Binder for secondary battery, electrode mixture, electrode, and non-aqueous electrolyte secondary battery

Abstract

The present invention is a binder for a secondary battery, the binder containing a vinylidene fluoride polymer comprising a structural unit derived from vinylidene fluoride and a structural unit derived from a compound containing a sulfonyl group, wherein the content of the structural unit derived from the compound containing the sulfonyl group in the vinylidene fluoride polymer is 0.15 mol% to 1 mol%, inclusive, relative to the structural unit derived from vinylidene fluoride.

Description

Binder for secondary battery, electrode mixture, electrode, and non-aqueous electrolyte secondary battery

[0001] The present invention relates to a binder for a secondary battery, an electrode mixture, an electrode, and a non-aqueous electrolyte secondary battery.

[0002] 2. Description of the Related Art Non-aqueous electrolyte secondary batteries, such as lithium ion secondary batteries, are widely used as batteries having high energy density.

[0003] Electrodes for lithium-ion secondary batteries are usually manufactured by coating a current collector with a slurry-like electrode mixture, in which an active material, a conductive additive, and a binder (binding agent) are dispersed in a solvent, and then drying the mixture. The binder used for the positive electrode is a binder containing a vinylidene fluoride polymer.

[0004] For example, Patent Document 1 discloses an ion-conductive material for use in lithium batteries and the like, which is a polymer having a structural unit derived from vinylidene fluoride monomer and a CF ２ =CF(CF ２ CF ２ ) nSO ２ and a vinylidene fluoride polymer containing structural units derived from the following:

[0005] In addition, in Patent Document 2, a hydrogen atom in a structural unit derived from vinylidene fluoride is substituted with a sulfonic acid group (—SO ３ A binder comprising a vinylidene fluoride polymer substituted with a hydroxyl group (H group) is disclosed.

[0006] Special Publication No. 2002-528433 Publication JP-A No. 10-298386

[0007] While cobalt-based positive electrode active materials are primarily used as positive electrode active materials for lithium secondary batteries, high-capacity active materials, such as high-nickel positive electrode active materials containing a large amount of nickel, are sometimes used from the viewpoint of achieving even higher capacity, etc. However, slurries containing such high-capacity active materials and binders containing conventional vinylidene fluoride polymers have the problem that their viscosity tends to increase over time (gelation) during the electrode manufacturing process, and their coatability tends to decrease.

[0008] In response to this, the present inventors attempted to suppress the increase in slurry viscosity by changing the type of copolymerizable monomer of the vinylidene fluoride polymer binder. As a result, it became clear that even if the increase in slurry viscosity could be suppressed, the adhesion of the electrode mixture layer to the current collector may be reduced. Therefore, there is a need for a binder that can suppress the increase in slurry viscosity while maintaining adhesion to the current collector.

[0009] An object of the present invention is to provide a binder for a secondary battery, an electrode mixture, an electrode, and a non-aqueous electrolyte secondary battery that can suppress an increase in the viscosity of the slurry while maintaining adhesion to a current collector.

[0010] [1] A binder for a secondary battery, comprising a vinylidene fluoride polymer containing structural units derived from vinylidene fluoride and structural units derived from a compound containing a sulfonyl group, wherein the content of the structural units derived from the compound containing a sulfonyl group in the vinylidene fluoride polymer is 0.15 mol % or more and 1 mol % or less relative to the structural units derived from vinylidene fluoride. [2] The binder for a secondary battery according to [1], wherein the compound containing a sulfonyl group is a compound represented by the following formula (1): (In formula (1), R １ , R ２ , R ３ are each independently a hydrogen atom, a chlorine atom, a fluorine atom, an alkyl group having 1 to 6 carbon atoms or a fluorine-substituted alkyl group having 1 to 6 carbon atoms, and RX is —SO ２ Atomic group containing —Ra or —SO ２ [3] The binder for secondary batteries according to [1] or [2], wherein the compound containing a sulfonyl group further contains an ester bond. [4] The binder for secondary batteries according to any one of [1] to [3], wherein the compound containing a sulfonyl group is a compound represented by the following formula (2): (In formula (2), R １ , R ２ , R ３are each independently a hydrogen atom, a chlorine atom, a fluorine atom, an alkyl group having 1 to 6 carbon atoms, or a fluorine-substituted alkyl group having 1 to 6 carbon atoms; R ４ is -SO ２ -Ra or -SO ２ - is an atomic group containing F, and Ra is an atomic group containing at least one carbon atom. ４ is -(CH ２ ) n-SO ２ a group containing —Ra, wherein Ra is an alkyl group, and —(CH ２ ) The binder for secondary batteries according to [4], wherein the carbon atom of n- may be bonded to a carbon atom of n- to form a ring, and n is an integer of 1 or more. [6] The binder for secondary batteries according to any one of [1] to [5], wherein when a slurry is prepared under the following conditions, the viscosity ratio of the slurry measured under the following conditions is 150% or less. 1) The binder for secondary batteries is prepared by mixing the binder for secondary batteries with a Li １．００ Ni ０．８０ Co ０．１５ Al ０．０５ O ２ (Average particle size: 13 μm, specific surface area: 0.2 m ２ / g, pH: 11.5), carbon black (average particle size: 40 nm, specific surface area: 60 m ２ 1) The active material is mixed with carbon black (carbon black / g) and N-methyl-2-pyrrolidone having a water content of 300 mass ppm or less to prepare a slurry having a mass ratio of the active material, the carbon black, and the vinylidene fluoride polymer of 100:1.5:1.5 and a solids concentration of 75 mass %. 2) The viscosity of the slurry before storage is measured using an E-type viscometer at 25°C and a shear rate of 2 s －１ 3) The slurry is stored at 25°C under a nitrogen atmosphere for 264 hours. 4) The viscosity of the slurry after storage is measured using an E-type viscometer at 25°C and a shear rate of 2 s －１Measure. 5) Calculate the viscosity ratio of the slurry based on the following formula: Viscosity ratio (%) = (viscosity of slurry after storage) / (viscosity of slurry before storage) × 100. The steps 1) to 5) are performed in an environment with a dew point of -30°C or lower. [7] An electrode mixture comprising an active material, a conductive additive, and the binder for a secondary battery according to any one of [1] to [6]. [8] The electrode mixture according to [7], wherein the active material is a positive electrode active material. [9] The electrode mixture according to [8], wherein the positive electrode active material contains a compound represented by the following formula (3): LiMxO ２ ... (3) (In formula (3), M represents at least one metal element including Ni, and when the total of the metal elements represented by M is taken as 100 mol %, the content ratio of Ni is 55 mol % or more, and 0.5≦x≦1.5)

[10] An electrode comprising a current collector and an electrode mixture layer held on the current collector, the electrode mixture layer comprising the electrode mixture according to any one of [7] to [9].

