Additive for non-aqueous electrolyte, non-aqueous electrolyte containing the same, and non-aqueous electrolyte secondary battery

Abstract

This additive for nonaqueous electrolyte solutions contains a bisalkoxysilyl compound which has two or more silyl groups that are connected by means of an alkylene group or an amino group, wherein: each of the two or more silyl groups has at least one group that is selected from the group consisting of an alkoxy group and an oxyalkyl group; and the oxyalkyl group is represented by -O-(CxH2x+1Oy), wherein x represents an integer of 1 or more and y represents an integer of 1 or more.

Description

Technical Field

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

Background Art

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

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

Prior Art Documents

Non-Patent Documents

[0004]

Non-Patent Document 1

Summary of the Invention

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

[0006] One aspect of the present disclosure relates to an additive for a non-aqueous electrolyte, which contains an alkoxysilyl compound, the alkoxysilyl compound has two or more silyl groups linked by an alkylene group or an amino group, the two or more silyl groups each have at least one selected from the group consisting of an alkoxy group and an oxyalkyl group, and the oxyalkyl group is represented by -O-(C x H 2x+1 O y ), where x is an integer of 1 or more and y is an integer of 1 or more.

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

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

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

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Figure 3

Figure 4

Embodiments for Carrying Out the Invention

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

[0012] The alkoxysilyl compound may be a bis(alkoxysilyl) compound or a tris(alkoxysilyl) compound. In the case of the bis(alkoxysilyl) compound, two silyl groups are linked by an alkylene group or a secondary amino group. In the case of the tris(alkoxysilyl) compound, three alkoxysilyl groups are linked by a tertiary amino group.

[0013] In the above configuration, it is considered that each alkoxy group or oxyalkyl group of each silyl group forms an X-O-Si bond with the surface of the material containing a silicon element. Here, X represents the surface of the material containing a silicon element, and O bonded to X represents, for example, an O atom (or a residue of an OH group) present on the surface of the material containing a silicon element. By each of the alkoxy group or oxyalkyl group forming a bond with the surface of the material containing a silicon element, the surface of the material containing a silicon element is covered with a bissilylalkane or bissilylamine structure (including a trisilylamine structure) having stable siloxane bonds at both ends. That is, the surface of the material containing a silicon element is covered with a film containing a bissilylalkane or bissilylamine structure (hereinafter also referred to as an SRS film). The SRS film has high elasticity, is stable against reversible elastic deformation, and is less likely to be damaged even when repeating charge-discharge cycles. As a result, side reactions at the negative electrode are suppressed, and the capacity retention rate in the charge-discharge cycle is stably improved.

[0014] The alkoxysilyl compound may be at least one selected from the group consisting of bis(alkoxysilyl)alkanes represented by the general formula (1):

[0015]

Chemical formula

[0016] and bis(alkoxysilylalkyl)amines having an alkylene group between N and Si.

[0017] Here, R1 is an alkylene group or a secondary or tertiary amino 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 ) represented by, x1 is an integer of 1 or more, and at least one selected from the group consisting of oxyalkyl groups where y1 is an integer of 1 or more. At least one of R5 to R7 is an alkoxy group having 1 to 6 carbon atoms and -O-(C x2 H 2x2+1 O y2 ) represented by, x2 is an integer of 1 or more, and at least one selected from the group consisting of oxyalkyl groups where y2 is an integer of 1 or more. The rest of R2 to R7 are each independently C x3 H 2x3+1 O y3 represented by, x3 is an integer of 1 or more, and an alkyl group or an oxyalkyl group where y3 is an integer of 0 or more. However, the oxyalkyl group is a group other than an alkoxy group.

[0018] The alkoxy group or oxyalkyl group contained in R2 to R4 and R5 to R7 each forms an X-O-Si-R1 bond with the surface of the material containing a silicon element, and the surface of the material containing a silicon element is covered with an Si-R1-Si structure having stable siloxane bonds at both ends. That is, the surface of the material containing a silicon element is covered with an SRS film containing an Si-R1-Si structure.

