Non-aqueous electrolyte secondary battery

Abstract

The disclosed nonaqueous electrolyte secondary battery includes a positive electrode, a negative electrode including a negative electrode mixture layer, and a nonaqueous electrolyte. The negative electrode mixture layer includes a negative electrode active material and a binder component. The binder component includes a binder compound and a phosphorus-containing compound. The phosphorus-containing compound includes at least one phosphorus-containing group selected from the group consisting of a phosphoric acid group, a phosphate group, a phosphonic acid group, and a phosphonate group. The number of the at least one phosphorus-containing group contained in the phosphorus-containing compound is 2 or more and 5 or less. The negative electrode active material includes a silicon-containing material.

Description

[0001] Cross-reference of related applications

[0002] This disclosure claims priority to Japanese Patent Application No. 2024-054058, filed with the Japan Patent Office on March 28, 2024, the contents of which are incorporated herein by reference in their entirety. Technical Field

[0003] This disclosure relates to non-aqueous electrolyte secondary batteries. Background Technology

[0004] Non-aqueous electrolyte secondary batteries are used as high-capacity secondary batteries for various applications. Various schemes have been proposed for non-aqueous electrolyte secondary batteries. For example, it has been proposed to use silicon-containing materials as the negative electrode active material.

[0005] Claim 1 of Patent Document 1 (Japanese Patent Application Publication No. 2021-180083) discloses a polymeric binder composition for the negative electrode of a secondary battery comprising a compound represented by a prescribed formula and a polyacid. Claim 4 of Patent Document 1 discloses a binder composition wherein the polyacid is polyacrylic acid or phytic acid.

[0006] Existing technical documents

[0007] Patent documents

[0008] Patent Document 1: Japanese Patent Application Publication No. 2021-180083 Summary of the Invention

[0009] The problem the invention aims to solve

[0010] Silicon-containing materials can achieve high capacity, but on the other hand, they suffer from significant expansion / contraction during charging and discharging. If the negative electrode expands significantly during charging, the battery characteristics (charge-discharge cycle characteristics, etc.) are greatly reduced. One objective of this disclosure is to provide a non-aqueous electrolyte secondary battery that uses a silicon-containing negative electrode active material and exhibits minimal negative electrode expansion during charging.

[0011] Solution for solving the problem

[0012] One aspect of this disclosure relates to a non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode containing a negative electrode binder layer, and a non-aqueous electrolyte. The negative electrode binder layer comprises a negative electrode active material and a binder component. The binder component comprises a binder compound and a phosphorus-containing compound. The phosphorus-containing compound comprises at least one phosphorus-containing group selected from the group consisting of phosphate group, phosphate group, phosphonic acid group, and phosphonate group. The number of the at least one phosphorus-containing group contained in the phosphorus-containing compound is 2 or more and 5 or less. The negative electrode active material comprises a silicon-containing material.

[0013] The effects of the invention

[0014] According to this disclosure, a non-aqueous electrolyte secondary battery that uses a silicon-containing negative electrode active material and exhibits minimal negative electrode expansion during charging can be obtained.

[0015] The novel features of the invention are set forth in the claims, but the invention relates to both its structure and content, and will be better understood, together with other objects and features of the invention, by reference to the following detailed description of the accompanying drawings. Attached Figure Description

[0016] Figure 1 This is a schematic cross-sectional view illustrating an example of a non-aqueous electrolyte secondary battery of this disclosure. Detailed Implementation

[0017] The following description provides examples of embodiments of this disclosure, but this disclosure is not limited to the examples described below. In the following description, specific numerical values ​​and materials are sometimes used as examples, but other numerical values ​​and materials can be applied as long as the effects of this disclosure are achieved. In this specification, the description of "numerical value A to numerical value B" includes both numerical value A and numerical value B, and can be replaced with "numerical value A or higher and numerical value B or lower." In the following description, when lower and upper limits of numerical values ​​related to specific physical properties, conditions, etc., are exemplified, any of the exemplified lower limits and any of the exemplified upper limits can be arbitrarily combined, as long as the lower limit does not exceed the upper limit. In the following description, when examples of constituent elements and methods are listed, unless otherwise specified, only one of the listed examples can be used, or multiple of the listed examples can be used in combination.

[0018] (Non-aqueous electrolyte secondary battery)

[0019] Hereinafter, the non-aqueous electrolyte secondary battery of this embodiment will sometimes be referred to as "non-aqueous electrolyte secondary battery (B)" or "secondary battery (B)". The secondary battery (B) includes a positive electrode, a negative electrode containing a negative electrode binder layer, and a non-aqueous electrolyte. The negative electrode binder layer includes a negative electrode active material and a binder component. The binder component includes a binder compound and a phosphorus-containing compound. Hereinafter, this phosphorus-containing compound will sometimes be referred to as "phosphorus-containing compound (PC)". The phosphorus-containing compound (PC) includes at least one phosphorus-containing group selected from the group consisting of phosphate group (-OP(=O)(OH)2), phosphate group, phosphonate group (-P(=O)(OH)2), and phosphonate group. The number of at least one phosphorus-containing group contained in the phosphorus-containing compound (PC) is 2 or more and 5 or less. The negative electrode active material includes a silicon-containing material.

[0020] Because the negative electrode active material of the secondary battery (B) contains silicon-containing materials, high capacity can be achieved. The binder component of the secondary battery (B) includes a binder compound and a phosphorus-containing compound (PC) containing phosphorus groups. Since the phosphorus-containing compound (PC) contains multiple phosphorus groups, the expansion of the negative electrode binder layer can be suppressed through the interaction between the phosphorus-containing compound (PC) and the binder compound. Furthermore, since the phosphorus-containing compound (PC) contains multiple phosphorus groups, it can function as a chelating agent. In the negative electrode binder layer, the phosphorus-containing compounds (PC) are connected to each other via cations, thereby suppressing the expansion of the negative electrode binder layer. Therefore, although the secondary battery (B) uses a silicon (Si)-containing negative electrode active material, its negative electrode exhibits minimal expansion during charging. Thus, the secondary battery (B) can achieve both high discharge capacity and good charge-discharge cycle characteristics.

