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

Abstract

A non-aqueous electrolyte solution according to the present disclosure contains a non-aqueous solvent, an electrolyte that is dissolved in the non-aqueous solvent, and inorganic particles that are dispersed in the non-aqueous solvent. The inorganic particles contain an inorganic material that has a spinel-type crystal structure. The inorganic material may have a composition that is expressed by compositional formula (1). In composition formula (1), A and B are mutually different metal elements, and X is an anion.　(1): AB2X4...

Description

Non-aqueous electrolytes and non-aqueous electrolyte secondary batteries

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

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

[0003] Japanese Patent Publication No. 2005-268230

[0004] In non-aqueous electrolyte secondary batteries, the decomposition of the electrolyte is one of the causes of reduced battery cycle performance. This disclosure provides a technology for improving the cycle performance of non-aqueous electrolyte secondary batteries.

[0005] This disclosure provides a non-aqueous electrolyte comprising a non-aqueous solvent, an electrolyte dissolved in the non-aqueous solvent, and inorganic particles dispersed in the non-aqueous solvent, wherein the inorganic particles include an inorganic material having a spinel-type crystal structure.

[0006] The non-aqueous electrolyte of this disclosure can improve the cycle characteristics of non-aqueous electrolyte secondary batteries.

[0007] Figure 1 is a schematic cross-sectional view showing an example of a non-aqueous electrolyte secondary battery in Embodiment 2. Figure 2 is a graph showing the relationship between the number of cycles and discharge capacity in the batteries of Example 1 and Comparative Example 1. Figure 3 is a graph showing the relationship between the number of cycles and capacity retention rate in the batteries of Example 1 and Comparative Example 1.

[0008] The embodiments of this disclosure will be described below with reference to the drawings. This disclosure is not limited to the embodiments described below.

[0009] (Embodiment 1) The non-aqueous electrolyte in Embodiment 1 comprises a non-aqueous solvent, an electrolyte dissolved in the non-aqueous solvent, and inorganic particles. The inorganic particles are dispersed in the non-aqueous solvent. The inorganic particles include an inorganic material having a spinel-type crystal structure. By using the non-aqueous electrolyte in Embodiment 1 in a battery, the battery's capacity retention rate can be improved.

[0010] The mechanism by which the non-aqueous electrolyte in Embodiment 1 achieves the above effect is not entirely clear, but the following mechanism is hypothesized. That is, inorganic particles are attracted to the active material and adhere to its surface. The inorganic particles adhering to the surface of the active material suppress the decomposition of the non-aqueous solvent on the surface of the active material. Since the inorganic particles are dispersed in the non-aqueous electrolyte, even if a new surface is formed due to repeated charging and discharging of the active material, the inorganic particles can act on the new surface. As a result, the effect of the inorganic particles is sustained.

[0011] Generally, when the active material of a battery has a spinel-type crystal structure, that active material tends to exhibit good reversibility with respect to the battery's charge-discharge cycle. Therefore, it is presumed that inorganic particles containing an inorganic material having a spinel-type crystal structure will form a stable film on the electrode even when dispersed in a non-aqueous electrolyte, as in this embodiment, with respect to the battery's charge-discharge cycle.

[0012] The presence of inorganic materials with a spinel-type crystal structure in inorganic particles can be confirmed by powder X-ray diffraction measurements.

[0013] The inorganic material having a spinel-type crystal structure may contain lithium. In this case, the non-aqueous electrolyte of this embodiment is suitable for lithium secondary batteries. Preferably, the inorganic particles have lithium ion conductivity. When inorganic particles have lithium ion conductivity, they are less likely to inhibit lithium ion conduction in the battery. In other words, inorganic particles are less likely to increase the resistance of the battery.

[0014] Inorganic materials having a spinel-type crystal structure may have a composition represented by the following composition formula (1). In composition formula (1), A and B are different metal ions. Examples of metal atoms constituting the metal ions include Li, Mn, Al, Mg, Ca, Ti, Ba, Cr, Fe, Co, Ni, Cu, Zn, and V. X is an anion. An example of an anion is O 2- S 2- , Cl - These are some examples.

[0015] AB2X4... (1)

[0016] When an inorganic material having a spinel-type crystal structure contains lithium, A in the composition formula (1) is a lithium ion. In this case, B in the composition formula (1) can be at least one selected from the group consisting of Mn, Al, Mg, Ca, Ti, Ba, Cr, Fe, Co, Ni, Cu, Zn, and V. Examples of the inorganic material having a spinel-type crystal structure represented by the composition formula (1) include LiMn2O4, Li4Ti5O 12 and the like.

