Electrode-forming composition, additive, and gelation inhibitor

Abstract

This composition for electrode formation contains a compound having a ring structure and an unsaturated bond, a positive electrode active material, a binder, and a solvent. The compound has dissociative protons in the molecules thereof. The proton dissociation energy of the compound is less than 1484.2 (kJ / mol). The highest occupied molecular orbital (HOMO) of the compound is greater than -0.27736 (a.u.).

Description

[Technical Field]

[0001] The present invention relates to an electrode-forming composition, an additive, and a gelation inhibitor. The present invention also relates to an electrode layer, a secondary battery, a method for producing an electrode-forming composition, and a method for inhibiting gelation of an electrode-forming composition. [Background technology]

[0002] Lithium-ion secondary batteries have a high energy density per weight and volume, which contributes to the miniaturization and lightening of electronic devices. In recent years, the spread of electric vehicles has accelerated as part of efforts to achieve zero-emissions automobiles, and there is a demand for batteries with even lower resistance, longer life, higher capacity, safety, and lower cost.

[0003] Lithium-ion secondary batteries generally have a three-layer structure consisting of a positive electrode, a separator, and a negative electrode, each containing an electrolyte. The positive electrode and the negative electrode are manufactured, for example, by coating a current collector with an electrode slurry, which is a mixture of an active material, a conductive material, and a binder. Currently, the most common method for manufacturing a negative electrode is to coat a copper foil current collector with the negative electrode slurry and then dry it. The most common method for manufacturing a positive electrode is to prepare a positive electrode slurry using an organic solvent such as N-methyl-2-pyrrolidone as a solvent, and then coat the resulting positive electrode slurry on an aluminum foil current collector.

[0004] Inorganic compounds such as transition metal oxides and transition metal chalcogens containing alkali metals are known as positive electrode active materials for lithium-ion secondary batteries, as they can provide a battery voltage of around 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 xHigh-nickel positive electrode active materials, such as NiO2, have a high discharge capacity and are attractive positive electrode materials, but alkaline components such as LiOH, Li2O, LiHCO3, and Li2CO3 are generated on the surface through proton exchange reactions with raw material residues or moisture, and reactions with moisture and carbon dioxide in the air.

[0006] When such a positive electrode active material is used, the electrode slurry may thicken or gel, gradually losing its fluidity, which not only makes it difficult to achieve a uniform coating thickness but also makes it impossible to apply the electrode slurry, resulting in waste of material.

[0007] The main cause of this is thought to be that during the process of manufacturing the positive electrode, alkaline components present on the surface of the positive electrode active material, in the presence of trace amounts of moisture, promote the dehydrofluorination reaction of the fluorine-based binder, such as polyvinylidene fluoride (PVdF), which has a vinylidene fluoride structure and is used as a binder.

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

[0009] The thickening and gelation described above can be suppressed by handling the raw materials and the electrode slurry in a dry environment and controlling the water content. However, this requires large-scale facilities for a series of mass production processes from the preparation of the electrode slurry to the manufacture of the battery, and also poses problems of increased costs and increased environmental load due to the use of large amounts of electricity.

[0010] To solve this problem, for example, Patent Document 1 discloses a technique for suppressing gelation of an electrode slurry by preparing the electrode slurry (cathode material slurry) so that it does not exhibit strong alkalinity even when dispersed in water. However, preparing an electrode slurry that does not exhibit strong alkalinity using the method described in Patent Document 1 not only requires strict pH control, but also requires a process in which the cathode active material is first dispersed in water, filtered to extract the cathode active material from the dispersion, and then dried. This results in cumbersome operations and a reduced yield. Furthermore, such a process may cause a decrease in the performance of the cathode active material itself.

[0011] Furthermore, Patent Document 2 reports a technology that uses a compound such as ultra-high molecular weight (weight average molecular weight of 2.2 million or more) polyethylene oxide to bind water through interactions with water (e.g., hydrogen bonding), thereby suppressing the reaction between the alkaline component of the positive electrode active material and water, thereby suppressing thickening and gelation. However, ultra-high molecular weight polymers with strong thickening effects have handling issues, such as the time and cost required for uniform dissolution in a solvent and the difficulty of producing a highly concentrated solution. Furthermore, because the above-mentioned ultra-high molecular weight polymers have a high ability to bind water, there is a concern that the polymer itself may bring in water, and to prevent this, strict control over pre-drying is required.

[0012] Patent Documents 3 and 4 propose adding an organic or inorganic acid to the positive electrode of a lithium-ion secondary battery to suppress gelation of the electrode slurry (positive electrode mixture slurry). Patent Document 3 uses maleic acid, citraconic acid, and malonic acid in the positive electrode mixture, while Patent Document 4 uses acetic acid, phosphoric acid, sulfuric acid, or the like in the electrode slurry (positive electrode paste). However, neutralizing the alkali with an acid requires the addition of a large amount of acid, which may result in a decrease in the battery's energy density or an increase in battery resistance. Another problem is that the acid corrodes the device used to fabricate the electrode. Furthermore, with this method, the high acidity of the organic or inorganic acid may cause a neutralization reaction with the lithium ions in the active material, potentially leading to a deterioration in battery performance.

[0013] Patent Document 5 reports a method for treating a positive electrode active material with fluorine gas and immobilizing the remaining LiOH as LiF, thereby preventing gelation and suppressing gas generation. However, fluorine gas is highly toxic and difficult to handle. In addition, LiF produced as a by-product increases the internal resistance of the battery, reducing capacity, and corrosion of the positive electrode active material by fluorine gas also reduces capacity. Furthermore, there is a problem in that the residual fluorine reacts with traces of moisture present in the active material and electrolyte to produce hydrogen fluoride, which easily causes cycle deterioration.