[0021] The binder compound is preferably a compound that forms bonds (e.g., hydrogen bonds) with a phosphorus-containing compound (PC). A preferred example of a binder component is one that contains a compound that forms hydrogen bonds with a phosphorus-containing compound (PC) as the binder compound.

[0022] Examples of functional groups that interact well with the phosphorus-containing groups of phosphorus-containing compounds (PC) include carbonyl, hydroxyl, amino, and mercapto groups. The carbonyl group can be a carboxylic acid group (-COOH) and / or a carboxyl salt group. The binder compound may have at least one group selected from the group consisting of carbonyl, hydroxyl, amino, and mercapto groups. The binder compound may have at least one group selected from the group consisting of carboxylic acid and carboxyl salt groups.

[0023] The binder compound may contain compounds commonly used as binders, but preferably includes compounds that form bonds with the phosphorus-containing compound (PC). The types of bonds formed between the binder compound and the phosphorus-containing compound (PC) include covalent bonds, ionic bonds, hydrogen bonds, etc. Examples of binder compounds include polyacrylic acid, salts of polyacrylic acid, carboxymethyl cellulose, and salts of carboxymethyl cellulose. The weight-average molecular weight of the binder compound can be in the range of 5,000 to 5,000,000 (e.g., 100,000 to 1,000,000).

[0024] The binder compound may contain at least one selected from the group consisting of polyacrylic acid, salts of polyacrylic acid, carboxymethyl cellulose, and salts of carboxymethyl cellulose. These can be used as binder compounds. The binder component may contain only polyacrylic acid and / or salts of polyacrylic acid as binder compounds. Alternatively, the binder component may also contain only carboxymethyl cellulose and / or salts of carboxymethyl cellulose as binder compounds. Examples of cations constituting the salt include lithium ions, sodium ions, potassium ions, ammonium ions, etc.

[0025] The phosphorus-containing compound (PC) may include at least one etidronic acid compound selected from the group consisting of etidronic acid and etidronate. The phosphorus-containing compound (PC) may be etidronic acid and / or etidronate. When the phosphorus-containing compound (PC) is a salt of an acid, examples of cations constituting the salt include lithium ions, sodium ions, potassium ions, ammonium ions, etc. Etidromic acid (1-hydroxyethane-1,1-bisphosphonic acid) is represented by the following chemical formula.

[0026]

[0027] The binder component can contain polyvalent cations. By including polyvalent cations in the binder component, phosphorus compounds (PC) in the negative electrode binder layer are linked to each other via polyvalent cations. As a result, the expansion of the negative electrode binder layer is particularly suppressed.

[0028] Polyvalent cations are cations with a valence of two or more. Examples of polyvalent cations include divalent, trivalent, and tetravalent cations. Polyvalent cations can contain cations selected from Ca. 2+ Mg 2+ Ba 2+ 、Ge 2+ Cu 2+ Ni 2+ Co 2+ Sn 2+ 、Sr 2+ Zn 2 + Pd 2+ Pt 2+ Mn 2+ Mn 3+ Ti 3+ 、Nb 3+ Bi 3+ Ce 3+ Cr 3+ La 3+ In 3+ ,Rh 3+ Sb 3+ 、Sm 3+ Dy 3+ Eu 3+ Mn 3+ Fe 3+ Al 3+ Hf 4+ Zr 4+ ,Th 4+ At least one of the group. The polyvalent cation can be any one selected from the group.

[0029] Polyvalent cations can include divalent cations or be divalent cations themselves. It is believed that divalent cations readily form stable cross-linked structures.

[0030] Multivalent cations can include those selected from Ca 2+ Mg 2+ and Sr 2+ At least one of the constituent groups. The polyvalent cation can be Ca. 2+ It can also be Mg 2+ It can also be used for Sr 2+ .

[0031] Non-aqueous electrolytes can contain the aforementioned polyvalent cations. The polyvalent cations contained in the non-aqueous electrolyte permeate into the negative electrode binder layer, causing the phosphorus-containing compounds (PC) to bond with each other.

[0032] The concentration of polyvalent cations in non-aqueous electrolytes can be above 0.001 mol / L, above 0.005 mol / L, above 0.01 mol / L, above 0.1 mol / L, or above 1.0 mol / L, and below 20 mol / L, below 10 mol / L, below 2.0 mol / L, below 1.0 mol / L, below 0.1 mol / L, or below 0.01 mol / L. For example, the concentration of polyvalent cations can be in the range of 0.001 mol / L to 20 mol / L, 0.005 mol / L to 20 mol / L, 0.01 mol / L to 20 mol / L, 0.1 mol / L to 20 mol / L, or 1.0 mol / L to 20 mol / L. Within any of these ranges, as long as the lower limit does not exceed the upper limit, the upper limit can also be set to 10 mol / L, 2.0 mol / L, 1.0 mol / L, 0.1 mol / L, or 0.01 mol / L. For example, the concentration of polyvalent cations can be in the range of 0.005 mol / L to 1.0 mol / L, or in the range of 0.005 mol / L to 0.01 mol / L. The concentration of polyvalent cations in non-aqueous electrolytes can be above 0.001 mol / L and below 20 mol / L.

[0033] It is believed that a higher concentration of polyvalent cations promotes the cross-linking of phosphorus compounds (PC) in the negative electrode flux layer, further reducing the negative electrode expansion rate during charging. Conversely, a lower concentration of polyvalent cations suppresses excessive viscosity increases in the non-aqueous electrolyte, improving the battery's charge-discharge characteristics. For example, by setting the polyvalent cation concentration in the range of 0.005 mol / L to 0.01 mol / L, the plate expansion rate during charging can be further reduced without a significant decrease in charging capacity.