[0017] An inorganic material having a spinel-type crystal structure is typically an oxide. Oxides tend to be chemically stable and are suitable as materials for non-aqueous electrolytes.

[0018] An inorganic material having a spinel-type crystal structure may have a composition represented by the following composition formula (2). In the composition formula (2), M is at least one selected from the group consisting of Co, Ni, Mn, V, and Ti. x, y, and z are natural numbers independent of each other and satisfy x < y < z.

[0019] Li x M y O z ... (2)

[0020] In the composition formula (2), M may be Ti. That is, the inorganic material having a spinel-type crystal structure may contain lithium titanate.

[0021] Lithium titanate may have a composition of Li4Ti5O 12 (Li[Li 1 / 3 Ti 5 / 3 O4). Lithium titanate represented by Li4Ti5O 12 is a material known to have a spinel-type crystal structure. Li4Ti5O 12 has high lithium ion conductivity and is suitable for the non-aqueous electrolyte of this embodiment.

[0022] The inorganic material may be reduced. For example, the composition of lithium titanate in the oxidized state is Li[Li 1 / 3 Ti 5 / 3When it is O4, the composition of lithium titanate in the reduced state is Li2[Li 1 / 3 Ti 5 / 3 O4. In this case, the inorganic material can have a composition represented by Li 1+x [Li 1 / 3 Ti 5 / 3 O4 (0 < x ≤ 1).

[0023] The non-aqueous electrolyte in Embodiment 1 is, for example, liquid at 25°C. The liquid includes sols. The non-aqueous electrolyte in Embodiment 1 can have fluidity at 25°C.

[0024] In the present disclosure, "having fluidity at 25°C" means having a viscosity of 20,000 mPa·s or less at 25°C.

[0025] The viscosity of the non-aqueous electrolyte 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.

[0026] The non-aqueous electrolyte in Embodiment 1 may be a non-aqueous colloidal solution in which inorganic particles are dispersed. The inorganic particles may be insoluble in the non-aqueous solvent. In this case, the inorganic particles adhere to the surface of the active material, and the effect of the inorganic particles is exerted on the surface of the active material.

[0027] In the present disclosure, "inorganic particles insoluble in a non-aqueous solvent" means inorganic particles that require 100 mL or more of a non-aqueous solvent to dissolve 1 g at 25°C. That is, the solubility of the inorganic particles in 100 mL of the non-aqueous solvent is 1 g or less. Here, dissolution means that the permeability of the solution obtained when the inorganic particles are dissolved in the non-aqueous solvent in the container does not change from the permeability of the solvent, that is, both that the solution is not cloudy and that no precipitate is confirmed on the bottom of the container after standing for 24 hours. For example, electrolyte salts such as LiPF6 and LiBF6 are sufficiently soluble in non-aqueous solvents and are not included in the inorganic particles in the present disclosure.

[0028] The shape of the inorganic particles is not particularly limited and can be needle-like, flaky, spherical, or ellipsoidal.

[0029] The method for producing the inorganic particles is not particularly limited. Examples of the method for synthesizing an inorganic material having a spinel-type crystal structure include various methods such as a flux method, a firing method, and a coprecipitation method. In one example, lithium titanate can be synthesized by firing a lithium compound such as lithium carbonate or lithium hydroxide and a titanate. However, commercially available inorganic particles may be used, or commercially available inorganic particles may be pulverized to an appropriate average particle size using a pulverizing device such as a ball mill and then used.

[0030] The content ratio of the inorganic particles in the non-aqueous electrolyte may be 0.1% by volume or more and 10% by volume or less. The content ratio of the inorganic particles may be 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 6% by volume or less, or 1% by volume or more and 4% by volume or less. With the above configuration, the dispersibility of the inorganic particles and the fluidity of the non-aqueous electrolyte can be improved.