[11] A nonaqueous electrolyte secondary battery comprising the electrode according to

[10] .

[0011] According to the present invention, it is possible to provide a binder for a secondary battery, an electrode mixture, an electrode, and a non-aqueous electrolyte secondary battery that can suppress thickening of the slurry while maintaining adhesion to the current collector.

[0012] Fig. 1 is a graph showing the change in viscosity over time for the slurries of Examples 1 to 3 and Comparative Examples 1 to 3. Fig. 2 is a graph showing the change in viscosity over time for the slurries of Example 4 and Comparative Examples 4 to 7.

[0013] As described above, there has been a problem in that a slurry obtained by mixing a vinylidene fluoride polymer with a high-capacity active material, particularly a positive electrode active material containing a large amount of nickel, is prone to gelation.

[0014] The mechanism is thought to be as follows: Positive electrode active materials contain bases, and positive electrode active materials with a high nickel content contain particularly large amounts of bases. Therefore, when a vinylidene fluoride polymer comes into contact with a positive electrode active material, the base accelerates degradation of the polymer. Specifically, vinylidene fluoride in the polymer undergoes dehydrofluorination, generating conjugated double bonds. A vinylidene fluoride polymer with generated conjugated double bonds is prone to crosslinking in a slurry-like electrode mixture (hereinafter also referred to as a slurry), which tends to gel the slurry.

[0015] In response to this, the present inventors have found that the content of sulfonyl groups (—SO ) is 0.15 mol % or more and 1 mol % or less relative to the constituent units derived from vinylidene fluoride. ２ It has been found that a vinylidene fluoride polymer containing a structural unit derived from a compound containing a hydroxyl group (-) can effectively suppress gelation without reducing adhesiveness.

[0016] Although the details of the mechanism are not clear, it is thought that the following occurs. The sulfonyl group possessed by the vinylidene fluoride polymer has a relatively high electron density, and therefore is likely to coordinate with conductive additives and the like in the slurry. Furthermore, compounds containing sulfonyl groups are likely to be introduced into the low molecular weight range (highly dispersible) of the vinylidene fluoride polymer. Therefore, the coordination ability of the sulfonyl group described above and the introduction of the compound containing a sulfonyl group into the low molecular weight range increase the dispersibility of the vinylidene fluoride polymer into which the compound containing a sulfonyl group has been introduced, making it difficult for the polymers to crosslink with each other, and thus suppressing thickening.

[0017] As described above, the sulfonyl group (—SO ) in the vinylidene fluoride polymer ２ Even if the content of structural units derived from compounds containing vinylidene fluoride is small, thickening of the slurry can be suppressed, and the adhesiveness derived from vinylidene fluoride can be maintained to a greater extent.

[0018] That is, a binder according to one embodiment of the present invention contains a vinylidene fluoride polymer that includes a structural unit derived from vinylidene fluoride and a structural unit derived from a compound containing a sulfonyl group.

[0019] Hereinafter, a binder according to one embodiment of the present invention will be described.

[0020] 1. Binder The binder according to this embodiment contains a vinylidene fluoride polymer.

[0021] 1-1. Vinylidene fluoride polymer The vinylidene fluoride polymer contains a structural unit derived from vinylidene fluoride and a structural unit derived from a compound containing a sulfonyl group.

[0022] The content of the structural unit derived from the compound containing a sulfonyl group is 0.15 mol% or more and 1.0 mol% or less relative to the structural unit derived from vinylidene fluoride. When the content is 0.15 mol% or more, thickening of the electrode mixture can be further suppressed without reducing adhesiveness. When the content is 1.0 mol% or less, not only is synthesis easy, but also it is possible to make it more difficult for adhesiveness to be reduced. From the same viewpoint, the content of the structural unit derived from the compound containing a sulfonyl group is preferably 0.2 mol% or more and 0.5 mol% or less, more preferably 0.25 mol% or more and 0.4 mol% or less.

[0023] From the same viewpoint, the content of the structural units derived from the compound containing a sulfonyl group is preferably 0.5 parts by mass or more and 2 parts by mass or less, and more preferably 0.7 parts by mass or more and 1.5 parts by mass or less, relative to 100 parts by mass of the total amount of the structural units derived from vinylidene fluoride and the structural units derived from the compound containing a sulfonyl group.

[0024] The presence of a sulfonyl group in a constituent unit of a vinylidene fluoride polymer can be confirmed by XPS measurement. Specifically, XPS measurement is performed under the following conditions. Peaks attributable to sulfur in the sulfonyl group (peaks around 165 to 170 eV and 220 to 240 eV) are observed in the obtained spectrum, and sulfur is detected by elemental analysis, thereby confirming that the constituent unit of a vinylidene fluoride polymer contains a sulfonyl group.

[0025] XPS measurements can be performed under the following conditions. The binder powder obtained by polymerization is sandwiched between aluminum foils and heat-pressed at 200°C and 10 MPa to obtain a film-like sample. This is cut into 1 cm squares and fixed to a sample stage for XPS measurement using double-sided carbon tape. An XPS measurement device (e.g., PS9010MC manufactured by JEOL Ltd.) can be used as the measurement device. A 30 W (10 kV x 5 mA) Al-Kα ray source is used, and electrons are replenished using a 2 W (1 kV x 1 mA) neutralization gun, and measurements can be performed at a photoelectron detection angle of 90 degrees.

[0026] The content of each structural unit in the vinylidene fluoride polymer is determined under the following conditions: １ It can be calculated from the integral ratio of the signals in the obtained spectrum by performing H-NMR measurement.

[0027] １ H-NMR measurement can be performed under the following conditions. 10 mg of the binder powder obtained by polymerization is added to 0.75 mL of DMSO-d6 and heated at 50°C for 3 hours to completely dissolve. This solution is placed in a 5 mm diameter NMR sample tube to prepare a sample. An NMR measurement device (e.g., an AVANCE AC 400FT NMR spectrometer manufactured by Bruker) can be used as the measurement device.

[0028] The compound containing a sulfonyl group is preferably a compound represented by the following formula (1):

[0029] R in formula (1) １ ~R ３ are each a hydrogen atom, a chlorine atom, a fluorine atom, an alkyl group having 1 to 6 carbon atoms, or a fluorine-substituted alkyl group having 1 to 6 carbon atoms. Examples of the alkyl group having 1 to 6 carbon atoms include a methyl group and an ethyl group, and a methyl group is preferred. The fluorine-substituted alkyl group having 1 to 6 carbon atoms is preferably a fluorine-substituted alkyl group having 1 to 3 carbon atoms, more preferably a fluorine-substituted alkyl group having 1 carbon atom, and even more preferably a trifluoromethyl group. Among these, R １ ~R ３ ​are each preferably a hydrogen atom or an alkyl group having 1 to 6 carbon atoms, and more preferably a hydrogen atom.