[0014] Patent Document 6 reports that unreacted lithium hydroxide and impurities derived from raw materials can be removed by washing with an aqueous solution containing a lithium salt. However, this method has issues such as increased environmental impact due to the wastewater generated during washing and the costs associated with treating the wastewater. [Prior art documents] [Patent documents]

[0015] [Patent Document 1] Japanese Patent Application Laid-Open No. 2000-90917 [Patent Document 2] Japanese Patent Application Publication No. 2019-121471 [Patent Document 3] Japanese Patent Application Publication No. 9-306502 [Patent Document 4] Japanese Patent Application Publication No. 10-79244 [Patent Document 5] Japanese Patent Application Laid-Open No. 2006-286240 [Patent Document 6] International Publication No. 2017 / 034001 Summary of the Invention [Problem to be solved by the invention]

[0016] In view of the above circumstances, an object of the present invention is to provide an electrode-forming composition that has improved storage stability by suppressing thickening and gelation using a simple method, as well as an additive for the electrode-forming composition and a method for suppressing gelation. Another object of the present invention is to provide an electrode layer and a secondary battery that use the electrode-forming composition, as well as a method for producing the electrode-forming composition and a method for suppressing gelation of the electrode-forming composition. [Means for solving the problem]

[0017] The present inventors have conducted extensive research to solve the above problems, and as a result have found that the above problems can be solved, and have completed the present invention having the following gist.

[0018] That is, the present invention includes the following. [1] An electrode-forming composition comprising a compound having a ring structure and an unsaturated bond, a positive electrode active material, a binder, and a solvent, The compound has a dissociable proton in the molecule, The proton dissociation energy of the compound is less than 1484.2 (kJ / mol), The highest occupied molecular orbital (HOMO) of the compound is greater than -0.27736 (au); Composition for forming electrodes. [2] The electrode-forming composition according to [1], wherein the positive electrode active material includes a first positive electrode active material that is a polycrystalline body and a second positive electrode active material that is a single crystal body. [3] The electrode-forming composition according to [2], wherein the first positive electrode active material is lithium-containing transition metal oxide particles having a layered rock salt structure, and the crystallite size determined by Scherrer's equation based on the diffraction peak of the (104) plane obtained from an X-ray diffraction pattern of the lithium-containing transition metal oxide particles using a CuKα radiation source is 20 nm or more and less than 500 nm. [4] The electrode-forming composition according to [2] or [3], wherein the second positive electrode active material is lithium-containing transition metal oxide particles having a layered rock salt structure, and the crystallite size determined by Scherrer's equation based on the diffraction peak of the (104) plane obtained from an X-ray diffraction pattern of the lithium-containing transition metal oxide particles using a CuKα radiation source is 50 nm or more and less than 800 nm. [5] The lithium-containing transition metal oxide particles having a layered rock salt structure in the first positive electrode active material are represented by the general formula Li a Ni (1-x-y) Co x M 1 y M 2 z O2 (in the formula, M 1 is at least one selected from the group consisting of Mn and Al, M 2 represents at least one selected from the group consisting of Zr, Ti, Mg, B, W, and V, and is 1.00≦a≦1.50, 0.00≦x≦0.50, 0.00≦y≦0.50, and 0.000≦z≦0.020. [6] The lithium-containing transition metal oxide particles having a layered rock salt structure in the second positive electrode active material are represented by the general formula Li a Ni (1-x-y) Co x M 1 y M 2 z O2 (in the formula, M 1 is 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, B, W, and V, and is 1.00≦a≦1.50, 0.00≦x≦0.50, 0.00≦y≦0.50, and 0.000≦z≦0.020. [7] The electrode-forming composition according to any one of [1] to [6], wherein the ring structure is an aromatic ring. [8] The electrode-forming composition according to any one of [1] to [7], wherein the compound has a heteroatom. [9] The electrode-forming composition according to any one of [1] to [8], wherein the positive electrode active material contains a metal oxide containing Ni.

[10] The electrode-forming composition according to any one of [1] to [9], wherein the positive electrode active material contains Ni, and the Ni content in the positive electrode active material is 30% by mass or more and 61% by mass or less.

[11] The electrode-forming composition according to any one of [1] to

[10] , wherein the solvent is an aprotic solvent.

[12] The electrode-forming composition according to any one of [1] to

[11] , wherein the binder is a fluorine-based binder.

[13] The electrode-forming composition according to any one of [1] to

[12] , further comprising a conductive additive.

[14] An electrode layer obtained from the electrode-forming composition according to any one of [1] to

[13] .

[15] A secondary battery comprising the electrode layer according to

[14] .

[16] A method for producing an electrode-forming composition according to any one of [1] to

[13] , a method for producing an electrode-forming composition, the method comprising: mixing the compound, the binder, the solvent, a first positive electrode active material that is a polycrystalline body, and a second positive electrode active material that is a single crystal body.

[17] The method for producing an electrode-forming composition according to

[16] , wherein a mass ratio of the first positive electrode active material to the second positive electrode active material in the electrode-forming composition (first positive electrode active material:second positive electrode active material) is 2:8 to 8:2.

[18] An additive for an electrode-forming composition comprising a first positive electrode active material that is a polycrystalline body, a second positive electrode active material that is a single crystal body, a binder, and a solvent, An additive having a dissociable proton in the molecule, a proton dissociation energy of less than 1484.2 (kJ / mol), and a highest occupied molecular orbital (HOMO) of greater than -0.27736 (au).

