Nonaqueous electrolyte for nonaqueous electrolyte battery, and nonaqueous electrolyte battery

Abstract

The wastewater electrolyte of the present disclosure is a non-aqueous electrolyte for a non-aqueous electrolyte battery. The nonaqueous electrolyte contains a nonaqueous solvent, an electrolyte salt, and an additive. The additive contains two electron withdrawing groups R, and the two electron withdrawing groups R have the same structure. And the electron withdrawing group R contains at least one element selected from oxygen, nitrogen and sulfur.

Description

Technical Field

[0001] This disclosure relates to non-aqueous electrolyte and non-aqueous electrolyte batteries for use in non-aqueous electrolyte batteries. Background Technology

[0002] Non-aqueous electrolyte batteries, such as lithium-ion rechargeable batteries, have a positive electrode, a negative electrode, and a non-aqueous electrolyte. Sometimes, metallic foreign matter such as copper or iron is mixed into the positive electrode of a non-aqueous electrolyte battery. In this case, the metallic foreign matter may dissolve during battery charging and discharging, precipitating on the negative electrode. If the metallic foreign matter precipitates on the negative electrode, the battery's characteristics (such as voltage) are prone to deterioration.

[0003] Patent document 1 (Japanese Patent No. 5935228) discloses a lithium-ion secondary battery containing an electrolyte, characterized in that the electrolyte contains a lithium salt, an electrolyte solvent, and methanethiol, and the methanethiol contains 1 to 10 parts by weight relative to 100 parts by weight of the electrolyte, wherein the methanethiol reacts with copper ions generated during battery operation, thereby preventing dendrites from forming on the negative electrode surface due to copper reduction.

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent No. 5935228 Summary of the Invention

[0007] The problem that the invention aims to solve

[0008] There is a current need for novel additives capable of suppressing the dissolution and precipitation of metallic foreign matter. In this context, one objective of the present invention is to provide a non-aqueous electrolyte capable of suppressing the degradation of non-aqueous electrolyte battery characteristics caused by the dissolution and precipitation of metallic foreign matter.

[0009] Methods for solving problems

[0010] One aspect of this disclosure relates to a non-aqueous electrolyte for use in non-aqueous electrolyte batteries. The non-aqueous electrolyte comprises a non-aqueous solvent, an electrolyte salt, and an additive, said additive containing two electron-withdrawing groups R having the same structure as each other, said electron-withdrawing groups R containing at least one element selected from oxygen, nitrogen, and sulfur.

[0011] Another aspect of this disclosure relates to a non-aqueous electrolyte battery. This non-aqueous electrolyte battery includes a positive electrode containing a positive electrode active material, a negative electrode opposite the positive electrode, and the non-aqueous electrolyte of this disclosure.

[0012] Invention Effects

[0013] According to this disclosure, it is possible to suppress the reduction in the characteristics of non-aqueous electrolyte batteries caused by the dissolution and precipitation of metallic foreign matter.

[0014] Although novel features of the invention are described in the appended claims, the following detailed description, taken with reference to the accompanying drawings, is intended to better understand both the composition and content of the invention in conjunction with other objects and features of the invention. Attached Figure Description

[0015] Figure 1 This is a schematic perspective view of a non-electrolyte battery according to one embodiment of the present disclosure.

[0016] Figure 2A The structures of the three additives (A) used in the examples are shown.

[0017] Figure 2B The structures of the three additives (A) used in the examples are shown.

[0018] Figure 3 The structures of the four compounds used in the comparative examples are shown. Detailed Implementation

[0019] The following examples illustrate embodiments related to this disclosure, but this disclosure is not limited to the examples described below. In the following description, specific numerical values ​​or materials are sometimes illustrated, but other numerical values ​​or materials can be applied as long as the invention related to this disclosure can be implemented. In this specification, the phrase "numerical value A to numerical value B" includes both numerical value A and numerical value B, and can be interpreted as "numerical value A or higher and numerical value B or lower." In the following description, when lower and upper limits of numerical values ​​related to specific physical properties or conditions are illustrated, any combination of any illustrated lower limit and any illustrated upper limit can be made as long as the lower limit is not above the upper limit. In the following description, the phrase "containing A" includes "a form substantially composed of A" and "a form composed of A."

[0020] (Non-aqueous electrolyte)

[0021] The non-aqueous electrolyte of this embodiment is a non-aqueous electrolyte for use in non-aqueous electrolyte batteries. This non-aqueous electrolyte contains a non-aqueous solvent, an electrolyte salt, and an additive. Hereinafter, this additive is sometimes referred to as "additive (A)". Additive (A) contains two electron-withdrawing groups R having the same structure. The electron-withdrawing groups R contain at least one element selected from oxygen, nitrogen, and sulfur. Additive (A) contains only two electron-withdrawing groups R having the same structure as each other. In other words, additive (A) does not contain three or more electron-withdrawing groups R having the same structure as each other. Furthermore, the electron-withdrawing groups R particularly preferably contain nitrogen atoms.

