Non-aqueous electrolyte additive, non-aqueous electrolyte containing the same, and non-aqueous electrolyte secondary battery

Abstract

The additive for non-aqueous electrolyte solution comprises a bisalkoxysilyl compound, wherein the bisalkoxysilyl compound has two silyl groups connected by a chain containing a thioether group, wherein the two silyl groups each have at least one selected from the group consisting of an alkoxy group and an oxyalkyl group, and the oxyalkyl group is replaced by -O-(C x H 2x+1 O y ) represents that x is an integer greater than 1, and y is an integer greater than 1.

Description

Technical Field

[0001] The present disclosure relates to a non-aqueous electrolyte additive, a non-aqueous electrolyte containing the same, and a non-aqueous electrolyte secondary battery. Background Art

[0002] Silicon-containing materials hold promise as high-capacity negative electrode materials for secondary batteries. However, these materials experience significant expansion and contraction during charge and discharge, which can easily induce side reactions and reduce capacity retention during charge and discharge cycles.

[0003] Non-Patent Document 1 reports that the capacity retention rate during charge and discharge cycles is improved by adding a vinyl-containing silane coupling agent to the electrolyte of a monopolar battery using a Si / C composite.

[0004] Prior art literature

[0005] Non-patent literature

[0006] Non-Patent Literature 1: Ionics, 2018, 24, 3691-3698 Summary of the Invention

[0007] In the proposal of Non-Patent Document 1, it is difficult to stably improve the capacity retention rate during charge and discharge cycles.

[0008] One aspect of the present disclosure relates to an additive for a non-aqueous electrolyte solution, comprising a dialkoxysilyl compound having two silyl groups connected by a chain containing a thioether group, wherein the two silyl groups each have at least one selected from the group consisting of an alkoxy group and an oxyalkyl group, and the oxyalkyl group is replaced by -O-(C x H 2x+ 1O y ) represents that x is an integer greater than 1, and y is an integer greater than 1.

[0009] Another aspect of the present disclosure relates to a non-aqueous electrolyte solution comprising: a non-aqueous solvent, a salt dissolved in the non-aqueous solvent, and the non-aqueous electrolyte solution additive.

[0010] Another aspect of the present disclosure relates to a non-aqueous electrolyte secondary battery comprising: a negative electrode having a negative electrode mixture layer; a positive electrode; and the non-aqueous electrolyte. The negative electrode mixture layer contains a negative electrode active material containing a material containing silicon.

[0011] According to the present disclosure, when the negative electrode active material contains a material containing silicon, the capacity retention rate of the non-aqueous electrolyte secondary battery during charge and discharge cycles can be stably improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 This is a partially cutaway plan view schematically illustrating the structure of a non-aqueous electrolyte secondary battery according to one embodiment of the present disclosure.

[0013] Figure 2 for Figure 1 A cross-sectional view of the non-aqueous secondary battery taken along line XX' is shown.

[0014] Figure 3 A diagram illustrating a method for preparing a negative electrode for performance evaluation.

[0015] Figure 4 Graph showing the relationship between the number of charge and discharge cycles and the capacity retention rate of a non-aqueous electrolyte secondary battery. DETAILED DESCRIPTION

[0016] (Additives for non-aqueous electrolytes)

[0017] The additive for non-aqueous electrolyte solution of the embodiment of the present disclosure includes a dialkoxysilyl compound. The dialkoxysilyl compound has two silyl groups connected by a chain containing a thioether group. The two silyl groups each have at least one selected from the group consisting of an alkoxy group and an oxyalkyl group, and the oxyalkyl group is replaced by -O-(C x H 2x+1 O y ) represents that x is an integer greater than 1, and y is an integer greater than 1.

[0018] It is believed that in the above-mentioned structure, the alkoxy group or oxyalkyl group possessed by each silyl group forms an XO-Si bond with the surface of the material containing the silicon element. Here, X represents the surface of the material containing the silicon element, and O bonded to X represents, for example, an O atom (or a residue of an OH group) present on the surface of the material containing the silicon element. The alkoxy group or oxyalkyl group forms a bond with the surface of the material containing the silicon element, so that the surface of the material containing the silicon element is covered with a bis-silyl sulfide structure having stable siloxane bonds at both ends. That is, the surface of the material containing the silicon element is covered by a coating (hereinafter also referred to as an SSS coating) containing a bis-silyl sulfide structure. The SSS coating has high elasticity and is stable to reversible elastic deformation. Even in the case of repeated charge and discharge cycles, the SSS coating is not easily damaged. As a result, side reactions in the negative electrode are suppressed, and the capacity retention rate during the charge and discharge cycle is stably improved.

