Nonaqueous electrolyte for secondary battery, and secondary battery

Abstract

A nonaqueous electrolyte for a secondary battery, the nonaqueous electrolyte containing a nonaqueous solvent, a salt dissolved in the nonaqueous solvent, and an additive dissolved in the nonaqueous solvent, wherein: the additive contains a 1,4-dioxane compound and a sulfur-containing compound; and the sulfur-containing compound has a SO3 structure and / or a SO4 structure.

Description

Non-aqueous electrolyte for secondary battery and secondary battery CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This disclosure claims the benefit of priority to Japanese Patent Application No. 2023-203136, filed on November 30, 2023, in the Japan Patent Office, the entire contents of which are incorporated herein by reference.

[0002] The present disclosure relates to a non-aqueous electrolyte for a secondary battery and a secondary battery.

[0003] Patent Document 1 describes a non-aqueous electrolyte secondary battery comprising a positive electrode and a negative electrode containing a material capable of reversibly absorbing and releasing lithium, a non-aqueous electrolyte containing a lithium salt, and a separator, wherein the non-aqueous electrolyte contains a cyclic carbonate, a chain carbonate, and 0.1% by volume or more and 7% by volume or less of at least one cyclic ether selected from tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, 1,3-dioxane, 1,4-dioxane, trioxane, and derivatives thereof, and the water content is 0.5 ppm or more and 50 ppm or less and the free acid content is 2 ppm or more and 100 ppm or less in terms of HF, and the lithium salt contained in the non-aqueous electrolyte is LiPF ６ and LiBF ４ The present inventors have proposed a non-aqueous electrolyte secondary battery comprising:

[0004] Patent Document 2 proposes a "non-aqueous electrolyte secondary battery having a positive electrode, a negative electrode and an electrolyte solution, the electrolyte solution containing lithium bis(fluorosulfonyl)imide and 1,4-dioxane."

[0005] Patent Document 3 proposes a "non-aqueous electrolyte solution containing an unsaturated sultone, a non-aqueous solvent, and an electrolyte," in which the unsaturated sultone is a predetermined compound such as 1,3-propene sultone, and the "non-aqueous electrolyte solution in which the amount of unsaturated sultone added is 0.001 to 10 mass % with respect to the total amount of the non-aqueous electrolyte solution."

[0006] Japanese Patent No. 4066465 International Publication No. 2020 / 158169 Japanese Patent No. 4190162

[0007] Patent Document 3 reports that the use of unsaturated sultone significantly suppresses the reductive decomposition of non-aqueous electrolytes during high-temperature storage. On the other hand, when a non-aqueous electrolyte contains a sulfur-containing compound, there is a disadvantage in that corrosion of the battery can rapidly progresses when the secondary battery is overdischarged. It is presumed that sulfate ions or sulfite ions are generated from the sulfur-containing compound in an overdischarged battery, and these ions corrode the battery can.

[0008] One aspect of the present disclosure is a method for producing a liquid crystal display device comprising: a non-aqueous solvent; a salt soluble in the non-aqueous solvent; and an additive soluble in the non-aqueous solvent, wherein the additive comprises a 1,4-dioxane compound and a sulfur-containing compound, and the sulfur-containing compound is SO ３ Structure and SO ４ The present invention relates to a non-aqueous electrolyte for a secondary battery having at least one of the following structures:

[0009] Another aspect of the present disclosure relates to a secondary battery including a positive electrode, a separator, a negative electrode facing the positive electrode with the separator interposed therebetween, a non-aqueous electrolyte, and a battery can accommodating the positive electrode, the separator, the negative electrode, and the non-aqueous electrolyte, wherein the non-aqueous electrolyte is the non-aqueous electrolyte for secondary batteries described above.

[0010] According to the present disclosure, even when the non-aqueous electrolyte contains a sulfur-containing compound, corrosion of the battery can is suppressed when the secondary battery is in an overdischarge state. 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 longitudinal sectional view of a secondary battery according to an embodiment of the present disclosure.

[0012] 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, materials, etc. may be exemplified. However, other numerical values, materials, etc. may be applied as long as the effects of the present disclosure are obtained. Note that components other than those characteristic of the present disclosure may be those of known secondary batteries. In this specification, when a "range of numerical value A to numerical value B" is used, the range includes numerical value A and numerical value B. For example, "A to B mol %" is synonymous with "A mol % or more and B mol % or less." 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 the upper limit. When multiple materials are exemplified, one material may be selected from the materials and used alone, or two or more 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] Non-aqueous electrolyte secondary batteries include lithium ion secondary batteries that use a material that reversibly absorbs and releases at least lithium ions as a negative electrode active material, lithium metal secondary batteries in which lithium metal precipitates at the negative electrode during charging and dissolves during discharging, and solid-state batteries that contain a gel electrolyte.

[0015] The non-aqueous electrolyte secondary battery according to the present disclosure includes a positive electrode, a negative electrode, a non-aqueous electrolyte, and a battery can containing these. A separator is typically disposed between the positive electrode and the negative electrode. The non-aqueous electrolyte typically has lithium ion conductivity.

[0016] In this specification, the "overdischarge characteristics" can be evaluated by the content of components eluted from the battery can in the nonaqueous electrolyte in a battery that has been overdischarged by short-circuiting the positive and negative electrodes. Since the battery can used in the examples of this specification is made of a metal containing iron (Fe), the components eluted from the battery can include Fe.

[0017] The "high temperature cycle characteristics" can be evaluated by the capacity retention rate when the secondary battery is subjected to constant current constant voltage charging (CCCV charging) for a predetermined number of cycles in a 45°C environment.

[0018] [Non-aqueous electrolyte] The non-aqueous electrolyte contains a non-aqueous solvent, a salt, and an additive. The non-aqueous electrolyte containing a non-aqueous solvent may be a liquid electrolyte, or may have limited fluidity using a gelling agent or the like. In the case of lithium ion secondary batteries, lithium metal secondary batteries, etc., a lithium salt is used as the salt. The salt and additive are basically dissolved in the non-aqueous solvent. As long as the effects of the invention are not significantly impaired, a portion of the salt or additive may not dissolve in the non-aqueous solvent but may precipitate or separate. The additive defined by the general formula described below may be a salt. In this case, another salt is dissolved in the non-aqueous solvent as a supporting electrolyte.

[0019] The nonaqueous electrolyte recovered from the secondary battery may contain almost no additives. In this case, oxidation products or reduction products of the additives may be contained in the battery. Even in such cases, the additives usually remain in the nonaqueous electrolyte collected from the secondary battery at levels above the detection limit. Therefore, it is possible to confirm that the nonaqueous electrolyte contains the additives.

