Negative electrode and non-aqueous electrolyte secondary battery

Abstract

A negative electrode 10 of the present disclosure comprises a negative electrode mixture layer 12. The negative electrode mixture layer 12 contains a negative electrode active material and a binder component. The negative electrode active material contains a silicon-containing material. The binder component contains a binder compound and a chelating agent, and the chelating agent has five or more chelating functional groups in one molecule. The negative electrode 10 is furthermore provided with a negative electrode current collector 11, for example. A non-aqueous electrolyte secondary battery of the present disclosure is provided with the negative electrode 10, a positive electrode, and a non-aqueous electrolyte.

Description

Negative electrode and non-aqueous electrolyte secondary battery

[0001] This disclosure relates to a negative electrode and 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 silicon-containing materials as the negative electrode active material.

[0003] Patent Document 1 discloses an electrode comprising silicon particles that form an active substance at the electrode, a cellulose-based binder, and a chelating agent capable of binding to divalent and / or trivalent metal impurities, wherein the binder is mixed with the silicon particles to form an adhesive that adheres to a substrate.

[0004] Patent Document 2 discloses a composition for manufacturing a negative electrode, characterized by containing a silicon-containing negative electrode active material, an aqueous binder, water, and a water-soluble reducing agent.

[0005] Non-patent document 1 discloses the effect of EDTA on polyacrylic acid in a silicon-based negative electrode.

[0006] Non-patent document 2 discloses the effect of a crosslinking binder on the volume change of a silicon-based negative electrode.

[0007] Japanese Patent Publication No. 2012-527069, Japanese Patent Publication No. 2021-77545

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

[0009] This disclosure provides a negative electrode in which the resistance of the negative electrode mixture layer is reduced.

[0010] The anode of this disclosure comprises an anode mixture layer, the anode mixture layer comprises an anode active material and a binder component, the anode active material comprises a silicon-containing material, the binder component comprises a binder compound and a chelating agent, and the chelating agent has five or more chelating functional groups per molecule.

[0011] This disclosure provides a negative electrode in which the resistance of the negative electrode mixture layer is reduced.

[0012] Figure 1 is a cross-sectional view showing the schematic configuration of the negative electrode according to Embodiment 1. Figure 2 is a longitudinal cross-sectional view schematically showing an example of a battery according to Embodiment 2.

[0013] The embodiments of this disclosure will be described in detail below with reference to the drawings. This disclosure is not limited to the embodiments described below.

[0014] [Embodiments of the Disclosure] (Embodiment 1) The negative electrode according to Embodiment 1 comprises a negative electrode mixture layer. Figure 1 is a cross-sectional view showing the schematic configuration of the negative electrode according to Embodiment 1. The negative electrode 10 according to Embodiment 1 comprises a negative electrode current collector 11 and a negative electrode mixture layer 12 disposed on the negative electrode current collector 11.

[0015] The negative electrode mixture layer 12 contains a negative electrode active material and a binder component. The negative electrode active material contains a silicon-containing material. The binder component contains a binder compound and a chelating agent, the chelating agent having five or more chelating functional groups per molecule.

[0016] Silicon-containing negative electrode active materials are effective in increasing the capacity of batteries. Therefore, by including a silicon-containing material in the negative electrode active material, the capacity of a battery using the negative electrode 10 can be increased.

[0017] The binder component contains both a binder compound and a chelating agent, which allows for the formation of bonds (e.g., hydrogen bonds) between the binder compound and the chelating agent. As a result, the crosslinking between the compounds constituting the binder component becomes stronger, enabling a high discharge capacity for the battery using the negative electrode 10. Furthermore, in the negative electrode 10 according to Embodiment 1, the number of chelating functional groups in one molecule of the chelating agent is five or more. This reduces the resistance of the negative electrode mixture layer 12. Moreover, in the negative electrode 10 according to Embodiment 1, the elastic modulus of the negative electrode mixture layer 12 can be improved. This reduces the swelling of the negative electrode 10 during charging while maintaining the battery capacity.

[0018] There is no particular upper limit to the number of chelating functional groups in one molecule of a chelating agent, but for example, it is 15 or less.

[0019] In this specification, "chelating agent" means a compound (ligand) that can coordinate with a metal ion to form a chelate. Therefore, a chelating agent is not limited to those that actually form a chelate.

[0020] A chelating agent has five or more chelating functional groups in one molecule. That is, the binder component contains a chelating agent having five or more chelating functional groups in one molecule. In this specification, a chelating functional group is a functional group that can coordinate with a metal ion to form a chelate and is located at the end of the molecule. In other words, in this specification, a chelating functional group is a functional group that can coordinate with a metal ion to form a chelate, and in the chelate, it is a functional group that can coordinate with the metal ion by gripping it like the tip of a crab's claw. Therefore, even if a functional group can coordinate with a metal ion, functional groups located in the so-called crab's body part of the chelating agent are not included in the definition of a chelating functional group.

[0021] The chelate functional group may be a functional group capable of forming hydrogen bonds, or a functional group capable of forming hydrogen bonds with the binder compound. Examples of such functional groups include carboxylic acid groups (-COOH), carboxylic acid bases, phosphonic acid groups (-P(=O)(OH)2), and phosphonic acid bases. In this specification, a carboxylic acid group has the same meaning as a carboxyl group. A carboxylic acid base is a group in which a carboxyl group has been neutralized to form a salt.

[0022] The chelate functional group may include at least one selected from the group consisting of carboxylic acid groups, carboxylic acid bases, phosphonic acid groups, and phosphonic acid bases. Since these functional groups can interact well (hydrogen bonding) with the binder compound, such a configuration allows for stronger crosslinking of the binder compound in the negative electrode mixture layer 12. This improves the binding properties of the binder compound and enhances the adhesion between negative electrode active material particles in the negative electrode mixture layer 12. Consequently, conductive contact between negative electrode active material particles is improved, and the resistance of the negative electrode mixture layer 12 can be further reduced. In addition, the elastic modulus of the negative electrode mixture layer 12 can be further improved, and swelling of the negative electrode mixture layer 12 can be further suppressed.

