Alkoxysilyl compounds, additives for nonaqueous electrolytes containing the same, and nonaqueous electrolytes and nonaqueous electrolyte secondary batteries containing the same

Abstract

The alkoxy silyl compound has 2 or more silyl groups connected by a chain including an ether group, and the 2 or more silyl groups each have at least one selected from the group consisting of an alkoxy group and an oxyalkyl group. The alkoxy silyl compound is added to a nonaqueous electrolyte as an additive for a nonaqueous electrolyte.

Description

Technical Field

[0001] This disclosure relates to: alkoxysilyl compounds and additives for non-aqueous electrolytes containing the same, as well as non-aqueous electrolytes containing the same and non-aqueous electrolyte secondary batteries. Background Technology

[0002] Materials containing silicon show promise as high-capacity anode materials for secondary batteries. However, silicon-containing materials expand and contract significantly during charging and discharging, which can easily induce side reactions and reduce capacity retention during charge-discharge cycles.

[0003] Non-Patent Literature 1 reports an improvement in capacity retention during charge-discharge cycles by adding a vinyl-containing silane coupling agent to the electrolyte of a unipolar cell using a Si / C composite.

[0004] Existing technical documents

[0005] Non-patent literature

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

[0007] The problem the invention aims to solve

[0008] However, in the proposal of Non-Patent Literature 1, it is difficult to consistently improve the capacity retention rate during charge-discharge cycles.

[0009] Solution for solving the problem

[0010] One aspect of this disclosure relates to an alkoxysilyl compound having two or more silyl groups linked by a chain comprising an ether group, wherein the two or more silyl groups are each selected from at least one of the groups consisting of alkoxy and oxyalkyl groups.

[0011] Another aspect of this disclosure relates to an additive for a non-aqueous electrolyte, comprising the aforementioned alkoxysilyl compound.

[0012] Another further aspect of this disclosure relates to a non-aqueous electrolyte comprising: a non-aqueous solvent, a salt dissolved in the aforementioned non-aqueous solvent, and an additive for the aforementioned non-aqueous electrolyte.

[0013] Another further aspect of this disclosure relates to a non-aqueous electrolyte secondary battery comprising: a negative electrode having a negative electrode binder layer, a positive electrode, and the aforementioned non-aqueous electrolyte, wherein the aforementioned negative electrode binder layer comprises a negative electrode active material, and the aforementioned negative electrode active material contains a material comprising silicon.

[0014] The effects of the invention

[0015] According to this disclosure, when the negative electrode active material contains a material containing silicon, the capacity retention rate during charge-discharge cycles of a non-aqueous electrolyte secondary battery can be stably improved.

[0016] The novel features of the invention are set forth in the appended claims, but the invention will be more fully understood from the following detailed description with reference to the accompanying drawings, in terms of both its structure and content, along with its other objects and features. Attached Figure Description

[0017] Figure 1 The top view is shown schematically, showing a portion of the structure of a non-aqueous electrolyte secondary battery according to an embodiment of the present disclosure.

[0018] Figure 2 for Figure 1 The cross-sectional view of the non-aqueous secondary battery shown on the X-X' line.

[0019] Figure 3 This diagram illustrates the manufacturing method of the negative electrode used for performance evaluation.

[0020] Figure 4 A graph showing the relationship between the number of charge-discharge cycles and capacity retention of a non-aqueous electrolyte secondary battery.

[0021] Figure 5 A graph showing the relationship between the number of charge-discharge cycles and capacity retention of a non-aqueous electrolyte secondary battery. Detailed Implementation

[0022] (Alkoxysilane compounds and additives for non-aqueous electrolytes)

[0023] The alkoxysilyl compound 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 is selected from at least one of the groups consisting of alkoxy and oxyalkyl groups. This alkoxysilyl compound can be used as an additive for non-aqueous electrolytes. Additives for non-aqueous electrolytes include alkoxysilyl compounds. Additives for non-aqueous electrolytes are particularly suitable for use in non-aqueous electrolyte secondary batteries using anode active materials containing silicon. The alkoxysilyl compound can also be a dialkoxysilyl compound having two silyl groups.

[0024] In the above configuration, it is assumed that the alkoxy or oxoalkyl groups of each silane ether form XO-Si bonds 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 an OH group residue) present on the surface of the silicon-containing material. The alkoxy or oxoalkyl groups form bonds with the surface of the silicon-containing material, thereby covering the surface of the silicon-containing material with a dimethicone ether structure having stable siloxane bonds at both ends.

