Nonaqueous electrolyte battery and nonaqueous electrolyte used in same

Abstract

The present invention provides a nonaqueous electrolyte for nonaqueous electrolyte batteries, the nonaqueous electrolyte containing a nonaqueous solvent, an electrolyte salt and a thiophene compound that contains oxygen or nitrogen, while having at least one electron-withdrawing group R. With respect to this nonaqueous electrolyte for nonaqueous electrolyte batteries, the content of the thiophene compound is 0.01% by mass to 10% by mass.

Description

Nonaqueous electrolyte battery and nonaqueous electrolyte used therein

[0001] The present disclosure relates primarily to non-aqueous electrolytes for non-aqueous electrolyte batteries.

[0002] A nonaqueous electrolyte battery, such as a lithium-ion secondary battery, includes a positive electrode, a negative electrode, and a nonaqueous electrolyte. If metallic foreign matter such as copper or iron is present in a nonaqueous electrolyte battery that utilizes an electrochemical oxidation-reduction reaction, dissolution and precipitation of the metallic foreign matter may occur, resulting in a decrease in the voltage of the nonaqueous electrolyte battery.

[0003] Patent Document 1 proposes a method in which a compound containing one or more thiol groups in the molecule is provided inside a unit cell of a battery, and the compound containing the thiol group reacts with or captures copper ions generated during operation of the battery, thereby reducing the copper ions on the surface of the negative electrode and preventing the formation of dendrites.

[0004] Patent Document 2 proposes improving the cycle characteristics of a secondary battery using a negative electrode active material containing at least one atom selected from the group consisting of Si, Sn, and Pb by using a nonaqueous electrolyte solution containing an isocyanate compound having at least one aromatic ring in the molecule.

[0005] JP-T-2014-531720A JP-A-2009-87934A

[0006] However, even if the method described in Patent Document 1 is used, the prevention of dissolution and precipitation of metallic foreign matter is insufficient. Further prevention of dissolution and precipitation of metallic foreign matter is desired.

[0007] One aspect of the present disclosure relates to a non-aqueous electrolyte for a non-aqueous electrolyte battery, comprising: a non-aqueous solvent; an electrolyte salt; and a thiophene compound having at least one electron-withdrawing group R containing oxygen or nitrogen, wherein the content of the thiophene compound is 0.01 mass % or more and 10 mass % or less.

[0008] Another aspect of the present disclosure relates to a nonaqueous electrolyte battery including a positive electrode containing a positive electrode active material, a separator, a negative electrode facing the positive electrode with the separator interposed therebetween, and the above-described nonaqueous electrolyte.

[0009] According to the present disclosure, it is possible to suppress a decrease in voltage of a nonaqueous electrolyte battery due to a dissolution and precipitation reaction of metal.

[0010] 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.

[0011] FIG. 1 is a partially cutaway perspective view of a non-electrolytic battery according to an embodiment of the present disclosure.

[0012] Hereinafter, embodiments of the present disclosure will be described using examples, but the present disclosure is not limited to the examples described below. In the following description, specific numerical values, materials, etc. may be exemplified, but other numerical values, materials, etc. may be applied as long as the effects of the present disclosure are obtained. 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 "numerical value A or more and numerical value B or less." In the following description, when lower and upper limits of numerical values ​​related to 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 equal to or greater than the upper limit. When multiple materials are exemplified, one of the materials may be selected and used alone, or two or more of the materials may be used in combination.

[0013] The present disclosure also encompasses combinations of two or more features arbitrarily selected from the appended claims, i.e., two or more features arbitrarily selected from the appended claims can be combined unless a technical contradiction arises.

[0014] The nonaqueous electrolyte for a nonaqueous electrolyte battery according to the present disclosure includes a nonaqueous solvent, an electrolyte salt, and a thiophene compound having at least one electron-withdrawing group R containing oxygen or nitrogen. The content of the thiophene compound relative to the total amount of the nonaqueous electrolyte is 0.01 mass % or more and 10 mass % or less.

[0015] A nonaqueous electrolyte battery according to the present disclosure includes a positive electrode containing a positive electrode active material, a separator, a negative electrode facing the positive electrode with the separator interposed therebetween, and the nonaqueous electrolyte.