[19] A gelation inhibitor for an electrode-forming composition comprising a first positive electrode active material that is a polycrystalline body, a second positive electrode active material that is a single crystal body, a binder, and a solvent, A gelation inhibitor having a dissociable proton in the molecule, a proton dissociation energy of less than 1484.2 (kJ / mol), and a highest occupied molecular orbital (HOMO) of greater than -0.27736 (au).

[20] A method for suppressing gelation of an electrode-forming composition including a first positive electrode active material that is a polycrystalline body, a second positive electrode active material that is a single crystal body, a binder, and a solvent, comprising: A method for suppressing gelation, in which the electrode-forming composition contains a compound having a dissociable proton in the molecule, a proton dissociation energy of less than 1484.2 (kJ / mol), and a highest occupied molecular orbital (HOMO) of more than -0.27736 (au). [Effects of the Invention]

[0019] According to the present invention, it is possible to provide an electrode-forming composition that is inhibited from thickening and gelling and has improved storage stability by a simple method, as well as an additive for the electrode-forming composition and a method for inhibiting gelling. Furthermore, it is possible to provide an electrode layer and a secondary battery that use the electrode-forming composition, as well as a method for producing the electrode-forming composition and a method for inhibiting gelling of the electrode-forming composition. [Brief explanation of the drawings]

[0020] [Figure 1] FIG. 1 is a diagram in which the proton dissociation energy is plotted on the horizontal axis and the HOMO is plotted on the vertical axis for additives A1 to A28, a1 to a12, a25 and a26. DETAILED DESCRIPTION OF THE INVENTION

[0021] (Composition for electrode formation) The electrode-forming composition of the present invention contains at least a compound having a ring structure and an unsaturated bond (hereinafter sometimes referred to as a "specific compound"), a positive electrode active material, a binder, and a solvent. The electrode-forming composition may contain other components.

[0022] The specific compound has a dissociable proton in the molecule. The proton dissociation energy of the specific compound is less than 1484.2 (kJ / mol). The highest occupied molecular orbital (HOMO) of a particular compound is greater than -0.27736 (au).

[0023] The electrode-forming composition of the present invention is resistant to thickening and gelation and has high storage stability, making it suitable for use in forming positive electrodes for secondary batteries. When a secondary battery equipped with an electrode made using this composition is manufactured, benefits such as improved quality and yield due to the improved storage stability of the composition, cost reduction and reduced environmental impact due to a high solids concentration, and suppression of deterioration within the battery caused by alkaline components can be expected, contributing to reduced manufacturing costs of the secondary battery and improved battery characteristics. An electrode-forming composition is more likely to thicken and gel when it contains two types of positive electrode active materials (particularly, a first positive electrode active material that is a polycrystalline body and a second positive electrode active material that is a single crystal body). In one aspect of the electrode-forming composition of the present invention, by adding a specific compound to an electrode-forming composition containing a positive electrode active material that includes two types of positive electrode active materials (particularly, a first positive electrode active material that is a polycrystalline body and a second positive electrode active material that is a single crystal body), it is possible to suppress thickening and gelling of a composition that is more likely to thicken and gel. Although the mechanisms of thickening and gelling, and the mechanism by which the inhibitory effect is exerted, are not clear, the inventors believe that one factor is that, when a specific compound is added to an electrode-forming composition, the specific compound inactivates radicals that are generated in the composition and promote thickening and gelling. If a compound has a dissociative proton and the compound's proton dissociation energy is small, the compound is likely to release a proton, and the released proton is easily reduced by one electron, easily generating hydrogen radicals. If the highest occupied molecular orbital (HOMO) of a compound is high, the compound is more likely to radicalize and easily generate hydrogen radicals. This can be illustrated as follows. [ka]

[0024] The hydrogen radicals react (e.g., radical coupling) with binder radicals that have been generated due to alkaline components present in or generated in the composition. When the binder radicals are inactivated by the above reaction, binder reactions that promote thickening and gelation are suppressed. As a result, thickening and gelation of the composition can be suppressed, and storage stability is thought to be improved. However, these are speculations, and the present invention should not be interpreted as being limited to these mechanisms. By suppressing thickening and gelation of the electrode-forming composition, it is possible to form a homogeneous positive electrode layer. It is also possible to increase the solids concentration in the electrode slurry, thereby reducing the cost and environmental impact of producing energy storage devices. Furthermore, it is possible to suppress corrosion of aluminum foil, which is commonly used as a current collector foil, caused by alkaline components, and deterioration of battery characteristics due to reaction with the electrolyte.

[0025] <Specific compound> The specific compound is a compound having a ring structure and an unsaturated bond. The specific compound has a dissociable proton in the molecule. The proton dissociation energy of the specific compound is less than 1484.2 (kJ / mol). The highest occupied molecular orbital (HOMO) of a particular compound is greater than -0.27736 (au). Although the specific compound has a ring structure and an unsaturated bond, the presence or absence of the ring structure and the unsaturated bond is not important in terms of whether or not the effects of the present invention are exhibited.

[0026] The ring structure of the specific compound may be an aliphatic ring or an aromatic ring. The ring structure of the specific compound may be a hydrocarbon ring or a heterocyclic ring. The specific compound may or may not have a heterocycle. The specific compound may or may not have an aromatic ring.

[0027] The unsaturated bond contained in the specific compound may be a double bond or a triple bond. The unsaturated bond contained in the specific compound may be an unsaturated bond that forms a ring structure. For example, benzene is a compound that has a ring structure and three unsaturated bonds. Examples of double bonds include carbon-carbon double bonds, carbon-oxygen double bonds, carbon-nitrogen double bonds, carbon-sulfur double bonds, and nitrogen-nitrogen double bonds. Examples of triple bonds include carbon-carbon triple bonds and carbon-nitrogen triple bonds. The number of unsaturated bonds in the specific compound is not particularly limited, and may be one or two or more.