[0019] The alkylene group constituting R1 has better flexibility as the number of carbon atoms increases, so it facilitates reversible deformation of the SRS film. However, if the number of carbon atoms of R1 becomes excessively large, the alkylene chain becomes too long, the density of the SRS film decreases, and the effect of suppressing side reactions is considered to decrease. Therefore, the number of carbon atoms of the alkylene group is desirably 1 to 6 carbon atoms, and more desirably 2 to 4 carbon atoms. The bis(alkoxysilyl)alkane is desirably bis(alkoxysilyl)C 1-6 alkane, and may also be bis(alkoxysilyl)C 2-4 alkane.

[0020] The amino group constituting R1 may have a structure represented by R11-N-R12. Here, R11 and R12 are each independently an alkylene group having 1 or more carbon atoms. Such R1 is considered to be excellent in flexibility, have a large electron shielding property, and have a greater effect of suppressing side reactions.

[0021] The larger the number of carbon atoms in the amino group, the better the flexibility, so it facilitates the reversible deformation of the SRS film. However, if the number of carbon atoms in the amino group becomes excessively large, R1 becomes too long, the density of the SRS film decreases, and the effect of suppressing side reactions is considered to decrease. Therefore, the number of carbon atoms in the alkylene group is desirably 1 to 6, and more desirably 2 to 4. For example, bis(alkoxysilylalkyl)amine is desirably bis(alkoxysilyl C 1-6 alkyl)amine, and may also be bis(alkoxysilyl C 2-4 alkyl)amine.

[0022] At least one of R2 to R4 is at least one selected from the group consisting of an alkoxy group having 1 to 6 carbon atoms and an oxyalkyl group represented by -O-(C x1 H 2x1+1 O y1 )), where x1 is an integer from 1 to 6 and y1 is 1 or 2, and at least one of R5 to R7 is an alkoxy group having 1 to 6 carbon atoms and -O-(C x2 H 2x2+1 O y2 ), where x2 is an integer from 1 to 6 and y2 is 1 or 2. The alkoxy group and the oxyalkyl group may be smaller from the viewpoint of enhancing the reactivity with the surface of the silicon-containing material, and the number of carbon atoms in the alkoxy group and the oxyalkyl group may be, for example, 1 to 3.

[0023] The rest of R2 to R7 are each independently C x3 H 2x3+1 O y3It is an alkyl group represented by [x3 is an integer of 1 or more, and y3 is an integer of 0 or more (for example, an integer of 0 or more and 2 or less)] or an oxyalkyl group other than an alkoxy group. From the viewpoint of reducing steric hindrance during the reaction, the carbon number of the group represented by C x3 H 2x3+1 O y3 may be 1 to 6, or may be 1 to 3. R2 to R4 are each independent, and all of R2 to R4 may have the same carbon number, may all have different carbon numbers, or 2 of R2 to R4 may have the same carbon number. Similarly, R5 to R7 are each independent, and all of R5 to R7 may have the same carbon number, may all have different carbon numbers, or 2 of R5 to R7 may have the same carbon number.

[0024] In formula (1), the two alkoxysilyl groups (R2R3R4Si- or R5R6R7Si-) linked to R1 may be the same as or different from each other. However, in order to enhance the symmetry of the structure of the SRS film to obtain a more stable structure, the two alkoxysilyl groups linked to R1 may have the same structure.

[0025] In formula (1), when R1 is an alkylene group, the alkoxysilyl compound is a kind of bis(alkoxysilyl)alkane. The SRS film formed when using bis(alkoxysilyl)alkane is composed of a stable siloxane structure and an alkylene structure. Such an SRS film is not only easily elastically deformed but also chemically and structurally stable.

[0026] Among bis(alkoxysilyl)alkanes, at least one selected from the group consisting of 1,2-bis(trialkoxysilyl)ethane and 1,6-bis(trialkoxysilyl)hexane is mentioned as being easily available. 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.

[0027] In formula (1), when R1 is an amino group, the alkoxysilyl compound is a kind of alkoxysilylalkylamine. More specifically, the alkoxysilylalkylamine may be at least one selected from the group consisting of bis(alkoxysilylalkyl)amine and tris(alkoxysilylalkyl)amine.

[0028] Among bis- or tris(alkoxysilylalkyl)amines, as those that are easily available, at least one selected from the group consisting of bis[3-(trialkoxysilyl)propyl]amine and tris[3-(trialkoxysilyl)propyl]amine can be mentioned. 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.