[0016] When a metal is exposed to a positive electrode potential, metal ions may dissolve from the metal into the non-aqueous electrolyte. Metal ions may also dissolve from the positive electrode active material. For example, the positive electrode of a non-aqueous electrolyte battery contains a positive electrode active material, which has a high potential and contains a metal component (often a transition metal). 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. If such a dissolution-precipitation reaction proceeds, the voltage of the non-aqueous electrolyte battery decreases. It is important to suppress metal dissolution and deposition in non-aqueous electrolyte batteries.

[0017] According to the present disclosure, by adding a thiophene compound to a non-aqueous electrolyte, metal dissolution and precipitation reactions are significantly suppressed, and a decrease in battery voltage is suppressed.

[0018] The thiophene compound captures metal ions in the non-aqueous electrolyte at the structural site of the thiophene ring, thereby suppressing the reductive deposition reaction of the metal ions at the negative electrode. In addition, the electron-withdrawing group R contained in the thiophene compound has the effect of enhancing the metal ion-capturing function of the thiophene ring, and further, it is thought that the electron-withdrawing group R itself also captures metal ions in the non-aqueous electrolyte and suppresses the reductive deposition reaction of the metal ions at the negative electrode. The enhanced metal ion-capturing function of the thiophene compound, or the thiophene compound having multiple different functional groups capable of capturing metal ions, allows the compound to efficiently capture a large number of metal ions, thereby significantly suppressing the reductive deposition of metal ions.

[0019] Generally, metal ions can exist in a number of different valences in a non-aqueous electrolyte. For example, copper ions exist in a non-aqueous electrolyte as Cu ＋ and Cu ２＋The functional group can exist in two different valences, each with a different electron-accepting property. If there is only one type of functional group capable of forming a coordinate bond with a metal ion, it may be easy to form a coordinate bond with one of the metal ions with different valences (e.g., a monovalent copper ion), but difficult to form a coordinate bond with the other ion (e.g., a divalent copper ion), making it difficult to capture all of the metal ions generated in the battery. In contrast, a compound having two or more different functional groups that easily coordinate depending on the valence of the metal ion can capture metal ions with high efficiency.

[0020] The electron-withdrawing group R contained in the thiophene compound may have coordinate bonding properties with a metal ion. The electron-withdrawing group R contains oxygen or nitrogen. The electron-withdrawing group R may contain both oxygen and nitrogen. Examples of the electron-withdrawing group R include at least one selected from the group consisting of a carbonyl group, a nitrile group, and an isocyanate group. The carbonyl group may be an aldehyde group in which one end of the carbonyl group is bonded to a hydrogen atom, a carboxy group in which one end of the carbonyl group is bonded to a hydroxyl group, or a ketone group. The carboxy group may form an anion or a salt. The carbonyl group, the nitrile group, and the isocyanate group may be bonded to the thiophene ring. That is, the electron-withdrawing group R may be directly bonded to the thiophene ring. The carbonyl group may be an ester carbonyl group. The thiophene compound may further have an alkyl group (e.g., a methyl group, an ethyl group, a cyclopropyl group), an alkenyl group, or the like bonded to the thiophene ring.

[0021] Specific examples of thiophene compounds are shown below. However, the thiophene compounds are not limited to the following. Furthermore, the thiophene compounds may be used alone or in any combination of two or more. The thiophene ring of the thiophene compound may be hydrogenated.

[0022] Examples of thiophene compounds having a carbonyl group include 5-methylthiophene-2-carbaldehyde, 3,5-dimethylthiophene-2-carbaldehyde, 5-cyclopropylthiophene-2-carbaldehyde, and 2-((trimethylsilyl)methyl)tetrahydrothiophene-2-carbaldehyde.

[0023] Examples of thiophene compounds having a nitrile group include 5-ethynylthiophene-2-carbonitrile, 2-(5-methylthiophen-2-yl)propanenitrile, and 4-(2-(5-hexylthiophen-2-yl)vinyl)-1,3,5-triazine-2-carbonitrile.

