Non-aqueous electrolyte secondary battery

Abstract

This nonaqueous electrolytic solution additive contains a bisalkoxysilyl compound. The bisalkoxysilyl compound has two silyl groups bonded to each other with a chain including a sulfide group. The two silyl groups each have at least one selected from the group consisting of alkoxy groups and oxy-alkyl groups. The oxy-alkyl groups are represented by -O-(CxH2x+1Oy), where x represents an integer of 1 or greater and y represents an integer of 1 or greater.

Description

Technical Field

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

Background Art

[0002] Materials containing silicon elements are promising as high-capacity negative electrode materials for secondary batteries. However, since materials containing silicon elements have large expansion and contraction during charge and discharge, they are likely to induce side reactions and the capacity retention rate in charge and discharge cycles is likely to decrease.

[0003] Non-Patent Document 1 reports that adding a vinyl group-containing silane coupling agent to the electrolyte of a single-pole battery using an Si / C composite improves the capacity retention rate in charge and discharge cycles.

Prior Art Documents

Non-Patent Documents

[0004]

Non-Patent Document 1

Summary of the Invention

[0005] In the proposal of Non-Patent Document 1, it is difficult to stably improve the capacity retention rate in charge and discharge cycles.

[0006] One aspect of the present disclosure relates to an additive for a non-aqueous electrolyte, which contains a bisalkoxysilyl compound, the bisalkoxysilyl compound has two silyl groups linked by a chain containing a sulfide 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 represented by -O-(C x H 2x+1 O y ), where x is an integer of 1 or more and y is an integer of 1 or more.

[0007] Another aspect of the present disclosure relates to a non-aqueous electrolyte comprising a non-aqueous solvent, a salt dissolved in the non-aqueous solvent, and an additive for the non-aqueous electrolyte.

[0008] Still another aspect of the present disclosure relates to a non-aqueous electrolyte secondary battery including a negative electrode having a negative electrode active material layer, a positive electrode, and the non-aqueous electrolyte, wherein the negative electrode active material layer contains a negative electrode active material, and the negative electrode active material contains a material containing a silicon element.

[0009] According to the present disclosure, when the negative electrode active material contains a material containing a silicon element, the capacity retention rate in the charge-discharge cycle of the non-aqueous electrolyte secondary battery can be stably improved.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Figure 3

Figure 4

Modes for Carrying Out the Invention

[0011] (Additive for Non-aqueous Electrolyte) The additive for a non-aqueous electrolyte according to an embodiment of the present disclosure contains a bis(alkoxysilyl) compound. The bis(alkoxysilyl) compound has two silyl groups linked by a chain containing a sulfide group. Each of the two silyl groups has at least one selected from the group consisting of an alkoxy group and an oxyalkyl group, and the oxyalkyl group is represented by -O-(C x H 2x+1 O y ), where x is an integer of 1 or more, and y is an integer of 1 or more.

[0012] In the above configuration, the alkoxy group or oxyalkyl group of each silyl group is considered to form an X-O-Si bond with the surface of the material containing a silicon element. Here, X represents the surface of the material containing a 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 a silicon element. By each of the alkoxy group or oxyalkyl group forming a bond with the surface of the material containing a silicon element, the surface of the material containing a silicon element is covered with a bissilyl sulfide structure having stable siloxane bonds at both ends. That is, the surface of the material containing a silicon element is covered with a film containing a bissilyl sulfide structure (hereinafter, also referred to as an SSS film). The SSS film has high elasticity, is stable against reversible elastic deformation, and is less likely to be damaged even when repeating charge and discharge cycles. As a result, side reactions at the negative electrode are suppressed, and the capacity retention rate in the charge and discharge cycles is stably improved.

