Nonaqueous electrolyte for nonaqueous-electrolyte cell, and nonaqueous-electrolyte cell

Abstract

The disclosed nonaqueous electrolyte is a nonaqueous electrolyte for a nonaqueous-electrolyte cell. Said nonaqueous electrolyte includes a nonaqueous solvent, an electrolyte salt, and an additive. Said additive contains two electron-withdrawing groups R having the same structure. Each electron-withdrawing group R contains at least one element selected from the group consisting of oxygen, nitrogen, and sulfur.

Description

Nonaqueous electrolyte for nonaqueous electrolyte battery and nonaqueous electrolyte battery

[0001] The present disclosure relates to a nonaqueous electrolyte for a nonaqueous electrolyte battery and a nonaqueous electrolyte battery.

[0002] A nonaqueous electrolyte battery, such as a lithium-ion secondary battery, includes a positive electrode, a negative electrode, and a nonaqueous electrolyte. Metallic foreign matter such as copper or iron may be present in the positive electrode of a nonaqueous electrolyte battery. In such cases, the metallic foreign matter may dissolve and deposit on the negative electrode during charging and discharging of the battery. The deposition of metallic foreign matter on the negative electrode can lead to a decrease in battery characteristics (e.g., voltage).

[0003] Patent Document 1 (Japanese Patent No. 5935228) discloses "a lithium ion secondary battery including an electrolyte solution, the electrolyte solution including a lithium salt, an electrolyte solvent, and methanethiol, the methanethiol being included in an amount of 1 to 10 parts by weight relative to 100 parts by weight of the electrolyte solution, the methanethiol reacting with copper ions generated during operation of the battery to prevent the formation of dendrites due to the reduction of copper on the surface of the negative electrode."

[0004] Patent No. 5935228

[0005] Currently, there is a need for a new additive that can suppress the dissolution and precipitation of metallic foreign matter. In this situation, one of the objects of the present disclosure is to provide a nonaqueous electrolyte that can suppress the deterioration of the characteristics of nonaqueous electrolyte batteries due to the dissolution and precipitation of metallic foreign matter.

[0006] One aspect of the present disclosure relates to a nonaqueous electrolyte for a nonaqueous electrolyte battery, the nonaqueous electrolyte comprising a nonaqueous solvent, an electrolyte salt, and an additive, the additive containing two electron-withdrawing groups R having the same structure, and the electron-withdrawing group R containing at least one element selected from the group consisting of oxygen, nitrogen, and sulfur.

[0007] Another aspect of the present disclosure relates to a nonaqueous electrolyte battery, which includes a positive electrode including a positive electrode active material, a negative electrode facing the positive electrode, and the nonaqueous electrolyte according to the present disclosure.

[0008] According to the present disclosure, it is possible to suppress the deterioration of the characteristics of non-aqueous electrolyte batteries due to the dissolution and precipitation of metallic foreign matter. The novel features of the present invention are set forth in the appended claims, but the present invention, both in terms of structure and content, together with other objects and features of the present invention, will be better understood from the following detailed description taken in conjunction with the drawings.

[0009] Fig. 1 is a partially cutaway perspective view schematically illustrating a non-electrolytic battery according to an embodiment of the present disclosure. Fig. 2A shows the structures of three additives (A) used in the examples. Fig. 2B shows the structures of three additives (A) used in the examples. Fig. 3 shows the structures of four compounds used in comparative examples.

[0010] The following describes embodiments of the present disclosure using examples, but the present disclosure is not limited to the examples described below. In the following description, specific numerical values ​​and materials may be exemplified, but other numerical values ​​and other materials may be applied as long as the invention of the present disclosure can be implemented. In this specification, the expression "numerical value A to numerical value B" includes numerical value A and numerical value B and can be read as "greater than or equal to numerical value A and less than or equal to numerical value B." In the following description, when lower and upper limits for specific physical properties or conditions are exemplified, any of the exemplified lower limits and any of the exemplified upper limits can be arbitrarily combined, as long as the lower limit is not greater than or equal to the upper limit. In the following description, the expression "comprising A" can include "an embodiment substantially consisting of A" and "an embodiment consisting of A."

[0011] (Nonaqueous Electrolyte) The nonaqueous electrolyte according to this embodiment is a nonaqueous electrolyte for a nonaqueous electrolyte battery. The nonaqueous electrolyte includes a nonaqueous solvent, an electrolyte salt, and an additive. Hereinafter, the additive may be referred to as "additive (A)." The additive (A) contains two electron-withdrawing groups R having the same structure. The electron-withdrawing groups R contain at least one element selected from the group consisting of oxygen, nitrogen, and sulfur. The additive (A) contains only two electron-withdrawing groups R having the same structure. In other words, the additive (A) does not contain three or more electron-withdrawing groups R having the same structure. It is particularly preferable that the electron-withdrawing group R contains a nitrogen atom.

