Secondary battery and nonaqueous electrolyte solution

Abstract

A secondary battery 100 according to the present disclosure comprises: a wound electrode group 4 including a positive electrode 5, a negative electrode 6, and a separator 7; and a nonaqueous electrolyte solution. The nonaqueous electrolyte solution contains a nonaqueous solvent and inorganic ceramic particles. The inorganic ceramic particles have lithium ion conductivity, and the content ratio of the inorganic ceramic particles in the nonaqueous electrolyte solution is 0.1-30 vol% inclusive.

Description

Secondary battery and non-aqueous electrolyte

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

[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] In non-aqueous electrolyte secondary batteries, decomposition of the electrolyte is one cause of deterioration in battery performance. The present disclosure provides a secondary battery with improved characteristics.

[0005] The secondary battery of the present disclosure is a secondary battery comprising: a wound electrode group including a positive electrode, a negative electrode, and a separator; and a non-aqueous electrolyte solution, wherein the non-aqueous electrolyte solution contains a non-aqueous solvent and inorganic ceramic particles, the inorganic ceramic particles have lithium ion conductivity, and the content of the inorganic ceramic particles in the non-aqueous electrolyte solution is 0.1 vol% or more and 30 vol% or less.

[0006] According to the technology of the present disclosure, it is possible to provide a secondary battery with improved characteristics, for example, a secondary battery with improved cycle characteristics while maintaining the initial capacity and rate characteristics.

[0007] FIG. 1 is a schematic cross-sectional view showing an example of a secondary battery according to this 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) FIG. 1 is a schematic cross-sectional view showing an example of a secondary battery according to this embodiment.

[0010] The secondary battery 100 includes a container 1, an electrode group 4, and a nonaqueous electrolyte (not shown). 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 an electrolyte. 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 gasket 3 is disposed around the periphery of 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 a 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. Insulating rings 8 are disposed on the top and bottom surfaces of the electrode group 4.

[0011] Each component of the secondary battery 100 will be specifically described below.

[0012] The positive electrode 5, the negative electrode 6, and the separator 7 are impregnated with the nonaqueous electrolyte. The nonaqueous electrolyte may fill the internal space of the container 1. The nonaqueous electrolyte allows lithium ions to move between the positive electrode 5 and the negative electrode 6.

[0013] The non-aqueous electrolyte solution includes a non-aqueous solvent and inorganic ceramic particles. The inorganic ceramic particles have lithium ion conductivity. The content of the inorganic ceramic particles in the non-aqueous electrolyte solution is 0.1% by volume or more and 30% by volume or less. With the above configuration, the battery performance of the secondary battery of this embodiment is improved, for example, the cycle characteristics are improved while maintaining the initial capacity and rate characteristics.

[0014] Although the mechanism by which the secondary battery of this embodiment achieves the above-described effects is not entirely clear, the following mechanism is presumed. When the secondary battery of this embodiment is operated, the inorganic ceramic particles contained in the non-aqueous electrolyte are attracted to the active material particles, suppressing decomposition of the non-aqueous solvent on the surface of the active material particles. Furthermore, because the inorganic ceramic particles have lithium ion conductivity, it is possible to reduce changes in resistance on the surface of the active material particles due to the inorganic ceramic particles being attracted to the active material particles. Because the inorganic ceramic particles are well dispersed in the non-aqueous electrolyte depending on their content, even if new surfaces are formed by repeated charge and discharge of the active material particles, the particles can act on the new surfaces. As a result, the effects of the particles are sustained.

[0015] The inorganic ceramic particles have lithium ion conductivity when, for example, the inorganic ceramic particles have a lithium ion conductivity of 1×10 -6 This means that the lithium ion conductivity is 200 S / cm or more.

[0016] The non-aqueous electrolyte is, for example, liquid at 25°C. The liquid state includes a sol. The non-aqueous electrolyte can have fluidity at 25°C.

[0017] In the present disclosure, "having fluidity at 25°C" means having a viscosity of 20,000 mPa·s or less at 25°C.

[0018] The viscosity of the non-aqueous electrolyte 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.