[0034] Polyvalent cations can be contained in a non-aqueous electrolyte by dissolving the salt that produces the polyvalent cation in the non-aqueous electrolyte. The non-aqueous electrolyte may also contain at least one compound selected from the group consisting of calcium (II) bis(trifluoromethanesulfonyl)imide, magnesium (II) bis(trifluoromethanesulfonyl)imide, and strontium (II) bis(trifluoromethanesulfonyl)imide. These compounds (salts) are preferred from the viewpoint of not generating chloride ions. In the non-aqueous electrolyte containing these salts, the anions constituting the salts are dissolved.

[0035] The non-aqueous electrolyte may also include at least one selected from the group consisting of ethylene carbonate, methyl ethyl carbonate, dimethyl carbonate, diethyl carbonate, and fluoroethylene carbonate. These constitute a non-aqueous solvent. These solvents cause the binder compound to swell, thereby distributing the polyvalent cations in the non-aqueous electrolyte throughout the domains of the binder compound. Therefore, these solvents are preferred from the viewpoint of promoting the crosslinking of the phosphorus-containing compound (PC) in the negative electrode binder layer.

[0036] Silicon-containing materials may also contain composite particles containing a carbon phase and a particulate silicon phase dispersed in the carbon phase.

[0037] The average diameter of the silicon phase can be greater than 1 nm, greater than 10 nm, greater than 100 nm, or greater than 500 nm. The average diameter of the silicon phase can also be less than 1000 nm, less than 500 nm, less than 100 nm, or less than 10 nm. For example, the average diameter of the silicon phase can be greater than 1 nm and less than 1000 nm. Particulate silicon phases dispersed within a carbon phase can be considered as silicon particles dispersed within a carbon phase. The average diameter of the particulate silicon phase is determined by observing the cross-section of the composite particles using SEM or TEM. Specifically, the average diameter of the particulate silicon phase is calculated by taking the arithmetic mean of the largest diameters of any 100 silicon phases in the cross-section.

[0038] The binder compound may further comprise at least one polyacrylic acid compound selected from the group consisting of polyacrylic acid and salts of polyacrylic acid, and the phosphorus-containing compound (PC) may comprise at least one etidronate compound selected from the group consisting of etidronate and etidronate salts. In this case, the ratio We / Wp of the mass We of the at least one etidronate compound in the negative electrode binder layer to the mass Wp of the at least one polyacrylic acid compound in the negative electrode binder layer may be 0.01 or more, 0.05 or more, 0.10 or more, 0.11 or more, or 0.20 or more, and may be 1.0 or less, 0.50 or less, 0.20 or less, 0.10 or less, or 0.05 or less. By setting the ratio We / Wp to 0.01 or more (e.g., 0.11 or more), a lower expansion amount can be achieved. By setting the ratio We / Wp to 1.0 or less, a higher charge / discharge capacity can be achieved.

[0039] The ratio We / Wp can also be in the range of 0.01 to 1.0 (e.g., 0.01 to 0.50). The lower and / or upper limits of this range can be replaced with the aforementioned lower and / or upper limits, provided the lower limit does not exceed the upper limit. For example, the ratio We / Wp can be in the range of 0.11 to 1.0, 0.50 to 1.0, or 0.11 to 0.50.

[0040] The phosphorus-containing compound (PC) may include at least one etidronate-based compound selected from the group consisting of etidronate and etidronate salts, and the non-aqueous electrolyte may include polyvalent cations. In this case, the ratio Mc / Me, which is the molar number of polyvalent cations Mc in the non-aqueous electrolyte relative to the molar number Me of at least one etidronate-based compound in the negative electrode mixture layer, may be 1.0 or more or 5.0 or more. The ratio Mc / Me may also be 20 or less, 15 or less, 10 or less, or 5.0 or less. The ratio Mc / Me may be in the range of 1.0 to 20, 5.0 to 15, or 5.0 to 10. When the ratio Mc / Me is in the range of 1.0 to 20, a significant decrease in charging capacity will not occur, and the expansion rate of the electrode plate during charging can be further reduced. It should be noted that the molar number Mc of polyvalent cations in the non-aqueous electrolyte includes not only the molar number of polyvalent cations present in the non-aqueous electrolyte outside the electrodes (positive and negative electrodes), but also the molar number of polyvalent cations in the non-aqueous electrolyte that permeates into the electrodes.

[0041] The secondary battery (B) preferably satisfies at least one of the following conditions (1) to (3), more preferably satisfies two or more, and particularly preferably satisfies all of them.

[0042] (1) The phosphorus-containing compound (PC) includes at least one etidronic acid compound selected from the group consisting of etidronic acid and etidronate.

[0043] (2) The binder contains divalent cations.

[0044] (3) The binder compound comprises at least one selected from the group consisting of polyacrylic acid, salts of polyacrylic acid, carboxymethyl cellulose and salts of carboxymethyl cellulose.

[0045] Regarding condition (3), the adhesive compound may also contain at least one of polyacrylic acid and a salt of polyacrylic acid, and at least one of carboxymethyl cellulose and a salt of carboxymethyl cellulose.

[0046] (Manufacturing method of secondary battery (B))

[0047] The manufacturing method of the secondary battery (B) is not limited as long as the necessary components of the secondary battery (B) are met. The manufacturing method of one example is described below. The matters described for the secondary battery (B) can be applied to the manufacturing method below, therefore repeated descriptions are omitted. The matters described for the manufacturing method below can also be applied to the secondary battery (B). In the following example, the electrode assembly includes a separator, and the negative electrode includes a negative current collector.

[0048] The manufacturing method includes step (i) and step (ii). Step (i) is the process of fabricating the electrode assembly and the non-aqueous electrolyte. The electrode assembly includes a positive electrode, a negative electrode, and a separator.