[0020] (Additives) In this specification, 1,4-dioxane compounds and sulfur-containing compounds are classified as additives.

[0021] 1,4-dioxane compounds are a general term for compounds that have a 1,4-dioxane skeleton. The 1,4-dioxane skeleton is a six-membered ring composed of four carbon atoms and two oxygen atoms. The 1,4-dioxane skeleton does not contain a ketone group. For example, cyclic carboxylic acid anhydrides are not 1,4-dioxane compounds.

[0022] The 1,4-dioxane compound is 1,4-dioxane (C ４ H ８ O ２) or a 1,4-dioxane derivative. That is, the 1,4-dioxane compound may include at least one selected from the group consisting of 1,4-dioxane and 1,4-dioxane derivatives.

[0023] A 1,4-dioxane derivative is a general term for compounds in which at least one hydrogen atom of 1,4-dioxane is substituted with a substituent. The substituent may be, for example, at least one of a halogen atom, a hydrocarbon group, or an oxyhydrocarbon group. At least one hydrogen atom of the hydrocarbon group that is the substituent of the 1,4-dioxane derivative may be substituted with a halogen atom. Among halogen atoms, a fluorine atom (F) is preferred.

[0024] The 1,4-dioxane compound is represented by the general formula (1):

[0025]

[0026] R1 to R8 are each independently a hydrogen atom or the above-mentioned substituents.

[0027] Sulfur-containing compounds include SO ３ Structure and SO ４ Hereinafter, the SO ３ Structure and SO ４ A compound having at least one of the structures is also referred to as a "sulfur-containing compound (S)". ３ The structure refers to a structure having a sulfur atom and three oxygen atoms directly bonded to the sulfur atom. ４ The structure refers to a structure having a sulfur atom and four oxygen atoms directly bonded to the sulfur atom.

[0028] The sulfur-containing compound (S) may include, for example, at least one selected from the group consisting of a hexavalent sulfur compound and a tetravalent sulfur compound. The hexavalent sulfur compound includes a sulfur atom having a valence of 6. The tetravalent sulfur compound includes a sulfur atom having a valence of 4.

[0029] The hexavalent sulfur compound is represented by the general formula (2):

[0030]

[0031] X1 is a halogen atom, a hydrocarbon group, or an oxyhydrocarbon group, and X2 is a hydrocarbon group, a silyl group, or an alkali metal. X1 and X2 may form a ring. That is, the hexavalent sulfur compound may be a cyclic sulfur compound. At least one hydrogen atom of the hydrocarbon group may be substituted with a halogen atom. Among halogen atoms, a fluorine atom (F) is preferred.

[0032] The tetravalent sulfur compound is represented by the general formula (3):

[0033]

[0034] X3 and X4 each independently represent a hydrocarbon group, a silyl group, or an alkali metal. X3 and X4 may form a ring. That is, the tetravalent sulfur compound may be a cyclic sulfur compound. At least one hydrogen atom of the hydrocarbon group may be substituted with a halogen atom. Among halogen atoms, a fluorine atom (F) is preferred.

[0035] Here, the sulfur-containing compound (S) is a useful additive that has the effect of improving high-temperature cycle characteristics. However, when the non-aqueous electrolyte contains the sulfur-containing compound (S), a phenomenon in which corrosion of the battery can progresses rapidly when the secondary battery enters an overdischarge state is observed. In contrast, the 1,4-dioxane compound has the effect of significantly suppressing corrosion of the battery can that occurs when the sulfur-containing compound (S) is contained in the non-aqueous electrolyte.

[0036] In addition, when the non-aqueous electrolyte does not contain a sulfur-containing compound (S), corrosion of the battery can does not become apparent, and therefore the 1,4-dioxane compound does not exhibit any notable effect of suppressing corrosion of the battery can. ３ The structure is also SO ４ While it has no structure, ２ Lithium bisfluorosulfonylimide (Li(FSO) ２ ) ２ ) does not rapidly accelerate corrosion of the battery can even when the secondary battery is in an over-discharged state. In this case, the 1,4-dioxane compound does not have a notable effect of improving the over-discharge characteristics. ２Although the sulfur-containing compound having the structure also has the effect of improving the high-temperature cycle characteristics, the improving effect of the sulfur-containing compound (S) is more remarkable.

[0037] The above-described effect of improving overdischarge characteristics is a phenomenon observed only in 1,4-dioxane compounds among dioxane compounds. Compounds similar to 1,4-dioxane compounds, such as 1,3-dioxane, which has a six-membered ring structure, do not have the effect of improving overdischarge characteristics. Therefore, the effect of improving overdischarge characteristics is unique to 1,4-dioxane compounds. 1,4-dioxane compounds have been confirmed to have the ability to trap ionic species (sulfate ions, sulfite ions, etc.) derived from sulfur-containing compounds (S) in non-aqueous electrolytes and to form a dense coating primarily composed of oxides and sulfides on the inner surface of the battery can. Such a coating protects the surface of the battery can and is thought to inhibit the reaction between ionic species derived from the sulfur-containing compounds (S) and the battery can.

[0038] In addition, the 1,4-dioxane compound can further improve the high-temperature cycle characteristics. ２ Sulfur-containing compounds (e.g., Li(FSO) ２ ) ２ ) is not obtained. ２ When a sulfur-containing compound having the structure is used in combination with a 1,4-dioxane compound, SO ２ When a sulfur-containing compound having the structure is used alone, the high-temperature cycle characteristics tend to be lowered.

[0039] The further improvement in cycle characteristics is believed to be due to the hybrid coating of the 1,4-dioxane compound and the sulfur-containing compound (S). The formation of a strong hybrid protective coating on both the positive and negative electrodes that does not impede lithium ion permeation is thought to highly suppress side reactions. As a result, the charge transfer resistance of the positive and negative electrodes is reduced, leading to improved high-temperature cycle characteristics.

[0040] The hybrid coating can, for example, inhibit excessive reaction of the transition metal element constituting the positive electrode active material contained in the positive electrode with the nonaqueous electrolyte, thereby suppressing deterioration of the positive electrode active material. In particular, when the positive electrode active material contains a lithium-containing composite oxide containing a high content of Ni, the effect of suppressing deterioration is remarkable.

[0041] Furthermore, the hybrid coating can suppress excessive reaction of the negative electrode active material (e.g., graphite or a silicon-containing material) contained in the negative electrode with the nonaqueous electrolyte, thereby suppressing deterioration of the negative electrode active material. This effect is particularly pronounced when the negative electrode active material contains a silicon-containing material.

