Additive for nonaqueous electrolyte and nonaqueous electrolyte and nonaqueous electrolyte secondary battery containing the same

Abstract

The additive for nonaqueous electrolyte solution contains a bisalkoxysilyl compound having 2 or more silyl groups connected by an alkylene group or an amino group, the 2 or more silyl groups each having at least one selected from the group consisting of an alkoxy group and an oxyalkyl group, the oxyalkyl group being represented by -O-(C x H 2x+1 O y ) represents, x is an integer of 1 or more, and y is an integer of 1 or more.

Description

Technical Field

[0001] This disclosure relates to additives for non-aqueous electrolytes, 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 exhibit significant expansion and contraction during charge and discharge, which can easily induce side reactions and reduce capacity retention during charge-discharge cycles.

[0003] Non-patent literature 1 reports that capacity retention during charge-discharge cycles is improved by adding a vinylsilane-containing 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] In the proposal of Non-Patent Literature 1, it is difficult to consistently improve the capacity retention rate during charge-discharge cycles.

[0008] One aspect of this disclosure relates to an additive for non-aqueous electrolytes, comprising an alkoxysilyl compound having two or more silyl groups linked by an alkylene or amino group, wherein each of the two or more silyl groups is selected from at least one group selected from the group consisting of alkoxy and oxyalkyl groups, and the oxyalkyl group is represented by -O-(C x H 2x+1 O y ) indicates that x is an integer greater than or equal to 1 and y is an integer greater than or equal to 1.

[0009] Another 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.

[0010] Another 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.

[0011] 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. Attached Figure Description

[0012] Figure 1 The top view has been cut off to schematically show a portion of the structure of a non-aqueous electrolyte secondary battery according to an embodiment of the present disclosure.

[0013] Figure 2 for Figure 1 The cross-sectional view of the non-aqueous secondary battery shown along line X-X'.

[0014] Figure 3 A diagram illustrating the fabrication method of the negative electrode used for performance evaluation.

[0015] Figure 4 A graph showing the relationship between the number of charge-discharge cycles and capacity retention of a non-aqueous electrolyte secondary battery. Detailed Implementation

[0016] (Additives for non-aqueous electrolytes)

[0017] The non-aqueous electrolyte additives of the present disclosure comprise alkoxysilyl compounds. The alkoxysilyl compound has two or more silyl groups linked by an alkylene or amino group. Each of the two or more silyl groups is selected from at least one group composed of alkoxy and oxyalkyl groups, wherein the oxyalkyl group is represented by -O-(C x H 2x+1 O y ) indicates that x is an integer greater than or equal to 1 and y is an integer greater than or equal to 1.

[0018] Alkoxysilyl compounds can be either diekoxysilyl compounds or trialkoxysilyl compounds. In the case of diekoxysilyl compounds, the two silyl groups are linked by an alkylene group or a secondary amino group. In the case of trialkoxysilyl compounds, the three alkoxysilyl groups are linked by a tertiary amino group.

[0019] In the above configuration, the alkoxy or oxyalkyl groups of each silane group 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. Through the formation of bonds between the alkoxy or oxyalkyl groups and the surface of the silicon-containing material, the surface of the silicon-containing material is covered by a disilyl alkane or disilylamine structure (including a trisilylamine structure) with stable siloxane bonds at both ends. That is, the surface of the silicon-containing material is covered by a coating (hereinafter also referred to as an SRS coating) containing a disilyl alkane or disilylamine structure. The SRS coating has high elasticity, is stable against reversible elastic deformation, and is not easily damaged even under repeated charge-discharge cycles. As a result, side reactions in the negative electrode are suppressed, and the capacity retention rate during charge-discharge cycles is steadily improved.

