Nonaqueous electrolyte secondary battery

Abstract

A disclosed nonaqueous electrolyte secondary battery (10) includes a positive electrode (11), a negative electrode (12) including a negative electrode mixture layer, and a nonaqueous electrolyte. The negative electrode mixture layer contains a negative electrode active material and a binder component. The binder component contains a binder compound and a chelating agent. The negative electrode active material contains a silicon-containing material. The nonaqueous electrolyte contains a polyvalent cation.

Description

Nonaqueous electrolyte secondary battery

[0001] The present disclosure relates to a non-aqueous electrolyte secondary battery.

[0002] Non-aqueous electrolyte secondary batteries are used in a variety of applications as high-capacity secondary batteries. Various proposals have been made regarding non-aqueous electrolyte secondary batteries. For example, it has been proposed to use a silicon-containing material as a negative electrode active material.

[0003] Claim 1 of Patent Document 1 (JP 2012-527069 A) discloses "an electrode for a lithium-ion rechargeable battery cell, the electrode comprising: a substrate, for example a current collector; silicon particles forming an active material in the electrode; a cellulose-based binder; and at least a chelating agent capable of binding to the metal impurities, such as divalent and / or trivalent metal impurities, wherein the binder is mixed with the silicon particles to form an adhesive material that adheres to the substrate."

[0004] Claim 1 of Patent Document 2 (JP 2021-77545 A) discloses a "composition for manufacturing a negative electrode, comprising a silicon-containing negative electrode active material, an aqueous binder, water, and a water-soluble reducing agent."

[0005] Non-Patent Document 1 (App. Sur. Sci., 447(2018), pp. 442-451, "Influence of EDTA in poly(acrylic acid) binder for enhancing electrochemical performance and thermal stability of silicon anode") discloses the effect of EDTA on polyacrylic acid (binder) in a silicon-based anode.

[0006] Non-Patent Document 2 (Mater. Today Sus., 19(2022), 100178, "Cross-linked binder enables reversible volume changes of Si-based anodes from sustainable photovoltaic waste silicon") discloses the effect of a cross-linked binder on the volume change of a silicon-based anode.

[0007] JP 2012-527069 A JP 2021-77545 A

[0008] App. Sur. Sci., 447(2018), pp 442-451Mater. Today Sus., 19(2022), 100178

[0009] While silicon-containing materials can achieve high capacity, they suffer from the problem of large expansion and contraction during charge and discharge. Large expansion of the negative electrode during charge significantly deteriorates battery characteristics (such as charge and discharge cycle characteristics). One of the objectives of the present disclosure is to provide a nonaqueous electrolyte secondary battery that uses a silicon-containing negative electrode active material and exhibits small expansion of the negative electrode during charge.

[0010] One aspect of the present disclosure relates to a non-aqueous electrolyte secondary battery including: a positive electrode; a negative electrode including a negative electrode mixture layer; and a non-aqueous electrolyte, wherein the negative electrode mixture layer contains a negative electrode active material and a binder component, the binder component contains a binder compound and a chelating agent, the negative electrode active material contains a silicon-containing material, and the non-aqueous electrolyte contains a polyvalent cation.

[0011] According to the present disclosure, a non-aqueous electrolyte secondary battery is provided that uses a silicon-containing negative electrode active material and exhibits small negative electrode expansion during charging. The novel features of the present invention are set forth in the appended claims, but the present invention, both in terms of structure and content, together with other objects and features of the present invention, will be better understood from the following detailed description taken in conjunction with the drawings.

[0012] FIG. 1 is a cross-sectional view schematically illustrating an example of a nonaqueous electrolyte secondary battery according to the present disclosure.

[0013] The following describes embodiments of the present disclosure using examples, but the present disclosure is not limited to the examples described below. In the following description, specific numerical values ​​and materials may be exemplified, but other numerical values ​​and materials may be applied as long as the effects of the present disclosure are obtained. In this specification, the term "numerical value A to numerical value B" includes numerical value A and numerical value B and can be read as "numerical value A or greater and numerical value B or less." In the following description, when lower and upper limits for specific physical properties or conditions 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 is not greater than the upper limit. In the following description, when examples of components or methods are listed, only one of the listed examples may be used, or multiple of the listed examples may be used in combination, unless otherwise specified.

[0014] (Non-aqueous electrolyte secondary battery) The non-aqueous electrolyte secondary battery according to this embodiment may be referred to hereinafter as a "nonaqueous electrolyte secondary battery (B)" or a "secondary battery (B)." The secondary battery (B) includes a positive electrode, a negative electrode including a negative electrode mixture layer, and a non-aqueous electrolyte. The negative electrode mixture layer contains a negative electrode active material and a binder component. The binder component contains a binder compound and a chelating agent. The negative electrode active material contains a silicon-containing material. The non-aqueous electrolyte contains a polyvalent cation.

[0015] The negative electrode active material of the secondary battery (B) contains a silicon-containing material, enabling a high capacity. The binder component of the secondary battery (B) contains a binder compound and a chelating agent, and the non-aqueous electrolyte contains a polyvalent cation. By selecting the binder compound and the chelating agent, it is possible to form bonds (e.g., hydrogen bonds) between the binder compound and the chelating agent. Furthermore, the chelating agents in the negative electrode mixture layer are crosslinked with each other via the polyvalent cations of the non-aqueous electrolyte that have permeated the negative electrode mixture layer. As a result, the crosslinks between the compounds constituting the binder component are strengthened, suppressing expansion of the negative electrode during charge. Therefore, despite the use of a negative electrode active material containing silicon (Si), the negative electrode of the secondary battery (B) exhibits small expansion during charge. Therefore, the secondary battery (B) can achieve both a high discharge capacity and good charge / discharge cycle characteristics.

[0016] The binder compound is preferably a compound that forms a bond (e.g., a hydrogen bond) with the chelating agent. That is, a preferred example of the binder component includes, as the binder compound, a compound that forms a hydrogen bond with the chelating agent.