[0013] The bisalkoxysilyl compound may be a bis(alkoxysilylalkyl) sulfide represented by the general formula (1):

[0014]

Chemical formula

[0015] Here, R1 is a sulfide group represented by C x1 H 2x1 S z and x1 and z are each an integer of 1 or more. At least one of R2 to R4 is at least one selected from the group consisting of an alkoxy group having 1 to 6 carbon atoms and an oxyalkyl group represented by -O-(C x2 H 2x2+1 O y2 ), x2 is an integer of 1 or more, and y2 is at least one selected from the group consisting of oxyalkyl groups which are integers of 1 or more. At least one of R5 to R7 is at least one selected from the group consisting of an alkoxy group having 1 to 6 carbon atoms and an oxyalkyl group represented by -O-(C x3 H 2x3+1 O y3) represented by x3 is an integer of 1 or more, and at least one selected from the group consisting of oxyalkyl groups where y3 is an integer of 1 or more. The rest of R2 to R7 are each independently C x4 H 2x4+1 O y4 represented by x4 is an integer of 1 or more, and is an alkyl group or an oxyalkyl group where y4 is an integer of 0 or more. However, the oxyalkyl group is a group other than an alkoxy group.

[0016] The alkoxy group or oxyalkyl group contained in R2 to R4 and R5 to R7 each forms an X-O-Si-R1 bond with the surface of the material containing a silicon element, and the surface of the material containing a silicon element is covered with an Si-R1-Si structure having stable siloxane bonds at both ends. That is, the surface of the material containing a silicon element is covered with an SSS film containing an Si-R1-Si structure.

[0017] In formula (1), C x1 H 2x1 S z The sulfide group (R1) represented by may have a structure represented by R11-S z -R12. Here, R11 and R12 are each independently an alkylene group having 1 or more carbon atoms. Such R1 is considered to be excellent in flexibility, have a large electron shielding effect due to the S z structure, and have a greater effect of suppressing side reactions.

[0018] The larger the number of carbon atoms of R11 and R12, the better the flexibility, so the reversible deformation of the SSS film becomes easier. However, if the number of carbon atoms of R11 and R12 becomes excessively large, the alkylene chain becomes too long, the density of the SSS film decreases, and the effect of suppressing side reactions is considered to decrease. Therefore, it is desirable that the number of carbon atoms of R11 and R12 is 1 to 6, and more preferably 2 to 4. Bis(alkoxysilylalkyl) sulfide is desirably bis(alkoxysilyl C 1-6 alkyl) sulfide, and may be bis(alkoxysilyl C 2-4 alkyl) sulfide.

[0019] In addition, the S that constitutes R1 z groups are more flexible as the number of consecutive sulfur atoms increases, making it easier for the SSS film to deform reversibly. However, if the number of sulfur atoms is excessively large, the density of the SSS film decreases and the S z groups themselves may cause side reactions. Therefore, it is desirable that the number of sulfur atoms in the S z groups be 1 to 6, and more preferably 2 to 4. That is, bis(alkoxysilylalkyl) sulfide is preferably bis(alkoxysilyl C 1-6 alkyl) S 1-6 sulfide, and may also be bis(alkoxysilyl C 2-4 alkyl) S 2-4 sulfide.

[0020] At least one of R2 to R4 is an alkoxy group having 1 to 6 carbon atoms and -O-(C x2 H 2x2+1 O y2 ) represented by, x2 may be an integer of 1 to 6, and at least one selected from the group consisting of oxyalkyl groups where y2 is 1 or 2, and at least one of R5 to R7 is an alkoxy group having 1 to 6 carbon atoms and -O-(C x3 H 2x3+1 O y3 ) represented by, x3 is an integer of 1 to 6, and may be at least one selected from the group consisting of oxyalkyl groups where y3 is 1 or 2. From the viewpoint of enhancing the reactivity with the surface of the material containing silicon element, the alkoxy group or oxyalkyl group may be smaller, and the carbon number of the alkoxy group or oxyalkyl group may be, for example, 1 to 3.

[0021] The rest of R2 to R7 are each independently C x4 H 2x4+1 O y4 represented by, x4 may be an integer of 1 to 6, and may be an alkyl group or oxyalkyl group where y4 is an integer of 0 or more and 2 or less. From the viewpoint of reducing steric hindrance during the reaction, C x4 H 2x4+1 O y4The number of carbon atoms in the group represented by may be from 1 to 6, or may be from 1 to 3. R2 to R4 are each independent, and all of R2 to R4 may have the same number of carbon atoms, may all have different numbers of carbon atoms, or two of R2 to R4 may have the same number of carbon atoms. Similarly, R5 to R7 are each independent, and all of R5 to R7 may have the same number of carbon atoms, may all have different numbers of carbon atoms, or two of R5 to R7 may have the same number of carbon atoms.