[0049] Process (i) includes the process of forming the negative electrode (ia) and the process of forming the positive electrode (ib). Except for the fact that the negative electrode material contains specific components, the method of forming the negative electrode is not limited, and known methods can be used. In one example of a method for manufacturing the negative electrode, firstly, a negative electrode slurry is prepared by mixing the components of the negative electrode with a dispersion medium. The dispersion medium can be water, alcohol (ethanol, etc.), ether (tetrahydrofuran, etc.), N-methyl-2-pyrrolidone (NMP), or mixtures thereof. The components of the negative electrode include a negative electrode active material (e.g., particles of the negative electrode active material) and a binder component, and other components may be included as needed. The negative electrode active material includes a silicon-containing material.

[0050] Negative electrode slurries may or may not contain polyvalent cations. If the negative electrode slurry contains phosphorus compounds (PC) and polyvalent cations, the viscosity of the slurry increases, which can sometimes increase the difficulty of negative electrode formation or decrease the quality of the negative electrode. Even when the negative electrode slurry does not contain polyvalent cations, polyvalent cations can be present in the negative electrode mixture layer by adding polyvalent cations to a non-aqueous electrolyte. In this case, the polyvalent cations in the negative electrode mixture layer originate from the non-aqueous electrolyte.

[0051] Next, by coating the negative electrode slurry onto the negative electrode current collector and then drying it, a laminate containing the negative electrode current collector and a negative electrode additive layer formed on the negative electrode current collector can be obtained. Then, the negative electrode is fabricated by calendering the laminate. The thickness of the negative electrode additive layer can be 3 μm or more, 5 μm or more, or less than 200 μm or less, or less than 150 μm. The fabricated negative electrode is cut to a specified size as needed. The negative electrode additive layer is formed on one or both sides of the negative electrode current collector.

[0052] There is no limitation on the method for forming the positive electrode; well-known methods can be used. For example, the positive electrode can be formed using the same method as the method for forming the negative electrode, except that a positive electrode slurry can be used instead of a negative electrode slurry, or a positive electrode current collector can be used instead of a negative electrode current collector. The positive electrode slurry can be prepared using a positive electrode active material, additives, and a dispersion medium.

[0053] The shape of the electrode assembly is not limited. For example, the electrode assembly can be either wound or stacked. An example of a wound electrode assembly is formed by winding a positive electrode, a negative electrode, and a separator. In this case, a separator is placed between the positive and negative electrodes. An example of a stacked electrode assembly is formed by stacking one or more flat positive electrodes, one or more flat negative electrodes, and one or more flat separators in one direction. In this case, a separator is placed between the positive and negative electrodes.

[0054] Non-aqueous electrolytes can be prepared, for example, by dissolving specified components (salts, additives, etc.) in a non-aqueous solvent. By using salts that generate polyvalent cations, non-aqueous electrolytes containing polyvalent cations can be prepared.

[0055] Step (ii) is the process of housing the electrode assembly and non-aqueous electrolyte within the outer casing. The method for performing step (ii) is not limited and can be performed using known methods. The outer casing is not limited and can be any known casing. As described above, a secondary battery (B) can be manufactured.

[0056] The components other than the essential components of the secondary battery (B) are not particularly limited, and the components used in known non-aqueous electrolyte secondary batteries may also be used. Examples of the components of the secondary battery (B) are described below. However, the secondary battery (B) is not limited to the examples described below.

[0057] The secondary battery (B) includes a housing and an electrode assembly and a non-aqueous electrolyte housed within the housing. The electrode assembly includes a positive electrode, a negative electrode, and a separator.

[0058] (negative electrode)

[0059] The negative electrode includes a negative electrode binder layer. The negative electrode may also include a negative electrode current collector and a negative electrode binder layer disposed on the negative electrode current collector. The negative electrode binder layer contains negative electrode active material and binder components, and may further contain other additives.

[0060] There are no particular limitations on the negative current collector; any known negative current collector can be used. The negative current collector can be a conductive sheet (e.g., metal foil). For example, copper foil, copper alloy foil, copper-plated resin sheets (e.g., polyethylene terephthalate sheets), and copper-plated stainless steel foil can be used as negative current collectors.

[0061] The negative electrode active material can be a material that reversibly absorbs, stores, and releases lithium ions. Negative electrode active materials include silicon-containing materials. They can also include other negative electrode active materials besides silicon-containing materials. Examples of other negative electrode active materials include carbonaceous materials and Sn-containing materials. The negative electrode additive layer can contain only one type of negative electrode active material or two or more. Examples of carbonaceous materials include graphite, easily graphitized carbon (soft carbon), and difficult-to-graphitize carbon (hard carbon).

[0062] Examples of silicon-containing materials include silicon oxide, silicon, and composite materials. Composite materials can contain multiple phases selected from carbon, lithium silicate, silicon, and silicon oxide. One example of a composite material is one containing a carbon phase and a particulate silicon phase dispersed within the carbon phase. Another example of a composite material is one containing a lithium silicate phase and a particulate silicon phase dispersed within the lithium silicate phase.

[0063] The components other than the negative electrode active material and binder (conductive materials, etc.) are not particularly limited, and known components can be used. The conductive material can be the material exemplified by the conductive material used as the positive electrode binder layer.

[0064] (positive electrode)

[0065] The positive electrode includes a positive electrode flux layer. The positive electrode may include a positive electrode current collector and a positive electrode flux layer disposed on the positive electrode current collector. There are no particular limitations on the positive electrode current collector and the positive electrode flux layer; the positive electrode current collector and positive electrode flux layer used in known non-aqueous electrolyte secondary batteries may be used.

[0066] Examples of materials for the positive current collector include metallic materials containing Al, Ti, Fe, etc. These metallic materials can be Al, Al alloys, Ti, Ti alloys, Fe alloys, etc. Fe alloys can also be stainless steel (SUS).