[0022] When a metallic foreign object mixed into a battery is exposed to the positive electrode potential, metal ions may sometimes dissolve from the foreign object into the non-aqueous electrolyte. These dissolved metal ions migrate from the positive electrode side to the negative electrode side and precipitate on the negative electrode side. When such a dissolution and precipitation reaction occurs, the precipitated metal grows in a dendritic pattern, reducing the characteristics (e.g., voltage) of the non-aqueous electrolyte battery. Therefore, in non-aqueous electrolyte batteries, it is important to suppress the reduction in characteristics caused by the dissolution and precipitation of metallic foreign objects.

[0023] Various additives were studied, and the inventors of this application have made a new discovery: by using the above-mentioned additive (A), the degradation of properties caused by the dissolution and precipitation of metals can be significantly suppressed. This disclosure is based on this new discovery.

[0024] The reason why additive (A) achieves a significant effect is currently unclear. However, it can be considered as follows: Additive (A) captures metal ions (e.g., copper ions) in the non-aqueous electrolyte through its electron-withdrawing group R, inhibiting the reduction and precipitation reaction of metal ions in the negative electrode. It is thought that, in this case, the electron-withdrawing group R can not only capture metal ions but also coordinate on the surface of the positive electrode active material. It can be assumed that the result is a significant inhibition of the dissolution and precipitation of metal foreign matter, etc.

[0025] The content of additive (A) in the non-aqueous electrolyte can be 0.01% by mass or more and 10.0% by mass or less. This content can 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, or it can be less than 10.0% by mass, less than 5.0% by mass, less than 2.0% by mass, less than 1.0% by mass, less than 0.5% by mass, or less than 0.1% by mass. This content can also be in the range of 0.01–10.0% by mass, 0.1–10.0% by mass, 0.5–10.0% by mass, 1.0–10.0% by mass, 2.0–10.0% by mass, or 5.0–10.0% by mass. Within these ranges, as long as the lower limit is not above the upper limit, the upper limit can also be 5.0% by mass, 2.0% by mass, 1.0% by mass, 0.5% by mass, or 0.1% by mass. By keeping the content in the range of 0.1 to 5.0% by mass (e.g., 1.0 to 5.0% by mass), particularly high effects can be obtained. By keeping the content below 5.0% by mass, the adverse effects of additive (A) on the charge and discharge characteristics of the battery can be mitigated.

[0026] Non-aqueous electrolytes may contain only one compound as an additive (A), or they may contain multiple compounds.

[0027] The electron-withdrawing group R can be selected from any one of nitrile (-C≡N), cyanate (-OC≡N), thiocyanate (-SC≡N), isocyanate (-N=C=O), and isothiocyanate (-N=C=S). Additive (A), as an electron-withdrawing group, can contain only any one of nitrile, cyanate, thiocyanate, isocyanate, and isothiocyanate groups. Furthermore, considering that additive (A) containing a thiocyanate group is an additive (A) containing a nitrile group, the electron-withdrawing group R can also be selected from any one of nitrile, cyanate, isocyanate, and isothiocyanate groups. The electron-withdrawing group R can contain at least one element selected from oxygen and nitrogen, or it can contain nitrogen.

[0028] In one viewpoint, additive (A) can be a compound (A') containing two functional groups having the same structure as each other. The functional group is selected from nitrile, cyanate, thiocyanate, isocyanate, and isothiocyanate groups. That is, this disclosure discloses a non-aqueous electrolyte containing a non-aqueous solvent, an electrolyte salt, and compound (A'). The descriptions regarding additive (A) also apply to compound (A').

[0029] Additive (A) can be a compound soluble in a non-aqueous solvent of a non-aqueous electrolyte. The molecular weight of additive (A) can be in the range of 100 to 300. The number of atoms constituting the shortest chain segment connecting the two electron-withdrawing groups R can be in the range of 3 to 10 (e.g., 4 to 9).

[0030] Regarding the portion X in additive (A) other than the electron-withdrawing group R, there are no particular limitations as long as the aforementioned effects can be achieved. For example, this portion X can be a saturated hydrocarbon chain or an unsaturated hydrocarbon chain. This portion X may also contain an aromatic ring.

[0031] Additive (A) preferably contains at least one selected from N,N-bis(2-cyanoethyl)formamide, 2,2-bis(4-cyanopropylphenyl)propane, terephthalamide dithiocyanate, 1,6-diisocyanate-2,2,4-trimethylhexane, isophthalamide diisocyanate, and 1,4-diisocyanate butane, and may be any one of these groups. These compounds, as additive (A), can achieve particularly high efficacy.