[0025] That is, the surface of the silicon-containing material is covered by a coating containing a silane ether structure (hereinafter also referred to as SE coating). The SE coating is highly elastic, stable to reversible elastic deformation, and not easily damaged under repeated charge-discharge cycles. As a result, side reactions in the negative electrode are suppressed, and the capacity retention rate is steadily improved during charge-discharge cycles. Furthermore, the oxygen (-O-) contained in the silane ether structure promotes the movement of cations (e.g., lithium ions) into and out of the silicon-containing material. Consequently, cation conductivity is improved, and the capacity retention rate is further enhanced.

[0026] Alkoxysilyl compounds can be bis(alkoxysilyl) ethers as shown in general formula (1):

[0027]

[0028] Here, R1 does not contain an ether group chain. At least one of R2 to R4 is an alkoxy group selected from 1 to 6 carbon atoms and is represented by -O-(C x1 H 2x1+1 O y1 At least one of the group consisting of alkyl groups, where x1 is an integer from 1 to 6 and y1 is an integer greater than 1. At least one of R5 to R7 is an alkoxy group selected from those having 1 to 6 carbon atoms and is represented by -O-(C x2 H 2x2+1 O y2 R2 represents at least one of the groups consisting of alkyl groups, where x2 is an integer from 1 to 6 and y2 is an integer greater than 1. The remaining groups R2 to R7 are each independently composed of C. x3 H 2x3+1 O y3 It represents an alkyl or oxyalkyl group where x3 is an integer greater than or equal to 1 and y3 is an integer greater than or equal to 0. The oxyalkyl group is a group other than an alkoxy group.

[0029] The alkoxy or oxyalkyl groups contained in R2 to R4 and R5 to R7 respectively form XO-Si-R1 bonds with the surface of the silicon-containing material, and the surface of the silicon-containing material is covered by a Si-R1-Si structure with stable siloxane bonds at both ends. That is, the surface of the silicon-containing material is covered by an SE coating containing a Si-R1-Si structure.

[0030] In equation (1), R1 can have R11-(O-R12) n The structure shown is -O-R13. Here, R11, R12, and R13 are each independently an alkylene group with one or more carbon atoms, and n is an integer greater than or equal to 0. This R1 exhibits excellent flexibility, and the oxygen atoms of R11 and R12, and R12 and R13, are coordinated to cations, thereby promoting the movement of cations into and out of materials containing silicon. Therefore, it is believed that the increased cation conductivity and the reduced inhibition rate are more significant. It should be noted that when n is 2 or more, the multiple R12s contained in the (O-R12) unit can all be the same alkylene group, or they can contain alkylene groups with different carbon atoms.

[0031] The higher the carbon number of R11 and R13, the better the flexibility, thus facilitating reversible deformation of the SE coating. However, it is believed that if the carbon number of R11 and R13 becomes excessively high, the alkylene chains become excessively long, reducing the compactness of the coating and diminishing its effectiveness in suppressing side reactions. Therefore, the ideal carbon number for R11 and R13 is 1–6, with 2–4 being more desirable. The desired carbon number for bis(alkoxysilyl) ether is bis(alkoxysilyl C... 1-6 Alkyl ethers, or bis(alkoxysilyl C) ethers, can also be bis(alkoxysilyl C) ethers. 2-4 Alkyl ether.

[0032] Furthermore, the -O- groups constituting R1 are beneficial for improving cation conductivity and capacity retention. However, if the number of -O- groups becomes excessively large, the density of the SE coating decreases. Therefore, the number of -O- groups is preferably set to 1 to 5, and more preferably 1 to 3. That is, the number n of (O-R12) units contained in R1 is preferably 0 to 4, and more preferably 0 to 2.

[0033] On the other hand, from the viewpoint of promoting cation movement between adjacent oxygen atoms, the number of carbon atoms in R12 is expected to be 4 or less, and more preferably 2 or more but less than 4.

[0034] At least one of R2 to R4 can be an alkoxy group selected from carbon 1 to 6 and a group containing -O-(C x1 H 2x1+1 O y1 () represents, x1 can be an integer from 1 to 6, and y1 is at least one of the group consisting of 1 or 2 alkyl groups. At least one of R5 to R7 can be an alkoxy group selected from 1 to 6 carbon atoms and a group consisting of -O-(C x2 H 2x2+1 O y2The group consisting of at least one alkoxy or oxoalkyl group, where x2 is an integer from 1 to 6 and y2 is 1 or 2. From the viewpoint of improving reactivity with surfaces containing silicon, the alkoxy or oxoalkyl group can be smaller, and the carbon number of the alkoxy or oxoalkyl group can be, for example, 1 to 3.