[0019] The inorganic ceramic particles may be dispersed in a non-aqueous solvent. The inorganic ceramic particles may be insoluble in the non-aqueous solvent. The non-aqueous electrolyte may contain inorganic ceramic particles insoluble in the non-aqueous solvent. The non-aqueous electrolyte may be a non-aqueous colloidal solution in which the inorganic ceramic particles are dispersed.

[0020] In the present disclosure, "insoluble inorganic ceramic particles in a non-aqueous solvent" refers to inorganic ceramic 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 inorganic ceramic 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 inorganic ceramic 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.

[0021] The inorganic ceramic particles may have at least one crystal structure selected from the group consisting of a perovskite-type crystal structure and a NASICON-type crystal structure. With this configuration, the above-mentioned effects of the non-aqueous electrolyte containing the inorganic ceramic particles can be fully obtained.

[0022] The inorganic ceramic particles may have a composition represented by the following formula (1). In formula (1), M1 is at least one selected from the group consisting of La, Sr, Na, Nd, Pr, Sm, Gd, Dy, Y, Eu, Tb, and Ba. M2 is at least one selected from the group consisting of Ti, Mg, W, Mn, Al, Ge, Ru, Nb, Ta, Co, Zr, Hf, Fe, Cr, and Ga. In formula (1), 0<p<2 / 3 is satisfied. With this configuration, the lithium ion conductivity of the inorganic ceramic particles can be increased, and the above-mentioned effects can be sufficiently obtained. Li 3p M1 2 / 3-p M2O3 (1)

[0023] M1 may be at least one selected from the group consisting of La, Sr, and Ba, and M2 may be at least one selected from the group consisting of Ti, Cr, Mn, Zr, Nb, and W. Such inorganic ceramic particles are relatively easy to obtain.

[0024] M1 may contain La. M2 may contain Ti.

[0025] In formula (1), 0.1≦p≦0.3 may be satisfied.

[0026] The inorganic ceramic particles may consist essentially of only Li, M1, M2, and O. This configuration allows the aforementioned effects of the inorganic ceramic particles to be fully achieved. "The inorganic ceramic particles consist essentially of only Li, M1, M2, and O" means that the molar ratio (i.e., molar fraction) of the total amount of substance of Li, M1, M2, and O to the total amount of substance of all elements constituting the inorganic ceramic particles is 90% or more. As an example, this molar ratio may be 95% or more. The inorganic ceramic particles may not intentionally contain raw material elements other than Li, M1, M2, and O.

[0027] The inorganic ceramic particles may have a perovskite crystal structure and a composition represented by formula (1).

[0028] The inorganic ceramic particles may have a composition represented by the following formula (2): In formula (2), M3 is at least one selected from the group consisting of Ge, Ce, Co, Cr, Fe, Hf, In, Mg, Mn, Mo, Na, Nb, Ni, Sb, Sc, Se, Sn, Ta, Ti, U, V, Y, Yb, Zn, and Zr. In formula (2), 0<q<2 is satisfied. With this configuration, the lithium ion conductivity of the inorganic ceramic particles can be increased, and the above-mentioned effects can be sufficiently obtained. Li 1+q Al q M3 2-q (PO4)3...(2)

[0029] M3 may include Ge.

[0030] In formula (2), 0.1≦q≦1 may be satisfied.

[0031] The inorganic ceramic particles may consist essentially of Li, Al, M3, and O. This configuration allows the aforementioned effects of the inorganic ceramic particles to be fully achieved. "The inorganic ceramic particles consist essentially of Li, Al, M3, and O" means that the molar ratio (i.e., molar fraction) of the total amount of substance of Li, Al, M3, and O to the total amount of substance of all elements constituting the inorganic ceramic particles is 90% or more. As an example, the molar ratio may be 95% or more. The inorganic ceramic particles may not intentionally contain raw material elements other than Li, Al, M3, and O.

[0032] The inorganic ceramic particles may have a NASICON-type crystal structure and a composition represented by formula (2).