[0031] The content ratio of the inorganic particles in the non-aqueous electrolyte is determined, for example, by the following method. After measuring the volume of the non-aqueous electrolyte, the non-aqueous electrolyte is filtered through a filter to separate the particles. The separated particles are washed with a solvent such as dimethyl carbonate, and after the washing solvent is volatilized and dried, the mass of the particles is measured. The volume of the particles is calculated from the mass of the particles and the specific gravity specified from the components of the particles. The components of the particles can be specified by various analytical methods such as high-frequency inductively coupled plasma analysis (ICP), X-ray diffraction method (XRD), infrared absorption spectroscopy (IR), and nuclear magnetic resonance analysis (NMR). In this way, the content ratio of the inorganic particles in the non-aqueous electrolyte can be calculated. Incidentally, the volume of the non-aqueous electrolyte can also be calculated from the composition and the mass. The composition of the non-aqueous electrolyte can be measured by a liquid chromatograph, a gas chromatograph, or the like.

[0032] The inorganic particles may be nanoparticles.

[0033] The average particle size of the inorganic particles may be 1 nm or more and 500 nm or less. With the above configuration, the dispersibility of inorganic particles in the non-aqueous electrolyte is improved, and the industrial productivity of the non-aqueous electrolyte can be increased. The average particle size of the inorganic particles may be 5 nm or more and 400 nm or less, or 10 nm or more and 300 nm or less. When the average particle size of the inorganic particles is 500 nm or less, in a battery using the non-aqueous electrolyte of this embodiment, when the non-aqueous electrolyte penetrates the active material layer, the inorganic particles can penetrate between the active material particles arranged inside the active material layer. As a result, the decomposition of the non-aqueous solvent inside the active material layer can be suppressed.

[0034] The average particle size of the inorganic particles may be less than or equal to the pore size of the separator in a battery using a non-aqueous electrolyte. With this configuration, the inorganic particles do not clog the pores of the separator, and therefore the circulation of the electrolyte within the electrode group is not obstructed even during charging and discharging.

[0035] The average particle size of inorganic particles can be determined by dynamic light scattering (DLS) spectroscopy.

[0036] Inorganic particles may be primary or secondary particles. Inorganic particles are typically primary particles.

[0037] The electrolyte includes, for example, a lithium salt. Examples of lithium salts include lithium hexafluoride phosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bisperfluoroethylsulfonylimide (LiN(SO2C2F5)2), LiAsF6, LiCF3SO3, and lithium difluoro(oxalato)borate. At least one of the above-mentioned substances can be used as the lithium salt. The lithium salt may contain fluorine (F). The lithium salt may also be LiPF6.

[0038] The concentration of lithium salt in the non-aqueous electrolyte may be, for example, 0.5 mol / liter or more and 2 mol / liter or less. By controlling the lithium salt concentration within the above range, an electrolyte with excellent ionic conductivity and appropriate viscosity can be obtained. However, the lithium salt concentration is not limited to the above.

[0039] The non-aqueous solvent is not particularly limited, and examples include cyclic carbonate esters, linear carbonate esters, and cyclic carboxylic acid esters.

[0040] Examples of cyclic carbonate esters include propylene carbonate (PC) and ethylene carbonate (EC).

[0041] Examples of linear carbonate esters include diethyl carbonate (DEC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC).

[0042] Examples of cyclic carboxylic acid esters include γ-butyrolactone (GBL) and γ-valerolactone (GVL).

[0043] The non-aqueous solvent may be used alone or in combination of two or more types. The non-aqueous solvent may also contain ethylene carbonate. This can increase the solubility of electrolytes such as lithium salts in the non-aqueous solvent.

[0044] The non-aqueous electrolyte in Embodiment 1 may further contain other substances besides those mentioned above. For example, the non-aqueous electrolyte in Embodiment 1 may further contain additives to improve the dispersibility of inorganic particles. The additives are, for example, fluorine-containing solvents. That is, the non-aqueous electrolyte in Embodiment 1 may further contain a fluorine-containing solvent. With the above configuration, aggregation of inorganic particles over time and the resulting sedimentation of particles can be reduced.

[0045] Examples of fluorine-containing solvents include fluorinated cyclic esters and fluorinated ethers. Fluorinated cyclic esters may also include fluoroethylene carbonate. Fluorinated ethers may also include 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether.

[0046] The non-aqueous electrolyte in Embodiment 1 can be produced, for example, by the following method.

[0047] A lithium salt is dissolved in a non-aqueous solvent. The resulting solution, the inorganic particles mentioned above, and ZrO2 balls as a mixing medium are mixed using a ball mill. By removing the mixing medium from the resulting mixture, the non-aqueous electrolyte of Embodiment 1 is obtained.