[0029] (Non-aqueous electrolyte) The non-aqueous electrolyte contains a non-aqueous solvent, a salt (solute) dissolved in the non-aqueous solvent, and the additive for the non-aqueous electrolyte. The salt (solute) is an electrolyte salt that dissociates into ions in the non-aqueous solvent. When the non-aqueous electrolyte is used in a lithium-ion secondary battery, the salt contains at least a lithium salt. Components of the non-aqueous electrolyte other than the non-aqueous solvent and the salt are additives, and at least a part of the additives is the above alkoxysilyl compound.

[0030] The concentration of the alkoxysilyl compound in the non-aqueous electrolyte may be, for example, 10% by mass or less, 8% by mass or less, or even 5% by mass or less. Within this range, regardless of the amount of the material containing silicon element included in the negative electrode active material, it is sufficient to form a good and appropriate SRS film. When the concentration of the alkoxysilyl compound represented by the formula (1) in the non-aqueous electrolyte is, for example, 0.2% by mass or more, a considerable SRS film is considered to be formed, and a significant effect of improving the capacity retention rate in the charge-discharge cycle of the non-aqueous electrolyte secondary battery can be obtained.

[0031] However, since the alkoxysilyl compound reacts in the non-aqueous electrolyte secondary battery, the concentration in the non-aqueous electrolyte gradually decreases. Therefore, in the completed non-aqueous electrolyte secondary battery or the non-aqueous electrolyte secondary battery distributed in the market, it is sufficient that the alkoxysilyl compound remains above the detection limit in the taken-out non-aqueous electrolyte.

[0032] As the non-aqueous solvent, for example, cyclic carbonates, chain carbonates, cyclic carboxylic acid esters, chain carboxylic acid esters, etc. are used. Examples of the cyclic carbonate include propylene carbonate (PC), ethylene carbonate (EC), vinylene carbonate (VC), etc. Examples of the chain carbonate include diethyl carbonate (DEC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), etc. Examples of the cyclic carboxylic acid ester include γ-butyrolactone (GBL), γ-valerolactone (GVL), etc. Examples of the chain carboxylic acid ester include methyl acetate, ethyl acetate, propyl acetate, methyl propionate (MP), ethyl propionate (EP), etc. The non-aqueous solvent may be used alone or in combination of two or more.

[0033] Among them, the chain carboxylic acid ester is suitable for preparing a non-aqueous electrolyte with low viscosity. Therefore, the non-aqueous electrolyte may contain 1% by mass or more and 90% by mass or less of the chain carboxylic acid ester. Among the chain carboxylic acid esters, methyl acetate has particularly low viscosity. Therefore, 90% by mass or more of the chain carboxylic acid ester may be methyl acetate.

[0034] Examples of other non-aqueous solvents include cyclic ethers, chain ethers, nitriles such as acetonitrile, and amides such as dimethylformamide.

[0035] Examples of the cyclic ether include 1,3-dioxolane, 4-methyl-1,3-dioxolane, tetrahydrofuran, 2-methyltetrahydrofuran, propylene oxide, 1,2-butylene oxide, 1,3-dioxane, 1,4-dioxane, 1,3,5-trioxane, furan, 2-methylfuran, 1,8-cineole, crown ether, etc.

[0036] Examples of the chain ether include 1,2-dimethoxyethane, dimethyl ether, diethyl ether, dipropyl ether, diisopropyl ether, dibutyl ether, dihexyl ether, ethyl vinyl ether, butyl vinyl ether, methyl phenyl ether, ethyl phenyl ether, butyl phenyl ether, pentyl phenyl ether, methoxytoluene, benzyl ethyl ether, diphenyl ether, dibenzyl ether, o-dimethoxybenzene, 1,2-diethoxyethane, 1,2-dibutoxyethane, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol dibutyl ether, 1,1-dimethoxymethane, 1,1-diethoxyethane, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, etc.

[0037] These solvents may be fluorinated solvents in which some of the hydrogen atoms are substituted with fluorine atoms. As the fluorinated solvent, fluoroethylene carbonate (FEC) may be used.