[0030] RX in formula (1) is an atomic group containing a sulfonyl group. The atomic group containing a sulfonyl group is —SO ２ an atomic group containing —Ra (Ra is an atomic group containing at least one carbon atom), —SO ２ Any of the atomic groups containing —F may be used, but —SO ２ It is preferably an atomic group containing —Ra. ２ -Ra is because the electron-withdrawing property of the group adjacent to the sulfur atom of the sulfonyl group is lower than that of other groups, which increases the electron density of the sulfonyl moiety, making it easier to enhance the alignment ability and further suppressing the crosslinking reaction of the polymer. Examples of the atomic group represented by Ra include alkyl groups and aryl groups, and preferably alkyl groups. These groups may be substituted with substituents such as halogen atoms, sulfur atoms, nitrogen atoms, and oxygen atoms, as long as the effects of the present invention are not impaired. The sulfonyl group is a sulfo group (-SO ３ H) and salts thereof.

[0031] RX is preferably -(CR ５ R ６ ) n-SO ２ -Atomic group containing Ra (R ５ and R ６ are each a hydrogen atom or a fluorine atom), and more preferably —(CH ２ ) n-SO ２ -Ra is an atomic group containing, for example, -L-(CH ２ ) n-SO ２ n is an integer of 1 or more, preferably 1 or 2. In addition, Ra and -(CR ５ R ６ )n- or -(CH ２ ) and the carbon atoms of n- may be bonded to each other to form a ring. The ring is preferably a 5- or 6-membered aliphatic ring. L is a single bond or a linking group consisting of one or more groups selected from the group consisting of -COO-, -CO-, and -O-. In these cases, the atomic group represented by RX is -C-SO ２Since it can contain a —C— bond, it is easier to increase the electron density of the sulfonyl moiety, and the crosslinking reaction of the polymer can be further suppressed.

[0032] The molecular weight of the atomic group represented by RX is preferably, for example, 76 or more and 200 or less, and more preferably 79 or more and 150 or less. When the molecular weight of the atomic group represented by RX is 200 or less, the synthesis of the compound represented by formula (1) tends to be easier. Furthermore, when the molecular weight of the atomic group represented by RX is 76 or more, the compound has an appropriate bulkiness, so that the viscosity increase of the slurry can be further suppressed. The molecular weight can be calculated from the chemical structure.

[0033] Among these, it is preferable that the compound containing a sulfonyl group further contains an ester bond (—COO—).

[0034] The fact that the constituent unit of the vinylidene fluoride polymer contains an ester bond can be confirmed by NMR measurement and IR measurement. Specifically, in the spectrum obtained by NMR measurement, a signal (ester -CH ２ -(“(CO)O-CH ２ -" "-CH" ２ - ")) was observed, and in the spectrum obtained by IR measurement, －１ When a peak is observed in the vicinity of (ester -COO-), it can be confirmed that the constituent units of the vinylidene fluoride polymer contain an ester bond.

[0035] Of the compounds containing a sulfonyl group, the compound containing a sulfonyl group and an ester bond is preferably a compound represented by the following formula (2).

[0036] R in formula (2) １ ~R ３ is R in formula (1). １ ~R ３ is synonymous with.

[0037] R in formula (2) ４ is -SO ２ Atomic group containing —Ra or —SO ２ is an atomic group containing —F, preferably —(CR５ R ６ ) n-SO ２ A group containing —Ra, more preferably —(CH ２ ) n-SO ２ n is an integer of 1 or more, preferably 1, 2 or 3, and more preferably 1 or 2. Ra has the same meaning as the above-mentioned Ra, and is preferably an alkyl group. In addition, when the alkyl group and -(CH ２ ) and the carbon atoms of n- may be bonded to each other to form a ring. ５ and R ６ Also, the above-mentioned R ５ and R ６ and is preferably a hydrogen atom.

[0038] Specific examples of compounds containing a sulfonyl group include the following:

[0039] The vinylidene fluoride polymer may further contain structural units derived from compounds other than vinylidene fluoride and compounds containing a sulfonyl group, as long as the objects and effects of the present invention are not impaired.

[0040] The vinylidene fluoride polymer may contain only one type of structural unit derived from another compound, or may contain two or more types of structural units derived from another compound, provided that the total amount of the structural units derived from vinylidene fluoride and the structural units derived from the compound containing a sulfonyl group relative to all the structural units of the vinylidene fluoride polymer is preferably 90 mass% or more, more preferably 95 mass% or more.

[0041] Examples of other compounds include fluorine-based monomers copolymerizable with vinylidene fluoride, hydrocarbon monomers such as ethylene and propylene, and monomers copolymerizable with compounds containing a sulfonyl group. Examples of fluorine-based monomers copolymerizable with vinylidene fluoride include vinyl fluoride, trifluoroethylene, tetrafluoroethylene, chlorotrifluoroethylene, hexafluoropropylene, fluoroalkyl vinyl ethers, and perfluoroalkyl vinyl ethers such as perfluoromethyl vinyl ether. Examples of monomers copolymerizable with compounds containing a sulfonyl group include alkyl (meth)acrylate compounds such as methyl (meth)acrylate.

[0042] The vinylidene fluoride polymer may be a block polymer or a random polymer.

[0043] The melting point of the vinylidene fluoride polymer is, for example, preferably 160° C. or higher, and more preferably 165° C. or higher. When the vinylidene fluoride polymer has a melting point of 160° C. or higher, it is less likely to swell with the electrolyte solution, and the performance of the resulting lithium ion secondary battery is likely to be better.

[0044] The melting point of the vinylidene fluoride polymer can be determined by calorimetry using a differential scanning calorimeter (DSC). Specifically, the vinylidene fluoride polymer is heated from 30°C to 230°C at a rate of 10°C / min (first heating), cooled from 230°C to 30°C at a rate of 10°C / min (first cooling), and then heated from 30°C to 230°C at a rate of 10°C / min (second heating). The melting peak is then determined by DSC. In this specification, the maximum melting peak temperature observed in the second heating is defined as the melting point of the vinylidene fluoride polymer.

[0045] The inherent viscosity of the vinylidene fluoride polymer is, for example, preferably 0.5 dL / g or more and 5.0 dL / g or less, more preferably 1.0 dL / g or more and 4.0 dL / g or less, and most preferably 1.0 dL / g or more and 3.5 dL / g or less. When the inherent viscosity is 0.5 dL / g or more, the adhesive strength between the binder (vinylidene fluoride polymer) and the active material or current collector can be further increased. On the other hand, when the inherent viscosity is 5.0 or less, the viscosity of the slurry does not become too high when an electrode slurry is prepared, resulting in excellent workability.