[0042] In the general formula (1), when one or more of R1 to R8 of the 1,4-dioxane compound are aliphatic hydrocarbon groups or aliphatic oxyhydrocarbon groups (alkoxy groups, etc.), it is desirable that the steric hindrance is small. For example, C １－５ It may be a hydrocarbon group or an oxyhydrocarbon group (such as an alkoxy group). When one or more of R1 to R8 is an aromatic hydrocarbon group (aryl group), the number of aromatic rings may be one.

[0043] R1 to R8 may all be hydrogen atoms, or one or more may be fluorine atoms and the rest may be hydrogen atoms. Alternatively, at least one of R1 to R8 may be an alkyl group, an alkenyl group, or an aryl group, and the rest may be independently hydrogen atoms or fluorine atoms. The alkyl group is preferably one with small steric hindrance, and is preferably, for example, a C 1 to 5 carbon atom group. １－５ Alkyl group (preferably having 1 to 3 carbon atoms) １－３ Similarly, the alkenyl group may be a C alkyl group having 2 to 5 carbon atoms. ２－５ The hydrocarbon group may be, for example, a methyl group, an ethyl group, an ethylene group, a propyl group, a propylene group, or the like.

[0044] A typical example of the 1,4-dioxane compound is 1,4-dioxane, which preferably accounts for 50% by mass or more, and more preferably 80% by mass or more, of the 1,4-dioxane compounds.

[0045] In the general formula (2), when X1 of the hexavalent sulfur compound is a fluorine atom, X2 is preferably an alkyl group, an alkenyl group, an aryl group, a silyl group, or an alkali metal. X1 and X2 of the sulfur compound (2) may be alkylene groups, alkenylene groups, ether groups, or the like to form a ring. The hexavalent sulfur compound may also contain two hexavalent sulfur atoms. In this case, X1 may be an ether group shared by two sulfur atoms, and X2 may be an alkylene group shared by two sulfur atoms.

[0046] In general formula (3), X3 and X4 of the tetravalent sulfur compound may be an alkyl group, an alkenyl group, or an aryl group. X3 and X4 may be an alkylene group, an alkenylene group, an ether group, or the like to form a ring. The tetravalent sulfur compound may also contain two tetravalent sulfur atoms. In that case, X3 and X4 may be an alkylene group or an ether group shared by two sulfur atoms.

[0047] The hexavalent sulfur compound is -O-S(=O) ２ Sulfuric acid esters having the —O— structure and —S(═O) ２ The tetravalent sulfur compound includes a sulfonate ester having an —O— structure. The tetravalent sulfur compound is a sulfite ester having an —O—S(═O)—O— structure. Therefore, it can be said that the sulfur-containing compound (S) is at least one selected from the group consisting of sulfate esters, sulfite esters, and sulfonate esters.

[0048] As the sulfate ester, C ２－４ Alkyl sulfates are preferred, and specific examples thereof include ethylene sulfate, propylene sulfate, trimethylene sulfate, butylene sulfate, vinylene sulfate, ethyl sulfate, and methyl sulfate.

[0049] Sulfite esters include C ２－４ Alkylene sulfites are preferred, and specific examples include ethylene sulfite (ES), propylene sulfite, trimethylene sulfite, butylene sulfite, and vinylene sulfite.

[0050] The sulfonic acid esters include C ３－５Alkanesultone and C ３－５ At least one selected from the group consisting of alkene sultones is preferred, specifically 1,3-propane sultone, 1,4-butane sultone, 1,3-propene sultone, etc.

[0051] The sulfur-containing compound (S) may have one or more hydrogen atoms of the compounds exemplified above substituted with a substituent. Examples of the substituent include an alkyl group, a hydroxyalkyl group, a hydroxy group, an alkoxy group, and a halogen atom. The number of carbon atoms in the substituent may be 1 to 3. The halogen atom is preferably a fluorine atom.

[0052] Among hexavalent sulfur compounds, lithium fluorosulfonate (LiFSO ３ At least one selected from the group consisting of 1-propene-1,3-sultone (PRS), ethylene sulfate (DTD), and 1,5,2,4-dioxadithiane-2,2,4,4-tetraoxide (MMDS) is desirable because it is easily available and has a significant effect of improving high-temperature cycle characteristics. It is desirable that one or more of these account for 50 mass % or more, and even 80 mass % or more, of the hexavalent sulfur compounds.

[0053] Among tetravalent sulfur compounds, at least one selected from the group consisting of ethylene sulfite (ES) and vinyl ethylene sulfite (VES) is particularly desirable because it is easily available and has a significant effect of improving high-temperature cycle characteristics. It is desirable that one or more of these compounds account for 50 mass % or more, and even 80 mass % or more, of the tetravalent sulfur compounds.

[0054] The mass content of the 1,4-dioxane compound contained in the non-aqueous electrolyte is, for example, 5% or less, and may be 0.01% to 5%, 0.1% to 5.0%, 0.1% to 2.0%, or 0.5% to 1.5%. In this case, a sufficient effect of suppressing corrosion of the battery can due to the sulfur-containing compound (S) is obtained. Furthermore, since a hybrid coating is appropriately formed and charge / discharge reactions tend to proceed uniformly, it is believed that the effect of improving high-temperature cycle characteristics is enhanced.

[0055] The mass content of the sulfur-containing compound (S) contained in the non-aqueous electrolyte is, for example, 5% or less, and may be 0.01% to 5%, 0.1% to 5%, 0.1% to 2.0%, or 0.5% to 1.5%. In this case, a sufficient effect of improving high-temperature cycle characteristics can be obtained. It is believed that the hybrid coating is appropriately formed, and the charge / discharge reaction tends to proceed uniformly, thereby enhancing the effect of suppressing side reactions.

[0056] The mass content Ca of the 1,4-dioxane compound and the mass content Cb of the sulfur-containing compound (S) may satisfy, for example, 0.25≦Cb / Ca≦3. More preferably, Cb / Ca may satisfy 0.5≦Cb / Ca≦3, 1≦Cb / Ca≦3, 1<Cb / Ca≦3, or 1.3≦Cb / Ca≦2.5. In this case, it is believed that the 1,4-dioxane compound acts more effectively on the sulfur-containing compound (S). When Cb / Ca is controlled as described above, it is believed that the 1,4-dioxane compound is contained at a content that does not inhibit the film formation of the sulfur-containing compound (S). Therefore, the effect of improving high-temperature cycle characteristics can be enhanced. Furthermore, when Cb / Ca is controlled as described above, the 1,4-dioxane compound is also sufficiently effective in trapping sulfate ions, sulfite ions, and the like released by the sulfur-containing compound (S), thereby suppressing corrosion of the battery can.

[0057] The non-aqueous electrolyte may contain additives other than those described above, such as at least one selected from the group consisting of vinylene carbonate, fluoroethylene carbonate, and vinylethylene carbonate.