[0017] Examples of functional groups involved in hydrogen bonding include carbonyl groups, hydroxyl groups, amino groups, thiol groups, etc. The carbonyl group may be a carbonyl group in a carboxylic acid group and / or a carboxylic acid salt group. In one example where a chelating agent and a binder compound form a hydrogen bond, at least one of the chelating agent and the binder compound contains a carbonyl group, and the other contains a hydroxyl group. In another example where a chelating agent and a binder compound form a hydrogen bond, each of the chelating agent and the binder compound contains a carboxylic acid group and / or a carboxylic acid salt group.

[0018] The binder compound may be a compound commonly used as a binder, but preferably includes a compound that forms a bond with a chelating agent. Types of bonds formed between the binder compound and the chelating agent include covalent bonds, ionic bonds, and hydrogen bonds. A preferred example of a binder compound is a compound that forms a hydrogen bond with a chelating agent. 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 may be in the range of 5,000 to 5,000,000 (e.g., in the range of 100,000 to 1,000,000).

[0019] The binder compound may include at least one selected from the group consisting of polyacrylic acid, a salt of polyacrylic acid, carboxymethyl cellulose, and a salt of carboxymethyl cellulose. These are used as binder compounds. The binder component may include only polyacrylic acid and / or a salt of polyacrylic acid as the binder compound. Alternatively, the binder component may include only carboxymethyl cellulose and / or a salt of carboxymethyl cellulose as the binder compound. Examples of cations that constitute the salt include lithium ions, sodium ions, potassium ions, ammonium ions, etc.

[0020] The chelating agent may include at least one selected from the group consisting of a carboxylic acid group, a carboxylate group, a phosphonic acid group, and a phosphonate group. The chelating agent may be a carboxylic acid group and / or a carboxylate group. Alternatively, the chelating agent may be a phosphonic acid group and / or a phosphonate group.

[0021] The chelating agent may include an ethylenediamine moiety. The ethylenediamine moiety is represented by the formula: ═N—CH ２ CH ２ It is represented by the formula -N=. The ethylenediamine moiety forms a coordinate bond with a cation.

[0022] The chelating agent may include at least one selected from the group consisting of ethylenediaminetetraacetic acid (EDTA) and ethylenediaminetetraacetate salts. These chelating agents have four carbonyl groups as functional groups capable of forming hydrogen bonds with the binder compound, and are therefore preferred in that they can more strongly crosslink the binder compound than chelating agents with two or three functional groups.

[0023] The ethylenediaminetetraacetate may be a lithium salt, a sodium salt, a potassium salt, or an ammonium salt. Examples of the ethylenediaminetetraacetate include ethylenediamine-N,N,N',N'-tetraacetic acid disodium salt dihydrate, etc.

[0024] Polyvalent cations are cations with a valence of two or more. Examples of polyvalent cations include divalent cations, trivalent cations, tetravalent cations, etc. Polyvalent cations include 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＋ The polyvalent cation may be any one selected from the group consisting of:

[0025] The polyvalent cation may include or be a divalent cation. Divalent cations are thought to be more likely to form a stable crosslinked structure.

[0026] The multivalent cation is Ca ２＋ and Mg ２＋ The polyvalent cation may include at least one selected from the group consisting of Ca ２＋ or Mg ２＋ may be.

[0027] Polyvalent cations can be incorporated into the non-aqueous electrolyte by dissolving a salt that generates the polyvalent cation in the non-aqueous electrolyte. The non-aqueous electrolyte may contain at least one compound selected from the group consisting of calcium(II) bis(trifluoromethanesulfonyl)imide and magnesium(II) bis(trifluoromethanesulfonyl)imide. That is, the non-aqueous electrolyte may contain at least one compound selected from the group consisting of calcium(II) bis(trifluoromethanesulfonyl)imide and magnesium(II) bis(trifluoromethanesulfonyl)imide. These compounds (salts) are preferred because they do not generate chloride ions. The anions that constitute the salts are also dissolved in the non-aqueous electrolyte containing these salts.

[0028] The nonaqueous electrolyte may contain at least one selected from the group consisting of ethylene carbonate, ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate, and fluoroethylene carbonate. These constitute nonaqueous solvents. These solvents swell the binder compound, thereby distributing polyvalent cations in the nonaqueous electrolyte throughout the domains of the binder compound. Therefore, these solvents are preferred in that they can promote crosslinking of the chelating agent in the binder compound.

[0029] The silicon-containing material may include composite particles that include a carbon phase and a particulate silicon phase dispersed in the carbon phase.

[0030] The average diameter of the silicon phase may be 1 nm or more, 10 nm or more, 100 nm or more, or 500 nm or more. The average diameter of the silicon phase may be 1000 nm or less, 500 nm or less, 100 nm or less, or 10 nm or less. For example, the average diameter of the silicon phase may be 1 nm or more and 1000 nm or less. The particulate silicon phase dispersed in the carbon phase can be considered as silicon particles dispersed in the carbon phase. The average diameter of the particulate silicon phase is measured by observing the cross section of the composite particle using SEM or TEM. Specifically, it is determined by arithmetically averaging the maximum diameters of any 100 silicon phases in the cross section.

[0031] The binder component may further include at least one polyacrylic acid compound selected from the group consisting of polyacrylic acid and salts of polyacrylic acid. In this case, the ratio Wc / Wp of the mass Wc of the chelating agent in the negative electrode mixture layer to the mass Wp of the polyacrylic acid compound in the negative electrode mixture layer may be 0.01 or more, 0.05 or more, 0.10 or more, or 0.20 or more, or 0.50 or less, 0.20 or less, 0.10 or less, or 0.05 or less. For example, the ratio Wc / Wp may be in the range of 0.01 to 0.50. The lower and / or upper limits of this range may be replaced with the above-mentioned lower and / or upper limits, as long as the lower limit is not greater than or equal to the upper limit.