[0046] Inherent viscosity (η ｉ ) is expressed as logarithmic viscosity. First, 80 mg of vinylidene fluoride polymer is dissolved in 20 mL of N,N-dimethylformamide, and the viscosity is measured using an Ubbelohde viscometer in a thermostatic bath at 30°C. Then, the viscosity is calculated from the obtained value based on the following formula: η ｉ =(1 / C)・ln(η / η ０ In the above formula, η is the viscosity of the solution, η ０ is the viscosity of the solvent N,N-dimethylformamide alone, and C is the concentration of the vinylidene fluoride polymer in the solution, that is, 0.4 g / dL.

[0047] The vinylidene fluoride polymer can be prepared, for example, by copolymerizing vinylidene fluoride, a compound containing a sulfonyl group, and, if necessary, other compounds by a known method. Examples of the copolymerization method include suspension polymerization, emulsion polymerization, solution polymerization, etc., but suspension polymerization is preferred from the viewpoints that a binder with high adhesive strength can be easily obtained and that the amount of impurities is small.

[0048] Compound (2-1), which is one of the compounds containing a sulfonyl group, can be obtained, for example, by reacting 3-hydroxysulfolane with acryloyl chloride in dichloromethane, and compound (2-4) can be obtained, for example, by reacting 2-hydroxyethylmethylsulfone with acryloyl chloride in the presence of dichloromethane.

[0049] 1-2. Non-aqueous solvent The binder may contain a non-aqueous solvent as needed. When the binder contains a non-aqueous solvent, the vinylidene fluoride polymer can be dissolved or dispersed therein, and the binder can be made into a liquid state.

[0050] Examples of non-aqueous solvents include polar solvents (polar solvents). Examples of polar solvents include amide compounds such as dimethylformamide, N,N-dimethylacetamide, and N-methylpyrrolidone; alcohols such as methanol, ethanol, isopropyl alcohol, 2-ethyl-1-hexanol, 1-nonanol, lauryl alcohol, and tripropylene glycol; amine compounds such as o-toluidine, m-toluidine, and p-toluidine; 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide; lactones such as γ-butyrolactone and δ-butyrolactone; and sulfoxide / sulfone compounds such as dimethyl sulfoxide and sulfolane. The binder may contain only one type of non-aqueous solvent, or may contain two or more types.

[0051] The amount of the non-aqueous solvent in the binder is preferably 400 parts by mass or more and 5,000 parts by mass or less, and more preferably 500 parts by mass or more and 5,000 parts by mass or less, relative to 100 parts by mass of the vinylidene fluoride polymer. When the amount of the non-aqueous solvent in the binder is within this range, the vinylidene fluoride polymer can be more uniformly dispersed or dissolved in the non-aqueous solvent.

[0052] 1-3. Other Components The binder may further contain, for example, other resins such as acrylic resins, fillers such as inorganic fillers, various additives, and the like, within the scope of not impairing the object and effect of the present invention.

[0053] 1-4. Physical Properties of Binder As described above, the binder can suppress thickening when mixed with an active material and a conductive agent to form a slurry. Specifically, when a slurry is prepared using the binder under the following conditions, the viscosity ratio of the slurry measured under the following conditions is preferably 150% or less, more preferably 100% or less, and even more preferably 80% or less. The lower limit of the viscosity ratio is not particularly limited, but is preferably 10% or more from the viewpoint of easily forming a coating film with a predetermined thickness or more. 1) The binder is used in a manner that the viscosity ratio of the binder is 150% or less, more preferably 100% or less, and even more preferably 80% or less, when the binder is mixed with the active material Li １．００ Ni ０．８０ Co ０．１５ Al ０．０５ O ２ (Average particle size: 13 μm, specific surface area: 0.2 m ２ / g, pH: 11.5), carbon black (average particle size: 40 nm, specific surface area: 60 m ２ 1) The slurry is mixed with an active material, carbon black, and vinylidene fluoride polymer in a mass ratio of 100:1.5:1.5 and a solids concentration of 75 mass %. 2) The viscosity of the slurry before storage is measured using an E-type viscometer at 25°C and a shear rate of 2 s －１ 3) The slurry is stored at 25°C under a nitrogen atmosphere for 264 hours. 4) The viscosity of the slurry after storage is measured using an E-type viscometer at 25°C and a shear rate of 2 s －１ 5) Calculate the viscosity ratio of the slurry based on the following formula: Viscosity ratio (%) = (viscosity of slurry after storage) / (viscosity of slurry before storage) × 100. The above steps 1) to 5) are carried out in an environment with a dew point of -30°C or lower.

[0054] The viscosity ratio of the slurry can be adjusted, for example, by the content of the structural unit derived from the compound containing a sulfonyl group in the vinylidene fluoride polymer, the type of the compound containing a sulfonyl group, etc. Increasing the content of the structural unit derived from the compound containing a sulfonyl group tends to decrease the viscosity ratio.

[0055] 2. Electrode Mix The electrode mix contains an active material, a conductive additive, and the binder described above. The electrode mix can be preferably used as an electrode mix for a non-aqueous electrolyte secondary battery, which will be described later. The electrode mix may further contain a conductive additive, a solvent, other additives, and the like.

[0056] 2-1. Active Material The active material may be a positive electrode active material or a negative electrode active material. Of these, the active material is preferably a positive electrode active material.

[0057] The positive electrode active material is not particularly limited, but is preferably a lithium metal oxide.

[0058] Examples of lithium metal oxides include LiMnO ２ , LiMn ２ O ４ , LiCoO ２ , LiNiO ２ , LiNi ｘ Co １－ｘ O ２ (0<x<1), LiNi ｘ Co ｙ Mn １－ｘ－ｙ O ２ (0<x<1, 0<y<1), LiNi ｘ Co ｙ Al １－ｘ－ｙ O ２ (0<x<1, 0<y<1), LiMaPO ４ (wherein Ma is one or more elements selected from Co, Ni, Mn, Fe, Mg, Nb, Ti, Al, and Zr), Li ２ MnO ３ -LiMbO ２ Lithium-excess solid solution cathode represented by (Mb=Mn, Co, Ni), lithium titanate (Li ４ Ti ５ O １２ ), titanium oxide (TiO ２ ), Li ｓ Ni ｔ Co ｕ Al ｖ O ２ (0.9<s<1.3, 0.9<t+u+v<1.1), etc.

[0059] From the viewpoint of increasing the capacity density and thereby increasing the capacity of the secondary battery, the positive electrode active material is preferably a lithium metal compound containing Ni, and from the viewpoint of suppressing crystal structure changes during charge / discharge processes and stabilizing cycle characteristics, the positive electrode active material is more preferably a lithium metal compound containing Ni and Co.