[0024] Examples of thiophene compounds having an isocyanate group include 2-isocyanato-5-methylthiophene and 2-isocyanato-5-(trifluoromethyl)thiophene.

[0025] Among these exemplified thiophene compounds, 5-methylthiophene-2-carbaldehyde is preferred because of its high compatibility with non-aqueous solvents. The structural formula of 5-methylthiophene-2-carbaldehyde is shown below.

[0026]

[0027] The nonaqueous electrolyte battery of the present disclosure will be described in more detail below, with each component being described in detail below. The nonaqueous electrolyte battery includes, for example, a positive electrode, a negative electrode, a nonaqueous electrolyte, and a separator as described below.

[0028] [Non-aqueous Electrolyte] The non-aqueous electrolyte contains a non-aqueous solvent, an electrolyte salt, and a thiophene compound. The thiophene compound has the electron-withdrawing group R described above.

[0029] The content of the thiophene compound in the nonaqueous electrolyte as a whole is 0.01% by mass or more and 10% by mass or less, so that the effect of suppressing the reductive precipitation of metal ions is sufficiently obtained. In order to obtain a significantly high effect of suppressing the reductive precipitation of metal ions, the content of the thiophene compound in the nonaqueous electrolyte as a whole is preferably 0.1% by mass or more and 5% by mass or less.

[0030] The content of the thiophene compound 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 )

[0031] (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 one type of non-aqueous solvent or a combination of two or more types.

[0032] (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 CO ２ , LiAsF ６ , LiB １０ Cl １０Examples 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 one type of electrolyte salt or a combination of two or more types of electrolyte salts.

[0033] 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.

[0034] 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.

[0035] The non-aqueous electrolyte may also contain an isocyanate compound having an isocyanate group and / or a nitrile compound having two or more nitrile groups as an additive for suppressing the dissolution and precipitation reaction of metal ions. The isocyanate compound is reductively decomposed at the negative electrode to form a film on the surface of the negative electrode active material (e.g., a carbon material such as graphite), thereby suppressing the reductive decomposition of the non-aqueous electrolyte. This can suppress the reductive precipitation reaction of metal ions. Meanwhile, the nitrile compound is oxidized at the positive electrode to form a film on the positive electrode active material. This can suppress the dissolution of metal ions constituting the positive electrode active material into the non-aqueous electrolyte. However, the thiophene compound of the present disclosure is significantly superior to isocyanate compounds and nitrile compounds in terms of suppressing the dissolution and precipitation reaction of metal ions.

[0036] [Positive Electrode] The positive electrode contains a positive electrode active material. The positive electrode usually includes a positive electrode current collector and a layer of positive electrode mixture (hereinafter referred to as "positive electrode mixture layer") held on the positive electrode current collector. The positive electrode mixture layer can be formed by applying a positive electrode slurry, in which the components of the positive electrode mixture are dispersed in a dispersion medium, to the surface of the positive electrode current collector and drying the slurry. The dried coating may be rolled as necessary. The positive electrode mixture contains a positive electrode active material as an essential component and may contain a binder, a thickener, etc. as optional components.

[0037] (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 (particularly 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 selected from the group consisting of Co, Mn, and Al.

[0038] From the viewpoint of obtaining a high capacity, it is desirable that the proportion of Ni in the metal elements other than Li contained in the lithium transition metal composite oxide is 80 atomic % or more. The proportion of Ni in the metal elements other than Li may be 85 atomic % or more, or may be 90 atomic % or more. The proportion of Ni in the metal elements other than Li is desirably, for example, 95 atomic % or less. When limiting the range, these upper and lower limits can be combined arbitrarily.

[0039] Hereinafter, a lithium transition metal composite oxide having a layered rock-salt structure and containing Ni and at least one selected from the group consisting of Co, Mn, and Al, with Ni accounting for 80 atomic % or more of the metal elements other than Li, will also be referred to as a "composite oxide HN." Li ions can be reversibly inserted and extracted between the layers of the layered rock-salt structure of the composite oxide HN. The higher the Ni content, the more lithium ions can be extracted from the composite oxide HN during charging, thereby increasing the capacity.

[0040] 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 lower Co content is preferable. The composite oxide HN having a low Co content or no Co may contain Mn and Al.