[0067] The positive electrode active material can be a material that reversibly absorbs and releases lithium ions. Examples of positive electrode active materials include composite oxides containing lithium and a metal element Me other than lithium, transition metal fluorides, polyanions, fluorinated polyanions, transition metal sulfides, etc. Composite oxides containing lithium and the metal element Me can be lithium-containing transition metal oxides that contain at least one transition metal as the metal element Me. Considering low manufacturing cost and high average discharge voltage, lithium-containing transition metal oxides are preferred as positive electrode active materials.

[0068] Examples of transition metal elements contained in lithium-containing transition metal oxides include Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Y, Zr, and W. Lithium-containing transition metal oxides may contain only one or more transition metal elements. Preferably, lithium-containing transition metal oxides contain at least one element selected from the group consisting of Ni, Co, Mn, and Al.

[0069] There are no particular limitations on additives other than the positive electrode active material (binders, conductive materials, etc.), and well-known additives can be used. Conductive carbon materials can be used. Examples of conductive carbon materials include carbon black, carbon nanotubes, and graphite. Examples of binders include fluoropolymers, polyacrylonitrile, polyimide resins, acrylic resins, polyolefin resins, and rubber-like polymers. Examples of fluoropolymers include polytetrafluoroethylene and polyvinylidene fluoride.

[0070] (Separator)

[0071] The separator uses a porous sheet with ion-permeable and insulating properties. Examples of porous sheets include microporous films, woven fabrics, and nonwoven fabrics. The material of the separator is not particularly limited, and polymeric materials can be used. Examples of polymeric materials include polyolefin resins, polyamide resins, and cellulose. Examples of polyolefin resins include polyethylene, polypropylene, and copolymers with ethylene-propylene. The separator may contain additives (inorganic fillers, etc.) as needed. The thickness of the separator is not particularly limited and can be 10 μm or more, 15 μm or more, or less than 30 μm or less than 20 μm.

[0072] (Non-aqueous electrolyte)

[0073] Non-aqueous electrolytes can be non-aqueous electrolytes with lithium-ion conductivity. Non-aqueous electrolytes contain a non-aqueous solvent and ions (lithium ions, anions, etc.) dissolved in the non-aqueous solvent. Non-aqueous electrolytes can be in liquid or gel form.

[0074] Non-aqueous electrolytes are prepared by dissolving lithium salts in non-aqueous solvents. Dissolving lithium salts in non-aqueous solvents generates lithium ions and anions. Dissolving salts of polyvalent cations in non-aqueous solvents generates polyvalent cations and anions.

[0075] Examples of lithium salts include: lithium salts containing chloric acid (LiClO4, LiAlCl4, LiB). 10 Cl 10 Lithium salts include those containing fluorinated 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.). A single lithium salt can be used, or two or more can be used in combination. The concentration of lithium salts in non-aqueous electrolytes can be above 0.5 mol / L and below 3.5 mol / L.

[0076] One example of a non-aqueous electrolyte is that it is substantially chloride-free. For instance, the chloride ion concentration in the non-aqueous electrolyte can be less than 0.001 mol / L (e.g., less than 0.0001 mol / L). A substantially chloride-free non-aqueous electrolyte is preferred from the perspective of not substantially generating chloride-based gases originating from chloride ions during charging and discharging. A substantially chloride-free non-aqueous electrolyte can be prepared using a non-chloride salt.

[0077] There are no particular limitations on the non-aqueous solvent; any known non-aqueous solvent can be used. Examples of non-aqueous solvents 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), fluoroethylene carbonate (FEC), and vinylene carbonate (VC). Examples of chain carbonates include dimethyl carbonate (DMC), diethyl carbonate (DEC), and methyl ethyl carbonate (EMC). Examples of cyclic carboxylic acid esters include γ-butyrolactone (GBL) and γ-valerolactone. Examples of chain carboxylic acid esters include methyl acetate, ethyl acetate, propyl acetate, methyl propionate, and ethyl propionate. One non-aqueous solvent can be used alone, or two or more can be used in combination.

[0078] (Outer shell)

[0079] The electrode assembly and non-aqueous electrolyte are housed within the outer casing (battery housing). The outer casing is not particularly limited and can use any known casing. The outer casing typically comprises an outer can and a sealing body that seals the opening of the outer can. The outer can functions as the negative terminal, and the sealing body functions as the positive terminal. The sealing body may also include a sealing plate and a gasket.

[0080] Hereinafter, an example of the secondary battery (B) of this disclosure will be described with reference to the accompanying drawings. The aforementioned constituent elements can be applied in the constituent elements of the example described below. Furthermore, the constituent elements of the example described below can be modified based on the above description. Additionally, the matters to be explained below can also be applied to the above-described embodiments. Furthermore, in the example described below, constituent elements not required for the secondary battery (B) of this disclosure can be omitted.

[0081] (Implementation Method 1)

[0082] Figure 1 This is a longitudinal cross-sectional view schematically showing an example of a non-aqueous electrolyte secondary battery according to Embodiment 1. Figure 1The cylindrical non-aqueous electrolyte secondary battery 10 shown includes a cylindrical battery casing and an electrode assembly 14 and a non-aqueous electrolyte (not shown) housed within the battery casing. The electrode assembly 14 is a wound electrode assembly, including a positive electrode 11, a negative electrode 12, and a separator 13. As described above, the negative electrode 12 includes a negative electrode binder layer. The negative electrode binder layer contains a negative electrode active material and a binder component.

[0083] The battery casing includes: a casing body 15 as a bottomed cylindrical metal container, and a sealing body 16 that seals the opening of the casing body 15. A gasket 27 is disposed between the casing body 15 and the sealing body 16. The gasket 27 ensures the airtightness of the battery casing. Inside the casing body 15, insulating plates 17 and 18 are respectively disposed at both ends of the electrode assembly 14 in the winding axis direction. The casing body 15 has a stepped portion 21.