[0023] The chelating agent may contain five or more of at least one selected from the group consisting of carboxylic acid groups, carboxylate groups, phosphonic acid groups, and phosphonate groups. In the chelating agent, it is desirable that the carboxylic acid groups, carboxylate groups, phosphonic acid groups, and phosphonate groups are directly bonded to carbon atoms. That is, it is desirable that the phosphonic acid groups and phosphonate groups are not a part constituting a phosphate group but are directly bonded to carbon atoms.

[0024] The carboxylate and phosphonate may be a lithium salt, sodium salt, potassium salt, or ammonium salt.

[0025] The chelating functional group may contain at least one selected from the group consisting of carboxylic acid groups and carboxylate groups. Since these functional groups have a better interaction (bonding) with the binder compound, according to the above configuration, the binder compound can be more firmly cross-linked in the negative electrode binder layer 12. Thereby, the binding property of the binder compound is improved, and the adhesiveness between the negative electrode active material particles in the negative electrode binder layer 12 can be enhanced. Therefore, the conductive contact between the negative electrode active material particles is improved, and the resistance of the negative electrode binder layer 12 can be reduced. Also, the elastic modulus of the negative electrode binder layer 12 can be improved, and the swelling of the negative electrode 10 during charging can be reduced. The chelating agent may contain five or more of at least one selected from the group consisting of carboxylic acid groups and carboxylate groups.

[0026] The chelating agent may be ethylenediamine. The ethylenediamine may have three or more tertiary amino groups. For example, the chelating agent is a linear ethylenediamine having a substituent, and the chelating functional group is located at the end of the substituent or is the substituent. The chelating agent may contain at least one selected from the group consisting of diethylenetriamine moieties and triethylenetetramine moieties.

[0027] The chelating agent may include at least one selected from the group consisting of diethylenetriaminepentaacetic acid (DTPA), diethylenetriaminepentaacetic acid salt, triethylenetetraminehexaacetic acid (TTHA), and triethylenetetraminehexaacetic acid salt. These chelating agents have five or six carboxylic acid groups or carboxylic acid bases as chelating functional groups capable of forming hydrogen bonds with the binder compound. Therefore, these chelating agents can crosslink the binder compound more strongly than chelating agents with four or fewer chelating functional groups (e.g., ethylenediaminetetraacetic acid (EDTA) and its salts). This improves the binding properties of the binder compound and enhances the adhesion between negative electrode active material particles in the negative electrode mixture layer 12. Consequently, conductive contact between negative electrode active material particles is improved, and the resistance of the negative electrode mixture layer 12 can be further reduced. Furthermore, the above configuration can improve the elastic modulus of the negative electrode mixture layer 12. Improving the elastic modulus of the negative electrode mixture layer 12 can contribute to improving the strength of the negative electrode mixture layer 12, i.e., the strength of the negative electrode 10. In this specification, the tertiary amino groups of the ethylenediamine moiety in EDTA and its salts, the tertiary amino groups of the diethylenetriamine moiety in DTPA and its salts, and the tertiary amino groups of the triethylenetetramine moiety in TTHA and its salts are not included in the chelate functional groups. It is common practice in the field of chemistry to consider the carboxylic acid group located at the molecular end of chelating agents, such as EDTA, DTPA, and TTHA, i.e., the chelate functional group in this specification, as the so-called crab claws, and the amine moiety as the crab's body.

[0028] Diethylenetriamine pentaacetate and triethylenetetramine hexaacetate may be lithium salts, sodium salts, potassium salts, or ammonium salts. Diethylenetriamine pentaacetate is, for example, diethylenetriamine-N,N,N',N'',N''-pentasodium pentaacetate. Triethylenetetramine hexaacetate is, for example, triethylenetetramine-N,N,N',N'',N''',N'''-trisodium hexaacetate trihydrate.

[0029] The molecular weight of the chelating agent may be 5000 or less. According to the above configuration, the chelating agent can be well dispersed in the negative electrode mixture layer 12. Thereby, it can be better combined with the binder compound, and the resistance of the negative electrode mixture layer 12 can be further reduced. The molecular weight of the chelating agent may be 200 or more, may be 300 or more, and may be 380 or more.

[0030] The binder compound may be a compound that forms a bond (e.g., hydrogen bond) with the chelating agent. That is, the binder component may contain a compound that forms a hydrogen bond with the chelating agent as the binder compound.

[0031] The binder compound may contain at least one selected from the group consisting of a carboxylic acid group, a carboxylate group, a carbonyl group, a hydroxyl group, an amino group, and a thiol group, and may contain at least one selected from the group consisting of a carboxylic acid group and a carboxylate group. For example, at least one of the chelating agent and the binder compound may contain at least one selected from the group consisting of a carboxylic acid group and a carboxylate group, and the other may contain a hydroxyl group, or each of the chelating agent and the binder compound may contain at least one selected from the group consisting of a carboxylic acid group and a carboxylate group.

[0032] The binder compound may contain at least one selected from the group consisting of polyacrylic acid, a salt of polyacrylic acid, carboxymethyl cellulose, and a salt of carboxymethyl cellulose. That is, the binder component may contain at least one selected from the group consisting of polyacrylic acid, a salt of polyacrylic acid, carboxymethyl cellulose, and a salt of carboxymethyl cellulose as the binder compound. According to the above configuration, since the binder compound can form a hydrogen bond with the chelating agent, it can be more firmly cross-linked in the negative electrode mixture layer 12. Therefore, the resistance of the negative electrode mixture layer 12 can be further reduced. In addition, the elastic modulus of the negative electrode mixture layer 12 is further improved, and the swelling of the negative electrode mixture layer 12 can be further suppressed. The cation constituting the salt is, for example, a lithium ion, a sodium ion, a potassium ion, an ammonium ion, or the like.