[0019] The bisalkoxysilyl compound may be a bis(alkoxysilylalkyl) sulfide represented by the general formula (1).

[0020]

[0021] Here, R1 is C x1 H 2x1 Sz The thioether group represented by x1 and z are each an integer greater than 1. At least one of R2 to R4 is selected from an alkoxy group having 1 to 6 carbon atoms and an alkoxy group represented by -O-(C x2 H 2x2+1 O y2 ) represented by, x2 is an integer greater than 1, y2 is an integer greater than 1, and at least one of the group consisting of an oxyalkyl group. At least one of R5 to R7 is selected from an alkoxy group having 1 to 6 carbon atoms and an alkyl group represented by -O-(C x3 H 2x3+1 O y3 ) represented by, x3 is an integer greater than 1, y3 is an integer greater than 1, and at least one of the group consisting of an oxyalkyl group. The remainder of R2 to R7 are each independently C x4 H 2x4+1 O y4 alkyl or oxyalkyl, wherein x4 is an integer greater than or equal to 1 and y4 is an integer greater than or equal to 0. The oxyalkyl group is a group other than an alkoxy group.

[0022] The alkoxy groups or oxyalkyl groups contained in R2-R4 and R5-R7 each form an XO-Si-R1 bond with the surface of the silicon-containing material, and the surface of the silicon-containing material is covered with a Si-R1-Si structure having stable siloxane bonds at both ends. In other words, the surface of the silicon-containing material is covered with an SSS film containing the Si-R1-Si structure.

[0023] In formula (1), C x1 H 2x1 S z The sulfide group (R1) represented by R11-S z -R12 represents a structure. Here, R11 and R12 are independently an alkylene group with a carbon number of 1 or more. It is believed that such R1 has excellent flexibility, and S z The electron shielding property generated by the structure is large, and the effect of suppressing side reactions is further enhanced.

[0024] The more carbon numbers R11 and R12 have, the better the flexibility is, and therefore, the reversible deformation of the SSS coating becomes easier. However, it is believed that if the carbon numbers of R11 and R12 are too many, the alkylene chain will be too long, the density of the SSS coating will be reduced, and the effect of suppressing side reactions will be reduced. Therefore, the carbon numbers of R11 and R12 are preferably set to 1 to 6, and more preferably to 2 to 4. Bis(alkoxysilylalkyl)sulfide is preferably bis(alkoxysilyl C 1-6 Alkyl) sulfide, which can be bis (alkoxysilyl C 2-4 alkyl) sulfide.

[0025] In addition, S constituting R1 zThe more continuous sulfur numbers in the base, the better the flexibility, thus making the reversible deformation of the SSS film easier. However, if the sulfur number is too high, the density of the SSS film decreases, and the SSS film z The basic itself may produce side reactions. z The number of sulfur atoms in the group is preferably 1 to 6, more preferably 2 to 4. That is, the bis(alkoxysilylalkyl)sulfide is preferably a bis(alkoxysilyl C 1-6 Alkyl)S 1-6 Thioether, can be bis (alkoxysilyl C 2-4 Alkyl)S 2-4 sulfide.

[0026] At least one of R2 to R4 is selected from an alkoxy group having 1 to 6 carbon atoms and an alkyl group represented by -O-(C x2 H 2x2+1 O y2 ), x2 can be an integer of 1 to 6, y2 is 1 or 2, and at least one of the group consisting of an oxyalkyl group, and at least one of R5 to R7 can be selected from an alkoxy group having 1 to 6 carbon atoms and an alkoxy group represented by -O-(C x3 H 2x3+1 O y3 ), x3 is an integer of 1 to 6, and y3 is 1 or 2. From the viewpoint of improving reactivity with the surface of a material containing silicon, the alkoxy group or oxyalkyl group may be smaller, and the number of carbon atoms in the alkoxy group or oxyalkyl group may be, for example, 1 to 3.