[0020] The alkoxysilyl compound can be at least one selected from the group consisting of bis(alkoxysilyl)alkanes represented by general formula (1) and bis(alkoxysilyl)amines having an alkylene group between N and Si:

[0021]

[0022] Here, R1 is an alkylene group or a secondary or tertiary amino group. 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 of 1 or more and y1 is an integer of 1 or more. 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 At least one of the groups consisting of alkyl groups, where x2 is an integer greater than or equal to 1 and y2 is an integer greater than or equal to 1. The remaining groups R2 to R7 are each independently represented by C. x3 H 2x3+1 O y3 The alkyl or oxoalkyl group is represented by x3 being an integer greater than or equal to 1 and y3 being an integer greater than or equal to 0. Oxoalkyl groups are groups other than alkoxy groups.

[0023] 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 SRS coating containing a Si-R1-Si structure.

[0024] The more carbon atoms in the alkylene group constituting R1, the better the flexibility, thus facilitating reversible deformation of the SRS coating. However, it is believed that if the number of carbon atoms in R1 becomes excessively high, the alkylene chain becomes excessively long, reducing the compactness of the SRS coating and diminishing its effectiveness in suppressing side reactions. Therefore, the desired number of carbon atoms in the alkylene group is 1–6, with 2–4 being more desirable. The bis(alkoxysilyl)alkane is ideally bis(alkoxysilyl)C 1-6 Alkanes can be bis(alkoxysilyl)C 2-4 Alkanes.

[0025] The amino group constituting R1 can have a structure represented by R11-N-R12. Here, R11 and R12 are each independently an alkylene group having one or more carbon atoms. It is believed that this type of R1 exhibits excellent flexibility and strong electron shielding, resulting in a greater effect in suppressing side reactions.

[0026] The higher the carbon number of the amino group, the better the flexibility, thus facilitating reversible deformation of the SRS coating. However, it is believed that if the number of carbons in the amino group becomes excessively high, the R1 phase becomes excessively long, reducing the density of the SRS coating and decreasing its effectiveness in suppressing side reactions. Therefore, the carbon number of the alkylene group is ideally set at 1 to 6, and more preferably 2 to 4. For example, bis(alkoxysilylalkyl)amines are ideally bis(alkoxysilylC) 1-6 Alkylamines can be bis(alkoxysilyl)C 2-4 Alkylamine.

[0027] At least one of R2 to R4 can be an alkoxy group selected from carbon 1 to 6 and a group using -O-(C x1 H 2x1+1 O y1 The group consisting of at least one of the following: x1 being an integer from 1 to 6, y1 being 1 or 2 alkyl groups, and at least one of R5 to R7 being an alkoxy group selected from 1 to 6 carbon atoms, and using -O-(C x2 H 2x2+1 O y2 It is at least one of the group consisting of alkoxyalkyl groups, where x2 is an integer from 1 to 6 and y2 is 1 or 2. From the viewpoint of improving reactivity with the surface of materials containing silicon, the alkoxy and alkoxyalkyl groups can be smaller, and the carbon number of the alkoxy and alkoxyalkyl groups can be, for example, 1 to 3.

[0028] The remainder of R2 to R7 are each used independently by C. x3 H 2x3+1 O y3 The term refers to alkyl groups other than alkoxy groups, where x3 is an integer greater than or equal to 1 and y3 is an integer greater than or equal to 0 (e.g., an integer greater than or equal to 0 and less than 2). From the viewpoint of reducing steric hindrance during the reaction, C3 is used. x3 H 2x3+1 O y3 The number of carbon atoms in the represented groups can be 1 to 6, or 1 to 3. R2 to R4 are independent; all of R2 to R4 can have the same number of carbon atoms, or all of R2 to R4 can have different numbers of carbon atoms, and two of R2 to R4 can have the same number of carbon atoms. Similarly, R5 to R7 are independent; all of R5 to R7 can have the same number of carbon atoms, or all of R5 to R7 can have different numbers of carbon atoms, and two of R5 to R7 can have the same number of carbon atoms.

[0029] In formula (1), the two alkoxysilyl groups (R2R3R4Si- or R5R6R7Si-) connected to R1 can be the same or different. However, in order to improve the structural symmetry of the SRS coating and form a more stable structure, the two alkoxysilyl groups connected to R1 can be set to have the same structure.