[0028] The specific compound is composed of, for example, hydrogen and at least one non-metallic element selected from elements in groups 14 to 17. Examples of the non-metallic elements selected from elements in groups 14 to 17 include boron, carbon, silicon, nitrogen, phosphorus, oxygen, sulfur, and halogens. The specific compound may or may not have a heteroatom. Examples of heteroatoms include oxygen atoms, nitrogen atoms, phosphorus atoms, silicon atoms, sulfur atoms, and halogen atoms. Examples of halogen atoms include fluorine atoms, chlorine atoms, iodine atoms, and bromine atoms. For example, when the specific compound has a heteroatom, the heteroatom contained in the specific compound is at least one of an oxygen atom, a sulfur atom, and a nitrogen atom. For example, when a specific compound has heteroatoms, the heteroatoms contained in the specific compound are only nitrogen atoms.

[0029] The specific compound is different from the solvent in the present invention. In this respect, the specific compound is, for example, solid at room temperature. In the present invention, being solid at room temperature means that the melting point at 1 atmosphere is 25°C or higher.

[0030] The molecular weight of the specific compound is not particularly limited, and may be, for example, 60 to 1,000, 60 to 700, 100 to 700, or 100 to 350.

[0031] The number of dissociable protons possessed by the specific compound is not particularly limited, and may be one or two or more. If the proton dissociation energy can be calculated, the compound is said to have a dissociable proton.

[0032] The proton dissociation energy of the specific compound is less than 1484.2 (kJ / mol), and may be 1479.4 (kJ / mol) or less, or 1474.5 (kJ / mol) or less. The lower limit of the proton dissociation energy is not particularly limited, but the proton dissociation energy may be, for example, 1254.0 (kJ / mol) or more, 1300.0 (kJ / mol) or more, or 1345.9 (kJ / mol) or more. The method for calculating the proton dissociation energy is as follows. [Method for calculating proton dissociation energy] The most stable structure of the target molecule (HA) in the ground state under vacuum is calculated using B3LYP as the functional and 6-31+G(d) as the basis set, and its total energy E(HA) is calculated. Furthermore, the dissociative protons (H + ) dissociated into one anion (A - ) is calculated using the functional B3LYP and the basis set 6-31+G(d) to find the most stable structure in the ground state under vacuum. The total energy E(A - ) is calculated to obtain the proton dissociation energy ΔE defined by the following equation (a) pd Calculate the amount (unit: kJ / mol). (a) ΔE pd =[E(A - )+E(H + )]-E(HA) However, protons (H + ) has no electrons, so the total energy cannot be evaluated by quantum chemical calculations. Therefore, the total energy of the proton here, E(H + For molecules with multiple dissociative protons, only the first stage of proton dissociation is considered, and the total energy E(A - ) is calculated for the proton dissociation position where it is minimum.

[0033] The highest occupied molecular orbital (HOMO) of the specific compound is greater than -0.27736 (au), and may be -0.27423 (au) or greater, or may be -0.27109 (au) or greater. The upper limit of the highest occupied molecular orbital (HOMO) is not particularly limited, but the highest occupied molecular orbital (HOMO) may be, for example, −0.15780 (au) or less, −0.17617 (au) or less, or −0.19533 (au) or less. The highest occupied molecular orbital (HOMO) is calculated as follows: [How to calculate the highest occupied molecular orbital (HOMO)] The most stable structure of the target molecule in its ground state under vacuum is calculated using the B3LYP functional and 6-31+G(d) basis set, and the energy level (unit: atomic unit (au)) of the highest occupied molecular orbital (HOMO) is calculated.

[0034] Examples of specific compounds are shown below. [ka] [ka]

[0035] The content of the specific compound in the electrode-forming composition is not particularly limited, but is preferably 0.001 to 4 mass % of the solid content, more preferably 0.001 to 2 mass %, even more preferably 0.001 to 0.5 mass %, even more preferably 0.001 to 0.3 mass %, and particularly preferably 0.001 to 0.2 mass %. Furthermore, an even more preferable lower limit of the content of the specific compound is 0.01 mass % of the solid content. By setting the content of the specific compound within the above range, gelation of the electrode-forming composition can be effectively suppressed, and the battery characteristics of the obtained battery can be maintained. In the present invention, the solid content means components other than the solvent that constitute the composition (the same applies hereinafter).

[0036] The content of the specific compound in the electrode-forming composition is preferably 0.001 to 4 parts by mass, more preferably 0.001 to 2 parts by mass, even more preferably 0.001 to 0.5 parts by mass, even more 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 specific 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.

[0037] The content of the specific compound in the electrode-forming composition 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 specific 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.

[0038] Furthermore, when the electrode-forming composition contains a conductive additive, the content of the specific compound in the electrode-forming composition 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, per 100 parts by mass of the conductive additive.

[0039] <Cathode active material> The positive electrode active material is not particularly limited.

[0040] As the positive electrode active material, those containing S, Fe, or Ni are preferred, and those containing 30% by mass or more of S, Fe, or Ni are more preferred, from the viewpoints of further improving battery capacity, using less rare metals, and being low cost. Considering further reducing the amount of rare metals used and obtaining a battery with an even longer life, those containing 35% by mass or more of Fe or Ni are even more preferred, and those containing 45% by mass or more are even more preferred. The upper limit is not particularly limited, but is usually 61% by mass or less.

[0041] Electrode-forming compositions containing a positive electrode active material with a high nickel content tend to thicken and gel. Therefore, in order to suppress thickening and gelling in electrode-forming compositions containing a positive electrode active material with a high nickel content, the positive electrode active material preferably contains Ni, more preferably has a Ni content of 30% by mass or more, and particularly preferably has a Ni content of 40% by mass or more. The upper limit of the Ni content in the positive electrode active material is not particularly limited, but is, for example, 61% by mass or less.