[0060] An example of a lithium-based positive electrode active material is a lithium metal oxide represented by the following formula (3): LiMxO ２ ...(3)

[0061] In formula (3), M represents at least one metal element including Ni. The metal element other than Ni is preferably selected from the group consisting of Co, Al, Fe, Mn, Cr, and V. It is more preferable that M further contains one or more elements selected from the group consisting of Co, Mn, and Al in addition to Ni. Furthermore, in the lithium metal oxide represented by formula (3), when the total amount of metal elements constituting M is 100 mol%, the content of Ni is preferably 55 mol% or more, more preferably 70 mol% or more.

[0062] In formula (3), 0.5≦x≦1.5, and more preferably 0.7≦x≦1.3.

[0063] From the viewpoint of increasing the charging potential of the secondary battery and further improving the cycle characteristics, the positive electrode compound is preferably a lithium metal oxide (ternary lithium metal oxide) represented by the following formula (4).

[0064] Li １－ａ Ni ｘ Co ｙ M ｚ O ２ ...(4)

[0065] In formula (4), M is Mn or Al, −0.5≦a≦0.5, 0<x<1, 0<y<1, 0<z<1, and x+y+z=1.

[0066] Examples of lithium-based positive electrode active materials and ternary lithium metal oxides represented by formula (3) include Li １．００ Ni ０．３５ Co ０．３４ Mn ０．３４O ２ (NCM111), Li １．００ Ni ０．５０ Co ０．２０ Mn ０．３０ O ２ (NCM523), Li １．００ Ni ０．５０ Co ０．３０ Mn ０．２０ O ２ (NCM532), Li １．００ Ni ０．６ Co ０．２ Mn ０．２ O ２ (NCM622), Li １．００ Ni ０．８０ Co ０．１０ Mn ０．1０ O ２ (NCM811), and Li １．００ Ni ０．８０ Co ０．１５ Al ０．０５ O ２ (NCA811) and the like.

[0067] Among the positive electrode active materials exemplified above, Li １．００ Ni ０．８０ Co ０．１０ Mn ０．1０ O ２ (NCM811), and LiNi ０．８０ Co ０．１５ Al ０．０５ O ２ (NCA811) is preferred.

[0068] Examples of the negative electrode active material include carbon materials, silicon materials, metal oxides, and lithium alloys.

[0069] The pH of the active material is not particularly limited, but in the case of a positive electrode active material, it is, for example, 8.5 or more and 12.0 or less. The pH of the active material refers to the pH of the water when extracted at room temperature (25°C) using the extraction method specified in JIS K 5101-16-2. Specifically, the pH value can be obtained by adding the active material to ultrapure water in an amount 50 times the weight of the active material, stirring with a magnetic stirrer at a rotation speed of 600 rpm for 10 minutes, and measuring the pH of the supernatant using a pH meter model F-21 manufactured by Horiba, Ltd.

[0070] The content of the active material in the electrode mixture is appropriately selected depending on the application of the electrode mixture, and is preferably 40% by mass or more and 99.7% by mass or less based on the total amount of the active material, the conductive additive, and the solid content derived from the binder. When the content of the active material is within this range, for example, a more sufficient charge / discharge capacity is obtained, and the battery performance is likely to be better.

[0071] The conductive additive is not particularly limited as long as it is a compound that can further increase the conductivity between active materials or between an active material and a current collector. Examples of the conductive additive include acetylene black, ketjen black, carbon black, graphite powder, graphene, carbon nanofibers, carbon nanotubes, and carbon fibers.

[0072] The content of the conductive additive in the electrode mixture is appropriately selected depending on the type thereof, etc. From the viewpoint of further improving the conductivity and dispersibility of the conductive additive, the content is preferably 0.1% by mass to 15% by mass, more preferably 0.1% by mass to 7% by mass, and even more preferably 0.1% by mass to 5% by mass, based on the total amount of the solid content derived from the active material, the conductive additive, and the binder.

[0073] 2-3 Binder The binder described above is less likely to cause gelation, even when mixed with the active material described above, particularly with a positive electrode active material containing a relatively large amount of Ni, while maintaining the adhesiveness of the electrode mixture to the current collector.

[0074] The content of the binder is not particularly limited, but from the viewpoint of battery performance and adhesiveness, it is preferably 0.2 parts by mass or more and 15 parts by mass or less, more preferably 0.5 parts by mass or more and 10 parts by mass or less, and even more preferably 0.5 parts by mass or more and 4 parts by mass or less, relative to 100 parts by mass of the active material.

[0075] 2-4. Other Components The electrode mixture may further contain a solvent that is different from the non-aqueous solvent contained in the binder. The solvent can be selected from the non-aqueous solvents that can be contained in the binder.

[0076] The total amount of solvent in the electrode mixture (including the amount of non-aqueous solvent in the binder) is not particularly limited, but is usually preferably 20 parts by mass or more and 150 parts by mass or less per 100 parts by mass of the active material.

[0077] The electrode mixture may further contain a dispersant, an adhesive aid, a thickener, etc. Known compounds can be used for these. The amount of these is not particularly limited as long as it does not impair the object and effect of the present invention, but it is preferably 15 mass % or less based on the total amount of the solid content derived from the binder and the active material.

[0078] The electrode mixture may further contain additives such as nitrogen compounds such as phosphorus compounds, sulfur compounds, organic acids, amine compounds, and ammonium compounds; organic esters, various silane-based, titanium-based, and aluminum-based coupling agents; vinylidene fluoride polymers other than the above-mentioned vinylidene fluoride polymers, and resins such as polytetrafluoroethylene (PTFE), styrene-butadiene rubber (SBR), and polyacrylonitrile (PAN). These are not particularly limited as long as they do not impair the objects and effects of the present invention, but are preferably 15 mass% or less with respect to the total amount of the solid content derived from the binder and the positive electrode active material.

[0079] The viscosity of the electrode mixture is not particularly limited as long as it can further suppress dripping, coating unevenness, or drying delay after coating when applying the electrode mixture to form an electrode mixture layer, and provides good workability and applicability when preparing the electrode mixture layer. Typically, the viscosity (slurry viscosity) measured with a B-type viscometer at 20 ° C. and a rotation speed of 12 rpm is preferably 100 mPa s or more and 100,000 mPa s or less, more preferably 1,000 mPa s or more and 80,000 mPa s or less, and particularly preferably 2,000 mPa s or more and 70,000 mPa s or less. The viscosity (slurry viscosity) of the electrode mixture in this specification is the value measured 2 minutes after the start of rotation with the B-type rotational viscometer.