[0035] The remainder of R2 to R7 can each be used independently for C. x3 H 2x3+1 O y3 This refers to alkyl or oxyalkyl groups where x3 is an integer from 1 to 6 and y3 is an integer greater than 0 and less than 2. From the viewpoint of reducing steric hindrance during the reaction, C... x3 H 2x3+1 O y3 The number of carbon atoms in the shown bases can be 1 to 6, or 1 to 3. R2 to R4 are independent; all carbon atoms in R2 to R4 can be the same or different, and two carbon atoms in R2 to R4 can be the same. Similarly, R5 to R7 are independent; all carbon atoms in R5 to R7 can be the same or different, and two carbon atoms in R5 to R7 can be the same.

[0036] The two alkoxysilyl groups attached to R1 (R2R3R4Si- or R5R6R7Si-) can be the same or different. In order to improve the structural symmetry of the SE coating and form a more stable structure, the two alkoxysilyl groups attached to R1 can form the same structure.

[0037] R1 can be -C3H6-O-C3H6- or -C2H4-O-C2H4-O-C3H6-. R2 to R7 can be methoxy groups, respectively.

[0038] As a specific example of a desired alkoxysilyl compound, bis(alkoxysilylalkyl) ethers as shown in the following formula can be cited.

[0039]

[0040] (Non-aqueous electrolyte)

[0041] The non-aqueous electrolyte comprises: a non-aqueous solvent, a salt (solute) dissolved in the non-aqueous solvent, and the aforementioned additives for the non-aqueous electrolyte. The salt (solute) is an electrolyte salt that undergoes ion dissociation 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. The components of the non-aqueous electrolyte other than the non-aqueous solvent and the salt are additives, at least a portion of which are the aforementioned alkoxysilyl compounds.

[0042] The concentration of alkoxysilyl compounds in the non-aqueous electrolyte can be, for example, 10% by mass or less, 5% by mass or less, 2% by mass or less, or 1% by mass or less. If it falls within this range, a good and adequate SE coating is sufficiently formed regardless of the amount of silicon-containing material in the negative electrode active material. It is considered that if the concentration of alkoxysilyl compounds in the non-aqueous electrolyte is, for example, 0.05% by mass or more, a substantial SE coating is formed, resulting in a significant improvement in capacity retention during charge-discharge cycles of the non-aqueous electrolyte secondary battery.

[0043] However, alkoxysilane compounds react within non-aqueous electrolyte secondary batteries, thus reducing their concentration in the non-aqueous electrolyte. Therefore, in non-aqueous electrolyte secondary batteries that have undergone decomposition, or in the non-aqueous electrolyte secondary batteries circulating in the market, only the residual alkoxysilane compounds above the detection limit are acceptable.

[0044] As a non-aqueous solvent, examples 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). A single non-aqueous solvent can be used, or two or more can be used in combination.

[0045] Among these, chain carboxylic esters are suitable for preparing low-viscosity non-aqueous electrolytes. Therefore, the non-aqueous electrolyte can contain more than 1% by mass and less than 90% by mass of chain carboxylic esters. Methyl acetate is particularly suitable for low viscosity among chain carboxylic esters. Therefore, more than 90% by mass of the chain carboxylic ester can be methyl acetate.

[0046] Other examples of non-aqueous solvents include cyclic ethers, chain ethers, nitriles such as acetonitrile, and amides such as dimethylformamide.

[0047] Examples of cyclic ethers include 1,3-dioxolane, 4-methyl-1,3-dioxolane, tetrahydrofuran, 2-methyltetrahydrofuran, propylene oxide, 1,2-epoxybutane, 1,3-dioxane, 1,4-dioxane, 1,3,5-trioxane, furan, 2-methylfuran, 1,8-eucalyptol, crown ethers, etc.

[0048] 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 ethyl ether, diethylene glycol dibutyl ether, 1,1-dimethoxymethane, 1,1-diethoxyethane, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, etc.

[0049] These solvents can be fluorinated solvents obtained by replacing some of the hydrogen atoms with fluorine atoms. Fluorinated ethylene carbonate (FEC) can be used as a fluorinated solvent.

[0050] As lithium salts, lithium salts containing chloric acid (LiClO4, LiAlCl4, LiB) can be used, for example. 10 Cl 10 Lithium salts include those containing fluorine acids (LiPF6, LiPF2O2, LiBF4, LiSbF6, LiAsF6, LiCF3SO3, LiCF3CO2, etc.), lithium salts containing fluorinated imides (LiN(FSO2)2, LiN(CF3SO2)2, LiN(CF3SO2)(C4F9SO2), LiN(C2F5SO2)2, etc.), and lithium halides (LiCl, LiBr, LiI, etc.). Lithium salts can be used alone or in combination of two or more.