[0042] The positive electrode active material can be appropriately selected from various active materials conventionally used in electrodes for secondary batteries. For example, in the case of lithium secondary batteries or lithium ion secondary batteries, chalcogen compounds capable of absorbing and releasing lithium ions or lithium ion-containing chalcogen compounds, polyanionic compounds, elemental sulfur and its compounds, etc. can be used.

[0043] 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, and 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 is at least one selected from the group consisting of Mn and Al, M 2 represents at least one selected from the group consisting of Zr, Ti, Mg, B, Zr, Si, W, and V, and examples thereof include 1.00≦a≦1.50, 0.00≦x≦0.50, 0.00≦y≦0.50, and 0.000≦z≦0.020). Examples of polyanion compounds include LiFePO4, Li a Mn b Fe c D d PO4 (wherein 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, and at least a portion of which has an olivine structure). Examples of sulfur compounds include sulfur, Li2S, FeS2, TiS2, MoS2, rubeanic acid, and the like. These positive electrode active materials can be used alone or in combination of two or more.

[0044] Among the above positive electrode active materials, the general formula Li a Ni (1-x-y) Co x M 1 y M 2 z O2 (in the formula, M 1 is at least one selected from the group consisting of Mn and Al, M 2 represents at least one selected from the group consisting of Zr, Ti, Mg, B, W, and V, and preferably satisfies 1.00≦a≦1.50, 0.00≦x≦0.50, 0.00≦y≦0.50, and 0.000≦z≦0.020). x may be in the range of 0.01≦x≦0.30, or 0.03≦x≦0.20. y may be in the range of 0.01≦x≦0.30, or 0.03≦x≦0.20. x+y may be 0.02≦(x+y)≦0.40, or 0.05≦(x+y)≦0.30. Li a Ni (1-x-y) Co x M 1 y M 2 z O2 preferably has a Ni content of 30% by mass or more, more preferably 40% by mass or more, more preferably 45% by mass or more, and particularly preferably 47% by mass or more. The upper limit of the Ni content is not particularly limited, but is, for example, 61% by mass or less.

[0045] These active materials can be used alone or in combination of two or more.

[0046] An electrode-forming composition is more likely to thicken and gel when it contains two types of positive electrode active materials (particularly, a first positive electrode active material that is polycrystalline and a second positive electrode active material that is single crystalline). By adding a specific compound to an electrode-forming composition containing two types of positive electrode active materials (particularly, a first positive electrode active material that is polycrystalline and a second positive electrode active material that is single crystalline), it is possible to suppress thickening and gelling of the composition, which is more likely to thicken and gel. In this regard, it is preferable that the positive electrode active material contains a first positive electrode active material that is polycrystalline and a second positive electrode active material that is single crystalline.

[0047] The polycrystalline first positive electrode active material is, for example, lithium-containing transition metal oxide particles having a layered rock salt structure. The crystallite size of the lithium-containing transition metal oxide particles, which is the first positive electrode active material, determined by the Scherrer equation based on the diffraction peak of the (104) plane obtained from an X-ray diffraction pattern using a CuKα radiation source, is, for example, 20 nm or more and less than 500 nm.

[0048] The second positive electrode active material, which is a single crystal, is, for example, a lithium-containing transition metal oxide particle having a layered rock salt structure. The crystallite size of the lithium-containing transition metal oxide particle, which is the second positive electrode active material, is determined by the Scherrer equation based on the diffraction peak of the (104) plane obtained from an X-ray diffraction pattern using a CuKα radiation source, and is, for example, 50 nm or more and less than 800 nm.

[0049] For example, the crystallite diameter of the first positive electrode active material and the crystallite diameter of the second positive electrode active material satisfy the relationship of the following formula (X). x1<(τ2)-(τ1)≦x2...Equation (X) τ1: Crystallite diameter (nm) of the first positive electrode active material τ2: Crystallite diameter (nm) of the second positive electrode active material x1 is 0 nm, preferably 10 nm, more preferably 30 nm, and particularly preferably 70 nm. x2 is 400 nm, preferably 350 nm, more preferably 300 nm, and particularly preferably 250 nm.

[0050] The crystallite size can be determined, for example, as follows. [X-ray diffraction measurement] X-ray diffraction patterns of the positive electrode active material were collected using an X'Pert Pro MPD (PANaltical) with a CuKα radiation source (45 kV, 40 mA) emitting at a wavelength of 1.5418 Å. The instrument configuration was as follows: on the incident side, a 0.02 rad Soller slit, a 10 mm automatic variable divergence slit, and a 1 / 2° anti-scatter slit; on the receiving side, an 8 mm anti-scatter slit and a 0.02 rad Soller slit. The goniometer radius was 240 mm. For XRD, diffraction patterns were acquired from 10 to 100° (2θ) with a step size of 0.013° / scan and a step time of 250 seconds.

[0051] The crystallite size of the positive electrode active material is calculated using the known Scherrer equation from the diffraction angle of the (104) plane peak obtained from the X-ray diffraction pattern and the full width at half maximum (FWHM) obtained by subtracting the device-specific full width at half maximum.

[0052] [Scherrer equation]

number

[0053] When the positive electrode active material includes a first positive electrode active material that is a polycrystalline body and a second positive electrode active material that is a single crystal body, the mass ratio of the first positive electrode active material to the second positive electrode active material (first positive electrode active material:second positive electrode active material) in the electrode-forming composition is not particularly limited, but is preferably 2:8 to 8:2, more preferably 4:6 to 8:2, and particularly preferably 4:6 to 7:3.