[0038] Examples of the lithium salt include lithium salts of chlorine-containing acids (such as LiClO4, LiAlCl4, LiB 10 Cl 10 etc.), lithium salts of fluorine-containing acids (such as LiPF6, LiPF2O2, LiBF4, LiSbF6, LiAsF6, LiCF3SO3, LiCF3CO2, etc.), lithium salts of fluorine-containing acid imides (such as LiN(FSO2)2, LiN(CF3SO2)2, LiN(CF3SO2)(C4F9SO2), LiN(C2F5SO2)2, etc.), lithium halides (such as LiCl, LiBr, LiI, etc.). The lithium salt may be used alone or in combination of two or more.

[0039] The concentration of the lithium salt in the non-aqueous electrolyte may be 0.5 mol / liter or more and 2 mol / liter or less, or may be 1 mol / liter or more and 1.5 mol / liter or less. By controlling the lithium salt concentration within the above range, a non-aqueous electrolyte having excellent ionic conductivity and low viscosity can be obtained.

[0040] Examples of the additives other than the alkoxysilyl compound include 1,3-propanesultone, methylbenzenesulfonate, cyclohexylbenzene, biphenyl, diphenyl ether, fluorobenzene, etc.

[0041] (Non-aqueous electrolyte secondary battery) The non-aqueous electrolyte secondary battery according to the present disclosure includes a negative electrode, a positive electrode, and the above non-aqueous electrolyte.

[0042] (Negative electrode) The negative electrode includes, for example, a negative electrode current collector and a negative electrode mixture layer formed on the surface of the negative electrode current collector. The negative electrode mixture layer contains a negative electrode active material as an essential component and may contain optional components such as a binder, a conductive material, and a thickening material. Known materials can be used for the optional components such as the binder, the conductive material, and the thickening material.

[0043] The negative electrode mixture layer can be formed, for example, by applying a negative electrode slurry in which a negative electrode mixture containing a negative electrode active material and a predetermined optional component is dispersed in a dispersion medium onto the surface of a negative electrode current collector and drying it. The dried coating film may be rolled if necessary. The negative electrode mixture layer may be formed on one surface of the negative electrode current collector or on both surfaces thereof.

[0044] The negative electrode active material includes a material containing a silicon element. The material containing a silicon element may be treated as a kind of alloy-based material. Here, the alloy-based material refers to a material containing an element capable of forming an alloy with lithium. Examples of the element capable of forming an alloy with lithium include silicon and tin, and silicon (Si) is particularly promising.

[0045] The material containing silicon may be a silicon alloy, a silicon compound, etc., or may be a composite material. Among them, a composite material containing a lithium ion conductive phase and silicon particles dispersed in the lithium ion conductive phase is promising. As the lithium ion conductive phase, for example, a silicon oxide phase, a silicate phase, a carbon phase, etc. can be used. The silicon oxide phase is a material with a relatively large irreversible capacity. On the other hand, the silicate phase is preferable in that it has a small irreversible capacity.

[0046] The main component (for example, 95 to 100% by mass) of the silicon oxide phase may be silicon dioxide. The composition of the composite material containing the silicon oxide phase and the silicon particles dispersed therein can be represented as SiO x in general. SiO x has a structure in which fine particles of silicon are dispersed in amorphous SiO2. The content ratio x of oxygen to silicon is, for example, 0.5 ≦ x < 2.0, and more preferably 0.8 ≦ x ≦ 1.5.

[0047] The silicate phase may contain, for example, at least one selected from the group consisting of Group 1 elements and Group 2 elements of the long-period type periodic table. As the Group 1 elements and Group 2 elements of the long-period type periodic table, for example, lithium (Li), potassium (K), sodium (Na), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), etc. can be used. Other elements may include aluminum (Al), boron (B), lanthanum (La), phosphorus (P), zirconium (Zr), titanium (Ti), etc. Among them, a silicate phase containing lithium (hereinafter also referred to as a lithium silicate phase) is preferable because it has a small irreversible capacity and high initial charge-discharge efficiency.

[0048] 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 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), etc.

[0049] 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.

