Composition for forming electrode, additive, and gelation inhibitor

Abstract

Provided is a composition for forming an electrode, the composition being suppressed in thickening and gelling by a simple method, having improved storage stability, and being capable of increasing the concentration of solid content. For example, the composition for forming an electrode contains a positive electrode active material, a binder, a solvent, and a heterocyclic ring-containing compound, and the heterocyclic ring-containing compound has a nitrogen-containing five-membered ring, the five-membered ring does not contain an oxygen atom, and the five-membered ring has a carbonyl structure.

Description

Technical Field

[0001] The present invention relates to an electrode-forming composition, an additive, and a gelation inhibitor. Background Art

[0002] Lithium-ion secondary batteries have high energy density per unit weight and volume, contributing to the miniaturization and lightweighting of electronic devices. In recent years, as part of the drive towards zero-emission vehicles, the spread of electric vehicles has accelerated, leading to demands for further reductions in resistance, longer lifespans, higher capacity, safety, and lower costs.

[0003] Lithium-ion secondary batteries typically have a three-layer structure consisting of a positive electrode, a separator, and a negative electrode, including an electrolyte. The positive and negative electrodes are manufactured by mixing an active material, a conductive material, and a binder, and applying the resulting electrode slurry to a current collector. Currently, the mainstream method for manufacturing negative electrodes involves applying the negative electrode slurry to copper foil, which serves as the current collector, and then drying it. The mainstream method for manufacturing positive electrodes involves preparing a positive electrode slurry using an organic solvent such as N-methyl-2-pyrrolidone and applying it to aluminum foil, which serves as the current collector.

[0004] As positive electrode active materials for lithium-ion secondary batteries, inorganic compounds such as transition metal oxides and transition metal chalcogenides containing alkali metals are known as materials capable of achieving a battery voltage of approximately 4 V. Among these, highly alkaline positive electrode active materials containing large amounts of nickel and manganese are used to obtain high-capacity lithium-ion secondary batteries.

[0005] For example, Li x High nickel positive electrode active materials represented by NiO2 are attractive positive electrode materials with high discharge capacitance, but there are alkaline components such as LiOH, Li2O, LiHCO3, and Li2CO3 on the surface, which are generated by raw material residues or proton exchange reactions with water, and reactions with water and carbon dioxide gas in the air.

[0006] When using such positive electrode active materials, the electrode slurry thickens or gels, gradually losing fluidity. If the electrode slurry loses fluidity, it is not only difficult to obtain a uniform coating thickness, but in some cases, coating may not be possible, resulting in material waste.

[0007] The main reason for this is believed to be that during the positive electrode production process, alkaline components present on the surface of the positive electrode active material promote the dehydrofluorination reaction of the fluorine-based binder represented by polyvinylidene fluoride (PVdF) having a vinylidene fluoride structure used as a binder in the presence of a small amount of water.

[0008] Furthermore, alkaline components can corrode the aluminum foil typically used as a current collector for the positive electrode, thereby increasing the resistance of the battery. Furthermore, these alkaline components can react with the electrolyte within the battery, increasing the resistance of the battery and shortening its lifespan.

[0009] The above-mentioned thickening and gelation can be suppressed by handling the raw materials and electrode slurry in a dry environment and controlling the water content. However, large-scale equipment is required in a series of mass production processes from preparing the electrode slurry to manufacturing the battery. In addition, the cost increase and increased environmental load caused by the use of large amounts of electricity have become problems.

[0010] In order to solve this problem, for example, the following technology is disclosed in Patent Document 1: the electrode slurry (positive electrode material slurry) is prepared in a manner that does not show strong alkalinity even when dispersed in water, thereby suppressing the gelation of the electrode slurry. However, in the method described in Patent Document 1, preparing the electrode slurry in a manner that does not show strong alkalinity requires not only strict pH management, but also the following treatment: temporarily dispersing the positive electrode active material in water, filtering and removing the positive electrode active material from the dispersion, and then drying. As a result, the operation becomes complicated and the yield rate is reduced. In addition, the treatment as described above may also cause the performance of the positive electrode active material itself to be reduced.

[0011] In addition, the following technology is reported in patent document 2: by using compounds such as polyethylene oxide with ultra-high molecular weight (weight average molecular weight of 2.2 million or more), water is constrained by interaction with water (such as hydrogen bond), and the reaction of the alkaline component of the positive electrode active material with water is suppressed, thereby suppressing thickening and gelation. However, the existence of a polymer with a strong thickening effect of ultra-high molecular weight to uniformly dissolve it in a solvent takes time and costs money. In addition, it is difficult to make an operational problem such as a high concentration solution. In addition, the ability of the above-mentioned ultra-high molecular weight polymer to constrain water is high, so the polymer itself may bring in water. In order to prevent this, it is necessary to strictly manage the prior drying.

[0012] Patent Documents 3 and 4 propose that an organic acid or an inorganic acid is added to the positive electrode of a lithium-ion secondary battery in order to suppress the gelation of the electrode slurry (positive electrode mixture slurry). In Patent Document 3, maleic acid, citraconic acid, and malonic acid are used for the positive electrode mixture, and in Patent Document 4, acetic acid, phosphoric acid, sulfuric acid, etc. are used for the electrode slurry (positive electrode paste). However, the use of acid to neutralize the alkali requires a large amount of addition, as a result, the energy density of the battery may be reduced and the resistance of the battery may be increased. In addition, there is also the problem that the acid will corrode the device for making the electrode. In addition, in this method, the acidity of the organic acid and the inorganic acid is high, so a neutralization reaction with the lithium ions in the active material occurs, which may cause the problem of deterioration of the battery performance.

[0013] Patent Document 5 reports a method that uses fluorine gas to treat the positive electrode active material, fixing the residual LiOH as LiF, thereby preventing gelation and suppressing gas generation. However, fluorine gas is highly toxic and difficult to handle. In addition, the LiF produced as a byproduct increases the internal resistance of the battery, reducing the capacity. Furthermore, the capacity is reduced due to corrosion of the positive electrode active material caused by fluorine gas. Furthermore, there is the problem that the residual fluorine reacts with trace amounts of water present in the active material and the electrolyte to produce hydrogen fluoride, which is prone to cycle degradation.

[0014] Patent Document 6 reports that unreacted lithium hydroxide and impurities derived from the raw materials are removed by washing with an aqueous solution containing a lithium salt. However, this method poses problems in terms of the increased environmental load caused by wastewater discharged during washing and the costs associated with wastewater treatment.

[0015] Prior art literature

[0016] Patent Literature

[0017] Patent Document 1: Japanese Patent Application Laid-Open No. 2000-90917

[0018] Patent Document 2: Japanese Patent Application Laid-Open No. 2019-121471

[0019] Patent Document 3: Japanese Patent Application Laid-Open No. 9-306502

[0020] Patent Document 4: Japanese Patent Application Laid-Open No. 10-79244

[0021] Patent Document 5: Japanese Patent Application Laid-Open No. 2006-286240

[0022] Patent Document 6: International Publication No. 2017-034001 Summary of the Invention

[0023] Problems to be solved by the invention

[0024] In view of such circumstances, the present invention aims to provide an electrode-forming composition and an additive and gelation inhibitor for an electrode slurry comprising a positive electrode active material, a binder, and a solvent, wherein the electrode-forming composition suppresses the thickening and gelation of the electrode slurry by a simple method, thereby improving storage stability, and enabling a high concentration of solid components and suppressing battery deterioration.

[0025] Solutions for solving problems

[0026] To achieve the above-mentioned objectives, the present inventors have conducted extensive research and have discovered that by adding a specific heterocyclic compound having a nitrogen-containing five-membered ring and no oxygen atoms to an electrode slurry comprising at least a positive electrode active material, a binder, and a solvent, the thickening and gelation of the composition can be suppressed, thereby improving storage stability. Furthermore, the degradation of electrodes produced using the electrode-forming composition of the present invention caused by alkaline components in the battery is suppressed, thereby improving battery characteristics.

[0027] That is, the present invention provides the following electrode-forming composition, additive, and gelation inhibitor.

[0028] 1. An electrode-forming composition comprising a positive electrode active material, a binder, a solvent, and a heterocyclic compound, wherein the heterocyclic compound has a nitrogen-containing five-membered ring, the five-membered ring does not contain an oxygen atom, and has a carbonyl structure on the five-membered ring.

[0029] 2. The electrode-forming composition according to 1, wherein the heterocyclic ring-containing compound is attached to the positive electrode active material.

[0030] 3. The electrode-forming composition according to item 1, wherein the heterocyclic compound is an uncondensed nitrogen-containing five-membered heterocyclic compound.

[0031] 4. The electrode-forming composition according to 1, wherein the carbonyl structure exhibits proton tautomerism.

[0032] 5. The electrode-forming composition according to 4, wherein the proton tautomerism is keto-enol tautomerism.

[0033] 6. The electrode-forming composition according to item 1, wherein the heterocyclic ring-containing compound is represented by any of the following formulae (3) to (4).

[0034]

[0035] (In formulas (3) to (4), R a ~R c are each independently a hydrogen atom, a halogen atom, a carboxyl group, a hydroxyl group, a thiol group, an amino group, an optionally substituted alkyl group having 1 to 6 carbon atoms, an optionally substituted alkenyl group having 2 to 6 carbon atoms, or an optionally substituted aryl group having 6 to 12 carbon atoms, R a and R b are optionally bonded to each other to form a ring having 4 to 12 carbon atoms which may have a substituent, L is independently a single bond, a carbonyl group, an ether bond, an ester bond or an amide bond, X a and X bEach is independently a hydrogen atom, a lithium atom, a sodium atom, an optionally substituted alkyl group having 1 to 6 carbon atoms, an optionally substituted aryl group having 6 to 12 carbon atoms, or -CH2NR d 2, R d Each is independently an alkyl group having 1 to 10 carbon atoms, an alkanol group having 1 to 10 carbon atoms, an alkenyl group having 2 to 10 carbon atoms, or an aryl group having 6 to 12 carbon atoms.

[0036] 7. The electrode-forming composition according to item 1, wherein the R a ~R c 、X a and X b The substituent is at least one selected from the group consisting of a carboxyl group, a hydroxyl group, an aldehyde group, an ester group, a ketone group, an amino group, a phenyl group, a halogen atom, an alkoxysilyl group, an epoxy group, a carboxylic acid chloride group, and a thiol group.

[0037] 8. The electrode-forming composition according to 6, wherein the heterocyclic ring-containing compound is represented by the following formula (4b).

[0038]

[0039] (Where R a ~R c Same as above, R e is a hydrogen atom, a carboxyl group, a hydroxyl group, an aldehyde group, an ester group, a ketone group, an amino group, a phenyl group, a halogen atom, an alkoxysilyl group, an epoxy group, a carboxylic acid chloride group, or a thiol group.

[0040] 9. The electrode-forming composition according to item 1, wherein the heterocyclic ring-containing compound is solid at room temperature.

[0041] 10. The electrode-forming composition according to 1, further comprising a conductive auxiliary agent.

[0042] 11. The electrode-forming composition according to 1, wherein the positive electrode active material contains 30% by mass or more of Ni.

[0043] 12. The electrode-forming composition according to 1, wherein the positive electrode active material contains 40% by mass or more of Ni.

[0044] 13. The electrode-forming composition according to 1, wherein the positive electrode active material contains 50% by mass or more of Ni.

[0045] 14. The electrode-forming composition according to 1, further comprising a nonionic polymer.

[0046] 15. The electrode-forming composition according to 14, wherein the nonionic polymer is a polymer having a pyrrolidone structure or a nitrile group.

[0047] 16. The electrode-forming composition according to 15, wherein the nonionic polymer is at least one selected from the group consisting of polyvinyl pyrrolidone and polyacrylonitrile.

[0048] 17. The electrode-forming composition according to item 1, wherein the content of the heterocyclic ring-containing compound is 0.001 to 0.5% by mass in the solid content.

[0049] 18. An electrode-forming composition comprising a positive electrode active material, a binder, a solvent, and a heterocyclic compound, wherein the heterocyclic compound is represented by any of the following formulae (1) to (2).

[0050]

[0051] (In formula (1), R a and R b are each independently a hydrogen atom, a carboxyl group, a hydroxyl group, a thiol group, an alkyl group having 1 to 6 carbon atoms which may have a substituent, an alkenyl group having 2 to 6 carbon atoms which may have a substituent, or an aryl group having 6 to 12 carbon atoms which may have a substituent, R a and R b are optionally bonded to each other to form a ring having 4 to 12 carbon atoms which may have a substituent, L is independently a single bond, a carbonyl group, an ether bond, an ester bond or an amide bond, and Z is N or C-L-R c , R c is a hydrogen atom, a halogen atom, a carboxyl group, a hydroxyl group, a thiol group, an optionally substituted alkyl group having 1 to 6 carbon atoms, an optionally substituted alkenyl group having 2 to 6 carbon atoms, or an optionally substituted aryl group having 6 to 12 carbon atoms, X a A hydrogen atom, a lithium atom, a sodium atom, an alkyl group having 1 to 6 carbon atoms which may have a substituent, an aryl group having 6 to 12 carbon atoms which may have a substituent, or -CH2NR d 2, R d Each independently represents an alkyl group having 1 to 10 carbon atoms, an alkanol group having 1 to 10 carbon atoms, an alkenyl group having 2 to 10 carbon atoms, or an aryl group having 6 to 12 carbon atoms.

[0052] In formula (2), R a and R bare each independently a hydrogen atom, a halogen atom, a carboxyl group, a hydroxyl group, a thiol group, an optionally substituted alkyl group having 1 to 6 carbon atoms, an optionally substituted alkenyl group having 2 to 6 carbon atoms, or an optionally substituted aryl group having 6 to 12 carbon atoms, L is each independently a single bond, a carbonyl group, an ether bond, an ester bond, or an amide bond, X a A hydrogen atom, a lithium atom, a sodium atom, an alkyl group having 1 to 6 carbon atoms which may have a substituent, an aryl group having 6 to 12 carbon atoms which may have a substituent, or -CH2NR d 2, R d Each is independently an alkyl group having 1 to 10 carbon atoms, an alkanol group having 1 to 10 carbon atoms, an alkenyl group having 2 to 10 carbon atoms, or an aryl group having 6 to 12 carbon atoms.

[0053] 19. The electrode-forming composition according to 18, wherein the heterocyclic ring-containing compound is attached to the positive electrode active material.

[0054] 20. The electrode-forming composition according to 18, wherein the R a ~R c 、X a and X b The substituent is at least one selected from the group consisting of a carboxyl group, a hydroxyl group, an aldehyde group, an ester group, a ketone group, a phenyl group, a halogen atom, an alkoxysilyl group, an epoxy group, a carboxylic acid chloride group, and a thiol group.

[0055] 21. The electrode-forming composition according to 18, wherein the heterocyclic ring-containing compound is a heterocyclic ring-containing compound represented by the following formula (5).

[0056]

[0057] (where Ar 1 is an aromatic ring having 4 to 12 carbon atoms and optionally having a substituent, or an aliphatic ring having 4 to 10 carbon atoms and optionally having a substituent. a Same as above.)

[0058] 22. The electrode-forming composition according to 21, wherein the heterocyclic ring-containing compound is a heterocyclic ring-containing compound represented by any of the following formulae (6) to (7).

[0059]

[0060] (Where Z and X a Same as above.)

[0061] 23. The electrode-forming composition according to 18, wherein Z is N.

[0062] 24. The electrode-forming composition according to 18, further comprising a conductive auxiliary agent.

[0063] 25. The electrode-forming composition according to 18, wherein the positive electrode active material contains 30% by mass or more of Ni.

[0064] 26. The electrode-forming composition according to 18, wherein the positive electrode active material contains 40% by mass or more of Ni.