[0048] The method for producing a non-aqueous electrolyte is not limited to those described above. For example, inorganic particles may be dispersed in a non-aqueous solvent containing a dissolved lithium salt using an ultrasonic homogenizer.

[0049] (Embodiment 2) The non-aqueous electrolyte secondary battery in Embodiment 2 comprises a positive electrode, a negative electrode, and a non-aqueous electrolyte according to Embodiment 1. By using the non-aqueous electrolyte in Embodiment 1, the cycle characteristics of the secondary battery can be improved.

[0050] Figure 1 is a schematic cross-sectional view showing an example of a non-aqueous electrolyte secondary battery in Embodiment 2. The secondary battery 100 comprises a container 1, an electrode group 4, and an electrolyte (not shown). The electrolyte is the non-aqueous electrolyte in Embodiment 1. The electrode group 4 has a wound structure. The electrode group 4 is housed in the container 1. The electrode group 4 has a positive electrode 5, a negative electrode 6, and a pair of separators 7. The electrode group 4 is impregnated with the electrolyte. The opening of the container 1 is sealed with a sealing plate 2. The positive electrode 5 has 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 arranged around the sealing plate 2. The negative electrode 6 has 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 positioned on the upper and lower surfaces of the electrode group 4, respectively.

[0051] The components of the secondary battery 100 will be described in detail below.

[0052] As the positive electrode current collector 5a, a sheet or film made of a metallic material such as aluminum, stainless steel, titanium, or their alloys can be used. Aluminum and its alloys are suitable materials for the positive electrode current collector 5a because they are inexpensive and easy to make into thin films. The sheet or film may be porous or non-porous. Metal foil, metal mesh, etc., can be used as the sheet or film. A carbon material such as carbon may be coated on the surface of the positive electrode current collector 5a as a conductive auxiliary material.

[0053] The positive electrode active material layer 5b contains a positive electrode active material. The positive electrode active material may be a material that has the ability to intercept and release lithium ions. As the positive electrode active material, lithium-containing transition metal oxides, lithium-containing transition metal phosphates, transition metal fluorides, polyanionic materials, fluorinated polyanionic materials, transition metal sulfides, transition metal oxysulfides, transition metal oxynitrides, etc., can be used. In particular, when lithium-containing transition metal oxides or lithium-containing transition metal phosphates are used as the positive electrode active material, the manufacturing cost of the battery can be reduced and the average discharge voltage can be increased. 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.

[0054] The positive electrode active material may include lithium nickel oxide having a layered rock salt-type crystalline structure. The proportion of Ni among the metal elements other than Li in the lithium nickel oxide may be 50 atomic percent or more. Other transition metals may be included in the lithium nickel oxide. Lithium nickel oxide is useful for achieving a high operating voltage.

[0055] Lithium nickel oxide may be represented by the following compositional formula (3). Element M3 is at least one selected from the group consisting of V, Co, and Mn. Element M4 is at least one selected from the group consisting of Mg, Al, Ca, Ti, Cu, Zn, and Nb. Compositional 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.

[0056] Li α Ni x1 M3 x2 M4 (1-x1-x2) O 2+β ... (3)

[0057] The positive electrode active material layer 5b may contain other materials such as conductive additives and binders.

[0058] Conductive additives are used to reduce the resistance of the positive electrode 5. Examples of conductive additives include carbon materials and conductive polymer compounds. Examples of carbon materials include carbon black, graphite, acetylene black, carbon nanotubes, carbon nanofibers, graphene, fullerene, and graphite oxide. Examples of conductive polymer compounds include polyaniline, polypyrrole, and polythiophene.

[0059] A binder is used to improve the binding properties of the materials constituting the positive electrode 5. Possible binders include polymer materials such as polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, polytetrafluoroethylene, carboxymethylcellulose, polyacrylic acid, styrene-butadiene copolymer rubber, polypropylene, polyethylene, and polyimide.

[0060] As the negative electrode current collector 6a, a sheet or film made of a metallic material such as stainless steel, nickel, copper, or alloys thereof may be used. The sheet or film may be porous or non-porous. As the sheet or film, metal foil, metal mesh, etc., may be used. A carbon material such as carbon may be coated on the surface of the negative electrode current collector 6a as a conductive auxiliary material.