[0080] The electrode mixture may be prepared by mixing all of the components at once, or by first mixing some of the components and then mixing the remaining components.

[0081] The binder, electrode mixture, and electrode described above can be used as an electrode, preferably a positive electrode, of a non-aqueous electrolyte secondary battery.

[0082] 3. Electrode The electrode may include an electrode mixture layer containing the above-described electrode mixture. In the present embodiment, the electrode includes a current collector and an electrode mixture layer disposed on the current collector.

[0083] 3-1. Current Collector The current collector is a terminal for extracting electricity. There are no particular limitations on the current collector, and metal foils or metal meshes of aluminum, copper, iron, stainless steel, steel, nickel, titanium, etc. can be used. Among these, aluminum foil is preferred as the current collector for the positive electrode.

[0084] 3-2. Electrode mixture layer The electrode mixture layer is a layer formed by applying a composition containing an active material, a conductive additive, and the binder (for example, the electrode mixture described above) onto a current collector and drying it. The electrode mixture layer may be disposed on only one surface of the current collector, or on both surfaces thereof.

[0085] The electrode mixture layer contains at least an active material, a conductive additive, and a solid content derived from the binder (vinylidene fluoride polymer), and may further contain various additives such as a dispersant, an adhesive aid, a thickener, etc. as needed. These are the same as those described for the electrode mixture.

[0086] The thickness of the electrode mixture layer is not particularly limited, but in one example, it is preferably 1 μm or more and 1000 μm or less. The basis weight of the electrode mixture layer formed on one surface of the current collector is not particularly limited, but in one example, it is 50 g / m ２ More than 1000g / m ２ Preferably, 100 g / m or less ２ More than 500g / m ２ The following is more preferred:

[0087] The electrode mixture layer can be formed by carrying out a step of applying the above-described electrode mixture onto a current collector and a step of drying the applied mixture.

[0088] The method for applying the electrode mixture is not particularly limited, and methods such as a doctor blade method, a reverse roll method, a comma bar method, a gravure method, an air knife method, a die coating method, and a dip coating method can be used.

[0089] After application of the electrode mixture, the mixture is heated at an arbitrary temperature to dry the non-aqueous solvent. In one example, the drying temperature is preferably 60°C or higher and 500°C or lower, and more preferably 80°C or higher and 200°C or lower. Heating may be performed multiple times at different temperatures. The solvent in the mixture may be dried under atmospheric pressure, increased pressure, or reduced pressure. After drying, a further heat treatment may be performed.

[0090] After the electrode mixture is applied and dried, a pressing process may be further performed. The pressing process can improve the electrode density. In one example, the pressing pressure is preferably 1 kPa or more and 10 GPa or less.

[0091] 4. Non-aqueous electrolyte secondary battery The non-aqueous electrolyte secondary battery according to the present embodiment includes the above-described electrode. In the present embodiment, the non-aqueous electrolyte secondary battery preferably includes the above-described electrode as a positive electrode. Examples of non-aqueous electrolyte secondary batteries include lithium ion secondary batteries.

[0092] In the above embodiment, an example has been shown in which the vinylidene fluoride polymer is used as a binder for a non-aqueous electrolyte secondary battery, but the present invention is not limited to this and the polymer may be used as a binder for other secondary batteries, such as all-solid-state batteries.

[0093] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0094] 1. Preparation of vinylidene fluoride polymer [Preparation of vinylidene fluoride polymer 1 (VDF / SA)] A 2-liter autoclave was charged with 1,213 g of ion-exchanged water, 27.6 g of a 1.45 mass% aqueous solution of SM-100 (manufactured by Shin-Etsu Chemical Co., Ltd.), 2.2 g of a 50 mass% diisopropyl peroxydicarbonate-HFE-347pc-f solution, 400 g of vinylidene fluoride, and 4 g of a compound represented by the following formula (SA, a compound containing a sulfonyl group), and the mixture was heated to 45°C to allow a reaction to occur. The resulting polymer slurry was dehydrated and dried to obtain vinylidene fluoride polymer 1 (VDF / SA = 100 / 0.34 molar ratio, 99 / 1 mass ratio).

[0095] [Preparation of vinylidene fluoride polymer 2 (VDF / MSEA)] A 2-liter autoclave was charged with 1,213 g of ion-exchanged water, 27.6 g of a 1.45 mass % aqueous solution of SM-100 (manufactured by Shin-Etsu Chemical Co., Ltd.), 2.4 g of a 50 mass % diisopropyl peroxydicarbonate-HFE-347pc-f solution, 400 g of vinylidene fluoride, and 4 g of a compound represented by the following formula (MSEA, a compound containing a sulfonyl group), and the mixture was heated to 45° C. to react. The resulting polymer slurry was dehydrated and dried to obtain vinylidene fluoride polymer 3 (VDF / MSEA = 100 / 0.36 molar ratio, 99 / 1 mass ratio).

[0096] [Preparation of vinylidene fluoride polymer 3 (VDF / SA)] Vinylidene fluoride polymer 3 (VDF / SA = 100 / 0.24 molar ratio, 99.3 / 0.7 mass ratio) was obtained in the same manner as in preparation of vinylidene fluoride polymer 1, except that the amount of SA added was changed.

[0097] [Preparation of vinylidene fluoride polymer 4 (VDF / APS)] A 2-liter autoclave was charged with 1096 g of ion-exchanged water, 0.2 g of Metrose 90SH-100 (manufactured by Shin-Etsu Chemical Co., Ltd.), 2.2 g of a 50 wt% diisopropyl peroxydicarbonate-HFE-347pc-f solution, 426 g of vinylidene fluoride, and an initial amount of 0.2 g of acryloyloxypropyl succinic acid (APS), and the temperature was raised to 26 ° C. over 1 hour. Thereafter, while maintaining the temperature at 26 ° C., a 6 wt% aqueous acryloyloxypropyl succinic acid solution was gradually added at a rate of 0.5 g / min. The resulting polymer slurry was dehydrated and dried to obtain a polar group-containing vinylidene fluoride polymer 4 (VDF / APS = 100 / 0.28 molar ratio, 99 / 1 mass ratio). The total amount of acryloyloxypropyl succinic acid added was 4.0 g, including the amount added initially.

[0098] [Vinylidene Fluoride Polymer 5 (PVDF)] Polyvinylidene fluoride (KF#7300, manufactured by Kureha Corporation) was used.