[0033] The binder compound may contain at least one polyacrylic acid compound selected from the group consisting of polyacrylic acid and salts of polyacrylic acid. The binder compound contains at least one polyacrylic acid compound selected from the group consisting of polyacrylic acid and salts of polyacrylic acid, and the ratio Wc / Wp of the mass Wc of the chelating agent in the negative electrode mixture layer 12 to the mass Wp of the polyacrylic acid compound in the negative electrode mixture layer 12 may be 0.01 or more, may be 0.05 or more, and further may be 0.10 or more. The ratio Wc / Wp may be 0.50 or less, may be 0.30 or less, 0.20 or less, and further may be 0.15 or less. The ratio Wc / Wp may be, for example, 0.01 or more and 0.50 or less. According to the above configuration, the resistance of the negative electrode mixture layer 12 can be further reduced. Further, the elastic modulus of the negative electrode mixture layer 12 can be improved more, and the expansion of the negative electrode mixture layer 12 can be suppressed more.

[0034] The weight average molecular weight of the binder compound may be 5000 or more and 5000000 or less, and may be 100000 or more and 1000000 or less.

[0035] The binder compound may further contain styrene-butadiene copolymer rubber (SBR).

[0036] The binder component may further contain a polyvalent cation. The polyvalent cation is a cation of 2 or more valences, and is, for example, a divalent cation, a trivalent cation, a tetravalent cation, or the like.

[0037] The polyvalent cation is 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+ , Cr3+ La 3+ In 3+ , Rh 3+ Sb 3+ Sm 3+ , Dy 3+ , Eu 3+ Fe 3+ Al 3+ , Hf 4+ , Zr 4+ , and Th 4+ It may include at least one selected from the group consisting of the following. The polyvalent cation may also include a divalent cation. The divalent cation is thought to easily form a stable crosslinking structure. The polyvalent cation is Ca 2+ and Mg 2+ It may include at least one selected from the group consisting of the following. The polyvalent cation is Ca 2+ It may also be Mg 2+ This may also be the case. By further including polyvalent cations in the binder component, the chelating agents in the negative electrode mixture layer 12 are linked to each other via the polyvalent cations, thereby improving the binding properties of the binder compound and potentially increasing the adhesion between negative electrode active material particles in the negative electrode mixture layer 12. Consequently, conductive contact between negative electrode active material particles is improved, and the resistance of the negative electrode mixture layer 12 can be further reduced. In addition, the elastic modulus of the negative electrode mixture layer 12 can be further improved, and swelling of the negative electrode mixture layer 12 can be suppressed.

[0038] Polyvalent cations can be incorporated into the negative electrode mixture layer 12, for example, by dissolving a salt that generates polyvalent cations in the negative electrode mixture slurry that forms the negative electrode mixture layer 12. Alternatively, they can be incorporated into the negative electrode mixture layer 12 by bringing the negative electrode 10 into contact with a non-aqueous electrolyte containing polyvalent cations, thereby allowing the polyvalent cations to permeate the negative electrode mixture layer 12. Non-aqueous electrolytes containing polyvalent cations can be incorporated into the non-aqueous electrolyte, for example, by dissolving a salt that generates polyvalent cations in the non-aqueous electrolyte. Salts that generate polyvalent cations will be described later.

[0039] The negative electrode active material includes a silicon-containing material. Examples of silicon-containing materials include silicon, silicon alloys, silicon compounds, and silicon-containing composite materials. A silicon-containing composite material is, for example, a composite material comprising an ionic conductive phase and a silicon phase dispersed in the ionic conductive phase. The ionic conductive phase includes, for example, at least one selected from the group consisting of a carbon phase, an aluminate phase, a silicate phase, a silicide phase, and a silicon oxide phase. The ionic conductive phase may consist of one phase or multiple phases. The ionic conductive phase may be a carbon phase. The silicon-containing material may also include composite particles containing a carbon phase and particulate silicon phase dispersed in the carbon phase. The carbon phase is a matrix composed of a carbonaceous material.

[0040] The average particle size of the silicon phase may be 1 nm or more, 10 nm or more, 100 nm or more, or even 500 nm or more. The average particle size of the silicon phase may be 1000 nm or less, 500 nm or less, 100 nm or less, or even 10 nm or less. For example, the average particle size of the silicon phase is 1 nm or more and 1000 nm or less. In the composite particles, the dispersion of fine silicon phase in the carbon phase as described above reduces the volume change of the composite particles during charging and discharging, thereby improving the structural stability of the negative electrode active material.

[0041] The average particle size of the particulate silicon phase is measured by observing a cross-section of the composite particles using a scanning electron microscope (SEM) or transmission electron microscope (TEM). Specifically, it is determined by taking the arithmetic mean of the maximum diameters of any 100 silicon phases in the cross-section.

[0042] The negative electrode mixture layer 12 may contain other materials such as conductive additives.

[0043] Conductive additives are used to reduce the resistance of the negative electrode 10. Examples of conductive additives include carbon materials and conductive polymer compounds. Examples of carbon materials include carbon black, graphite, acetylene black, carbon nanotubes, carbon nanofibers, graphene, fullerene, and graphite oxide. Examples of conductive polymer compounds include polyaniline, polypyrrole, and polythiophene.

[0044] The shape of the negative electrode 10 is not particularly limited, but for example, if the negative electrode 10 constitutes an electrode group having a wound structure in the battery, the negative electrode 10 has a strip-like shape.

[0045] The negative electrode 10 can be manufactured, for example, by the following method. First, a negative electrode mixture slurry containing a negative electrode active material, a binder component, and a dispersion medium is prepared. Next, the negative electrode mixture slurry is applied to one or both sides of a negative electrode current collector and dried to obtain a laminate containing a negative electrode current collector and a negative electrode mixture layer formed on the negative electrode current collector. Next, the negative electrode 10 is manufactured by rolling the laminate. The negative electrode 10 is cut to a predetermined size as needed.