[0022] The two alkoxysilyl groups (R2R3R4Si- or R5R6R7Si-) linked to R1 may be the same as or different from each other. However, in order to enhance the symmetry of the structure of the SSS film and obtain a more stable structure, the two alkoxysilyl groups linked to R1 may have the same structure.

[0023] Bis(trialkoxysilyl C 1-6 alkyl)S 1-6 Among bis(alkoxysilyl) sulfides, those that are easily available include at least one selected from the group consisting of bis(triethoxysilylpropyl) sulfide, bis(triethoxysilylpropyl) disulfide, bis(triethoxysilylpropyl) trisulfide, and bis(triethoxysilylpropyl) tetrasulfide.

[0024] (Non-aqueous electrolyte) The non-aqueous electrolyte contains a non-aqueous solvent, a salt (solute) dissolved in the non-aqueous solvent, and the additive for the non-aqueous electrolyte. The salt (solute) is an electrolyte salt that dissociates into ions in the non-aqueous solvent. When the non-aqueous electrolyte is used in a lithium-ion secondary battery, the salt contains at least a lithium salt. Components of the non-aqueous electrolyte other than the non-aqueous solvent and the salt are additives, and at least a part of the additives is the above bisalkoxysilyl compound.

[0025] The concentration of the bis(alkoxysilyl) compound in the non-aqueous electrolyte may be, for example, 5% by mass or less, 2% by mass or less, or 1% by mass or less. Within this range, regardless of the amount of the material containing silicon element included in the negative electrode active material, it is sufficient to form a good and appropriate SSS film. If the concentration of the bis(alkoxysilyl) compound in the non-aqueous electrolyte is, for example, 0.05% by mass or more, a considerable SSS film is considered to be formed, and a significant effect of improving the capacity retention rate in the charge-discharge cycles of the non-aqueous electrolyte secondary battery can be obtained.

[0026] However, since the bis(alkoxysilyl) compound reacts in the non-aqueous electrolyte secondary battery, the concentration in the non-aqueous electrolyte decreases. Therefore, in the completed non-aqueous electrolyte secondary battery or the non-aqueous electrolyte secondary battery distributed in the market, it is sufficient that the bis(alkoxysilyl) compound remains in the non-aqueous electrolyte taken out after decomposition above the detection limit.

[0027] As the non-aqueous solvent, for example, cyclic carbonates, chain carbonates, cyclic carboxylic acid esters, chain carboxylic acid esters, etc. are used. Examples of the cyclic carbonate include propylene carbonate (PC), ethylene carbonate (EC), vinylene carbonate (VC), etc. Examples of the chain carbonate include diethyl carbonate (DEC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), etc. Examples of the cyclic carboxylic acid ester include γ-butyrolactone (GBL), γ-valerolactone (GVL), etc. Examples of the chain carboxylic acid ester include methyl acetate, ethyl acetate, propyl acetate, methyl propionate (MP), ethyl propionate (EP), etc. The non-aqueous solvent may be used alone or in combination of two or more.

[0028] Among them, the chain carboxylic acid ester is suitable for preparing a non-aqueous electrolyte with low viscosity. Therefore, the non-aqueous electrolyte may contain 1% by mass or more and 90% by mass or less of the chain carboxylic acid ester. Among the chain carboxylic acid esters, methyl acetate has particularly low viscosity. Therefore, 90% by mass or more of the chain carboxylic acid ester may be methyl acetate.

[0029] Examples of the non-aqueous solvent further include cyclic ethers, chain ethers, nitriles such as acetonitrile, and amides such as dimethylformamide.

[0030] Examples of the cyclic ether 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, crown ether, and the like.

[0031] Examples of the chain ether include 1,2-dimethoxyethane, dimethyl ether, diethyl ether, dipropyl ether, diisopropyl ether, dibutyl ether, dihexyl ether, ethyl vinyl ether, butyl vinyl ether, methyl phenyl ether, ethyl phenyl ether, butyl phenyl ether, pentyl phenyl 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, tetraethylene glycol dimethyl ether, and the like.