[0054] The content of the positive electrode active material in the electrode-forming composition is not particularly limited, but is preferably 88.0 to 99.949 mass % of the solid content, more preferably 88.0 to 99.899 mass %, and even more preferably 95.0 to 99.0 mass %.

[0055] <Binder> The binder can be appropriately selected from known materials and is not particularly limited, but examples thereof include fluorine-based binders, polyimides, ethylene-propylene-diene terpolymers, styrene-butadiene rubber, polyethylene, polypropylene, etc. These are non-aqueous binders. Examples of fluorine-based binders include polyvinylidene fluoride (PVdF); polytetrafluoroethylene (PTFE); and copolymers containing at least one monomer selected from the group consisting of vinylidene fluoride, tetrafluoroethylene, and hexafluoropropylene.

[0056] From the viewpoint of improving the storage stability of the electrode-forming composition, it is preferable to use a fluorine-based binder. Furthermore, the fluorine-based binder is preferably modified with a polar functional group such as a carboxyl group or a hydroxyl group. The polar functional group can be confirmed by the presence or absence of a clear peak detected in the range of 10 to 15 ppm in measurement using a nuclear magnetic resonance (NMR) device.

[0057] The binders can be used alone or in combination of two or more.

[0058] The weight average molecular weight (Mw) of the binder is not particularly limited, but from the viewpoint of improving the adhesion between the current collector and the electrode layer, it is 600,000 to 3,000,000, preferably 700,000 to 2,000,000, and more preferably 700,000 to 1,500,000. The weight average molecular weight is a polystyrene-equivalent value determined by gel permeation chromatography (GPC).

[0059] The content of the binder in the electrode-forming composition is not particularly limited, but from the viewpoint of reducing costs and obtaining a high energy density, it is preferably 0.05 to 8 mass % of the solid content, more preferably 0.05 to 5 mass %, even more preferably 0.05 to 4 mass %, even more preferably 0.1 to 3 mass %, particularly preferably 0.2 to 2 mass %, and most preferably 0.3 to 1.5 mass %.

[0060] <Solvent> The solvent is not particularly limited, and examples thereof include solvents that are conventionally used in preparing electrode-forming compositions. Examples of the solvent include water and organic solvents.

[0061] Examples of the organic solvent include ethers, halogenated hydrocarbons, amides, ketones, alcohols, aliphatic hydrocarbons, aromatic hydrocarbons, glycol ethers, glycols, carbonates, and other organic solvents.

[0062] Examples of ethers include tetrahydrofuran (THF), diethyl ether, and 1,2-dimethoxyethane (DME). Examples of halogenated hydrocarbons include methylene chloride, chloroform, and 1,2-dichloroethane. Examples of amides include N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), and N-methyl-2-pyrrolidone (NMP). Examples of ketones include acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone. Examples of alcohols include methanol, ethanol, n-propanol, isopropanol, n-butanol, and t-butanol. Examples of the aliphatic hydrocarbons include n-heptane, n-hexane, and cyclohexane. Examples of aromatic hydrocarbons include benzene, toluene, xylene, and ethylbenzene. Examples of glycol ethers include ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, and propylene glycol monomethyl ether. Examples of glycols include ethylene glycol and propylene glycol. Examples of carbonates include ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate. Other organic solvents include, for example, γ-butyrolactone, dimethyl sulfoxide (DMSO), dioxolane, sulfolane, and the like.

[0063] The organic solvent may be either a protic solvent or an aprotic solvent, but an aprotic solvent is preferred. The aprotic solvent may be, for example, polar or non-polar. The aprotic solvent is preferably an amide, a ketone, or a carbonate, and more preferably an amide.

[0064] These solvents can be used alone or in combination of two or more.

[0065] The binder may be dissolved or dispersed in these solvents as needed. Suitable solvents in this case include water, NMP, DMSO, ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, γ-butyrolactone, THF, dioxolane, sulfolane, DMF, DMAc, etc. The solvent may be selected appropriately depending on the type of binder, but NMP is suitable for water-insoluble binders such as PVdF, and water is suitable for water-soluble binders.

[0066] The solid content of the electrode-forming composition is set appropriately taking into consideration the coatability of the composition, the thickness of the electrode to be formed, and the like, but is typically 60 to 92 mass %, preferably 65 to 90 mass %, and more preferably 70 to 85 mass %.

[0067] <Other ingredients> Examples of other components that may be contained in the electrode-forming composition include a conductive assistant and a dispersant.

[0068] <<Conductive additives>> The conductive additive is used, for example, to improve electrical conductivity. The conductive assistant is not particularly limited, but examples thereof include carbon materials and conductive polymers. Examples of carbon materials include graphite, carbon black, acetylene black (AB), vapor-grown carbon fiber, carbon nanotubes (CNT), carbon nanohorns, and graphene. Examples of conductive polymers include polyaniline, polypyrrole, polythiophene, polyacetylene, and polyacene. The conductive additives can be used alone or in combination of two or more.

[0069] The content of the conductive additive in the electrode-forming composition is not particularly limited, but is preferably 0.05 to 5 mass % of the solid content, more preferably 0.05 to 4 mass %, even more preferably 0.1 to 3 mass %, and even more preferably 0.2 to 2 mass %. By keeping the content of the conductive additive within the above range, good electrical conductivity can be obtained.

[0070] The electrode-forming composition does not contain, for example, graphene. When the electrode-forming composition contains graphene, the content of graphene in the conductive additive is not particularly limited, but is preferably 45% by mass or less, more preferably 40% by mass or less, and particularly preferably 10% by mass or less.