[0032] The content of additive (A) in the non-aqueous electrolyte can be determined, for example, by gas chromatography under the following conditions.

[0033] Machine used: GC-2010 Plus, manufactured by Shimadzu Corporation.

[0034] Chromatographic column: J&W, HP-1 (1μm film thickness, 0.32mm inner diameter, 60m length)

[0035] Column temperature: Increase the temperature from 50℃ to 90℃ at a rate of 5℃ / min, hold at 90℃ for 15 minutes, then increase the temperature from 90℃ to 250℃ at a rate of 10℃ / min, and hold at 250℃ for 15 minutes.

[0036] Flow split ratio: 1 / 50

[0037] Linear velocity: 30.0 cm / sec

[0038] Inlet temperature: 270℃

[0039] Injection volume: 1μL

[0040] Detector: FID 290℃ (sens.10) 1 )

[0041] (Non-aqueous electrolyte battery)

[0042] The non-aqueous electrolyte battery of this embodiment includes a positive electrode containing a positive electrode active material, a negative electrode opposite to the positive electrode, and a non-aqueous electrolyte. This non-aqueous electrolyte is the non-aqueous electrolyte of this embodiment. The non-aqueous electrolyte battery may also include other components. For example, a non-aqueous electrolyte battery typically also includes a separator and an outer casing. The separator is disposed between the positive and negative electrodes. The outer casing houses the electrode assembly containing the positive electrode, negative electrode, separator, and non-aqueous electrolyte. There are no particular limitations on the positive electrode, negative electrode, separator, and outer casing; known materials can also be used.

[0043] Regarding the configuration of non-aqueous electrolyte batteries, there are no particular limitations as long as the effects of this disclosure are achieved. Examples of non-aqueous electrolyte batteries include non-aqueous electrolyte secondary batteries and non-aqueous electrolyte primary batteries. Examples of non-aqueous electrolyte secondary batteries include lithium-ion secondary batteries. Examples of non-aqueous electrolyte primary batteries include lithium metal primary batteries. There are no limitations on the shape of non-aqueous electrolyte batteries; they can be cylindrical or square. There are no limitations on the shape of the electrode assembly of non-aqueous electrolyte batteries; they can be wound or stacked.

[0044] The positive electrode active material is a lithium transition metal composite oxide with a layered rock salt structure, or it may contain a lithium transition metal composite oxide containing at least one element selected from Co, Mn, and Al, and Ni. In this lithium transition metal composite oxide, the proportion of Ni among the elements other than Li and oxygen (O) can be 80 atomic% or more.

[0045] The following describes examples of the constituent elements of a non-aqueous electrolyte and a non-aqueous electrolyte battery according to this embodiment. However, the constituent elements of this embodiment are not limited to the examples below. The constituent elements other than the non-aqueous electrolyte in a non-aqueous electrolyte battery are not limited to the examples below, and known constituent elements may also be used. The following description mainly focuses on the case where the non-aqueous electrolyte battery is a lithium-ion secondary battery; however, for other non-aqueous electrolyte batteries besides lithium-ion secondary batteries, the constituent elements corresponding to that battery can be selected.

[0046] (Non-aqueous electrolyte)

[0047] As described above, the non-aqueous electrolyte contains a non-aqueous solvent, an electrolyte salt, and an additive (A). Additive (A) is the additive described above. Examples of the non-aqueous solvent and the electrolyte salt are described below.

[0048] (Non-aqueous solvent)

[0049] 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. Non-aqueous electrolytes may contain only one non-aqueous solvent or two or more non-aqueous solvents.

[0050] (electrolyte salts)

[0051] Lithium salts are preferred as electrolyte salts. Examples of lithium salts include LiClO4, LiBF4, LiPF6, LiAlCl4, LiSbF6, LiSCN, LiCF3SO3, LiCF3CO2, LiAsF6, and LiB. 10 Cl 10 Examples of non-aqueous electrolytes include lower aliphatic carboxylic acids such as lithium, LiCl, LiBr, LiI, borates, and imide salts. Examples of borates include lithium difluorooxalate borate and lithium bis(oxalate borate). Examples of imide salts include lithium bis(fluorosulfonyl)imide (LiN(FSO2)2) and lithium bis(trifluoromethanesulfonyl)imide (LiN(CF3SO2)2). Non-aqueous electrolytes may contain only one electrolyte salt or two or more electrolyte salts.

[0052] The concentration of electrolyte salts in non-aqueous electrolytes is, for example, 0.5 mol / L or more and 2 mol / L or less.

[0053] Non-aqueous electrolytes may contain other additives. Examples of other additives include at least one selected from vinylene carbonate, fluoroethylene carbonate, and vinyl ethylene carbonate.

