Alkoxysilyl compound and additive for non-aqueous electrolyte containing the same, as well as non-aqueous electrolyte and non-aqueous electrolyte secondary battery containing the same

Abstract

This alkoxysilyl compound has two or more silyl groups that are linked by a chain including an ether group. The two or more silyl groups each have at least one selected from the group consisting of alkoxy groups and oxyalkyl groups. The alkoxysilyl compound is added to a nonaqueous electrolytic solution as a nonaqueous electrolytic solution additive.

Description

[Technical Field]

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

[0002] Silicon-containing materials are promising as high-capacity anode materials for secondary batteries. However, because silicon-containing materials expand and contract significantly during charging and discharging, they are prone to side reactions and a decrease in capacity retention during charge-discharge cycles.

[0003] Non-Patent Document 1 reports that the capacity retention rate during charge-discharge cycles is improved by adding a vinyl group-containing silane coupling agent to the electrolyte of a single-electrode battery using a Si / C composite. [Prior art documents] [Non-patent literature]

[0004] [Non-Patent Document 1] Ionics, 2018, 24, 3691-3698 Summary of the Invention [Problem to be solved by the invention]

[0005] However, with the proposal in Non-Patent Document 1, it is difficult to stably improve the capacity retention rate in charge-discharge cycles. [Means for solving the problem]

[0006] One aspect of the present disclosure relates to an alkoxysilyl compound having two or more silyl groups linked by a chain containing an ether group, wherein the two or more silyl groups each have at least one type selected from the group consisting of an alkoxy group and an oxyalkyl group.

[0007] Another aspect of the present disclosure relates to an additive for a non-aqueous electrolyte solution, which contains the above-mentioned alkoxysilyl compound.

[0008] Yet another aspect of the present disclosure relates to a non-aqueous electrolyte solution including a non-aqueous solvent, a salt that dissolves in the non-aqueous solvent, and the additive for a non-aqueous electrolyte solution.

[0009] Yet another aspect of the present disclosure relates to a nonaqueous electrolyte secondary battery including: a negative electrode having a negative electrode mixture layer; a positive electrode; and the nonaqueous electrolyte solution, wherein the negative electrode mixture layer contains a negative electrode active material, and the negative electrode active material contains a material containing elemental silicon. [Effects of the Invention]

[0010] According to the present disclosure, when the negative electrode active material contains a material containing elemental silicon, the capacity retention rate of a non-aqueous electrolyte secondary battery during charge-discharge cycles can be stably improved. 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. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a partially cutaway plan view schematically illustrating the structure of a nonaqueous electrolyte secondary battery according to an embodiment of the present disclosure. [Figure 2] 2 is a cross-sectional view of the nonaqueous secondary battery shown in FIG. 1 taken along line XX'. [Figure 3] 1A to 1C are diagrams illustrating a method for producing a negative electrode for performance evaluation. [Figure 4] 1 is a graph showing the relationship between the number of charge / discharge cycles and the capacity retention rate of a non-aqueous electrolyte secondary battery. [Figure 5] 1 is a graph showing the relationship between the number of charge / discharge cycles and the capacity retention rate of a non-aqueous electrolyte secondary battery. DETAILED DESCRIPTION OF THE INVENTION

[0012] (Alkoxysilyl compounds and additives for non-aqueous electrolytes) The alkoxysilyl compound according to an embodiment of the present disclosure has two or more silyl groups linked by a chain containing an ether group, and each of the two or more silyl groups has at least one type selected from the group consisting of an alkoxy group and an oxyalkyl group. This alkoxysilyl compound can be used as an additive for a non-aqueous electrolyte. The additive for a non-aqueous electrolyte includes the alkoxysilyl compound. The additive for a non-aqueous electrolyte can be used particularly for a non-aqueous electrolyte secondary battery using a negative electrode active material containing elemental silicon. The alkoxysilyl compound may be a bisalkoxysilyl compound having two silyl groups.

[0013] In the above structure, it is believed that the alkoxy group or oxyalkyl group of each silyl group forms an XO-Si bond with the surface of the silicon-containing material. Here, X represents the surface of the silicon-containing material, and the O bonded to X represents, for example, an O atom (or a residue of an OH group) that was present on the surface of the silicon-containing material. By each alkoxy group or oxyalkyl group forming a bond with the surface of the silicon-containing material, the surface of the silicon-containing material is covered with a bis-silyl ether structure having stable siloxane bonds at both ends.