[0061] The negative electrode active material layer 6b contains a negative electrode active material. The negative electrode active material may be a material having the ability to intercept and release 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 alloys with lithium. Examples of carbon materials include graphite. Examples of materials capable of forming alloys with lithium include silicon, silicon-containing oxides, tin, zinc alloys, bismuth, and germanium. One of these negative electrode active materials may be used, or two or more may be used in combination.

[0062] 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. Alternatively, only graphite may be included in the negative electrode active material layer 6b. Graphite is recommended because it does not degrade easily even when repeatedly charged and discharged at great depths. Other carbon materials may be used as the negative electrode active material. Silicon exhibits a larger capacity than graphite, which is advantageous for increasing the capacity of the secondary battery 100.

[0063] The negative electrode active material layer 6b may contain other materials such as conductive additives and binders. Materials that can be used in the positive electrode active material layer 5b can also be used in the negative electrode active material layer 6b as conductive additives and binders.

[0064] The electrolyte is the non-aqueous electrolyte in Embodiment 1. The electrolyte is impregnated into the positive electrode 5, the negative electrode 6, and the separator 7. The electrolyte may also fill the internal space of the container 1. Due to the action of the electrolyte, lithium ions can move between the positive electrode 5 and the negative electrode 6.

[0065] The average particle size of the inorganic particles contained in the electrolyte may be less than or equal to the pore size of the separator 7.

[0066] The separator 7 is lithium ion conductive. The material of the separator 7 is not particularly limited as long as the passage of lithium ions is permitted. The material of the separator 7 may be at least one selected from the group consisting of gel electrolytes, ion exchange resin membranes, semipermeable membranes, and porous membranes. If the separator 7 is made of these materials, the safety of the secondary battery 100 can be sufficiently ensured. 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 resin and porous membranes containing glass paper obtained by weaving glass fibers into a nonwoven fabric. By using the non-aqueous electrolyte in Embodiment 1 in the secondary battery 100, oxidation of the separator 7 is suppressed and the decrease in the strength of the separator 7 can be reduced.

[0067] Container 1 is, for example, a metal container such as aluminum or stainless steel. Container 1 may have a cylindrical shape or a rectangular tube shape.

[0068] The electrode group 4 may be wound in a cylindrical shape or in an elliptical shape.

[0069] The shape of the secondary battery 100 is not particularly limited. In this disclosure, as an example of the structure of a non-aqueous electrolyte secondary battery according to Embodiment 2, the configuration example shown in Figure 1, namely a secondary battery in which an electrode group in which a positive electrode and a negative electrode are wound around a separator, and an electrolyte are housed in an outer casing, is described. However, the secondary battery according to this disclosure is not limited to this configuration example. The secondary battery according to this disclosure may take any form, such as cylindrical, prismatic, coin-shaped, button-shaped, laminated, etc. Furthermore, as the electrode group in the secondary battery according to this disclosure, other forms of electrode groups may be used instead of wound electrode groups, such as laminated electrode groups in which a positive electrode and a negative electrode are stacked around a separator.

[0070] The application of the non-aqueous electrolyte described herein is not limited to secondary batteries 100. In addition to lithium secondary batteries, the non-aqueous electrolyte described herein can be applied to various secondary batteries such as sodium secondary batteries and magnesium secondary batteries.

[0071] (Other Embodiments) (Note) The above description of embodiments discloses the following technologies.

[0072] (Technical 1) A non-aqueous electrolyte comprising: a non-aqueous solvent; an electrolyte dissolved in the non-aqueous solvent; and inorganic particles dispersed in the non-aqueous solvent, wherein the inorganic particles include an inorganic material having a spinel-type crystal structure.

[0073] The non-aqueous electrolyte of this disclosure can improve the cycle characteristics of non-aqueous electrolyte secondary batteries.

[0074] (Technology 2) The non-aqueous electrolyte according to Technology 1, wherein the inorganic material contains lithium. In this case, the non-aqueous electrolyte of this embodiment is suitable for lithium secondary batteries.

[0075] (Technology 3) A non-aqueous electrolyte according to Technology 1 or 2, wherein the inorganic particles are lithium ion conductive. When the inorganic particles are lithium ion conductive, the inorganic particles are less likely to inhibit lithium ion conduction in the battery.