[0054] (positive electrode)

[0055] The positive electrode contains a positive electrode active material. The positive electrode typically contains a positive electrode current collector and a layered positive electrode additive (hereinafter referred to as the "positive electrode additive layer") held on the positive electrode current collector. In one example of a method for forming the positive electrode additive layer, firstly, a positive electrode slurry is prepared by dispersing the constituent components of the positive electrode additive in a dispersion medium. Next, the positive electrode slurry can be coated onto the surface of the positive electrode current collector to form a coating film, and then the coating film is dried to form the positive electrode additive layer. The dried coating film can also be rolled as needed. The positive electrode active material is an essential component of the positive electrode additive, and binders, thickeners, etc., may be included as optional components.

[0056] (Positive electrode active material)

[0057] The positive electrode active material is any material that can be used as the positive electrode active material in non-aqueous electrolyte batteries (such as lithium-ion secondary batteries), and there are no particular limitations. Preferred positive electrode active materials include, for example, lithium transition metal composite oxides having a layered rock salt-type structure and containing at least one element selected from Co, Mn, and Al and Ni.

[0058] From the viewpoint of obtaining high capacity, it is preferable that the proportion of Ni (Rni) in the lithium transition metal composite oxide, excluding Li and oxygen, is 80 atomic% or more. This proportion Rni can be 85 atomic% or more, or 90 atomic% or more. Preferably, this proportion Rni is 95 atomic% or less. Within the defined range, these lower and upper limits can be combined arbitrarily.

[0059] Hereinafter, lithium transition metal composite oxides that meet the following conditions (1) to (3) are sometimes referred to as "composite oxides HN".

[0060] (1) The composite oxide HN has a layered rock salt-type structure.

[0061] (2) The composite oxide HN contains at least one selected from Co, Mn and Al and Ni.

[0062] (3) In the composite oxide HN, Ni accounts for more than 80 atomic% of the elements other than Li and oxygen.

[0063] Between the layers of the layered rock-salt structure of the composite oxide HN, Li ions can reversibly insert and detach. The higher the Ni ratio, the more lithium ions can be extracted from the composite oxide HN during charging, thus increasing the capacity.

[0064] Co, Mn, and Al help stabilize the crystal structure of composite oxide HN with a high Ni content. However, from the viewpoint of reducing manufacturing costs, a low Co content is preferred. Composite oxide HN with low or no Co content can contain Mn and Al.

[0065] In the composite oxide HN, the proportion of Co (Rco) among elements other than Li and oxygen is preferably 10 atomic% or less, more preferably 5 atomic% or less, and may also be free of Co. From the viewpoint of stabilizing the crystal structure of the composite oxide HN, the proportion of Co (Rco) can be 1 atomic% or more or 1.5 atomic% or more.

[0066] In the composite oxide HN, the proportion of Mn among elements other than Li and oxygen, Rmn, can be less than 10 atomic% or less than 5 atomic%. The proportion of Mn, Rmn, can be more than 1 atomic%, more than 3 atomic%, or more than 5 atomic%.

[0067] In the composite oxide HN, the proportion of Al (Ral) among elements other than Li and oxygen can be less than 10 atomic% or less than 5 atomic%. The proportion of Al (Ral) can be more than 1 atomic%, more than 3 atomic%, or more than 5 atomic%.

[0068] Composite oxides HN, for example, are derived from the formula: Li α Ni (1-x1-x2-y-z) Co x1 Mn x2 Al y M z O 2+β It indicates that element M is any element other than Li, Ni, Co, Mn, Al, and oxygen.

[0069] In the above formula, α, representing the atomic ratio of lithium, satisfies, for example, 0.95 ≤ α ≤ 1.05. However, α can increase or decrease due to charging and discharging. In (2+β), representing the atomic ratio of oxygen, β satisfies: -0.05 ≤ β ≤ 0.05.

[0070] The atomic ratio of Ni, 1-x1-x2-yz (=v), is 0.8 or more, or it can be 0.85 or more, 0.90 or more, or 0.95 or more. Alternatively, the atomic ratio of Ni, v, can be 0.98 or less, or 0.95 or less.

[0071] The atomic ratio of Co, x1, is for example 0.1 or less (0 ≤ x1 ≤ 0.1), or it can be 0.08 or less, 0.05 or less, or 0.01 or less. When x1 is 0, it includes cases where Co is less than the detection limit.

[0072] The atomic ratio of Mn, x2, is for example 0.1 or less (0 ≤ x2 ≤ 0.1), or it can be 0.08 or less, 0.05 or less, or 0.03 or less. x2 can be greater than 0.01 or greater than 0.03. Mn contributes to the stabilization of the crystal structure of the composite oxide HN. Furthermore, the inclusion of inexpensive Mn in the composite oxide HN helps to reduce costs.