[0058] (Non-aqueous Solvent) Examples of the non-aqueous solvent include cyclic carbonate esters, chain carbonate esters, cyclic carboxylic acid esters, chain carboxylic acid esters, cyclic ethers, chain ethers, etc. The non-aqueous electrolyte may contain one type of non-aqueous solvent or a combination of two or more types.

[0059] Examples of cyclic carbonates include propylene carbonate (PC), ethylene carbonate (EC), fluoroethylene carbonate (FEC), and vinylene carbonate (VC).

[0060] Examples of the chain carbonate ester include diethyl carbonate (DEC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC).

[0061] Examples of the cyclic carboxylic acid ester include γ-butyrolactone (GBL) and γ-valerolactone (GVL).

[0062] Examples of the chain carboxylic acid ester include methyl formate, ethyl formate, propyl formate, methyl acetate (MA), ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, and propyl propionate.

[0063] Examples of cyclic ethers include 1,3-dioxolane, 4-methyl-1,3-dioxolane, tetrahydrofuran, and 2-methyltetrahydrofuran.

[0064] Examples of chain ethers include 1,2-dimethoxyethane, diethyl ether, ethyl vinyl ether, methyl phenyl ether, benzyl ethyl ether, diphenyl ether, dibenzyl ether, 1,2-diethoxyethane, diethylene glycol dimethyl ether, 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether.

[0065] (Salt) In lithium ion secondary batteries, lithium metal secondary batteries, etc., lithium salts are used as salts. For example, LiClO ４ , LiBF ４ , LiPF ６ , LiAlCl ４ , LiSbF ６ , LiSCN, LiCF ３ SO ３ , LiCF ３ CO ２ , LiAsF ６ , LiB１０ Cl １０ , lower aliphatic lithium carboxylates, LiCl, LiBr, LiI, phosphates, borates, and imide salts. Examples of phosphates include lithium difluorophosphate (LiPO ２ F ２ Examples of the borate salt include lithium bis(oxalato)borate (LiBOB) and lithium difluoro(oxalato)borate (LiDFFOB). Examples of the imide salt include lithium bisfluorosulfonylimide (LiN(FSO ２ ) ２ ), lithium bistrifluoromethanesulfonyl imide (LiN(CF ３ SO ２ ) ２ ), lithium trifluoromethanesulfonate nonafluorobutanesulfonate imide (LiN(CF ３ SO ２ ) (C ４ F ９ SO ２ )), lithium bispentafluoroethanesulfonyl imide (LiN(C ２ F ５ SO ２ ) ２ The non-aqueous electrolyte may contain one lithium salt or a combination of two or more lithium salts.

[0066] The concentration of the lithium salt in the non-aqueous electrolyte is, for example, 0.5 mol / L or more and 2 mol / L or less.

[0067] The content of each component in the non-aqueous electrolyte is determined, for example, by gas chromatography under the following conditions: Measuring device: GC-2010 Plus manufactured by Shimadzu Corporation Column: HP-1 (1 μm×60 m) manufactured by J&W Linear velocity: 30.0 cm / sec Injection port temperature: 270° C. Detector: FID 290° C. (sens. 10 １ )

[0068] Other components of the nonaqueous electrolyte secondary battery of the present disclosure will be specifically described below. [Positive Electrode] The positive electrode comprises a positive electrode current collector and a positive electrode mixture layer provided on the surface of the positive electrode current collector. The positive electrode current collector is made of a sheet-like conductive material. The positive electrode mixture layer is supported on one or both surfaces of the positive electrode current collector. The positive electrode mixture layer is usually a layer or film made of a positive electrode mixture. The thickness of the positive electrode mixture layer is, for example, 10 μm to 150 μm per side of the positive electrode current collector. The positive electrode mixture contains a positive electrode active material as an essential component.

[0069] The positive electrode mixture layer may contain a conductive agent as an optional component. Examples of the conductive agent include carbon-based materials such as carbon black (CB), acetylene black (AB), ketjen black, carbon nanotubes (CNT), graphene, and graphite. These may be used alone or in combination of two or more.

[0070] The positive electrode mixture layer may contain a binder. Examples of binders include fluorine-based resins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF), polyacrylonitrile (PAN), polyimide-based resins, acrylic-based resins, and polyolefin-based resins. These may be used alone or in combination of two or more.

[0071] The positive electrode current collector may be a non-porous conductive substrate (such as a metal foil) or a porous conductive substrate (such as a mesh, net, or punched sheet). Examples of the material for the positive electrode current collector include aluminum, an aluminum alloy, titanium, and a titanium alloy.

[0072] A lithium-containing composite oxide can be used as the positive electrode active material. The lithium-containing composite oxide may have a layered rock salt structure. The layered rock salt structure may belong to, for example, space group R-3m, space group C2 / m, etc. Among these, a layered rock salt structure belonging to space group R-3m is preferred in terms of high capacity and highly stable crystal structure. The layered rock salt structure of the lithium-containing composite oxide may include a transition metal layer, a Li layer, and an oxygen layer.

[0073] From the viewpoint of increasing the capacity, the ratio of Ni to the metal elements other than Li contained in the lithium-containing composite oxide (Ni content) may be set to 50 atomic % or more, 80 atomic % or more, or 90 atomic % or more.

[0074] From the viewpoint of stabilizing the crystal structure of the lithium-containing composite oxide and improving the heat resistance of the battery, the ratio of Co to the metal elements other than Li contained in the lithium-containing composite oxide (Co content) may be set to 0 atomic % or more and 16 atomic % or less, or may be set to 1.5 atomic % or more and 16 atomic % or less.

[0075] Similarly, from the viewpoint of stabilizing the crystal structure of the lithium-containing composite oxide and improving the heat resistance of the battery, the ratio of Al to the metal elements other than Li contained in the lithium-containing composite oxide (Al content) may be set to 0 atomic % or more and 18.5 atomic % or less, or may be set to 4 atomic % or more and 10 atomic % or less.

[0076] From the viewpoint of cost reduction, the ratio of Mn to the metal elements other than Li contained in the lithium-containing composite oxide (Mn content) may be set to 0 atomic % or more and 50 atomic % or less, or 0 atomic % or more and 30 atomic % or less.

[0077] The content of each metal element contained in the lithium-containing composite oxide is measured, for example, by inductively coupled plasma (ICP) emission spectrometry.

[0078] The lithium-containing composite oxide is, for example, a compound represented by the general formula LiNi ｘ Co ｙ Al ｚ M1 ｗ O ２－ｂ (wherein 0.8≦a≦1.2, 0.80≦x≦0.95, 0.015≦y≦0.16, 0.04≦z≦0.185, 0≦w≦0.145, 0≦b<0.05, x+y+z+w=1, and M1 is at least one element selected from Mn, Fe, Ti, Si, Nb, Zr, Mo, and Zn.) In this case, M1 is preferably Mn.