[0032] These solvents may be fluorinated solvents in which some of the hydrogen atoms are substituted with fluorine atoms. As the fluorinated solvent, fluoroethylene carbonate (FEC) may be used.

[0033] Examples of the lithium salt include lithium salts of chlorine-containing acids (such as LiClO4, LiAlCl4, LiB 10 Cl 10 etc.), lithium salts of fluorine-containing acids (such as LiPF6, LiPF2O2, LiBF4, LiSbF6, LiAsF6, LiCF3SO3, LiCF3CO2, etc.), lithium salts of fluorine-containing acid imides (such as LiN(FSO2)2, LiN(CF3SO2)2, LiN(CF3SO2)(C4F9SO2), LiN(C2F5SO2)2, etc.), lithium halides (such as LiCl, LiBr, LiI, etc.), and the like. The lithium salt may be used alone or in combination of two or more.

[0034] The concentration of the lithium salt in the non-aqueous electrolyte may be 0.5 mol / liter or more and 2 mol / liter or less, or may be 1 mol / liter or more and 1.5 mol / liter or less. By controlling the lithium salt concentration within the above range, a non-aqueous electrolyte having excellent ionic conductivity and low viscosity can be obtained.

[0035] Examples of the additives other than the alkoxysilyl compound include 1,3-propanesultone, methylbenzenesulfonate, cyclohexylbenzene, biphenyl, diphenyl ether, fluorobenzene, and the like.

[0036] (Non-aqueous electrolyte secondary battery) The non-aqueous electrolyte secondary battery according to the present disclosure includes a negative electrode, a positive electrode, and the above non-aqueous electrolyte.

[0037] (Negative electrode) The negative electrode includes, 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 contain optional components such as a binder, a conductive material, and a thickening material. Known materials can be used for the optional components such as the binder, the conductive material, and the thickening material, respectively.

[0038] The negative electrode mixture layer can be formed, for example, by applying a negative electrode slurry in which a negative electrode mixture containing a negative electrode active material and a predetermined optional component is dispersed in a dispersion medium onto the surface of a negative electrode current collector and drying it. The dried coating film may be rolled if necessary. The negative electrode mixture layer may be formed on one surface of the negative electrode current collector or on both surfaces.

[0039] The negative electrode active material contains a material containing silicon element. The material containing silicon element may be treated as a kind of alloy-based material. Here, the alloy-based material refers to a material containing an element capable of forming an alloy with lithium. Examples of elements capable of forming an alloy with lithium include silicon and tin, and silicon (Si) is particularly promising.

[0040] The material containing silicon may be a silicon alloy, a silicon compound, etc., or may be a composite material. Among them, a composite material containing a lithium ion conductive phase and silicon particles dispersed in the lithium ion conductive phase is promising. As the lithium ion conductive phase, for example, a silicon oxide phase, a silicate phase, a carbon phase, etc. can be used. The silicon oxide phase is a material with a relatively large irreversible capacity. On the other hand, the silicate phase is preferable in that it has a small irreversible capacity.

[0041] The main component (for example, 95 to 100% by mass) of the silicon oxide phase may be silicon dioxide. The composition of the composite material containing the silicon oxide phase and silicon particles dispersed therein can be represented as SiO x for the whole. SiO x has a structure in which fine particles of silicon are dispersed in amorphous SiO2. The content ratio x of oxygen to silicon is, for example, 0.5 ≦ x < 2.0, and 0.8 ≦ x ≦ 1.5 is more preferable.

[0042] The silicate phase may contain, for example, at least one selected from the group consisting of Group 1 elements and Group 2 elements of the long-period periodic table. As the Group 1 elements and Group 2 elements of the long-period periodic table, for example, lithium (Li), potassium (K), sodium (Na), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), etc. can be used. Other elements may include aluminum (Al), boron (B), lanthanum (La), phosphorus (P), zirconium (Zr), titanium (Ti), etc. Among them, a silicate phase containing lithium (hereinafter also referred to as a lithium silicate phase) is preferable because it has a small irreversible capacity and high initial charge-discharge efficiency.