[0073] The atomic ratio y of Al can be, for example, less than 0.1 (0 ≤ y ≤ 0.1), or less than 0.08, 0.05, or 0.03. y can be greater than 0.01 or greater than 0.03. Al contributes to the stabilization of the crystal structure of the composite oxide HN.

[0074] z represents the atomic ratio of element M, and can satisfy, for example, 0 ≤ z ≤ 0.10, 0 < z ≤ 0.05, or 0.001 ≤ z ≤ 0.01. The lower and upper limits of these ranges can be combined arbitrarily.

[0075] Element M can be at least one selected from Ti, Zr, Nb, Mo, W, Fe, Zn, B, Si, Mg, Ca, Sr, Sc, and Y. When the composite oxide HN contains at least one selected from Nb, Sr, and Ca, the surface structure of the composite oxide HN is considered to be stabilized, the electrical resistance is reduced, and the dissolution of the metal is further suppressed. The effect is even better when element M is predominantly present near the particle surface of the composite oxide HN.

[0076] The content of elements constituting the composite oxide HN can be determined using inductively coupled plasma atomic emission spectroscopy (ICP-AES), electron probe microanalyzer (EPMA), or energy dispersive X-ray spectroscopy (EDX).

[0077] The composite oxide HN can be a secondary particle formed by the aggregation of multiple primary particles. The particle size of the primary particles can be greater than 0.05 μm and less than 1 μm. The average particle size of the secondary particles of the composite oxide HN can also be greater than 3 μm and less than 30 μm, or greater than 5 μm and less than 25 μm.

[0078] In this specification, the average particle size of secondary particles refers to the particle size at which the cumulative volume of the particle size distribution measured by laser diffraction scattering is 50% (volume average particle size). Such a particle size is sometimes referred to as D50. The measuring device can be, for example, the "LA-750" manufactured by Horiba Corporation.

[0079] The positive electrode active material may contain lithium transition metal composite oxides other than composite oxides (HN), with a higher proportion of composite oxides (HN) preferred. The proportion of composite oxides (HN) in the positive electrode active material may be, for example, 90% by mass or more, 95% by mass or more, or 100%.

[0080] (other)

[0081] Resin materials are used as adhesives. Examples of adhesives include fluoropolymers, polyolefin resins, polyamide resins, polyimide resins, acrylic resins, vinyl resins, and rubber-like materials (such as styrene-butadiene copolymer (SBR)). One type of adhesive may be used alone, or two or more may be used in combination.

[0082] Examples of thickeners include cellulose derivatives such as cellulose ethers. Examples of cellulose derivatives include carboxymethyl cellulose (CMC) and its modified forms, methyl cellulose, etc. Thickeners can be used alone or in combination of two or more.

[0083] Examples of conductive materials include carbon nanotubes (CNTs), carbon fibers other than CNTs, and conductive particles (e.g., carbon black, graphite).

[0084] There are no particular limitations on the dispersion medium used in positive electrode slurries; examples include water, alcohols, N-methyl-2-pyrrolidone (NMP), and mixed solvents thereof.

[0085] Metal foil can be used as the positive current collector, for example. The positive current collector can also be porous. Examples of porous current collectors include mesh, perforated sheets, and expanded metal mesh. Materials used for the positive current collector include stainless steel, aluminum, aluminum alloys, and titanium. There is no particular limitation on the thickness of the positive current collector; it can be in the range of 1–50 μm (e.g., 5–30 μm).

[0086] (negative electrode)

[0087] The negative electrode contains a negative electrode active material. The negative electrode typically has a negative electrode current collector and a layered negative electrode additive (hereinafter referred to as the negative electrode additive layer) held on the negative electrode current collector. The negative electrode additive layer can be formed by coating a negative electrode slurry, consisting of the components of the negative electrode additive dispersed in a dispersion medium, onto the surface of the negative electrode current collector and allowing it to dry. Alternatively, the dried coating can be rolled out as needed.

[0088] Negative electrode mixtures contain negative electrode active substances as essential components, and can also contain binders, thickeners, conductive agents, etc. as optional components.

[0089] (Negative electrode active material)

[0090] As the negative electrode active material, metallic lithium, lithium alloys, etc., can be used, but materials capable of electrochemically absorbing and releasing lithium ions are preferred. Examples of such materials include carbon materials and silicon-containing materials. The negative electrode can contain one type of negative electrode active material, or it can contain two or more types in combination.

[0091] Examples of carbon materials include graphite, easily graphitized carbon (soft carbon), and difficult-to-graphitize carbon (hard carbon). A single carbon material can be used, or two or more can be used in combination. Graphite is preferred as a carbon material due to its excellent charge-discharge stability and low irreversible capacity. Examples of graphite include natural graphite, artificial graphite, and graphitized mesophase carbon particles.