[0050] In addition to materials containing silicon element, the negative electrode active material may include materials that electrochemically intercalate and deintercalate lithium ions, lithium metal, lithium alloys, and the like. As the material that electrochemically intercalates and deintercalates lithium ions, a carbon material is preferred. Examples of the carbon material include graphite, graphitizable carbon (soft carbon), non-graphitizable carbon (hard carbon), and the like. Among them, graphite, which is excellent in charge-discharge stability and has a small irreversible capacity, is preferred.

[0051] 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.

[0052] (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.

[0053] 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.

[0054] The positive electrode active material includes, for example, a lithium-containing composite oxide. The lithium-containing composite oxide is not particularly limited, but those having a layered rock salt-type crystal structure containing lithium and a transition metal are promising. Specifically, the lithium-containing composite oxide is, for example, Li a Ni 1-x-y Co x M yO2 (where 0 < a ≤ 1.2, 0 ≤ x ≤ 0.1, 0 ≤ y ≤ 0.1, 0 < x + y ≤ 0.1, and M is at least one selected from the group consisting of Na, Mg, Sc, Y, Mn, Fe, Cu, Zn, Al, Cr, Pb, Sb, and B) may be used. From the viewpoint of the stability of the crystal structure, M may contain Al. Note that the a value indicating the molar ratio of lithium increases or decreases during charge and discharge. As a specific example, LiNi 0.9 Co 0.05 Al 0.05 O2, LiNi 0.91 Co 0.06 Al 0.03 O2, etc. may be mentioned.

[0055] The positive electrode active material (particularly a lithium-containing composite oxide) usually has a form of secondary particles in which primary particles are aggregated. The average particle diameter of the positive electrode active material may be, for example, 2 μm or more and 20 μm or less. Here, the average particle diameter refers to the median diameter at which the cumulative volume in the volume-based particle size distribution becomes 50%. The volume-based particle size distribution can be measured by a laser diffraction type particle size distribution measuring device.

[0056] For the positive electrode current collector, for example, a metal sheet or a metal foil is used. Examples of the material of the positive electrode current collector include stainless steel, aluminum, aluminum alloy, titanium, and the like.

[0057] Examples of the conductive material used for the positive electrode binder layer and the negative electrode binder layer include carbon materials such as carbon black (CB), acetylene black (AB), ketjen black (KB), carbon nanotube (CNT), and graphite. These may be used alone or in combination of two or more.

[0058] Examples of the binder used for the positive electrode binder layer and the negative electrode binder layer include fluororesins (such as polytetrafluoroethylene and polyvinylidene fluoride), polyacrylonitrile (PAN), polyimide resin, acrylic resin, polyolefin resin, and the like. These may be used alone or in combination of two or more.

[0059] (Separator) A separator is interposed between the positive electrode and the negative electrode. The separator has a high ion permeability and appropriate mechanical strength and insulation. As the separator, a microporous thin film, a woven fabric, a non-woven fabric, etc. can be used. As the material of the separator, polyolefins such as polypropylene and polyethylene are preferred.

[0060] As an example of the structure of the secondary battery, there is a structure in which an electrode group in which a positive electrode and a negative electrode are wound with a separator interposed therebetween and a non-aqueous electrolyte are housed in an outer package. Alternatively, instead of the wound electrode group, other forms of electrode groups such as a laminated electrode group in which a positive electrode and a negative electrode are laminated with a separator interposed therebetween may be applied. The non-aqueous electrolyte secondary battery may be in any form such as a cylindrical shape, a rectangular shape, a coin shape, a button shape, a sheet shape (laminate shape), etc.

[0061] Hereinafter, with reference to FIGS. 1 and 2, a non-aqueous electrolyte secondary battery according to an embodiment of the present disclosure will be described. FIG. 1 is a partially cutaway plan view schematically showing an example of the structure of the non-aqueous electrolyte secondary battery. FIG. 2 is a cross-sectional view taken along the line X-X' of FIG. 1.

[0062] As shown in FIGS. 1 and 2, the non-aqueous electrolyte secondary battery 100 is a sheet-type battery and includes a plate group 4 and an outer case 5 that houses the plate group 4.

[0063] The plate group 4 has a structure in which a positive electrode 10, a separator 30, and a negative electrode 20 are laminated in this order, and the positive electrode 10 and the negative electrode 20 face each other with the separator 30 interposed therebetween. Thereby, the plate group 4 is formed. The plate group 4 is impregnated with a non-aqueous electrolyte.