[0084] The sealing body 16 includes a perforated metal plate 22, a lower valve body 23, an insulating member 24, an upper valve body 25, and a cover 26. The lower valve body 23 and the upper valve body 25 are connected at their respective central portions. The insulating member 24 is disposed between the peripheral portions of the lower valve body 23 and the upper valve body 25. The perforated metal plate 22 and the lower valve body 23 are connected at their respective peripheral portions. The upper valve body 25 and the cover 26 are connected at their respective peripheral portions. All components constituting the sealing body 16, except for the insulating member 24, are electrically connected.

[0085] A vent hole is formed on the lower valve body 23. Therefore, when the internal pressure of the battery casing rises due to abnormal heating, the upper valve body 25 expands towards the cover 26 and separates from the lower valve body 23. As a result, the electrical connection between the lower valve body 23 and the upper valve body 25 is cut off. When the internal pressure rises further, the upper valve body 25 breaks, and gas is discharged from the opening formed in the cover 26.

[0086] The positive electrode 11 is electrically connected to the cover 26, which functions as the positive terminal, via the positive lead 19. The negative electrode 12 is electrically connected to the housing body 15, which functions as the negative terminal, via the negative lead 20.

[0087] (Postscript)

[0088] The following technologies are disclosed through the above records.

[0089] (Technology 1)

[0090] A non-aqueous electrolyte secondary battery includes a positive electrode, a negative electrode containing a negative electrode mixture layer, and a non-aqueous electrolyte.

[0091] The aforementioned negative electrode mixture layer contains negative electrode active material and binder components.

[0092] The aforementioned binder components include binder compounds and phosphorus-containing compounds.

[0093] The aforementioned phosphorus-containing compounds include at least one phosphorus-containing group selected from the group consisting of phosphate group, phosphate group, phosphonic acid group, and phosphonate group.

[0094] The aforementioned phosphorus-containing compounds contain at least 2 and less than 5 phosphorus-containing groups.

[0095] The aforementioned negative electrode active material includes silicon-containing materials.

[0096] (Technology 2)

[0097] According to the non-aqueous electrolyte secondary battery of technology 1, the aforementioned binder compound comprises at least one selected from the group consisting of polyacrylic acid, salts of polyacrylic acid, carboxymethyl cellulose, and salts of carboxymethyl cellulose.

[0098] (Technology 3)

[0099] According to the non-aqueous electrolyte secondary battery of technology 1 or 2, the aforementioned phosphorus-containing compound comprises at least one etidronate compound selected from the group consisting of etidronate and etidronate salts.

[0100] (Technology 4)

[0101] In any one of the techniques 1 to 3, the non-aqueous electrolyte secondary battery comprises a polyvalent cation.

[0102] (Technology 5)

[0103] According to the non-aqueous electrolyte secondary battery of technology 4, the aforementioned multivalent cation includes divalent cations.

[0104] (Technology 6)

[0105] According to the non-aqueous electrolyte secondary battery of technology 4, the aforementioned multivalent cation includes Ca... 2+ Mg 2+ and Sr 2+ At least one of the groups.

[0106] (Technology 7)

[0107] According to any one of the techniques 4 to 6, the non-aqueous electrolyte secondary battery comprises the aforementioned multivalent cations.

[0108] (Technology 8)

[0109] According to the non-aqueous electrolyte secondary battery of technology 7, the concentration of the aforementioned polyvalent cations in the aforementioned non-aqueous electrolyte is 0.001 mol / L or more and 20 mol / L or less.

[0110] (Technology 9)

[0111] According to the non-aqueous electrolyte secondary battery of technology 8, at least one of the following is dissolved in the aforementioned non-aqueous electrolyte: calcium (II) bis(trifluoromethanesulfonyl)imide, magnesium (II) bis(trifluoromethanesulfonyl)imide, and strontium (II) bis(trifluoromethanesulfonyl)imide.

[0112] (Technology 10)

[0113] According to any one of the techniques 1 to 9, the non-aqueous electrolyte secondary battery comprises at least one selected from the group consisting of ethylene carbonate, ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate, and fluoroethylene carbonate.

[0114] (Technology 11)

[0115] According to any one of the techniques 1 to 10, the non-aqueous electrolyte secondary battery comprises composite particles containing a carbon phase and a particulate silicon phase dispersed in the carbon phase.

[0116] (Technology 12)

[0117] According to the non-aqueous electrolyte secondary battery of technology 11, the average diameter of the aforementioned silicon phase is more than 1 nm and less than 1000 nm.

[0118] (Technology 13)

[0119] According to any one of techniques 1 to 12, in the non-aqueous electrolyte secondary battery, the aforementioned binder compound comprises at least one polyacrylic acid compound selected from the group consisting of polyacrylic acid and salts of polyacrylic acid.

[0120] The aforementioned phosphorus-containing compounds include at least one etidronate compound selected from the group consisting of etidronate and etidronate salts.

[0121] The ratio of the mass We of the aforementioned at least one etidronic acid compound in the aforementioned negative electrode mixture layer to the mass Wp of the aforementioned at least one polyacrylic acid compound in the aforementioned negative electrode mixture layer, We / Wp, is in the range of 0.01 to 1.0.

[0122] (Technology 14)

[0123] According to any one of techniques 1 to 13, in the non-aqueous electrolyte secondary battery, the aforementioned phosphorus-containing compound comprises at least one etidronate compound selected from the group consisting of etidronate and etidronate salts.

[0124] The aforementioned non-aqueous electrolytes contain polyvalent cations.

[0125] The ratio Mc / Me of the molar number Mc of the aforementioned polyvalent cation in the aforementioned non-aqueous electrolyte to the molar number Me of the aforementioned at least one etidronic acid compound in the aforementioned negative electrode mixture layer is in the range of 1.0 to 20.

[0126] Example

[0127] The non-aqueous electrolyte secondary battery of this disclosure will be specifically described below through embodiments. However, this disclosure is not limited to the following embodiments. In these embodiments, multiple test battery cells with different configurations were fabricated and evaluated.