[0027] The rest of R2 to R7 can be independently C x4 H 2x4+1 O y4 The alkyl or oxyalkyl group represented by x4 is an integer of 1 to 6, and y4 is an integer of 0 to 2. From the viewpoint of reducing steric hindrance during the reaction, C x4 H 2x4+1 O y4 The carbon number of the group represented by can be 1 to 6, or 1 to 3. R2 to R4 are each independent, and all of R2 to R4 may have the same carbon number, or all of them may be different, or two of R2 to R4 may have the same carbon number. Similarly, R5 to R7 are each independent, and all of R5 to R7 may have the same carbon number, or all of them may be different, or two of R5 to R7 may have the same carbon number.

[0028] The two alkoxysilyl groups (R2R3R4Si- or R5R6R7Si-) connected to R1 may be the same or different. However, in order to improve the symmetry of the SSS film structure and form a more stable structure, the two alkoxysilyl groups connected to R1 can be of the same structure.

[0029] Bis(trialkoxysilyl C 1-6 Alkyl)S 1-6 Among the sulfides, readily available ones include at least one selected from the group consisting of bis(triethoxysilylpropyl)sulfide, bis(triethoxysilylpropyl)disulfide, bis(triethoxysilylpropyl)trisulfide, and bis(triethoxysilylpropyl)tetrasulfide.

[0030] (Non-aqueous electrolyte)

[0031] The non-aqueous electrolyte solution comprises a non-aqueous solvent, a salt (solute) dissolved in the non-aqueous solvent, and the aforementioned non-aqueous electrolyte additive. The salt (solute) is an electrolyte salt that undergoes ion dissociation in the non-aqueous solvent. When the non-aqueous electrolyte solution is used in a lithium-ion secondary battery, the salt comprises at least a lithium salt. Components of the non-aqueous electrolyte solution other than the non-aqueous solvent and the salt are additives, at least a portion of which is the aforementioned bis-alkoxysilyl compound.

[0032] The concentration of the bisalkoxysilyl compound in the non-aqueous electrolyte solution may be, for example, 5% by mass or less, 2% by mass or less, or 1% by mass or less. Within this range, a good and appropriate SSS coating is fully formed regardless of the amount of the material containing the silicon element contained in the negative electrode active material. If the concentration of the bisalkoxysilyl compound in the non-aqueous electrolyte solution is, for example, 0.05% by mass or more, it is believed that an appropriate SSS coating is formed, which can significantly improve the capacity retention rate during the charge and discharge cycle of the non-aqueous electrolyte secondary battery.

[0033] However, the bisalkoxysilyl compound reacts within the non-aqueous electrolyte secondary battery, thereby reducing its concentration in the non-aqueous electrolyte solution. Therefore, the bisalkoxysilyl compound can remain above the detection limit in the non-aqueous electrolyte solution extracted from a completed non-aqueous electrolyte secondary battery or a commercially available non-aqueous electrolyte secondary battery after disassembly.

[0034] As the non-aqueous solvent, for example, cyclic carbonates, chain carbonates, cyclic carboxylates, chain carboxylates, etc. can be used. As cyclic carbonates, propylene carbonate (PC), ethylene carbonate (EC), vinylene carbonate (VC), etc. can be mentioned. As chain carbonates, diethyl carbonate (DEC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), etc. can be mentioned. In addition, as cyclic carboxylates, γ-butyrolactone (GBL), γ-valerolactone (GL), etc. can be mentioned. As chain carboxylates, methyl acetate, ethyl acetate, propyl acetate, methyl propionate (MP), ethyl propionate (EP), etc. can be mentioned. The non-aqueous solvent can be used alone or in combination of two or more.

[0035] Among them, chain carboxylic acid esters are suitable for preparing low-viscosity non-aqueous electrolytes. Thus, the non-aqueous electrolyte can contain from 1% to 90% by mass of chain carboxylic acid esters. Among chain carboxylic acid esters, methyl acetate has a particularly low viscosity. Therefore, methyl acetate can constitute at least 90% by mass of the chain carboxylic acid ester.

[0036] Examples of the nonaqueous solvent include cyclic ethers, chain ethers, nitriles such as acetonitrile, and amides such as dimethylformamide.

[0037] Examples of cyclic ethers include 1,3-dioxolane, 4-methyl-1,3-dioxolane, tetrahydrofuran, 2-methyltetrahydrofuran, propylene oxide, 1,2-butylene oxide, 1,3-dioxane, 1,4-dioxane, 1,3,5-trioxane, furan, 2-methylfuran, 1,8-cineole, and crown ethers.