[0064] 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.

[0065] The negative electrode 20 includes a negative electrode active material layer 2a and a negative electrode current collector 2b. The negative electrode active material layer 2a is formed on the surface of the negative electrode current collector 2b.

[0066] A negative electrode tab lead 1c is connected to the negative electrode current collector 1b, and a negative electrode tab lead 2c is connected to the negative electrode current collector 2b. The positive electrode tab lead 1c and the negative electrode tab lead 2c each extend to the outside of the exterior case 5.

[0067] The space between the positive electrode tab lead 1c and the exterior case 5 and the space between the negative electrode tab lead 2c and the exterior case 5 are each insulated by an insulating tab film 6.

[0068] 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.

[0069] 《Example 1》 (1) Fabrication of 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 SiO x : carbon black: polyacrylamide was 75:15:10, and further water was added and stirred to prepare a negative electrode slurry. Next, the negative electrode slurry was applied to one side of a negative electrode current collector (electrolytic copper foil) to form a coating film. After drying the coating film, the coating film together with the negative electrode current collector was rolled by a rolling roller to obtain a negative electrode having a negative electrode active material layer.

[0070] The negative electrode was cut out in the shape shown in Fig. 3(a) to obtain a negative electrode 20 for evaluation. In Fig. 3(a), the area of 60 mm × 40 mm is the area that functions as the negative electrode, and the protruding portion of 10 mm × 10 mm is the connection area with the tab lead 2c. Then, as shown in Fig. 3(b), the negative electrode mixture layer 2a formed on the connection area 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 area on the outer periphery of the negative electrode tab lead 2c was covered with an insulating tab film 6.

[0071] (2) Preparation of the counter electrode The counter electrode was prepared by attaching a lithium metal foil to one side of an electrolytic copper foil (current collector).

[0072] The counter electrode was cut out in the same shape as the negative electrode, and the lithium metal foil formed on the connection area formed in the same manner as the negative electrode was peeled off to expose the current collector. Then, in the same manner as the negative electrode, the exposed portion of the current collector was connected to the tab lead, and a predetermined area on the outer periphery of the tab lead was covered with an insulating tab film.

[0073] (3) Preparation of the non-aqueous electrolyte A non-aqueous electrolyte was prepared by dissolving LiPF6 at a concentration of 1 mol / L in a mixed solvent of fluoroethylene carbonate (FEC) and dimethyl carbonate (DMC) with a volume ratio of 20:80. To the non-aqueous electrolyte, 0.25 mass% of 1,2-bis(trimethoxysilyl)ethane (EBTMOS) represented by the following formula (1-1) was added.

[0074] [Chemical formula]

[0075] (4) Preparation of the evaluation cell Using the above-described negative electrode for evaluation and a counter electrode, a cell with a designed capacity of 114 mAh under negative electrode regulation was fabricated. First, the negative electrode and the counter electrode were opposed to each other through two polyethylene separators (thickness 15 μm) having an aramid coat so that the negative electrode mixture layer and the lithium metal foil overlapped, thereby obtaining a group of electrode plates. Next, an Al laminate film (thickness 100 μm) cut into a rectangle was folded in half, and the end portion on the long side was heat-sealed at 230° C. to form a cylinder. Then, the fabricated group of electrode plates was inserted into the cylinder from one of the short sides, and the end face of the Al laminate film and the position of the heat-sealing resin of each tab lead were aligned and heat-sealed at 230° C. Next, non-aqueous electrolyte was injected from the non-heat-sealed short side of the cylinder by 1.2 cm 3 After the injection, the operation of returning to atmospheric pressure after standing for 3 minutes under a reduced pressure of 0.02 MPa was performed twice to impregnate the non-aqueous electrolyte into the negative electrode mixture layer. Finally, the end face of the Al laminate film on the injection side was heat-sealed at 230° C. to obtain the evaluation cell A1. The fabrication of the evaluation cell was carried out in a dry air atmosphere with a dew point of -60° C. or lower.

[0076] (5) Evaluation of the battery The evaluation cell was sandwiched between a pair of stainless steel (thickness 6 mm) clamps of 10×5 cm and fixed under pressure at 3.2 MPa.