[0051] The concentration of lithium salt in the non-aqueous electrolyte can be above 0.5 mol / L and below 2 mol / L, or above 1 mol / L and below 1.5 mol / L. By controlling the lithium salt concentration within the above range, a non-aqueous electrolyte with excellent ion conductivity and low viscosity can be obtained.

[0052] Examples of additives other than alkoxysilyl compounds include 1,3-propanesulfonate lactone, methylbenzene sulfonate, cyclohexylbenzene, biphenyl, diphenyl ether, and fluorobenzene.

[0053] (Non-aqueous electrolyte secondary battery)

[0054] The non-aqueous electrolyte secondary battery disclosed herein comprises: a negative electrode, a positive electrode, and the aforementioned non-aqueous electrolyte.

[0055] (negative electrode)

[0056] The negative electrode, for example, comprises: a negative current collector and a negative electrode binder layer formed on the surface of the negative current collector. The aforementioned negative electrode binder layer contains a negative electrode active material as an essential component, and may also contain any component such as a binder, conductive material, or thickener. The binder, conductive material, thickener, and other components can each utilize known materials.

[0057] The negative electrode additive layer can be formed, for example, by coating a negative electrode slurry containing a negative electrode active material and a specified component of any kind, dispersed in a dispersion medium onto the surface of the negative electrode current collector and drying it. The dried coating can be calendered as needed. The negative electrode additive layer can be formed on one surface of the negative electrode current collector or on both surfaces.

[0058] The negative electrode active material contains silicon. Silicon-containing materials are sometimes treated as alloying materials. Here, alloying materials refer to materials containing elements that can form alloys with lithium. Examples of elements that can form alloys with lithium include silicon and tin, with silicon (Si) being particularly promising.

[0059] Silicon-containing materials can be silicon alloys, silicon compounds, or composite materials. Composite materials comprising a lithium-ion conductive phase and a silicon phase dispersed within the lithium-ion conductive phase are promising. Examples of lithium-ion conductive phases that can be used include silicon oxide phases, silicate phases, and carbon phases. Silicon oxide phases have a relatively high irreversible capacity. On the other hand, silicate phases are preferred due to their low irreversible capacity.

[0060] The main component of the silicon oxide phase (e.g., 95–100% by mass) can be silicon dioxide. The composition of the composite material containing the silicon oxide phase and silicon particles dispersed therein can be SiO₂ as a whole. x Indicates. SiO x It has a structure in which silicon particles are dispersed in amorphous SiO2. The oxygen content ratio x relative to silicon is, for example, 0.5 ≤ x < 2.0, more preferably 0.8 ≤ x ≤ 1.5.

[0061] The silicate phase may include at least one element selected from the group consisting of Group 1 and Group 2 elements of the long-period periodic table. Examples of Group 1 and Group 2 elements of the long-period periodic table include lithium (Li), potassium (K), sodium (Na), magnesium (Mg), calcium (Ca), strontium (Sr), and barium (Ba). Other elements may 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 due to its low irreversible capacity and high initial charge / discharge efficiency.

[0062] 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 may have a 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.

[0063] The carbon phase can be constituted by, for example, amorphous carbon with low crystallinity (i.e., amorphous carbon). The amorphous carbon can be, for example, hard carbon, soft carbon, or others.

[0064] The negative electrode active material may contain, in addition to the material containing silicon element, 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), hardly graphitizable carbon (hard carbon), etc. can be exemplified. Among them, graphite with excellent charge-discharge stability and less irreversible capacity is preferred.

[0065] In the negative electrode current collector, a metal sheet or metal foil is used, for example. As the material of the negative electrode current collector, stainless steel, nickel, nickel alloy, copper, copper alloy, etc. can be exemplified.

[0066] (Positive electrode)

[0067] 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 also contain optional components such as a binder material, a conductive material, a thickening material, etc. Known materials can be used for the optional components such as the binder material, the conductive material, the thickening material, etc.

[0068] The positive electrode mixture layer can be formed, for example, as follows: a positive electrode slurry in which a positive electrode mixture containing a positive electrode active material and a prescribed optional component is dispersed in a dispersion medium is coated on the surface of the positive electrode current collector and dried, thereby forming. 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 can be formed on both surfaces.