[0012] When metal foreign matter contaminated in a battery is exposed to the positive electrode potential, metal ions may be dissolved from the metal foreign matter into the non-aqueous electrolyte. These metal ions dissolved into the non-aqueous electrolyte migrate from the positive electrode side to the negative electrode side and precipitate on the negative electrode side. As this dissolution-precipitation reaction progresses, the precipitated metal grows into a dendrite-like structure, resulting in a decrease in the characteristics (e.g., voltage) of the non-aqueous electrolyte battery. Therefore, it is important to suppress the deterioration of characteristics due to the dissolution and precipitation of metal foreign matter in non-aqueous electrolyte batteries.

[0013] As a result of investigating various additives, the present inventors have newly discovered that the use of the additive (A) can significantly suppress deterioration of properties due to dissolution and precipitation of metals. The present disclosure is based on this new finding.

[0014] The reason why the use of additive (A) produces such a remarkable effect is currently unknown. However, it can be considered as follows. Additive (A) captures metal ions (e.g., copper ions) in the non-aqueous electrolyte with its electron-withdrawing group R, suppressing the reduction and precipitation reaction of the metal ions at the negative electrode. In this case, it is thought that the electron-withdrawing group R not only captures metal ions but also coordinates to the surface of the positive electrode active material. As a result, it is thought that the dissolution and precipitation of metal foreign matter and the like are significantly suppressed.

[0015] The content of additive (A) in the non-aqueous electrolyte may be 0.01% by mass or more and 10.0% by mass or less. The content may be 0.01% by mass or more, 0.1% by mass or more, 0.5% by mass or more, 1.0% by mass or more, 2.0% by mass or more, or 5.0% by mass or more, and may be 10.0% by mass or less, 5.0% by mass or less, 2.0% by mass or less, 1.0% by mass or less, 0.5% by mass or less, or 0.1% by mass or less. The content may be in the range of 0.01 to 10.0% by mass, 0.1 to 10.0% by mass, 0.5 to 10.0% by mass, 1.0 to 10.0% by mass, 2.0 to 10.0% by mass, or 5.0 to 10.0% by mass. Within these ranges, the upper limit may be 5.0 mass%, 2.0 mass%, 1.0 mass%, 0.5 mass%, or 0.1 mass%, as long as the lower limit is not equal to or greater than the upper limit. By setting the content in the range of 0.1 to 5.0 mass% (e.g., 1.0 to 5.0 mass%), particularly high effects can be obtained. By setting the content to 5.0 mass% or less, the adverse effects of the addition of additive (A) on the charge / discharge characteristics of the battery can be mitigated.

[0016] The non-aqueous electrolyte may contain only one type of compound as the additive (A), or may contain multiple types of compounds.

[0017] The electron-withdrawing group R may be any one selected from the group consisting of a nitrile group (-C≡N), a cyanate group (-O-C≡N), a thiocyanate group (-S-C≡N), an isocyanate group (-N=C=O), and an isothiocyanate group (-N=C=S). The additive (A) may contain, as the electron-withdrawing group, only any one selected from the group consisting of a nitrile group, a cyanate group, a thiocyanate group, an isocyanate group, and an isothiocyanate group. If the additive (A) containing a thiocyanate group is considered to be a type of additive (A) containing a nitrile group, the electron-withdrawing group R may be any one selected from the group consisting of a nitrile group, a cyanate group, an isocyanate group, and an isothiocyanate group. The electron-withdrawing group R may contain at least one element selected from the group consisting of oxygen and nitrogen, and may also contain nitrogen.

[0018] In one aspect, the additive (A) may be a compound (A') containing two functional groups having the same structure. The functional group is any one selected from the group consisting of a nitrile group, a cyanate group, a thiocyanate group, an isocyanate group, and an isothiocyanate group. That is, the present disclosure discloses a nonaqueous electrolyte containing a nonaqueous solvent, an electrolyte salt, and the compound (A'). The matters described for the additive (A) can also be applied to the compound (A').

[0019] The additive (A) may be a compound that dissolves in the nonaqueous solvent of the nonaqueous electrolyte. The molecular weight of the additive (A) may be in the range of 100 to 300. The number of atoms constituting the chain portion connecting the two electron-withdrawing groups R at the shortest distance may be in the range of 3 to 10 (e.g., in the range of 4 to 9).

[0020] The portion X of the additive (A) other than the electron-withdrawing group R is not particularly limited as long as the above-described effects can be obtained. For example, the portion X may be a saturated hydrocarbon chain or an unsaturated hydrocarbon chain. The portion X may contain an aromatic ring.

[0021] The additive (A) preferably includes at least one selected from the group consisting of N,N-bis(2-cyanoethyl)formamide, 2,2-bis(4-cyanatophenyl)propane, p-xylylene dithiocyanate, 1,6-diisocyanato-2,2,4-trimethylhexane, m-xylylene diisocyanate, and 1,4-diisocyanatobutane, and may be any one selected from this group. These compounds are particularly effective as the additive (A).