[0043] 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 a composition represented by the formula: Li 2z SiO 2+z (0 < z < 2). z preferably satisfies the relationship 0 < z < 1, and z = 1 / 2 is more preferable. Examples of elements other than Li, Si, and O that may be contained in the lithium silicate phase include iron (Fe), chromium (Cr), nickel (Ni), manganese (Mn), copper (Cu), molybdenum (Mo), zinc (Zn), aluminum (Al), etc.

[0044] The carbon phase may be composed of, for example, low-crystalline amorphous carbon (i.e., amorphous carbon). The amorphous carbon may be, for example, hard carbon, soft carbon, or others.

[0045] In addition to materials containing silicon element, the negative electrode active material may include materials that electrochemically intercalate and deintercalate lithium ions, lithium metal, lithium alloys, and the like. As the material that electrochemically intercalates and deintercalates lithium ions, a carbon material is preferred. Examples of the carbon material include graphite, graphitizable carbon (soft carbon), non-graphitizable carbon (hard carbon), and the like. Among them, graphite, which is excellent in charge-discharge stability and has a small irreversible capacity, is preferred.

[0046] For the negative electrode current collector, for example, a metal sheet or a metal foil is used. Examples of the material of the negative electrode current collector include stainless steel, nickel, nickel alloy, copper, copper alloy, and the like.

[0047] (Positive Electrode) The positive electrode includes, for example, 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, a conductive material, and a thickening material. Known materials can be used for the optional components such as the binder, the conductive material, and the thickening material.

[0048] The positive electrode mixture layer can be formed, for example, by applying a positive electrode slurry in which a positive electrode mixture containing a positive electrode active material and a predetermined optional component is dispersed in a dispersion medium onto the surface of the positive electrode current collector and drying it. The dried coating film may be rolled if necessary. The positive electrode mixture layer may be formed on one surface of the positive electrode current collector or on both surfaces.

[0049] The positive electrode active material includes, for example, a lithium-containing composite oxide. The lithium-containing composite oxide is not particularly limited, but those having a layered rock salt-type crystal structure containing lithium and a transition metal are promising. Specifically, the lithium-containing composite oxide is, for example, Li a Ni 1-x-y Co x M yO2 (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) may be used. From the perspective of the stability of the crystal structure, M may contain Al. Note that the value of a indicating the molar ratio of lithium increases or decreases during 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 O2, etc. may be mentioned.

[0050] The positive electrode active material (especially the lithium-containing composite oxide) usually has the form of secondary particles in which primary particles are aggregated. The average particle diameter of the positive electrode active material may be, for example, 2 μm or more and 20 μm or less. Here, the average particle diameter refers to the median diameter at which the cumulative volume in the volume-based particle size distribution is 50%. The volume-based particle size distribution can be measured by a laser diffraction type particle size distribution measuring device.

[0051] For the positive electrode current collector, for example, a metal sheet or a metal foil is used. Examples of the material of the positive electrode current collector include stainless steel, aluminum, aluminum alloy, titanium, etc.

[0052] Examples of the conductive material used in the positive electrode binder layer and the negative electrode binder layer include carbon materials such as carbon black (CB), acetylene black (AB), ketjen black (KB), carbon nanotube (CNT), and graphite. These may be used alone or in combination of two or more.

[0053] Examples of the binder used in the positive electrode binder layer and the negative electrode binder layer include fluororesins (such as polytetrafluoroethylene and polyvinylidene fluoride), polyacrylonitrile (PAN), polyimide resin, acrylic resin, polyolefin resin, etc. These may be used alone or in combination of two or more.

[0054] (Separator) A separator is interposed between the positive electrode and the negative electrode. The separator has a high ion permeability and appropriate mechanical strength and insulation. As the separator, a microporous thin film, a woven fabric, a non-woven fabric, etc. can be used. As the material of the separator, polyolefins such as polypropylene and polyethylene are preferable.

[0055] As an example of the structure of the secondary battery, there is a structure in which an electrode group formed by winding a positive electrode and a negative electrode with a separator interposed therebetween and a non-aqueous electrolyte are housed in an exterior body. Alternatively, instead of the wound electrode group, other forms of electrode groups such as a laminated electrode group formed by laminating a positive electrode and a negative electrode with a separator interposed therebetween may be applied. The non-aqueous electrolyte secondary battery may be in any form such as a cylindrical shape, a rectangular shape, a coin shape, a button shape, a sheet shape (laminate shape), etc.