[0076] (Technical 4) The inorganic material has a composition represented by the following composition formula (1), wherein A and B are different metal ions and X is an anion, as described in any one of Technical 1 to 3, and is a non-aqueous electrolyte. AB2X4...(1)

[0077] (Technology 5) The inorganic material has a composition represented by the following composition formula (2), wherein in composition formula (2), M is at least one selected from the group consisting of Co, Ni, Mn, V, and Ti, and x, y, and z are each mutually independent natural numbers satisfying x < y < z, the non-aqueous electrolyte according to any one of Techniques 1 to 3. Li x M y O z ... (2)

[0078] (Technical 6) The non-aqueous electrolyte according to Technical 5, wherein M is Ti.

[0079] (Technical 7) A non-aqueous electrolyte according to any one of Technical 1 to 6, wherein the inorganic material contains lithium titanium oxide.

[0080] (Technical 8) The lithium titanium oxide is Li4Ti5O 12 A non-aqueous electrolyte according to Technical 7, having the composition represented by Li4Ti5O. 12 Because it has high lithium-ion conductivity, it is suitable for the non-aqueous electrolyte in this embodiment.

[0081] (Technical 9) The inorganic particles are insoluble in the non-aqueous solvent, and the non-aqueous electrolyte is as described in any one of Technical 1 to 8. In this case, the inorganic particles adhere to the surface of the active material, and the effect of the inorganic particles is exerted on the surface of the active material.

[0082] (Technical 10) The non-aqueous electrolyte according to any one of Technical 1 to 9, wherein the content of the inorganic particles in the non-aqueous electrolyte is 0.1 volume% or more and 10 volume% or less. With the above configuration, the dispersibility of the inorganic particles and the fluidity of the non-aqueous electrolyte can be improved.

[0083] (Technical 11) A non-aqueous electrolyte according to any one of Technical 1 to 10, wherein the average particle size of the inorganic particles is 1 nm or more and 500 nm or less. With such a configuration, in a battery using the non-aqueous electrolyte of the present disclosure, when the non-aqueous electrolyte penetrates the active material layer, the inorganic particles can penetrate between the active material particles arranged inside the active material layer. As a result, the decomposition of the non-aqueous solvent inside the active material layer can be suppressed.

[0084] (Technical 12) A non-aqueous electrolyte secondary battery comprising a non-aqueous electrolyte as described in any one of Technical 1 to 11.

[0085] (Example 1) Ethylene carbonate (EC), fluoroethylene carbonate (FEC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) were mixed in a volume ratio of EC:FEC:EMC:DMC = 10:10:5:75 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. 15 mL of the obtained solution was mixed with Li4Ti5O as inorganic particles. 12 4.38 g of particles (average particle size 12 μm) and 70 g of ZrO2 balls (average particle size 0.5 mm) as a mixing medium were placed in a ball mill and mixed at 300 rpm for 2 hours. The resulting Li4Ti5O12 The average particle size was 500 nm. The ZrO2 balls were removed by drawing up the supernatant of the obtained mixture with a dropper, and the non-aqueous electrolyte of Example 1 was obtained. In the non-aqueous electrolyte of Example 1, 4 volume% Li4Ti5O 12 The particles were dispersed. The non-aqueous electrolyte of Example 1 was fluid at 25°C. Li4Ti5O used in Example 1 12 The powder X-ray diffraction pattern of the particles showed a diffraction pattern consistent with a spinel-type crystal structure.

[0086] (Comparative Example 1) Ethylene carbonate (EC), fluoroethylene carbonate (FEC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) were mixed in a volume ratio of EC:FEC:EMC:DMC = 10:10:5:75 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 the non-aqueous electrolyte of Comparative Example 1. That is, the non-aqueous electrolyte of Comparative Example 1 was prepared in the same manner as in Example 1, except that it did not contain lithium titanium oxide particles.

[0087] (Battery manufacturing) LiNi 0.8 Co 0.15 Al 0.05 A positive electrode slurry was prepared by mixing and stirring a positive electrode active material (NCA) having an O2 composition, acetylene black (AB), polyvinylidene fluoride (PVDF), and N-methylpyrrolidone (NMP). The mass ratio of NCA, AB, and PVDF was NCA:AB:PVDF = 96:2:2. The positive electrode slurry was applied to the surface of aluminum foil to form a coating film, and after drying the coating film, it was rolled. This yielded a positive electrode common to both Example 1 and Comparative Example 1.