[0092] Examples of silicon-containing materials include elemental Si, silicon alloys, silicon compounds (silicon oxides, etc.), and composite materials in which a silicon phase is dispersed within a lithium-ion conducting phase (matrix). Examples of silicon oxides include SiOx particles. x is, for example, 0.5 ≤ x < 2, or 0.8 ≤ x ≤ 1.6. As the lithium-ion conducting phase, at least one selected from the SiO2 phase, silicate phase, and carbon phase can be used.

[0093] As a dispersion medium used in binders, thickeners, conductive agents and negative electrode slurries, materials such as those exemplified in the positive electrode can also be used.

[0094] Metal foil can be used as the negative current collector, for example. The negative current collector can also be porous. Examples of materials used as the negative current collector include stainless steel, nickel, nickel alloys, copper, and copper alloys. There is no particular limitation on the thickness of the negative current collector, which is in the range of 1 to 50 μm (e.g., 5 to 30 μm).

[0095] (Septum)

[0096] Preferably, a separator is disposed between the positive and negative electrodes. The separator is preferably a membrane with high ion permeability, appropriate mechanical strength, and insulation properties. Microporous membranes, woven fabrics, non-woven fabrics, etc., can be used as the separator. Polyolefins (polypropylene, polyethylene, etc.) or other materials can be used as the separator material.

[0097] As an example of a non-aqueous electrolyte battery structure, one can exemplify a structure in which an electrode assembly consisting of a positive and negative electrode separated by a separator is packaged together with a non-aqueous electrolyte within an outer casing. However, this is not a limitation; other electrode assembly forms can also be used. For example, a stacked electrode assembly consisting of positive and negative electrodes separated by a separator can also be used. The shape of the non-aqueous electrolyte battery is also not limited; for example, it can be cylindrical, square, coin-shaped, button-shaped, laminated, etc. A non-aqueous electrolyte battery can be a primary battery or a secondary battery.

[0098] As an example of the non-aqueous electrolyte battery involved in this disclosure, refer to Figure 1 This will illustrate the structure of a square non-aqueous electrolyte secondary battery.

[0099] Figure 1 The non-aqueous electrolyte battery shown includes a square-bottomed battery casing 4, an electrode assembly 1 housed within the battery casing 4, and a non-aqueous electrolyte (not shown). The electrode assembly 1 includes a long strip-shaped negative electrode, a long strip-shaped positive electrode, and a separator disposed between them. The negative electrode current collector is electrically connected to a negative terminal 6 provided on a sealing plate 5 via a negative electrode lead 3. The negative terminal 6 is insulated from the sealing plate 5 by a resin sealing ring 7. The positive electrode current collector is electrically connected to the back side of the sealing plate 5 via a positive electrode lead 2. That is, the positive electrode is electrically connected to the battery casing 4, which also serves as the positive terminal. The periphery of the sealing plate 5 fits into the open end of the battery casing 4, and the fitting portion is laser-welded. The sealing plate 5 has an injection hole for the non-aqueous electrolyte. The injection hole is plugged by a cap 8 after the non-aqueous electrolyte is injected. The non-aqueous electrolyte of this embodiment is used as the non-aqueous electrolyte.

[0100] (Postscript)

[0101] Based on the above record, the following technologies are disclosed.

[0102] (Technology 1)

[0103] A non-aqueous electrolyte for use in non-aqueous electrolyte batteries, comprising a non-aqueous solvent, an electrolyte salt, and additives.

[0104] The additive contains two electron-withdrawing groups R, which have the same structure as each other.

[0105] The electron-withdrawing group R contains at least one element selected from oxygen, nitrogen, and sulfur.

[0106] (Technology 2)

[0107] The non-aqueous electrolyte as described in Technique 1, wherein the additive contains 0.01% by mass or more and 10.0% by mass or less.

[0108] (Technology 3)

[0109] The non-aqueous electrolyte as described in technique 1 or 2, wherein the electron-withdrawing group R is selected from any one of nitrile group, cyanate group, thiocyanate group, isocyanate group and isothiocyanate group.

[0110] (Technology 4)

[0111] The non-aqueous electrolyte as described in technique 1 or 2, wherein the additive contains at least one selected from N,N-bis(2-cyanoethyl)formamide, 2,2-bis(4-cyanopropylphenyl)propane, terephthalamide dithiocyanate, 1,6-diisocyanate-2,2,4-trimethylhexane, isophthalamide diisocyanate, and 1,4-diisocyanate butane.

[0112] (Technology 5)

[0113] A non-aqueous electrolyte battery, comprising:

[0114] Positive electrode containing positive active material,

[0115] The negative electrode opposite to the positive electrode, and

[0116] The non-aqueous electrolyte described in any one of techniques 1 to 4.