[0041] The proportion of Co in the metal elements other than Li 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, it is desirable for the composite oxide HN to contain 1 atomic % or more or 1.5 atomic % or more of Co.

[0042] The ratio of Mn to the metal elements other than Li may be 10 atomic % or less, or 5 atomic % or less. The ratio of Mn to the metal elements other than Li may be 1 atomic % or more, 3 atomic % or more, or 5 atomic % or more. When limiting the range, these upper and lower limits may be combined arbitrarily.

[0043] The proportion of Al in the metal elements other than Li may be 10 atomic % or less, or 5 atomic % or less. The proportion of Al in the metal elements other than Li may be 1 atomic % or more, 3 atomic % or more, or 5 atomic % or more. When limiting the range, these upper and lower limits may be combined arbitrarily.

[0044] 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.

[0045] 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.

[0046] The value 1-x1-x2-y-z (=v), which indicates the atomic ratio of Ni, is 0.8 or more, and may be 0.85 or more, 0.90 or more, or 0.95 or more. Furthermore, the value v, which indicates the atomic ratio of Ni, may be 0.98 or less, or may be 0.95 or less. When limiting the range, these upper and lower limits may be combined arbitrarily.

[0047] 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.

[0048] x2, which indicates the atomic ratio 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, and containing inexpensive Mn in the composite oxide HN is advantageous for cost reduction. When limiting the range, these upper and lower limits may be combined arbitrarily.

[0049] The value y, which indicates the atomic ratio 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. The value y may be 0.01 or more, or 0.03 or more. Al contributes to stabilizing the crystal structure of the composite oxide HN. When limiting the range, these upper and lower limits may be combined arbitrarily.

[0050] The value z representing the atomic ratio of the element M is, for example, 0≦z≦0.10, or may be 0<z≦0.05, or 0.001≦z≦0.01. When limiting the range, these upper and lower limits can be combined arbitrarily.

[0051] 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. In particular, 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.

[0052] The content of the 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).

[0053] The composite oxide HN is, for example, a secondary particle formed by agglomeration of a plurality of primary particles. The particle size of the primary particles is, for example, 0.05 μm or more and 1 μm or less. The average particle size of the secondary particles of the composite oxide HN is, for example, 3 μm or more and 30 μm or less, or may be 5 μm or more and 25 μm or less.

[0054] 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.

[0055] 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%.

[0056] (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.

[0057] 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.

[0058] Examples of conductive materials include carbon nanotubes (CNTs), carbon fibers other than CNTs, and conductive particles (for example, carbon black and graphite).

[0059] 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.

[0060] 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, but may be, for example, 1 to 50 μm, or 5 to 30 μm.

[0061] [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 film may be rolled if necessary.

[0062] 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.

[0063] (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.

[0064] 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. Among these, 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.

[0065] 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.

[0066] As the binder, thickener, conductive agent and dispersion medium used in the negative electrode slurry, for example, the materials exemplified for the positive electrode can be used.

[0067] 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, but may be, for example, 1 to 50 μm, or 5 to 30 μm.

[0068] [Separator] It is desirable to interpose a separator between the positive electrode and the negative electrode. The separator has high ion permeability and adequate mechanical strength and insulating properties. The separator may be made of a microporous thin film, woven fabric, nonwoven fabric, or the like. The separator is preferably made of polyolefin such as polypropylene or polyethylene.

[0069] 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 form of the nonaqueous electrolyte secondary 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.

[0070] Hereinafter, 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.

[0071] The battery includes a bottomed, rectangular battery case 4, and 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 interposed 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. In other words, 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 end of the battery case 4, and the fitting is laser-welded. The sealing plate 5 has an injection hole for the nonaqueous electrolyte, which is closed with a seal plug 8 after injection.

[0072] Hereinafter, the present disclosure will be specifically described based on examples and comparative examples, but the present disclosure is not limited to the following examples.

[0073] Examples 1 to 5 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 NMP were mixed to obtain a positive electrode slurry. Next, the positive electrode slurry was applied to one side of an aluminum foil, the coating was dried, and then rolled to form a positive electrode mixture layer (thickness 95 μm, density 3.6 g / cm ) on both sides of the aluminum foil. ３ ) was formed to obtain a positive electrode.