[0033] In another aspect, the present disclosure provides a non-aqueous electrolyte solution comprising a non-aqueous solvent and inorganic ceramic particles dispersed in the non-aqueous solvent, the inorganic ceramic particles having lithium ion conductivity and a NASICON-type crystal structure, the content of the inorganic ceramic particles in the non-aqueous electrolyte solution being 0.1% by volume or more and 30% by volume or less. This non-aqueous electrolyte solution is suitable for improving the battery performance of secondary batteries, and secondary batteries equipped with this non-aqueous electrolyte solution exhibit improved cycle characteristics while maintaining initial capacity and rate characteristics.

[0034] The shape of the inorganic ceramic particles is not particularly limited, and may be needle-like, scale-like, spherical, or oval-spherical.

[0035] The inorganic ceramic particles may be crystalline, amorphous, or may have both phases.

[0036] The content of the inorganic ceramic particles in the non-aqueous electrolyte may be 0.1 vol% or more and 10 vol% or less, or 4 vol% or more and 10 vol% or less. The content of the inorganic ceramic particles in the non-aqueous electrolyte may be 0.1 vol% or more and 8 vol% or less, 0.1 vol% or more and 6 vol% or less, 0.5 vol% or more and 4 vol% or less, or 1 vol% or more and 4 vol% or less. This configuration improves the dispersibility of the inorganic ceramic particles in the non-aqueous electrolyte and the fluidity of the non-aqueous electrolyte.

[0037] The content of inorganic ceramic particles in the nonaqueous electrolyte can be determined, for example, by the following method. After measuring the volume of the nonaqueous electrolyte in the secondary battery 100, the nonaqueous 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 identified using 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 particles in the nonaqueous electrolyte can be calculated. The volume of the nonaqueous electrolyte can also be calculated from the composition and mass. The composition of the nonaqueous electrolyte can be measured using liquid chromatography, gas chromatography, etc.

[0038] The inorganic ceramic particles may be nanoparticles.

[0039] The inorganic ceramic particles may have an average particle diameter of 1 nm or more and 500 nm or less. This configuration improves the dispersibility of the particles in the nonaqueous electrolyte, thereby increasing the industrial productivity of the nonaqueous electrolyte and the secondary battery 100 including the same. The inorganic ceramic particles may have an average particle diameter of 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 particles is 500 nm or less, in the secondary battery 100, when the nonaqueous electrolyte permeates the positive electrode active material layer 5b, the inorganic ceramic particles may permeate between the positive electrode active material particles arranged within the positive electrode active material layer 5b. As a result, oxidative decomposition of the nonaqueous solvent within the positive electrode active material layer 5b can be suppressed. This can improve the characteristics of the secondary battery. The average particle diameter of the inorganic ceramic particles may be equal to or less than the pore diameter of the separator 7.

[0040] The average particle size of the inorganic ceramic particles may be equal to or smaller than the pore size of the separator 7. With the above configuration, the particles do not clog the pores of the separator 7, and therefore the circulation of the nonaqueous electrolyte inside the electrode group 4 is not hindered even during charge and discharge.

[0041] 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.

[0042] 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.

[0043] The concentration of the lithium salt in the non-aqueous 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, a non-aqueous electrolyte having excellent ionic conductivity and appropriate viscosity can be obtained. However, the lithium salt concentration is not limited to the above.

[0044] 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.

[0045] Examples of the cyclic carbonate include propylene carbonate (PC) and ethylene carbonate (EC).

[0046] Examples of the chain carbonate ester include diethyl carbonate (DEC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC).

[0047] Examples of the cyclic carboxylic acid ester include γ-butyrolactone (GBL) and γ-valerolactone (GVL).

[0048] 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.

[0049] The nonaqueous electrolyte may further contain other substances in addition to those mentioned above. For example, the nonaqueous electrolyte may further contain an additive to improve the dispersibility of the inorganic ceramic particles. The additive may be, for example, a fluorine-containing solvent. That is, the nonaqueous electrolyte may further contain a fluorine-containing solvent. With the above configuration, it is possible to reduce aggregation of inorganic ceramic particles over time and the resulting sedimentation of the particles.

[0050] 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.

[0051] 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.

[0052] 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.

[0053] 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.

[0054] The lithium nickel oxide may be represented by the following composition formula (3): 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 (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. Li α Ni x1 M4 x2 M5 (1-x1-x2) O 2+β ...(3)

[0055] The positive electrode active material layer 5b may contain other materials such as a conductive additive and a binder.