[0069] The positive electrode active material contains, for example, a lithium-containing composite oxide. The lithium-containing composite oxide is not particularly limited, and those having a layered rock salt-type crystal structure containing lithium and a transition metal are promising. 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 and 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 O2, etc. can be cited.

[0070] 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 means 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.

[0071] In the positive electrode current collector, a metal sheet or metal foil is used, for example. As the material of the positive electrode current collector, stainless steel, aluminum, aluminum alloy, titanium, etc. can be exemplified, for example.

[0072] Examples of the conductive materials 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 nanotubes (CNT), and graphite. They can be used alone or in combination of two or more kinds.

[0073] Examples of the binder materials used in the positive electrode binder layer and the negative electrode binder layer include fluororesins (such as polytetrafluoroethylene and polyvinylidene fluoride), polyacrylonitrile (PAN), polyimide resins, acrylic resins, polyolefin resins, etc. They can be used alone or in combination of two or more kinds.

[0074] (Separator)

[0075] The separator is sandwiched between the positive and negative electrodes. The separator has high ion permeability and moderate mechanical strength and insulation. Microporous membranes, woven fabrics, non-woven fabrics, etc., can be used as separators. Polyolefins such as polypropylene and polyethylene are preferred as materials for the separator.

[0076] As an example of a secondary battery structure, one can exemplify a structure in which an electrode assembly consisting of a positive and a negative electrode wound together and separated by a separator, and a non-aqueous electrolyte, are housed within the outer casing. Alternatively, other forms of electrode assemblies, such as a stacked electrode assembly with the positive and negative electrodes separated by a separator, can be used instead of the wound electrode assembly. Non-aqueous electrolyte secondary batteries can take any shape, such as cylindrical, square, coin-shaped, button-shaped, or sheet-shaped (laminated).

[0077] The following is a reference. Figure 1 and Figure 2 The following describes a non-aqueous electrolyte secondary battery according to one embodiment of the present disclosure. Figure 1 The top view is shown schematically, showing a portion of the structure of a non-aqueous electrolyte secondary battery according to an embodiment of the present disclosure. Figure 2 for Figure 1 A cross-sectional view along the X-X' line.

[0078] like Figure 1 and Figure 2 As shown, the non-aqueous electrolyte secondary battery 100 is a sheet-type battery, which includes an electrode assembly 4 and an outer casing 5 for housing the electrode assembly 4.

[0079] The electrode assembly 4 is a structure in which a positive electrode 10, a separator 30, and a negative electrode 20 are stacked sequentially, with the positive electrode 10 and the negative electrode 20 facing each other across the separator 30. Thus, the electrode assembly 4 is formed. The electrode assembly 4 is impregnated with a non-aqueous electrolyte (not shown).

[0080] The positive electrode 10 includes a positive electrode flux layer 1a and a positive electrode current collector 1b. The positive electrode flux layer 1a is formed on the surface of the positive electrode current collector 1b.

[0081] The negative electrode 20 includes a negative electrode flux layer 2a and a negative electrode current collector 2b. The negative electrode flux layer 2a is formed on the surface of the negative electrode current collector 2b.

[0082] A positive electrode tab 1c is connected to the positive current collector 1b, and a negative electrode tab 2c is connected to the negative current collector 2b. The positive electrode tab 1c and the negative electrode tab 2c extend to the outside of the outer casing 5.

[0083] The positive electrode lead 1c and the outer casing 5 and the negative electrode lead 2c and the outer casing 5 are respectively insulated by insulating electrode film 6.

[0084] The present disclosure will now be described in detail based on the embodiments and comparative examples, but the present disclosure is not limited to the following embodiments.

[0085] Example 1

[0086] (1) Synthesis of alkoxysilyl compounds

[0087] In a dried 100 mL four-necked container, add 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 stir to allow the reaction shown in the following formula to proceed. Heat and stir from room temperature to 50 °C until the allyl ether used as the starting material disappears. After confirming that the starting material has disappeared, stop heating and stirring, and remove the dichloroethane used as the solvent by distillation in an evaporator to obtain a crude brown oil X1 (4.0 g) containing alkoxysilyl compound A.

[0088]

[0089] Then, in a dried 500 mL eggplant-shaped container, add 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), and heat and stir from room temperature to 50 °C. After confirming that the raw materials have disappeared, stop heating and stirring, and remove the dichloroethane used as a solvent by distillation in a vacuum pump. Add brown oil X1 to the crude product after distillation, and use a distillation purification apparatus connected to a flask, T-tube, thermometer, condenser, vacuum pump, and pressure gauge to perform distillation purification at an oil bath temperature of 190 °C and a vacuum degree of 0.1-0.01 mmHg to obtain brown oil X2 (9.3 g) containing alkoxysilyl compound A.