[0032] The concentration of the polyvalent cation in the non-aqueous electrolyte may be 0.001 mol / L or more, 0.005 mol / L or more, 0.01 mol / L or more, 0.1 mol / L or more, or 1.0 mol / L or more, or 20 mol / L or less, 10 mol / L or less, 1.0 mol / L or less, 0.1 mol / L or less, or 0.01 mol / L or less. For example, the concentration of the polyvalent cation may 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. In any of these ranges, the upper limit may be 10 mol / L, 1.0 mol / L, 0.1 mol / L, or 0.01 mol / L, as long as the lower limit is not equal to or greater than the upper limit. For example, the concentration of the polyvalent cation may 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 the polyvalent cation in the nonaqueous electrolyte may be 0.001 mol / L or greater and 20 mol / L or less.

[0033] It is believed that a higher concentration of polyvalent cations promotes cross-linking between chelating agents in the negative electrode mixture layer, thereby further reducing the expansion rate of the electrode plate during charging. On the other hand, a lower concentration of polyvalent cations suppresses excessive increases in the viscosity of the nonaqueous electrolyte, thereby improving the charge / discharge characteristics of the battery. For example, by setting the concentration of polyvalent cations in the range of 0.005 mol / L to 0.01 mol / L, the expansion rate of the electrode plate during charging can be further reduced without causing a significant decrease in charge capacity.

[0034] The ratio Mca / Mch of the number of moles Mca of polyvalent cations in the non-aqueous electrolyte to the number of moles Mch of chelating agent in the negative electrode mixture layer may be 1.0 or more, or 5.0 or more. The ratio Mca / Mch may be 20 or less, 15 or less, 10 or less, or 5.0 or less. Mca / Mch may be in the range of 1.0 to 20, 5.0 to 15, or 5.0 to 10. For example, when the ratio Mca / Mch is in the range of 5.0 to 10, the swelling rate of the electrode plate during charging can be further reduced without causing a significant decrease in charge capacity. Note that the number of moles Mca of polyvalent cations in the non-aqueous electrolyte includes the number of moles of polyvalent cations in the non-aqueous electrolyte present outside the electrodes (positive electrode, negative electrode) as well as the number of moles of polyvalent cations in the non-aqueous electrolyte that have penetrated the electrodes.

[0035] The secondary battery (B) preferably satisfies at least one selected from the following conditions (1) to (4), more preferably two or more, even more preferably three or more, and particularly preferably all: (1) The binder compound and the chelating agent form hydrogen bonds; (2) The non-aqueous electrolyte contains a divalent cation; (3) The chelating agent contains an ethylenediamine moiety; and (4) The ratio Mca / Mch of the number of moles Mca of polyvalent cations in the non-aqueous electrolyte to the number of moles Mch of the chelating agent in the negative electrode mixture layer is in the range of 1.0 to 20.

[0036] Regarding condition (1), the binder compound and the chelating agent may each independently contain one selected from the group consisting of a carboxylic acid group, a carboxylate salt group, and a hydroxyl group. In this case, at least one of the binder compound and the chelating agent may contain a hydroxyl group. The binder compound may be at least one selected from the group consisting of polyacrylic acid, a salt of polyacrylic acid, carboxymethyl cellulose, and a salt of carboxymethyl cellulose. For example, the binder compound may be polyacrylic acid and / or a salt of polyacrylic acid, or may be carboxymethyl cellulose and / or a salt of carboxymethyl cellulose.

[0037] Regarding condition (2), the non-aqueous electrolyte is Ca ２＋ and Mg ２＋ The non-aqueous electrolyte may contain at least one selected from the group consisting of Ca as a polyvalent cation. ２＋ It may contain only Mg as a polyvalent cation. ２＋ It may contain only

[0038] Regarding condition (3), the chelating agent may be at least one selected from the group consisting of ethylenediaminetetraacetic acid and ethylenediaminetetraacetate salts. Regarding condition (4), the ratio Mca / Mch may be in the above-mentioned range.

[0039] It is also possible to use a non-aqueous electrolyte containing a monovalent cation other than lithium instead of a polyvalent cation as the non-aqueous electrolyte, although in this case, the same effects as those obtained in the secondary battery (B) cannot be obtained.

[0040] (Method for manufacturing secondary battery (B)) As long as the essential components of the secondary battery (B) can be satisfied, the method for manufacturing the secondary battery (B) is not limited. An example of the manufacturing method will be described below. The matters described for the secondary battery (B) can be applied to the manufacturing method below, so duplicated explanations will be omitted. The matters described for the manufacturing method below may also be applied to the secondary battery (B). In the example below, the electrode group includes a separator, and the negative electrode includes a negative electrode current collector.

[0041] This production method includes steps (i) and (ii). Step (i) is a step of preparing an electrode group and a non-aqueous electrolyte. The electrode group includes a positive electrode, a negative electrode, and a separator.

[0042] Step (i) includes a step (ia) of forming a negative electrode and a step (ib) of forming a positive electrode. The method for forming the negative electrode is not limited, and known methods may be used, except that the negative electrode material contains specific components. In one example of a method for producing a negative electrode, a negative electrode slurry is first prepared by mixing the negative electrode components with a dispersion medium. The dispersion medium may be water, alcohol (such as ethanol), ether (such as tetrahydrofuran), N-methyl-2-pyrrolidone (NMP), or a mixture thereof. The negative electrode components include a negative electrode active material (particles of the negative electrode active material) and a binder component, and may further contain other components as necessary. The negative electrode active material includes a silicon-containing material.