[0056] 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.

[0057] 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.

[0058] 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.

[0059] 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.

[0060] 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.

[0061] 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.

[0062] 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. Making the separator 7 from these materials 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. In the secondary battery disclosed herein, oxidation of the separator 7 is suppressed, thereby reducing the decrease 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 secondary battery of the present disclosure is not limited to the secondary battery 100. In addition to lithium secondary batteries, the technology of the present disclosure can be applied to various types of secondary batteries such as sodium secondary batteries and magnesium secondary batteries.

[0066] The secondary battery 100 can be manufactured, for example, by the following method.

[0067] First, a non-aqueous electrolyte solution is prepared. Specifically, a lithium salt is dissolved in a non-aqueous solvent. The resulting solution is mixed with the inorganic ceramic particles and ZrO balls as a mixing medium in a ball mill. The mixing medium is removed from the resulting mixture to obtain a non-aqueous electrolyte solution.

[0068] Next, the electrode group 4 is produced. Specifically, the positive electrode 5, the negative electrode 6, and a pair of separators 7 are stacked and wound. In this way, the electrode group 4 is obtained.

[0069] The positive electrode 5 is fabricated, for example, as follows: A positive electrode mixture is applied to one or both surfaces of a positive electrode current collector 5a, followed by drying and rolling. The positive electrode mixture is obtained by kneading and uniformly dispersing materials such as a positive electrode active material, a binder, and a conductive material using a dispersion medium. After rolling, a positive electrode lead 5c for extracting power is welded to the positive electrode current collector 5a.

[0070] A dry method may be used instead of the above-described wet method as a method for producing the positive electrode 5. Examples of dry film formation methods include vapor deposition, sputtering, and CVD (chemical vapor deposition) methods.

[0071] The negative electrode 6 can be fabricated, for example, by applying a negative electrode mixture to one or both surfaces of a negative electrode current collector 6a, drying the mixture, and rolling it. The negative electrode mixture is obtained by kneading and uniformly dispersing materials such as a negative electrode active material, a binder, and a conductive material in a dispersion medium. After rolling, a negative electrode lead 6c for extracting power is welded to the negative electrode current collector 6a.

[0072] As a method for producing the negative electrode 6, a dry method may be adopted instead of the above-mentioned wet method.

[0073] Next, the electrode group 4 is placed in the container 1, and a non-aqueous electrolyte solution is poured into the container 1. Finally, the container 1 is sealed. In this manner, the secondary battery 100 is obtained.

[0074] The method for manufacturing the secondary battery 100 is not limited to the above. For example, in preparing the non-aqueous electrolyte, inorganic ceramic particles may be dispersed in a non-aqueous solvent in which a lithium salt has been dissolved, using an ultrasonic homogenizer.

[0075] (Other Embodiments) (Additional Notes) The above description of the embodiments discloses the following techniques.

[0076] (Technology 1) A secondary battery comprising: a wound electrode group including a positive electrode, a negative electrode, and a separator; and a non-aqueous electrolyte solution, wherein the non-aqueous electrolyte solution contains a non-aqueous solvent and inorganic ceramic particles, the inorganic ceramic particles have lithium ion conductivity, and a content of the inorganic ceramic particles in the non-aqueous electrolyte solution is 0.1% by volume or more and 30% by volume or less.

[0077] According to the above configuration, the initial capacity and rate characteristics of the secondary battery can be maintained, and the cycle characteristics can be improved.

[0078] (Technology 2) The secondary battery according to Technology 1, wherein the inorganic ceramic particles have at least one crystal structure selected from the group consisting of a perovskite-type crystal structure and a NASICON-type crystal structure.

[0079] (Technology 3) The inorganic ceramic particles have a composition represented by the following formula (1): Li 3p M1 2 / 3-pM2O3... (1) The M1 is at least one selected from the group consisting of La, Sr, Na, Nd, Pr, Sm, Gd, Dy, Y, Eu, Tb, and Ba, and the M2 is at least one selected from the group consisting of Ti, Mg, W, Mn, Al, Ge, Ru, Nb, Ta, Co, Zr, Hf, Fe, Cr, and Ga, and 0<p<2 / 3 is satisfied. This configuration allows the aforementioned effects of the inorganic ceramic particles to be sufficiently obtained.