[0014] That is, the surface of the silicon-containing material is covered with a coating containing a silyl ether structure (hereinafter also referred to as an SE coating). The SE coating has high elasticity and is stable against reversible elastic deformation, making it less susceptible to damage even during repeated charge-discharge cycles. As a result, side reactions at the negative electrode are suppressed, and the capacity retention rate during charge-discharge cycles is stably improved. In addition, the oxygen (-O-) contained in the silyl ether structure acts to promote the migration of cations (e.g., lithium ions) into and out of the silicon-containing material. As a result, cationic conductivity is increased, further improving the capacity retention rate.

[0015] The alkoxysilyl compound is represented by the general formula (1):

[0016] [ka]

[0017] Here, R1 is a chain containing an ether group. At least one of R2 to R4 is an alkoxy group having 1 to 6 carbon atoms and -O-(C x1 H 2x1+1 O y1 ), where x1 is an integer of 1 to 6, and y1 is at least one selected from the group consisting of an oxyalkyl group having 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 x2 H 2x2+1 O y2 ), where x2 is an integer of 1 to 6, and y2 is at least one selected from the group consisting of oxyalkyl groups each of which is an integer of 1 or more. The remainder of R2 to R7 are each independently C x3 H 2x3+1 O y3 where x3 is an integer of 1 or more, and y3 is an alkyl group or oxyalkyl group, and is an integer of 0 or more. However, the oxyalkyl group is a group other than an alkoxy group.

[0018] The alkoxy or oxyalkyl groups contained in R2 to R4 and R5 to 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 an 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 SE coating containing an Si-R1-Si structure.

[0019] In formula (1), R1 is R11-(O-R12) nThe (O-R12) unit may have a structure represented by the formula -O-R13. Here, R11, R12, and R13 are each independently an alkylene group having one or more carbon atoms, and n is an integer of 0 or greater. Such an R1 has excellent flexibility, and the oxygen bonding R11 and R12 and the oxygen bonding R12 and R13 coordinate to cations, thereby promoting the movement of cations into and out of the silicon-containing material. This is thought to increase the cationic conductivity and further suppress the decrease in capacity retention. Note that when n is 2 or greater, the multiple R12s contained in the (O-R12) unit may all be the same alkylene group, or may contain alkylene groups with different numbers of carbon atoms.

[0020] The greater the number of carbon atoms in R11 and R13, the greater the flexibility, making it easier for the SE coating to undergo reversible deformation. However, if the number of carbon atoms in R11 and R13 is excessively large, the alkylene chain becomes too long, reducing the density of the coating and the effect of suppressing side reactions. Therefore, it is desirable that the number of carbon atoms in R11 and R13 be 1 to 6, and more desirably 2 to 4. Bis(alkoxysilyl alkyl) ethers are bis(alkoxysilyl C 1-6 alkyl) ether, and bis(alkoxysilyl C 2-4 It may also be an alkyl ether.

[0021] Furthermore, the -O- groups constituting R1 enhance cationic conductivity and contribute to improving the capacity retention rate. However, since an excessively large number of -O- groups reduces the density of the SE coating, the number of -O- groups is preferably 1 to 5, and more preferably 1 to 3. That is, the number n of (O-R12) units contained in the above R1 is preferably 0 to 4, and more preferably 0 to 2.

[0022] On the other hand, the number of carbon atoms in R12 is preferably 4 or less, more preferably 2 or more and 4 or less, from the viewpoint of promoting the transfer of cations between adjacent oxygen atoms.

[0023] At least one of R2 to R4 is an alkoxy group having 1 to 6 carbon atoms and —O—(Cx1 H 2x1+1 O y1 ), where x1 may be an integer of 1 to 6, and y1 may be at least one selected from the group consisting of oxyalkyl groups, where y1 is 1 or 2. At least one of R5 to R7 is an alkoxy group having 1 to 6 carbon atoms and -O-(C x2 H 2x2+1 O y2 ), where x2 is an integer of 1 to 6 and y2 is 1 or 2. The alkoxy group or oxyalkyl group may be smaller in size from the viewpoint of increasing the reactivity with the surface of the silicon-containing material, and the number of carbon atoms in the alkoxy group or oxyalkyl group may be, for example, 1 to 3.