[0056] Hereinafter, with reference to FIGS. 1 and 2, a non-aqueous electrolyte secondary battery according to an embodiment of the present disclosure will be described. FIG. 1 is a partially cutaway plan view schematically showing an example of the structure of the non-aqueous electrolyte secondary battery. FIG. 2 is a cross-sectional view taken along the line X-X' of FIG. 1.

[0057] As shown in FIGS. 1 and 2, the non-aqueous electrolyte secondary battery 100 is a sheet-type battery and includes a plate group 4 and an exterior case 5 that houses the plate group 4.

[0058] The plate group 4 has a structure in which a positive electrode 10, a separator 30, and a negative electrode 20 are laminated in this order, and the positive electrode 10 and the negative electrode 20 face each other with the separator 30 interposed therebetween. Thus, the plate group 4 is formed. The plate group 4 is impregnated with a non-aqueous electrolyte.

[0059] 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.

[0060] The negative electrode 20 includes a negative electrode active material layer 2a and a negative electrode current collector 2b. The negative electrode active material layer 2a is formed on the surface of the negative electrode current collector 2b.

[0061] 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 each extend to the outside of the exterior case 5.

[0062] The space between the positive electrode tab lead 1c and the exterior case 5 and the space between the negative electrode tab lead 2c and the exterior case 5 are each insulated by an insulating tab film 6.

[0063] 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.

[0064] 《Example 1》 (1) Fabrication of negative electrode SiO x (x = 1) (Shin-Etsu Chemical Co., Ltd., KSC1064), graphite, and an aqueous solution of polyacrylamide (binder) were mixed so that the mass ratio of SiOx:graphite:polyacrylamide was 75:15:10, and further water was added and stirred to prepare a negative electrode slurry. Next, the negative electrode slurry was applied to one side of a negative electrode current collector (electrolytic copper foil) to form a coating film. After drying the coating film, the coating film together with the negative electrode current collector was rolled by a rolling roller to obtain a negative electrode having a negative electrode active material layer.

[0065] The negative electrode was cut into the shape shown in Fig. 3(a) to obtain a negative electrode 20 for evaluation. In Fig. 3(a), the region of 60 mm × 40 mm is the region that functions as the negative electrode, and the protruding portion of 10 mm × 10 mm is the connection region with the tab lead 2c. Thereafter, as shown in Fig. 3(b), the negative electrode active material layer 2a formed on the connection region was scraped off to expose the negative electrode current collector 2b. Thereafter, as shown in Fig. 3(c), the exposed portion of the negative electrode current collector 2b was connected to the negative electrode tab lead 2c, and a predetermined region on the outer periphery of the negative electrode tab lead 2c was covered with an insulating tab film 6.

[0066] (2) Fabrication of the counter electrode The counter electrode was fabricated by attaching a lithium metal foil to one side of an electrolytic copper foil (current collector).

[0067] The counter electrode was cut into the same shape as the negative electrode, and the lithium metal foil formed on the connection region formed in the same manner as the negative electrode was peeled off to expose the current collector. Then, the exposed portion of the current collector was connected to the tab lead in the same manner as the negative electrode, and a predetermined region on the outer periphery of the tab lead was covered with an insulating tab film.

[0068] (3) Preparation of the non-aqueous electrolyte A non-aqueous electrolyte was prepared by dissolving LiPF6 at a concentration of 1 mol / L in a mixed solvent of fluoroethylene carbonate (FEC) and dimethyl carbonate (DMC) with a volume ratio of 20:80. 0.25 mass% of bis(triethoxysilylpropyl)tetrasulfide (TESPT) represented by the following formula (1-1) was added to the non-aqueous electrolyte.