[0117] (Technology 6)

[0118] As described in Technique 5, in the non-aqueous electrolyte battery, the positive electrode active material contains a lithium transition metal composite oxide, which has a layered rock-salt structure and contains at least one element selected from Co, Mn, and Al, and Ni.

[0119] The lithium transition metal composite oxide contains Ni accounting for more than 80 atomic percent of the elements other than Li and oxygen.

[0120] Example

[0121] The present disclosure will now be described in detail based on the embodiments, but the present disclosure is not limited to the following embodiments.

[0122] (Batteries A1 to A30)

[0123] Construct and evaluate a non-aqueous electrolyte secondary battery according to the following steps.

[0124] (1) Production of the positive electrode

[0125] 100 parts by mass of positive electrode active material particles (LiNi) 0.88 Co 0.09 Al 0.03 A positive electrode slurry was prepared by mixing 1 part by mass of O2, 1 part by mass of carbon nanotubes, 1 part by mass of polyvinylidene fluoride, and an appropriate amount of N-methyl-2-pyrrolidone (NMP). Next, the positive electrode slurry was coated onto one side of an aluminum foil to form a coating film. The coating film was then dried and rolled. This yielded a positive electrode mixture layer containing aluminum foil and formed on the aluminum foil (thickness: 95 μm, density: 3.6 g / cm³). 3 The positive electrode of ).

[0126] (2) Fabrication of the negative electrode

[0127] A negative electrode slurry is prepared by mixing 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. Next, the negative electrode slurry is coated onto one side of a copper foil, which serves as the negative electrode current collector, to form a coating film. The coating film is then dried and rolled. This yields a negative electrode containing a copper foil and a negative electrode binder layer formed on the copper foil.

[0128] (3) Preparation of non-aqueous electrolytes (electrolytes)

[0129] An electrolyte (non-aqueous electrolyte) was prepared by dissolving LiPF6 and additive (A) in a mixed solvent of ethylene carbonate (EC) and methyl ethyl carbonate (EMC) (EC:EMC = 3:7 (volume ratio)). The concentration of LiPF6 in the electrolyte was 1.0 mol / L. The compounds shown in Table 1 were used as additive (A). The content (concentration) of additive (A) in the electrolyte is shown in Table 1.

[0130] (4) Fabrication of non-aqueous electrolyte secondary batteries

[0131] The positive electrode is cut into a specified shape. Next, a portion of the positive electrode binder layer is scraped away, exposing the positive current collector and forming a region for connection with the positive electrode lead. This yields a positive electrode containing a functional area (20mm x 20mm) and a region for connection with the positive electrode lead. Near the center of the positive electrode binder layer, spherical copper particles (approximately 100μm in diameter) are intentionally embedded. Next, the exposed portion of the positive current collector is connected to the positive electrode lead. Finally, a specified area around the positive electrode lead is covered with an insulating diaphragm. This yields the positive electrode for evaluation.

[0132] The negative electrode is cut into the same shape as the positive electrode. Next, it undergoes the same processing as the positive electrode, resulting in a negative electrode containing a region that functions as the negative electrode and a region connected to the negative electrode lead. Next, the exposed portion of the negative electrode current collector is connected to the negative electrode lead. Next, a predetermined area around the negative electrode lead is covered with an insulating diaphragm. This yields the negative electrode for evaluation.

[0133] Batteries are fabricated using positive and negative electrodes for evaluation. First, an electrode assembly is obtained by arranging the positive and negative electrodes with a separator in place, with the positive and negative electrode binder layers facing each other. A polyethylene separator (thickness: 12 μm) is used. Next, an Al laminate (thickness: 100 μm) cut into a rectangle (size: 60 mm × 90 mm) is folded in half. Then, the 60 mm long side of the folded laminate is heat-sealed to form a cylindrical shape with dimensions of 60 mm × 45 mm. The fabricated electrode assembly is then placed into the cylinder. Next, the end face of the Al laminate is aligned with the position of the heat-bonding resin for each lead and sealed. Next, a non-aqueous electrolyte is injected from the unsealed short side of the Al laminate, impregnating each binder layer. Finally, the end face of the injected Al laminate is sealed. This yields evaluation batteries A1 to A30 with an outer casing made of Al laminate.

[0134] (Battery C1)

[0135] A comparative example battery C1 was manufactured using the same methods and conditions as battery A1, except that the electrolyte (non-aqueous electrolyte) was changed. The electrolyte of battery C1 was prepared using the same methods and conditions as those for battery A1, except that no additive (A) was added.

[0136] (Batteries C2~C9)

[0137] Comparative example batteries C2 to C9 were prepared using the same method and conditions as battery A1, except that the electrolyte (non-aqueous electrolyte) was changed. Regarding the electrolytes of batteries C2 to C9, they were prepared using the same method and conditions as battery A1, except that the compounds shown in Table 1 were used to replace additive (A) at the contents shown in Table 1.