[0074] (2) Preparation of Negative Electrode 98 parts by mass of the negative electrode active material (graphite), 1 part by mass of carboxymethyl cellulose sodium salt (CMC-Na), 1 part by mass of 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 a copper foil serving as a negative electrode current collector, and the coating was dried and then rolled to form a negative electrode mixture layer on both sides of the copper foil.

[0075] (3) Preparation of non-aqueous electrolyte (electrolyte solution) An electrolyte solution was prepared by dissolving LiPF6 and 5-methylthiophene-2-carbaldehyde as a thiophene compound in a mixed solvent of EC and EMC (EC:EMC = 3:7 (volume ratio)). The concentration of LiPF6 in the electrolyte solution was 1.0 mol / L. The content of the thiophene compound was the mass% shown in Table 1 relative to the total amount of the electrolyte solution.

[0076] (4) Fabrication of a Non-Aqueous Electrolyte Secondary Battery The positive electrode was cut into a predetermined shape to obtain a positive electrode for evaluation. The positive electrode had a 20 mm × 20 mm region to function as a positive electrode and a 5 mm × 5 mm region for connection with the tab lead. The positive electrode mixture layer formed on the connection region was then scraped off to expose the positive electrode current collector. A metallic copper ball with a diameter of approximately 100 μm was intentionally embedded near the center of the positive electrode mixture layer. The exposed portion of the positive electrode current collector was then connected to the positive electrode tab lead, and a predetermined region around the periphery of the positive electrode tab lead was covered with an insulating tab film.

[0077] The negative electrode was cut into the same shape as the positive electrode to obtain a negative electrode for evaluation. The negative electrode mixture layer formed on the connection area formed in the same manner as the positive electrode was peeled off to expose the negative electrode current collector. Thereafter, the exposed portion of the negative electrode current collector was connected to a negative electrode tab lead in the same manner as the positive electrode, and a predetermined area on the periphery of the negative electrode tab lead was covered with an insulating tab film.

[0078] A cell was fabricated using the evaluation positive and negative electrodes. First, the positive and negative electrodes were placed face-to-face with a polyethylene separator (12 μm thick) between them, with the positive electrode mixture layer and the negative electrode mixture layer overlapping, to obtain an electrode assembly. Next, a 60 × 90 mm rectangular Al laminate film (100 μm thick) was cut into a half, and the end of the 60 mm long side was heat-sealed to form a 60 × 45 mm cylindrical shape. The electrode assembly was then placed into the cylinder, and the end face of the Al laminate film was aligned with the heat-sealed resin of each tab lead for sealing. Next, a 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 to obtain evaluation cells A1 to A5 for Examples 1 to 5.

[0079] (5) Evaluation The evaluation cell was clamped between a pair of 80 x 80 cm stainless steel clamps (thickness: 2 mm) and pressurized and fixed at 0.2 MPa.

[0080] A reference cell was also fabricated with the same configuration as evaluation cells A1 to A5, but without metallic copper spheres embedded in the positive electrode and without adding a thiophene compound to the non-aqueous electrolyte. The reference cell 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. It 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. The cell was left in an open circuit for 20 minutes between charges and discharges.

[0081] Each evaluation cell was charged at a constant current of 0.3 C in a temperature environment of 25° C. until the voltage reached 3.58 V, and then charged at a constant voltage of 3.58 V until the current reached 0.02 C. The evaluation cells were then stored in a temperature environment of 25° C., and the battery voltage V １ and the battery voltage V after 72 hours ２ was measured.

[0082] Battery voltage V １ and V ２ From the state of charge SOC after 48 hours １ and the state of charge SOC after 72 hours ２was calculated based on the charge / discharge curve. The self-discharge rate sd per day was calculated and evaluated based on the following formula: Self-discharge rate sd (% / day) = SOC １ (%)-SOC ２ (%)

[0083] Comparative Example 1: 5-methylthiophene-2-carbaldehyde was not added in the preparation of the non-aqueous electrolyte. A non-aqueous electrolyte secondary battery was fabricated in the same manner as in Examples 1 to 5, and an evaluation cell B1 of Comparative Example 1 was obtained. The self-discharge rate (sd) was calculated and evaluated in the same manner as in Examples 1 to 5.