[0038] Examples of chain ethers include 1,2-dimethoxyethane, dimethyl ether, ethyl ether, dipropyl ether, diisopropyl ether, dibutyl ether, dihexyl ether, ethyl vinyl ether, butyl vinyl ether, methylphenyl ether, ethylphenyl ether, butylphenyl ether, pentylphenyl ether, methoxytoluene, benzyl ethyl ether, diphenyl ether, dibenzyl ether, o-dimethoxybenzene, 1,2-diethoxyethane, 1,2-dibutoxyethane, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol dibutyl ether, 1,1-dimethoxymethane, 1,1-diethoxyethane, triethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether.

[0039] These solvents may be fluorinated solvents in which a portion of hydrogen atoms are substituted with fluorine atoms. Fluoroethylene carbonate (FEC) can be used as the fluorinated solvent.

[0040] As lithium salts, for example, lithium salts containing chloric acid (LiClO4, LiAlCl4, LiB 10 Cl 10 etc.), lithium salts of fluorinated acids (LiPF6, LiPF2O2, LiBF4, LiSbF6, LiAsF6, LiCF3SO3, LiCF3CO2, etc.), lithium salts of fluorinated acid imides (LiN(FSO2)2, LiN(CF3SO2)2, LiN(CF3SO2)(C4F9SO2), LiN(C2F5SO2)2, etc.), lithium halides (LiCl, LiBr, LiI, etc.). The lithium salts may be used alone or in combination of two or more.

[0041] The concentration of the lithium salt in the non-aqueous electrolyte solution can be 0.5 mol / L or more and 2 mol / L or less, and can be 1 mol / L or more and 1.5 mol / L or less. By controlling the lithium salt concentration within the above range, a non-aqueous electrolyte solution having excellent ion conductivity and low viscosity can be obtained.

[0042] Examples of additives other than the alkoxysilyl compound include 1,3-propane sultone, toluenesulfonate, cyclohexylbenzene, biphenyl, diphenyl ether, and fluorobenzene.

[0043] (Non-aqueous electrolyte secondary battery)

[0044] The non-aqueous electrolyte secondary battery disclosed herein includes a negative electrode, a positive electrode, and the non-aqueous electrolyte described above.

[0045] (negative electrode)

[0046] The negative electrode comprises, for example, a negative electrode current collector and a negative electrode mixture layer formed on the surface of the negative electrode current collector. The negative electrode mixture layer contains a negative electrode active material as an essential component and may also contain optional components such as a binder, a conductive material, and a thickener. These optional components, such as the binder, the conductive material, and the thickener, can each utilize a known material.

[0047] The negative electrode mixture layer can be formed, for example, by applying a negative electrode slurry containing a negative electrode mixture containing a negative electrode active material and predetermined optional components dispersed in a dispersion medium to the surface of a negative electrode current collector and drying the slurry. The dried coating can be rolled as needed. The negative electrode mixture layer can be formed on one surface or both surfaces of the negative electrode current collector.

[0048] The negative electrode active material contains a material containing silicon. Silicon-containing materials are sometimes referred to as alloy materials. Here, alloy materials refer to materials containing an element capable of forming an alloy with lithium. Examples of elements capable of forming an alloy with lithium include silicon and tin, with silicon (Si) being particularly desirable.

[0049] The material containing silicon may be a silicon alloy, a silicon compound, or a composite material. Ideally, a composite material comprising a lithium ion conductive phase and silicon particles dispersed in the lithium ion conductive phase is used. For example, a silicon oxide phase, a silicate phase, or a carbon phase may be used as the lithium ion conductive phase. Silicon oxide phases have a relatively high irreversible capacity. On the other hand, silicate phases are preferred due to their low irreversible capacity.

[0050] The main component (e.g., 95-100% by mass) of the silicon oxide phase may be silicon dioxide. The overall composition of the composite material comprising the silicon oxide phase and silicon particles dispersed therein may be represented by SiO x Indicates. SiO x It has a structure in which fine particles of silicon are dispersed in amorphous SiO 2. The content ratio x of oxygen relative to silicon is, for example, 0.5≤x<2.0, and more preferably 0.8≤x≤1.5.

[0051] The silicate phase may, for example, contain at least one selected from the group consisting of Group 1 elements and Group 2 elements of the long-period form of the periodic table. As the Group 1 elements and Group 2 elements of the long-period form of the periodic table, for example, lithium (Li), potassium (K), sodium (Na), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), etc. can be used. As other elements, aluminum (Al), boron (B), lanthanum (La), phosphorus (P), zirconium (Zr), titanium (Ti), etc. can be contained. Among them, from the aspect of small irreversible capacity and high initial charge-discharge efficiency, a silicate phase containing lithium (hereinafter, also referred to as a lithium silicate phase) is preferred.