[0024] The rest of R2 to R7 are each independently C x3 H 2x3+1 O y3 where x3 is an integer of 1 to 6, and y3 is an integer of 0 to 2, and may be an alkyl or oxyalkyl group. x3 H 2x3+1 O y3 The group represented by the formula (I) may have 1 to 6 carbon atoms, or may have 1 to 3 carbon atoms. R2 to R4 are each independent, and R2 to R4 may all have the same number of carbon atoms, or 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 R5 to R7 may all have the same number of carbon atoms, or may all have different numbers of carbon atoms, or two of R5 to R7 may have the same number of carbon atoms.

[0025] The two alkoxysilyl groups (R2R3R4Si- or R5R6R7Si-) linked to R1 may be the same or different, but in order to increase the symmetry of the SE coating structure and make it more stable, the two alkoxysilyl groups linked to R1 may have the same structure.

[0026] R1 may be -C3H6-O-C3H6- or -C2H4-O-C2H4-O-C3H6-. R2 to R7 may each be a methoxy group.

[0027] Specific examples of desirable alkoxysilyl compounds include bis(alkoxysilylalkyl) ethers represented by the following formula: [ka] [ka]

[0028] (Non-aqueous electrolyte) The nonaqueous electrolyte solution contains a nonaqueous solvent, a salt (solute) that dissolves in the nonaqueous solvent, and the nonaqueous electrolyte solution additive. The salt (solute) is an electrolyte salt that ionically dissociates in the nonaqueous solvent. When the nonaqueous electrolyte solution is used in a lithium ion secondary battery, the salt contains at least a lithium salt. The components of the nonaqueous electrolyte solution other than the nonaqueous solvent and the salt are additives, and at least a portion of the additives is the alkoxysilyl compound.

[0029] The concentration of the alkoxysilyl compound in the non-aqueous electrolyte may be, for example, 10% by mass or less, 5% by mass or less, 2% by mass or less, or 1% by mass or less. This range is sufficient to form a good and appropriate SE coating regardless of the amount of silicon-containing material contained in the negative electrode active material. If the concentration of the alkoxysilyl compound in the non-aqueous electrolyte is, for example, 0.05% by mass or more, it is believed that a substantial SE coating is formed, and a significant effect of improving the capacity retention rate during charge-discharge cycles of a non-aqueous electrolyte secondary battery can be obtained.

[0030] However, since the alkoxysilyl compound reacts in the nonaqueous electrolyte secondary battery, its concentration in the nonaqueous electrolyte decreases. Therefore, it is sufficient that the alkoxysilyl compound remains in an amount equal to or greater than the detection limit in the nonaqueous electrolyte extracted by disassembling a completed nonaqueous electrolyte secondary battery or a nonaqueous electrolyte secondary battery on the market.

[0031] Examples of non-aqueous solvents that can be used include cyclic carbonates, chain carbonates, cyclic carboxylic acid esters, and chain carboxylic acid esters. Examples of cyclic carbonates include propylene carbonate (PC), ethylene carbonate (EC), and vinylene carbonate (VC). Examples of chain carbonates include diethyl carbonate (DEC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC). Examples of cyclic carboxylic acid esters include γ-butyrolactone (GBL) and γ-valerolactone (GVL). Examples of chain carboxylic acid esters include methyl acetate, ethyl acetate, propyl acetate, methyl propionate (MP), and ethyl propionate (EP). One type of non-aqueous solvent may be used alone, or two or more types may be used in combination.

[0032] Among these, chain carboxylic acid esters are suitable for preparing a non-aqueous electrolyte solution with low viscosity. Therefore, the non-aqueous electrolyte solution may contain 1 mass % or more and 90 mass % or less of chain carboxylic acid esters. Among chain carboxylic acid esters, methyl acetate has a particularly low viscosity. Therefore, 90 mass % or more of the chain carboxylic acid ester may be methyl acetate.

[0033] Other examples of non-aqueous solvents include cyclic ethers, chain ethers, nitriles such as acetonitrile, and amides such as dimethylformamide.

[0034] 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.

[0035] Examples of chain ethers 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, and tetraethylene glycol dimethyl ether.