[0030] In formula (1), when R1 is an alkylene group, the alkoxysilyl compound is a type of bis(alkoxysilyl)alkane. The SRS coating formed when using bis(alkoxysilyl)alkane consists of a stable siloxane structure and an alkylene structure. This SRS coating not only becomes easier to elastically deform, but is also chemically and structurally stable.

[0031] Among bis(alkoxysilyl)alkanes, at least one readily available example is selected from the group consisting of 1,2-bis(trialkoxysilyl)ethane and 1,6-bis(trialkoxysilyl)hexane. Examples of 1,2-bis(trialkoxysilyl)ethane include 1,2-bis(trimethoxysilyl)ethane and 1,2-bis(triethoxysilyl)ethane. Examples of 1,6-bis(trialkoxysilyl)hexane include 1,6-bis(trimethoxysilyl)hexane and 1,6-bis(triethoxysilyl)hexane.

[0032] In formula (1), when R1 is an amino group, the alkoxysilyl compound is a type of alkoxysilyl alkylamine. More specifically, the alkoxysilyl alkylamine can be at least one selected from the group consisting of bis(alkoxysilyl)amine and tri(alkoxysilyl)amine.

[0033] Among bis- or tris(alkoxysilyl)amines, at least one selected from the group consisting of bis[3-(trialkoxysilyl)propyl]amine and tris[3-(trialkoxysilyl)propyl]amine is readily available. Examples of bis[3-(trialkoxysilyl)propyl]amine include bis[3-(trimethoxysilyl)propyl]amine and bis[3-(triethoxysilyl)propyl]amine. Examples of tris[3-(trialkoxysilyl)propyl]amine include tris[3-(trimethoxysilyl)propyl]amine and tris[3-(triethoxysilyl)propyl]amine.

[0034] (Non-aqueous electrolyte)

[0035] The non-aqueous electrolyte comprises: a non-aqueous solvent, a salt (solute) dissolved in the non-aqueous solvent, and the aforementioned additives for use in 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.

[0036] The concentration of the alkoxysilyl compound in the non-aqueous electrolyte can be, for example, 10% by mass or less, 8% by mass or less, or 5% by mass or less. If it is within this range, a good and adequate SRS coating is sufficiently formed regardless of the amount of silicon-containing material contained in the negative electrode active material. It is believed that if the concentration of the alkoxysilyl compound represented by formula (1) in the non-aqueous electrolyte is, for example, 0.2% by mass or more, a considerable SRS coating can be formed, and a significant effect on improving the capacity retention rate during charge-discharge cycles of the non-aqueous electrolyte secondary battery can be obtained.

[0037] However, alkoxysilane compounds react within non-aqueous electrolyte secondary batteries, thus gradually decreasing their concentration in the non-aqueous electrolyte. Consequently, alkoxysilane compounds exceeding the detection limit may remain in the non-aqueous electrolyte extracted from completed non-aqueous electrolyte secondary batteries or commercially available non-aqueous electrolyte secondary batteries.

[0038] As a non-aqueous solvent, cyclic carbonates, chain carbonates, cyclic carboxylic acid esters, and chain carboxylic acid esters can be used, for example. 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 non-aqueous solvent can be used alone, or two or more can be used in combination.

[0039] 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 low in viscosity among the chain carboxylic esters. Therefore, more than 90% by mass of the chain carboxylic ester can be methyl acetate.

[0040] Other examples of non-aqueous solvents include cyclic ethers, chain ethers, nitriles such as acetonitrile, and amides such as dimethylformamide.

[0041] 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.

[0042] 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, tetraethylene glycol dimethyl ether, etc.

[0043] These solvents can be fluorinated solvents in which some of the hydrogen atoms are replaced by fluorine atoms. Ethyl fluorocarbonate (FEC) can be used as a fluorinated solvent.

[0044] 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 fluorine acid imides (LiN(FSO2)2, LiN(CF3SO2)2, LiN(CF3SO2)(C4F9SO2), LiN(C2F5SO2)2, etc.), and lithium halides (LiCl, LiBr, LiI, etc.). A single lithium salt can be used, or two or more can be combined.