[0052] The lithium silicate phase only needs to be an oxide phase containing lithium (Li), silicon (Si), and oxygen (O), and other elements can be contained. 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 can have a composition represented by the formula: Li 2z SiO 2+z (0 < z < 2). z preferably satisfies the relationship of 0 < z < 1, and more preferably z = 1 / 2. As elements other than Li, Si, and O that can be contained in the lithium silicate phase, for example, iron (Fe), chromium (Cr), nickel (Ni), manganese (Mn), copper (Cu), molybdenum (Mo), zinc (Zn), aluminum (Al), etc. can be cited.

[0053] The carbon phase may, for example, be composed of amorphous carbon with low crystallinity (i.e., non-crystalline carbon). The amorphous carbon can be, for example, hard carbon, soft carbon, or other substances.

[0054] In addition to the material containing silicon element, the negative electrode active material can also contain a material that electrochemically stores and releases lithium ions, lithium metal, lithium alloy, etc. As the material that electrochemically stores and releases lithium ions, a carbon material is preferred. As the carbon material, graphite, easily graphitizable carbon (soft carbon), difficult-to-graphitize carbon (hard carbon), etc. can be exemplified. Among them, graphite with excellent charge-discharge stability and less irreversible capacity is preferred.

[0055] In the negative electrode current collector, for example, a metal sheet or metal foil is used. As the material of the negative electrode current collector, stainless steel, nickel, nickel alloy, copper, copper alloy, etc. can be exemplified.

[0056] (Positive electrode)

[0057] The positive electrode, for example, includes a positive electrode current collector and a positive electrode mixture layer formed on the surface of the positive electrode current collector. The positive electrode mixture layer contains a positive electrode active material as an essential component and may contain optional components such as a binder material, a conductive material, a thickening material, etc. Known materials can be used for each of the optional components such as the binder material, the conductive material, and the thickening material.

[0058] The positive electrode mixture layer can be formed, for example, by coating a positive electrode paste in which a positive electrode mixture containing a positive electrode active material and a prescribed optional component is dispersed in a dispersion medium on the surface of the positive electrode current collector and drying it. The dried coating film can be calendered as needed. The positive electrode mixture layer can be formed on one surface of the positive electrode current collector or on both surfaces.

[0059] The positive electrode active material, for example, contains a lithium-containing composite oxide. The lithium-containing composite oxide is not particularly limited, and preferably has a layered rock salt-type crystal structure containing lithium and a transition metal. Specifically, the lithium-containing composite oxide can be, for example, Li a Ni 1-x-y Co x M y O2 (where 0 < a ≤ 1.2, 0 ≤ x ≤ 0.1, 0 ≤ y ≤ 0.1, 0 < x + y ≤ 0.1, and M is at least one selected from the group consisting of Na, Mg, Sc, Y, Mn, Fe, Cu, Zn, Al, Cr, Pb, Sb, and B). From the viewpoint of the stability of the crystal structure, Al can be included as M. It should be noted that the value of a representing the molar ratio of lithium increases or decreases according to charge and discharge. As a specific example, LiNi 0.9 Co 0.05 Al 0.05 O2, LiNi 0.91 Co 0.06 Al 0.03 O_{2}, etc.

[0060] The positive electrode active material (especially the lithium-containing composite oxide) usually has a morphology of secondary particles aggregated from primary particles. The average particle diameter of the positive electrode active material can be, for example, 2 μm or more and 20 μm or less. Here, the average particle diameter refers to the median particle diameter at which the cumulative volume in the volume-based particle size distribution becomes 50%. The volume-based particle size distribution can be measured by a laser diffraction type particle size distribution measuring device.

[0061] A metal sheet or metal foil is used, for example, as the positive electrode current collector. As the material of the positive electrode current collector, stainless steel, aluminum, aluminum alloy, titanium, etc. can be exemplified, for example.

[0062] Examples of conductive materials used in the positive electrode mixture layer and the negative electrode mixture layer include carbon materials such as carbon black (CB), acetylene black (AB), Ketjen black (KB), carbon nanotubes (CNT), and graphite. These materials may be used alone or in combination of two or more.

[0063] Examples of binders used in the positive electrode mixture layer and the negative electrode mixture layer include fluororesins (polytetrafluoroethylene, polyvinylidene fluoride, etc.), polyacrylonitrile (PAN), polyimide resins, acrylic resins, polyolefin resins, etc. These may be used alone or in combination of two or more.