[0043] The negative electrode slurry preferably does not contain polyvalent cations. If the negative electrode slurry contains a chelating agent and a polyvalent cation, the viscosity of the negative electrode slurry increases, which may increase the difficulty of forming the negative electrode or reduce the quality of the negative electrode. Even if 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 the non-aqueous electrolyte. In this case, the polyvalent cations in the negative electrode mixture layer are derived from the non-aqueous electrolyte.

[0044] Next, the negative electrode slurry is applied to a negative electrode current collector and then dried to obtain a laminate including the negative electrode current collector and a negative electrode mixture layer formed on the negative electrode current collector. The laminate is then rolled to produce a negative electrode. The thickness of the negative electrode mixture layer may be 3 μm or more, or 5 μm or more, and may be 200 μm or less, or 150 μm or less. The produced negative electrode is cut to a predetermined size as needed. The negative electrode mixture layer is formed on one or both sides of the negative electrode current collector.

[0045] The method for forming the positive electrode is not limited, and a known method may be used. For example, the positive electrode can be formed in the same manner as the negative electrode formation method described above, except that a positive electrode slurry is used instead of the negative electrode slurry and a positive electrode current collector is used instead of the negative electrode current collector. The positive electrode slurry can be prepared using a positive electrode active material, an additive, and a dispersion medium.

[0046] The form of the electrode assembly is not limited. For example, the electrode assembly may be a wound type or a stacked type. An example of a wound type electrode assembly is formed by winding a positive electrode, a negative electrode, and a separator. At this time, a separator is disposed between the positive electrode and the negative electrode. An example of a stacked type 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. At this time, a separator is disposed between the positive electrode and the negative electrode.

[0047] The non-aqueous electrolyte can be prepared, for example, by dissolving predetermined components (salts, additives, etc.) in a non-aqueous solvent. A non-aqueous electrolyte containing polyvalent cations can be prepared by using a salt that generates polyvalent cations.

[0048] Step (ii) is a step of housing the electrode group and the non-aqueous electrolyte in an outer casing. The method for carrying out step (ii) is not limited, and it may be carried out by a known method. The outer casing is not limited, and a known outer casing may be used. In this manner, the secondary battery (B) can be produced.

[0049] The components other than the essential components of the secondary battery (B) are not particularly limited, and components used in known non-aqueous electrolyte secondary batteries may be applied. 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.

[0050] The secondary battery (B) includes an outer casing, an electrode group housed in the outer casing, and a non-aqueous electrolyte. The electrode group includes a positive electrode, a negative electrode, and a separator.

[0051] (Negative Electrode) The negative electrode includes a negative electrode mixture layer. The negative electrode may include a negative electrode current collector and a negative electrode mixture layer disposed on the negative electrode current collector. The negative electrode mixture layer contains a negative electrode active material and a binder component, and may further contain other additives.

[0052] The negative electrode current collector is not particularly limited, and a known negative electrode current collector may be used. A conductive sheet (e.g., metal foil) may be used as the negative electrode current collector. For example, copper foil, copper alloy foil, a resin sheet (e.g., a polyethylene terephthalate sheet) on which copper is vapor-deposited, or a stainless steel foil on which copper is vapor-deposited may be used as the negative electrode current collector.

[0053] The negative electrode active material may be a material that reversibly absorbs and releases lithium ions. The negative electrode active material includes a silicon-containing material. The negative electrode active material may include a negative electrode active material other than the silicon-containing material. Examples of other negative electrode active materials include a carbonaceous material and an Sn-containing material. The negative electrode mixture layer may include only one type of negative electrode active material, or may include two or more types of negative electrode active materials. Examples of carbonaceous materials include graphite, easily graphitizable carbon (soft carbon), and hardly graphitizable carbon (hard carbon).

[0054] Examples of silicon-containing materials include silicon oxide, silicon, and composite materials. The composite materials may contain multiple phases selected from a carbon phase, a lithium silicate phase, a silicon phase, and a silicon oxide phase. One example of a composite material contains a carbon phase and a particulate silicon phase dispersed in the carbon phase. Another example of a composite material contains a lithium silicate phase and a particulate silicon phase dispersed in the lithium silicate phase.

[0055] The components other than the negative electrode active material and the binder component (such as the conductive material) are not particularly limited, and known components may be used. The conductive material may be any of the materials exemplified as the conductive material for the positive electrode mixture layer.

[0056] (Positive Electrode) The positive electrode includes a positive electrode mixture layer. The positive electrode may include a positive electrode current collector and a positive electrode mixture layer disposed on the positive electrode current collector. The positive electrode current collector and the positive electrode mixture layer are not particularly limited, and those used in the positive electrodes of known non-aqueous electrolyte secondary batteries may be applied.

[0057] Examples of the material of the positive electrode current collector include metal materials containing Al, Ti, Fe, etc. The metal material may be Al, an Al alloy, Ti, a Ti alloy, an Fe alloy, etc. The Fe alloy may be stainless steel (SUS).

[0058] 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. The composite oxide containing lithium and the metal element Me may be a lithium-containing transition metal oxide containing at least a transition metal as the metal element Me. Lithium-containing transition metal oxides are preferably used as the positive electrode active material because of their low production cost and high average discharge voltage.

[0059] Examples of transition metal elements contained in the lithium-containing transition metal oxide include Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Y, Zr, and W. The lithium-containing transition metal oxide may contain only one type of transition metal element, or two or more types. The lithium-containing transition metal oxide preferably contains at least one element selected from the group consisting of Ni, Co, Mn, and Al.

[0060] Additives other than the positive electrode active material (binders, conductive materials, etc.) are not particularly limited, and known additives may be used. Conductive carbon materials may be used as conductive materials. Examples of conductive carbon materials include carbon black, carbon nanotubes, and graphite. Examples of binders include fluororesins, polyacrylonitrile, polyimide resins, acrylic resins, polyolefin resins, and rubber-like polymers. Examples of fluororesins include polytetrafluoroethylene and polyvinylidene fluoride.