[0036] These solvents may be fluorinated solvents in which some of the hydrogen atoms are substituted with fluorine atoms. Fluoroethylene carbonate (FEC) may be used as the fluorinated solvent.

[0037] Examples of lithium salts include lithium salts of chlorine-containing acids (LiClO4, LiAlCl4, LiB 10 Cl 10 etc.), lithium salts of fluorine-containing acids (LiPF6, LiPF2O2, LiBF4, LiSbF6, LiAsF6, LiCF3SO3, LiCF3CO2, etc.), lithium salts of fluorine-containing acid imides (LiN(FSO2)2, LiN(CF3SO2)2, LiN(CF3SO2)(C4F9SO2), LiN(C2F5SO2)2, etc.), lithium halides (LiCl, LiBr, LiI, etc.), etc., can be used. One type of lithium salt may be used alone, or two or more types may be used in combination.

[0038] The concentration of the lithium salt in the non-aqueous electrolyte may be 0.5 mol / L or more and 2 mol / L or less, or may 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 having excellent ionic conductivity and low viscosity can be obtained.

[0039] Examples of additives other than alkoxysilyl compounds include 1,3-propane sultone, methylbenzenesulfonate, cyclohexylbenzene, biphenyl, diphenyl ether, and fluorobenzene.

[0040] (Nonaqueous electrolyte secondary battery) The nonaqueous electrolyte secondary battery according to the present disclosure includes a negative electrode, a positive electrode, and the nonaqueous electrolyte.

[0041] (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 thickener. Known materials can be used for the optional components such as the binder, the conductive material, and the thickener.

[0042] 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 predetermined optional components is dispersed in a dispersion medium, to the surface of the negative electrode current collector and drying the applied film. The dried coating may be rolled as necessary. The negative electrode mixture layer may be formed on one surface or both surfaces of the negative electrode current collector.

[0043] The negative electrode active material includes a material containing silicon. A material containing silicon is sometimes considered a type of alloy material. Here, alloy material refers to a material containing an element that can form an alloy with lithium. Examples of elements that can form an alloy with lithium include silicon and tin, with silicon (Si) being particularly promising.

[0044] The silicon-containing material may be a silicon alloy, a silicon compound, or a composite material. Among these, a composite material containing a lithium ion conductive phase and a silicon phase dispersed in the lithium ion conductive phase is particularly promising. Examples of the lithium ion conductive phase that can be used include a silicon oxide phase, a silicate phase, and a carbon phase. The silicon oxide phase is a material with a relatively high irreversible capacity. On the other hand, the silicate phase is preferred because it has a low irreversible capacity.

[0045] The main component of the silicon oxide phase (for example, 95 to 100 mass%) may be silicon dioxide. The composition of the composite material containing the silicon oxide phase and silicon particles dispersed therein is, as a whole, SiO x It can be expressed as SiO x has a structure in which silicon particles are dispersed in amorphous SiO2. The content ratio x of oxygen to silicon is, for example, 0.5≦x<2.0, and more preferably 0.8≦x≦1.5.

[0046] The silicate phase may contain, for example, at least one element selected from the group consisting of Group 1 and Group 2 elements of the long periodic table. Examples of Group 1 and Group 2 elements of the long periodic table include lithium (Li), potassium (K), sodium (Na), magnesium (Mg), calcium (Ca), strontium (Sr), and barium (Ba). Other elements that may be included include aluminum (Al), boron (B), lanthanum (La), phosphorus (P), zirconium (Zr), and titanium (Ti). Among these, a silicate phase containing lithium (hereinafter also referred to as a lithium silicate phase) is preferred because of its small irreversible capacity and high initial charge / discharge efficiency.

[0047] 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). It is preferable that z satisfies the relationship of 0 < z < 1, and z = 1 / 2 is more preferable. Examples of elements other than Li, Si, and O that may be included in the lithium silicate phase include iron (Fe), chromium (Cr), nickel (Ni), manganese (Mn), copper (Cu), molybdenum (Mo), zinc (Zn), aluminum (Al), and the like.

[0048] 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.

[0049] 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 preferable. Examples of the carbon material include graphite, graphitizable carbon (soft carbon), non-graphitizable carbon (hard carbon), and the like. Among them, graphite, which has excellent charge-discharge stability and low irreversible capacity, is preferable.

[0050] 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.

[0051] (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 each of the optional components such as the binder, the conductive material, and the thickening material.