[0064] (Separator)

[0065] A separator is placed between the positive and negative electrodes. The separator has high ion permeability and possesses appropriate mechanical strength and insulation properties. Microporous films, woven fabrics, nonwoven fabrics, and the like can be used as separators. Polyolefins such as polypropylene and polyethylene are preferred materials for the separator.

[0066] As an example of a secondary battery structure, an outer body can be provided with an electrode group in which a positive electrode and a negative electrode are wound with a separator interposed therebetween, and a non-aqueous electrolyte. Alternatively, a stacked electrode group in which a positive electrode and a negative electrode are stacked with a separator interposed therebetween can be used in place of a wound electrode group. Non-aqueous electrolyte secondary batteries can be in any form, such as cylindrical, rectangular, coin-shaped, button-shaped, or sheet-shaped (laminated).

[0067] Below, refer to Figure 1 and Figure 2 , while describing a non-aqueous electrolyte secondary battery according to one embodiment of the present disclosure. Figure 1 This is a partially cutaway plan view schematically showing an example of the structure of a non-aqueous electrolyte secondary battery. Figure 2 for Figure 1 Cross-sectional view on line X-X'.

[0068] like Figure 1 and Figure 2 As shown, the nonaqueous electrolyte secondary battery 100 is a sheet-type battery including an electrode plate assembly 4 and an exterior case 5 that houses the electrode plate assembly 4 .

[0069] The electrode plate assembly 4 is a structure in which a positive electrode 10, a separator 30, and a negative electrode 20 are stacked in this order, with the positive electrode 10 and the negative electrode 20 facing each other with the separator 30 interposed therebetween.

[0070] The positive electrode 10 includes a positive electrode active material layer 1a and a positive electrode current collector 1b. The positive electrode active material layer 1a is formed on the surface of the positive electrode current collector 1b.

[0071] The negative electrode 20 includes a negative electrode mixture layer 2a and a negative electrode current collector 2b. The negative electrode mixture layer 2a is formed on the surface of the negative electrode current collector 2b.

[0072] A negative electrode tab lead 1c is connected to the negative electrode current collector 1b, and a negative electrode tab lead 2c is connected to the negative electrode current collector 2b. The positive electrode tab lead 1c and the negative electrode tab lead 2c extend outside the outer casing 5.

[0073] The positive electrode tab lead 1 c and the outer case 5 and the negative electrode tab lead 2 c and the outer case 5 are insulated by insulating tab films 6 , respectively.

[0074] 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.

[0075] Example 1

[0076] (1) Preparation of negative electrode

[0077] SiO x (x=1) (Shin-Etsu Chemical Co., Ltd., KSC1064) and aqueous solution of graphite and polyacrylamide (binder) with SiO x Graphite: polyacrylamide were mixed to a mass ratio of 75:15:10, and water was added and stirred to prepare a negative electrode slurry. The negative electrode slurry was then applied to one side of a negative electrode current collector (electrolytic copper foil) to form a coating. After the coating dried, the negative electrode current collector and the coating were rolled using a calendering roller to obtain a negative electrode having a negative electrode mixture layer.

[0078] Cut the negative electrode Figure 3 The shape of (a) was obtained to obtain the negative electrode 20 for evaluation. Figure 3 In (a), the 60mm×40mm area is the area that functions as the negative electrode, and the 10mm×10mm protrusion is the connection area with the tab lead 2c. Figure 3 As shown in (b), the negative electrode mixture layer 2a formed on the connection area is cut away to expose the negative electrode current collector 2b. Figure 3 As shown in (c), the exposed portion of the negative electrode current collector 2b is connected to the negative electrode tab lead 2c, and a predetermined area around the negative electrode tab lead 2c is covered with the insulating tab film 6.

[0079] (2) Fabrication of the electrode

[0080] A counter electrode was prepared by adhering a lithium metal foil to one side of an electrolytic copper foil (current collector).

[0081] The counter electrode is cut into the same shape as the negative electrode. The lithium metal foil formed on the connection area formed in the same manner as the negative electrode is peeled off to expose the current collector. Then, similarly to the negative electrode, the exposed portion of the current collector is connected to the tab lead. A predetermined area around the tab lead is covered with an insulating tab film.