[0079] [Negative Electrode] The negative electrode includes a negative electrode current collector and may have a negative electrode mixture layer provided on the surface of the negative electrode current collector. The negative electrode current collector is made of a sheet-like conductive material. The negative electrode mixture layer is supported on one or both surfaces of the negative electrode current collector. The negative electrode mixture layer is usually a layer or film made of a negative electrode mixture. The thickness of the negative electrode mixture layer is, for example, 10 μm to 150 μm per surface of the negative electrode current collector. The negative electrode mixture contains a negative electrode active material as an essential component and may contain a binder, a conductive agent, a thickener, etc. as optional components. Known materials can be used as the binder, conductive agent, and thickener.

[0080] The negative electrode active material includes a material that electrochemically absorbs and releases lithium ions, lithium metal, lithium alloy, etc. As the material that electrochemically absorbs and releases lithium ions, a carbon material, an alloy-based material, etc. are used.

[0081] Examples of carbon materials include graphite, easily graphitizable carbon (soft carbon), and hard carbon, among which graphite is preferred because it has excellent charge / discharge stability and a small irreversible capacity.

[0082] Graphite is a carbonaceous material with a developed graphite crystal structure. The interplanar spacing d002 of the (002) plane of graphite measured by X-ray diffraction may be, for example, 0.340 nm or less, or 0.3354 nm or more and 0.340 nm or less. The crystallite size Lc(002) of graphite may be, for example, 5 nm or more, or 5 nm or more and 200 nm or less. The crystallite size Lc(002) is measured, for example, by the Scherrer method. When the interplanar spacing d002 of the (002) plane of graphite and the crystallite size Lc(002) are within the above ranges, high capacity is easily obtained.

[0083] An alloy-based material is a material that contains at least one metal that can form an alloy with lithium, such as silicon, tin, silicon alloys, tin alloys, silicon oxide, tin oxide, and silicon-containing materials.

[0084] The silicon-containing material includes, for example, a lithium ion conductive phase and a silicon phase dispersed in the lithium ion conductive phase. Examples of the lithium ion conductive phase that can be used include a silicon oxide phase, a silicate phase, and a carbon phase. The content of the silicon phase dispersed in the lithium ion conductive phase is, for example, 30% by mass or more and 95% by mass or less, and may be 35% by mass or more and 75% by mass or less. One type of silicon-containing material may be used alone, or two or more types may be used in combination.

[0085] The silicon oxide phase may be mainly composed of silicon dioxide (e.g., 95 to 100% by mass). A silicon-containing material containing a silicon oxide phase and a silicon phase dispersed in the silicon oxide phase may be composed of SiO ｘ where x is, for example, 0.5≦x<2, and may be 0.8≦x≦1.6. The silicon oxide phase may be an amorphous phase. SiO ｘ can be obtained, for example, by the disproportionation reaction of silicon monoxide.

[0086] The silicate phase is preferred because it has a small irreversible capacity. Among them, a silicate phase containing lithium (hereinafter also referred to as a lithium silicate phase) can be preferably used as a lithium ion conductive phase having a high initial charge / discharge efficiency.

[0087] The lithium silicate phase may be an oxide phase containing lithium (Li), silicon (Si), and oxygen (O), and may contain other elements. The atomic ratio of O to Si in the lithium silicate phase, O / Si, is, for example, greater than 2 and less than 4. Preferably, O / Si is greater than 2 and less than 3. The atomic ratio of Li to Si in the lithium silicate phase, Li / Si, is, for example, greater than 0 and less than 4. The lithium silicate phase has the formula: Li ２ｚ SiO ２＋ｚ(0<z<2). Preferably, z satisfies the relationship 0<z<1, and more preferably z=1 / 2. Examples of elements other than Li, Si, and O that can be contained in the lithium silicate phase include iron (Fe), chromium (Cr), nickel (Ni), manganese (Mn), copper (Cu), molybdenum (Mo), zinc (Zn), and aluminum (Al).

[0088] The carbon phase may be composed of, for example, amorphous carbon with low crystallinity (i.e., amorphous carbon). The amorphous carbon may be, for example, hard carbon, soft carbon, or other.

[0089] A silicon-containing material in which a silicon phase is dispersed within a carbon phase can be obtained, for example, by pulverizing a mixture of a carbon source and raw silicon material while stirring it in a ball mill or the like to form fine particles, and then heat-treating the mixture in an inert atmosphere. The carbon source can be, for example, a sugar such as carboxymethyl cellulose (CMC) or a water-soluble resin such as polyvinylpyrrolidone.

[0090] A silicon-containing material and a carbon material may be used in combination as the negative electrode active material. Since the silicon-containing material expands and contracts in volume with charge and discharge, a large proportion of the silicon-containing material in the negative electrode active material is likely to cause poor contact between the negative electrode active material and the negative electrode current collector with charge and discharge. On the other hand, by using a silicon-containing material and a carbon material in combination, it is possible to achieve excellent cycle characteristics while imparting a high capacity to the negative electrode.

[0091] The proportion of the silicon-containing material in the total of the silicon-containing material and the carbon material is, for example, preferably 0.5 to 15 mass %, more preferably 1 to 10 mass %, which makes it easier to achieve both high capacity and improved cycle characteristics.

[0092] The negative electrode current collector may be a non-porous conductive substrate (such as a metal foil) or a porous conductive substrate (such as a mesh, net, or punched sheet). Examples of the material for the negative electrode current collector include stainless steel, nickel, nickel alloys, copper, and copper alloys.

[0093] The composition of the silicon-containing material can be determined, for example, by obtaining a backscattered electron image of a cross section of the negative electrode mixture layer using a field emission scanning electron microscope (FE-SEM), observing the silicon-containing material particles, and performing elemental analysis on the observed silicon-containing material particles. For the elemental analysis, for example, an electron probe microanalyzer (EPMA) analysis or the like is used.

[0094] The negative electrode mixture layer may contain a binder. Examples of binders include fluororesins (e.g., polytetrafluoroethylene, polyvinylidene fluoride), polyolefin resins (e.g., polyethylene, polypropylene), polyamide resins (e.g., aramid resins), polyimide resins (e.g., polyimide, polyamideimide), acrylic resins (e.g., polyacrylic acid, polymethacrylic acid, acrylic acid-methacrylic acid copolymer, ethylene-acrylic acid copolymer, or salts thereof), vinyl resins (e.g., polyvinyl acetate), and rubber-like materials (e.g., styrene-butadiene copolymer rubber (SBR)). One type of binder may be used alone, or two or more types may be used in combination.