[0065] 27. The electrode-forming composition according to 18, wherein the positive electrode active material contains 50% by mass or more of Ni.

[0066] 28. The electrode-forming composition according to 18, further comprising a nonionic polymer.

[0067] 29. The electrode-forming composition according to 28, wherein the nonionic polymer is a polymer having a pyrrolidone structure or a nitrile group.

[0068] 30. The electrode-forming composition according to 29, wherein the nonionic polymer is at least one selected from the group consisting of polyvinyl pyrrolidone and polyacrylonitrile.

[0069] 31. The electrode-forming composition according to 18, wherein the content of the heterocyclic ring-containing compound is 0.001 to 0.5% by mass in the solid content.

[0070] 32. An electrode layer obtained from the electrode-forming composition according to any one of 1 to 31.

[0071] 33. An electrode comprising the electrode layer according to 32.

[0072] 34. A secondary battery comprising the electrode according to 33.

[0073] 35. A method for producing an electrode-forming composition, which is the method for producing an electrode-forming composition as described in 1, comprising: a step of mixing a positive electrode active material, a binder, and a solvent to prepare a dispersion; and a step of mixing the dispersion with a heterocyclic compound.

[0074] 36. The method for producing an electrode-forming composition according to 35, wherein a conductive auxiliary agent is further mixed in the step of preparing the dispersion.

[0075] 37. A method for manufacturing an electrode-forming composition, which is the method for manufacturing an electrode-forming composition as described in 18, comprising: a process of mixing a positive electrode active material, a binder, and a solvent to prepare a dispersion; and a process of mixing the above-mentioned dispersion with a heterocyclic compound.

[0076] 38. The method for producing an electrode-forming composition according to 37, wherein a conductive auxiliary agent is further mixed in the step of preparing the dispersion.

[0077] 39. An additive for an electrode slurry comprising a positive electrode active material, a binder, and a solvent, wherein the additive comprises a heterocyclic compound, wherein the heterocyclic compound has a nitrogen-containing five-membered ring, the five-membered ring does not contain an oxygen atom, and has a carbonyl structure on the five-membered ring.

[0078] 40. The additive according to 39, wherein the heterocyclic compound is an uncondensed nitrogen-containing five-membered heterocyclic compound.

[0079] 41. The additive according to 39, wherein the carbonyl structure represents proton tautomerism.

[0080] 42. The additive according to 41, wherein the proton tautomerism is keto-enol tautomerism.

[0081] 43. The additive according to 39, wherein the heterocyclic ring-containing compound is represented by any of the following formulae (3) to (4).

[0082]

[0083] (Where R a ~R c are each independently a hydrogen atom, a halogen atom, a carboxyl group, a hydroxyl group, a thiol group, an amino group, an optionally substituted alkyl group having 1 to 6 carbon atoms, an optionally substituted alkenyl group having 2 to 6 carbon atoms, or an optionally substituted aryl group having 6 to 12 carbon atoms, R a and R b are optionally bonded to each other to form a ring having 4 to 12 carbon atoms which may have a substituent, L is independently a single bond, a carbonyl group, an ether bond, an ester bond or an amide bond, X a and X b Each is independently a hydrogen atom, a lithium atom, a sodium atom, an optionally substituted alkyl group having 1 to 6 carbon atoms, an optionally substituted aryl group having 6 to 12 carbon atoms, or -CH2NR d 2, R d Each is independently an alkyl group having 1 to 10 carbon atoms, an alkanol group having 1 to 10 carbon atoms, an alkenyl group having 2 to 10 carbon atoms, or an aryl group having 6 to 12 carbon atoms.

[0084] 44. The additive according to 43, wherein the above R a ~R c 、X a and X bThe substituent is at least one selected from the group consisting of a carboxyl group, a hydroxyl group, an aldehyde group, an ester group, a ketone group, an amino group, a phenyl group, a halogen atom, an alkoxysilyl group, an epoxy group, a carboxylic acid chloride group, and a thiol group.

[0085] 45. The additive according to 43, wherein the heterocyclic ring-containing compound is represented by the following formula (4b).

[0086]

[0087] (Where R a ~R c Same as above, R e is a hydrogen atom, a carboxyl group, a hydroxyl group, an aldehyde group, an ester group, a ketone group, an amino group, a phenyl group, a halogen atom, an alkoxysilyl group, an epoxy group, a carboxylic acid chloride group, or a thiol group.

[0088] 46. The additive according to 39, wherein the heterocyclic compound is solid at room temperature.

[0089] 47. The additive according to 39, wherein the positive electrode active material contains 30% by mass or more of Ni.

[0090] 48. The additive according to 39, further comprising a nonionic polymer.

[0091] 49. The additive according to 48, wherein the nonionic polymer is a polymer having a pyrrolidone structure or a nitrile group.

[0092] 50. The additive according to 49, wherein the nonionic polymer is at least one selected from the group consisting of polyvinyl pyrrolidone and polyacrylonitrile.

[0093] 51. The additive according to 39, further comprising a solvent.

[0094] 52. An additive for an electrode slurry comprising a positive electrode active material, a binder, and a solvent, wherein the additive comprises a heterocyclic ring-containing compound represented by any of the following formulas (1) to (2).

[0095]

[0096] (In formula (1), R a and R b are each independently a hydrogen atom, a carboxyl group, a hydroxyl group, a thiol group, an alkyl group having 1 to 6 carbon atoms which may have a substituent, an alkenyl group having 2 to 6 carbon atoms which may have a substituent, or an aryl group having 6 to 12 carbon atoms which may have a substituent, R a and R bare optionally bonded to each other to form a ring having 4 to 12 carbon atoms which may have a substituent, L is independently a single bond, a carbonyl group, an ether bond, an ester bond or an amide bond, and Z is N or C-L-R c , R c is a hydrogen atom, a halogen atom, a carboxyl group, a hydroxyl group, a thiol group, an optionally substituted alkyl group having 1 to 6 carbon atoms, an optionally substituted alkenyl group having 2 to 6 carbon atoms, or an optionally substituted aryl group having 6 to 12 carbon atoms, X a A hydrogen atom, a lithium atom, a sodium atom, an alkyl group having 1 to 6 carbon atoms which may have a substituent, an aryl group having 6 to 12 carbon atoms which may have a substituent, or -CH2NR d 2, R d Each independently represents an alkyl group having 1 to 10 carbon atoms, an alkanol group having 1 to 10 carbon atoms, an alkenyl group having 2 to 10 carbon atoms, or an aryl group having 6 to 12 carbon atoms.

[0097] In formula (2), R a and R b are each independently a hydrogen atom, a halogen atom, a carboxyl group, a hydroxyl group, a thiol group, an optionally substituted alkyl group having 1 to 6 carbon atoms, an optionally substituted alkenyl group having 2 to 6 carbon atoms, or an optionally substituted aryl group having 6 to 12 carbon atoms, L is each independently a single bond, a carbonyl group, an ether bond, an ester bond, or an amide bond, X a A hydrogen atom, a lithium atom, a sodium atom, an alkyl group having 1 to 6 carbon atoms which may have a substituent, an aryl group having 6 to 12 carbon atoms which may have a substituent, or -CH2NR d 2, R d Each is independently an alkyl group having 1 to 10 carbon atoms, an alkanol group having 1 to 10 carbon atoms, an alkenyl group having 2 to 10 carbon atoms, or an aryl group having 6 to 12 carbon atoms.

[0098] 53. The additive according to 52, wherein the positive electrode active material contains 30% by mass or more of Ni.

[0099] 54. The additive according to 52, further comprising a nonionic polymer.

[0100] 55. The additive according to 54, wherein the nonionic polymer is a polymer having a pyrrolidone structure or a nitrile group.

[0101] 56. The additive according to 55, wherein the nonionic polymer is at least one selected from the group consisting of polyvinyl pyrrolidone and polyacrylonitrile.

[0102] 57. The additive according to 52, further comprising a solvent.

[0103] 58. A gelation inhibitor for an electrode slurry comprising a positive electrode active material, a binder, and a solvent, wherein the gelation inhibitor comprises a heterocyclic compound having a nitrogen-containing five-membered ring, and the nitrogen-containing five-membered ring does not contain an oxygen atom.

[0104] 59. The gelation inhibitor according to 58, wherein the heteroatom contained in the nitrogen-containing five-membered ring is only a nitrogen atom.

[0105] 60. The gelation inhibitor according to 59, wherein the nitrogen-containing five-membered ring contains two or three nitrogen atoms.

[0106] 61. The gelation inhibitor according to 58, wherein the heterocyclic ring-containing compound has a carbonyl structure on the five-membered ring.

[0107] 62. The gelation inhibitor according to 61, wherein the heterocyclic compound is an uncondensed nitrogen-containing five-membered heterocyclic compound.

[0108] 63. The gelation inhibitor according to 61, wherein the carbonyl structure represents proton tautomerism.

[0109] 64. The gelation inhibitor according to 63, wherein the proton tautomerism is keto-enol tautomerism.

[0110] 65. The gelation inhibitor according to 58, comprising a heterocyclic ring-containing compound represented by any of the following formulas (3) to (4).

[0111]

[0112] (Where R a ~R c are each independently a hydrogen atom, a halogen atom, a carboxyl group, a hydroxyl group, a thiol group, an amino group, an optionally substituted alkyl group having 1 to 6 carbon atoms, an optionally substituted alkenyl group having 2 to 6 carbon atoms, or an optionally substituted aryl group having 6 to 12 carbon atoms, R a and R b are optionally bonded to each other to form a ring having 4 to 12 carbon atoms which may have a substituent, L is independently a single bond, a carbonyl group, an ether bond, an ester bond or an amide bond, X a and X b Each is independently a hydrogen atom, a lithium atom, a sodium atom, an optionally substituted alkyl group having 1 to 6 carbon atoms, an optionally substituted aryl group having 6 to 12 carbon atoms, or -CH2NR d 2, R d Each is independently an alkyl group having 1 to 10 carbon atoms, an alkanol group having 1 to 10 carbon atoms, an alkenyl group having 2 to 10 carbon atoms, or an aryl group having 6 to 12 carbon atoms.

[0113] 66. The gelation inhibitor according to 65, wherein the above R a ~R c 、X a and X b The substituent is at least one selected from the group consisting of a carboxyl group, a hydroxyl group, an aldehyde group, an ester group, a ketone group, an amino group, a phenyl group, a halogen atom, an alkoxysilyl group, an epoxy group, a carboxylic acid chloride group, and a thiol group.

[0114] 67. The gelation inhibitor according to 65, wherein the heterocyclic ring-containing compound is represented by the following formula (4b).

[0115]

[0116] (Where R a ~R c Same as above, R e is a hydrogen atom, a carboxyl group, a hydroxyl group, an aldehyde group, an ester group, a ketone group, an amino group, a phenyl group, a halogen atom, an alkoxysilyl group, an epoxy group, a carboxylic acid chloride group, or a thiol group.

[0117] 68. The gelation inhibitor according to 58, wherein the heterocyclic ring-containing compound is solid at room temperature.

[0118] 69. The gelation inhibitor according to 58, wherein the positive electrode active material contains 30 mass % or more of Ni.

[0119] 70. The gelation inhibitor according to 58, further comprising a nonionic polymer.

[0120] 71. The gelation inhibitor according to 70, wherein the nonionic polymer is a polymer having a pyrrolidone structure or a nitrile group.

[0121] 72. The gelation inhibitor according to 71, wherein the nonionic polymer is at least one selected from the group consisting of polyvinyl pyrrolidone and polyacrylonitrile.

[0122] 73. The gelation inhibitor according to 58, further comprising a solvent.

[0123] 74. A gelation inhibitor for an electrode slurry comprising a positive electrode active material, a binder, and a solvent, wherein the gelation inhibitor comprises a heterocyclic ring-containing compound represented by any of the following formulas (1) to (2).

[0124]

[0125] (In formula (1), R a and R bare each independently a hydrogen atom, a carboxyl group, a hydroxyl group, a thiol group, an alkyl group having 1 to 6 carbon atoms which may have a substituent, an alkenyl group having 2 to 6 carbon atoms which may have a substituent, or an aryl group having 6 to 12 carbon atoms which may have a substituent, R a and R b are optionally bonded to each other to form a ring having 4 to 12 carbon atoms which may have a substituent, L is independently a single bond, a carbonyl group, an ether bond, an ester bond or an amide bond, and Z is N or C-L-R c , R c is a hydrogen atom, a halogen atom, a carboxyl group, a hydroxyl group, a thiol group, an optionally substituted alkyl group having 1 to 6 carbon atoms, an optionally substituted alkenyl group having 2 to 6 carbon atoms, or an optionally substituted aryl group having 6 to 12 carbon atoms, X a A hydrogen atom, a lithium atom, a sodium atom, an alkyl group having 1 to 6 carbon atoms which may have a substituent, an aryl group having 6 to 12 carbon atoms which may have a substituent, or -CH2NR d 2, R d Each independently represents an alkyl group having 1 to 10 carbon atoms, an alkanol group having 1 to 10 carbon atoms, an alkenyl group having 2 to 10 carbon atoms, or an aryl group having 6 to 12 carbon atoms.

[0126] In formula (2), R a and R b are each independently a hydrogen atom, a halogen atom, a carboxyl group, a hydroxyl group, a thiol group, an optionally substituted alkyl group having 1 to 6 carbon atoms, an optionally substituted alkenyl group having 2 to 6 carbon atoms, or an optionally substituted aryl group having 6 to 12 carbon atoms, L is each independently a single bond, a carbonyl group, an ether bond, an ester bond, or an amide bond, X a and X b Each is independently a hydrogen atom, a lithium atom, a sodium atom, an optionally substituted alkyl group having 1 to 6 carbon atoms, an optionally substituted aryl group having 6 to 12 carbon atoms, or -CH2NR d 2, R d Each is independently an alkyl group having 1 to 10 carbon atoms, an alkanol group having 1 to 10 carbon atoms, an alkenyl group having 2 to 10 carbon atoms, or an aryl group having 6 to 12 carbon atoms.

[0127] 75. The gelation inhibitor according to 74, wherein the above R a ~R c 、X a and X b The substituent is at least one selected from the group consisting of a carboxyl group, a hydroxyl group, an aldehyde group, an ester group, a ketone group, a phenyl group, a halogen atom, an alkoxysilyl group, an epoxy group, a carboxylic acid chloride group, and a thiol group.

[0128] 76. The gelation inhibitor according to 74, wherein the heterocyclic compound is a heterocyclic compound represented by the following formula (5).

[0129]

[0130] (where Ar 1 is an aromatic ring having 4 to 12 carbon atoms and optionally having a substituent, or an aliphatic ring having 4 to 10 carbon atoms and optionally having a substituent. a Same as above.)

[0131] 77. The gelation inhibitor according to 76, wherein the heterocyclic compound is a heterocyclic compound represented by any of the following formulas (6) to (7).

[0132]

[0133] (Where Z and X a Same as above.)

[0134] 78. The gelation inhibitor according to 74, wherein the above Z is N.

[0135] 79. The gelation inhibitor according to 74, wherein the positive electrode active material contains 30% by mass or more of Ni.

[0136] 80. The gelation inhibitor according to 74, further comprising a nonionic polymer.

[0137] 81. The gelation inhibitor according to 80, wherein the nonionic polymer is a polymer having a pyrrolidone structure or a nitrile group.

[0138] 82. The gelation inhibitor according to 81, wherein the nonionic polymer is at least one selected from the group consisting of polyvinyl pyrrolidone and polyacrylonitrile.

[0139] 83. The gelation inhibitor according to 74, further comprising a solvent.