[0022] The content of the additive (A) in the non-aqueous electrolyte can be determined, for example, using gas chromatography under the following conditions. Instrument used: GC-2010 Plus, manufactured by Shimadzu Corporation Column: HP-1 (film thickness 1 μm, inner diameter 0.32 mm, length 60 m), manufactured by J&W Corporation Column temperature: heated from 50°C to 90°C at a heating rate of 5°C / min, maintained at 90°C for 15 minutes, then heated from 90°C to 250°C at a heating rate of 10°C / min, and maintained at 250°C for 15 minutes Split ratio: 1 / 50 Linear velocity: 30.0 cm / sec Injection port temperature: 270°C Injection volume: 1 μL Detector: FID 290°C (sens. 10 １ )

[0023] (Non-aqueous electrolyte battery) The non-aqueous electrolyte battery according to this embodiment includes a positive electrode containing a positive electrode active material, a negative electrode facing the positive electrode, and a non-aqueous electrolyte. The non-aqueous electrolyte is the non-aqueous electrolyte according to this embodiment. The non-aqueous electrolyte battery may include other components. For example, the non-aqueous electrolyte battery typically further includes a separator and an exterior body. The separator is disposed between the positive electrode and the negative electrode. The exterior body houses the non-aqueous electrolyte and an electrode group including the positive electrode, the negative electrode, and the separator. There are no particular limitations on the positive electrode, the negative electrode, the separator, and the exterior body, and known materials may be used.

[0024] The configuration of the nonaqueous electrolyte battery is not particularly limited as long as the effects of the present disclosure can be obtained. Examples of nonaqueous electrolyte batteries include nonaqueous electrolyte secondary batteries and nonaqueous electrolyte primary batteries. Examples of nonaqueous electrolyte secondary batteries include lithium ion secondary batteries. Examples of nonaqueous electrolyte primary batteries include metal lithium primary batteries. There is no limitation on the shape of the nonaqueous electrolyte battery, and it may be cylindrical or rectangular. There is no limitation on the form of the electrode group of the nonaqueous electrolyte battery, and it may be wound or stacked.

[0025] The positive electrode active material may contain a lithium transition metal composite oxide having a layered rock salt structure, the lithium transition metal composite oxide containing Ni and at least one element selected from the group consisting of Co, Mn, and Al, and the proportion of Ni to the elements other than Li and oxygen (O) contained in the lithium transition metal composite oxide may be 80 atomic % or more.

[0026] Examples of components of the nonaqueous electrolyte and nonaqueous electrolyte battery of this embodiment are described below. However, the components of this embodiment are not limited to the following examples. Components of the nonaqueous electrolyte battery other than the nonaqueous electrolyte are not limited to the following examples, and known components may be used. The following mainly describes the case where the nonaqueous electrolyte battery is a lithium ion secondary battery, but components of a nonaqueous electrolyte battery other than a lithium ion secondary battery may be selected according to the battery.

[0027] (Non-aqueous electrolyte) As described above, the non-aqueous electrolyte includes a non-aqueous solvent, an electrolyte salt, and an additive (A). The additive (A) is the additive described above. Examples of the non-aqueous solvent and the electrolyte salt are described below.

[0028] (Non-aqueous Solvent) Examples of non-aqueous solvents include cyclic carbonates, chain carbonates, cyclic carboxylic acid esters, and chain carboxylic acid esters. Examples of cyclic carbonates include propylene carbonate (PC) and ethylene carbonate (EC). Examples of chain carbonates include diethyl carbonate (DEC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC). Examples of cyclic carboxylic acid esters include γ-butyrolactone (GBL) and γ-valerolactone (GVL). Examples of chain carboxylic acid esters include methyl formate, ethyl formate, propyl formate, methyl acetate (MA), ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, and propyl propionate. The non-aqueous electrolyte may contain only one non-aqueous solvent, or may contain two or more non-aqueous solvents.

[0029] (Electrolyte Salt) As the electrolyte salt, a lithium salt is suitable. Examples of the lithium salt include LiClO ４ , LiBF ４ , LiPF ６ , LiAlCl ４ , LiSbF ６ , LiSCN, LiCF ３ SO ３ , LiCF ３ CO２ , LiAsF ６ , LiB １０ Cl １０ Examples of the lithium salts include lithium carboxylates, lower aliphatic carboxylates, LiCl, LiBr, LiI, borates, and imide salts. Examples of the borates include lithium difluorooxalate borate and lithium bis(oxalate) borate. Examples of the imide salts include lithium bisfluorosulfonylimide (LiN(FSO ２ ) ２ ), lithium bistrifluoromethanesulfonyl imide (LiN(CF ３ SO ２ ) ２ The non-aqueous electrolyte may contain only one type of electrolyte salt, or may contain two or more types of electrolyte salts.