[0088] An appropriate amount of water was added to the negative electrode mixture (graphite) 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. The binder used was sodium polyacrylate (PAA-Na), sodium salt of CMC (CMC-Na), and styrene-butadiene rubber (SBR). The content of PAA-Na, CMC-Na, and SBR in the negative electrode mixture was 1% by mass each. Next, the negative electrode slurry was applied to the surface of a copper foil, the coating film was dried, and then rolled to form a negative electrode mixture layer and obtain a negative electrode.

[0089] Current collector leads were attached to both the positive and negative electrodes. The positive electrode, separator (Celgard Co., Ltd., #2320), and negative electrode were combined and placed in a laminate film container. The non-aqueous electrolyte from Example 1 was poured into the container and sealed. This obtained the battery of Example 1.

[0090] Instead of the non-aqueous electrolyte of Example 1, the non-aqueous electrolyte of Comparative Example 1 was placed in a container to obtain the battery of Comparative Example 1.

[0091] (Cycle Test) The batteries of Example 1 and Comparative Example 1 were subjected to cycle tests using the following method. The batteries were placed in a constant temperature bath at 45°C. Constant current charging was performed at a current of 0.3C until the voltage reached 4.3V, and then constant voltage charging was performed at a voltage of 4.3V until the current reached 0.02C. After that, constant current discharge was performed at a current of 0.3C until the voltage reached 2.5V. A 20-minute rest period was provided between charging and discharging. This charge-discharge cycle was repeated 100 times. However, at the 50th and 100th cycles, the discharge current was set to 0.05C or 0.2C and the discharge capacity was measured. Specifically, discharge was performed at a current of 0.05C at the 49th and 99th cycles, and at a current of 0.2C at the 50th and 100th cycles. The results are shown in Table 1 and Figure 2.

[0092]

[0093] The "capacity retention rate" was calculated as the ratio of each discharge capacity to the discharge capacity of the first cycle. The results are shown in Table 2 and Figure 3.

[0094]

[0095] Figure 2 is a graph showing the relationship between the number of cycles and discharge capacity in the batteries of Example 1 and Comparative Example 1. Figure 3 is a graph showing the relationship between the number of cycles and capacity retention rate in the batteries of Example 1 and Comparative Example 1. A high capacity retention rate indicates that the battery has excellent cycle characteristics.

[0096] As shown in Table 1, Figure 2, Table 2 and Figure 3, Li4Ti5O 12 The discharge capacity and capacity retention rate of the battery in Example 1, which used a non-aqueous electrolyte containing particles, were higher than those of the battery in Comparative Example 1.

[0097] The technology disclosed herein is useful, for example, in lithium-ion secondary batteries.

Claims

1. A non-aqueous electrolyte comprising a non-aqueous solvent, an electrolyte dissolved in the non-aqueous solvent, and inorganic particles dispersed in the non-aqueous solvent, wherein the inorganic particles include an inorganic material having a spinel-type crystal structure.

2. The non-aqueous electrolyte according to claim 1, wherein the inorganic material contains lithium.

3. The non-aqueous electrolyte according to claim 1, wherein the inorganic particles are lithium ion conductive.

4. The inorganic material has a composition represented by the following composition formula (1), wherein A and B are different metal ions and X is an anion: AB2X4...(1) The non-aqueous electrolyte according to claim 1.

5. The inorganic material has a composition represented by the following composition formula (2), where M is at least one selected from the group consisting of Co, Ni, Mn, V, and Ti, and x, y, and z are mutually independent natural numbers satisfying x < y < z, Li x M y O z ... (2) The non-aqueous electrolyte according to claim 1.

6. The non-aqueous electrolyte according to claim 5, wherein M is Ti.

7. The non-aqueous electrolyte according to claim 1, wherein the inorganic material contains lithium titanium oxide.

8. The lithium titanium oxide is Li4Ti5O 12 The non-aqueous electrolyte according to claim 7, having the composition represented by [formula].

9. The non-aqueous electrolyte according to claim 1, wherein the inorganic particles are insoluble in the non-aqueous solvent.

10. The non-aqueous electrolyte according to claim 1, wherein the content of the inorganic particles in the non-aqueous electrolyte is 0.1% by volume or more and 10% by volume or less.

11. The non-aqueous electrolyte according to claim 1, wherein the average particle diameter of the inorganic particles is 1 nm or more and 500 nm or less.

12. A non-aqueous electrolyte secondary battery comprising the non-aqueous electrolyte according to claim 1.

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