[0069] [Chemical formula]

[0070] (4) Fabrication of the evaluation cell Using the above-described evaluation negative electrode and counter electrode, a cell with a designed capacity of 114 mAh under negative electrode regulation was fabricated. First, the negative electrode and the counter electrode were opposed to each other through two polyethylene separators (thickness 15 μm) having an aramid coat so that the negative electrode mixture layer and the lithium metal foil overlapped to obtain a group of electrode plates. Next, a rectangularly cut Al laminate film (thickness 100 μm) was folded in half, and the end portion on the long side was heat-sealed at 230 °C to form a cylinder. Then, the fabricated group of electrode plates was inserted into the cylinder from one of the short sides, and the end face of the Al laminate film was aligned with the position of the heat-sealing resin of each tab lead and heat-sealed at 230 °C. Next, non-aqueous electrolyte was introduced from the unsealed short side of the cylinder at 1.2 cm 3Liquid injection was carried out, and after the liquid injection, the operation of returning to atmospheric pressure after standing for 3 minutes under a reduced pressure of 0.02 MPa was performed twice to impregnate the non-aqueous electrolyte into the negative electrode mixture layer. Finally, the end face of the Al laminate film on the liquid injection side was heat-sealed at 230 °C to obtain Evaluation Cell A1. The production of the evaluation cell was carried out in a dry air atmosphere with a dew point of -60 °C or lower.

[0071] (5) Evaluation of the battery The evaluation cell was sandwiched between a pair of 10×5 cm stainless steel (6 mm thick) clamps and fixed under pressure at 3.2 MPa.

[0072] <First cycle> In a constant temperature bath at 25 °C, lithium was charged to the negative electrode at a constant current of 0.05C (1C is the current value for discharging the designed capacity in 1 hour) over 2 hours, and then left to rest for 12 hours. Next, lithium was further charged to the negative electrode at a constant current of 0.05C until the cell voltage reached 0.01V, and then left to rest for 20 minutes. Next, lithium was discharged from the negative electrode at a constant current of 0.05C until the cell voltage reached 1.5V, and then left to rest for 20 minutes.

[0073] <Second to third cycles> Next, lithium was charged to the negative electrode at a constant current of 0.05C until the cell voltage reached 0.01V, and then left to rest for 20 minutes. Next, lithium was discharged from the negative electrode at a constant current of 0.05C until the cell voltage reached 1.5V, and then left to rest for 20 minutes.

[0074] <Fourth to 50th cycles> The cycle of charging lithium to the negative electrode at a constant current of 0.3C until the cell voltage reached 0.01V, then leaving it to rest for 20 minutes, and then continuously discharging lithium from the negative electrode at a constant current of 0.3C until the cell voltage reached 1.5V and then leaving it to rest for 20 minutes was repeated.

[0075] The ratio of the capacity obtained by lithium discharge in the 50th cycle to the capacity obtained by lithium discharge in the first cycle was determined as the 50-cycle capacity retention rate. The results are shown in Table 1.

[0076] 《Examples 2 to 3》 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.

[0077] 《Examples 4 to 6》 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 content 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.

[0078]

Chemical formula

[0079] 《Comparative Example 1》 In the preparation of the non-aqueous electrolyte, except that vinyltris(2-methoxyethoxy)silane (VTMS) represented by the following formula (2) was added to the non-aqueous electrolyte in the content shown in Table 1 instead of TESPT, evaluation cell B1 was prepared in the same manner as in Example 1 and evaluated in the same manner. Note that VTMS is an additive used in Non-Patent Document 1.

[0080]

Chemical formula

[0081] 《Comparative Example 2》 In the preparation of the non-aqueous electrolyte, except that TESPT was not added, evaluation cell B2 was prepared in the same manner as in Example 1 and evaluated in the same manner.

[0082]

Table 1

[0083] Figure 4 shows the relationship between the number of charge-discharge cycles and the capacity retention rate of evaluation cells A2, A5, B1, and B2.

[0084] From Table 1 and Figure 4, it can be understood that when TESPT, which is an alkoxysilyl compound represented by the formula (1-1), and TESPD, which is an alkoxysilyl compound represented by the formula (1-2), are added to the non-aqueous electrolyte, the capacity retention rate is improved.

[0085] On the other hand, as shown in Figure 4, with VTMS used in Non-Patent Document 1, the capacity retention rate could not be improved.

Industrial Applicability

[0086] The additive for non-aqueous electrolyte according to the present disclosure is preferably used in a non-aqueous electrolyte secondary battery in which the negative electrode active material contains a material containing silicon element.