[0084] Comparative Example 2: In the preparation of the non-aqueous electrolyte, 2,4-difluoro-1-isocyanatobenzene was added as an isocyanate compound instead of 5-methylthiophene-2-carbaldehyde to prepare an electrolyte solution. The content of 2,4-difluoro-1-isocyanatobenzene was 1 mass% based on the total amount of the electrolyte solution. The structural formula of 2,4-difluoro-1-isocyanatobenzene is shown below.

[0085]

[0086] A nonaqueous electrolyte secondary battery was fabricated in the same manner as in Examples 1 to 5, to obtain evaluation cell B2 of Comparative Example 2. The self-discharge rate sd was calculated and evaluated in the same manner as in Examples 1 to 5.

[0087] The evaluation results of the self-discharge rate (sd) for the evaluation cells A1 to A5, B1, and B2 are shown in Table 1. Table 1 also shows the type and content of additives that have the effect of suppressing the dissolution and deposition of metal ions in each cell.

[0088]

[0089] Comparing Cells B1 and B2 from Table 1, the self-discharge rate sd of Cell B2 was reduced by adding an isocyanate compound compared to Cell B1, indicating a slight effect of suppressing metal ion deposition. However, the reduction in the self-discharge rate sd was small.

[0090] In contrast, the self-discharge rates (sd) of cells A1 to A5, which contained 0.01 to 10% by mass of a thiophene compound, were lower than those of cell B2, indicating that metal ion deposition was suppressed. In particular, the self-discharge rates (sd) of cells A2 to A4, which contained 0.1 to 5% by mass of a thiophene compound, were significantly lower.

[0091] The nonaqueous electrolyte battery according to the present disclosure is suitable for use as a main power source for mobile communication devices, portable electronic devices, and the like, an in-vehicle power source, but is not limited to these applications.

[0092] While the present invention has been described in terms of presently preferred embodiments, such disclosure is not to be interpreted as limiting. Various changes and modifications will no doubt become apparent to those skilled in the art to which the present invention pertains upon reading the above disclosure. It is therefore intended that the appended claims be interpreted to cover all changes and modifications that do not depart from the true spirit and scope of the invention.

[0093] 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 solvent, an electrolyte salt, and a thiophene compound, and the thiophene compound includes at least one selected from the group consisting of 5-methylthiophene-2-carbaldehyde, 3,5-dimethylthiophene-2-carbaldehyde, 5-cyclopropylthiophene-2-carbaldehyde, 2-((trimethylsilyl)methyl)tetrahydrothiophene-2-carbaldehyde, 5-ethynylthiophene-2-carbonitrile, 2-(5-methylthiophene-2-yl)propanenitrile, 4-(2-(5-hexylthiophene-2-yl)vinyl)-1,3,5-triazine-2-carbonitrile, 2-isocyanato-5-methylthiophene, and 2-isocyanato-5-(trifluoromethyl)thiophene, A non-aqueous electrolyte for a non-aqueous electrolyte battery, wherein the content of the thiophene compound is 0.01% by mass or more and 10% by mass or less.

2. The non-aqueous electrolyte according to Claim 1, wherein the content of the thiophene compound is 0.1% by mass or more and 5% by mass or less.

3. The non-aqueous electrolyte according to Claim 1 or 2, wherein the thiophene compound includes at least 5-methylthiophene-2-carbaldehyde.

4. A positive electrode including a positive electrode active material, a separator, a negative electrode facing the positive electrode via the separator, and the non-aqueous electrolyte according to Claim 1 or 2. A non-aqueous electrolyte battery comprising:

5. The positive electrode active material includes a lithium transition metal composite oxide having a layered rock salt structure and including Ni and at least one selected from the group consisting of Co, Mn, and Al, The non-aqueous electrolyte battery according to Claim 4, wherein the ratio of Ni in the metal elements other than Li contained in the lithium transition metal composite oxide is 80 atomic% or more.