[0030] The concentration of the electrolyte salt in the nonaqueous electrolyte is, for example, 0.5 mol / L or more and 2 mol / L or less.

[0031] The non-aqueous electrolyte may contain other additives, such as at least one selected from the group consisting of vinylene carbonate, fluoroethylene carbonate, and vinylethylene carbonate.

[0032] (Positive Electrode) The positive electrode includes a positive electrode active material. The positive electrode typically includes a positive electrode current collector and a layer of positive electrode mixture (hereinafter referred to as a "positive electrode mixture layer") held on the positive electrode current collector. In one example of a method for forming the positive electrode mixture layer, first, the components of the positive electrode mixture are dispersed in a dispersion medium to prepare a positive electrode slurry. Next, the positive electrode slurry is applied to the surface of the positive electrode current collector to form a coating film, and the coating film is then dried to form the positive electrode mixture layer. The dried coating film may be rolled as necessary. The positive electrode mixture includes a positive electrode active material as an essential component, and may include a binder, a thickener, and the like as optional components.

[0033] (Positive Electrode Active Material) The positive electrode active material is not particularly limited as long as it can be used as a positive electrode active material for a nonaqueous electrolyte battery (e.g., a lithium ion secondary battery). A preferred positive electrode active material is, for example, a lithium transition metal composite oxide having a layered rock salt structure and containing Ni and at least one element selected from the group consisting of Co, Mn, and Al.

[0034] Here, from the viewpoint of obtaining a high capacity, it is desirable that the proportion Rni of Ni in the elements other than Li and oxygen contained in the lithium transition metal composite oxide is 80 atomic % or more. The proportion Rni may be 85 atomic % or more, or may be 90 atomic % or more. The proportion Rni is desirably 95 atomic % or less. When limiting the range, these lower and upper limits can be combined arbitrarily.

[0035] Hereinafter, a lithium transition metal composite oxide that satisfies the following conditions (1) to (3) may be referred to as a "composite oxide HN." (1) The composite oxide HN has a layered rock salt structure. (2) The composite oxide HN contains Ni and at least one element selected from the group consisting of Co, Mn, and Al. (3) In the composite oxide HN, the proportion Rni of Ni in the elements other than Li and oxygen is 80 atomic % or more.

[0036] The layered rock-salt structure of the composite oxide HN allows for reversible insertion and desorption of Li ions between the layers. The higher the Ni content, the more lithium ions can be extracted from the composite oxide HN during charging, thereby increasing the capacity.

[0037] Co, Mn, and Al contribute to stabilizing the crystal structure of the composite oxide HN having a high Ni content. However, from the viewpoint of reducing production costs, a low Co content is preferable. The composite oxide HN having a low Co content or no Co may contain Mn and Al.

[0038] In the composite oxide HN, the ratio Rco of Co to elements other than Li and oxygen is preferably 10 atomic % or less, more preferably 5 atomic % or less, and the composite oxide HN may not contain Co. From the viewpoint of stabilizing the crystal structure of the composite oxide HN, the ratio Rco of Co may be 1 atomic % or more, or 1.5 atomic % or more.

[0039] In the composite oxide HN, the ratio R of Mn to elements other than Li and oxygen may be 10 atomic % or less, or 5 atomic % or less, and may be 1 atomic % or more, 3 atomic % or more, or 5 atomic % or more.

[0040] In the composite oxide HN, the ratio Ral of Al to elements other than Li and oxygen may be 10 atomic % or less, or 5 atomic % or less. The ratio Ral of Al may be 1 atomic % or more, 3 atomic % or more, or 5 atomic % or more.

[0041] The composite oxide HN may be, for example, a compound represented by the formula: Li α Ni(1-x1-x2-yz)Co ｘ１ Mn ｘ２ Al ｙ M ｚ O ２＋β The element M is an element other than Li, Ni, Co, Mn, Al, and oxygen.

[0042] In the above formula, α, which indicates the atomic ratio of lithium, is, for example, 0.95≦α≦1.05. However, α increases or decreases with charge and discharge. In (2+β), which indicates the atomic ratio of oxygen, β satisfies −0.05≦β≦0.05.

[0043] The atomic ratio of Ni, 1-x1-x2-y-z (=v), is 0.8 or more, and may be 0.85 or more, 0.90 or more, or 0.95 or more. The atomic ratio of Ni, v, may be 0.98 or less, or 0.95 or less.

[0044] The x1, which indicates the atomic ratio of Co, is, for example, 0.1 or less (0≦x1≦0.1), and may be 0.08 or less, 0.05 or less, or 0.01 or less. When x1 is 0, this includes cases where Co is below the detection limit.