[0090] Then, in a dried 500 mL eggplant-shaped container, 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, and the mixture was heated and stirred from room temperature to 50 °C. After confirming that the raw materials had disappeared, heating and stirring were stopped, and the dichloroethane used as a solvent was removed by distillation in a vacuum pump. Brown oil X2 was added to the crude mixture after distillation, and the mixture was purified again by distillation at an oil bath temperature of 190 °C and a vacuum degree of 0.1-0.01 mmHg to obtain a colorless oil compound X3 (13.3 g, 38.8 mol, yield 34.6%) containing alkoxysilyl compound A. 1 Purity was confirmed by NMR and gas chromatography (GC).

[0091] (2) Fabrication of the negative electrode

[0092] SiO x An aqueous solution of (x=1) (Shin-Etsu Chemical Industry Co., Ltd., KSC1064) and carbon black (Denka Co., Ltd., HS-100) and polyacrylamide (binder) with SiO x Carbon black and polyacrylamide are mixed in a mass ratio of 75:15:10, and water is further added and stirred to prepare a negative electrode slurry. Next, the negative electrode slurry is coated onto one side of the negative electrode current collector (electrolytic copper foil) to form a coating film. After the coating film dries, it is calendered together with the negative electrode current collector using calendering rollers to obtain a negative electrode with a negative electrode additive layer.

[0093] Cut the negative electrode into Figure 3 (a) shape, to obtain the negative electrode 20 for evaluation. Figure 3 In (a), the 60mm × 40mm area functions as the negative electrode, and the 10mm × 10mm protrusion is the connection area with the tab lead 2c. Then, further, as... Figure 3 As shown in (b), the negative electrode binder layer 2a formed on the aforementioned connection region is cut away, exposing the negative electrode current collector 2b. Then, as... Figure 3 As shown in (c), the exposed portion of the negative current collector 2b is connected to the negative electrode tab lead 2c, and the specified area around the negative electrode tab lead 2c is covered by the insulating tab film 6.

[0094] (3) Fabrication of the electrodes

[0095] The counter electrode is made by adhering lithium metal foil to one side of an electrolytic copper foil (current collector).

[0096] The counter electrode is cut into the same shape as the negative electrode, and the lithium metal foil formed on the connection area, which is also formed on the negative electrode, is peeled off to expose the current collector. Then, the exposed part of the current collector is connected to the tab lead in the same way as the negative electrode, and the designated area around the tab lead is covered by an insulating tab film.

[0097] (4) Preparation of non-aqueous electrolyte

[0098] 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) at a volume ratio of 20:80. Alkoxysilane compound A was added to the non-aqueous electrolyte at a concentration of 0.1% by mass.

[0099] (5) Evaluation of the manufacturing of battery cells

[0100] Using the aforementioned negative and counter electrodes, a battery cell with a standard negative electrode design capacity of 114 mAh was fabricated. First, the negative and counter electrodes were placed opposite each other with two sheets of polyethylene separators (15 μm thick) coated with aramid, with the negative electrode adhesive layer overlapping the lithium metal foil, to obtain an electrode assembly. Next, a rectangular Al laminate film (100 μm thick) was folded in half, and the long side end was heat-sealed at 230°C to form a tube. Then, the fabricated electrode assembly was placed into the tube from one of the short sides, aligning the end face of the Al laminate film with the position of the heat-sealing resin for each electrode lead, and heat-sealed at 230°C. Finally, a non-aqueous electrolyte was injected 1.2 cm from the un-heat-sealed short side of the tube. 3 After electrolyte injection, the cells were allowed to stand for 3 minutes under reduced pressure of 0.02 MPa, then restored to atmospheric pressure. This process was repeated twice to allow the non-aqueous electrolyte to permeate the negative electrode binder layer. Finally, the end face of the Al laminate film on the injected side was heat-sealed at 230°C to obtain the evaluation battery cell A1. It should be noted that the evaluation battery cell was fabricated in a dry gas atmosphere with a dew point below -60°C.

[0101] (6) Battery evaluation

[0102] The evaluation battery unit was clamped with a pair of 10×5cm stainless steel (6mm thick) clamps and fixed with pressure of 3.2MPa.