[0061] (Separator) A porous sheet having ion permeability and insulating properties is used for the separator. Examples of porous sheets include thin films, woven fabrics, nonwoven fabrics, etc. having micropores. The material of the separator is not particularly limited, and a polymeric material may be used. Examples of polymeric materials include polyolefin resins, polyamide resins, cellulose, etc. Examples of polyolefin resins include polyethylene, polypropylene, and ethylene-propylene copolymers. The separator may contain additives (such as inorganic fillers) as necessary. The thickness of the separator is not particularly limited, and may be 10 μm or more, or 15 μm or more, or 30 μm or less, or 20 μm or less.

[0062] (Non-aqueous electrolyte) The non-aqueous electrolyte may be a non-aqueous electrolyte having lithium ion conductivity. The non-aqueous electrolyte contains a non-aqueous solvent and ions (lithium ions, polyvalent cations, anions, etc.) dissolved in the non-aqueous solvent. The non-aqueous electrolyte may be in a liquid or gel state.

[0063] The non-aqueous electrolyte can be prepared by dissolving a lithium salt and a salt of a polyvalent cation in a non-aqueous solvent. Dissolving the lithium salt in the non-aqueous solvent produces lithium ions and anions. Dissolving the salt of the polyvalent cation in the non-aqueous solvent produces polyvalent cations and anions.

[0064] Examples of lithium salts include lithium salts of chlorine-containing acids (LiClO ４ , LiAlCl ４ , LiB １０ Cl １０ etc.), lithium salts of fluorine-containing acids (LiPF ６ , LiPF ２ O ２ , LiBF ４ , LiSbF ６ , LiAsF ６ , LiCF ３ SO ３ , LiCF ３ CO ２ etc.), lithium salt of fluorine-containing acid imide (LiN(FSO ２ ) ２ , LiN(CF３ SO ２ ) ２ , LiN(CF ３ SO ２ ) (C ４ F ９ SO ２ ), LiN(C ２ F ５ SO ２ ) ２ Lithium salts include lithium halides (LiCl, LiBr, LiI, etc.), and lithium halides (LiCl, LiBr, LiI, etc.). The lithium salts may be used alone or in combination of two or more. The concentration of the lithium salt in the non-aqueous electrolyte may be 0.5 mol / L or more and 3.5 mol / L or less.

[0065] An example of a non-aqueous electrolyte is substantially free of chloride ions. For example, the concentration of chloride ions in the non-aqueous electrolyte may be less than 0.001 mol / L (e.g., less than 0.0001 mol / L). A non-aqueous electrolyte substantially free of chloride ions is preferable in that it does not substantially generate chlorine-based gas derived from chloride ions during charging and discharging. A non-aqueous electrolyte substantially free of chloride ions can be prepared by using a salt other than chloride.

[0066] The nonaqueous solvent is not particularly limited, and known nonaqueous solvents may be used. Examples of nonaqueous 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 ethyl methyl carbonate (EMC). Examples of cyclic carboxylic acid esters include γ-butyrolactone (GBL) and γ-valerolactone. Examples of chain carboxylic acid esters include nonaqueous solvents such as methyl acetate, ethyl acetate, propyl acetate, methyl propionate, and ethyl propionate. One type of nonaqueous solvent may be used alone, or two or more types may be used in combination.

[0067] (Exterior Body) The exterior body (battery case) houses the electrode group and the non-aqueous electrolyte. The exterior body is not particularly limited, and any known exterior body may be used. The exterior body usually includes an exterior can and a sealing member that seals the opening of the exterior can. The exterior can functions as a negative electrode terminal, and the sealing member functions as a positive electrode terminal. The sealing member may include a sealing plate and a gasket.

[0068] An example of a secondary battery (B) according to the present disclosure will be described below with reference to the drawings. The components described above can be applied to the components of the example described below. The components of the example described below can be modified based on the above description. The matters described below may also be applied to the above embodiment. In the example described below, components that are not essential for the secondary battery (B) according to the present disclosure may be omitted.

[0069] (Embodiment 1) Fig. 1 is a longitudinal cross-sectional view schematically illustrating an example of a nonaqueous electrolyte secondary battery according to Embodiment 1. The cylindrical nonaqueous electrolyte secondary battery 10 shown in Fig. 1 includes a cylindrical battery case, and an electrode group 14 and a nonaqueous electrolyte (not shown) housed in the battery case. The electrode group 14 is a wound electrode group and includes a positive electrode 11, a negative electrode 12, and a separator 13.

[0070] The battery case includes a case body 15, which is a cylindrical metal container with a bottom, and a sealing body 16 that seals the opening of the case body 15. A gasket 27 is disposed between the case body 15 and the sealing body 16. The gasket 27 ensures the airtightness of the battery case. Within the case body 15, insulating plates 17 and 18 are disposed at both ends of the electrode group 14 in the winding axis direction. The case body 15 has a step portion 21.

[0071] The sealing body 16 includes a filter 22, a lower valve body 23, an insulating member 24, an upper valve body 25, and a cap 26. The lower valve body 23 and the upper valve body 25 are connected at their respective centers. An insulating member 24 is disposed between the peripheral edge of the lower valve body 23 and the peripheral edge of the upper valve body 25. The filter 22 and the lower valve body 23 are connected at their respective peripheral edges. The upper valve body 25 and the cap 26 are connected at their respective peripheral edges. All of the components constituting the sealing body 16, except for the insulating member 24, are electrically connected.

[0072] A vent hole is formed in the lower valve body 23. Therefore, if the internal pressure of the battery case increases due to abnormal heat generation or the like, the upper valve body 25 bulges toward the cap 26 and separates from the lower valve body 23. This cuts off the electrical connection between the lower valve body 23 and the upper valve body 25. If the internal pressure increases further, the upper valve body 25 breaks, and gas is discharged from an opening formed in the cap 26.