[0099] [Preparation of vinylidene fluoride polymer 6 (VDF / CTFE)] A 2-liter autoclave was charged with 1036 g of ion-exchanged water, 0.4 g of Metrose SM-100 (manufactured by Shin-Etsu Chemical Co., Ltd.), 8 g of a 50 wt% diisopropyl peroxydicarbonate-HFE-347pc-f solution, 6.0 g of ethyl acetate, 20 g of a 2 wt% aqueous solution of sodium acid pyrophosphate, 20 g of a 2 wt% aqueous solution of sodium pyrophosphate, 360 g of vinylidene fluoride, and 40 g of chlorotrifluoroethylene, and heated to 28° C. The resulting polymer slurry was dehydrated and dried to obtain vinylidene fluoride polymer 6 (VDF / CTFE = 100 / 2.3 molar ratio, 96 / 4 mass ratio).

[0100] [Measurement of Inherent Viscosity] The inherent viscosity of a vinylidene fluoride polymer was measured as follows. First, 80 mg of a vinylidene fluoride polymer was dissolved in 20 mL of N,N-dimethylformamide, and the viscosity was measured using an Ubbelohde viscometer in a thermostatic bath at 30°C. Then, the inherent viscosity (η ｉ) was calculated. ｉ =(1 / C)・ln(η / η ０ In the above formula, η is the viscosity of the solution, η ０ is the viscosity of the solvent N,N-dimethylformamide alone, and C is the concentration of the vinylidene fluoride polymer in the solution, that is, 0.4 g / dL.

[0101]

[0102] 2. Preparation and Evaluation of Electrode Mixture and Electrode (1) [Example 1] (Preparation of Binder) As a binder, the vinylidene fluoride polymer 1 was dissolved in N-methyl-2-pyrrolidone (hereinafter also referred to as "NMP") having a water content of 300 ppm by mass or less to prepare a 6% by mass vinylidene fluoride polymer solution.

[0103] (Preparation of electrode mixture) In an environment with a dew point of −30° C. or less, NCA811 (Li １．００ Ni ０．８０ Co ０．１５ Al ０．０５ O ２ , average particle diameter: 13 μm, specific surface area: 0.2 m ２ / g, pH: 11.5), and carbon black (SP: SuperP (registered trademark) manufactured by Timcal Japan, average particle size: 40 nm, specific surface area: 60 m) as a conductive aid. ２ 1 / g) and NMP having a water content of 300 mass ppm or less were added, and the mixture was kneaded using a Thinky Mixer. Specifically, the vinylidene fluoride polymer solution and carbon black were first kneaded at 2000 rpm for 1 minute, and then NCA811 was added and the mixture was secondly kneaded at 2000 rpm for 2 minutes. NMP having a water content of 300 mass ppm or less was then added to the mixture to adjust the solids concentration to 75 mass%, and the mixture was thirdly kneaded at 2000 rpm for 3 minutes to obtain an electrode mixture. The mass ratio of NCA811, carbon black, and vinylidene fluoride polymer 1 was 100:1.5:1.5. The pH of the active material was measured using the above-mentioned measurement method.

[0104] (Preparation of Electrode) The obtained electrode mixture was applied to a 15 μm thick aluminum foil as a current collector using a bar coater, and the resulting current collector was subjected to primary drying at 110° C. for 30 minutes in a nitrogen atmosphere in a thermostatic chamber. Subsequently, the resultant was subjected to secondary drying at 130° C. for 2 hours in a nitrogen atmosphere to obtain a coating weight of about 250 g / m. ２ As a result, an electrode (electrode peeling measurement sample) was obtained.

[0105] Examples 2 to 3, Comparative Examples 1 to 3 Electrode mixtures and electrodes were prepared in the same manner as in Example 1, except that vinylidene fluoride polymer 1 was changed to the vinylidene fluoride polymers shown in Table 1.

[0106] [Evaluation] (1) Storage Test 1 of Electrode Mixture The electrode mixture slurry prepared above was stored for a predetermined time (24 hours, 96 hours, 168 hours, 264 hours) under a nitrogen atmosphere at 25°C with a dew point of -30°C or less. The viscosity of the slurry before and after storage was measured using an E-type viscometer at 25°C and a shear rate of 2 s －１ The viscosity was measured by waiting for 60 seconds after the slurry was charged into the measuring device and then rotating the rotor. The viscosity of the slurry was measured 300 seconds after the rotor started to rotate.

[0107] The viscosity of the slurry before storage (viscosity of the slurry after storage for 0 hours) and the viscosity of the slurry after storage (viscosity of the slurry after storage for 264 hours) were applied to the following formula to calculate the viscosity ratio of the slurry: Viscosity ratio (%) = (viscosity of the slurry after storage) / (viscosity of the slurry before storage) × 100

[0108] (2) Electrode Peel Strength Test The electrode prepared above was cut into a length of 100 mm and a width of 20 mm. A 90° peel test was then performed at a head speed of 10 mm / min using a tensile tester (ORIENTE CHSIA-1150 manufactured by UNIVERSAL TESTING MACHINE) in accordance with JIS F6854-1 to measure the peel strength.

[0109] The evaluation results of Examples 1 to 3 and Comparative Examples 1 to 3 are shown in Table 2. A graph showing the change in viscosity over time is shown in Figure 1.

[0110]

[0111] As shown in Table 2, the slurry of Comparative Example 3 containing vinylidene fluoride polymer 6 containing structural units derived from CTFE showed little increase in viscosity over time, demonstrating the effect of suppressing thickening. However, it is clear that the peel strength was lower than that of Comparative Example 2 containing vinylidene fluoride polymer 5 (homopolymer), indicating reduced adhesiveness. On the other hand, it is clear that the slurry of Comparative Example 1 containing vinylidene fluoride polymer 4 containing structural units derived from APS showed a significant increase in viscosity over time.

[0112] In contrast, the slurries of Examples 1 to 3, which contain vinylidene fluoride polymers containing structural units derived from compounds containing sulfonyl groups (SA, MSEA), are found to exhibit high adhesiveness and the effect of suppressing thickening.

[0113] 3. Preparation and Evaluation of Electrode Mixture (2) [Comparative Examples 4 to 7] (Preparation of Binder) The vinylidene fluoride polymer 5 (#7300) was dissolved in NMP having a water content of 300 ppm by mass or less to prepare a 6% by mass vinylidene fluoride polymer solution.

[0114] (Preparation of electrode mixture) In an environment with a dew point of −30° C. or less, NCA811 (Li １．００ Ni ０．８０ Co ０．１５ Al ０．０５ O ２ , average particle diameter: 13 μm, specific surface area: 0.2 m ２ / g, pH: 11.5), and carbon black (SP: SuperP (registered trademark) manufactured by Timcal Japan, average particle size: 40 nm, specific surface area: 60 m) as a conductive aid. ２The mixture was kneaded using a Thinky Mixer (Thinky). Specifically, the active material and carbon black were subjected to a primary kneading process at 800 rpm for 1 minute, followed by the addition of a vinylidene fluoride polymer solution and secondary kneading at 2000 rpm for 2.5 minutes. An NMP solution of additives was further added to the mixture to adjust the solid content to 75% by mass, and the mixture was subjected to a third kneading process at 2000 rpm for 3 minutes, yielding an electrode mixture containing NCA811 / SP / binder / additive = 100 / 2 / 2 (mass ratio) and the additives listed in Table 2. The pH of the active material was measured using the above-mentioned measurement method.