[0045] The atomic ratio x2 of Mn is, for example, 0.1 or less (0≦x2≦0.1), and may be 0.08 or less, 0.05 or less, or 0.03 or less. x2 may be 0.01 or more, or 0.03 or more. Mn contributes to stabilizing the crystal structure of the composite oxide HN. Furthermore, the inclusion of inexpensive Mn in the composite oxide HN is advantageous for cost reduction.

[0046] The atomic ratio y of Al is, for example, 0.1 or less (0≦y≦0.1), and may be 0.08 or less, 0.05 or less, or 0.03 or less. y may be 0.01 or more, or 0.03 or more. Al contributes to stabilizing the crystal structure of the composite oxide HN.

[0047] The value z representing the atomic ratio of the element M satisfies, for example, 0≦z≦0.10, and may also satisfy 0<z≦0.05 or 0.001≦z≦0.01. The lower and upper limits of these ranges can be combined in any manner.

[0048] The element M may be at least one selected from the group consisting of Ti, Zr, Nb, Mo, W, Fe, Zn, B, Si, Mg, Ca, Sr, Sc, and Y. When at least one selected from the group consisting of Nb, Sr, and Ca is contained in the composite oxide HN, it is thought that the surface structure of the composite oxide HN is stabilized, the resistance is reduced, and metal elution is further suppressed. It is more effective if the element M is unevenly distributed in the vicinity of the particle surface of the composite oxide HN.

[0049] The content of elements constituting the composite oxide HN can be measured using an inductively coupled plasma atomic emission spectroscopy (ICP-AES), an electron probe microanalyzer (EPMA), or an energy dispersive X-ray spectroscopy (EDX).

[0050] The composite oxide HN may be a secondary particle formed by agglomeration of a plurality of primary particles. The particle size of the primary particles may be 0.05 μm or more and 1 μm or less. The average particle size of the secondary particles of the composite oxide HN may be 3 μm or more and 30 μm or less, or 5 μm or more and 25 μm or less.

[0051] In this specification, the average particle size of secondary particles refers to the particle size (volume average particle size) at which the volume cumulative value is 50% in the particle size distribution measured by a laser diffraction scattering method. Such a particle size is sometimes referred to as D50. For example, an "LA-750" manufactured by Horiba Ltd. can be used as a measuring device.

[0052] The positive electrode active material may contain a lithium transition metal composite oxide other than the composite oxide HN, but preferably contains a large proportion of the composite oxide HN. The proportion of the composite oxide HN in the positive electrode active material is, for example, 90% by mass or more, or may be 95% by mass or more, or may be 100%.

[0053] (Others) As the binder, for example, a resin material is used. Examples of the binder include fluororesin, polyolefin resin, polyamide resin, polyimide resin, acrylic resin, vinyl resin, and rubber-like material (for example, styrene butadiene copolymer (SBR)). One type of binder may be used alone, or two or more types may be used in combination.

[0054] Examples of thickeners include cellulose derivatives such as cellulose ether. Examples of cellulose derivatives include carboxymethyl cellulose (CMC) and its modified forms, methyl cellulose, etc. One type of thickener may be used alone, or two or more types may be used in combination.

[0055] Examples of conductive materials include carbon nanotubes (CNTs), carbon fibers other than CNTs, and conductive particles (for example, carbon black and graphite).

[0056] The dispersion medium used in the positive electrode slurry is not particularly limited, but examples thereof include water, alcohol, N-methyl-2-pyrrolidone (NMP), and mixed solvents thereof.

[0057] The positive electrode current collector may be, for example, a metal foil. The positive electrode current collector may be porous. Examples of porous current collectors include nets, punched sheets, and expanded metals. Examples of materials for the positive electrode current collector include stainless steel, aluminum, aluminum alloys, and titanium. The thickness of the positive electrode current collector is not particularly limited and may be in the range of 1 to 50 μm (for example, in the range of 5 to 30 μm).

[0058] (Negative Electrode) The negative electrode contains a negative electrode active material. The negative electrode usually includes a negative electrode current collector and a layer of negative electrode mixture (hereinafter referred to as a negative electrode mixture layer) held on the negative electrode current collector. The negative electrode mixture layer can be formed by applying a negative electrode slurry, in which the components of the negative electrode mixture are dispersed in a dispersion medium, to the surface of the negative electrode current collector and drying the slurry. The dried coating may be rolled if necessary.

[0059] The negative electrode mixture contains a negative electrode active material as an essential component, and may contain a binder, a thickener, a conductive agent, and the like as optional components.

[0060] (Negative electrode active material) As the negative electrode active material, metallic lithium, lithium alloys, etc. may be used, but materials capable of electrochemically absorbing and releasing lithium ions are preferably used. Examples of such materials include carbonaceous materials and Si-containing materials. The negative electrode may contain one type of negative electrode active material or a combination of two or more types.