[0046] (Embodiment 2) The non-aqueous electrolyte secondary battery according to Embodiment 2 comprises a positive electrode, a negative electrode, and a non-aqueous electrolyte. The negative electrode is the same as the negative electrode according to Embodiment 1. Therefore, with this configuration, the non-aqueous electrolyte secondary battery according to Embodiment 2 can reduce the resistance of the negative electrode. Furthermore, it can have a sufficiently high capacity and reduce the swelling of the negative electrode during charging.

[0047] Figure 2 is a schematic longitudinal cross-sectional view showing an example of a non-aqueous electrolyte secondary battery according to Embodiment 2. The battery 100 comprises a cylindrical battery case, an electrode group 24 having a wound structure, and a non-aqueous electrolyte (not shown). The electrode group 24 is housed in the battery case and is in contact with the non-aqueous electrolyte.

[0048] The battery case consists of a case body 25, which is a bottomed cylindrical metal container, and a sealing body 26 that seals the opening of the case body 25. A gasket 37 is placed between the case body 25 and the sealing body 26. The gasket 37 ensures that the battery case is airtight. Inside the case body 25, insulating plates 27 and 28 are placed at both ends of the electrode group 24 in the winding axis direction of the electrode group 24, respectively.

[0049] The case body 25 has, for example, a stepped portion 31. The stepped portion 31 can be formed by partially pressing the side wall of the case body 25 from the outside. The stepped portion 31 may be formed in an annular shape on the side wall of the case body 25 along the circumferential direction of a virtual circle defined by the case body 25. In this case, the sealing body 26 is supported, for example, by the opening side surface of the stepped portion 31.

[0050] The sealing body 26 comprises a filter 32, a lower valve body 33, an insulating member 34, an upper valve body 35, and a cap 36. In the sealing body 26, these members are stacked in this order. The sealing body 26 is installed in the opening of the case body 25 such that the cap 36 is located on the outside of the case body 25 and the filter 32 is located on the inside of the case body 25.

[0051] Each of the above-mentioned components constituting the sealing body 26 is, for example, disc-shaped or ring-shaped. Except for the insulating member 34, each of the above-mentioned components is electrically connected to one another.

[0052] The electrode group 24 includes a positive electrode 21, a separator 22, and a negative electrode 23. The positive electrode 21, the separator 22, and the negative electrode 23 are all strip-shaped. The width direction of the strip-shaped positive electrode 21 and negative electrode 23 is, for example, parallel to the winding axis of the electrode group 24. The separator 22 is positioned between the positive electrode 21 and the negative electrode 23. The positive electrode 21 and the negative electrode 23 are wound in a spiral shape with the separator 22 interposed between them.

[0053] When observing a cross-section of the battery 100 in a direction perpendicular to the winding axis of the electrode group 24, the positive electrode 21 and the negative electrode 23 are alternately stacked in the radial direction of a virtual circle defined by the case body 25, with a separator 22 interposed between them.

[0054] The positive electrode 21 is electrically connected to the cap 36, which also serves as the positive electrode terminal, via a positive electrode lead 29. One end of the positive electrode lead 29 is connected, for example, near the center of the positive electrode 21 in the longitudinal direction. The positive electrode lead 29 extends from the positive electrode 21 to the filter 32 through a through hole formed in the insulating plate 27. The other end of the positive electrode lead 29 is welded, for example, to the electrode group 24 side of the filter 32.

[0055] The negative electrode 23 is electrically connected to the case body 25, which also serves as the negative electrode terminal, via a negative electrode lead 30. One end of the negative electrode lead 30 is connected, for example, to the end of the negative electrode 23 in the longitudinal direction of the negative electrode 23. The other end of the negative electrode lead 30 is welded, for example, to the inner bottom surface of the case body 25.

[0056] The components of battery 100 will be described in detail below.

[0057] The positive electrode 21 includes a material having the property of intercalating and releasing metal ions (e.g., lithium ions). The positive electrode 21 includes, for example, a positive electrode active material. The positive electrode 21 comprises, for example, a positive electrode current collector and a positive electrode mixture layer supported on the surface of the positive electrode current collector.

[0058] As the positive electrode current collector, a sheet or film made of a metallic material such as aluminum, stainless steel, titanium, or their alloys can be used. Aluminum and its alloys are suitable as materials for positive electrode current collectors because they are inexpensive and easy to make into thin films. The sheet or film may be porous or non-porous. Metal foil, metal mesh, etc., can be used as the sheet or film. A carbon material such as carbon may be coated on the surface of the positive electrode current collector as a conductive auxiliary material.

[0059] The positive electrode mixture layer contains a positive electrode active material. The positive electrode active material may be a material that has the ability to intercept and release metal ions (e.g., lithium ions). As the positive electrode active material, lithium-containing transition metal oxides, lithium-containing transition metal phosphates, transition metal fluorides, polyanionic materials, fluorinated polyanionic materials, transition metal sulfides, transition metal oxysulfides, transition metal oxynitrides, etc., can be used. In particular, when lithium-containing transition metal oxides or lithium-containing transition metal phosphates are used as the positive electrode active material, the manufacturing cost of the battery can be reduced and the average discharge voltage can be increased. Examples of lithium-containing transition metal oxides include lithium cobalt oxide, lithium nickel cobalt aluminum oxide, lithium nickel cobalt manganese oxide, and lithium nickel manganese oxide. Examples of lithium-containing transition metal phosphates include lithium iron phosphate, lithium vanadium phosphate, lithium cobalt phosphate, and lithium nickel phosphate.

[0060] The positive electrode mixture layer may further contain a binder. Possible binders include polymer materials such as polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, polytetrafluoroethylene, carboxymethylcellulose, polyacrylic acid, styrene-butadiene copolymer rubber, polypropylene, polyethylene, and polyimide.

[0061] The positive electrode mixture layer may further contain a conductive additive. As the conductive additive, the materials described in Embodiment 1 as conductive additives usable in the negative electrode mixture layer can also be used in the positive electrode mixture layer.

[0062] The negative electrode 23 is the negative electrode 10 according to Embodiment 1.