[0095] The negative electrode mixture layer may contain a thickener. Examples of thickeners include cellulose derivatives such as cellulose ether. Examples of cellulose derivatives include carboxymethyl cellulose (CMC), its modified forms, and methyl cellulose. Modified forms of CMC also include salts of CMC. Examples of salts include alkali metal salts (e.g., sodium salts) and ammonium salts. One type of thickener may be used alone, or two or more types may be used in combination.

[0096] The negative electrode mixture layer may contain a conductive agent. Examples of the conductive agent include carbon nanotubes (CNTs) and conductive particles. Examples of the conductive particles include conductive carbon (carbon black, etc.) and metal powder. One type of conductive agent may be used alone, or two or more types may be used in combination.

[0097] The negative electrode current collector is selected depending on the type of nonaqueous electrolyte secondary battery. Examples of the negative electrode current collector include a sheet-like one. Metal foil or the like may also be used as the current collector. Alternatively, a porous current collector may also be used. Examples of porous current collectors include a mesh-like one, a punched sheet, and an expanded metal.

[0098] Examples of the material for the negative electrode current collector include stainless steel, nickel, nickel alloy, copper, and copper alloy.

[0099] [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, for example, a microporous thin film, a woven fabric, a nonwoven fabric, or a laminate of at least two selected from these. The separator is preferably made of polyolefin (e.g., polypropylene, polyethylene).

[0100] An example of the structure of a non-aqueous electrolyte secondary 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 exterior body such as a battery can together with a non-aqueous electrolyte. However, this is not limited thereto, and other forms of electrode groups may also be applied. For example, the electrode group may be a laminate type in which a positive electrode and a negative electrode are stacked with a separator interposed therebetween.

[0101] A typical battery can is cylindrical with a bottom, but is not limited thereto. A cylindrical battery can with a bottom has a bottom and a cylindrical side rising from the bottom. The end opposite the bottom is open. The battery can is preferably made of a metal containing at least iron. Such a battery can has high mechanical strength. The material of the battery can may be iron (Fe), an Fe alloy, stainless steel, or the like. A nickel-plated layer is preferably formed on the inner surface of the battery can.

[0102] The exterior body is not limited to a battery can, and the shape of the nonaqueous electrolyte secondary battery is not limited either. The nonaqueous electrolyte secondary battery may be, for example, cylindrical, prismatic, coin, or button type.

[0103] The structure of a nonaqueous electrolyte secondary battery will be described below with reference to Fig. 1. Fig. 1 is a longitudinal cross-sectional view of a cylindrical secondary battery as an example of this embodiment. However, the present disclosure is not limited to the following configuration.

[0104] The nonaqueous electrolyte secondary battery (hereinafter referred to as battery 10) includes an electrode group 18, a nonaqueous electrolyte, and a cylindrical battery can 22 with a bottom that accommodates these. The battery can 22 is made of iron, stainless steel, or the like. The inner surface of the battery can 22 may be nickel-plated or the like. A sealing body 11 is crimped to the opening of the battery can 22 via a gasket 21, thereby sealing the battery. The sealing body 11 includes a valve body 12, a metal plate 13, and an annular insulating member 14 interposed between the valve body 12 and the metal plate 13. The valve body 12 and the metal plate 13 are connected to each other at their respective centers. A positive electrode lead 15a extending from a positive electrode 15 is connected to the metal plate 13. Thus, the valve body 12 functions as an external terminal for the positive electrode. A negative electrode lead 16a extending from a negative electrode 16 is connected to the inner bottom surface of the battery can 22. An annular groove 22a is formed near the open end of the battery can 22. A first insulating plate 23 is disposed between one end face of the electrode group 18 and the annular groove 22a. A second insulating plate 24 is disposed between the other end face of the electrode group 18 and the bottom of the battery can 22. The electrode group 18 is formed by winding a positive electrode 15 and a negative electrode 16 with a separator 17 interposed therebetween.

[0105] (Additional Note) The above description discloses the following techniques: (Technology 1) A method for producing a liquid crystal display device comprising: a non-aqueous solvent; a salt soluble in the non-aqueous solvent; and an additive soluble in the non-aqueous solvent, wherein the additive comprises a 1,4-dioxane compound and a sulfur-containing compound; and the sulfur-containing compound is SO ３ Structure and SO ４(Technology 2) The nonaqueous electrolyte for secondary batteries according to Technology 1, wherein the 1,4-dioxane compound includes at least one selected from the group consisting of 1,4-dioxane and 1,4-dioxane derivatives. (Technology 3) The nonaqueous electrolyte for secondary batteries according to Technology 2, wherein the 1,4-dioxane derivative is a compound in which at least one hydrogen atom of 1,4-dioxane is substituted with a substituent, the substituent being a halogen atom, a hydrocarbon group, or an oxyhydrocarbon group, and at least one hydrogen atom of the hydrocarbon group may be substituted with a halogen atom. (Technology 4) The 1,4-dioxane compound is a compound represented by general formula (1):

[0106]

[0107] and R1 to R8 are each independently a hydrogen atom or the substituent. (Technology 5) The nonaqueous electrolyte for secondary batteries according to any one of Techniques 1 to 4, wherein the sulfur-containing compound includes at least one selected from the group consisting of a hexavalent sulfur compound and a tetravalent sulfur compound. (Technology 6) The hexavalent sulfur compound is represented by the general formula (2):

[0108]

[0109] The nonaqueous electrolyte for a secondary battery according to technology 5 has a structure represented by the following formula: X1 is a halogen atom, a hydrocarbon group, or an oxyhydrocarbon group, X2 is a hydrocarbon group, a silyl group, or an alkali metal, at least one hydrogen atom of the hydrocarbon group may be substituted with a halogen atom, and X1 and X2 may form a ring. (Technology 7) The tetravalent sulfur compound is a nonaqueous electrolyte for a secondary battery according to technology 5, having a structure represented by the following formula:

[0110]