[0103] <Cycle 1>

[0104] The lithium electrode was charged with a constant current of 0.05C (1C is the current value for discharging the designed capacity within 1 hour) for 2 hours in a constant temperature bath at 25°C. Afterward, the charge was stopped for 12 hours. Next, the lithium electrode was further charged with a constant current of 0.05C until the battery cell voltage reached 0.01V, followed by a 20-minute stop. Then, the lithium electrode was discharged from the negative electrode with a constant current of 0.05C until the battery cell voltage reached 1.5V, followed by a 20-minute stop.

[0105] <Cycle 2-3>

[0106] Next, the lithium is charged at the negative electrode with a constant current of 0.05C until the battery cell voltage reaches 0.01V, then paused for 20 minutes. Then, the lithium is discharged from the negative electrode with a constant current of 0.05C until the battery cell voltage reaches 1.5V, then paused for 20 minutes.

[0107] <Cycles 4-50>

[0108] Charge the lithium at the negative electrode with a constant current of 0.3C until the battery cell voltage is 0.01V. Then, pause for 20 minutes. Next, discharge the lithium from the negative electrode with a constant current of 0.3C until the battery cell voltage is 1.5V. Then, pause for 20 minutes. Repeat this cycle.

[0109] The capacity obtained in the 50th lithium discharge cycle relative to the capacity obtained in the 1st lithium discharge cycle was calculated as the 50-cycle capacity retention rate. The results are shown in Table 1.

[0110] Examples 2-4

[0111] In the preparation of the non-aqueous electrolyte, the content of alkoxysilyl compound A added to the non-aqueous electrolyte was changed as shown in Table 1. Otherwise, the evaluation battery cells A2 to A4 were prepared in the same manner as in Example 1, and the evaluation was carried out in the same manner.

[0112] Examples 5-8

[0113] In the synthesis of alkoxysilyl compounds, ethylene glycol monoethylene ether (5.0 g, 1.0 eq.), superhydrodimethylformamide (DMF) 50 mL, and allyl bromide (7.55 g, 1.1 eq.) were added to a 200 mL reactor at room temperature. NaH (2.27 g, 1.0 eq.) was added slowly in multiple portions over 20 minutes while stirring, yielding a white suspension. The white suspension was stirred at room temperature for 16 hours to allow 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.

[0114]

[0115] The reaction solution was placed in a separatory funnel, 30 mL of diethyl ether was added and stirred, and the organic phase was extracted. This operation was repeated 3 times. The extracted organic phases were combined and injected back into the separatory funnel. 100 mL of water was added and stirred, and the aqueous phase was discharged. This operation was repeated 3 times. Then, 100 mL of saturated saline solution was added and stirred, and the aqueous phase was discharged. Afterward, 20 g of anhydrous sodium sulfate was added to the remaining organic phase and stirred to remove water. The anhydrous sodium sulfate was removed by filtration. Then, the diethyl ether was removed under normal pressure and at a bath temperature of 50 °C. The residue was purified by distillation using a distillation purification apparatus connected to a flask, a T-tube, a thermometer, a condenser, a vacuum pump, and a pressure gauge (vacuum: 20 mmHg, oil bath temperature: 70 °C, vapor temperature: 50 °C) to obtain a colorless solid Y1 containing compound B.

[0116] Then, in a 50 mL reactor, compound B (1.0 g, 1.0 eq.), 30 mL of dehydrated dichloromethane, and 52 g, 0.01 eq. of cyclooctadiene iridium chloride dimer ([Ir(COD)Cl]2) were added to obtain an orange solution. Trimethoxysilane (HSi(OMe)3) (3.0 mL, 3.0 eq.) was slowly added dropwise over 15 minutes while stirring the orange solution. The solution was stirred at room temperature for 2 hours to allow the reaction shown in the following formula to proceed, yielding a solution Y2 containing alkoxysilyl compound C.

[0117]

[0118] Subsequently, at room temperature, compound B (5.0 g, 1.0 eq.), 125 mL of dehydrated dichloromethane, and 0.26 g of cyclooctadiene iridium chloride dimer ([Ir(COD)Cl]2) were added to a 50 mL reactor 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. After stirring the solution at room temperature for 2 hours, solution Y2 was added to the stirred solution. A distillation purification apparatus was installed on the reactor, and dichloromethane was removed at a bath temperature of 50 °C. Volatile components were further removed under reduced pressure of 20 mmHg / 70 °C. The residue was purified by distillation (vacuum: 0.1-0.3 mmHg, oil bath temperature: 180-195℃, steam temperature: 139-142℃) to obtain alkoxysilyl compound C (10.4 g, 27.9 mol, yield 59.6%) as a light brown solution.