[0080] (Technology 4) The secondary battery according to Technology 3, wherein M1 is at least one selected from the group consisting of La, Sr, and Ba, and M2 is at least one selected from the group consisting of Ti, Cr, Mn, Zr, Nb, and W. With this configuration, the above-described effects of the inorganic ceramic particles can be sufficiently obtained.

[0081] (Technology 5) The inorganic ceramic particles have a composition represented by the following formula (2): Li 1+q Al q M3 2-q (PO4)3 (2) The secondary battery according to Technology 1 or 2, wherein M3 is at least one selected from the group consisting of Ge, Ce, Co, Cr, Fe, Hf, In, Mg, Mn, Mo, Na, Nb, Ni, Sb, Sc, Se, Sn, Ta, Ti, U, V, Y, Yb, Zn, and Zr, and 0<q<2 is satisfied. With this configuration, the above-described effects of the inorganic ceramic particles can be sufficiently obtained.

[0082] (Technology 6) The secondary battery according to any one of Technologies 1 to 5, wherein the inorganic ceramic particles have an average particle size of 1 nm or more and 500 nm or less. With this configuration, the dispersibility of the particles in the non-aqueous electrolyte solution is improved, and it is possible to increase the industrial productivity of the non-aqueous electrolyte solution and the secondary battery including the same.

[0083] (Technology 7) The secondary battery according to any one of Technologies 1 to 6, wherein the content of the inorganic ceramic particles in the non-aqueous electrolyte is 0.1% by volume or more and 6% by volume or less. The above-described effects of the inorganic ceramic particles can be sufficiently obtained. Furthermore, the dispersibility of the particles in the non-aqueous electrolyte is improved, thereby enabling the industrial productivity of the non-aqueous electrolyte to be increased.

[0084] (Technology 8) A non-aqueous electrolyte solution comprising: a non-aqueous solvent; and inorganic ceramic particles, wherein the inorganic ceramic particles have lithium ion conductivity and a NASICON crystal structure, and the content of the inorganic ceramic particles in the non-aqueous electrolyte solution is 0.1 vol% or more and 30 vol% or less.

[0085] The nonaqueous electrolyte solution of the present disclosure can improve the cycle characteristics of the battery while maintaining the initial capacity and rate characteristics.

[0086] (Technology 9) The inorganic ceramic particles have a composition represented by the following formula (2): Li 1+q Al q M3 2-q (PO4)3 (2) wherein M3 is at least one selected from the group consisting of Ge, Ce, Co, Cr, Fe, Hf, In, Mg, Mn, Mo, Na, Nb, Ni, Sb, Sc, Se, Sn, Ta, Ti, U, V, Y, Yb, Zn, and Zr, and 0<q<2 is satisfied. With this configuration, the above-described effects of the inorganic ceramic particles can be sufficiently obtained.

[0087] (Technology 10) The nonaqueous electrolyte according to Technology 8 or 9, wherein the inorganic ceramic particles have an average particle size of 1 nm or more and 500 nm or less. With this configuration, the dispersibility of the particles in the nonaqueous electrolyte is improved, and the industrial productivity of the nonaqueous electrolyte can be increased.

[0088] (Technology 11) A secondary battery comprising: a positive electrode; a negative electrode; and the nonaqueous electrolyte solution according to any one of Technologies 8 to 10.

[0089] The nonaqueous electrolyte solution of the present disclosure is suitable for nonaqueous electrolyte secondary batteries.

[0090] (Technology 12) A non-aqueous electrolyte solution comprising a non-aqueous solvent and inorganic ceramic particles, wherein the inorganic ceramic particles have lithium ion conductivity and have a composition represented by the following formula (2): Li 1+q Al q M3 2-q (PO4)3... (2) wherein M3 is at least one selected from the group consisting of Ge, Ce, Co, Cr, Fe, Hf, In, Mg, Mn, Mo, Na, Nb, Ni, Sb, Sc, Se, Sn, Ta, Ti, U, V, Y, Yb, Zn, and Zr, 0<q<2 is satisfied, and a content of the inorganic ceramic particles in the non-aqueous electrolyte is 0.1% by volume or more and 30% by volume or less.