[0140] Effects of the Invention

[0141] The electrode-forming composition of the present invention is less susceptible to thickening and gelling, exhibits high storage stability, and is therefore preferably used to form a positive electrode for an energy storage device. When manufacturing an energy storage device comprising an electrode produced using this composition, the following advantages are expected: improved storage stability of the composition leads to improved quality and yield; high solids concentration leads to reduced costs and reduced environmental impact; and degradation within the battery caused by alkaline components is suppressed, contributing to reduced manufacturing costs and improved battery characteristics for the energy storage device.

[0142] In the present invention, the aforementioned thickening and gelation inhibition effects are achieved by adding a specific heterocyclic compound to an electrode slurry comprising a positive electrode active material, a binder, and a solvent. More than half of the heterocyclic compound adheres to the positive electrode active material, forming a protective film on the surface of the positive electrode active material. This protective film inhibits proton exchange reactions between the active material and water, and also inhibits reactions between alkaline components derived from the positive electrode active material and the binder, particularly a fluorine-based binder. As a result, thickening and gelation of the composition can be inhibited, improving storage stability.

[0143] It is known that when a positive electrode active material containing a large amount of Ni is used in an electrode slurry containing a positive electrode active material, a binder, and a solvent, for example, when a positive electrode active material containing 30% by mass or more of Ni is used, gelation of the electrode slurry is likely to occur. By adding the additive or gelation inhibitor of the present invention to the electrode slurry, the gelation of the electrode slurry can be significantly inhibited.

[0144] According to the present invention, by suppressing the thickening and gelation of the electrode slurry, a homogeneous positive electrode layer can be formed. Furthermore, the solids concentration in the electrode slurry can be increased, reducing the cost and environmental impact of manufacturing energy storage devices. Furthermore, corrosion of aluminum foil, typically used as a current collector foil, caused by alkaline components and degradation of battery characteristics due to reactions with the electrolyte can be suppressed. Therefore, according to the present invention, regardless of the type of conductive additive or binder, the gelation of the electrode slurry can be inhibited. However, the present invention is not limited to these mechanisms. DETAILED DESCRIPTION

[0145] [Electrode-forming composition]

[0146] The present invention is characterized in that when an additive comprising a heterocyclic compound or a gelation inhibitor comprising a heterocyclic compound is added to an electrode slurry comprising a positive electrode active material, a binder, and a solvent, more than half of the additive adheres to the positive electrode active material. Adhesion is not limited to the method of adhesion, and adhesion may occur via chemical bonds such as ionic bonds and hydrogen bonds, in addition to physical adsorption and chemical adsorption.

[0147] Of the additive comprising a heterocyclic compound or the gelation inhibitor comprising a heterocyclic compound contained in the electrode-forming composition, preferably 60% by mass or more is attached to the positive electrode active material, more preferably 70% by mass or more is attached to the positive electrode active material, further preferably 75% by mass or more is attached to the positive electrode active material, and particularly preferably 80% by mass or more is attached to the positive electrode active material.

[0148] In the present invention, the term “gelation inhibition” related to the inhibition of gelation means that the gelation of the electrode-forming composition is inhibited compared to a case where the additive or gelation inhibitor of the present invention is not contained.

[0149] <Heterocyclic compounds>

[0150] The electrode-forming composition of the present invention includes a positive electrode active material, a binder, a solvent, and a heterocyclic compound. The heterocyclic compound has a nitrogen-containing five-membered ring and the five-membered ring does not contain an oxygen atom.

[0151] The heterocyclic ring-containing compound of the present invention is different from the solvent of the present invention and is preferably solid at room temperature. In the present invention, "solid at room temperature" means that the melting point at 1 atmosphere is 25°C or higher.

[0152] The five-membered ring does not contain an oxygen atom means that the five atoms constituting the five-membered ring are not oxygen atoms.

[0153] Having a carbonyl structure (carbonyl group) on a ring means that at least one carbon atom among the five atoms constituting the five-membered ring is bonded to an oxygen atom via a double bond.

[0154] For example, furan contains an oxygen atom in the five-membered ring and does not have a carbonyl structure (carbonyl group) on the ring.

[0155] For example, pyrazolone contains two nitrogen atoms in the five-membered ring, the five-membered ring does not contain an oxygen atom, and has a carbonyl structure (carbonyl group) on the ring.

[0156] For example, oxazoline contains one oxygen atom and one nitrogen atom in each of the five-membered rings and does not have a carbonyl structure (carbonyl group) on the ring.

[0157] As the heterocyclic ring-containing compound, it is preferred that the hetero atoms contained in the nitrogen-containing five-membered ring are only nitrogen atoms, and it is more preferred that the nitrogen atoms contained in the nitrogen-containing five-membered ring are two or three.

[0158] Furthermore, the heterocyclic compound preferably has a carbonyl structure (carbonyl group) on the nitrogen-containing five-membered ring. In this case, the nitrogen-containing five-membered ring is more preferably uncondensed. Furthermore, the carbonyl structure further preferably exhibits proton tautomerism, and even more preferably exhibits keto-enol tautomerism.

[0159] It should be noted that keto-enol tautomerism refers to tautomerism between a ketone (ketone, aldehyde) and an enol.

[0160] In the present invention, the heterocyclic ring-containing compound is preferably not a compound having two or more bonds selected from the group consisting of amide bonds and thioether bonds in a nitrogen-containing five-membered ring.

[0161] Furthermore, the heterocyclic ring-containing compound preferably does not have a partial structure represented by the following formula.

[0162]

[0163] (*Indicates a bond.)

[0164] Specific examples of the heterocyclic ring-containing compound include compounds represented by any of the following formulae (1) to (4).

[0165]

[0166] (In formula (1), R a and R b are each independently a hydrogen atom, a carboxyl group, a hydroxyl group, a thiol group, an amino group, an alkyl group having 1 to 6 carbon atoms which may have a substituent, an alkenyl group having 2 to 6 carbon atoms which may have a substituent, or an aryl group having 6 to 12 carbon atoms which may have a substituent, R a and R b are bonded to each other to form a ring having 4 to 12 carbon atoms which may have a substituent, L is independently a single bond, a carbonyl group, an ether bond, an ester bond or an amide bond, and Z is N or C-L-R c , R c is a hydrogen atom, a halogen atom, a carboxyl group, a hydroxyl group, a thiol group, an amino group, an optionally substituted alkyl group having 1 to 6 carbon atoms, an optionally substituted alkenyl group having 2 to 6 carbon atoms, or an optionally substituted aryl group having 6 to 12 carbon atoms, X a Each is independently a hydrogen atom, a lithium atom, a sodium atom, an optionally substituted alkyl group having 1 to 6 carbon atoms, an optionally substituted aryl group having 6 to 12 carbon atoms, or -CH2NR d 2, R d Each independently represents an alkyl group having 1 to 10 carbon atoms, an alkanol group having 1 to 10 carbon atoms, an alkenyl group having 2 to 10 carbon atoms, or an aryl group having 6 to 12 carbon atoms.

[0167] In formulas (2) to (4), R a ~R c are each independently a hydrogen atom, a halogen atom, a carboxyl group, a hydroxyl group, a thiol group, an amino group, an optionally substituted alkyl group having 1 to 6 carbon atoms, an optionally substituted alkenyl group having 2 to 6 carbon atoms, or an optionally substituted aryl group having 6 to 12 carbon atoms, R a and R b are optionally bonded to each other to form a ring having 4 to 12 carbon atoms which may have a substituent, L is independently a single bond, a carbonyl group, an ether bond, an ester bond or an amide bond, X a and X bEach is independently a hydrogen atom, a lithium atom, a sodium atom, an optionally substituted alkyl group having 1 to 6 carbon atoms, an optionally substituted aryl group having 6 to 12 carbon atoms, or -CH2NR d 2, R d Each is independently an alkyl group having 1 to 10 carbon atoms, an alkanol group having 1 to 10 carbon atoms, an alkenyl group having 2 to 10 carbon atoms, or an aryl group having 6 to 12 carbon atoms.

[0168] The above formulas (2), (3), and (4) may also be structural isomers. Specifically, examples of isomers of the heterocyclic compound represented by formula (2) include heterocyclic compounds represented by the following formulas (2-A) to (2-C), examples of isomers of the heterocyclic compound represented by formula (3) include heterocyclic compounds represented by the following formulas (3-A) to (3-E), and examples of isomers of the heterocyclic compound represented by formula (4) include heterocyclic compounds represented by the following formulas (4-A) to (4-G).

[0169] In X a and X b When each of X is a hydrogen atom, a lithium atom, and a sodium atom, the tautomer is preferred among the above structural isomers. a and X b When both atoms are hydrogen atoms, the tautomers are also called proton tautomers.

[0170]

[0171] (Where R a ~R c , L, X a 、X b Same as above.)

[0172] As R a ~R c The alkyl group having 1 to 6 carbon atoms shown may be any of linear, branched, and cyclic types. Specific examples thereof include linear or branched alkyl groups having 1 to 6 carbon atoms, such as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, and n-hexyl; and cyclic alkyl groups having 3 to 6 carbon atoms, such as cyclopropyl, cyclobutyl, cyclopentyl, and cyclohexyl.

[0173] As R a ~R cExamples of the alkenyl group having 2 to 6 carbon atoms include vinyl, n-1-propenyl, n-2-propenyl, 1-methylvinyl, n-1-butenyl, n-2-butenyl, n-3-butenyl, 2-methyl-1-propenyl, 2-methyl-2-propenyl, 1-ethylvinyl, 1-methyl-1-propenyl, 1-methyl-2-propenyl, and n-1-pentenyl.

[0174] As R a ~R c Examples of the aryl group having 6 to 12 carbon atoms include phenyl, tolyl, 1-naphthyl, and 2-naphthyl.

[0175] As the above R a and R b Examples of the ring having 4 to 12 carbon atoms formed by bonding together include a cyclopentane ring, a cyclohexane ring, a benzene ring, a naphthalene ring, a triazole ring, a pyridine ring, and a pyrazine ring.

[0176] The above R a ~R c It may optionally have a substituent. Examples of the substituent include a carboxyl group, a hydroxyl group, an aldehyde group, an ester group, a ketone group, an amino group, a phenyl group, a halogen atom, an alkoxysilyl group, an epoxy group, a carboxylic acid chloride group, a thiol group, and the like. Examples of the alkoxysilyl group include a trimethoxysilyl group, a dimethoxymethylsilyl group, a methoxydimethylsilyl group, a triethoxysilyl group, a diethoxymethylsilyl group, and an ethoxydimethylsilyl group. In the present invention, a carboxyl group is preferred. In the above R a ~R c When the alkylene group has a substituent, the number of the substituents is preferably 1 to 6, more preferably 1 to 3.

[0177] As the above R a ~R c , preferably a hydrogen atom, a carboxyl group, an alkyl group having 1 to 6 carbon atoms which may have a substituent, or an aryl group having 6 to 12 carbon atoms which may have a substituent, and R a and R b They are bonded to each other to form a ring having 4 to 12 carbon atoms which may have a substituent.

[0178] In addition, as the above R a ~R c , more preferably a hydrogen atom, a carboxyl group, an alkyl group having 1 to 6 carbon atoms, or an aryl group having 6 to 12 carbon atoms, and R a and R b They are bonded to each other to form an aromatic ring having 4 to 12 carbon atoms which may have a substituent.

[0179] Moreover, as the above R a ~R c, more preferably a hydrogen atom, a carboxyl group, an alkyl group having 1 to 3 carbon atoms, or an aryl group having 6 to 10 carbon atoms, and R a and R b They are bonded to each other to form an aromatic ring having 6 to 10 carbon atoms which may have a substituent.

[0180] Moreover, as the above R a ~R c , further preferably a hydrogen atom, a carboxyl group, a methyl group, a phenyl group, and R a and R b They are bonded to each other to form a benzene ring which may have a substituent.

[0181] L is preferably a single bond, an ester bond, or an amide bond, and more preferably a single bond.

[0182] As Z, N is preferred.

[0183] As X a and X b The alkyl group having 1 to 6 carbon atoms shown may be any of linear, branched, and cyclic types. Specific examples thereof include linear or branched alkyl groups having 1 to 6 carbon atoms, such as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, and n-hexyl; and cyclic alkyl groups having 3 to 6 carbon atoms, such as cyclopropyl, cyclobutyl, cyclopentyl, and cyclohexyl.

[0184] As X a and X b Examples of the aryl group having 6 to 12 carbon atoms include phenyl, tolyl, 1-naphthyl, and 2-naphthyl.

[0185] The above X a and X b It may optionally have a substituent. Examples of the substituent include a carboxyl group, a hydroxyl group, an aldehyde group, an ester group, a ketone group, an amino group, a phenyl group, a halogen atom, an alkoxysilyl group, an epoxy group, a carboxylic acid chloride group, and a thiol group. Examples of the alkoxysilyl group include a trimethoxysilyl group, a dimethoxymethylsilyl group, a methoxydimethylsilyl group, a triethoxysilyl group, a diethoxymethylsilyl group, and an ethoxydimethylsilyl group. In the present invention, a carboxyl group and an alkoxysilyl group are preferred, and a carboxyl group and a trimethoxysilyl group are more preferred.

[0186] As R dThe alkyl group having 1 to 10 carbon atoms may be any of linear, branched or cyclic. Specific examples thereof include linear or branched alkyl groups having 1 to 10 carbon atoms, such as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, neopentyl, n-hexyl, n-octyl, n-nonyl and n-decyl; and cyclic alkyl groups having 3 to 10 carbon atoms, such as cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl and 1-adamantyl.

[0187] As R d Examples of the alkanol group having 1 to 10 carbon atoms include hydroxymethyl, hydroxyethyl, hydroxypropyl, hydroxybutyl, hydroxypentyl, hydroxyhexyl, hydroxyoctyl, hydroxynonyl, and hydroxydecyl.

[0188] As R d Examples of the alkenyl group having 2 to 10 carbon atoms include vinyl, n-1-propenyl, n-2-propenyl, 1-methylvinyl, n-1-butenyl, n-2-butenyl, n-3-butenyl, 2-methyl-1-propenyl, 2-methyl-2-propenyl, 1-ethylvinyl, 1-methyl-1-propenyl, 1-methyl-2-propenyl, n-1-pentenyl, and n-1-decenyl.

[0189] As R d Examples of the aryl group having 6 to 12 carbon atoms include phenyl, tolyl, 1-naphthyl, and 2-naphthyl.

[0190] As the above X a and X b , preferably a hydrogen atom, a lithium atom, a sodium atom, an alkyl group having 1 to 6 carbon atoms which may have a substituent, an aryl group having 6 to 12 carbon atoms which may have a substituent, and -CH2NR d 2.

[0191] In addition, as the above X a and X b , preferably a hydrogen atom, a lithium atom, a sodium atom, an alkyl group having 1 to 4 carbon atoms, an aryl group having 6 to 10 carbon atoms, and -CH2NR d 2.

[0192] Moreover, as the above X a and X b , more preferably a hydrogen atom, a lithium atom, a sodium atom, an alkyl group having 1 to 3 carbon atoms, an aryl group having 6 to 8 carbon atoms, and -CH2NR d 2.

[0193] Moreover, as the above X a and X b, more preferably hydrogen atom, lithium atom, sodium atom, methyl group, phenyl group and -CH2NR d 2.

[0194] As the above R d , preferably an alkyl group having 1 to 3 carbon atoms and an aryl group having 6 to 10 carbon atoms, more preferably a methyl group and a phenyl group.

[0195] As the heterocyclic ring-containing compounds represented by the above formulae (1) to (4), preferred are heterocyclic ring-containing compounds represented by the following formulae (1a) to (4a).

[0196]

[0197] (Where R a ~R c , Z, X a 、X b Same as above.)

[0198] Furthermore, the heterocyclic ring-containing compound is more preferably a heterocyclic ring-containing compound represented by the following formula (5).