[0128] (Fabrication of experimental battery cell A1)

[0129] The experimental battery cell A1 was fabricated following these steps.

[0130] (1) Fabrication of the negative electrode NA1

[0131] A negative electrode slurry SA1 was prepared by mixing a negative electrode active material, polyacrylic acid (PAA), styrene-butadiene copolymer rubber (SBR), carboxymethyl cellulose (CMC), carbon nanotubes (CNT), etidronic acid, and an appropriate amount of water. In the negative electrode active material, silicon-carbon composite particles (GSS manufactured by Giga Solar Materials Co.) and graphite were mixed at a mass ratio of 30:70. These silicon-carbon composite particles contain a carbon phase and particulate silicon phase dispersed within the carbon phase. The amounts of PAA, SBR, CMC, CNT, and etidronic acid added relative to 100 parts by mass of the negative electrode active material were set to 1 part by mass, 1 part by mass, 1 part by mass, 0.1 part by mass, and 0.11 parts by mass, respectively. The mass ratio We of etidronic acid (etidronic acid-based compound) to Wp of PAA (polyacrylic acid-based compound) was set to 0.11.

[0132] A negative electrode paste SA1 was coated onto one side of an electrolytic copper foil (current collector) to form a film, creating a laminate of the electrolytic copper foil and the coating film. The laminate was then punched to a specified size (2cm × 2cm) and dried. This process yielded a negative electrode NA1 containing a negative electrode binder layer. The initial thicknesses T(0)1 to T(0)9 of the negative electrode binder layer were measured at nine locations on the fabricated negative electrode NA1. Leads were then attached to the negative electrode NA1.

[0133] (2) Fabrication of the electrodes

[0134] A lithium metal foil was adhered to one side of an electrolytic copper foil (current collector) and punched into a square with a side length of 2.5 cm to create a counter electrode. Leads were then attached to the counter electrode.

[0135] (3) Preparation of non-aqueous electrolyte EA1

[0136] Ethyl carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) were mixed in a volume ratio of EC:EMC:DMC = 4:1:15 to obtain a non-aqueous solvent. LiPF6 was then dissolved in this non-aqueous solvent at a concentration of 1.3 mol / L. The non-aqueous electrolyte EA1 was prepared in this manner.

[0137] (4) Assembly of test battery cell A1

[0138] An electrode assembly was fabricated by arranging the negative electrode NA1 and the counter electrode opposite each other with a separator in between. The separator was a microporous membrane made of polyolefin. Next, the electrode assembly was housed in a housing. The housing was formed using aluminum laminates. Then, a non-aqueous electrolyte EA1 was injected into the housing, and the opening of the housing was sealed. At this point, a portion of the lead attached to the negative electrode NA1 and a portion of the lead attached to the counter electrode were exposed from the housing. This process was used to fabricate the test cell unit A1. The test cell unit A1 was evaluated as follows.

[0139] (1) Charge and discharge test

[0140] For test battery cell A1, the following charging and discharging were performed in a constant temperature bath at 25°C. The rest time between charging and discharging was set to 20 minutes.

[0141] (Charge)

[0142] For test battery cell A1, a constant current of 0.1C (1C being the current value required to discharge the designed capacity within 1 hour) was applied until the battery cell voltage reached 0.005V. A rest period of 20 minutes was then applied. Next, a constant current of 0.01C was applied until the battery cell voltage reached 0.005V. Another rest period of 20 minutes was then applied. Finally, a constant current of 0.001C was applied until the battery cell voltage reached 0.005V.

[0143] (Discharge)

[0144] For test battery cell A1, a constant current discharge of 0.1C was applied until the battery cell voltage reached 1V. A rest period of 20 minutes was then applied. Next, a constant current discharge of 0.01C was applied until the battery cell voltage reached 1V. A rest period of 20 minutes was then applied. Finally, a constant current discharge of 0.001C was applied until the battery cell voltage reached 1V.

[0145] Using the results of the above charge-discharge tests and the mass of the negative electrode active material, the charging capacity Ec and the discharging capacity Ed per unit mass of the negative electrode active material are calculated.

[0146] (2) Measurement of the expansion of the negative electrode during full charge

[0147] For the test battery cell A1 after the above charge and discharge test, the following charging was performed in a constant temperature bath at 25°C.

[0148] For test battery cell A1, a constant current of 0.1C (1C being the current value required to discharge the designed capacity within 1 hour) was applied until the battery cell voltage reached 0.005V. A rest period of 20 minutes was then applied. Next, a constant current of 0.01C was applied until the battery cell voltage reached 0.005V. Another rest period of 20 minutes was then applied. Finally, a constant current of 0.001C was applied until the battery cell voltage reached 0.005V.

[0149] The charged test battery cell A1 was disassembled and the negative electrode was removed. Then, the thickness T(C)1 to T(C)9 of the negative electrode's alloy layer under full charge was measured at nine locations identical to the measurement sites T(0)1 to T(0)9 of the negative electrode. Then, the expansion rates X1 to X9 of the negative electrode under full charge were calculated using the following formula, and the arithmetic mean of X1 to X9 was obtained to determine the average expansion rate X(%) of the negative electrode under full charge. As described above, the thickness T(0)... n It is the thickness of the initial negative electrode compound layer.

[0150] (expansion rate X) n [%])=((thickness T(C)) n ) / (thickness T(0) n ))×100

[0151] (n is an integer from 1 to 9)

[0152] Then, using the following formula, the expansion amount Y of the negative electrode per unit of charging capacity during charging can be calculated. As mentioned above, the charging capacity Ec is the charging capacity per unit mass of the negative electrode active material.