[0091] The nonaqueous electrolyte solution of the present disclosure can improve the cycle characteristics of the battery while maintaining the initial capacity and rate characteristics.

[0092] (Technology 13) The nonaqueous electrolyte according to Technology 12, wherein the inorganic ceramic particles have an average particle size of 1 nm or more and 500 nm or less. With this configuration, the dispersibility of the particles in the nonaqueous electrolyte is improved, and industrial productivity of the nonaqueous electrolyte can be increased.

[0093] (Technology 14) A secondary battery comprising: a positive electrode; a negative electrode; and the nonaqueous electrolyte solution according to Technology 12 or 13.

[0094] The nonaqueous electrolyte solution of the present disclosure is suitable for nonaqueous electrolyte secondary batteries.

[0095] (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 obtained non-aqueous solvent to a concentration of 1.35 mol / L to obtain a solution. The obtained solution, ZrO2 balls (particle diameter 0.5 mm) as a mixing medium, and LiPF6 as inorganic ceramic particles were mixed.0.29 La 0.57 TiO3 (LLTO) particles (average particle diameter 800 nm) were placed in a planetary ball mill container and sealed in a dry atmosphere. The amount of LLTO 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 diameter of the LLTO particles after mixing was 40 nm. The supernatant liquid of the resulting mixture was removed with a dropper to remove the ZrO2 balls, yielding the non-aqueous electrolyte of Sample 1. The non-aqueous electrolyte of Sample 1 contained 4% by volume of LLTO particles dispersed therein. The non-aqueous electrolyte of Example 1 had fluidity at 25°C. The lithium ion conductivity of LLTO was 1 x 10 at 25°C. -6 S / cm to 1 x 10 -5 S / cm.

[0096] LiNi 0.8 Co 0.15 Al 0.05 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.

[0097] 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.

[0098] A laminate half-cell was fabricated using a positive electrode, a Li metal foil (2 cm × 2 cm, 200 μm thick) as a counter electrode, a separator (a polyethylene separator, #2320, manufactured by Celgard Inc.), and the nonaqueous electrolyte solution. In this manner, the evaluation cell for Sample 1 was fabricated.

[0099] (Sample 2) Instead of LLTO particles, Li 1.5 Al 0.5 Ge 1.5A nonaqueous electrolyte solution of Sample 2 was obtained in the same manner as Sample 1, except that (PO4)3 (LAGP) particles (average particle diameter 1100 nm) were used. The average particle diameter of the LAGP particles in the nonaqueous electrolyte solution of Sample 2 was 50 nm. The nonaqueous electrolyte solution of Sample 2 had fluidity at 25°C. The lithium ion conductivity of LAGP was 1 x 10 -5 S / cm to 1 x 10 -4 S / cm.

[0100] An evaluation cell for Sample 2 was fabricated in the same manner as Sample 1, except that the nonaqueous electrolyte of Sample 2 was used.

[0101] (Sample 3) A non-aqueous electrolyte solution of Sample 3 was obtained in the same manner as Sample 1, except that the inorganic ceramic particles were not dispersed in the non-aqueous solvent.

[0102] An evaluation cell for Sample 3 was fabricated in the same manner as Sample 1, except that the nonaqueous electrolyte of Sample 3 was used.

[0103] (Sample 4) A nonaqueous electrolyte solution of Sample 4 was obtained in the same manner as Sample 1, except that AlO particles (average particle diameter 500 nm) were used instead of the LLTO particles. The average particle diameter of the AlO particles in the nonaqueous electrolyte solution of Sample 4 was 50 nm. The nonaqueous electrolyte solution of Sample 4 had fluidity at 25°C.

[0104] An evaluation cell for Sample 4 was fabricated in the same manner as Sample 1, except that the nonaqueous electrolyte of Sample 4 was used.

[0105] [Initial Capacity] The initial capacity of the evaluation cells of Samples 1 to 4 was evaluated according to the following procedure. The measurement was carried out at an ambient temperature of 25°C.