[0199]

[0200] (where Ar 1 is an aromatic ring having 4 to 12 carbon atoms and optionally having a substituent, or an aliphatic ring having 4 to 10 carbon atoms and optionally having a substituent. a Same as above.)

[0201] The heterocyclic ring-containing compound is more preferably a heterocyclic ring-containing compound represented by any of the following formulae (6) to (7).

[0202]

[0203] (Where Z and X a Same as above.)

[0204] Furthermore, the heterocyclic ring-containing compound is more preferably a heterocyclic ring-containing compound represented by the above-mentioned formula (5), and more preferably a heterocyclic ring-containing compound represented by the following formula (4b).

[0205]

[0206] (Where R a ~R c Same as above, R e is a hydrogen atom, a carboxyl group, a hydroxyl group, an aldehyde group, an ester group, a ketone group, an amino group, a phenyl group, a halogen atom, an alkoxysilyl group, an epoxy group, a carboxylic acid chloride group, or a thiol group.

[0207] It should be noted that in the above formula (4b), R e When it is a hydrogen atom, it corresponds to X in the above formula (4) a The scheme without substituents. In addition, in R e When R is other than a hydrogen atom, e Equivalent to X in the above formula (4) a The substituents possessed by a and X b The substituents are the same as those described in the description of the substituents possessed.

[0208] Furthermore, the heterocyclic ring-containing compound is more preferably a heterocyclic ring-containing compound represented by the following formula (8).

[0209]

[0210] (Where R a ~R c Same as above.)

[0211] Specific examples of the heterocyclic ring-containing compound represented by the above formula (1) include heterocyclic ring-containing compounds represented by the following formulas (1-1) to (1-15).

[0212]

[0213] *The structure of the heterocyclic ring-containing compound represented by formula (1-6) is the structure of a compound described as X-12-1214A manufactured by Shin-Etsu Chemical Co., Ltd. in the company's catalog.

[0214] Specific examples of the heterocyclic ring-containing compound represented by the above formula (2) include heterocyclic ring-containing compounds represented by the following formulas (2-1) to (2-7).

[0215]

[0216] Specific examples of the heterocyclic ring-containing compound represented by the above formula (3) include heterocyclic ring-containing compounds represented by the following formulas (3-1) to (3-13).

[0217]

[0218] Specific examples of the heterocyclic ring-containing compound represented by the above formula (4) include heterocyclic ring-containing compounds represented by the following formulas (4-1) to (4-14).

[0219]

[0220] The content of the above-mentioned heterocyclic compound is preferably 0.001 to 4% by mass in the solid component, more preferably 0.001 to 2% by mass, further preferably 0.001 to 0.5% by mass, further preferably 0.001 to 0.3% by mass, and particularly preferably 0.001 to 0.2% by mass. In addition, the further preferred lower limit of the content of the above-mentioned heterocyclic compound is 0.01% by mass in the solid component. By setting the content of the heterocyclic compound to be within the above range, the gelation of the electrode-forming composition can be effectively suppressed, and the battery characteristics of the obtained battery can also be maintained. It should be noted that, in the present invention, solid content refers to the components other than the solvent constituting the composition (hereinafter the same).

[0221] In addition, the content of the heterocyclic compound is preferably 0.001 to 4 parts by mass, more preferably 0.001 to 2 parts by mass, further preferably 0.001 to 0.5 parts by mass, further preferably 0.001 to 0.3 parts by mass, and particularly preferably 0.001 to 0.2 parts by mass relative to 100 parts by mass of the positive electrode active material. By setting the content of the heterocyclic compound within the above range, the gelation of the electrode-forming composition can be effectively suppressed, and the battery characteristics of the resulting battery can be maintained.

[0222] Furthermore, the content of the heterocyclic compound is preferably 0.1 to 50 parts by mass, more preferably 0.1 to 30 parts by mass, and even more preferably 0.1 to 20 parts by mass, relative to 100 parts by mass of the binder. By setting the content of the heterocyclic compound within the above range, gelation of the electrode-forming composition can be effectively suppressed, and the battery characteristics of the resulting battery can be maintained.

[0223] <Positive electrode active material>

[0224] As the positive electrode active material, a material that meets the above conditions can be appropriately selected from various active materials for electrodes used in energy storage devices such as secondary batteries. For example, in the case of lithium secondary batteries and lithium ion secondary batteries, chalcogen compounds or lithium ion-containing chalcogen compounds, polyanionic compounds, elemental sulfur and compounds thereof that can occlude / release lithium ions can be used. From the perspective of further improving battery capacity, using less rare metals and achieving low costs, it is preferred to contain 30% or more Ni by mass. In the present invention, when considering further reducing the amount of rare metals used to obtain a battery with a larger capacity, a positive electrode active material containing 35% or more Ni by mass is more preferred, a positive electrode active material containing 40% or more Ni by mass is further preferred, a positive electrode active material containing 50% or more Ni by mass is further preferred, and a positive electrode active material containing 55% or more Ni by mass is particularly preferred. In addition, the upper limit is not particularly limited and is generally 65% or less by mass.

[0225] Examples of lithium ion-containing chalcogen compounds include LiNiO2, Li x Ni y M 1－y O2 (M represents at least one metal element selected from Co, Mn, Ti, Cr, V, Al, Sn, Pb and Zn, 0.05≤x≤1.10, 0.3≤y≤1.0), Li a Ni (1－x－y) Co x M 1 y M 2 z O2(M 1 represents at least one selected from the group consisting of Mn and Al, M 2 It represents at least one selected from the group consisting of Zr, Ti, Mg, B, Zr, W, and V, 1.00≤a≤1.50, 0.00≤x≤0.50, 0≤y≤0.50, 0.000≤z≤0.020), etc.

[0226] Examples of polyanionic compounds include LiFePO4, Li a Mn b Fe c D d PO4 (1.00≤a≤1.15, 0.01≤b≤0.99, 0.01≤c≤0.99, 0.00≤d≤0.10, D is selected from Co, Mn, Ti, Cr, V, Al, Sn, Pb and Zn, at least a part of which has an olivine structure) etc.

[0227] Examples of the sulfur compound include sulfur, Li2S, FeS2, TiS2, MoS2, and rubicin.

[0228] These positive electrode active materials may be used alone or in combination of two or more.

[0229] In the present invention, among the above-mentioned positive electrode active materials, Li a Ni (1－x－y) Co x M 1 y M 2 z X w O2(M 1 represents at least one selected from the group consisting of Mn and Al, M 2represents at least one selected from the group consisting of Zr, Ti, Mg, W, and V, 1.00≤a≤1.50, 0.00≤x≤0.50, 0≤y≤0.50, 0.000≤z≤0.020, 0.000≤w≤0.020). These active materials may be used alone or in combination of two or more.

[0230] The content of the positive electrode active material in the solid content is preferably 88.0 to 99.949 mass %, more preferably 88.0 to 99.899 mass %, and even more preferably 95.0 to 99.0 mass %.

[0231] As the above-mentioned adhesive, it can be appropriately selected from known materials and used without particular limitation. Specific examples thereof include: polyvinylidene fluoride (PVdF), polytetrafluoroethylene; fluorine-based adhesives such as copolymers containing at least one monomer selected from the group consisting of vinylidene fluoride, tetrafluoroethylene and hexafluoropropylene; and non-aqueous adhesives such as polyimide, ethylene-propylene-diene terpolymer, styrene-butadiene rubber, polyethylene and polypropylene. In the present invention, from the perspective of improving the storage stability of the composition, it is preferred to use a fluorine-based adhesive. In addition, the above-mentioned fluorine-based adhesive is preferably modified with polar functional groups such as carboxyl groups and hydroxyl groups. It should be noted that the above-mentioned polar functional groups can be confirmed by the following method: in the measurement using a nuclear magnetic resonance device (NMR device), whether there is a clear peak detected in the range of 10 to 15 ppm. The above-mentioned adhesives can be used alone or in combination of two or more.

[0232] From the viewpoint of improving the adhesion between the current collector and the electrode layer, the weight average molecular weight (Mw) of the binder is 600,000 to 3,000,000, preferably 700,000 to 2,000,000, and more preferably 700,000 to 1,500,000.

[0233] In addition, the weight average molecular weight is a polystyrene conversion value obtained by gel permeation chromatography (GPC).

[0234] From the perspective of reducing costs and obtaining high energy density, the content of the above-mentioned binder in the solid component is preferably 0.05 to 8 mass %, more preferably 0.05 to 5 mass %, further preferably 0.05 to 4 mass %, further preferably 0.1 to 3 mass %, particularly preferably 0.2 to 2 mass %, and most preferably 0.3 to 1.5 mass %.

[0235] <Conductive additives>

[0236] In order to make conductivity better, in the electrode forming composition of the present invention, a conductive auxiliary agent can be further included. As a conductive auxiliary agent, carbon materials such as graphite, carbon black, acetylene black (AB), vapor-grown carbon fiber, carbon nanotube (CNT), carbon nanohorn, graphene, polyaniline, polypyrrole, polythiophene, polyacetylene, polyacene and other conductive polymers can be listed. From the viewpoint of the ease of preparation of the conductivity and electrode forming composition, it is preferably not containing graphene, preferably using carbon black, acetylene black, vapor-grown carbon fiber, carbon nanotube, carbon nanohorn, more preferably using carbon black, acetylene black, carbon nanotube. The above-mentioned conductive auxiliary agent can be used alone or in combination of two or more, most preferably using carbon black or acetylene black and carbon nanotube.

[0237] When the conductive additive is included, its content is not particularly limited, but is preferably 0.05 to 5% by mass, more preferably 0.05 to 4% by mass, further preferably 0.1 to 3% by mass, and further preferably 0.2 to 2% by mass, based on the solid content. By setting the content of the conductive additive within the above range, good conductivity can be obtained.

[0238] <Other ingredients>

[0239] The electrode forming composition of the present invention may further include other ingredients. For example, in order to improve the dispersibility of the above-mentioned active material and conductive auxiliary agent, a dispersant may be included. As the above-mentioned dispersant, it can be appropriately selected from the substances used as dispersants for conductive carbon materials such as CNT in the past. From the perspective of stability in the battery, it is preferred to include a non-ionic polymer. As the above-mentioned non-ionic polymer, polyvinyl pyrrolidone (PVP) and a polymer having at least one group selected from the group consisting of a nitrile group, a hydroxyl group, a carbonyl group, an amino group, a sulfonyl group and an ether group can be listed. As specific examples of the above-mentioned polymers, polyvinyl alcohol, polyacrylonitrile, polylactic acid, polyester, polyimide, polyphenyl ether, polyphenyl sulfone, polyethyleneimine, polyaniline, etc. can be listed. In the present invention, a polymer having a pyrrolidone structure or a nitrile group is preferred, and polyvinyl pyrrolidone and polyacrylonitrile are more preferred. The above-mentioned dispersant can be used alone or in combination of two or more.

[0240] The dispersant may be added simultaneously with the additive containing a specific heterocyclic compound or the gelation inhibitor, or the additive containing a heterocyclic compound or the gelation inhibitor and the dispersant may be added separately.

[0241] Furthermore, the addition of a nonionic polymer is expected to improve the dispersibility of the active material and the conductive additive and also enhance the adhesion to the current collector foil.

[0242] When the dispersant is included, its content is not particularly limited, but is preferably 0.001 to 0.5% by mass, more preferably 0.001 to 0.3% by mass, and even more preferably 0.001 to 0.2% by mass, based on the solid content. Furthermore, a further preferred lower limit of the dispersant content is 0.01% by mass, based on the solid content.

[0243] Furthermore, considering the adhesion between the obtained electrode layer and the current collector, the total amount of the heterocyclic ring-containing compound and the dispersant is preferably 0.001 to 1% by mass, more preferably 0.01 to 1% by mass, based on the solid content.

[0244] Solvents

[0245] The electrode forming composition of the present invention includes a solvent. The solvent is not particularly limited as long as it is a substance conventionally used for preparing an electrode forming composition, and examples thereof include: water; ethers such as tetrahydrofuran (THF), diethyl ether, and 1,2-dimethoxyethane (DME); halogenated hydrocarbons such as dichloromethane, chloroform, and 1,2-dichloroethane; amides such as N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), and N-methyl-2-pyrrolidone (NMP); acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone. Ketones such as methylbenzene; alcohols such as methanol, ethanol, n-propanol, isopropanol, n-butanol, and tert-butanol; aliphatic hydrocarbons such as n-heptane, n-hexane, and cyclohexane; aromatic hydrocarbons such as benzene, toluene, xylene, and ethylbenzene; glycol ethers such as ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, and propylene glycol monomethyl ether; glycols such as ethylene glycol and propylene glycol; carbonates such as ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate; and organic solvents such as γ-butyrolactone, dimethyl sulfoxide (DMSO), dioxolane, and sulfolane. These solvents may be used alone or in combination of two or more.

[0246] It should be noted that the above-mentioned binder can be used by being dissolved or dispersed in these solvents as needed.

[0247] Preferred solvents in this case include water, NMP, DMSO, ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, γ-butyrolactone, THF, dioxolane, sulfolane, DMF, and DMAc. The solvent may be appropriately selected depending on the type of binder. In the case of water-insoluble binders such as PVdF, NMP is preferred, and in the case of water-soluble binders, water is preferred.

[0248] The solid content concentration of the electrode-forming composition of the present invention is appropriately set in consideration of the coating properties of the composition, the thickness of the formed electrode, etc., and is usually about 60 to 92 mass %, preferably about 65 to 90 mass %, and more preferably about 70 to 85 mass %.

[0249] The viscosity of the electrode-forming composition of the present invention is appropriately set in consideration of the coating method, the thickness of the electrode to be formed, etc., and is generally about 100 to 2,000,000 mPa·s, preferably about 300 to 1,000,000 mPa·s, and more preferably about 400 to 800,000 mPa·s. The above viscosity is a value measured at 25°C using an E-type viscometer.

[0250] The electrode forming composition of the present invention can be obtained by mixing the above-mentioned components. It should be noted that, in the case of comprising any component other than the additive (compound containing a heterocycle) of the present invention, the positive electrode active material and the binder, the additive and the positive electrode active material can be mixed together with the arbitrary component, or after mixing the two components in advance, mixed with the arbitrary component. In any method, the effect of the present invention can be reflected.

[0251] [Method for producing electrode-forming composition]

[0252] As a method for producing an electrode-forming composition, for example, the following method can be cited, but is not limited thereto. The method for producing an electrode-forming composition includes: a step of mixing a positive electrode active material, a binder, and a solvent to prepare a dispersion; and a step of mixing the dispersion with a heterocyclic compound.

[0253] When a conductive auxiliary agent is used, it is preferably mixed in the step of preparing the dispersion.

[0254] Here, the heterocyclic ring-containing compound may be mixed alone or as an additive in which the heterocyclic ring-containing compound is combined with at least one selected from the group consisting of a polymer having a pyrrolidone structure or a nitrile group and a solvent.

[0255] Examples of the polymer having a pyrrolidone structure or a nitrile group include the same ones as exemplified in the description of the dispersant, with polyvinyl pyrrolidone and polyacrylonitrile being preferred.

[0256] When the compound containing the heterocycle is mixed with a solvent, the solvent that can be used includes the same substances as those exemplified above. In the present invention, NMP, propylene carbonate, ethylene carbonate, diethyl carbonate, dimethyl carbonate, and ethyl methyl carbonate can be particularly preferably used.

[0257] [electrode]

[0258] The electrode of the present invention includes an electrode layer formed from the above-described electrode-forming composition on at least one surface of a substrate serving as a current collector.