[0153] (Expansion amount Y [% / (Ah / g)]) = (Average expansion rate X - 100) / (Charging capacity Ec [Ah / g])

[0154] (Fabrication of experimental battery cells A2, A3 and C1)

[0155] Except for changing the negative electrode, test cells A2, A3, and C1 were fabricated using the same method as test cell A1. For the negative electrodes of test cells A2 and A3, except for changing the amount of etidronic acid added to achieve the We / Wp ratio shown in Table 1, they were fabricated using the same method and conditions as negative electrode NA1. For the negative electrode of test cell C1, except without the addition of etidronic acid, it was fabricated using the same method as negative electrode NA1.

[0156] The fabricated negative electrode and test cell were measured and evaluated in the same manner as the negative electrode NA1 and test cell A1. The fabrication conditions and evaluation results of the test cell are shown in Table 1. The charging capacity Ec and discharging capacity Ed are preferably larger. The average expansion rate X and expansion amount Y are preferably smaller.

[0157] [Table 1]

[0158]

[0159] Test battery cells A1 to A3 are test battery cells corresponding to the secondary battery (B) of this disclosure. Test battery cell C1 is a comparative example. As shown in Table 1, the negative electrode expansion of test battery cells A1 to A3 is less than that of test battery cell C1. Furthermore, the negative electrodes of test battery cells A1 to A3 have higher charging and discharging capacities compared to the negative electrode of test battery cell C1. Test battery cells A1 to A3 can achieve a balance between relatively high charging and discharging capacities and low expansion. Therefore, according to this disclosure, a non-aqueous electrolyte secondary battery with high capacity and good charge-discharge cycle characteristics can be obtained.

[0160] Industrial availability

[0161] This disclosure can be used in non-aqueous electrolyte secondary batteries.

[0162] The present invention has been described with reference to preferred embodiments, but such disclosure should not be interpreted restrictively. Various modifications and alterations will undoubtedly be apparent to those skilled in the art upon reading the above disclosure. Therefore, the appended claims should be construed as including all modifications and alterations without departing from the true spirit and scope of the invention.

[0163] Explanation of reference numerals in the attached figures

[0164] 10: Non-aqueous electrolyte secondary battery

[0165] 11: Positive electrode

[0166] 12: Negative electrode

[0167] 13: Separator

[0168] 14: Electrode assembly.

Claims

1. A non-aqueous electrolyte secondary battery, comprising a positive electrode, a negative electrode containing a negative electrode flux layer, and a non-aqueous electrolyte. The negative electrode mixture layer contains negative electrode active material and binder components. The binder components include binder compounds and phosphorus-containing compounds. The phosphorus-containing compound comprises at least one phosphorus-containing group selected from the group consisting of phosphate group, phosphate group, phosphonic acid group and phosphonate group. The number of at least one phosphorus-containing group contained in the phosphorus-containing compound is 2 or more and 5 or less. The negative electrode active material contains silicon.

2. The non-aqueous electrolyte secondary battery according to claim 1, wherein, The adhesive compound comprises at least one selected from the group consisting of polyacrylic acid, salts of polyacrylic acid, carboxymethyl cellulose, and salts of carboxymethyl cellulose.

3. The non-aqueous electrolyte secondary battery according to claim 1, wherein, The phosphorus-containing compound comprises at least one etidronic acid compound selected from the group consisting of etidronic acid and etidronate.

4. The non-aqueous electrolyte secondary battery according to any one of claims 1 to 3, wherein, The adhesive component contains polyvalent cations.

5. The non-aqueous electrolyte secondary battery according to claim 4, wherein, The multivalent cations include divalent cations.

6. The non-aqueous electrolyte secondary battery according to claim 4, wherein, The multivalent cations include those selected from Ca. 2+ Mg 2+ and Sr 2+ At least one of the groups.

7. The non-aqueous electrolyte secondary battery according to claim 4, wherein, The non-aqueous electrolyte contains the polyvalent cation.

8. The non-aqueous electrolyte secondary battery according to claim 7, wherein, The concentration of the polyvalent cation in the non-aqueous electrolyte is above 0.001 mol / L and below 20 mol / L.

9. The non-aqueous electrolyte secondary battery according to claim 8, wherein, The non-aqueous electrolyte contains at least one substance selected from the group consisting of calcium (II) bis(trifluoromethanesulfonyl)imide, magnesium (II) bis(trifluoromethanesulfonyl)imide, and strontium (II) bis(trifluoromethanesulfonyl)imide.

10. The non-aqueous electrolyte secondary battery according to any one of claims 1 to 3, wherein, The non-aqueous electrolyte comprises at least one selected from the group consisting of ethylene carbonate, methyl ethyl carbonate, dimethyl carbonate, diethyl carbonate, and fluoroethylene carbonate.

11. The non-aqueous electrolyte secondary battery according to any one of claims 1 to 3, wherein, The silicon-containing material comprises composite particles, wherein the composite particles contain a carbon phase and a particulate silicon phase dispersed in the carbon phase.

12. The non-aqueous electrolyte secondary battery according to claim 11, wherein, The average diameter of the silicon phase is greater than 1 nm and less than 1000 nm.

13. The non-aqueous electrolyte secondary battery according to claim 1, wherein, The adhesive compound comprises at least one polyacrylic acid compound selected from the group consisting of polyacrylic acid and salts of polyacrylic acid. The phosphorus-containing compound comprises at least one etidronic acid compound selected from the group consisting of etidronic acid and etidronate. The ratio of the mass We of the at least one etidronic acid compound in the negative electrode mixture layer to the mass Wp of the at least one polyacrylic acid compound in the negative electrode mixture layer, We / Wp, is in the range of 0.01 to 1.

0.

14. The non-aqueous electrolyte secondary battery according to claim 1 or 2, wherein, The phosphorus-containing compound comprises at least one etidronic acid compound selected from the group consisting of etidronic acid and etidronate. The non-aqueous electrolyte contains polyvalent cations. The ratio Mc / Me of the molar number Mc of the polyvalent cation in the non-aqueous electrolyte to the molar number Me of at least one etidronate compound in the negative electrode mixture layer is in the range of 1.0 to 20.

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