that O3 nanoparticles do not have dielectric properties suitable for use in non-aqueous electrolytes.

[0110] The nonaqueous electrolyte solution of the present disclosure can improve the cycle characteristics and output characteristics of a battery. The nonaqueous electrolyte solution of the present disclosure, in which particles contain at least one selected from the group consisting of Sr and Ca, as in Samples 1 to 3, can particularly exhibit the above effects.

[0111] The technology of the present disclosure is useful for, for example, lithium ion secondary batteries.

Claims

1. A non-aqueous solvent, an electrolyte dissolved in the non-aqueous solvent, and particles of a material having a composition represented by the following formula (1), α M2 β M3 γ O3... Formula (1) wherein M1 is at least one selected from the group consisting of Sr, Ca, and Ba, M2 is at least one selected from the group consisting of Zr and Ti, and M3 is at least one selected from alkaline earth metal elements and is an element different from M1, and 0.5≦α≦1.5, 0.5≦β≦1.5, and 0≦γ<1.5 are satisfied.

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

3. The nonaqueous electrolyte according to claim 1, wherein the material has a perovskite structure.

4. The nonaqueous electrolyte according to claim 1, wherein the material is a ferroelectric material.

5. The nonaqueous electrolyte according to claim 1, wherein the material has a relative dielectric constant of 40 or more and 7000 or less.

6. The nonaqueous electrolyte according to claim 1, wherein the material includes at least one selected from the group consisting of SrZrO3, CaTiO3, SrTiO3, and BaTiO3.

7. The nonaqueous electrolyte according to claim 1, wherein M1 is at least one selected from the group consisting of Sr and Ca.

8. The nonaqueous electrolyte according to claim 1, wherein the material includes at least one selected from the group consisting of SrZrO3, CaTiO3, and SrTiO3.

9. The nonaqueous electrolyte according to claim 1, wherein the particles have an average particle size of 1 nm or more and 90 nm or less.

10. The nonaqueous electrolyte according to claim 1, further comprising a fluorine-containing solvent.

11. The nonaqueous electrolyte according to claim 10, wherein the fluorine-containing solvent comprises at least one selected from the group consisting of fluoroethylene carbonate and 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether.

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

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