[0259] The following methods can be used to form an electrode layer on a substrate: a prepared electrode-forming composition is applied to the substrate to form a coating film, which is then dried. This method is not particularly limited, and various conventionally known methods can be used. Specific examples of coating methods include offset printing, screen printing, and other printing methods, blade coating, dip coating, spin coating, rod coating, slit coating, inkjet coating, and die coating.

[0260] The coating film may be dried by natural drying or heat drying, but heat drying is preferred from the viewpoint of production efficiency. When heat drying is performed, the temperature is preferably about 50 to 400°C, more preferably about 70 to 150°C.

[0261] Examples of substrates used for the electrodes include metal substrates such as platinum, gold, iron, stainless steel, copper, aluminum, and lithium; alloy substrates composed of any combination of these metals; oxide substrates such as indium tin oxide (ITO), indium zinc oxide (IZO), and antimony tin oxide (ATO); and carbon substrates such as glassy carbon, pyrolytic graphite, and carbon felt. The thickness of the substrate is not particularly limited, but in the present invention, it is preferably 1 to 100 μm, more preferably 3 to 30 μm, and most preferably 5 to 25 μm.

[0262] The thickness of the electrode layer is not particularly limited, but is preferably about 0.01 to 1000 μm, more preferably about 5 to 300 μm. When the electrode layer serves solely as an electrode, its thickness is preferably 10 μm or greater.

[0263] The electrodes may also be pressed as needed. Conventional pressing methods may be used, with die pressing and roller pressing being particularly preferred. The pressing pressure is not particularly limited, but is preferably 1 kN / cm or greater, preferably 2 kN / cm or greater, and more preferably 5 kN / cm or greater. The upper limit of the pressing pressure is not particularly limited, but is preferably 50 kN / cm or less.

[0264] [Secondary battery]

[0265] The secondary battery of the present invention comprises the aforementioned electrodes, more specifically, at least a pair of positive and negative electrodes, a separator interposed between these electrodes, and an electrolyte, wherein the positive electrode comprises the aforementioned electrodes. Other battery element components may be appropriately selected from conventionally known components.

[0266] Examples of the material used for the separator include glass fiber, cellulose, porous polyolefin, polyamide, and polyester.

[0267] The electrolyte may be any liquid or solid, and may be any aqueous or non-aqueous. From the perspective of being able to easily exhibit sufficient performance in practical applications, an electrolyte solution composed of an electrolyte salt and a solvent may be preferably used.

[0268] Examples of the electrolyte salt include lithium salts such as LiPF6, LiBF4, LiN(SO2F), LiN(C2F5SO2), LiAsF6, LiSbF6, LiAlF4, LiGaF4, LiInF4, LiClO4, LiN(CF3SO2), LiCF3SO3, LiSiF6, and LiN(CF3SO2)(C4F9SO2), metal iodides such as LiI, NaI, KI, CsI, and CaI2, iodide salts of quaternary imidazolium compounds, iodide salts of tetraalkylammonium compounds, and perchlorates, and metal bromides such as LiBr, NaBr, KBr, CsBr, and CaBr2. These electrolyte salts may be used alone or in combination of two or more.

[0269] The solvent is not particularly limited as long as it dissolves the electrolyte salt without corroding or decomposing the materials constituting the battery and thereby degrading performance. For example, non-aqueous solvents include cyclic esters such as ethylene carbonate, propylene carbonate, butylene carbonate, and γ-butyrolactone, ethers such as tetrahydrofuran and dimethoxyethane, chain esters such as methyl acetate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate, and nitriles such as acetonitrile. These solvents can be used alone or in combination of two or more.

[0270] In addition, as solid electrolytes, inorganic solid electrolytes such as sulfide solid electrolytes and oxide solid electrolytes, and organic solid electrolytes such as polymer electrolytes can be preferably used. By using these solid electrolytes, an all-solid-state battery without the use of an electrolyte solution can be obtained.

[0271] Examples of the above-mentioned sulfide-based solid electrolytes include: Li2S-SiS2-lithium compounds (here, the lithium compound is at least one selected from the group consisting of Li3PO4, LiI, and Li4SiO4), Li2S-P2O5, Li2S-B2S5, Li2S-P2S5-GeS2, and other sulfide-LISICON-based materials.

[0272] Examples of the oxide-based solid electrolyte include Li5La3M2O, which is an oxide of a garnet structure. 12 (M=Nb,Ta),Li7La3Zr2O12 , oxygen-containing salt compounds based on the γ-Li3PO4 structure, collectively known as LISICON, perovskite type, Lithium Phosphorus Oxygen Nitrogen (LIPON) 3.3 PO 3.8 N 0.22 , sodium / aluminum oxide, etc.

[0273] Examples of the polymeric solid electrolyte include polyethylene oxide-based materials and polymer compounds obtained by polymerizing or copolymerizing the following monomers: hexafluoropropylene, tetrafluoroethylene, trifluoroethylene, ethylene, propylene, acrylonitrile, vinylidene chloride, acrylic acid, methacrylic acid, methyl acrylate, ethyl acrylate, methyl methacrylate, styrene, and vinylidene fluoride. It should be noted that the polymeric solid electrolyte may contain a supporting salt and a plasticizer.

[0274] Examples of the supporting salt contained in the polymer-based solid electrolyte include lithium (fluorosulfonyl imide) and the like, and examples of the plasticizer include succinonitrile and the like.

[0275] A battery produced using the electrode-forming composition of the present invention has higher battery characteristics than conventional secondary batteries even though it contains less fluorine binder.

[0276] The form of the secondary battery and the type of electrolyte are not particularly limited, and any of lithium-ion secondary batteries, nickel-metal hydride batteries, manganese batteries, and air batteries can be used, with lithium-ion secondary batteries being preferred. The lamination method and production method are also not particularly limited.

[0277] When used in a coin-type battery, the electrode of the present invention can be punched into a predetermined disc shape. For example, a lithium-ion secondary battery can be manufactured as follows: a single electrode is placed on a lid welded with a coin cell gasket and separator, a separator of the same shape impregnated with electrolyte is stacked on top of the electrode, and the electrode of the present invention is stacked from above with the electrode layer facing downward. The outer casing and gasket are then placed, and the battery is sealed using a coin cell riveting machine.

[0278] [additive]

[0279] In addition, the present invention provides an additive for an electrode slurry comprising a positive electrode active material, a binder, and a solvent, wherein the additive comprises a heterocyclic compound having a nitrogen-containing five-membered ring, and the nitrogen-containing five-membered ring does not contain an oxygen atom. The additive can be preferably used as a gelation inhibitor for an electrode slurry comprising a positive electrode active material, a binder, and a solvent. Furthermore, the present invention can be preferably used as a method for inhibiting the gelation of an electrode slurry by adding the heterocyclic compound to the electrode slurry.

[0280] It should be noted that the heterocyclic ring-containing compound is preferably solid at room temperature. This aspect is as described in the description of the electrode-forming composition.

[0281] As the heterocyclic ring-containing compound, it is preferred that the hetero atoms contained in the nitrogen-containing five-membered ring are only nitrogen atoms, and it is more preferred that the nitrogen atoms contained in the nitrogen-containing five-membered ring are two or three.

[0282] Furthermore, the heterocyclic compound preferably has a carbonyl structure (carbonyl group) on the nitrogen-containing five-membered ring. In this case, the nitrogen-containing five-membered ring is more preferably uncondensed. Furthermore, the carbonyl structure preferably exhibits proton tautomerism, and even more preferably exhibits keto-enol tautomerism.

[0283] Specific examples of the heterocyclic ring-containing compound include additives containing a heterocyclic ring-containing compound represented by any of the following formulae (1) to (4).

[0284]

[0285] (In formula (1), R a and R b are each independently a hydrogen atom, a carboxyl group, a hydroxyl group, a thiol group, an alkyl group having 1 to 6 carbon atoms which may have a substituent, an alkenyl group having 2 to 6 carbon atoms which may have a substituent, or an aryl group having 6 to 12 carbon atoms which may have a substituent, R a and R b are optionally bonded to each other to form a ring having 4 to 12 carbon atoms which may have a substituent, L is independently a single bond, a carbonyl group, an ether bond, an ester bond or an amide bond, and Z is N or C-L-R c , R c is a hydrogen atom, a halogen atom, a carboxyl group, a hydroxyl group, a thiol group, an optionally substituted alkyl group having 1 to 6 carbon atoms, an optionally substituted alkenyl group having 2 to 6 carbon atoms, or an optionally substituted aryl group having 6 to 12 carbon atoms, X a A hydrogen atom, a lithium atom, a sodium atom, an alkyl group having 1 to 6 carbon atoms which may have a substituent, an aryl group having 6 to 12 carbon atoms which may have a substituent, or -CH2NR d 2, R d Each independently represents an alkyl group having 1 to 10 carbon atoms, an alkanol group having 1 to 10 carbon atoms, an alkenyl group having 2 to 10 carbon atoms, or an aryl group having 6 to 12 carbon atoms.

[0286] In formula (2), R a and R bare each independently a hydrogen atom, a halogen atom, a carboxyl group, a hydroxyl group, a thiol group, an optionally substituted alkyl group having 1 to 6 carbon atoms, an optionally substituted alkenyl group having 2 to 6 carbon atoms, or an optionally substituted aryl group having 6 to 12 carbon atoms, L is each independently a single bond, a carbonyl group, an ether bond, an ester bond, or an amide bond, X a A hydrogen atom, a lithium atom, a sodium atom, an alkyl group having 1 to 6 carbon atoms which may have a substituent, an aryl group having 6 to 12 carbon atoms which may have a substituent, or -CH2NR d 2, R d Each independently represents an alkyl group having 1 to 10 carbon atoms, an alkanol group having 1 to 10 carbon atoms, an alkenyl group having 2 to 10 carbon atoms, or an aryl group having 6 to 12 carbon atoms.

[0287] In formulas (3) to (4), R a ~R c are each independently a hydrogen atom, a halogen atom, a carboxyl group, a hydroxyl group, a thiol group, an amino group, an optionally substituted alkyl group having 1 to 6 carbon atoms, an optionally substituted alkenyl group having 2 to 6 carbon atoms, or an optionally substituted aryl group having 6 to 12 carbon atoms, R a and R b are optionally bonded to each other to form a ring having 4 to 12 carbon atoms which may have a substituent, L is independently a single bond, a carbonyl group, an ether bond, an ester bond or an amide bond, X a and X b Each is independently a hydrogen atom, a lithium atom, a sodium atom, an optionally substituted alkyl group having 1 to 6 carbon atoms, an optionally substituted aryl group having 6 to 12 carbon atoms, or -CH2NR d 2, R d Each is independently an alkyl group having 1 to 10 carbon atoms, an alkanol group having 1 to 10 carbon atoms, an alkenyl group having 2 to 10 carbon atoms, or an aryl group having 6 to 12 carbon atoms.

[0288] In the above formulas (1) to (4), R a ~R c , L, X a 、X b 、R d Specific examples are the same as those exemplified in the description of the electrode-forming composition.

[0289] The above-mentioned additives may further include a nonionic polymer.

[0290] Examples of the nonionic polymer include the same ones as exemplified as the dispersant in the description of other components of the electrode-forming composition. Polymers having a pyrrolidone structure or a nitrile group are preferred, with polyvinylpyrrolidone and polyacrylonitrile being more preferred.

[0291] When the polymer is included in the additive, its content is not particularly limited, but is preferably 0.001 to 0.5% by mass, more preferably 0.001 to 0.3% by mass, and even more preferably 0.001 to 0.2% by mass in the solid content. Furthermore, a further preferred lower limit of the polymer content is 0.01% by mass in the solid content.

[0292] The above-mentioned additives may further include a solvent. Examples of the solvent include the same substances as those exemplified in the description of the electrode-forming composition. In the present invention, NMP, propylene carbonate, ethylene carbonate, diethyl carbonate, dimethyl carbonate, and ethyl methyl carbonate are particularly preferably used.

[0293] When the additive contains a solvent, the heterocyclic ring-containing compound represented by any of the formulae (1) to (4) is preferably dissolved or dispersed in the solvent, and more preferably dissolved in the solvent.

[0294] When the additive of the present invention contains a solvent, the solid content concentration of the additive is appropriately set in consideration of saturated solubility in the solvent, storage stability, etc., and is usually about 1 to 60 mass%, preferably about 3 to 55 mass%, and more preferably about 3 to 50 mass%.

[0295] Furthermore, the positive electrode active material and the binder of the electrode slurry are the same as those described in the description of the electrode-forming composition.

[0296] [Gelation Inhibitor]

[0297] The present invention also provides a gelation inhibitor for an electrode slurry comprising a positive electrode active material, a binder, and a solvent. The gelation inhibitor comprises a heterocyclic compound having a nitrogen-containing five-membered ring, wherein the nitrogen-containing five-membered ring does not contain an oxygen atom. The gelation inhibitor of the present invention can more effectively inhibit gelation in an electrode slurry comprising a positive electrode active material, a binder, and a solvent.

[0298] Note that the heterocyclic ring-containing compound is different from the solvent in the present invention in that it is solid at room temperature. This point is as described in the description of the electrode-forming composition.

[0299] As the heterocyclic ring-containing compound, it is preferred that the hetero atoms contained in the nitrogen-containing five-membered ring are only nitrogen atoms, and it is more preferred that the nitrogen atoms contained in the nitrogen-containing five-membered ring are two or three.

[0300] Furthermore, the heterocyclic compound preferably has a carbonyl structure (carbonyl group) on the nitrogen-containing five-membered ring. In this case, the nitrogen-containing five-membered ring is more preferably uncondensed. Furthermore, the carbonyl structure preferably exhibits proton tautomerism, and even more preferably exhibits keto-enol tautomerism.

[0301] Specific examples of the heterocyclic ring-containing compound include compounds represented by any of the following formulae (1) to (4).

[0302]

[0303] (In formula (1), R a and R b are each independently a hydrogen atom, a carboxyl group, a hydroxyl group, a thiol group, an alkyl group having 1 to 6 carbon atoms which may have a substituent, an alkenyl group having 2 to 6 carbon atoms which may have a substituent, or an aryl group having 6 to 12 carbon atoms which may have a substituent, R a and R b are optionally bonded to each other to form a ring having 4 to 12 carbon atoms which may have a substituent, L is independently a single bond, a carbonyl group, an ether bond, an ester bond or an amide bond, and Z is N or C-L-R c , R c is a hydrogen atom, a halogen atom, a carboxyl group, a hydroxyl group, a thiol group, an optionally substituted alkyl group having 1 to 6 carbon atoms, an optionally substituted alkenyl group having 2 to 6 carbon atoms, or an optionally substituted aryl group having 6 to 12 carbon atoms, X a A hydrogen atom, a lithium atom, a sodium atom, an alkyl group having 1 to 6 carbon atoms which may have a substituent, an aryl group having 6 to 12 carbon atoms which may have a substituent, or -CH2NR d 2, R d Each independently represents an alkyl group having 1 to 10 carbon atoms, an alkanol group having 1 to 10 carbon atoms, an alkenyl group having 2 to 10 carbon atoms, or an aryl group having 6 to 12 carbon atoms.

[0304] In formula (2), R a and R b are each independently a hydrogen atom, a halogen atom, a carboxyl group, a hydroxyl group, a thiol group, an optionally substituted alkyl group having 1 to 6 carbon atoms, an optionally substituted alkenyl group having 2 to 6 carbon atoms, or an optionally substituted aryl group having 6 to 12 carbon atoms, L is each independently a single bond, a carbonyl group, an ether bond, an ester bond, or an amide bond, X a A hydrogen atom, a lithium atom, a sodium atom, an alkyl group having 1 to 6 carbon atoms which may have a substituent, an aryl group having 6 to 12 carbon atoms which may have a substituent, or -CH2NR d 2, R dEach independently represents an alkyl group having 1 to 10 carbon atoms, an alkanol group having 1 to 10 carbon atoms, an alkenyl group having 2 to 10 carbon atoms, or an aryl group having 6 to 12 carbon atoms.