[0045] 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.

[0046] Examples of additives other than alkoxysilyl compounds include 1,3-propanesulfonate lactone, methylbenzene sulfonate, cyclohexylbenzene, biphenyl, diphenyl ether, and fluorobenzene.

[0047] (Non-aqueous electrolyte secondary battery)

[0048] The non-aqueous electrolyte secondary battery disclosed herein comprises: a negative electrode, a positive electrode, and the aforementioned non-aqueous electrolyte.

[0049] (negative electrode)

[0050] 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. Known materials can be used for each of the binder, conductive material, and thickener components.

[0051] 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 arbitrary composition, 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 or on both surfaces of the negative electrode current collector.

[0052] 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 desirable.

[0053] The silicon-containing material can be a silicon alloy, a silicon compound, or a composite material. Ideally, it should be a composite material comprising a lithium-ion conductive phase and silicon particles dispersed within the lithium-ion conductive phase. Examples of lithium-ion conductive phases include silicon oxide, silicate, and carbon phases. Silicon oxide phases have a relatively high irreversible capacity. Conversely, silicate phases are preferred where the irreversible capacity is low.

[0054] 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 within it can be, as a whole, made of SiO₂. x Indicates. SiO x It has a structure in which fine 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.

[0055] The silicate phase may include at least one element selected from the group consisting of elements from Group 1 and Group 2 of the long-period periodic table. Examples of elements from Group 1 and Group 2 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). From the perspective of low irreversible capacity and high initial charge / discharge efficiency, a silicate phase containing lithium (hereinafter also referred to as a lithium silicate phase) is preferred.

[0056] 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 composition represented by the formula: Li 2z SiO 2+z (0 < z < 2). z preferably satisfies the relationship 0 < z < 1, and more preferably z = 1 / 2. Examples of elements other than Li, Si, and O that can be contained in the lithium silicate phase include iron (Fe), chromium (Cr), nickel (Ni), manganese (Mn), copper (Cu), molybdenum (Mo), zinc (Zn), aluminum (Al), etc.

[0057] The carbon phase can be composed of, for example, amorphous carbon with low crystallinity (i.e., non-crystalline carbon). The amorphous carbon can be, for example, hard carbon, soft carbon, or other substances.

[0058] In addition to materials containing silicon elements, the negative electrode active material may also contain materials that electrochemically absorb and release lithium ions, lithium metal, lithium alloys, etc. As the material that electrochemically absorbs and releases lithium ions, a carbon material is preferred. Examples of the carbon material include graphite, graphitizable carbon (soft carbon), non-graphitizable carbon (hard carbon), etc. Among them, graphite with excellent charge-discharge stability and less irreversible capacity is preferred.

[0059] In the negative electrode current collector, a metal sheet or metal foil is used, for example. Examples of the material of the negative electrode current collector include stainless steel, nickel, nickel alloy, copper, copper alloy, etc.

[0060] (Positive electrode)

[0061] 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 any components such as a binder material, a conductive material, a thickening material, etc. Known materials can be used respectively for any components such as the binder material, the conductive material, and the thickening material.

[0062] The positive electrode mixture layer can be formed, for example, as follows: A positive electrode paste containing a positive electrode active material and a specified optional component dispersed in a dispersion medium is coated on the surface of the positive electrode current collector and dried to form the layer. The dried coating film can be calendered as needed. The positive electrode mixture layer can be formed on one surface of the positive electrode current collector or on both surfaces.