[0073] The positive electrode 11 is electrically connected to a cap 26, which functions as a positive electrode terminal, via a positive electrode lead 19. The negative electrode 12 is electrically connected to a case body 15, which functions as a negative electrode terminal, via a negative electrode lead 20.

[0074] As described above, the negative electrode 12 includes a negative electrode mixture layer containing a negative electrode active material and a binder component, and a non-aqueous electrolyte containing a polyvalent cation.

[0075] (Additional Notes) The above disclosure discloses the following technologies. (Technology 1) A nonaqueous electrolyte secondary battery comprising: a positive electrode; a negative electrode including a negative electrode mixture layer; and a nonaqueous electrolyte, wherein the negative electrode mixture layer contains a negative electrode active material and a binder component, wherein the binder component contains a binder compound and a chelating agent, wherein the negative electrode active material contains a silicon-containing material, and wherein the nonaqueous electrolyte contains a polyvalent cation. (Technology 2) The nonaqueous electrolyte secondary battery according to Technology 1, wherein the binder compound contains at least one selected from the group consisting of polyacrylic acid, a salt of polyacrylic acid, carboxymethyl cellulose, and a salt of carboxymethyl cellulose. (Technology 3) The nonaqueous electrolyte secondary battery according to Technology 1 or 2, wherein the chelating agent contains at least one selected from the group consisting of a carboxylic acid group, a carboxylate group, a phosphonic acid group, and a phosphonate group. (Technology 4) The nonaqueous electrolyte secondary battery according to any one of Technology 1 to 3, wherein the chelating agent contains an ethylenediamino group. (Technology 5) The nonaqueous electrolyte secondary battery according to any one of Technologies 1 to 4, wherein the chelating agent includes at least one selected from the group consisting of ethylenediaminetetraacetic acid and ethylenediaminetetraacetate salts. (Technology 6) The nonaqueous electrolyte secondary battery according to any one of Technologies 1 to 5, wherein the polyvalent cation includes a divalent cation. (Technology 7) The polyvalent cation is Ca ２＋ and Mg ２＋The nonaqueous electrolyte secondary battery according to any one of Techniques 1 to 6, comprising at least one selected from the group consisting of: (Technology 8) The nonaqueous electrolyte secondary battery according to any one of Techniques 1 to 7, wherein the nonaqueous electrolyte contains dissolved therein at least one selected from the group consisting of calcium(II) bis(trifluoromethanesulfonyl)imide and magnesium(II) bis(trifluoromethanesulfonyl)imide. (Technology 9) The nonaqueous electrolyte secondary battery according to any one of Techniques 1 to 8, wherein the nonaqueous electrolyte contains at least one selected from the group consisting of ethylene carbonate, ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate, and fluoroethylene carbonate. (Technology 10) The nonaqueous electrolyte secondary battery according to any one of Techniques 1 to 9, wherein the silicon-containing material comprises composite particles containing a carbon phase and a particulate silicon phase dispersed in the carbon phase. (Technology 11) The nonaqueous electrolyte secondary battery according to Technique 10, wherein the silicon phase has an average diameter of 1 nm or more and 1000 nm or less. (Technology 12) The nonaqueous electrolyte secondary battery according to any one of Technologies 1 to 11, wherein the binder compound further comprises at least one polyacrylic acid-based compound selected from the group consisting of polyacrylic acid and salts of polyacrylic acid, and wherein a ratio Wc / Wp of a mass Wc of the chelating agent in the negative electrode mixture layer to a mass Wp of the polyacrylic acid-based compound in the negative electrode mixture layer is in the range of 0.01 to 0.50. (Technology 13) The nonaqueous electrolyte secondary battery according to any one of Technologies 1 to 12, wherein a concentration of the polyvalent cation in the nonaqueous electrolyte is 0.001 mol / L or more and 20 mol / L or less. (Technology 14) The nonaqueous electrolyte secondary battery according to any one of Technologies 1 to 13, wherein a ratio Mca / Mch of the number of moles Mca of the polyvalent cation in the nonaqueous electrolyte to the number of moles Mch of the chelating agent in the negative electrode mixture layer is in the range of 1.0 to 20.

[0076] The nonaqueous electrolyte secondary battery according to the present disclosure will be specifically described below using examples. However, the present disclosure is not limited to the following examples. In these examples, multiple test cells with different configurations were fabricated and evaluated.

[0077] (Preparation of Test Cell A1) Test cell A1 was prepared by the following procedure. (1) Preparation of Negative Electrode NA1 A negative electrode active material, polyacrylic acid (PAA), styrene-butadiene copolymer rubber (SBR), carboxymethyl cellulose (CMC), carbon nanotubes (CNT), and ethylenediamine-N,N,N',N'-tetraacetic acid disodium salt dihydrate (EDTA-2Na.2H ２ 0) and an appropriate amount of water were mixed to prepare a negative electrode slurry SA1. Silicon-carbon composite particles (GSS manufactured by Giga Solar Materials Co.) were used as the negative electrode active material. The silicon-carbon composite particles contain a carbon phase and a particulate silicon phase dispersed in the carbon phase. PAA, CMC, SBR, CNT, and EDTA-2Na.2H were mixed with 100 parts by mass of the negative electrode active material. ２ The amounts of O added were 5 parts by mass, 5 parts by mass, 5 parts by mass, 0.5 parts by mass, and 0.556 parts by mass, respectively.

[0078] The negative electrode slurry SA1 was applied to one side of an electrolytic copper foil (current collector) to form a coating film, forming a laminate of the electrolytic copper foil and the coating film. Next, the laminate was punched to a predetermined size (2 cm x 2 cm) and then dried. In this way, a negative electrode NA1 including a negative electrode mixture layer was obtained. The initial thickness T(0) of the negative electrode mixture layer was measured at nine positions on the fabricated negative electrode NA1. １ ~T(0) ９ A lead was attached to the negative electrode NA1.