[0305] In formulas (3) to (4), R a ~R c are each independently a hydrogen atom, a halogen atom, a carboxyl group, a hydroxyl group, a thiol group, an amino group, an optionally substituted alkyl group having 1 to 6 carbon atoms, an optionally substituted alkenyl group having 2 to 6 carbon atoms, or an optionally substituted aryl group having 6 to 12 carbon atoms, R a and R b are optionally bonded to each other to form a ring having 4 to 12 carbon atoms which may have a substituent, L is independently a single bond, a carbonyl group, an ether bond, an ester bond or an amide bond, X a and X b Each is independently a hydrogen atom, a lithium atom, a sodium atom, an optionally substituted alkyl group having 1 to 6 carbon atoms, an optionally substituted aryl group having 6 to 12 carbon atoms, or -CH2NR d 2, R d Each is independently an alkyl group having 1 to 10 carbon atoms, an alkanol group having 1 to 10 carbon atoms, an alkenyl group having 2 to 10 carbon atoms, or an aryl group having 6 to 12 carbon atoms.

[0306] In the above formulas (1) to (4), R a ~R c , L, X a 、X b 、R d Specific examples are the same as those exemplified in the description of the electrode-forming composition.

[0307] The gelation inhibitor may further contain a nonionic polymer.

[0308] Examples of the nonionic polymer include the same ones as exemplified as the dispersant in the description of other components of the electrode-forming composition. Polymers having a pyrrolidone structure or a nitrile group are preferred, with polyvinylpyrrolidone and polyacrylonitrile being more preferred.

[0309] When the gelation inhibitor includes the polymer, its content is not particularly limited, but is preferably 0.001 to 0.5% by mass, more preferably 0.001 to 0.3% by mass, and even more preferably 0.001 to 0.2% by mass, based on the solid content. Furthermore, a further preferred lower limit of the polymer content is 0.01% by mass, based on the solid content.

[0310] The gelation inhibitor may further include a solvent. Examples of the solvent include the same substances as those exemplified in the description of the electrode-forming composition. In the present invention, NMP, propylene carbonate, ethylene carbonate, diethyl carbonate, dimethyl carbonate, and ethyl methyl carbonate are particularly preferably used.

[0311] When the gelation inhibitor contains a solvent, the heterocyclic ring-containing compound represented by any of the formulae (1) to (4) is preferably dissolved or dispersed in the solvent, and more preferably dissolved in the solvent.

[0312] When the gelation inhibitor of the present invention contains a solvent, the solid content concentration of the gelation inhibitor is appropriately set in consideration of the saturated solubility in the solvent, storage stability, etc., and is usually about 1 to 60 mass %, preferably about 3 to 55 mass %, and more preferably about 3 to 50 mass %.

[0313] Furthermore, the positive electrode active material and the binder of the electrode slurry are the same as those described in the description of the electrode-forming composition.

[0314] Example

[0315] The present invention will be described in more detail below with reference to Examples and Comparative Examples, but the present invention is not limited to the following Examples.

[0316] (1) Rotation / revolution type mixer: Awatori Rentaro atmospheric pressure type ARE-310 manufactured by THINKY Co., Ltd.

[0317] (2) Drying chamber: manufactured by Nihon Spindle Manufacturing Co., Ltd.

[0318] (3) E-type viscometer: VISCOMETER TV-22 manufactured by Toki Sangyo Co., Ltd. The viscosity was measured 5 minutes after the start of the measurement under the following conditions: measurement temperature: 25°C, rotor: 1°34' x R24. The rotor speed was selected to an appropriate value between 0.1 and 10 rpm depending on the viscosity of the sample being measured. The viscosity of the slurry on the day of preparation was measured within 0.5 to 6 hours after preparation.

[0319] (4) Liquid chromatography-mass spectrometry (LC / MS)

[0320] Liquid chromatography apparatus: NexeraX2 (Shimadzu Corporation); mass spectrometer (MS): Q-Exactive (ThermoFisher Scientific).

[0321] Chromatographic column: XBridge C18 2.1×150mm (5μm).

[0322] Eluent: acetonitrile with formic acid added at a concentration of 0.1% (vol / vol) / pure water with formic acid added at a concentration of 0.1% (vol / vol) = 20 / 80 - 95 / 5 (12 min) - 95 / 5 (13 min).

[0323] Ionization method: ESI+.

[0324] In addition, the raw materials and the like used are as follows.

[0325] Active substances

[0326] NCA: Lithium Nickelate (LiNi 0.88 Co 0.11 Al 0.01 O2, NCA-034H, Ni content: 55 mass %), manufactured by Ecopro.

[0327] NCM811: Lithium Nickel Manganese Cobalt Oxide (LiNi 0.8 Co 0.1 Mn 0.1 O2, manufactured by Ningbo Ronbay New Energy Technology Co., Ltd., S-800, Ni content: 50 mass %).

[0328] Adhesives

[0329] Solef-5130: polyvinylidene fluoride (PVdF), manufactured by SOLVAY.

[0330] Solef-5140: polyvinylidene fluoride (PVdF), manufactured by SOLVAY.

[0331] <Conductive additives>

[0332] AB: DENKA BLACK (registered trademark) Li100 (high-purity acetylene black), manufactured by Denka Corporation.

[0333] Solvents

[0334] NMP: manufactured by Nippon Refine Co., Ltd.

[0335] Tetrahydrofuran: manufactured by Asahi Rika Seisakusho Co., Ltd.

[0336] 2-Propanol: manufactured by Junsei Chemical Co., Ltd.

[0337] Hexane: manufactured by Junsei Chemical Co., Ltd.

[0338] <Additive A>

[0339] [Additives used in Examples]

[0340] A1: 1H-1,2,3-Benzotriazole-5-carboxylic acid monohydrate (CBT-1), manufactured by Johoku Chemical Industry Co., Ltd. (corresponding to the monohydrate of formula (1-1)).

[0341] A2: 1H-benzotriazole, manufactured by FUJIFILM Wako Pure Chemical Co., Ltd. (corresponding to formula (1-2)).

[0342] A3: 1H-1,2,3-triazole, manufactured by FUJIFILM Wako Pure Chemical Co., Ltd. (corresponding to formula (1-3)).

[0343] A4: 1H-1,2,4-triazole, manufactured by Tokyo Chemical Industry Co., Ltd. (corresponding to formula (2-1)).

[0344] A5: 2,3-Dimethyl-1-phenyl-5-pyrazolone, manufactured by Tokyo Chemical Industry Co., Ltd. (corresponding to formula (3-1)).

[0345] A6: 3-methyl-1-phenyl-5-pyrazolone, manufactured by Tokyo Chemical Industry Co., Ltd. (corresponding to formula (4-6)).

[0346] A7: Benzimidazole, manufactured by Tokyo Chemical Industry Co., Ltd. (corresponding to formula (1-4)).

[0347] A8: Benzimidazole-5-carboxylic acid, manufactured by Tokyo Chemical Industry Co., Ltd. (corresponding to formula (1-5)).

[0348] A9: X-12-1214A, manufactured by Shin-Etsu Chemical Co., Ltd. (corresponding to formula (1-6)).

[0349] A10: LiOH 99 mol % neutralized product of CBT-1 (synthetic product) (corresponding to the monohydrate of formula (1-15)).

[0350] A11: 3-methyl-1-p-phenylmethyl-5-pyrazolone, manufactured by Tokyo Chemical Industry Co., Ltd. (corresponding to formula (3-9)).

[0351] A12: 1-(4-chlorophenyl)-3-methyl-5-pyrazolone, manufactured by Tokyo Chemical Industry Co., Ltd. (corresponding to formula (3-13)).

[0352] A13: 3-amino-1-phenyl-2-pyrazolin-5-one, manufactured by Tokyo Chemical Industry Co., Ltd. (corresponding to formula (4-10)).

[0353] A14: Li salt of 3-methyl-1-phenyl-5-pyrazolone (synthetic product) (corresponding to formula (3-5)).

[0354] A15: Hydantoin, manufactured by Tokyo Chemical Industry Co., Ltd.

[0355] A16: 5,5-dimethylhydantoin, manufactured by Tokyo Chemical Industry Co., Ltd.

[0356] A17: 1,2-Benzisothiazol-3(2H)-one, manufactured by Tokyo Chemical Industry Co., Ltd.

[0357] A18: 2-Mercaptobenzimidazole, manufactured by Tokyo Chemical Industry Co., Ltd.

[0358] A19: 5-mercapto-1-methyltetrazole, manufactured by Tokyo Chemical Industry Co., Ltd.

[0359] A20: 7-Hydroxy-5-methyl-[1,2,4]triazolo[1,5-a]pyrimidine, manufactured by Tokyo Chemical Industry Co., Ltd.

[0360] A21: Bis(3-methyl-1-phenyl-5-pyrazolone), manufactured by Tokyo Chemical Industry Co., Ltd.

[0361] [Additives used in Comparative Examples]

[0362] a1: 2-(2-hydroxyphenyl)pyridine, manufactured by FUJIFILM Wako Pure Chemical Co., Ltd.

[0363] a2: 1,10-phenanthroline, manufactured by Tokyo Chemical Industry Co., Ltd.

[0364] a3: 1,8-naphthyridine, manufactured by Tokyo Chemical Industry Co., Ltd.

[0365] a4: 4-vinylpyridine, manufactured by Tokyo Chemical Industry Co., Ltd.

[0366] a5: pyridine, manufactured by FUJIFILM Wako Pure Chemical Co., Ltd.

[0367] a6: poly(4-vinylpyridine), manufactured by Sigma-Aldrich.

[0368] a7: WS-700 (oxazoline group-containing polymer), manufactured by Nippon Shokubai Co., Ltd., Mw: 40,000, reactive crosslinking agent.

[0369] a8: 2-(1,3-phenylene)bis-2-oxazoline (PBO), manufactured by FUJIFILM Wako Pure Chemical Co., Ltd., a reactive crosslinking agent.

[0370] a9: Polyacrylic acid, Toagosei Co., Ltd., ARON AC-10P, Mw: 5000.

[0371] a10: Oxalic acid, manufactured by FUJIFILM Wako Pure Chemical Co., Ltd.

[0372] a11: phenylboric acid, manufactured by Cangzhou Pure Science Co., Ltd.

[0373] a12: Benzoic acid, manufactured by FUJIFILM Wako Pure Chemical Co., Ltd.

[0374] a13: Tannic acid, manufactured by FUJIFILM Wako Pure Chemical Co., Ltd.

[0375] a14: Water-soluble methylolmelamine (Nikaresin S176 (triazine structure)), manufactured by Nippon Carbonide Industries, Ltd.

[0376] a15: Isobam 18 (copolymer of isobutylene and maleic anhydride), manufactured by Kuraray Co., Ltd., Mw: 300,000 to 350,000.

[0377] a16: 2,1-Benzisoxazole, manufactured by Tokyo Chemical Industry Co., Ltd.

[0378] <Other additives>

[0379] PVP: Dai-ichi Kogyo Seiyaku Co., Ltd., PITZCOL K90, Mw: 1.2 million, dispersant.

[0380] PAN: Dolan GmbH, H-PAN, Mw: 200,000, dispersant.

[0381] [Synthesis Example 1] Synthesis of Additive A10 (LiOH 99 mol% Neutralized Product of CBT-1)

[0382] A solution of 4.43 g of 1H-1,2,3-benzotriazole-5-carboxylic acid (CBT-1) dissolved in 22.72 g of NMP, 111 g of NMP, and 0.58 g of LiOH (manufactured by Tokyo Chemical Industry Co., Ltd.) dissolved in 23.69 g of pure water were mixed, stirred for 1 hour, and then allowed to stand for 24 hours for neutralization. Using a vacuum distillation apparatus and an oil bath, vacuum distillation was performed at 85°C / 20 Torr for 0.5 hour, followed by vacuum distillation at 110-120°C / 50-20 Torr for 1 hour, yielding a 5% by mass NMP solution of LiOH-neutralized CBT-1.

[0383] [Synthesis Example 2] Synthesis of Additive A14 (Li Salt of 3-Methyl-1-phenyl-5-pyrazolone)

[0384] To a solution of 1.76 g of 3-methyl-1-phenyl-5-pyrazolone dissolved in 60.14 g of tetrahydrofuran was added 6.25 mL of a hexane solution of n-butyllithium (ca. 15% in hexane, ca. 1.6 mol / L) (manufactured by Tokyo Chemical Industry Co., Ltd.), and the mixture was stirred at room temperature for 1 hour. 5 g of 2-propanol was added, and the mixture was stirred for 1 hour. The solution was poured into 240 g of hexane for reprecipitation, and the resulting precipitate was recovered using a Kiriyama funnel. This was vacuum-dried at 80°C for 3 hours to obtain the lithium salt of 3-methyl-1-phenyl-5-pyrazolone.

[0385] The amount of heterocyclic compound (additive or gelation inhibitor) adhering to the active material can be determined, for example, by dispersing the active material in a solution of each compound dissolved in a solvent, filtering the solution, quantifying the compound concentration in the filtrate, and confirming the decrease in concentration from the charged concentration. The concentration of the heterocyclic compound in the filtrate can be quantified using any of the conventional quantitative analysis methods, such as liquid chromatography-mass spectrometry (LC / MS) and NMR. Alternatively, the adsorption rate (%) can be determined using the following formula.

[0386] Adhesion rate (%) = (charge concentration of each compound - concentration of each compound in the filtrate) / charge concentration of each compound

[0387] In a drying room, the positive electrode active material, additive (gelation inhibitor) and NMP are mixed in such a manner as to form the composition ratio shown in Table 1, and the mixing is carried out for 1 hour using a mixing rotor. The active material is removed by filtering it with a 0.2 μm filter, and the filtrate is recovered. The obtained filtrate is diluted with methanol as needed. As for the dilution, the implementation of Evaluation Example 1 is set to 1100 times dilution, Examples 2 to 3 are set to 110 times dilution, and Example 4 is set to 11 times dilution. Examples 5 to 6 are not diluted. They are measured using LC / MS, and extracted ion chromatograms are drawn. Based on the peak area values on the obtained chromatograms and the pre-made calibration curve, the concentration of the additives is quantified to determine the adsorption rate of each additive.

[0388] [Table 1]

[0389]

[0390] Preparation of positive electrode composition (electrode slurry)

[0391] [Examples 1-1 to 1-35, Comparative Examples 1-1 to 1-19]

[0392] Regarding each additive, a 5% by mass NMP solution was prepared. A 7% by mass NMP solution of PVdF was prepared. In a drying chamber, the positive electrode active material, binder solution, conductive additive, additive A solution, additive B solution, NMP, and water were mixed in a manner to obtain the composition ratios shown in Tables 2, 3, and 5, and mixed using a rotation / revolution stirrer to obtain an electrode slurry. The total amount of the prepared slurry was 20 g each, the solid content was 71% by mass, and the solvent composition of the slurry was adjusted to NMP / H2O=97 / 3 (mass ratio). It should be noted that the water was added in order to purposefully create a state in which the slurry had a high water content.

[0393] Hereinafter, the preparation method will be described in further detail.

[0394] For each additive, a 5% by mass NMP solution was prepared. A 7% by mass NMP solution of PVdF was prepared. In a drying chamber, the conductive additive and the binder solution were weighed in such a manner as to obtain the composition ratios shown in Tables 2, 3, and 5, and the mixture was mixed at 2000 rpm for 5 minutes using a rotation / revolution stirrer. Only half of the positive electrode active material was added thereto, and the mixture was mixed at 2000 rpm for 5 minutes. The remaining half of the positive electrode active material was added thereto, and the mixture was mixed at 2000 rpm for 5 minutes. Additive A solution, additive B solution, NMP, and water, and the mixture was mixed at 2000 rpm for 5 minutes. The whole was stirred with a spatula, and the mixture was mixed at 2000 rpm for 5 minutes to obtain an electrode slurry. The total amount of the prepared slurry was 20 g each, the solid content was 71% by mass, and the solvent composition of the slurry was adjusted to NMP / H2O=97 / 3 (mass ratio). It should be noted that the water is added in order to intentionally create a state in which the slurry has a high water content.