[0082] (3) Preparation of non-aqueous electrolyte

[0083] A non-aqueous electrolyte solution was prepared by dissolving LiPF6 at a concentration of 1 mol / L in a mixed solvent of fluoroethylene carbonate (FEC) and dimethyl carbonate (DMC) at a volume ratio of 20:80. To the non-aqueous electrolyte solution, 0.25% by mass of bis(triethoxysilylpropyl)tetrasulfide (TESPT), represented by the following formula (1-1), was added.

[0084]

[0085] (4) Preparation of battery cells for evaluation

[0086] Using the above-mentioned negative electrode and counter electrode for evaluation, a battery cell with a standard design capacity of 114 mAh for the negative electrode was produced. First, the negative electrode and the counter electrode were placed opposite each other with two polyethylene separators (15 μm thick) having an aramid coating so that the negative electrode mixture layer overlapped with the lithium metal foil to obtain a plate group. Next, the Al laminate film (100 μm thick) cut into a rectangle was folded in half, and the ends of the long sides were heat-sealed at 230°C to form a tube. After that, the prepared plate group was placed into the tube from one of the short sides, and the end faces of the Al laminate film were aligned with the positions of the hot-melt resins of each tab lead and heat-sealed at 230°C. Next, 1.2 cm of non-aqueous electrolyte was injected from the unheat-sealed short side of the tube. 3 After injection, the negative electrode mixture layer was allowed to stand for 3 minutes under a reduced pressure of 0.02 MPa, then returned to atmospheric pressure. This operation was repeated twice to allow the non-aqueous electrolyte to penetrate the negative electrode mixture layer. Finally, the end face of the Al laminate film on the injection side was heat-sealed at 230°C to obtain evaluation cell A1. The evaluation cell was fabricated in a dry air atmosphere with a dew point below -60°C.

[0087] (5) Battery evaluation

[0088] The battery cell for evaluation was clamped by a pair of 10×5 cm stainless steel (6 mm thick) clamps and fixed under pressure at 3.2 MPa.

[0089] <1st Cycle>

[0090] In a 25°C thermostat, the negative electrode was charged with lithium at a constant current of 0.05C (1C is the current value that discharges the designed capacity in 1 hour) for 2 hours, followed by a 12-hour rest. Next, the negative electrode was further charged with lithium at a constant current of 0.05C until the cell voltage reached 0.01V, followed by a 20-minute rest. Next, the negative electrode was discharged with a constant current of 0.05C until the cell voltage reached 1.5V, followed by a 20-minute rest.

[0091] <Cycle 2-3>

[0092] Next, the negative electrode was charged with lithium at a constant current of 0.05 C until the cell voltage reached 0.01 V, followed by a 20-minute rest. Next, the negative electrode was discharged with a constant current of 0.05 C until the cell voltage reached 1.5 V, followed by a 20-minute rest.

[0093] <Cycles 4-50>

[0094] The negative electrode was charged with lithium at a constant current of 0.3C until the cell voltage reached 0.01V, followed by a rest period of 20 minutes. The negative electrode was then discharged with a constant current of 0.3C until the cell voltage reached 1.5V, followed by a rest period of 20 minutes, and the cycle was repeated.

[0095] The ratio of the capacity obtained by lithium discharge in the 50th cycle to the capacity obtained by lithium discharge in the 1st cycle was determined as the 50-cycle capacity retention rate.

[0096] Examples 2-3

[0097] In the preparation of the non-aqueous electrolyte, except that the content of TESPT added to the non-aqueous electrolyte was changed as shown in Table 1, evaluation cells A2 to A3 were prepared in the same manner as in Example 1 and evaluated in the same manner.

[0098] Examples 4 to 6

[0099] In the preparation of the non-aqueous electrolyte, except that bis(triethoxysilylpropyl) disulfide (TESPD) represented by the following formula (1-2) was added to the non-aqueous electrolyte in the amount shown in Table 1 instead of TESPT, evaluation cells A4 to A6 were prepared in the same manner as in Example 1 and evaluated in the same manner.

[0100]

[0101] Comparative Example 1

[0102] In the preparation of the non-aqueous electrolyte, a battery cell B1 for evaluation was prepared in the same manner as in Example 1, except that vinyl tris(2-methoxyethoxy)silane (VTMS) represented by the following formula (2) was added to the non-aqueous electrolyte in the amount shown in Table 1 instead of TESPT. The battery cell was evaluated in the same manner as in Example 1. VTMS is an additive used in Non-Patent Document 1.