Explanation of Symbols

[0087] 1a Positive electrode mixture layer 1b Positive electrode current collector 1c Positive electrode tab lead 2a Negative electrode mixture layer 2b Negative electrode current collector 2c Negative electrode tab lead 4 Electrode plate group 5 Exterior case 6 Insulating tab film 10 Positive electrode 20 Negative electrode 30 Separator 100 Lithium-ion secondary battery

Claims

1. A negative electrode having a negative electrode active material layer, a positive electrode, a non-aqueous electrolyte containing a non-aqueous solvent, a salt dissolved in the non-aqueous solvent, and an additive for non-aqueous electrolyte, wherein the negative electrode active material layer contains a negative electrode active material, the negative electrode active material contains a material containing silicon element, the additive for non-aqueous electrolyte contains a bis(alkoxysilyl) compound (excluding bis[3-(triethoxysilyl)propyl]tetrasulfide), the bis(alkoxysilyl) compound has two silyl groups linked by a chain containing a sulfide group, each of the two silyl groups has only at least one selected from the group consisting of an alkoxy group and an oxyalkyl group, The oxyalkyl group is -O-(C ｘ H 2ｘ+1 O y ), x is an integer of 1 or more, and y is an integer of 1 or more, a non-aqueous electrolyte secondary battery.

2. A negative electrode having a negative electrode active material layer, a positive electrode, a non-aqueous electrolyte containing a non-aqueous solvent, a salt dissolved in the non-aqueous solvent, and an additive for non-aqueous electrolyte, wherein the negative electrode active material layer contains a negative electrode active material, the negative electrode active material contains a material containing silicon element, the additive for non-aqueous electrolyte contains a bis(alkoxysilyl) compound (excluding bis[3-(triethoxysilyl)propyl]tetrasulfide), the bis(alkoxysilyl) compound is a bis(alkoxysilylalkyl) sulfide represented by the general formula (1): 【Chemical 1】

3. R1 is C ｘ1 H 2ｘ1 S ｚ represented by, where x1 and z are each an integer of 1 or more, and is a sulfide group At least one of R2 to R4 is an alkoxy group having 1 to 6 carbon atoms and -O-(C ｘ2 H 2ｘ2+1 O y2 ) represented by, x2 is an integer of 1 or more, and at least one selected from the group consisting of oxyalkyl groups in which y2 is an integer of 1 or more. At least one of R5 to R7 is an alkoxy group having 1 to 6 carbon atoms and -O-(C ｘ3 H 2ｘ3+1 O y3 ) represented by, x3 is an integer of 1 or more, and at least one selected from the group consisting of oxyalkyl groups in which y3 is an integer of 1 or more, The remainder of R2 to R7 are each independently C ｘ4 H 2ｘ4+1 O y4 represented by, x4 is an integer of 1 or more, and y4 is an alkyl group or an oxyalkyl group which is an integer of 0 or more, a non-aqueous electrolyte secondary battery. The non-aqueous electrolyte secondary battery according to Claim 2, wherein R11 and R12 are each an alkylene group having 1 or more carbon atoms. R1 is represented by R11 - S z - R12,

4.

5. The bis(alkoxysilylalkyl)sulfide is bis(trialkoxysilyl C 1-6 alkyl)S 1-6 sulfide, and the non-aqueous electrolyte secondary battery according to claim 3.

6. The screw (trialkoxysilyl C 1-6 alkyl) S 1-6 ulfide is at least one selected from the group consisting of bis(triethoxysilylpropyl) sulfide, bis(triethoxysilylpropyl) disulfide, bis(triethoxysilylpropyl) trisulfide, and bis(triethoxysilylpropyl) tetrasulfide. The non-aqueous electrolyte secondary battery according to claim 4. The non-aqueous electrolyte secondary battery according to Claim 1 or 2, wherein the concentration of the additive for non-aqueous electrolyte is 5% by mass or less.

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

8. The material containing silicon element is a composite material, the composite material contains a lithium ion conductive phase and silicon particles dispersed in the lithium ion conductive phase, and the non-aqueous electrolyte secondary battery according to Claim 1 or 2. ​

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