[0077] <First cycle> In a constant temperature bath at 25° C., lithium was charged to the negative electrode at a constant current of 0.05 C (1 C is the current value for discharging the designed capacity in 1 hour) over 2 hours, and then left to rest for 12 hours. Next, lithium was further charged to the negative electrode at a constant current of 0.05 C until the cell voltage reached 0.01 V, and then left to rest for 20 minutes. Next, lithium was discharged from the negative electrode at a constant current of 0.05 C until the cell voltage reached 1.5 V, and then left to rest for 20 minutes.

[0078] <Second to third cycles> Next, lithium was charged to the negative electrode at a constant current of 0.05 C until the cell voltage reached 0.01 V, and then left to rest for 20 minutes. Next, lithium was discharged from the negative electrode at a constant current of 0.05 C until the cell voltage reached 1.5 V, and then left to rest for 20 minutes.

[0079] <Cycle 4 to 50> Lithium was charged to the negative electrode at a constant current of 0.3C until the cell voltage reached 0.01V, and then rested for 20 minutes. Subsequently, lithium was discharged from the negative electrode at a constant current of 0.3C until the cell voltage reached 1.5V, and then rested for 20 minutes. This cycle was repeated.

[0080] The ratio of the capacity obtained from the 50th lithium discharge to the capacity obtained from the 1st lithium discharge was determined as the 50-cycle capacity retention rate. The results are shown in Table 1.

[0081] 《Examples 2 to 7》 In the preparation of the non-aqueous electrolyte, except that the content of EBTMOS added to the non-aqueous electrolyte was changed as shown in Table 1, evaluation cells A2 to A7 were fabricated in the same manner as in Example 1 and evaluated in the same manner.

[0082] 《Examples 8 to 10》 In the preparation of the non-aqueous electrolyte, except that 1,6-bis(trimethoxysilyl)hexane (HBTMOS) represented by the following formula (1-2) was added to the non-aqueous electrolyte in the content shown in Table 1 instead of EBTMOS, evaluation cells A8 to A10 were fabricated in the same manner as in Example 1 and evaluated in the same manner.

[0083]

Chemical formula

[0084] 《Comparative Examples 1, 2》 In the preparation of the non-aqueous electrolyte, except that vinyltris(2-methoxyethoxy)silane (VTMS) represented by the following formula (2) was added to the non-aqueous electrolyte in the content shown in Table 1 instead of EBTMOS, evaluation cells B1 to B2 were fabricated in the same manner as in Example 1 and evaluated in the same manner. Note that VTMS is an additive used in Non-Patent Document 1.

[0085]

Chemical formula

[0086] Comparative Example 3 In the preparation of the non-aqueous electrolyte, an evaluation cell B3 was produced and evaluated in the same manner as in Example 1, except that EBTMOS was not added.

[0087] [Table 1]

[0088] Fig. 4 shows the relationship between the number of charge-discharge cycles and the capacity retention rate of the evaluation cells A6, A9, B1, B2 and B3.

[0089] From Table 1 and Fig. 4, it can be understood that when EBTMOS and HBTMOS, which are alkoxysilyl compounds represented by the formula (1), are added to the non-aqueous electrolyte, the capacity retention rate is improved. Among them, the effect of EBTMOS is large, and it can be seen that the effect becomes remarkable according to the content of EBTMOS. The effect of EBTMOS is generally saturated when the content in the non-aqueous electrolyte is 4 to 5% by mass.

[0090] On the other hand, as shown in Fig. 4, with VTMS used in Non-Patent Document 1, the capacity retention rate could not be improved.

Industrial Applicability

[0091] The additive for non-aqueous electrolyte according to the present disclosure is suitably used for a non-aqueous electrolyte secondary battery in which the negative electrode active material contains a material containing silicon element.