[0052] 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.

[0053] 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 may 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 perspective of the stability of the crystal structure, M may contain Al. 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. can be mentioned.

[0054] Positive electrode active materials (especially lithium-containing composite oxides) usually have the form of secondary particles formed by aggregation of primary particles. 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 using a laser diffraction particle size distribution measuring device.

[0055] The positive electrode current collector may be, for example, a metal sheet or a metal foil, and may be made of, for example, stainless steel, aluminum, an aluminum alloy, or titanium.

[0056] 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), graphite, etc. These may be used alone or in combination of two or more.

[0057] 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.

[0058] (separator) A separator is interposed between the positive electrode and the negative electrode. The separator has high ion permeability and adequate mechanical strength and insulation. The separator can be made of a microporous thin film, woven fabric, nonwoven fabric, or the like. The separator is preferably made of polyolefin such as polypropylene or polyethylene.

[0059] An example of the structure of the 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 and a non-aqueous electrolyte are housed in an outer casing. Alternatively, instead of a wound electrode group, other types of electrode groups may be used, such as a stacked electrode group formed by stacking a positive electrode and a negative electrode with a separator interposed therebetween. The non-aqueous electrolyte secondary battery may be in any shape, such as a cylindrical shape, a prismatic shape, a coin shape, a button shape, or a sheet shape (laminate shape).

[0060] A nonaqueous electrolyte secondary battery according to an embodiment of the present disclosure will be described below with reference to Figures 1 and 2. Figure 1 is a partially cutaway plan view schematically illustrating an example of the structure of a nonaqueous electrolyte secondary battery. Figure 2 is a cross-sectional view taken along line XX' in Figure 1.

[0061] As shown in FIGS. 1 and 2, the nonaqueous electrolyte secondary battery 100 is a sheet-type battery, and includes an electrode plate group 4 and an exterior case 5 that houses the electrode plate group 4.

[0062] The electrode plate group 4 has 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, thereby forming the electrode plate group 4. The electrode plate group 4 is impregnated with a nonaqueous electrolyte (not shown).

[0063] The positive electrode 10 includes a positive electrode mixture layer 1a and a positive electrode current collector 1b. The positive electrode mixture layer 1a is formed on the surface of the positive electrode current collector 1b.

[0064] 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.

[0065] A positive electrode tab lead 1c is connected to the positive 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 outer case 5.

[0066] The positive electrode tab lead 1c and the outer case 5, and the negative electrode tab lead 2c and the outer case 5 are insulated by insulating tab films 6, respectively.

[0067] 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.

[0068] Example 1 (1) Synthesis of alkoxysilyl compounds A dried 100 mL four-necked vessel was charged with 1.0 g of allyl ether, 40.0 mL of dichloroethane (C2H4Cl2), 3.7 g of trimethoxysilane (HSi(OMe)3), and 0.1 g of cyclooctadiene iridium chloride dimer ([Ir(COD)Cl]2), and the mixture was stirred to proceed with the reaction shown in the following formula. The mixture was heated and stirred from room temperature to 50°C until the raw material allyl ether was consumed. After confirming that the raw material had been consumed, heating and stirring were stopped, and the solvent dichloroethane was distilled off using an evaporator, yielding a crude brown oil X1 (4.0 g) containing alkoxysilyl compound A.

[0069] [ka]

[0070] Next, 5.0 g of allyl ether, 200 mL of dichloroethane (C2H4Cl2), 18.6 g of trimethoxysilane (HSi(OMe)3), and 0.68 g of cyclooctadiene iridium chloride dimer ([Ir(COD)Cl]2) were added to a dried 500 mL eggplant-shaped container and heated with stirring from room temperature to 50 °C. After confirming that the raw materials had disappeared, heating and stirring were stopped and the solvent dichloroethane was distilled off using a vacuum pump. After distillation, brown oil X1 was added to the crude product, and distillation purification was carried out using a distillation purification apparatus connected to a flask, a T-junction tube, a thermometer, a condenser, a vacuum pump, and a pressure gauge at an oil bath temperature of 190 °C and a vacuum of 0.1-0.01 mmHg to obtain brown oil X2 (9.3 g) containing alkoxysilyl compound A.