[0103]

[0104] Comparative Example 2

[0105] An evaluation cell B2 was produced in the same manner as in Example 1, except that TESPT was not added in the preparation of the non-aqueous electrolyte, and the evaluation was performed in the same manner.

[0106] [Table 1]

[0107]

[0108] Figure 4 2 shows the relationship between the number of charge and discharge cycles and the capacity retention rate of the evaluation battery cells A2, A5, B1, and B2.

[0109] According to Table 1 and Figure 4 It can be understood that when TESPT, which is an alkoxysilyl compound represented by formula (1-1), and TESPD, which is an alkoxysilyl compound represented by formula (1-2), are added to the non-aqueous electrolyte, the capacity retention rate is improved.

[0110] On the other hand, Figure 4 As shown, the VTMS used in Non-Patent Document 1 cannot improve the capacity maintenance rate.

[0111] Industrial applicability

[0112] The non-aqueous electrolyte additive disclosed herein is suitable for use in a non-aqueous electrolyte secondary battery in which the negative electrode active material contains a material containing silicon.

[0113] Description of Reference Numerals

[0114] 1a Positive electrode mixture layer

[0115] 1b Positive electrode current collector

[0116] 1c positive electrode tab lead

[0117] 2a Negative electrode mixture layer

[0118] 2b Negative electrode current collector

[0119] 2c negative electrode tab lead

[0120] 4-plate group

[0121] 5 Exterior shell

[0122] 6 Insulating tab film

[0123] 10 positive electrode

[0124] 20 negative electrode

[0125] 30 dividers

[0126] 100 lithium-ion secondary batteries

Claims

1. An additive for a non-aqueous electrolyte, comprising a bisalkoxysilyl compound, in, The bisalkoxysilyl compound is a bis(alkoxysilylalkyl) sulfide represented by the general formula (1): R1 is C x1 H 2x1 S z represented by, x1 and z are each an integer greater than or equal to 1, At least one of R2 to R4 is selected from an alkoxy group having 2 to 6 carbon atoms and an alkyl group represented by -O-(C x2 H 2x2+1 O y2 ), wherein x2 is an integer greater than or equal to 1, and y2 is an integer greater than or equal to 1, At least one of R5 to R7 is selected from an alkoxy group having 2 to 6 carbon atoms and an alkyl group represented by -O-(C x3 H 2x3+1 O y3 ), wherein x3 is an integer greater than or equal to 1, and y3 is an integer greater than or equal to 1, The rest of R2 to R7 are independently C x4 H 2x4+1 O y4 The alkyl group or oxyalkyl group represented by x4 is an integer greater than or equal to 1, and y4 is an integer greater than or equal to 0.

2. The non-aqueous electrolyte additive according to claim 1, wherein R1 uses R11-S z -R12 means, R11 and R12 are each an alkylene group having 1 or more carbon atoms.

3. The additive for non-aqueous electrolyte according to claim 2, wherein The bis(alkoxysilylalkyl)sulfide is a bis(trialkoxysilyl C 1-6 Alkyl)S 1-6 sulfide.

4. The additive for non-aqueous electrolyte according to claim 3, wherein The bis(trialkoxysilyl C 1-6 Alkyl)S 1-6 The sulfide is at least one selected from the group consisting of bis(triethoxysilylpropyl)sulfide, bis(triethoxysilylpropyl)disulfide, bis(triethoxysilylpropyl)trisulfide, and bis(triethoxysilylpropyl)tetrasulfide. 5 . A non-aqueous electrolyte solution comprising: a non-aqueous solvent; a salt dissolved in the non-aqueous solvent; and the additive for a non-aqueous electrolyte solution according to claim 1 . The non-aqueous electrolyte according to claim 5 , wherein The concentration of the non-aqueous electrolyte additive is 5% by mass or less.

7. The non-aqueous electrolyte according to claim 6, wherein The concentration of the non-aqueous electrolyte additive is 0.05% by mass or more.

8. A non-aqueous electrolyte secondary battery comprising: a negative electrode having a negative electrode mixture layer, a positive electrode, and the non-aqueous electrolyte according to any one of claims 5 to 7. The negative electrode mixture layer contains a negative electrode active material. The negative electrode active material contains a material containing silicon.

9. The non-aqueous electrolyte secondary battery according to claim 8, wherein The material containing silicon is a composite material. The composite material comprises a lithium ion conductive phase and silicon particles dispersed in the lithium ion conductive phase.

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