[0119] In the preparation of the non-aqueous electrolyte, alkoxysilane compound C is added in such a way that the concentration in the non-aqueous electrolyte is as shown in Table 1 by mass%.

[0120] In addition, the evaluation battery cells A5 to A8 were manufactured in the same manner as in Example 1, and the evaluation was performed in the same manner.

[0121] Comparative Examples 1 and 2

[0122] In the preparation of the non-aqueous electrolyte, instead of alkoxysilyl compounds, vinyltris(2-methoxyethoxy)silane (VTMS) as shown in Table 1 is added to the non-aqueous electrolyte in the amounts shown below.

[0123] Apart from the above, evaluation battery cells B1 and B2 were fabricated in the same manner as in Example 1, and evaluated in the same way. It should be noted that VTMS is the additive used in Non-Patent Document 1.

[0124]

[0125] Comparative Example 3

[0126] In the preparation of the non-aqueous electrolyte, no alkoxysilane compound was added. Otherwise, the evaluation cell B3 was prepared in the same manner as in Example 1 and evaluated in the same manner.

[0127] [Table 1]

[0128]

[0129] Figure 4 The diagram shows the relationship between the number of charge-discharge cycles and the capacity retention rate of battery cells A2, A3, and B1 to B3 used for evaluation. Figure 5 The diagram shows the relationship between the number of charge-discharge cycles and the capacity retention of battery cells A6, A7, and B1 to B3 used for evaluation.

[0130] According to Table 1 and Figure 4 , Figure 5 It is understandable that the capacity retention is improved when alkoxysilyl compounds A or C, which are bis(alkoxysilyl) ethers, are added to non-aqueous electrolytes.

[0131] On the other hand, such as Figure 4 and Figure 5 As shown, the VTMS used in non-patent literature 1 cannot improve capacity maintenance.

[0132] Industrial availability

[0133] The additives for non-aqueous electrolytes disclosed herein are suitable for use in non-aqueous electrolyte secondary batteries where the negative electrode active material contains silicon.

[0134] The present invention has been described with respect to the currently preferred embodiments, but it should be interpreted as not limiting such disclosure. Various modifications and alterations will be readily apparent to those skilled in the art who fall within the scope of the invention upon reading the foregoing disclosure. Therefore, the appended claims should be interpreted as encompassing all modifications and alterations without departing from the spirit and scope of the invention.

[0135] Explanation of reference numerals in the attached figures

[0136] 1a: Positive electrode flux layer, 1b: Positive electrode current collector, 1c: Positive electrode tab lead, 2a: Negative electrode flux layer, 2b: Negative electrode current collector, 2c: Negative electrode tab lead, 4: Plate assembly, 5: Outer shell, 6: Insulating tab film, 10: Positive electrode, 20: Negative electrode, 30: Separator, 100: Non-aqueous electrolyte secondary battery.

Claims

1. An additive for non-aqueous electrolytes, comprising an alkoxysilyl compound, said alkoxysilyl compound being a bis(alkoxysilyl) ether of general formula (1), R1 uses R11-(O-R12) n -O-R13 indicates that R11, R12, and R13 are each independently an alkylene group having 2 or more but less than 4 carbon atoms, and n is an integer from 0 to 2. R2 to R7 are each an alkoxy group with 1 to 3 carbon atoms.

2. The additive for non-aqueous electrolytes according to claim 1, wherein, R1 is either -C3H6-O-C3H6- or -C2H4-O-C2H4-O-C3H6-.

3. The additive for non-aqueous electrolytes according to claim 1 or 2, wherein, R2 to R7 are methoxy groups.

4. A non-aqueous electrolyte comprising: a non-aqueous solvent, a salt dissolved in the non-aqueous solvent, and an additive for a non-aqueous electrolyte according to any one of claims 1 to 3.

5. The non-aqueous electrolyte according to claim 4, wherein, The concentration of the additive used in the non-aqueous electrolyte is less than 10% by mass.

6. The non-aqueous electrolyte according to claim 4 or 5, wherein, The concentration of the additive used in the non-aqueous electrolyte is 0.05% by mass or more.

7. A non-aqueous electrolyte secondary battery, comprising: a negative electrode having a negative electrode binder layer, a positive electrode, and the non-aqueous electrolyte according to any one of claims 4 to 6. The negative electrode mixture layer contains negative electrode active materials. The negative electrode active material contains a material containing silicon.

8. The non-aqueous electrolyte secondary battery according to claim 7, wherein, The silicon-containing material is a composite material. The composite material comprises: a lithium-ion conductive phase and a silicon phase dispersed in the lithium-ion conductive phase.

Images