[0063] The non-aqueous electrolyte is, for example, a non-aqueous electrolyte having lithium ion conductivity. The non-aqueous electrolyte may contain a non-aqueous solvent and a lithium salt dissolved in the non-aqueous solvent. The concentration of the lithium salt in the electrolyte may be, for example, 0.5 mol / L or more and 2 mol / L or less. By controlling the lithium salt concentration within the above range, an electrolyte with excellent ion conductivity and appropriate viscosity can be obtained. However, the lithium salt concentration is not limited to the above.

[0064] The non-aqueous solvent is not particularly limited, and any known non-aqueous solvent may be used. Examples of non-aqueous solvents include cyclic carbonate esters, linear carbonate esters, cyclic carboxylic acid esters, and linear carboxylic acid esters. Examples of cyclic carbonate esters include propylene carbonate (PC), ethylene carbonate (EC), fluoroethylene carbonate (FEC), and vinylene carbonate (VC). Examples of linear carbonate esters 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 linear carboxylic acid esters include non-aqueous solvents such as methyl acetate, ethyl acetate, propyl acetate, methyl propionate, and ethyl propionate. The non-aqueous solvent may be used alone or in combination of two or more types. The non-aqueous electrolyte may include at least one selected from the group consisting of ethylene carbonate, ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate, and fluoroethylene carbonate.

[0065] Examples of lithium salts that can be used include lithium hexafluoride phosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bisperfluoroethylsulfonylimide (LiN(SO2C2F5)2), LiAsF6, LiCF3SO3, and lithium difluoro(oxalato)borate. One of these electrolyte salts may be used, or two or more may be used in combination.

[0066] The non-aqueous electrolyte may further contain polyvalent cations. The polyvalent cations described in Embodiment 1 as polyvalent cations that may be contained in the negative electrode mixture layer can also be used in the non-aqueous electrolyte.

[0067] Polyvalent cations can be incorporated into non-aqueous electrolytes by dissolving a salt that produces a polyvalent cation in the non-aqueous electrolyte. The non-aqueous electrolyte may contain at least one 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 selected from the group consisting of calcium(II) bis(trifluoromethanesulfonyl)imide and magnesium(II) bis(trifluoromethanesulfonyl)imide. These compounds (salts) are desirable because they do not generate chloride ions.

[0068] The concentration of polyvalent cations in the non-aqueous electrolyte may be 0.001 mol / L or higher, 0.005 mol / L or higher, 0.01 mol / L or higher, 0.1 mol / L or higher, and even 1.0 mol / L or higher. The concentration of polyvalent cations in the non-aqueous electrolyte may be 20 mol / L or lower, 10 mol / L or lower, 1.0 mol / L or lower, 0.1 mol / L or lower, and even 0.01 mol / L or lower. The concentration of the polyvalent cation may be 0.001 mol / L or more and 20 mol / L or less, 0.005 mol / L or more and 20 mol / L or less, 0.01 mol / L or more and 20 mol / L or less, 0.1 mol / L or more and 20 mol / L or less, and even 1.0 mol / L or more and 20 mol / L or less, 0.005 mol / L or more and 1.0 mol / L or less, or 0.005 mol / L or more and 0.01 mol / L or less.

[0069] The ratio Maca / Mch, which is the amount of polyvalent cations in the non-aqueous electrolyte to the amount of chelating agent in the negative electrode mixture layer, may be 1.0 or greater, or 5.0 or greater. The ratio Maca / Mch may be 20.0 or less, 15.0 or less, 10.0 or less, or even 5.0 or less. Maca / Mch may be 1.0 or greater and 20.0 or less, 5.0 or greater and 15.0 or less, or even 5.0 or greater and 10.0 or less. With the above configuration, the swelling of the electrode plates during charging can be further reduced without causing a significant decrease in charging capacity. Note that the amount of polyvalent cations in the non-aqueous electrolyte Maca includes not only the amount of polyvalent cations in the non-aqueous electrolyte present outside the electrodes (positive electrode, negative electrode), but also the amount of polyvalent cations in the non-aqueous electrolyte that have permeated into the electrodes.

[0070] Typically, it is desirable to interpose a separator between the positive and negative electrodes. The separator 22 has high ion permeability and appropriate mechanical strength and insulating properties. As the separator 22, a microporous thin film, woven fabric, and nonwoven fabric can be used. As the material of the separator 22, for example, a polymer can be used. The polymer may be polyolefin such as polypropylene and polyethylene.

[0071] In the battery according to Embodiment 2, the non-aqueous electrolyte may be impregnated into a polymer provided as a separator, for example. That is, the battery according to Embodiment 2 may have a structure in which a non-aqueous electrolyte and a polymer are used in combination.

[0072] The battery according to Embodiment 2 may further contain a solid electrolyte as the electrolyte. That is, the battery of this disclosure may have a hybrid structure in which a non-aqueous electrolyte (electrolyte) and a solid electrolyte are used in combination. Examples of solid electrolyte materials are halide solid electrolytes, sulfide solid electrolytes, oxide solid electrolytes, or organic polymer solid electrolytes. In this disclosure, "halide solid electrolyte" means a solid electrolyte containing a halogen element as the main component of the anions. "Sulfide solid electrolyte" means a solid electrolyte containing sulfur as the main component of the anions. "Oxide solid electrolyte" means a solid electrolyte containing oxygen as the main component of the anions. The main component of the anions means the anion with the largest amount of substance among all the anions constituting the solid electrolyte.

[0073] As an example of the structure of a non-aqueous electrolyte secondary battery according to Embodiment 2, a configuration example shown in Figure 2 is described, namely a cylindrical non-aqueous electrolyte secondary battery in which an electrode group having a wound structure in which a positive electrode and a negative electrode are wound around a separator, and an electrolyte are housed in an outer casing. However, the battery according to this disclosure is not limited to this configuration example. The battery according to Embodiment 2 may take any form, such as prismatic, coin-type, button-type, laminate-type, etc. Furthermore, as the electrode group in the battery according to Embodiment 2, other forms of electrode groups may be used instead of an electrode group having a wound structure, such as an electrode group in which a positive electrode and a negative electrode are stacked with a separator.