[0395] [Examples 1-36 to 1-41]

[0396] Prepare a 7% by mass NMP solution of PVdF. In a manner such that the composition ratios shown in Table 4 are obtained, the positive electrode active material, binder solution, conductive additive, additive A, NMP, and water are mixed in a drying chamber and mixed using a rotation / revolution stirrer to obtain an electrode slurry. The total amount of the prepared slurries is 20 g each, the solid content is set to 71% by mass, and the solvent composition of the slurry is adjusted to NMP / H2O=97 / 3 (mass ratio). It should be noted that the water is added to purposefully create a state where the slurry has a high water content.

[0397] Hereinafter, the preparation method will be described in further detail.

[0398] A 7% by mass NMP solution of PVdF was prepared. The conductive additive and the binder solution were weighed in a drying chamber in such a manner as to form the composition ratio shown in Table 4, and the mixture was mixed at 2000 rpm for 5 minutes using a rotation / revolution stirrer. Only half of the positive electrode active material was added thereto, and the mixture was mixed at 2000 rpm for 5 minutes. The remaining half of the positive electrode active material was added thereto, and the mixture was mixed at 2000 rpm for 5 minutes. Add additive A, NMP, and water, and the mixture was mixed at 2000 rpm for 5 minutes. The whole was stirred with a spatula, and the mixture was mixed at 2000 rpm for 5 minutes to obtain an electrode slurry. The total amount of the prepared slurry was 20 g each, the solid content was 71% by mass, and the solvent composition of the slurry was adjusted to NMP / H2O=97 / 3 (mass ratio). It should be noted that the water was added in order to purposefully create a state in which the slurry had a high water content.

[0399] [Example 1-42, Comparative Example 1-20]

[0400] Prepare a 7% by mass NMP solution of PVdF. In a manner such that the composition ratios shown in Tables 4 and 5 are obtained, the positive electrode active material, binder solution, additive A, NMP, and water are mixed in a drying chamber and mixed using a rotation / revolution stirrer to obtain an electrode slurry. The total amount of the prepared slurries is 19.76 g each, the solid content is set to 79.76% by mass, and the solvent composition of the slurry is adjusted to NMP / H2O=97 / 3 (mass ratio). It should be noted that the water is added to intentionally create a state where the slurry has a high water content.

[0401] Hereinafter, the preparation method will be described in further detail.

[0402] A 7% by mass NMP solution of PVdF was prepared. In a drying chamber, the binder solution and the additive A solution were weighed in such a manner as to obtain the composition ratios shown in Tables 4 and 5, and the mixture was mixed at 2000 rpm for 5 minutes using a rotation / revolution stirrer. Only half of the positive electrode active material was added thereto, and the mixture was mixed at 2000 rpm for 5 minutes. The remaining half of the positive electrode active material was added thereto, and the mixture was mixed at 2000 rpm for 5 minutes. A conductive additive, NMP, and water were added thereto, and the mixture was mixed at 2000 rpm for 5 minutes. The whole was stirred with a spatula, and the mixture was mixed at 2000 rpm for 5 minutes to obtain an electrode slurry. The total amount of the prepared slurries was 19.76 g each, the solid content was 79.76% by mass, and the solvent composition of the slurry was adjusted to NMP / H2O=97 / 3 (mass ratio). It should be noted that the water was added in order to purposefully create a state in which the slurry had a high water content.

[0403] [Examples 1-43 to 1-49, Comparative Example 1-21]

[0404] Regarding each additive, a 5% by mass NMP solution was prepared. A 7% by mass NMP solution of PVdF was prepared. In a drying chamber, the positive electrode active material, binder solution, conductive additive, additive A solution, NMP, and water were mixed in a manner to form the composition ratios shown in Tables 4 and 5, and mixed using a rotation / revolution stirrer to obtain an electrode slurry. The total amount of the prepared slurry was 20 g each, the solid content was 80% by mass, and the solvent composition of the slurry was adjusted to NMP / H2O=97 / 3 (mass ratio). It should be noted that the water was added in order to purposefully create a state in which the slurry had a high water content.

[0405] Hereinafter, the preparation method will be described in further detail.

[0406] For each additive, a 5% by mass NMP solution was prepared. A 7% by mass NMP solution of PVdF was prepared. In a drying room, the binder solution and the additive A solution were weighed in such a manner as to form the composition ratios shown in Tables 4 and 5, and the mixture was mixed at 2000 rpm for 5 minutes using a rotation / revolution stirrer. Only half of the positive electrode active material was added thereto, and the mixture was mixed at 2000 rpm for 5 minutes. The remaining half of the positive electrode active material was added thereto, and the mixture was mixed at 2000 rpm for 5 minutes. A conductive additive, NMP, and water were added thereto, and the mixture was mixed at 2000 rpm for 5 minutes. The whole was stirred with a spatula, and the mixture was mixed at 2000 rpm for 5 minutes to obtain an electrode slurry. The total amount of the prepared slurry was 20 g each, the solid content was 80% by mass, and the solvent composition of the slurry was adjusted to NMP / H2O=97 / 3 (mass ratio). It should be noted that the water was added in order to purposefully create a state in which the slurry had a high water content.

[0407] The viscosity of the slurry obtained above was measured using an E-type viscometer immediately after preparation. Furthermore, after 24 hours of storage at 40°C, the presence of gelation was visually inspected. For those without gelation, viscosity was similarly measured using an E-type viscometer to confirm the presence of thickening and gelation tendencies, and the results were determined based on the following criteria. These evaluations are summarized in the tables.

[0408] Judgment Criteria

[0409] A: No gelation, and the viscosity change rate is less than 200%.

[0410] B: There was no gelation, but the viscosity change rate was 200% or more, indicating significant thickening.

[0411] C: The composition was gelled and could not be used for electrode formation.

[0412] Viscosity change rate (%) = ((viscosity after storage - initial viscosity) / initial viscosity) × 100

[0413] [Table 2]

[0414]

[0415] [Table 3]

[0416]

[0417] [Table 4]

[0418]

[0419] [Table 5]

[0420]

[0421] The results in Tables 2 to 5 above confirmed that, in the electrode-forming composition of the present invention to which the specific heterocyclic-ring-containing compound was added, thickening and gelation were suppressed, and storage stability was improved.

[0422] Therefore, even if time passes after the preparation of the electrode-forming composition, the coating properties are not impaired, and the composition can be preferably used in the industrial production of lithium-ion secondary batteries.

[0423] [Examples 1-50 to 1-53]

[0424] Prepare a 7% by mass NMP solution of PVdF. In a manner to form the composition ratio shown in Table 6, the positive electrode active material, binder solution, conductive additive, additive A, additive B, NMP, and water were mixed in a drying chamber and mixed using a rotation / revolution stirrer to obtain an electrode slurry. The total amount of the prepared slurry was 20 g each, the solid content was set to 71% by mass, and the solvent composition of the slurry was adjusted to NMP / H2O=97 / 3 (mass ratio). It should be noted that the above-mentioned water was added in order to purposefully create a state with a high water content in the slurry.

[0425] Hereinafter, the preparation method will be described in further detail.

[0426] A 7% by mass NMP solution of PVdF was prepared. In a drying chamber, the conductive aid and the binder solution were weighed in such a manner as to form the composition ratio shown in Table 6, and the mixture was mixed at 2000 rpm for 5 minutes using a rotation / revolution stirrer. Only half of the positive electrode active material was added thereto, and the mixture was mixed at 2000 rpm for 5 minutes. The remaining half of the positive electrode active material was added thereto, and the mixture was mixed at 2000 rpm for 5 minutes. A 5% by mass NMP solution containing additives A and additive B, NMP, and water were added, and the mixture was mixed at 2000 rpm for 5 minutes. The whole was stirred with a spatula, and the mixture was mixed at 2000 rpm for 5 minutes to obtain an electrode slurry. The total amount of the prepared slurry was 20 g each, the solid content was 71% by mass, and the solvent composition of the slurry was adjusted to NMP / H2O=97 / 3 (mass ratio). It should be noted that the water was added in order to purposefully create a state in which the slurry has a high water content.

[0427] The viscosity of the slurry obtained above was measured using an E-type viscometer immediately after preparation, as in Example 1-1. Furthermore, after 24 hours of storage at 40°C, the presence of gelation was visually inspected. In the absence of gelation, viscosity was measured using an E-type viscometer to confirm the presence of thickening and gelation tendencies. The evaluation criteria and calculation methods for the viscosity change rate were the same as described above. These evaluations are also summarized in Table 6.

[0428] [Table 6]

[0429]

[0430] The results in Table 6 above confirmed that, in the electrode-forming composition of the present invention to which the specific heterocyclic-ring-containing compound was added, thickening and gelation were suppressed, and storage stability was improved.

[0431] Therefore, even if time passes after the preparation of the electrode-forming composition, the coating properties are not impaired, and the composition can be preferably used in the industrial production of lithium-ion secondary batteries.

Claims

1. An electrode forming composition comprising a positive electrode active material, a binder, a solvent, and a heterocyclic compound, The heterocyclic compound has a nitrogen-containing five-membered ring, the five-membered ring does not contain an oxygen atom, and has a carbonyl structure on the five-membered ring.

2. The electrode-forming composition according to claim 1, wherein The heterocyclic compound is attached to the positive electrode active material.

3. The electrode-forming composition according to claim 1, wherein The heterocyclic compound is an uncontracted nitrogen-containing five-membered heterocyclic compound.

4. The electrode-forming composition according to claim 1, wherein The carbonyl structure shows proton tautomerism.

5. The electrode-forming composition according to claim 4, wherein The proton tautomerism is keto-enol tautomerism.

6. The electrode-forming composition according to claim 1, wherein The heterocyclic compound is represented by any of the following formulas (3) to (4): In formulas (3) to (4), R a ~R c each independently represents a hydrogen atom, a halogen atom, a carboxyl group, a hydroxyl group, a thiol group, an amino group, an optionally substituted alkyl group having 1 to 6 carbon atoms, an optionally substituted alkenyl group having 2 to 6 carbon atoms, or an optionally substituted aryl group having 6 to 12 carbon atoms, R a and R b are optionally bonded to each other to form a ring having 4 to 12 carbon atoms which may have a substituent, L is each independently a single bond, a carbonyl group, an ether bond, an ester bond or an amide bond, X a and X b Each is independently a hydrogen atom, a lithium atom, a sodium atom, an optionally substituted alkyl group having 1 to 6 carbon atoms, an optionally substituted aryl group having 6 to 12 carbon atoms, or -CH2NR d 2, R d Each independently represents an alkyl group having 1 to 10 carbon atoms, an alkanol group having 1 to 10 carbon atoms, an alkenyl group having 2 to 10 carbon atoms, or an aryl group having 6 to 12 carbon atoms.

7. The electrode-forming composition according to claim 1, wherein The R a ~R c 、X a and X b The substituent is at least one selected from the group consisting of a carboxyl group, a hydroxyl group, an aldehyde group, an ester group, a ketone group, an amino group, a phenyl group, a halogen atom, an alkoxysilyl group, an epoxy group, a carboxylic acid chloride group, and a thiol group.

8. The electrode-forming composition according to claim 6, wherein The heterocyclic compound is represented by the following formula (4b): Where R a ~R c Same as above, R e It is a hydrogen atom, a carboxyl group, a hydroxyl group, an aldehyde group, an ester group, a ketone group, an amino group, a phenyl group, a halogen atom, an alkoxysilyl group, an epoxy group, a carboxylic acid chloride group or a thiol group.

9. The electrode-forming composition according to claim 1, wherein The heterocyclic compound is solid at room temperature.

10. The electrode-forming composition according to claim 1, wherein It further contains a conductive auxiliary agent.

11. The electrode-forming composition according to claim 1, wherein The positive electrode active material contains 30 mass % or more of Ni.

12. The electrode-forming composition according to claim 1, wherein The positive electrode active material contains 40 mass % or more of Ni.

13. The electrode-forming composition according to claim 1, wherein The positive electrode active material contains 50 mass % or more of Ni.

14. The electrode-forming composition according to claim 1, wherein It further contains a nonionic polymer.

15. The electrode-forming composition according to claim 14, wherein The nonionic polymer is a polymer having a pyrrolidone structure or a nitrile group.

16. The electrode-forming composition according to claim 15, wherein The nonionic polymer is at least one selected from the group consisting of polyvinyl pyrrolidone and polyacrylonitrile.

17. The electrode-forming composition according to claim 1, wherein The content of the heterocyclic ring-containing compound is 0.001 to 0.5% by mass in the solid content.

18. An electrode-forming composition comprising a positive electrode active material, a binder, a solvent, and a heterocyclic compound. The heterocyclic compound is represented by any of the following formulas (1) to (2): In formula (1), R a and R b each independently represents a hydrogen atom, a carboxyl group, a hydroxyl group, a thiol group, an optionally substituted alkyl group having 1 to 6 carbon atoms, an optionally substituted alkenyl group having 2 to 6 carbon atoms, or an optionally substituted aryl group having 6 to 12 carbon atoms, R a and R b are optionally bonded to each other to form a ring having 4 to 12 carbon atoms which may have a substituent, L is each independently a single bond, a carbonyl group, an ether bond, an ester bond or an amide bond, Z is N or C-L-R c , R c is a hydrogen atom, a halogen atom, a carboxyl group, a hydroxyl group, a thiol group, an alkyl group having 1 to 6 carbon atoms which may have a substituent, an alkenyl group having 2 to 6 carbon atoms which may have a substituent, or an aryl group having 6 to 12 carbon atoms which may have a substituent, X a A hydrogen atom, a lithium atom, a sodium atom, an alkyl group having 1 to 6 carbon atoms which may have a substituent, an aryl group having 6 to 12 carbon atoms which may have a substituent, or -CH2NR d 2, R d Each is independently an alkyl group having 1 to 10 carbon atoms, an alkanol group having 1 to 10 carbon atoms, an alkenyl group having 2 to 10 carbon atoms, or an aryl group having 6 to 12 carbon atoms; In formula (2), R a and R b each independently represents a hydrogen atom, a halogen atom, a carboxyl group, a hydroxyl group, a thiol group, an optionally substituted alkyl group having 1 to 6 carbon atoms, an optionally substituted alkenyl group having 2 to 6 carbon atoms, or an optionally substituted aryl group having 6 to 12 carbon atoms, L is each independently a single bond, a carbonyl group, an ether bond, an ester bond or an amide bond, X a A hydrogen atom, a lithium atom, a sodium atom, an alkyl group having 1 to 6 carbon atoms which may have a substituent, an aryl group having 6 to 12 carbon atoms which may have a substituent, or -CH2NR d 2, R d Each independently represents an alkyl group having 1 to 10 carbon atoms, an alkanol group having 1 to 10 carbon atoms, an alkenyl group having 2 to 10 carbon atoms, or an aryl group having 6 to 12 carbon atoms.

19. The electrode-forming composition according to claim 18, wherein The heterocyclic compound is attached to the positive electrode active material.

20. The electrode-forming composition according to claim 18, wherein The R a ~R c 、X a and X b The substituent is at least one selected from the group consisting of a carboxyl group, a hydroxyl group, an aldehyde group, an ester group, a ketone group, a phenyl group, a halogen atom, an alkoxysilyl group, an epoxy group, a carboxylic acid chloride group, and a thiol group.