[0061] Examples of carbonaceous materials include graphite, easily graphitizable carbon (soft carbon), and hardly graphitizable carbon (hard carbon). One type of carbonaceous material may be used alone, or two or more types may be used in combination. Graphite is preferred as the carbonaceous material because it has excellent charge / discharge stability and a small irreversible capacity. Examples of graphite include natural graphite, artificial graphite, and graphitized mesophase carbon particles.

[0062] Examples of the Si-containing material include simple Si, silicon alloys, silicon compounds (such as silicon oxides), and composite materials in which a silicon phase is dispersed in a lithium ion conductive phase (matrix). Examples of silicon oxides include SiO ｘ The x may be, for example, 0.5≦x<2, or 0.8≦x≦1.6. The lithium ion conductive phase may be SiO ２ At least one selected from the group consisting of a silicate phase and a carbon phase may be used.

[0063] As the binder, thickener, conductive agent, and dispersion medium used in the negative electrode slurry, for example, the materials exemplified for the positive electrode may be used.

[0064] The negative electrode current collector may be, for example, a metal foil. The negative electrode current collector may be porous. Examples of the material for the negative electrode current collector include stainless steel, nickel, nickel alloy, copper, and copper alloy. The thickness of the negative electrode current collector is not particularly limited and may be in the range of 1 to 50 μm (for example, in the range of 5 to 30 μm).

[0065] (Separator) A separator is preferably disposed between the positive electrode and the negative electrode. The separator preferably has high ion permeability and adequate mechanical strength and insulating properties. The separator may be made of a microporous thin film, a woven fabric, a nonwoven fabric, or the like. The separator may be made of polyolefin (polypropylene, polyethylene, etc.), or other materials.

[0066] An example of the structure of a nonaqueous electrolyte battery is a structure in which an electrode group formed by winding a positive electrode and a negative electrode with a separator interposed therebetween is housed in an outer casing together with a nonaqueous electrolyte. However, this is not limited thereto, and other forms of electrode groups may also be applied. For example, a stacked electrode group in which a positive electrode and a negative electrode are stacked with a separator interposed therebetween may also be used. The shape of the nonaqueous electrolyte battery is also not limited, and may be, for example, a cylindrical type, a prismatic type, a coin type, a button type, a laminate type, or the like. The nonaqueous electrolyte battery may be a primary battery or a secondary battery.

[0067] As an example of a nonaqueous electrolyte battery according to the present disclosure, the structure of a prismatic nonaqueous electrolyte secondary battery will be described with reference to FIG.

[0068] The nonaqueous electrolyte battery shown in FIG. 1 includes a bottomed prismatic battery case 4, an electrode group 1, and a nonaqueous electrolyte (not shown) housed within the battery case 4. The electrode group 1 includes a long strip-shaped negative electrode, a long strip-shaped positive electrode, and a separator disposed therebetween. The negative electrode current collector is electrically connected to a negative electrode terminal 6 provided on a sealing plate 5 via a negative electrode lead 3. The negative electrode terminal 6 is insulated from the sealing plate 5 by a resin gasket 7. The positive electrode current collector is electrically connected to the back surface of the sealing plate 5 via a positive electrode lead 2. That is, the positive electrode is electrically connected to the battery case 4, which also serves as the positive electrode terminal. The periphery of the sealing plate 5 fits into the open edge of the battery case 4, and the fitting is laser-welded. The sealing plate 5 has an injection hole for the nonaqueous electrolyte. The injection hole is closed with a seal plug 8 after the nonaqueous electrolyte is injected. The nonaqueous electrolyte according to this embodiment is used as the nonaqueous electrolyte.

[0069] (Additional Notes) The above description discloses the following technologies. (Technology 1) A nonaqueous electrolyte for a nonaqueous electrolyte battery, comprising: a nonaqueous solvent; an electrolyte salt; and an additive, wherein the additive contains two electron-withdrawing groups R having the same structure, and the electron-withdrawing group R contains at least one element selected from the group consisting of oxygen, nitrogen, and sulfur. (Technology 2) The nonaqueous electrolyte according to Technology 1, wherein the content of the additive is 0.01 mass% or more and 10.0 mass% or less. (Technology 3) The nonaqueous electrolyte according to Technology 1 or 2, wherein the electron-withdrawing group R is any one selected from the group consisting of a nitrile group, a cyanate group, a thiocyanate group, an isocyanate group, and an isothiocyanate group. (Technology 4) The nonaqueous electrolyte according to Technology 1 or 2, wherein the additive comprises at least one selected from the group consisting of N,N-bis(2-cyanoethyl)formamide, 2,2-bis(4-cyanatophenyl)propane, p-xylylene dithiocyanate, 1,6-diisocyanato-2,2,4-trimethylhexane, m-xylylene diisocyanate, and 1,4-diisocyanatobutane. (Technology 5) A nonaqueous electrolyte battery comprising: a positive electrode containing a positive electrode active material; a negative electrode facing the positive electrode; and the nonaqueous electrolyte according to any one of Technology 1 to 4. (Technology 6) The nonaqueous electrolyte battery according to Technology 5, wherein the positive electrode active material contains a lithium transition metal composite oxide having a layered rock salt structure and containing Ni and at least one element selected from the group consisting of Co, Mn, and Al, and a proportion of Ni to elements other than Li and oxygen contained in the lithium transition metal composite oxide is 80 atomic % or more.