[0063] The positive electrode active material contains, for example, a lithium-containing composite oxide. The lithium-containing composite oxide is not particularly limited, and preferably has a layered rock salt-type crystal structure containing lithium and a transition metal. Specifically, the lithium-containing composite oxide can be, for example, Li a Ni 1-x-y Co x M y O2 (where 0 < a ≤ 1.2, 0 ≤ x ≤ 0.1, 0 ≤ y ≤ 0.1, 0 < x + y ≤ 0.1, and M is at least one selected from the group consisting of Na, Mg, Sc, Y, Mn, Fe, Cu, Zn, Al, Cr, Pb, Sb, and B). From the viewpoint of the stability of the crystal structure, Al can be included as M. Note that the value of a representing the molar ratio of lithium increases or decreases according to charge and discharge. As a specific example, LiNi 0.9 Co 0.05 Al 0.05 O2, LiNi 0.91 Co 0.06 Al 0.03 O2, etc. can be cited.

[0064] The positive electrode active material (particularly the lithium-containing composite oxide) usually has a morphology of secondary particles aggregated from primary particles. The average particle size of the positive electrode active material can be, for example, 2 μm or more and 20 μm or less. Here, the average particle size refers to the median particle size 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.

[0065] For 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.

[0066] Examples of the conductive materials used in the positive electrode mixture layer and the negative electrode mixture layer include carbon materials such as carbon black (CB), acetylene black (AB), Ketjen black (KB), carbon nanotubes (CNT), and graphite. They can be used alone or in combination of two or more.

[0067] Examples of the binder materials used in the positive electrode mixture layer and the negative electrode mixture layer include fluororesins (such as polytetrafluoroethylene and polyvinylidene fluoride), polyacrylonitrile (PAN), polyimide resin, acrylic resin, polyolefin resin, etc. They can be used alone or in combination of two or more.

[0068] (Separator)

[0069] A separator is sandwiched between the positive and negative electrodes. The separator has high ion permeability and possesses moderate mechanical strength and insulation. Microporous membranes, woven fabrics, non-woven fabrics, etc., can be used as the separator. Polyolefins such as polypropylene and polyethylene are preferred as the material for the separator.

[0070] 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, along with a non-aqueous electrolyte, is housed within the outer casing. Alternatively, other forms of electrode assemblies, such as a stacked electrode assembly consisting of a positive and a negative electrode 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).

[0071] The following is a reference. Figure 1 and Figure 2 The following describes one embodiment of the non-aqueous electrolyte secondary battery of the present disclosure. Figure 1 A top view showing a portion of an example of a non-aqueous electrolyte secondary battery structure has been cut off. Figure 2 for Figure 1 A cross-sectional view along the X-X' line.

[0072] like Figure 1 and Figure 2 As shown, the non-aqueous electrolyte secondary battery 100 is a sheet-type battery, which has an electrode assembly 4 and an outer casing 5 for housing the electrode assembly 4.

[0073] 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. A non-aqueous electrolyte permeates the electrode assembly 4.

[0074] 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.

[0075] 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.

[0076] A negative electrode tab lead 1c is connected to the negative current collector 1b, and a negative electrode tab lead 2c is connected to the negative current collector 2b. The positive electrode tab lead 1c and the negative electrode tab lead 2c extend to the outer casing 5.

[0077] 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.

[0078] The present disclosure will now be described in detail based on embodiments and comparative examples, but the present disclosure is not limited to the following embodiments.

[0079] Example 1

[0080] (1) Fabrication of the negative electrode

[0081] SiO x (x=1)(Shin-Etsu Chemical Industry Co., Ltd., KSC1064) and an aqueous solution of 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, the negative electrode current collector and the coating film are calendered together using calendering rollers to obtain a negative electrode with a negative electrode additive layer.

[0082] Cut the negative electrode into Figure 3 The shape of (a) is used 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. 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 a specified area on the outer periphery of the negative electrode tab lead 2c is covered with an insulating tab film 6.

[0083] (2) Fabrication of the electrodes

[0084] A counter electrode is made by adhering a lithium metal foil to one side of an electrolytic copper foil (current collector).

[0085] 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 portion of the current collector is connected to the tab lead in the same way as the negative electrode, and a specified area around the outer periphery of the tab lead is covered with an insulating tab film.