[0071] Furthermore, 5.0 g of allyl ether, 200 mL of dichloroethane (C2H4Cl2), 18.6 g of trimethoxysilane (HSi(OMe)3), and 0.5 g of cyclooctadiene iridium chloride dimer ([Ir(COD)Cl]2) were added to a dried 500 mL eggplant-shaped container and heated and stirred from room temperature to 50°C. After confirming that the raw materials had disappeared, heating and stirring were stopped and the solvent dichloroethane was distilled off using a vacuum pump. The brown oil X2 was added to the distilled crude product, and distillation purification was carried out again at an oil bath temperature of 190°C and a vacuum of 0.1-0.01 mmHg, yielding colorless oil compound X3 (13.3 g, 38.8 mol, 34.6% yield) containing alkoxysilyl compound A. 1 The purity was confirmed by NMR and gas chromatography (GC).

[0072] (2) Preparation of the negative electrode SiO x (x=1) (Shin-Etsu Chemical Co., Ltd., KSC1064), carbon black (Denka Co., Ltd., HS-100), and an aqueous solution of polyacrylamide (binder) were mixed so that the mass ratio of SiOx:carbon black:polyacrylamide was 75:15:10, and 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 was rolled together with the negative electrode current collector using a rolling roller to obtain a negative electrode with a negative electrode mixture layer.

[0073] 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 60 mm × 40 mm region is the region that functions as the negative electrode, and the 10 mm × 10 mm protruding portion is the connection region with the tab lead 2c. Then, as shown in FIG. 3(b), the negative electrode mixture layer 2a formed on the connection region was scraped off to expose the negative electrode current collector 2b. Then, 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 periphery of the negative electrode tab lead 2c was covered with an insulating tab film 6.

[0074] (3) Preparation of the counter electrode A counter electrode was prepared by attaching a lithium metal foil to one side of an electrolytic copper foil (current collector).

[0075] The counter electrode was cut into the same shape as the negative electrode, and the lithium metal foil formed on the connection area was peeled off to expose the current collector. The exposed part of the current collector was then connected to a tab lead, and a predetermined area around the periphery of the tab lead was covered with an insulating tab film, just like the negative electrode.

[0076] (4) Preparation of non-aqueous electrolyte A non-aqueous electrolyte solution was prepared by dissolving LiPF at a concentration of 1 mol / L in a mixed solvent of fluoroethylene carbonate (FEC) and dimethyl carbonate (DMC) in a volume ratio of 20:80. Alkoxysilyl compound A was added to the non-aqueous electrolyte solution so that its concentration in the non-aqueous electrolyte solution was 0.1 mass%.

[0077] (5) Preparation of evaluation cells Using the above-described evaluation negative electrode and counter electrode, a cell with a negative electrode-regulated design capacity of 114 mAh was fabricated. First, the negative electrode and counter electrode were placed face to face with two aramid-coated polyethylene separators (15 μm thick) between them, with the negative electrode mixture layer and the lithium metal foil overlapping, to obtain an electrode plate assembly. Next, a rectangular Al laminate film (100 μm thick) was folded in half, and the long edge was heat-sealed at 230°C to form a cylinder. The electrode plate assembly was then placed into the cylinder from one of the short edges, and the end face of the Al laminate film was aligned with the heat-sealed resin of each tab lead, and heat-sealed at 230°C. Next, 1.2 cm of nonaqueous electrolyte was poured into the cylinder from the short edge that was not heat-sealed. 3 After the injection, the negative electrode mixture layer was impregnated with the nonaqueous electrolyte solution. After the injection, the negative electrode mixture layer was left standing under a reduced pressure of 0.02 MPa for 3 minutes and then returned to atmospheric pressure. This cycle was repeated twice to impregnate the negative electrode mixture layer with the nonaqueous electrolyte solution. Finally, the end face of the Al laminate film on the injected 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 of -60 °C or lower.

[0078] (6) Battery evaluation The evaluation cell was clamped between a pair of 10 x 5 cm stainless steel clamps (thickness: 6 mm) and pressurized and fixed at 3.2 MPa.

[0079] <First Cycle> In a thermostatic chamber at 25°C, the negative electrode was charged with lithium at a constant current of 0.05C (1C is the current value required to discharge the design capacity in 1 hour) for 2 hours, followed by a 12-hour rest period. Next, the negative electrode was further charged with lithium at a constant current of 0.05C up to a cell voltage of 0.01V, followed by a 20-minute rest period. Next, lithium was discharged from the negative electrode at a constant current of 0.05C up to a cell voltage of 1.5V, followed by a 20-minute rest period.