[0074] The non-aqueous electrolyte secondary battery according to Embodiment 2 can be manufactured, for example, by the following method.

[0075] First, the negative electrode is formed as described in Embodiment 1.

[0076] The method for forming the positive electrode is not limited, and known methods 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 a negative electrode slurry, and a positive electrode current collector is used instead of a negative electrode current collector. The positive electrode slurry can be prepared, for example, using a positive electrode active material, a conductive additive, and a dispersion medium.

[0077] When the electrode group has a wound structure, the electrode group is formed by winding a positive electrode, a negative electrode, and a separator. In this case, a separator is placed between the positive electrode and the negative electrode. When the electrode group has a stacked structure, the electrode group is formed by stacking a positive electrode, a separator, and a negative electrode in this order.

[0078] Non-aqueous electrolytes can be prepared, for example, by dissolving a lithium salt in a non-aqueous solvent. In some cases, a salt that generates polyvalent cations may be further dissolved in the non-aqueous solvent. By using a salt that generates polyvalent cations, a non-aqueous electrolyte containing polyvalent cations can be prepared. Furthermore, by adding polyvalent cations to the non-aqueous electrolyte in this way, polyvalent cations can also be present in the negative electrode mixture layer.

[0079] By housing the electrode group and the non-aqueous electrolyte in an outer casing, a non-aqueous electrolyte secondary battery can be obtained.

[0080] (Other Embodiments) (Note) The above description of embodiments discloses the following technologies.

[0081] (Technical 1) A negative electrode comprising a negative electrode mixture layer, wherein the negative electrode mixture layer comprises a negative electrode active material and a binder component, the negative electrode active material comprises a silicon-containing material, the binder component comprises a binder compound and a chelating agent, and the chelating agent has five or more chelating functional groups per molecule.

[0082] This configuration allows the negative electrode of Technology 1 to reduce resistance. Furthermore, it is possible to improve the elastic modulus of the negative electrode mixture layer, thereby reducing the swelling of the negative electrode during charging while maintaining the battery capacity.

[0083] (Technical 2) The negative electrode according to Technical 1, wherein the molecular weight of the chelating agent is 5000 or less.

[0084] This configuration allows the negative electrode of technology 2 to further reduce resistance. Furthermore, the elastic modulus of the negative electrode mixture layer can be improved, thereby reducing the swelling of the negative electrode during charging while maintaining the battery capacity.

[0085] (Technical 3) The negative electrode according to Technical 1 or 2, wherein the chelate functional group comprises at least one selected from the group consisting of a carboxylic acid group, a carboxylic acid base, a phosphonic acid group, and a phosphonic acid base.

[0086] This configuration allows the negative electrode of technology 3 to further reduce resistance. Furthermore, the elastic modulus of the negative electrode mixture layer can be improved, thereby reducing the swelling of the negative electrode during charging while maintaining the battery capacity.

[0087] (Technical 4) The negative electrode according to any one of Technical 1 to 3, wherein the chelate functional group comprises at least one selected from the group consisting of a carboxylic acid group and a carboxylic acid base.

[0088] This configuration allows the negative electrode of technology 4 to further reduce resistance. Furthermore, the elastic modulus of the negative electrode mixture layer can be further improved, thereby reducing the swelling of the negative electrode during charging while maintaining the battery capacity.

[0089] (Technical 5) The negative electrode according to any one of Technical 1 to 4, wherein the chelating agent comprises at least one selected from the group consisting of diethylenetriaminepentaacetic acid, diethylenetriaminepentaacetic acid salt, triethylenetetraminehexaacetic acid, and triethylenetetraminehexaacetic acid salt.

[0090] This configuration allows the negative electrode of technology 5 to further reduce resistance. Furthermore, the elastic modulus of the negative electrode mixture layer can be further improved, thereby reducing the swelling of the negative electrode during charging while maintaining the battery capacity.

[0091] (Technical 6) The negative electrode according to any one of Technical 1 to 5, wherein the binder compound comprises at least one selected from the group consisting of polyacrylic acid, a salt of polyacrylic acid, carboxymethylcellulose, and a salt of carboxymethylcellulose.

[0092] This configuration allows the negative electrode of technology 6 to further reduce resistance. Furthermore, the elastic modulus of the negative electrode mixture layer can be improved, thereby reducing the swelling of the negative electrode during charging while maintaining the battery capacity.

[0093] (Technical 7) The negative electrode according to any one of Technical 1 to 6, wherein the binder compound comprises at least one polyacrylic acid-based compound selected from the group consisting of polyacrylic acid and salts of polyacrylic acid, and 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-based compound in the negative electrode mixture layer is 0.01 or more and 0.50 or less.

[0094] This configuration allows the negative electrode of technology 7 to further reduce resistance. Furthermore, the elastic modulus of the negative electrode mixture layer can be further improved, thereby reducing the swelling of the negative electrode during charging while maintaining the battery capacity.

[0095] (Technical 8) The negative electrode according to any one of Technical 1 to 7, wherein the binder component further comprises a polyvalent cation.

[0096] (Technical 9) The negative electrode according to Technical 8, wherein the polyvalent cation includes a divalent cation.

[0097] (Technical 10) The polyvalent cation is Ca 2+ and Mg 2+ The negative electrode according to technology 8 or 9, comprising at least one selected from the group consisting of the following.

[0098] (Technical 11) The negative electrode according to any one of Technical 1 to 10, wherein the silicon-containing material comprises composite particles containing a carbon phase and particulate silicon phase dispersed in the carbon phase.

[0099] This configuration makes the negative electrode of technology 11 effective in further increasing the battery's capacity.

[0100] (Technical 12) The negative electrode according to Technical 11, wherein the average particle size of the silicon phase is 1 nm or more and 1000 nm or less.