[0071] <<Dispersant>> The dispersant is used to improve the dispersibility of substances such as the positive electrode active material and the conductive additive. The dispersant can be appropriately selected from those that have been conventionally used as dispersants for conductive carbon materials such as CNTs. As the dispersant, a nonionic polymer is preferred from the viewpoint of stability in the battery. Examples of nonionic polymers include polyvinylpyrrolidone (PVP) and polymers containing at least one functional group selected from the group consisting of a nitrile group, a hydroxy group, a carbonyl group, an amino group, a sulfonyl group, and an ether group. Examples of the functional group-containing polymer include polyvinyl alcohol, polyacrylonitrile, polylactic acid, polyester, polyimide, polyphenyl ether, polyphenyl sulfone, polyethyleneimine, and polyaniline. As the dispersant, a polymer containing a pyrrolidone structure or a nitrile group is preferred, and polyvinylpyrrolidone and polyacrylonitrile are more preferred. The dispersants can be used alone or in combination of two or more.

[0072] The content of the dispersant in the electrode-forming composition is not particularly limited, but is preferably 0.001 to 0.5 mass % of the solid content, more preferably 0.001 to 0.3 mass %, and even more preferably 0.001 to 0.2 mass %. An even more preferable lower limit of the dispersant content is 0.01 mass % of the solid content. Furthermore, in consideration of the adhesion between the resulting electrode layer and the current collector, the total amount of the specific compound and dispersant is preferably 0.001 to 1 mass % of the solid content, and more preferably 0.01 to 1 mass %.

[0073] The viscosity of the electrode-forming composition is set appropriately taking into consideration the coating method, the thickness of the electrode to be formed, and the like, but is typically 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 measured at 25°C using an E-type viscometer.

[0074] The electrode-forming composition of the present invention can be obtained by mixing the above-mentioned components. When the composition contains optional components other than the gelation inhibitor (specific compound) as an additive of the present invention, the positive electrode active material, and the binder, the gelation inhibitor as an additive and the positive electrode active material may be mixed together with the optional components, or both components may be mixed in advance and then mixed with the optional components. Either method can achieve the effects of the present invention.

[0075] (electrode layer) The electrode layer of the present invention is obtained from the electrode-forming composition of the present invention. An example of a method for forming an electrode layer is a method in which an electrode-forming composition is applied to a 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 various printing methods such as offset printing and screen printing, blade coating, dip coating, spin coating, bar coating, slit coating, inkjet printing, and die coating.

[0076] When drying the coating film, either natural drying or heat drying may be used, but heat drying is preferred from the viewpoint of production efficiency. When heat drying is performed, the temperature is preferably 50 to 400°C, more preferably 70 to 150°C.

[0077] The thickness of the electrode layer is not particularly limited, but is preferably 0.01 to 1,000 μm, more preferably 5 to 300 μm. In the secondary battery, when the electrode layer is used as an electrode alone, the thickness thereof is preferably 10 μm or more.

[0078] (electrode) The electrode of the present invention comprises, for example, an electrode layer of the present invention on at least one surface of a substrate that is a current collector. Examples of substrates used for electrodes include metal substrates such as platinum, gold, iron, stainless steel, copper, aluminum, and lithium; alloy substrates made 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 is preferably 1 to 100 μm, more preferably 3 to 30 μm, and particularly preferably 5 to 25 μm.

[0079] The electrode may be pressed as necessary. A commonly used pressing method can be used, but mold pressing and roll pressing are particularly preferred. The pressing pressure is not particularly limited, but is preferably 1 kN / cm or more, more preferably 2 kN / cm or more, and particularly preferably 5 kN / cm or more. The upper limit of the pressing pressure is not particularly limited, but is preferably 50 kN / cm or less.

[0080] (Secondary battery) The secondary battery of the present invention comprises the electrode layer of the present invention. The secondary battery of the present invention includes, for example, the electrode of the present invention. A secondary battery includes, for example, at least one pair of a positive electrode and a negative electrode, a separator interposed between the electrodes, and an electrolyte. The positive electrode is the electrode of the present invention.

[0081] The material used for the separator is not particularly limited, and examples thereof include glass fiber, cellulose, porous polyolefin, polyamide, polyester, and the like.

[0082] The electrolyte may be either liquid or solid, and may be either aqueous or non-aqueous. From the viewpoint of easily achieving practically sufficient performance, however, an electrolytic solution composed of an electrolyte salt, a solvent, etc. can be suitably used.

[0083] Examples of electrolyte salts include lithium salts such as LiPF6, LiBF4, LiN(SO2F)2, LiN(C2F5SO2)2, LiAsF6, LiSbF6, LiAlF4, LiGaF4, LiInF4, LiClO4, LiN(CF3SO2)2, LiCF3SO3, LiSiF6, LiN(CF3SO2), (C4F9SO2); metal iodides such as LiI, NaI, KI, CsI, and CaI2; iodide salts of quaternary imidazolium compounds; iodide salts and perchlorates of tetraalkylammonium compounds; and metal bromides such as LiBr, NaBr, KBr, CsBr, and CaBr2. These electrolyte salts can be used alone or in combination of two or more.

[0084] The solvent is not particularly limited as long as it does not corrode or decompose the materials constituting the battery, thereby deteriorating performance, and dissolves the electrolyte salt. Examples of the solvent that can be used include non-aqueous solvents such as 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.

[0085] In addition, as the solid electrolyte, inorganic solid electrolytes such as sulfide-based solid electrolytes and oxide-based solid electrolytes, and organic solid electrolytes such as polymer-based electrolytes can be suitably used. By using these solid electrolytes, an all-solid-state battery can be obtained that does not require an electrolytic solution.