[0086] (3) Preparation of non-aqueous electrolyte

[0087] A non-aqueous electrolyte was prepared by dissolving LiPF6 at a concentration of 1 mol / L in a mixed solvent of ethylene fluorocarbonate (FEC) and dimethyl carbonate (DMC) at a volume ratio of 20:80. 0.25% by mass of 1,2-bis(trimethoxysilyl)ethane (EBTMOS), represented by the following formula (1-1), was added to the non-aqueous electrolyte.

[0088]

[0089] (4) Evaluation of the manufacturing of battery cells

[0090] 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 face-to-face with two polyethylene separators (15 μm thick) with an aramid coating, overlapping the negative electrode adhesive layer and 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 inserted 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-sealing at 230°C. Finally, a non-aqueous electrolyte was injected 1.2 cm from the unsealed 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 air atmosphere with a dew point below -60°C.

[0091] (5) Battery evaluation

[0092] The evaluation battery unit was clamped with a pair of 10×5cm stainless steel (6mm thick) clamps and fixed under pressure at 3.2MPa.

[0093] <Cycle 1>

[0094] In a constant-temperature bath at 25°C, lithium was charged to the negative electrode for 2 hours at a constant current of 0.05C (1C is the current value for discharging the designed capacity within 1 hour), followed by a 12-hour rest period. Next, lithium was further charged to the negative electrode at a constant current of 0.05C until the battery cell voltage reached 0.01V, followed by a 20-minute rest period. Then, lithium was discharged from the negative electrode at a constant current of 0.05C until the battery cell voltage reached 1.5V, followed by a 20-minute rest period.

[0095] <Cycle 2-3>

[0096] Next, charge the lithium battery at the negative electrode with a constant current of 0.05C until the battery cell voltage reaches 0.01V, then pause for 20 minutes. Then, discharge the lithium battery from the negative electrode with a constant current of 0.05C until the battery cell voltage reaches 1.5V, then pause for 20 minutes.

[0097] <Cycles 4-50>

[0098] Charge the lithium at the negative electrode with a constant current of 0.3C until the battery cell voltage is 0.01V. Then, rest for 20 minutes. Then, discharge the lithium from the negative electrode with a constant current of 0.3C until the battery cell voltage is 1.5V. After that, rest for 20 minutes and repeat the cycle.

[0099] The capacity obtained after the 50th lithium discharge cycle, relative to the capacity obtained after the 1st lithium discharge cycle, was calculated as the 50-cycle capacity retention rate. The results are shown in Table 1.

[0100] Examples 2-7

[0101] In the preparation of the non-aqueous electrolyte, the content of EBTMOS added to the non-aqueous electrolyte was changed as shown in Table 1. Otherwise, the evaluation battery cells A2 to A7 were prepared in the same manner as in Example 1, and the evaluation was carried out in the same manner.

[0102] Examples 8-10

[0103] In the preparation of the non-aqueous electrolyte, 1,6-bis(trimethoxysilyl)hexane (HBTMOS) represented by the following formula (1-2) was added to the non-aqueous electrolyte in the amounts shown in Table 1 instead of EBTMOS. Otherwise, the evaluation battery cells A8 to A10 were prepared in the same manner as in Example 1, and the evaluation was performed in the same manner.

[0104]

[0105] Comparative Examples 1 and 2

[0106] In the preparation of the non-aqueous electrolyte, vinyltris(2-methoxyethoxy)silane (VTMS) represented by the following formula (2) was added to the non-aqueous electrolyte in the amounts shown in Table 1 instead of EBTMOS. Otherwise, the evaluation battery cells B1 to B2 were prepared in the same manner as in Example 1, and the evaluation was carried out in the same manner.

[0107] It should be noted that VTMS is the additive used in Non-Patent Document 1.

[0108]

[0109] Comparative Example 3

[0110] In the preparation of the non-aqueous electrolyte, no EBTMOS was added. Otherwise, the evaluation cell B3 was prepared in the same manner as in Example 1, and the evaluation was performed in the same manner.

[0111] [Table 1]

[0112]

[0113] Figure 4The diagram shows the relationship between the number of charge-discharge cycles and capacity retention for battery cells A6, A9, B1, B2, and B3 used for evaluation.