[0101] This configuration reduces the volume change of the composite particles during charging and discharging, improving the structural stability of the negative electrode active material. Therefore, the negative electrode of technology 12 is effective in further improving battery characteristics.

[0102] (Technical 13) A non-aqueous electrolyte secondary battery comprising a negative electrode, a positive electrode, and a non-aqueous electrolyte, as described in any one of Technical 1 to 12.

[0103] This configuration allows the non-aqueous electrolyte secondary battery of technology 13 to reduce resistance at the negative electrode. Furthermore, the elastic modulus of the negative electrode mixture layer can be further improved, thereby reducing the swelling of the negative electrode during charging while maintaining the battery capacity.

[0104] (Technical 14) The non-aqueous electrolyte secondary battery according to Technical 13, wherein the non-aqueous electrolyte comprises at least one selected from the group consisting of ethylene carbonate, ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate, and fluoroethylene carbonate.

[0105] (Technical 15) The non-aqueous electrolyte secondary battery according to Technical 13 or 14, wherein the non-aqueous electrolyte further comprises a polyvalent cation.

[0106] (Technical 16) The non-aqueous electrolyte secondary battery according to Technical 15, wherein the concentration of the polyvalent cation in the non-aqueous electrolyte is 0.001 mol / L or more and 20 mol / L or less.

[0107] (Technical 17) The non-aqueous electrolyte secondary battery according to Technical 15 or 16, wherein the ratio Maca / Mch of the amount of substance of the polyvalent cation in the non-aqueous electrolyte to the amount of substance of the chelating agent in the negative electrode mixture layer is 1.0 or more and 20.0 or less.

[0108] (Technical 18) The non-aqueous electrolyte secondary battery according to any one of Technical 13 to 17, wherein the non-aqueous electrolyte comprises at least one selected from the group consisting of calcium(II) bis(trifluoromethanesulfonyl)imide and magnesium(II) bis(trifluoromethanesulfonyl)imide.

[0109] The present disclosure will be described in more detail below with reference to examples. The following examples are merely illustrative and not limited to any one aspect.

[0110] <Preparation of the negative electrode> [Example 1] The negative electrode active material, polyacrylic acid (PAA), diethylenetriamine-N,N,N',N'',N''-pentasodium pentacetate (DTPA-5Na) as a chelating agent, styrene-butadiene copolymer rubber (SBR), carboxymethylcellulose (CMC), and carbon nanotubes (CNT) were mixed in a mass ratio of negative electrode active material:PAA:DTPA-5Na:SBR:CMC:CNT = 100:1:0.11:1:1:0.1, and an appropriate amount of water was added to prepare the negative electrode mixture slurry. For the negative electrode active material, a mixture of silicon-carbon composite particles (GSS manufactured by Giga Solar Materials Co.) and graphite was used in a mass ratio of silicon-carbon composite particles:graphite = 30:70. The silicon-carbon composite particles described above contain a carbon phase and particulate silicon phase dispersed in the carbon phase.

[0111] A negative electrode slurry was applied to one side of an electrolytic copper foil, which served as the negative electrode current collector, to form a coating film and create a laminate of the electrolytic copper foil and the coating film. Next, the laminate was punched out to a predetermined size (2.1 cm x 2.1 cm) and then dried. In this way, a negative electrode comprising a negative electrode mixture layer and a negative electrode current collector was obtained. This was used as the negative electrode of Example 1. A portion of the negative electrode was provided with an exposed area where the surface of the negative electrode current collector was exposed, and a lead was attached to this exposed area.

[0112] [Example 2] An anode mixture slurry was prepared in the same manner as in Example 1, except that triethylenetetramine-N,N,N',N'',N''',N'''-hexaacetate trisodium salt trihydrate (TTHA-3Na・3H2O) was used as a chelating agent instead of DTPA-5Na, and the anode of Example 2 was prepared in the same manner as in Example 1.

[0113] [Comparative Example 1] A negative electrode mixture slurry was prepared in the same manner as in Example 1, except that a chelating agent was not added, and the negative electrode of Comparative Example 1 was prepared in the same manner as in Example 1.

[0114] [Comparative Example 2] An anode mixture slurry was prepared in the same manner as in Example 1, except that ethylenediamine-N,N,N',N'-tetraacetate disodium salt dihydrate (EDTA-2Na・2H2O) was used as the chelating agent, and the anode of Comparative Example 2 was prepared in the same manner as in Example 1.

[0115] <Resistance Measurement> The resistance of the negative electrode mixture layer was measured using the negative electrodes of Examples 1 and 2 and Comparative Examples 1 and 2. The measurement was performed using an electrode resistance measurement system (HIOKI RM2610). Four measurements were taken, and the average value was taken as the resistance of the negative electrode mixture layer. The measurement results are shown in Table 1.

[0116] <Measurement of Elastic Modulus> The elastic modulus of the negative electrode mixture layer was measured using the nanoindentation method with the fabricated negative electrode as follows. A dynamic ultramicrohardness tester (Shimadzu Corporation, DUH-210S) was used as the measuring instrument. The negative electrode was fixed to the stage, and the elastic modulus of the negative electrode mixture layer was measured under the following conditions: Indenter shape: Triangular pyramidal indenter Test force: 202 mN Indentation depth: 8 μm to 15 μm The elastic modulus was measured at 26 points for each negative electrode, and the average value of these measurements was taken as the elastic modulus of the negative electrode mixture layer. The measurement results are shown in Table 1.

[0117] <Battery Fabrication> (Preparation of Positive Electrode) Lithium nickel cobalt aluminum oxide, acetylene black, and polyvinylidene fluoride were mixed in a mass ratio of 98:1:1 as the positive electrode active material, and N-methyl-2-pyrrolidone (NMP) was used as the dispersion medium to prepare a positive electrode mixture slurry. Next, the positive electrode mixture slurry was applied to a positive electrode current collector made of aluminum foil to form a coating film, thereby forming a laminate of aluminum foil and the coating film. Next, the laminate was punched out to a predetermined size (2 cm x 2 cm) and then dried. In this way, a positive electrode was obtained. A portion of the positive electrode was provided with an exposed area where the surface of the positive electrode current collector was exposed, and a lead was attached to this exposed area.