[0080] <2nd and 3rd cycles> Next, the negative electrode was charged with lithium at a constant current of 0.05 C until the cell voltage reached 0.01 V, after which the battery was left to rest for 20 minutes. Next, the negative electrode was discharged with lithium at a constant current of 0.05 C until the cell voltage reached 1.5 V, after which the battery was left to rest for 20 minutes.

[0081] <4th to 50th cycles> The negative electrode was charged with lithium at a constant current of 0.3 C until the cell voltage reached 0.01 V, after which the battery was allowed to rest for 20 minutes. Subsequently, lithium was discharged from the negative electrode at a constant current of 0.3 C until the cell voltage reached 1.5 V, after which the battery was allowed to rest for 20 minutes. This cycle was repeated.

[0082] The ratio of the capacity obtained in the 50th lithium discharge cycle to the capacity obtained in the 1st lithium discharge cycle was calculated as the 50th cycle capacity retention rate. The results are shown in Table 1.

[0083] Examples 2 to 4 In preparing the non-aqueous electrolyte solution, evaluation cells A2 to A4 were prepared in the same manner as in Example 1, except that the content of alkoxysilyl compound A added to the non-aqueous electrolyte solution was changed as shown in Table 1, and evaluated in the same manner.

[0084] Examples 5 to 8 In the synthesis of an alkoxysilyl compound, ethylene glycol monovinyl ether (5.0 g, 1.0 eq.), 50 mL of ultra-dehydrated dimethylformamide (DMF), and allyl bromide (7.55 g, 1.1 eq.) were added to a 200 mL reactor at room temperature. To this solution, NaH (2.27 g, 1.0 eq.) was added slowly in several portions over 20 minutes while stirring, yielding a white suspension. The white suspension was stirred at room temperature for 16 hours, allowing the reaction shown in the following formula to proceed. After stirring, water was added to quench the reaction, yielding a reaction solution containing compound B.

[0085] [ka]

[0086] The reaction mixture was placed in a separatory funnel, 30 mL of diethyl ether was added, and the mixture was stirred. The organic phase was extracted, and this procedure was repeated three times. The extracted organic phases were then combined and placed back in the separatory funnel. 100 mL of water was added and the mixture was stirred, and the aqueous phase was then discharged. This procedure was repeated three times. Next, 100 mL of saturated saline was added and the mixture was stirred, and the aqueous phase was then discharged. 20 g of anhydrous sodium sulfate was then added to the remaining organic phase, and the mixture was stirred to remove water. The anhydrous sodium sulfate was then removed by filtration. The diethyl ether was then removed at atmospheric pressure with a bath temperature of 50°C, and the residue was distilled and purified (vacuum: 20 mmHg, oil bath temperature: 70°C, vapor temperature: 50°C) using a distillation purification apparatus connected to a flask, a T-junction tube, a thermometer, a condenser, a vacuum pump, and a pressure gauge to obtain a colorless liquid Y1 containing compound B.

[0087] Next, compound B (1.0 g, 1.0 eq.), 30 mL of ultra-dehydrated dichloromethane, and cyclooctadiene iridium chloride dimer ([Ir(COD)Cl]2) (52 g, 0.01 eq.) were added to a 50 mL reactor to obtain an orange solution. Trimethoxysilane (HSi(OMe)3) (3.0 mL, 3.0 eq.) was slowly added dropwise to the orange solution over 15 minutes while stirring. The solution was stirred at room temperature for 2 hours, allowing the reaction shown in the following formula to proceed, yielding solution Y2 containing alkoxysilyl compound C.

[0088] [ka]

[0089] Furthermore, compound B (5.0 g, 1.0 eq.), 125 mL of ultra-dehydrated dichloromethane, and 0.26 g of cyclooctadiene iridium chloride dimer ([Ir(COD)Cl]2) were added to a 50 mL reactor at room temperature to obtain an orange solution. While stirring the orange solution, trimethoxysilane (HSi(OMe)3) (14.9 mL, 3.0 eq.) was slowly added dropwise over 15 minutes. The solution was stirred at room temperature for 2 hours, and then solution Y2 was added to the stirred solution. A distillation purification apparatus was attached to the reactor, and dichloromethane was removed at a bath temperature of 50 °C. Volatile components were then removed under reduced pressure of 20 mmHg / 70 °C. The residue was purified by distillation (vacuum degree: 0.1-0.3 mmHg, oil bath temperature: 180-195°C, vapor temperature: 139-142°C) to obtain alkoxysilyl compound C (10.4 g, 27.9 mol, yield 59.6%) as a pale brown solution.