[0111] wherein X3 and X4 are each independently a hydrocarbon group, a silyl group, or an alkali metal, at least one hydrogen atom of the hydrocarbon group may be substituted with a halogen atom, and X3 and X4 may form a ring. (Technology 8) The nonaqueous electrolyte for secondary batteries according to any one of Technologies 1 to 7, wherein the mass content of the 1,4-dioxane compound is 0.1% or more and 5% or less. (Technology 9) The nonaqueous electrolyte for secondary batteries according to any one of Technologies 1 to 8, wherein the mass content of the sulfur-containing compound is 0.1% or more and 5% or less. (Technology 10) The nonaqueous electrolyte for secondary batteries according to any one of Technologies 1 to 9, wherein the mass content Ca of the 1,4-dioxane compound and the mass content Cb of the sulfur-containing compound satisfy the relationship 0.5≦Cb / Ca≦3. (Technology 11) The nonaqueous electrolyte for secondary batteries according to any one of Techniques 1 to 10, wherein the mass content Ca of the 1,4-dioxane compound and the mass content Cb of the sulfur-containing compound satisfy 1≦Cb / Ca≦3. (Technology 12) The nonaqueous electrolyte for secondary batteries according to any one of Techniques 5 to 7, wherein the hexavalent sulfur compound includes at least one selected from the group consisting of lithium fluorosulfonate, 1-propene-1,3-sultone, ethylene sulfate, and 1,5,2,4-dioxadithiane-2,2,4,4-tetraoxide. (Technology 13) The nonaqueous electrolyte for secondary batteries according to any one of Techniques 5 to 7, wherein the tetravalent sulfur compound includes at least one selected from the group consisting of ethylene sulfite and vinyl ethylene sulfite. (Technology 14) A secondary battery comprising: a positive electrode, a separator, a negative electrode facing the positive electrode with the separator interposed therebetween, a nonaqueous electrolyte, and a battery can accommodating the positive electrode, the separator, the negative electrode, and the nonaqueous electrolyte, wherein the nonaqueous electrolyte is the nonaqueous electrolyte for secondary batteries according to any one of Technologies 1 to 13. (Technology 15) The secondary battery according to Technology 14, wherein the battery can is made of a metal containing at least iron.

[0112] EXAMPLES The present invention will be specifically described below based on examples and comparative examples, but the present invention is not limited to the following examples.

[0113] Examples 1 to 5 and Comparative Examples 1 to 10 Non-aqueous electrolyte secondary batteries were fabricated and evaluated according to the following procedures.

[0114] (1) Preparation of Positive Electrode An appropriate amount of N-methyl-2-pyrrolidinone (NMP) was added to the positive electrode mixture and mixed to obtain a positive electrode slurry. The positive electrode mixture was a lithium-containing composite oxide (LiNi ０．８ Co ０．１８ Al ０．０２ O ２ Next, the positive electrode slurry was applied to the surface of an aluminum foil, the coating was dried, and then the aluminum foil was rolled to form a positive electrode mixture layer (thickness 95 μm, density 3.6 g / cm 3 ) on both sides of the aluminum foil. ３ ) was formed to obtain a positive electrode.

[0115] (2) Preparation of Negative Electrode An appropriate amount of water was added to the negative electrode mixture and mixed to obtain a negative electrode slurry. The negative electrode mixture was a mixture of a negative electrode active material, a binder, and a conductive agent. The negative electrode active material was a mixture of a silicon-containing material and graphite (average particle size (D50) 25 μm). The silicon-containing material was SiO , the surface of which was coated with a conductive layer of conductive carbon. ｘ Particles (x = 1, average particle size (D50) 5 μm) were used. In the negative electrode active material, the mass ratio of the silicon-containing material excluding the conductive layer to graphite was 6:94. Sodium polyacrylate (PAA-Na), a sodium salt of CMC (CMC-Na), and SBR were used as binders. The contents of PAA-Na, CMC-Na, and SBR in the negative electrode mixture were each 1 mass %. Next, the negative electrode slurry was applied to the surface of the copper foil, the coating was dried, and then rolled to form negative electrode mixture layers (thickness 80 μm, density 1.6 g / cm ) on both sides of the copper foil. ３ ) was formed to obtain a negative electrode.

[0116] (3) Preparation of non-aqueous electrolyte: LiPF was dissolved in a mixed solvent of ethylene carbonate (EC), dimethyl carbonate (DMC), and methyl acetate (MA) (EC:DMC:MA = 20:60:20 (volume ratio)). ６and, if necessary, the additives shown in Table 1 were dissolved therein to prepare a non-aqueous electrolyte. ６ The concentration of the additive in the non-aqueous electrolyte (initial concentration) was set to the value (mass %) shown in Table 1.

[0117] (4) Fabrication of a Non-Aqueous Electrolyte Secondary Battery An Al positive electrode lead was attached to the positive electrode obtained above, and a Ni negative electrode lead was attached to the negative electrode obtained above. The positive and negative electrodes were spirally wound in an inert gas atmosphere with a polyethylene thin film (separator) interposed between them to produce a wound electrode assembly. A first insulating plate was placed on the lower end surface of the electrode assembly, the electrode assembly was inserted into a battery can, and the negative electrode lead was resistance-welded to the bottom of the battery can. An iron can with nickel plating on the inner surface was used as the battery can. A second insulating plate was placed on the upper end surface of the electrode assembly, and an annular groove was formed near the open edge of the battery can. Next, the positive electrode lead was connected to the metal plate of the safety mechanism provided in the sealing body, and the non-aqueous electrolyte was poured into the battery can. The battery can was then supported in the annular groove formed in the battery can via a gasket, and the open edge of the battery can was crimped to the periphery of the sealing body to complete the lithium-ion secondary battery.

[0118] [Evaluation 1] Overdischarge Characteristics A 1 kΩ resistor was connected between the positive and negative electrodes of the battery, and the battery was stored in a constant temperature bath at 60°C for 30 days while being discharged. The battery was then disassembled, and the Fe element content (by mass) in the non-aqueous electrolyte was quantified using ICP (Inductively Coupled Plasma) emission spectroscopy. The relative value (index) was calculated, with the Fe element content in the non-aqueous electrolyte in Comparative Example 1 set to 100.

[0119] [Evaluation 2] High-Temperature Cycle Characteristics In a 45°C environment, the nonaqueous electrolyte secondary battery was subjected to constant-current charging at a current of 0.3 It until the voltage reached 4.2 V, and then to constant-voltage charging at 4.2 V until the current reached 0.05 It. After a 20-minute rest, the nonaqueous electrolyte secondary battery was subjected to constant-current discharging at a current of 0.5 It until the voltage reached 2.5 V. The discharge capacity (Ci) at this time was determined. This cycle of charge, rest, and discharge was counted as one cycle, and 300 cycles were repeated to determine the discharge capacity (Cc) at the 300th cycle. The ratio (%) of the discharge capacity Cc to the initial discharge capacity Ci, taken as 100%, was calculated as the 45°C cycle capacity retention rate.

[0120] The results of the Examples and Comparative Examples are shown in Table 1. In Table 1, batteries E1 to E5 correspond to Examples 1 to 5, and batteries C1 to C10 correspond to Comparative Examples 1 to 10.