[0114] According to Table 1 and Figure 4 It can be understood that the capacity retention is improved when EBTMOS and HBTMOS, which are alkoxysilyl compounds represented by formula (1), are added to the non-aqueous electrolyte. It is evident that the effect of EBTMOS is greater, and the effect becomes significant depending on the content of EBTMOS. It should be noted that the effect of EBTMOS is approximately saturated when its content in the non-aqueous electrolyte is 4–5% by mass.

[0115] On the other hand, such as Figure 4 As shown, without the VTMS used in Patent Document 1, the capacity maintenance rate cannot be improved.

[0116] Industrial availability

[0117] 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.

[0118] Explanation of reference numerals in the attached figures

[0119] 1a Positive electrode mixture layer

[0120] 1b Positive current collector

[0121] 1c Positive electrode tab lead

[0122] 2a Negative electrode mixture layer

[0123] 2b Negative current collector

[0124] 2c Negative electrode tab lead

[0125] 4-plate assembly

[0126] 5. Exterior casing

[0127] 6. Insulating tab film

[0128] 10 Positive electrode

[0129] 20 Negative electrode

[0130] 30 separators

[0131] 100 Lithium-ion Secondary Battery

Claims

1. A non-aqueous electrolyte secondary battery, comprising: a negative electrode having a negative electrode binder layer, a positive electrode, and a non-aqueous electrolyte. The negative electrode mixture layer contains negative electrode active materials. The negative electrode active material contains a material containing silicon. The silicon-containing material is a composite material. The composite material comprises: a lithium-ion conductive phase and silicon particles dispersed in the lithium-ion conductive phase. The lithium-ion conductive phase comprises a silicon oxide phase, a silicate phase, or a carbon phase. The non-aqueous electrolyte comprises: a non-aqueous solvent, a salt dissolved in the non-aqueous solvent, and additives. The additive contains alkoxysilyl compounds. The alkoxysilyl compound has two or more silyl groups linked by alkylene or amino groups. The alkylene group has 4 to 6 carbon atoms. The alkylene group constituting the amino group is an alkylene group between N and Si, and each alkylene group between N and Si has 4 to 6 carbon atoms. The two or more silyl groups each have at least one selected from the group consisting of alkoxy and oxyalkyl groups. The oxyalkyl group is -O-(C x H 2x+1 O y ) indicates that x is an integer greater than or equal to 1 and y is an integer greater than or equal to 1.

2. The non-aqueous electrolyte secondary battery according to claim 1, wherein, The alkoxysilyl compound is selected from at least one of the following groups: bis(alkoxysilyl)alkanes represented by general formula (1) and bis(alkoxysilyl)amines having an alkylene group between N and Si: R1 is an alkylene, secondary, or tertiary amino group. At least one of R2 to R4 is an alkoxy group selected from carbons 1 to 6 and is made of -O-(C x1 H 2x1+1 O y1 At least one of the groups consisting of alkyl groups, where x1 is an integer greater than or equal to 1 and y1 is an integer greater than or equal to 1. At least one of R5 to R7 is an alkoxy group selected from carbon 1 to 6 and is made of -O-(C x2 H 2x2+1 O y2 At least one of the groups consisting of alkyl groups, where x2 is an integer greater than or equal to 1 and y2 is an integer greater than or equal to 1. The remainder of R2 to R7 are each used independently by C. x3 H 2x3+1 O y3 The alkyl or oxyalkyl group represented by x3 being an integer greater than or equal to 1 and y3 being an integer greater than or equal to 0.

3. The non-aqueous electrolyte secondary battery according to claim 2, wherein, The bis(alkoxysilyl)alkane is 1,6-bis(trialkoxysilyl)hexane.

4. The non-aqueous electrolyte secondary battery according to claim 1, wherein, The concentration of the additive is less than 10% by mass.

5. The non-aqueous electrolyte secondary battery according to claim 4, wherein, The concentration of the additive is 0.2% by mass or more.

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