[0079] (2) Preparation of Counter Electrode A lithium metal foil was attached to one side of an electrolytic copper foil (current collector), and the foil was punched out into a square shape with a side length of 2.5 cm to prepare a counter electrode. A lead was attached to the counter electrode.

[0080] (3) Preparation of non-aqueous electrolyte EA1 Ethylene 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. ６was dissolved in the solution at a concentration of 1.3 mol / L, and calcium(II) bis(trifluoromethanesulfonyl)imide was further dissolved in the solution at a concentration of 0.005 mol / L to prepare a non-aqueous electrolyte EA1.

[0081] (4) Assembly of Test Cell A1 An electrode assembly was prepared by arranging the negative electrode NA1 and the counter electrode so that they faced each other with a separator interposed therebetween. A microporous film made of polyolefin was used as the separator. Next, the electrode assembly was housed in an outer casing. An outer casing formed using an aluminum laminate sheet was used as the outer casing. Next, nonaqueous electrolyte EA1 was injected into the outer casing, and the opening of the outer casing was sealed. At this time, 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 outer casing. In this way, test cell A1 was prepared. The following evaluations were performed on test cell A1.

[0082] (1) Charge / Discharge Test Test cell A1 was charged and discharged as follows in a thermostatic chamber at 25° C. The rest time between charge and discharge was 20 minutes.

[0083] (Charging) Test cell A1 was subjected to constant current charging at a current value of 0.1 C (1 C is the current value at which the design capacity is discharged in 1 hour) until the cell voltage reached 0.005 V. The rest period thereafter was 20 minutes. Next, constant current charging was performed at a current value of 0.01 C until the cell voltage reached 0.005 V. The rest period thereafter was 20 minutes. Furthermore, constant current charging was performed at a current value of 0.001 C until the cell voltage reached 0.005 V.

[0084] (Discharge) Test cell A1 was subjected to constant current discharge at a current value of 0.1 C until the cell voltage reached 1 V. The rest period thereafter was 20 minutes. Next, constant current discharge was performed at a current value of 0.01 C until the cell voltage reached 1 V. The rest period thereafter was 20 minutes. Furthermore, constant current discharge was performed at a current value of 0.001 C until the cell voltage reached 1 V.

[0085] Using the results of the charge / discharge test and the mass of the negative electrode active material, the charge capacity Ec per unit mass of the negative electrode active material and the discharge capacity Ed per unit mass of the negative electrode active material were determined.

[0086] (2) Measurement of swelling of negative electrode at full charge After the above charge-discharge test, the test cell A1 was charged in a thermostatic chamber at 25° C. as follows.

[0087] Test cell A1 was subjected to constant current charging at a current value of 0.1 C (1 C is the current value required to discharge the design capacity in 1 hour) until the cell voltage reached 0.005 V. The rest period thereafter was 20 minutes. Next, constant current charging was performed at a current value of 0.01 C until the cell voltage reached 0.005 V. The rest period thereafter was 20 minutes. Furthermore, constant current charging was performed at a current value of 0.001 C until the cell voltage reached 0.005 V.

[0088] After charging, the test cell A1 was disassembled to remove the negative electrode. １ ~T(0) ９ The thickness T(C) of the negative electrode mixture layer in a fully charged state was measured at the same nine positions as those used for the measurement. １ ~T(C) ９ Then, the swelling rate X of the negative electrode at full charge was calculated using the following formula: １ ~X ９ Calculate X １ ~X ９ The average swelling ratio X (%) of the negative electrode at full charge was calculated by arithmetically averaging the thickness T(0) as described above. ｎ is the initial thickness of the negative electrode mixture layer. (Expansion ratio X ｎ Thickness T(C) [%] = ((Thickness T(C) ｎ ) / (thickness T(0) ｎ )) x 100 (n is an integer from 1 to 9)

[0089] Furthermore, the swelling amount Y of the negative electrode during charging per charge capacity was calculated using the following formula. As described above, the charge capacity Ec is the charge capacity per unit mass of the negative electrode active material. (Swelling amount Y [% / (Ah / g)]) = (average swelling ratio X - 100) / (charge capacity Ec [Ah / g])

[0090] (Preparation of Test Cells A2 and C1 to C4) Test cells A2 and C1 to C4 were prepared in the same manner as test cell A1, except that the negative electrode and / or non-aqueous electrolyte was changed as shown in Table 1. Negative electrodes NA1 and NC1 to NC3 and non-aqueous electrolytes EA2 and EC1 shown in Table 1 were prepared by the following method.

[0091] (1') Preparation of negative electrode NC1 EDTA-2Na·2H ２ A negative electrode slurry SC1 was prepared in the same manner as the negative electrode slurry SA1, except that O was not added. At this time, the amounts of PAA, CMC, SBR, and CNT added were 5 parts by mass, 5 parts by mass, 5 parts by mass, and 0.5 parts by mass, respectively, relative to 100 parts by mass of the negative electrode active material. A negative electrode NC1 was prepared in the same manner as the negative electrode NA1, except that a negative electrode slurry SC1 was used instead of the negative electrode slurry SA1.

[0092] (1') Preparation of negative electrode NC2 CaCl ２ A negative electrode slurry SC2 was prepared in the same manner as in the preparation of the negative electrode slurry SA1, except that PAA, CMC, SBR, CNT, EDTA-2Na.2H were added relative to 100 parts by mass of the negative electrode active material. ２ O, and CaCl ２ The amounts of CaCl added were 5 parts by mass, 5 parts by mass, 5 parts by mass, 0.5 parts by mass, 0.556 parts by mass, and 0.0222 parts by mass, respectively. Negative electrode NC2 was prepared in the same manner as negative electrode NA1, except that negative electrode slurry SC2 was used instead of negative electrode slurry SA1. (1') Preparation of negative electrode NC3 ２ A negative electrode slurry SC3 was prepared in the same manner as for the negative electrode slurry SC2, except that the amount of added was 0.0444 parts by mass. A negative electrode NC3 was prepared in the same manner as for the negative electrode NA1, except that the negative electrode slurry SC3 was used instead of the negative electrode slurry SA1. (3') Preparation of Non-Aqueous Electrolyte EA2 A non-aqueous electrolyte EC1 was prepared in the same manner as for the non-aqueous electrolyte EA1, except that the concentration of calcium(II) bis(trifluoromethanesulfonyl)imide was 0.01 mol / L.