[0121] The additives in the table are listed as follows: 1,4DOX: 1,4-dioxane 1,3DOX: 1,3-dioxane

[0122] LiFSO ３ : Lithium fluorosulfonate PRS: 1-propene-1,3-sultone DTD: Ethylene sulfate MMDS: 1,5,2,4-dioxadithiane-2,2,4,4-tetraoxide

[0123] LiFSI: Lithium bisfluorosulfonylimide

[0124]

[0125] Table 1 shows that the high-temperature cycle characteristics are improved when the non-aqueous electrolyte contains a sulfur-containing compound (S) or lithium bisfluorosulfonylimide (LiFSI) (comparison of batteries C1 to C6). Furthermore, the improvement in high-temperature cycle characteristics is slight when using LiFSI, but is significant when using a sulfur-containing compound (S) as the non-aqueous electrolyte. However, batteries C2 to C5, which contain a sulfur-containing compound (S) as the non-aqueous electrolyte, exhibit insufficient overdischarge characteristics due to a significant amount of Fe elution from the battery can during overdischarge. The overdischarge characteristics of battery C6, which contains LiFSI as the non-aqueous electrolyte, are within the acceptable range.

[0126] On the other hand, when the non-aqueous electrolyte contains both the sulfur-containing compound (S) and the 1,4-dioxane compound, the elution of Fe element from the battery can during overdischarge is significantly suppressed, and the high-temperature cycle performance is also improved compared to batteries C2 to C5 containing only the sulfur-containing compound (S) (compared to batteries E1 to E5). Furthermore, a comparison of batteries E4 to E6 reveals that the effect of improving the high-temperature cycle performance is significant when the Cb / Ca ratio is greater than 1.

[0127] Furthermore, a comparison between batteries C2 and C9 reveals that the improvement in high-temperature cycle characteristics and the effect of suppressing the elution of Fe element from the battery can during overdischarge are specific to 1,4-dioxane compounds, and that no effect is observed with 1,3-dioxane.

[0128] The amount of eluted Fe element from Battery C10, whose nonaqueous electrolyte contained a 1,4-dioxane compound and LiFSI, was slightly greater than that from Battery C6, and the high-temperature cycle characteristics of Battery C10 were also slightly worse than those of Battery C6.

[0129] Secondary batteries containing nonaqueous electrolytes according to the present disclosure are useful as main power sources for mobile communication devices, portable electronic devices, and the like. However, the applications of nonaqueous electrolyte secondary batteries are not limited thereto. While the present invention has been described with reference to presently preferred embodiments, such disclosure should not be construed as limiting. Various modifications and alterations will no doubt become apparent to those skilled in the art to which the present invention pertains upon reading the above disclosure. Accordingly, the appended claims should be construed to include all modifications and alterations without departing from the true spirit and scope of the present invention.

[0130] 10: Secondary battery, 11: Sealing body, 12: Valve body, 13: Metal plate, 14: Insulating member, 15: Positive electrode, 15a: Positive electrode lead, 16: Negative electrode, 16a: Negative electrode lead, 17: Separator, 18: Electrode group, 21: Gasket, 22: Battery can, 22a: Groove portion, 23: First insulating plate, 24: Second insulating plate

Claims

1. A method for producing a liquid crystal display comprising: a non-aqueous solvent; a salt that dissolves in the non-aqueous solvent; and an additive that dissolves in the non-aqueous solvent, the additive including a 1,4-dioxane compound and a sulfur-containing compound; the sulfur-containing compound including SO ３ Structure and SO ４ The non-aqueous electrolyte for a secondary battery has at least one of the following structures:

2. The nonaqueous electrolyte for secondary batteries according to claim 1, wherein the 1,4-dioxane compound includes at least one selected from the group consisting of 1,4-dioxane and 1,4-dioxane derivatives.

3. The nonaqueous electrolyte for secondary batteries according to claim 2, wherein the 1,4-dioxane derivative is a compound in which at least one hydrogen atom of 1,4-dioxane is substituted with a substituent, the substituent being a halogen atom, a hydrocarbon group or an oxyhydrocarbon group, and at least one hydrogen atom of the hydrocarbon group may be substituted with a halogen atom.

4. The 1,4-dioxane compound is represented by the general formula (1):

4. The nonaqueous electrolyte for secondary batteries according to claim 3, wherein R1 to R8 are each independently a hydrogen atom or the substituent.

5. The nonaqueous electrolyte for a secondary battery according to claim 1, wherein the sulfur-containing compound includes at least one selected from the group consisting of hexavalent sulfur compounds and tetravalent sulfur compounds.

6. The hexavalent sulfur compound has the general formula (2):

6. The nonaqueous electrolyte for secondary batteries according to claim 5, having a structure represented by the following formula: wherein X1 is a halogen atom, a hydrocarbon group or an oxyhydrocarbon group; X2 is a hydrocarbon group, a silyl group or an alkali metal; at least one hydrogen atom of the hydrocarbon group may be substituted with a halogen atom; and X1 and X2 may form a ring.

7. The tetravalent sulfur compound is represented by the general formula (3): wherein X3 and X4 are each independently a hydrocarbon group, a silyl group, or an alkali metal, at least one hydrogen atom of the hydrocarbon group may be substituted with a halogen atom, and X3 and X4 may form a ring.

8. The nonaqueous electrolyte for secondary batteries according to claim 1, wherein the mass content of the 1,4-dioxane compound is 0.1% or more and 5% or less.

9. The nonaqueous electrolyte for a secondary battery according to claim 1, wherein the mass content of the sulfur-containing compound is 0.1% or more and 5% or less.

10. The nonaqueous electrolyte for secondary batteries according to claim 1, wherein the mass content Ca of the 1,4-dioxane compound and the mass content Cb of the sulfur-containing compound satisfy 0.5≦Cb / Ca≦3.

11. The nonaqueous electrolyte for secondary batteries according to claim 1, wherein the mass content Ca of the 1,4-dioxane compound and the mass content Cb of the sulfur-containing compound satisfy the relationship 1≦Cb / Ca≦3.

12. The nonaqueous electrolyte for a secondary battery according to claim 5, wherein the hexavalent sulfur compound includes at least one selected from the group consisting of lithium fluorosulfonate, 1-propene-1,3-sultone, ethylene sulfate, and 1,5,2,4-dioxadithiane-2,2,4,4-tetraoxide.

13. The nonaqueous electrolyte for a secondary battery according to claim 5, wherein the tetravalent sulfur compound includes at least one selected from the group consisting of ethylene sulfite and vinyl ethylene sulfite.

14. A secondary battery comprising: a positive electrode; a separator; a negative electrode facing the positive electrode with the separator interposed therebetween; a nonaqueous electrolyte; and a battery can accommodating the positive electrode, the separator, the negative electrode and the nonaqueous electrolyte, wherein the nonaqueous electrolyte is the nonaqueous electrolyte for secondary batteries according to claim 1.

15. The secondary battery according to claim 14, wherein the battery can is made of a metal containing at least iron.