[0070] The present disclosure will be specifically described below based on examples, but the present disclosure is not limited to the following examples.

[0071] (Batteries A1 to A30) Non-aqueous electrolyte secondary batteries were fabricated and evaluated according to the following procedure. (1) Fabrication of Positive Electrode Positive electrode active material particles (LiNi ０．８８ Co ０．０９ Al ０．０３ O ２100 parts by mass of carbon nanotubes, 1 part by mass of polyvinylidene fluoride, and an appropriate amount of N-methyl-2-pyrrolidone (NMP) were mixed to prepare a positive electrode slurry. Next, the positive electrode slurry was applied to one side of an aluminum foil to form a coating film. Next, the coating film was dried and then rolled. In this way, the aluminum foil and the positive electrode mixture layer (thickness: 95 μm, density: 3.6 g / cm ) formed on the aluminum foil were mixed. ３ ) and a positive electrode containing the same.

[0072] (2) Preparation of Negative Electrode 98 parts by mass of negative electrode active material (graphite), 1 part by mass of sodium salt of carboxymethyl cellulose (CMC-Na), 1 part by mass of styrene-butadiene copolymer (SBR), and an appropriate amount of water were mixed to prepare a negative electrode slurry. Next, the negative electrode slurry was applied to one side of copper foil, which serves as a negative electrode current collector, to form a coating film. Next, the coating film was dried and then rolled. In this way, a negative electrode including copper foil and a negative electrode mixture layer formed on the copper foil was obtained.

[0073] (3) Preparation of non-aqueous electrolyte (electrolytic solution) LiPF was dissolved in a mixed solvent of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) (EC:EMC = 3:7 (volume ratio)). ６ , and additive (A) were dissolved in the electrolyte (non-aqueous electrolyte) to prepare an electrolyte solution (nonaqueous electrolyte). ６ The concentration of the additive (A) was 1.0 mol / L. The compounds shown in Table 1 were used as the additive (A). The content (concentration) of the additive (A) in the electrolytic solution was the value shown in Table 1.

[0074] (4) Fabrication of a Non-Aqueous Electrolyte Secondary Battery The positive electrode was cut into a predetermined shape. Next, a portion of the positive electrode mixture layer was scraped off to expose the positive electrode current collector, forming a connection area with the positive electrode lead. In this way, a positive electrode including a region functioning as a positive electrode (size: 20 mm × 20 mm) and a connection area with the positive electrode lead was obtained. Spherical copper particles (diameter: approximately 100 μm) were intentionally embedded near the center of the positive electrode mixture layer. Next, the exposed portion of the positive electrode current collector was connected to the positive electrode lead. Next, a predetermined region on the periphery of the positive electrode lead was covered with an insulating tab film. In this way, a positive electrode for evaluation was obtained.

[0075] The negative electrode was cut into the same shape as the positive electrode. Next, the same process as the positive electrode was performed to obtain a negative electrode including a region that functions as a negative electrode and a region that is connected to the negative electrode lead. Next, the exposed portion of the negative electrode current collector was connected to the negative electrode lead. Next, a predetermined region on the periphery of the negative electrode lead was covered with an insulating tab film. In this way, a negative electrode for evaluation was obtained.

[0076] A battery was fabricated using the evaluation positive and negative electrodes. First, an electrode group was obtained by arranging the positive and negative electrodes with a separator between them so that the positive electrode mixture layer and the negative electrode mixture layer faced each other. A polyethylene separator (thickness: 12 μm) was used as the separator. Next, a rectangular (size: 60 mm × 90 mm) Al laminate film (thickness: 100 μm) was cut and folded in half. Next, the 60 mm long edge of the folded laminate film was heat-sealed to form a cylindrical shape measuring 60 mm × 45 mm. The fabricated electrode group was then placed into the cylinder. Next, the end face of the Al laminate film was aligned with the heat-sealed resin of each lead and sealed. Next, nonaqueous electrolyte was injected from the short side of the Al laminate film that was not heat-sealed, impregnating each mixture layer with the nonaqueous electrolyte. Finally, the end face of the Al laminate film on the injected side was sealed. In this manner, evaluation batteries A1 to A30 using an exterior body made of an Al laminate film were obtained.

[0077] (Battery C1) Comparative Battery C1 was fabricated in the same manner and under the same conditions as those for Battery A1, except that the electrolyte solution (non-aqueous electrolyte) was changed. The electrolyte solution for Battery C1 was prepared in the same manner and under the same conditions as those for Battery A1, except that the additive (A) was not added.