[0106] The test cell was charged at a constant current of 0.2 C until the voltage reached 4.4 V, and then charged at a constant voltage of 4.4 V until the current reached 0.02 C. After a 20-minute break, the test cell was discharged at a constant current of 0.2 C until the voltage reached 2.5 V. The initial discharge capacity of the test cell was measured. The results are shown in Table 1.

[0107] [Cycle Test] A cycle test was carried out on the evaluation cells of Samples 1 to 4 according to the following procedure.

[0108] An initial charge-discharge treatment was performed before the cycle test. Specifically, 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 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 treatment was performed at an ambient temperature of 25°C.

[0109] The evaluation cells that had undergone the above charge and discharge were then changed to an ambient temperature of 45°C. These cells were charged at a constant current of 0.3 C until the voltage reached 4.3 V. After a 20-minute break, they were discharged at a constant current of 0.3 C until the voltage reached 2.5 V. The above charge and discharge constituted one cycle, and this cycle was repeated 100 times to evaluate the capacity retention rate. The capacity retention rate represents the ratio of the discharge capacity at the 100th cycle to the discharge capacity at the first cycle. The results are shown in Table 1.

[0110] Furthermore, one more charge / discharge cycle was performed on the evaluation cells of each sample. This 101st cycle was performed by constant current charging at a current value of 0.2 C until the voltage reached 4.3 V, followed by a 20-minute pause and constant current discharging at a current value of 0.2 C until the voltage reached 2.5 V. The ratio of the discharge capacity at the 100th cycle to the discharge capacity at the 101st cycle for each sample was calculated. The results are shown in Table 1. In Table 1, the "0.3 C / 0.2 C" column represents the ratio of the discharge capacity at the 100th cycle to the discharge capacity at the 101st cycle. This value can be considered an indicator of the rate characteristics of the evaluation cells.

[0111]

[0112] (Sample 5) A non-aqueous electrolyte solution of Sample 5 was obtained in the same manner as Sample 1, except that the amount of LLTO particles was adjusted so that the content ratio of the LLTO particles in the non-aqueous electrolyte solution was 10% by volume.

[0113] (Sample 6) A non-aqueous electrolyte solution of Sample 6 was obtained in the same manner as Sample 2, except that the amount of LAGP particles was adjusted so that the content in the non-aqueous electrolyte solution was 10% by volume.

[0114] [Evaluation of Dispersion Stability of Nonaqueous Electrolyte] The nonaqueous electrolytes of Samples 1 to 2 and 5 to 6 were each placed in a container and left to stand for 48 hours, and the dispersion state of the inorganic ceramic particles was visually confirmed. As a result of the evaluation, in the nonaqueous electrolytes of Samples 1 to 2 and 5 to 6, the particles did not settle even after 48 hours, and the nonaqueous electrolytes were in a single phase state.

[0115]

[0116] (Discussion) As can be seen from Table 1, the evaluation cells of Samples 1 and 2 had better initial discharge capacity and capacity retention than the evaluation cells of Samples 3 and 4. Furthermore, the rate characteristics of the evaluation cells of Samples 1 and 2 were equivalent to that of Sample 3 and better than that of Sample 4. From the above, the evaluation cells of Samples 1 and 2 had improved cycle characteristics while maintaining the initial discharge capacity and rate characteristics compared to the evaluation cell of Sample 3, which did not have particles added to the nonaqueous electrolyte. On the other hand, the evaluation cell of Sample 4 had improved capacity retention compared to the evaluation cell of Sample 3, but had decreased initial discharge capacity and rate characteristics.

[0117] As can be seen from Table 2, the particles did not settle and the dispersion stability was excellent in the nonaqueous electrolytes of Samples 1 and 2 and Samples 5 and 6. Since the nonaqueous electrolytes of Samples 5 and 6 contain the same particles as Samples 1 and 2, respectively, it is presumed that they can improve the battery characteristics in the same way as Samples 1 and 2.

[0118] The technology of the present disclosure is useful for, for example, lithium ion secondary batteries.