[0118] (Preparation of non-aqueous electrolyte) 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. A non-aqueous electrolyte was prepared by dissolving LiPF6 in this non-aqueous solvent at a concentration of 1.3 mol / L.

[0119] (Assembly of the test cell) A wound electrode body was fabricated by spirally winding the negative and positive electrodes of Example 1 via a polyolefin separator. Insulating plates were placed above and below the upper limit of the electrode body, and the electrode body was housed in an outer casing. The negative electrode lead was welded to the bottom of the bottomed cylindrical outer casing, and the positive electrode lead was welded to the sealing body. A non-aqueous electrolyte was injected into the outer casing, and the opening of the outer casing was sealed with the sealing body via a gasket to fabricate a non-aqueous electrolyte secondary battery as a test cell of Example 1.

[0120] The test cells of Example 2 and Comparative Examples 1 and 2 were obtained in the same manner as the test cell of Example 1, except that the negative electrodes of Example 2 and Comparative Examples 1 and 2 were used instead of the negative electrode of Example 1.

[0121] <Charge and Discharge Test> For the test cells of Examples 1 and 2 and Comparative Examples 1 and 2, charging was performed in a constant temperature bath at 25°C with a constant current of 0.1C until the cell voltage reached 4.2V, and then charging was performed with a constant voltage of 4.2V until the current value reached 0.05C. After that, the cells were discharged with a constant current of 0.1C until the cell voltage reached 2.5V. In this way, the initial charge capacity and discharge capacity were measured. The charge capacity and discharge capacity per unit mass of the positive electrode active material were determined by dividing the measured charge amount and discharge capacity by the mass of the positive electrode active material of the test cell. The measurement results are shown in Table 1.

[0122]

[0123] The negative electrodes of Examples 1 and 2 had lower resistance in the negative electrode mixture layer compared to the negative electrodes of Comparative Examples 1 and 2. Furthermore, the negative electrodes of Examples 1 and 2 had a higher elastic modulus in the negative electrode mixture layer compared to the negative electrodes of Comparative Examples 1 and 2. Therefore, it is presumed that the negative electrodes of Examples 1 and 2 will experience less swelling during battery charging than the negative electrodes of Comparative Examples 1 and 2.

[0124] The technology disclosed herein is useful for batteries such as lithium-ion secondary batteries.

Claims

1. A negative electrode comprising a negative electrode mixture layer, wherein the negative electrode mixture layer comprises a negative electrode active material and a binder component, the negative electrode active material comprises a silicon-containing material, the binder component comprises a binder compound and a chelating agent, and the chelating agent has five or more chelating functional groups per molecule.

2. The negative electrode according to claim 1, wherein the molecular weight of the chelating agent is 5000 or less.

3. The negative electrode according to claim 1, wherein the chelate functional group comprises at least one selected from the group consisting of a carboxylic acid group, a carboxylic acid base, a phosphonic acid group, and a phosphonic acid base.

4. The negative electrode according to claim 1, wherein the chelate functional group comprises at least one selected from the group consisting of a carboxylic acid group and a carboxylic acid base.

5. The negative electrode according to claim 1, wherein the chelating agent comprises at least one selected from the group consisting of diethylenetriaminepentaacetic acid, diethylenetriaminepentaacetic acid salt, triethylenetetraminehexaacetic acid, and triethylenetetraminehexaacetic acid salt.

6. The negative electrode according to claim 1, wherein the binder compound comprises at least one selected from the group consisting of polyacrylic acid, a salt of polyacrylic acid, carboxymethylcellulose, and a salt of carboxymethylcellulose.

7. The negative electrode according to claim 1, wherein the binder compound comprises at least one polyacrylic acid-based compound selected from the group consisting of polyacrylic acid and salts of polyacrylic acid, and 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-based compound in the negative electrode mixture layer is 0.01 or more and 0.50 or less.

8. The negative electrode according to claim 1, wherein the binder component further comprises a polyvalent cation.

9. The negative electrode according to claim 8, wherein the polyvalent cation includes a divalent cation.

10. The polyvalent cation is Ca 2+ and Mg 2+ The negative electrode according to claim 8, comprising at least one selected from the group consisting of the following.

11. The negative electrode according to claim 1, wherein the silicon-containing material comprises composite particles containing a carbon phase and particulate silicon phase dispersed in the carbon phase.

12. The negative electrode according to claim 11, wherein the average particle size of the silicon phase is 1 nm or more and 1000 nm or less.

13. A non-aqueous electrolyte secondary battery comprising a negative electrode according to any one of claims 1 to 12, a positive electrode, and a non-aqueous electrolyte.

14. The non-aqueous electrolyte secondary battery according to claim 13, wherein the non-aqueous electrolyte comprises at least one selected from the group consisting of ethylene carbonate, ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate, and fluoroethylene carbonate.

15. The non-aqueous electrolyte secondary battery according to claim 13, wherein the non-aqueous electrolyte further comprises a polyvalent cation.

16. The non-aqueous electrolyte secondary battery according to claim 15, wherein the concentration of the polyvalent cation in the non-aqueous electrolyte is 0.001 mol / L or more and 20 mol / L or less.

17. The non-aqueous electrolyte secondary battery according to claim 15, wherein the ratio Maca / Mch, which is the amount of substance of the polyvalent cation in the non-aqueous electrolyte to the amount of substance of the chelating agent in the negative electrode mixture layer Mch, is 1.0 or more and 20.0 or less.

18. The non-aqueous electrolyte secondary battery according to claim 13, wherein the non-aqueous electrolyte comprises at least one selected from the group consisting of calcium(II) bis(trifluoromethanesulfonyl)imide and magnesium(II) bis(trifluoromethanesulfonyl)imide.

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