[0078] (Batteries C2 to C9) Comparative batteries C2 to C9 were fabricated in the same manner and under the same conditions as battery A1, except that the electrolyte solution (nonaqueous electrolyte) was changed. The electrolyte solutions for batteries C2 to C9 were prepared in the same manner and under the same conditions as battery A1, except that the compounds shown in Table 1 were used in the amounts shown in Table 1 instead of additive (A).

[0079] (5) Evaluation of Self-Discharge Rate A reference battery R1 was prepared for reference. The configuration of the reference battery R1 was the same as that of battery A1, except that no metallic copper balls were embedded in the positive electrode and no additive (A) was added to the non-aqueous electrolyte. The resulting reference battery R1 was charged at a constant current of 0.05 C in a temperature environment of 25°C until the battery voltage reached 4.2 V. Here, 1 C is the 1-hour rate current, which is the current value that can use up the entire battery capacity in 1 hour. The battery was then discharged at a constant current of 0.05 C until the battery voltage reached 2.5 V, and a charge / discharge curve was obtained. Between charges and discharges, the battery was left standing in an open circuit state for 20 minutes.

[0080] The fabricated evaluation battery A1 was clamped between a pair of stainless steel clamps (thickness: 2 mm) and fixed at a pressure of 0.2 MPa. Next, three hours after fabrication of battery A1, battery A1 was charged at a constant current of 0.05 C in a temperature environment of 25 ° C until the battery voltage reached 4.2 V. Next, battery A1 was discharged at a constant current of 0.05 C until the battery voltage reached 2.5 V. Next, battery A1 was charged until the battery voltage reached 3.58 V. Battery A1 was then left undisturbed in a 25 ° C environment. Then, the battery voltage V after 48 hours of being left undisturbed in a 25 ° C environment was measured. １ and the battery voltage V after 72 hours ２ was measured.

[0081] Battery voltage V １ and V ２ From the charge / discharge curve of the reference battery R1, the state of charge SOC after 48 hours １ (%) and state of charge SOC after 72 hours ２ (%) was calculated based on the charge / discharge curve of the reference battery R1. Next, the self-discharge rate sd per day was calculated based on the following formula. A low self-discharge rate sd indicates a small deterioration in battery characteristics. Self-discharge rate sd (%) = SOC １ (%)-SOC ２ (%)

[0082] The self-discharge rates (sd) of the other evaluation batteries were determined in the same manner as for Battery A1. Table 1 shows some of the manufacturing conditions for each battery and the evaluation results of the self-discharge rates (sd). Table 1 also shows the cascode numbers of the compounds used as additives.

[0083]

[0084] Batteries A1 to A30 are nonaqueous electrolyte batteries according to the present disclosure. Batteries C1 to C9 are comparative examples. The structures of the three compounds used as additive (A) in batteries A1 to A15 are shown in FIG. 2A. The structures of the three compounds used as additive (A) in batteries A16 to A30 are shown in FIG. 2B. The structures of the four compounds added in batteries C2 to C9 are shown in FIG. 3.

[0085] As shown in Table 1, the batteries A1 to A30 containing the additive (A) had lower self-discharge rates (sd) than the comparative batteries C1 to C9. This is thought to be because the additive (A) trapped dissolved copper ions.

[0086] The present disclosure is applicable to non-aqueous electrolytes and non-aqueous electrolyte batteries. Although the present invention has been described with reference to presently preferred embodiments, such disclosure should not be construed as limiting. Various modifications and variations will no doubt become apparent to those skilled in the art to which the present invention pertains upon reading the above disclosure. Therefore, the appended claims should be construed to cover all modifications and variations that do not depart from the true spirit and scope of the present invention.

[0087] 1: electrode group, 2: positive electrode lead, 3: negative electrode lead, 4: battery case, 5: sealing plate, 6: negative electrode terminal, 7: gasket, 8: sealing plug

Claims

1. A non-aqueous electrolyte for a non-aqueous electrolyte battery, a non-aqueous solvent; Electrolyte salt; an additive, The additive includes at least one selected from the group consisting of N,N-bis(2-cyanoethyl)formamide and p-xylylenedithiocyanate. Non-aqueous electrolyte for non-aqueous electrolyte batteries.

2. The content of the additive is 0.01% by mass or more and 10.0% by mass or less. The non-aqueous electrolyte according to claim 1 .

3. a positive electrode including a positive electrode active material; a negative electrode facing the positive electrode; A nonaqueous electrolyte battery comprising the nonaqueous electrolyte according to claim 1 or 2.

4. the positive electrode active material contains a lithium transition metal composite oxide having a layered rock salt structure, the lithium transition metal composite oxide containing Ni and at least one element selected from the group consisting of Co, Mn, and Al; The proportion of Ni in the elements other than Li and oxygen contained in the lithium transition metal composite oxide is 80 atomic % or more. The nonaqueous electrolyte battery according to claim 3 .