[0090] In preparing the non-aqueous electrolyte solution, alkoxysilyl compound C was added so that the concentration in the non-aqueous electrolyte solution was the mass % shown in Table 1. Except for this, evaluation cells A5 to A8 were produced in the same manner as in Example 1 and evaluated in the same manner.

[0091] Comparative Examples 1 and 2 In preparing the non-aqueous electrolyte, vinyltris(2-methoxyethoxy)silane (VTMS) represented by the following formula was added to the non-aqueous electrolyte in the amount shown in Table 1, instead of the alkoxysilyl compound. Other than this, evaluation cells B1 and B2 were prepared and evaluated in the same manner as in Example 1. VTMS is an additive used in Non-Patent Document 1.

[0092] [ka]

[0093] Comparative Example 3 Evaluation cell B3 was produced in the same manner as in Example 1, except that no alkoxysilyl compound was added in the preparation of the non-aqueous electrolyte solution, and was evaluated in the same manner.

[0094] [Table 1]

[0095] Figure 4 shows the relationship between the number of charge-discharge cycles and the capacity retention rate for test cells A2, A3, and B1 to B3. Figure 5 shows the relationship between the number of charge-discharge cycles and the capacity retention rate for test cells A6, A7, and B1 to B3.

[0096] It can be seen from Table 1 and FIGS. 4 and 5 that when alkoxysilyl compound A or C, which is a bis(alkoxysilylalkyl) ether, is added to the non-aqueous electrolyte, the capacity retention rate is improved.

[0097] On the other hand, as shown in FIGS. 4 and 5, the VTMS used in Non-Patent Document 1 was unable to improve the capacity retention rate. [Industrial Applicability]

[0098] The non-aqueous electrolyte additive according to the present disclosure is suitably used in a non-aqueous electrolyte secondary battery in which the negative electrode active material contains a material containing elemental silicon. While the present invention has been described in terms of presently preferred embodiments, such disclosure is not to be interpreted as limiting. Various changes and modifications will no doubt become apparent to those skilled in the art to which the present invention pertains upon reading the above disclosure. It is therefore intended that the appended claims be interpreted to cover all changes and modifications that do not depart from the true spirit and scope of the invention. [Explanation of symbols]

[0099] 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: outer case, 6: insulating tab film, 10: positive electrode, 20: negative electrode, 30: separator, 100: nonaqueous electrolyte secondary battery

Claims

1. A battery comprising: a negative electrode having a negative electrode mixture layer; a positive electrode; and a nonaqueous electrolyte; The negative electrode mixture layer is a nonaqueous electrolyte secondary battery containing a negative electrode active material, the negative electrode active material includes a material containing elemental silicon, the non-aqueous electrolyte solution includes a non-aqueous solvent, a salt that dissolves in the non-aqueous solvent, and an additive for the non-aqueous electrolyte solution; The concentration of the additive for the non-aqueous electrolyte is 0.05% by mass or more and 10% by mass or less, the additive for the non-aqueous electrolyte solution contains an alkoxysilyl compound, The alkoxysilyl compound is represented by the general formula (1): 【Chemical 1】 is a bis(alkoxysilylalkyl) ether represented by the formula: R1 is a chain containing an ether group represented by —C 3 H 6 —O—C 3 H 6 — or —C 2 H 4 —O—C 2 H 4 —O—C 3 H 6 —; R2 to R7 each independently represent an alkoxy group having 1 to 3 carbon atoms; The two silyl groups connected by the chain R1 have the same structure.

2. 2. The nonaqueous electrolyte secondary battery according to claim 1, wherein R2 to R7 are methoxy groups.

3. the material containing silicon element is a composite material, 3. The nonaqueous electrolyte secondary battery according to claim 1, wherein the composite material comprises a lithium ion conductive phase and a silicon phase dispersed in the lithium ion conductive phase.

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