Explanation of Signs

[0092] 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 separators 100 lithium-ion secondary batteries

Claims

1. A negative electrode having a negative electrode active material layer, a positive electrode, and a non-aqueous electrolyte, wherein the negative electrode active material layer contains a negative electrode active material, the negative electrode active material contains a material containing silicon element, the material containing silicon element is a composite material, the composite material contains a lithium ion conductive phase and silicon particles dispersed in the lithium ion conductive phase, the lithium ion conductive phase contains a silicon oxide phase, a silicate phase or a carbon phase, the non-aqueous electrolyte contains a non-aqueous solvent, a salt dissolved in the non-aqueous solvent, and an additive for non-aqueous electrolyte, the additive for non-aqueous electrolyte contains an alkoxysilyl compound, the alkoxysilyl compound has two or more silyl groups linked by an alkylene group or an amino group, each of the two or more silyl groups has only at least one selected from the group consisting of an alkoxy group and an oxyalkyl group, the oxyalkyl group is represented by -O-(CxH2x+1Oy), where x is an integer of 1 or more and y is an integer of 1 or more, a non-aqueous electrolyte secondary battery.

2. A negative electrode having a negative electrode active material layer, a positive electrode, and a non-aqueous electrolyte, wherein the negative electrode active material layer contains a negative electrode active material, the negative electrode active material contains a material containing silicon element, the material containing silicon element is a composite material, the composite material contains a lithium ion conductive phase and silicon particles dispersed in the lithium ion conductive phase, the lithium ion conductive phase contains a silicon oxide phase, a silicate phase or a carbon phase, the non-aqueous electrolyte contains a non-aqueous solvent, a salt dissolved in the non-aqueous solvent, and an additive for non-aqueous electrolyte, the additive for non-aqueous electrolyte contains an alkoxysilyl compound, the alkoxysilyl compound is represented by the general formula (1): 【Chemical 1】 and is at least one selected from the group consisting of bis(alkoxysilyl)alkane and bis(alkoxysilylalkyl)amine having an alkylene group between N and Si, R1 is an alkylene group or a secondary or tertiary amino group, At least one of R2 to R4 is selected from the group consisting of an alkoxy group having 1 to 6 carbon atoms and an oxyalkyl group represented by -O-(C ｘ１ H ２ｘ１＋１ O ｙ１ )), x1 is an integer of 1 or more, and y1 is at least one selected from the group consisting of oxyalkyl groups which are integers of 1 or more. At least one of R5 to R7 is an alkoxy group having 1 to 6 carbon atoms and -O-(C ｘ２ H ２ｘ２＋１ O ｙ２ ) represented by, x2 is an integer of 1 or more, and y2 is at least one selected from the group consisting of oxyalkyl groups that are integers of 1 or more. The remainder of R2 to R7 are each independently C ｘ３ H ２ｘ＋１ O ｙ３ represented by, x3 is an integer of 1 or more, and y3 is an alkyl group or an oxyalkyl group which is an integer of 0 or more, a non-aqueous electrolyte secondary battery.

3. The alkoxysilyl compound contains the bis(alkoxysilyl)alkane, the non-aqueous electrolyte secondary battery according to Claim 2, wherein the bis(alkoxysilyl)alkane is at least one selected from the group consisting of 1,2-bis(trialkoxysilyl)ethane and 1,6-bis(trialkoxysilyl)hexane.

4. The alkoxysilyl compound includes the bis(alkoxysilylalkyl)amine, The non-aqueous electrolyte secondary battery according to claim 2, wherein the bis(alkoxysilylalkyl)amine is bis[3-(trialkoxysilyl)propyl]amine.

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

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

7. A non-aqueous electrolyte secondary battery comprising a negative electrode having a negative electrode mixture layer, a positive electrode, and a non-aqueous electrolyte, The negative electrode mixture layer contains a negative electrode active material, The negative electrode active material contains a material containing a silicon element, The non-aqueous electrolyte contains a non-aqueous solvent, a salt dissolved in the non-aqueous solvent, and an additive for the non-aqueous electrolyte, The additive for the non-aqueous electrolyte contains an alkoxysilyl compound, The alkoxysilyl compound has two or more silyl groups linked by an alkylene group having 4 to 6 carbon atoms, Each of the two or more silyl groups has only at least one selected from the group consisting of an alkoxy group and an oxyalkyl group, The non-aqueous electrolyte secondary battery, wherein the oxyalkyl group is represented by -O-(CxH2x+1Oy), x is an integer of 1 or more, and y is an integer of 1 or more.

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