[0093] (3') Preparation of Non-Aqueous Electrolyte EC1 Non-aqueous electrolyte EC1 was prepared in the same manner as non-aqueous electrolyte EA1, except that calcium(II) bis(trifluoromethanesulfonyl)imide was not added. That is, no polyvalent cation salt was added to non-aqueous electrolyte EC1.

[0094] The fabricated negative electrodes NA2 and NC1 to NC3 and the fabricated test cells NA2 and C1 to C4 were measured and evaluated in the same manner as the negative electrode NA1 and test cell A1.

[0095] The preparation conditions and evaluation results of the test cells are shown in Table 1. It is preferable that the charge capacity Ec and the discharge capacity Ed are high.

[0096]

[0097] Test cells A1 and A2 are test cells corresponding to the secondary battery (B) according to the present disclosure. Test cells C1 to C4 are comparative examples. As shown in Table 1, test cell C1, in which the negative electrode and non-aqueous electrolyte did not contain polyvalent cations, had a high average swelling ratio X and swelling amount Y. Comparing test cells C2 to C4, the addition of CaCl to the negative electrode was ２ The addition of polyvalent cations to the nonaqueous electrolyte resulted in a decrease in the average swelling ratio X and swelling amount Y, but also in a significant decrease in charge capacity. On the other hand, test cells A1 and A2, in which polyvalent cations were added to the nonaqueous electrolyte, achieved both a relatively high charge / discharge capacity and a low swelling amount. Therefore, according to the present disclosure, it is possible to obtain a nonaqueous electrolyte secondary battery with high capacity and good charge / discharge cycle characteristics.

[0098] The present disclosure can be used in non-aqueous electrolyte secondary batteries. Although the present invention has been described with reference to presently preferred embodiments, such disclosure should not be interpreted as limiting. Various modifications and alterations will undoubtedly become apparent to those skilled in the art to which the present invention pertains upon reading the above disclosure. Therefore, the appended claims should be construed to cover all modifications and alterations without departing from the true spirit and scope of the present invention.

[0099] 10: Non-aqueous electrolyte secondary battery 11: Positive electrode 12: Negative electrode 13: Separator 14: Electrode group

Claims

1. A non-aqueous electrolyte secondary battery comprising: a positive electrode; a negative electrode including a negative electrode mixture layer; and a non-aqueous electrolyte, wherein the negative electrode mixture layer contains a negative electrode active material and a binder component, the binder component contains a binder compound and a chelating agent, the negative electrode active material contains a silicon-containing material, and the non-aqueous electrolyte contains a polyvalent cation.

2. The nonaqueous electrolyte secondary battery according to claim 1, wherein the binder compound includes at least one selected from the group consisting of polyacrylic acid, a salt of polyacrylic acid, carboxymethyl cellulose, and a salt of carboxymethyl cellulose.

3. The nonaqueous electrolyte secondary battery according to claim 1, wherein the chelating agent contains at least one selected from the group consisting of a carboxylic acid group, a carboxylate group, a phosphonic acid group, and a phosphonate group.

4. The nonaqueous electrolyte secondary battery according to any one of claims 1 to 3, wherein the chelating agent contains an ethylenediamino group.

5. The nonaqueous electrolyte secondary battery according to any one of claims 1 to 3, wherein the chelating agent includes at least one selected from the group consisting of ethylenediaminetetraacetic acid and salts of ethylenediaminetetraacetate.

6. The nonaqueous electrolyte secondary battery according to any one of claims 1 to 3, wherein the polyvalent cations include divalent cations.

7. The polyvalent cation is Ca ２＋ and Mg ２＋ The nonaqueous electrolyte secondary battery according to any one of claims 1 to 3, comprising at least one selected from the group consisting of:

8. The nonaqueous electrolyte secondary battery according to any one of claims 1 to 3, wherein the nonaqueous electrolyte contains dissolved therein at least one selected from the group consisting of calcium(II) bis(trifluoromethanesulfonyl)imide and magnesium(II) bis(trifluoromethanesulfonyl)imide.

9. The nonaqueous electrolyte secondary battery according to any one of claims 1 to 3, wherein the nonaqueous electrolyte contains at least one selected from the group consisting of ethylene carbonate, ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate, and fluoroethylene carbonate.

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

11. The nonaqueous electrolyte secondary battery according to claim 10, wherein the average diameter of the silicon phase is 1 nm or more and 1,000 nm or less.

12. The nonaqueous electrolyte secondary battery according to any one of claims 1 to 3, wherein the binder compound further contains at least one polyacrylic acid-based compound selected from the group consisting of polyacrylic acid and salts of polyacrylic acid, and a ratio Wc / Wp of a mass Wc of the chelating agent in the negative electrode mixture layer to a mass Wp of the polyacrylic acid-based compound in the negative electrode mixture layer is in the range of 0.01 to 0.

50.

13. The nonaqueous electrolyte secondary battery according to any one of claims 1 to 3, wherein the concentration of the polyvalent cation in the nonaqueous electrolyte is 0.001 mol / L or more and 20 mol / L or less.

14. The nonaqueous electrolyte secondary battery according to any one of claims 1 to 3, wherein a ratio Mca / Mch of the number of moles Mca of the polyvalent cations in the nonaqueous electrolyte to the number of moles Mch of the chelating agent in the negative electrode mixture layer is in the range of 1.0 to 20.

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