[0138] (5) Evaluation of self-discharge rate

[0139] A reference battery R1 was constructed. The configuration of reference battery R1 was identical to that of battery A1, except that no copper spheres 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 0.05C at 25°C until the battery voltage reached 4.2V. Here, 1C is the 1-hour rate current, which is the current value that can fully utilize the battery capacity in 1 hour. Then, it was discharged at a constant current of 0.05C until the battery voltage reached 2.5V, and the charge-discharge curve was calculated. The battery was left to rest in an open-circuit state for 20 minutes between charging and discharging.

[0140] The evaluation battery A1, fabricated using a pair of stainless steel (2 mm thickness) clamps, was fixed under a pressure of 0.2 MPa. Three hours after fabrication, battery A1 was charged at a constant current of 0.05 C at 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. Then, battery A1 was charged until the battery voltage reached 3.58 V. Battery A1 was then left to stand at 25°C. The battery voltage V1 was then measured after 48 hours and V2 after 72 hours of standing at 25°C.

[0141] Based on battery voltages V1 and V2 and the charge / discharge curves of reference battery R1, the state of charge (SOC) after 48 hours and the state of charge (SOC) after 72 hours are calculated using the charge / discharge curve of reference battery R1. Next, the daily self-discharge rate (sd) is calculated using the following formula. A low self-discharge rate (sd) indicates a smaller deterioration in battery characteristics.

[0142] Self-discharge rate sd (%) = SOC1 (%) - SOC2 (%)

[0143] Similar to battery A1, the self-discharge rate (sd) was also determined for the other evaluation batteries. Table 1 shows a portion of the manufacturing conditions for each battery and the evaluation results for the self-discharge rate (sd). Table 1 also shows the CAS numbers of the compounds used as additives.

[0144]

[0145] Batteries A1 to A30 are non-aqueous electrolyte batteries involved in this disclosure. Batteries C1 to C9 are comparative examples. Figure 2A The structures of three compounds used as additives (A) in batteries A1 to A15 are shown. Figure 2B The structures of three compounds used as additives (A) in batteries A16 to A30 are shown. Figure 3The structure of four compounds added to batteries C2 through C9 is shown in the figure.

[0146] As shown in Table 1, the batteries A1 to A30 with additive (A) have a lower self-discharge rate (sd) compared to the comparative example batteries C1 to C9. This can be attributed to the fact that additive (A) captures dissolved copper ions.

[0147] Industry availability

[0148] This disclosure can be used in non-aqueous electrolyte and non-aqueous electrolyte batteries.

[0149] Although the invention has been described in conjunction with the presently preferred embodiments, such disclosure should not be interpreted as restrictive. Various variations and modifications will become apparent to those skilled in the art upon reading the foregoing disclosure. Therefore, the appended claims should be interpreted as encompassing all modifications and alterations without departing from the true spirit and scope of the invention.

[0150] Explanation of symbols in attached drawings

[0151] 1: Electrode assembly; 2: Positive lead; 3: Negative lead; 4: Battery casing; 5: Sealing plate; 6: Negative terminal; 7: Sealing ring; 8: Cap.

Claims

1. A non-aqueous electrolyte for use in a non-aqueous electrolyte battery, comprising a non-aqueous solvent, an electrolyte salt, and additives. The additive contains two electron-withdrawing groups R, which have the same structure as each other. The electron-withdrawing group R contains at least one element selected from oxygen, nitrogen, and sulfur.

2. The non-aqueous electrolyte as described in claim 1, wherein the content of the additive is 0.01% by mass or more and 10.0% by mass or less.

3. The non-aqueous electrolyte as described in claim 1 or 2, wherein the electron-withdrawing group R is selected from any one of nitrile group, cyanate group, thiocyanate group, isocyanate group and isothiocyanate group.

4. The non-aqueous electrolyte according to claim 1 or 2, wherein the additive contains at least one selected from N,N-bis(2-cyanoethyl)formamide, 2,2-bis(4-cyanopropylphenyl)propane, terephthalamide dithiocyanate, 1,6-diisocyanate-2,2,4-trimethylhexane, isophthalamide diisocyanate, and 1,4-diisocyanate butane.

5. A non-aqueous electrolyte battery, comprising: Positive electrode containing positive active material, The negative electrode opposite to the positive electrode, and The non-aqueous electrolyte according to claim 1 or 2.

6. The non-aqueous electrolyte battery of claim 5, wherein the positive electrode active material contains a lithium transition metal composite oxide, the lithium transition metal composite oxide having a layered rock salt structure and containing at least one element selected from Co, Mn and Al and Ni. The lithium transition metal composite oxide contains Ni accounting for more than 80 atomic percent of the elements other than Li and oxygen.

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