[0115] Example 4 (Preparation of Binder) A vinylidene fluoride polymer solution was prepared in the same manner as in Comparative Example 4, except that vinylidene fluoride polymer 5 was changed to vinylidene fluoride polymer 1.

[0116] (Preparation of Electrode Mixture) An electrode mixture was prepared in the same manner as in Comparative Example 4, except that the obtained vinylidene fluoride polymer solution was used and no additive was added.

[0117] [Evaluation] (Storage Test 2 of Electrode Mixture) The electrode mixture slurry prepared above was stored at 40°C, with a dew point of -30°C or less, under a nitrogen atmosphere for a predetermined time (3 hours, 6 hours, 24 hours, 48 ​​hours, 72 hours, 96 hours, 168 hours). The viscosity of the slurry before and after storage was measured using an E-type viscometer at 25°C and a shear rate of 2 s －１ The viscosity was measured by waiting for 60 seconds after the slurry was charged into the measuring device and then rotating the rotor. The viscosity of the slurry was measured 300 seconds after the rotor started to rotate.

[0118] The evaluation results of Example 4 and Comparative Examples 4 to 7 are shown in Table 3. A graph showing the change in viscosity over time is shown in Figure 2.

[0119]

[0120] As shown in Table 3, the electrode mixtures of Comparative Examples 4 to 7, in which a compound containing a sulfonyl group was added to a binder of vinylidene fluoride homopolymer, showed a significant increase in viscosity over time.

[0121] In contrast, it can be seen that the electrode mixture of Example 4, which uses a binder of a vinylidene fluoride polymer containing a structural unit derived from a compound containing a sulfonyl group (SA, MSEA), is inhibited from increasing in viscosity over time.

[0122] From these facts, in order to suppress the thickening of the electrode mixture, it is necessary to add sulfonyl groups (-SO ２ It is clear that the mere presence of (-) is insufficient, and that it is necessary to include in the slurry a polymer having a structural unit containing a sulfonyl group.

[0123] This application claims priority from Japanese Patent Application No. 2024-002573, filed January 11, 2024, the entire contents of which are incorporated herein by reference.

[0124] The binder of the present invention can suppress thickening of the slurry while maintaining adhesion of the electrode mixture to the current collector, especially when mixed with a positive electrode active material containing a large amount of nickel. Therefore, the binder and the electrode mixture and electrode containing the binder are very useful for manufacturing nonaqueous electrolyte secondary batteries such as lithium ion secondary batteries.

Claims

1. A binder for a secondary battery, comprising a vinylidene fluoride-based polymer containing a structural unit derived from vinylidene fluoride and a structural unit derived from a compound containing a sulfonyl group, wherein in the vinylidene fluoride-based polymer, the content of the structural unit derived from the compound containing a sulfonyl group is 0.15 mol% or more and 1 mol% or less based on the structural unit derived from vinylidene fluoride.

2. The binder for a secondary battery according to claim 1, wherein the compound containing a sulfonyl group is a compound represented by the following formula (1): (In formula (1), R １ , R ２ , R ３ are each independently a hydrogen atom, a chlorine atom, a fluorine atom, an alkyl group having 1 to 6 carbon atoms, or a fluorine-substituted alkyl group having 1 to 6 carbon atoms; ２ -Ra or -SO ２ - is an atomic group containing F, and Ra is an atomic group containing at least one carbon atom.

3. The binder for a secondary battery according to claim 1, wherein the compound containing a sulfonyl group further contains an ester bond.

4. The binder for a secondary battery according to claim 1, wherein the compound containing a sulfonyl group is a compound represented by the following formula (2). (In formula (2), １ R ２ R ３ are each independently a hydrogen atom, a chlorine atom, a fluorine atom, an alkyl group having 1 to 6 carbon atoms, or a fluorine-substituted alkyl group having 1 to 6 carbon atoms, and ４ R ２ is an atomic group containing -SO ２ -Ra or an atomic group containing -SO ２ -F, and Ra is an atomic group containing at least one carbon atom.) 5. R ４ is a group containing -(CH ２ )n-SO ２ -Ra, Ra is an alkyl group, the alkyl group and -(CH ２ )n- may be bonded to the carbon atoms to form a ring, n is an integer of 1 or more, the binder for a secondary battery according to claim 4.

6. The binder for a secondary battery according to claim 1, wherein when a slurry is prepared under the following conditions, the viscosity ratio of the slurry measured under the following conditions is 150% or less. 1) The binder for a secondary battery is mixed with Li １．００ Ni ０．８０ Co ０．１５ Al ０．０５ O ２ (average particle diameter: 13 μm, specific surface area: 0.2 m ２ / g, pH: 11.5), carbon black (average particle diameter: 40 nm, specific surface area: 60 m ２ / g) and N-methyl-2-pyrrolidone having a water content of 300 mass ppm or less to prepare a slurry in which the mass ratio of the active material, the carbon black and the vinylidene fluoride-based polymer is 100:1.5:1.5 and the solid content concentration is 75 mass%. 2) Measure the viscosity of the slurry before storage at 25° C. and a shear rate of 2 s －１ using an E-type viscometer. 3) Store the slurry at 25° C. under a nitrogen atmosphere for 264 hours. 4) Measure the viscosity of the slurry after storage at 25° C. and a shear rate of 2 s －１ using an E-type viscometer. 5) Calculate the viscosity ratio of the slurry based on the following formula. Viscosity ratio (%) = (viscosity of the slurry after storage) / (viscosity of the slurry before storage) × 100 The above 1) to 5) are carried out in an environment with a dew point of -30° C. or lower.

7. An electrode mixture comprising an active material, a conductive assistant, and the binder for a secondary battery according to any one of claims 1 to 6.

8. The electrode mixture according to claim 7, wherein the active material is a positive electrode active material.

9. The positive electrode active material contains a compound represented by the following formula (3), and the electrode binder according to claim 8. LiMxO ２ ... (3) (In formula (3), M represents at least one metal element containing Ni, and when the total of the metal elements represented by M is 100 mol%, the content ratio of Ni is 55 mol% or more, and 0.5 ≤ x ≤ 1.5) 10. An electrode comprising a current collector and an electrode mixture layer held on the current collector and containing the electrode mixture according to any one of claims 7 to 9.

11. A non-aqueous electrolyte secondary battery comprising the electrode according to claim 10.

Images