Claims

1. A secondary battery comprising: a wound electrode group including a positive electrode, a negative electrode, and a separator; and a non-aqueous electrolyte solution, wherein the non-aqueous electrolyte solution contains a non-aqueous solvent and inorganic ceramic particles, the inorganic ceramic particles have lithium ion conductivity, and the content of the inorganic ceramic particles in the non-aqueous electrolyte solution is 0.1% by volume or more and 30% by volume or less.

2. The secondary battery according to claim 1, wherein the inorganic ceramic particles have at least one crystal structure selected from the group consisting of a perovskite-type crystal structure and a NASICON-type crystal structure.

3. The inorganic ceramic particles have a composition represented by the following formula (1): Li 3p M1 2 / 3-p M2O3... (1) The secondary battery according to claim 1, wherein M1 is at least one selected from the group consisting of La, Sr, Na, Nd, Pr, Sm, Gd, Dy, Y, Eu, Tb, and Ba, and M2 is at least one selected from the group consisting of Ti, Mg, W, Mn, Al, Ge, Ru, Nb, Ta, Co, Zr, Hf, Fe, Cr, and Ga, and 0<p<2 / 3 is satisfied.

4. The secondary battery according to claim 3, wherein M1 is at least one selected from the group consisting of La, Sr, and Ba, and M2 is at least one selected from the group consisting of Ti, Cr, Mn, Zr, Nb, and W.

5. The inorganic ceramic particles have a composition represented by the following formula (2): Li 1+q Al q M3 2-q (PO4)3 (2) The secondary battery according to claim 1, wherein M3 is at least one selected from the group consisting of Ge, Ce, Co, Cr, Fe, Hf, In, Mg, Mn, Mo, Na, Nb, Ni, Sb, Sc, Se, Sn, Ta, Ti, U, V, Y, Yb, Zn, and Zr, and 0<q<2 is satisfied.

6. The secondary battery according to claim 1, wherein the inorganic ceramic particles have an average particle size of 1 nm or more and 500 nm or less.

7. The secondary battery according to claim 1, wherein the content of the inorganic ceramic particles in the non-aqueous electrolyte is 0.1% by volume or more and 6% by volume or less.

8. A non-aqueous electrolyte comprising: a non-aqueous solvent; and inorganic ceramic particles, wherein the inorganic ceramic particles have lithium ion conductivity and a NASICON-type crystal structure, and the content of the inorganic ceramic particles in the non-aqueous electrolyte is 0.1% by volume or more and 30% by volume or less.

9. The inorganic ceramic particles have a composition represented by the following formula (2): Li 1+q Al q M3 2-q (PO4)3 (2) The nonaqueous electrolyte solution according to claim 8, wherein M3 is at least one selected from the group consisting of Ge, Ce, Co, Cr, Fe, Hf, In, Mg, Mn, Mo, Na, Nb, Ni, Sb, Sc, Se, Sn, Ta, Ti, U, V, Y, Yb, Zn, and Zr, and 0<q<2 is satisfied.

10. The nonaqueous electrolyte according to claim 8, wherein the inorganic ceramic particles have an average particle size of 1 nm or more and 500 nm or less.

11. A secondary battery comprising: a positive electrode; a negative electrode; and the nonaqueous electrolyte solution according to claim 8.

12. A non-aqueous electrolyte solution comprising a non-aqueous solvent and inorganic ceramic particles, wherein the inorganic ceramic particles have lithium ion conductivity and have a composition represented by the following formula (2): Li 1+q Al q M3 2-q (PO4)3... (2) wherein M3 is at least one selected from the group consisting of Ge, Ce, Co, Cr, Fe, Hf, In, Mg, Mn, Mo, Na, Nb, Ni, Sb, Sc, Se, Sn, Ta, Ti, U, V, Y, Yb, Zn, and Zr, 0<q<2 is satisfied, and a content of the inorganic ceramic particles in the non-aqueous electrolyte is 0.1% by volume or more and 30% by volume or less.

13. The nonaqueous electrolyte according to claim 12, wherein the inorganic ceramic particles have an average particle size of 1 nm or more and 500 nm or less.

14. A secondary battery comprising: a positive electrode; a negative electrode; and the nonaqueous electrolyte solution according to claim 12.

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