21. The electrode-forming composition according to claim 18, wherein The heterocyclic compound is a heterocyclic compound represented by the following formula (5): Where Ar 1 is an aromatic ring having 4 to 12 carbon atoms and optionally having a substituent or an aliphatic ring having 4 to 10 carbon atoms and optionally having a substituent; Z, X a Same as above.

22. The electrode-forming composition according to claim 21, wherein The heterocyclic compound is a heterocyclic compound represented by any of the following formulas (6) to (7), Where Z and X a Same as above.

23. The electrode-forming composition according to claim 18, wherein The Z is N.

24. The electrode-forming composition according to claim 18, wherein It further contains a conductive auxiliary agent.

25. The electrode-forming composition according to claim 18, wherein The positive electrode active material contains 30 mass % or more of Ni.

26. The electrode-forming composition according to claim 18, wherein The positive electrode active material contains 40 mass % or more of Ni.

27. The electrode-forming composition according to claim 18, wherein The positive electrode active material contains 50 mass % or more of Ni.

28. The electrode-forming composition according to claim 18, wherein It further contains a nonionic polymer.

29. The electrode-forming composition according to claim 28, wherein The nonionic polymer is a polymer having a pyrrolidone structure or a nitrile group.

30. The electrode-forming composition according to claim 29, wherein The nonionic polymer is at least one selected from the group consisting of polyvinyl pyrrolidone and polyacrylonitrile.

31. The electrode-forming composition according to claim 18, wherein The content of the heterocyclic ring-containing compound is 0.001 to 0.5% by mass in the solid content. 32 . An electrode layer obtained from the electrode-forming composition according to claim 1 .

33. An electrode comprising the electrode layer according to claim 32. A secondary battery comprising the electrode according to claim 33 .

35. A method for producing an electrode-forming composition, which is the method for producing an electrode-forming composition according to claim 1, comprising: A step of mixing a positive electrode active material, a binder, and a solvent to prepare a dispersion; as well as A step of mixing the dispersion with a heterocyclic compound.

36. The method for producing an electrode-forming composition according to claim 35, wherein: In the step of preparing the dispersion, a conductive auxiliary agent is further mixed.

37. A method for producing an electrode-forming composition, which is the method for producing an electrode-forming composition according to claim 18, comprising: A step of mixing a positive electrode active material, a binder, and a solvent to prepare a dispersion; as well as A step of mixing the dispersion with a heterocyclic compound.

38. The method for producing an electrode-forming composition according to claim 37, wherein: In the step of preparing the dispersion, a conductive auxiliary agent is further mixed.

39. An additive for an electrode slurry comprising a positive electrode active material, a binder, and a solvent. The additive includes a heterocyclic compound having a nitrogen-containing five-membered ring, the five-membered ring not containing an oxygen atom, and a carbonyl structure on the five-membered ring.

40. The additive according to claim 39, wherein The heterocyclic compound is an uncontracted nitrogen-containing five-membered heterocyclic compound.

41. The additive according to claim 39, wherein The carbonyl structure shows proton tautomerism.

42. The additive according to claim 41, wherein The proton tautomerism is keto-enol tautomerism.

43. The additive according to claim 39, wherein The heterocyclic compound is represented by any of the following formulas (3) to (4): Where R a ~R c each independently represents a hydrogen atom, a halogen atom, a carboxyl group, a hydroxyl group, a thiol group, an amino group, an optionally substituted alkyl group having 1 to 6 carbon atoms, an optionally substituted alkenyl group having 2 to 6 carbon atoms, or an optionally substituted aryl group having 6 to 12 carbon atoms, R a and R b are optionally bonded to each other to form a ring having 4 to 12 carbon atoms which may have a substituent, L is each independently a single bond, a carbonyl group, an ether bond, an ester bond or an amide bond, X a and X b Each is independently a hydrogen atom, a lithium atom, a sodium atom, an optionally substituted alkyl group having 1 to 6 carbon atoms, an optionally substituted aryl group having 6 to 12 carbon atoms, or -CH2NR d 2, R d Each independently represents an alkyl group having 1 to 10 carbon atoms, an alkanol group having 1 to 10 carbon atoms, an alkenyl group having 2 to 10 carbon atoms, or an aryl group having 6 to 12 carbon atoms.

44. The additive according to claim 43, wherein The R a ~R c 、X a and X b The substituent is at least one selected from the group consisting of a carboxyl group, a hydroxyl group, an aldehyde group, an ester group, a ketone group, an amino group, a phenyl group, a halogen atom, an alkoxysilyl group, an epoxy group, a carboxylic acid chloride group, and a thiol group.

45. The additive according to claim 43, wherein The heterocyclic compound is represented by the following formula (4b): Where R a ~R c Same as above, R e It is a hydrogen atom, a carboxyl group, a hydroxyl group, an aldehyde group, an ester group, a ketone group, an amino group, a phenyl group, a halogen atom, an alkoxysilyl group, an epoxy group, a carboxylic acid chloride group or a thiol group.

46. The additive according to claim 39, wherein The heterocyclic compound is solid at room temperature.

47. The additive according to claim 39, wherein The positive electrode active material contains 30 mass % or more of Ni.

48. The additive according to claim 39, wherein It further contains a nonionic polymer.

49. The additive according to claim 48, wherein The nonionic polymer is a polymer having a pyrrolidone structure or a nitrile group.

50. The additive according to claim 49, wherein The nonionic polymer is at least one selected from the group consisting of polyvinyl pyrrolidone and polyacrylonitrile.

51. The additive according to claim 39, wherein Further comprising a solvent.

52. An additive for an electrode slurry comprising a positive electrode active material, a binder and a solvent, The additive comprises a heterocyclic compound represented by any of the following formulas (1) to (2), In formula (1), R a and R b each independently represents a hydrogen atom, a carboxyl group, a hydroxyl group, a thiol group, an optionally substituted alkyl group having 1 to 6 carbon atoms, an optionally substituted alkenyl group having 2 to 6 carbon atoms, or an optionally substituted aryl group having 6 to 12 carbon atoms, R a and R b are optionally bonded to each other to form a ring having 4 to 12 carbon atoms which may have a substituent, L is each independently a single bond, a carbonyl group, an ether bond, an ester bond or an amide bond, Z is N or C-L-R c , R c is a hydrogen atom, a halogen atom, a carboxyl group, a hydroxyl group, a thiol group, an alkyl group having 1 to 6 carbon atoms which may have a substituent, an alkenyl group having 2 to 6 carbon atoms which may have a substituent, or an aryl group having 6 to 12 carbon atoms which may have a substituent, X a A hydrogen atom, a lithium atom, a sodium atom, an alkyl group having 1 to 6 carbon atoms which may have a substituent, an aryl group having 6 to 12 carbon atoms which may have a substituent, or -CH2NR d 2, R d Each is independently an alkyl group having 1 to 10 carbon atoms, an alkanol group having 1 to 10 carbon atoms, an alkenyl group having 2 to 10 carbon atoms, or an aryl group having 6 to 12 carbon atoms; In formula (2), R a and R b each independently represents a hydrogen atom, a halogen atom, a carboxyl group, a hydroxyl group, a thiol group, an optionally substituted alkyl group having 1 to 6 carbon atoms, an optionally substituted alkenyl group having 2 to 6 carbon atoms, or an optionally substituted aryl group having 6 to 12 carbon atoms, L is each independently a single bond, a carbonyl group, an ether bond, an ester bond or an amide bond, X a A hydrogen atom, a lithium atom, a sodium atom, an alkyl group having 1 to 6 carbon atoms which may have a substituent, an aryl group having 6 to 12 carbon atoms which may have a substituent, or -CH2NR d 2, R d Each independently represents an alkyl group having 1 to 10 carbon atoms, an alkanol group having 1 to 10 carbon atoms, an alkenyl group having 2 to 10 carbon atoms, or an aryl group having 6 to 12 carbon atoms.

53. The additive according to claim 52, wherein The positive electrode active material contains 30 mass % or more of Ni.

54. The additive according to claim 52, wherein It further contains a nonionic polymer.

55. The additive according to claim 54, wherein The nonionic polymer is a polymer having a pyrrolidone structure or a nitrile group.

56. The additive according to claim 55, wherein The nonionic polymer is at least one selected from the group consisting of polyvinyl pyrrolidone and polyacrylonitrile.

57. The additive according to claim 52, wherein Further comprising a solvent.

58. A gelation inhibitor for an electrode slurry comprising a positive electrode active material, a binder, and a solvent. The gelation inhibitor includes a heterocyclic compound having a nitrogen-containing five-membered ring, wherein the nitrogen-containing five-membered ring does not contain an oxygen atom.

59. The gelation inhibitor according to claim 58, wherein The heteroatom contained in the nitrogen-containing five-membered ring is only a nitrogen atom.

60. The gelation inhibitor according to claim 59, wherein The nitrogen-containing five-membered ring contains two or three nitrogen atoms.

61. The gelation inhibitor according to claim 58, wherein The heterocyclic compound has a carbonyl structure on the five-membered ring.

62. The gelation inhibitor according to claim 61, wherein The heterocyclic compound is an uncontracted nitrogen-containing five-membered heterocyclic compound.

63. The gelation inhibitor according to claim 61, wherein The carbonyl structure shows proton tautomerism.

64. The gelation inhibitor according to claim 63, wherein The proton tautomerism is keto-enol tautomerism.

65. The gelation inhibitor according to claim 58, wherein A heterocyclic compound represented by any of the following formulae (3) to (4), Where R a ~R c each independently represents a hydrogen atom, a halogen atom, a carboxyl group, a hydroxyl group, a thiol group, an amino group, an optionally substituted alkyl group having 1 to 6 carbon atoms, an optionally substituted alkenyl group having 2 to 6 carbon atoms, or an optionally substituted aryl group having 6 to 12 carbon atoms, R a and R b are optionally bonded to each other to form a ring having 4 to 12 carbon atoms which may have a substituent, L is each independently a single bond, a carbonyl group, an ether bond, an ester bond or an amide bond, X a and X b Each is independently a hydrogen atom, a lithium atom, a sodium atom, an optionally substituted alkyl group having 1 to 6 carbon atoms, an optionally substituted aryl group having 6 to 12 carbon atoms, or -CH2NR d 2, R d Each independently represents an alkyl group having 1 to 10 carbon atoms, an alkanol group having 1 to 10 carbon atoms, an alkenyl group having 2 to 10 carbon atoms, or an aryl group having 6 to 12 carbon atoms.

66. The gelation inhibitor according to claim 65, wherein The R a ~R c 、X a and X b The substituent is at least one selected from the group consisting of a carboxyl group, a hydroxyl group, an aldehyde group, an ester group, a ketone group, an amino group, a phenyl group, a halogen atom, an alkoxysilyl group, an epoxy group, a carboxylic acid chloride group, and a thiol group.

67. The gelation inhibitor according to claim 65, wherein The heterocyclic compound is represented by the following formula (4b): Where R a ~R c Same as above, R e It is a hydrogen atom, a carboxyl group, a hydroxyl group, an aldehyde group, an ester group, a ketone group, an amino group, a phenyl group, a halogen atom, an alkoxysilyl group, an epoxy group, a carboxylic acid chloride group or a thiol group.

68. The gelation inhibitor according to claim 58, wherein The heterocyclic compound is solid at room temperature.

69. The gelation inhibitor according to claim 58, wherein The positive electrode active material contains 30 mass % or more of Ni.

70. The gelation inhibitor according to claim 58, wherein It further contains a nonionic polymer.

71. The gelation inhibitor according to claim 70, wherein The nonionic polymer is a polymer having a pyrrolidone structure or a nitrile group.

72. The gelation inhibitor according to claim 71, wherein The nonionic polymer is at least one selected from the group consisting of polyvinyl pyrrolidone and polyacrylonitrile.

73. The gelation inhibitor according to claim 58, wherein Further comprising a solvent.

74. A gelation inhibitor for an electrode slurry comprising a positive electrode active material, a binder, and a solvent. The gelation inhibitor comprises a heterocyclic compound represented by any of the following formulas (1) to (2), In formula (1), R a and R b each independently represents a hydrogen atom, a carboxyl group, a hydroxyl group, a thiol group, an optionally substituted alkyl group having 1 to 6 carbon atoms, an optionally substituted alkenyl group having 2 to 6 carbon atoms, or an optionally substituted aryl group having 6 to 12 carbon atoms, R a and R b are optionally bonded to each other to form a ring having 4 to 12 carbon atoms which may have a substituent, L is each independently a single bond, a carbonyl group, an ether bond, an ester bond or an amide bond, Z is N or C-L-R c , R c is a hydrogen atom, a halogen atom, a carboxyl group, a hydroxyl group, a thiol group, an alkyl group having 1 to 6 carbon atoms which may have a substituent, an alkenyl group having 2 to 6 carbon atoms which may have a substituent, or an aryl group having 6 to 12 carbon atoms which may have a substituent, X a A hydrogen atom, a lithium atom, a sodium atom, an alkyl group having 1 to 6 carbon atoms which may have a substituent, an aryl group having 6 to 12 carbon atoms which may have a substituent, or -CH2NR d 2, R d Each is independently an alkyl group having 1 to 10 carbon atoms, an alkanol group having 1 to 10 carbon atoms, an alkenyl group having 2 to 10 carbon atoms, or an aryl group having 6 to 12 carbon atoms; In formula (2), R a and R b each independently represents a hydrogen atom, a halogen atom, a carboxyl group, a hydroxyl group, a thiol group, an optionally substituted alkyl group having 1 to 6 carbon atoms, an optionally substituted alkenyl group having 2 to 6 carbon atoms, or an optionally substituted aryl group having 6 to 12 carbon atoms, L is each independently a single bond, a carbonyl group, an ether bond, an ester bond or an amide bond, X a and X b Each is independently a hydrogen atom, a lithium atom, a sodium atom, an optionally substituted alkyl group having 1 to 6 carbon atoms, an optionally substituted aryl group having 6 to 12 carbon atoms, or -CH2NR d 2, R d Each independently represents an alkyl group having 1 to 10 carbon atoms, an alkanol group having 1 to 10 carbon atoms, an alkenyl group having 2 to 10 carbon atoms, or an aryl group having 6 to 12 carbon atoms.

75. The gelation inhibitor according to claim 74, wherein The R a ~R c 、X a and X b The substituent is at least one selected from the group consisting of a carboxyl group, a hydroxyl group, an aldehyde group, an ester group, a ketone group, a phenyl group, a halogen atom, an alkoxysilyl group, an epoxy group, a carboxylic acid chloride group, and a thiol group.

76. The gelation inhibitor according to claim 74, wherein The heterocyclic compound is a heterocyclic compound represented by the following formula (5): Where Ar 1 is an aromatic ring having 4 to 12 carbon atoms and optionally having a substituent or an aliphatic ring having 4 to 10 carbon atoms and optionally having a substituent; Z, X a Same as above.

77. The gelation inhibitor according to claim 76, wherein The heterocyclic compound is a heterocyclic compound represented by any of the following formulas (6) to (7), Where Z and X a Same as above.

78. The gelation inhibitor according to claim 74, wherein The Z is N.

79. The gelation inhibitor according to claim 74, wherein The positive electrode active material contains 30 mass % or more of Ni.

80. The gelation inhibitor according to claim 74, wherein It further contains a nonionic polymer.

81. The gelation inhibitor according to claim 80, wherein The nonionic polymer is a polymer having a pyrrolidone structure or a nitrile group.

82. The gelation inhibitor according to claim 81, wherein The nonionic polymer is at least one selected from the group consisting of polyvinyl pyrrolidone and polyacrylonitrile.

83. The gelation inhibitor according to claim 74, wherein Further comprising a solvent.

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