[0086] Examples of sulfide-based solid electrolytes include Li2S-SiS2-lithium compounds (wherein the lithium compound is at least one selected from the group consisting of Li3PO4, LiI, and Li4SiO4), and thiolithium-based materials such as Li2S-P2O5, Li2S-B2S5, and Li2S-P2S5-GeS2.

[0087] As an oxide-based solid electrolyte, for example, Li5La3M2O, which is an oxide with a garnet structure, 12 (M=Nb, Ta) and Li7La3Zr2O 12 , γ-Li3PO4 structure-based oxygen acid salt compounds collectively known as LISICON, perovskite type, Li 3.3 PO 3.8 N 0.22 , sodium / alumina, etc.

[0088] Examples of polymer solid electrolytes include polyethylene oxide materials and polymer compounds obtained by polymerizing or copolymerizing monomers such as hexafluoropropylene, tetrafluoroethylene, trifluoroethylene, ethylene, propylene, acrylonitrile, vinylidene chloride, acrylic acid, methacrylic acid, methyl acrylate, ethyl acrylate, methyl methacrylate, styrene, and vinylidene fluoride. The polymer solid electrolyte may contain a supporting salt and a plasticizer. Examples of the supporting salt include lithium (fluorosulfonylimide). Examples of the plasticizer include succinonitrile.

[0089] A battery manufactured using the electrode-forming composition of the present invention has high battery characteristics even though it contains less binder (e.g., fluorine binder) than a general secondary battery. .

[0090] The type of secondary battery and the type of electrolyte are not particularly limited, and any type of battery such as a lithium ion secondary battery, a nickel-metal hydride battery, a manganese battery, or an air battery may be used, but a lithium ion secondary battery is preferred. There are no particular limitations on the lamination method or production method for the secondary battery.

[0091] When applied to a coin cell, the electrode of the present invention may be punched into a predetermined disk shape for use. For example, a lithium-ion secondary battery can be produced by placing one electrode (negative electrode) on a coin cell lid to which a washer and spacer are welded, placing a separator of the same shape impregnated with an electrolyte solution on top of that, and then placing the electrode (positive electrode) of the present invention on top with the electrode layer facing downwards, placing a case and a gasket on top, and sealing the coin cell using a coin cell crimping machine.

[0092] (Method of manufacturing electrode-forming composition) The method for producing an electrode-forming composition of the present invention is a method for producing an electrode-forming composition of the present invention. The method for producing an electrode-forming composition of the present invention includes mixing a specific compound, a binder, a solvent, and a positive electrode active material. The order of mixing these materials is not particularly limited. One embodiment of the method for producing an electrode-forming composition of the present invention includes mixing a specific compound, a binder, a solvent, a first positive electrode active material that is a polycrystalline body, and a second positive electrode active material that is a single crystal body. The order of mixing these materials is not particularly limited.

[0093] The mass ratio of the first positive electrode active material to the second positive electrode active material in the electrode-forming composition (first positive electrode active material:second positive electrode active material) is not particularly limited, but is preferably 2:8 to 8:2, more preferably 4:6 to 8:2, and particularly preferably 4:6 to 7:3.

[0094] (Additives and gelation inhibitors) The additive of the present invention is an additive for an electrode-forming composition containing a positive electrode active material, a binder, and a solvent. The gelation inhibitor of the present invention is a gelation inhibitor for an electrode-forming composition containing a positive electrode active material, a binder, and a solvent. The gelation inhibitor is added to the electrode-forming composition containing a positive electrode active material, a binder, and a solvent to suppress gelation of the electrode-forming composition. The additives and gelation inhibitors are the above-mentioned specific compounds, and examples and preferred examples thereof include the examples and preferred examples given in the description of the above-mentioned specific compounds. Examples and preferred examples of the positive electrode active material include the examples and preferred examples given in the description of the positive electrode active material as a component contained in the electrode-forming composition of the present invention. Examples and preferred examples of the binder include the examples and preferred examples given in the description of the binder as a component contained in the electrode-forming composition of the present invention. Examples and preferred examples of the solvent include the examples and preferred examples given in the description of the solvent as a component contained in the electrode-forming composition of the present invention. The electrode-forming composition in which the additive and the gelation inhibitor are used may contain other components. Examples and preferred examples of the other components include the examples and preferred examples given in the description of the other components contained in the electrode-forming composition of the present invention.

[0095] (Method and use for inhibiting gelation) The method for inhibiting gelation of an electrode-forming composition comprising a positive electrode active material, a binder, and a solvent is provided, and the electrode-forming composition is made to contain a specific compound. The use of the present invention is the use of a specific compound for suppressing gelation of an electrode-forming composition containing a positive electrode active material, a binder, and a solvent. Examples and preferred examples of the specific compound include the examples and preferred examples given in the description of the specific compound above. Examples and preferred examples of the positive electrode active material include the examples and preferred examples given in the description of the positive electrode active material as a component contained in the electrode-forming composition of the present invention. Examples and preferred examples of the binder include the examples and preferred examples given in the description of the binder as a component contained in the electrode-forming composition of the present invention. Examples and preferred examples of the solvent include the examples and preferred examples given in the description of the solvent as a component contained in the electrode-forming composition of the present invention. The electrode-forming composition used in the method for suppressing gelation may contain other components. Examples and preferred examples of the other components include the examples and preferred examples given in the description of the other components contained in the electrode-forming composition of the present invention. [Example]

[0096] EXAMPLES The present invention will be explained in more detail below with reference to examples and comparative examples, but the present invention is not limited to the following examples.

[0097] The proton dissociation energy and HOMO of the additives used in the examples and comparative examples of the present invention were calculated by quantum chemical calculation using the following method: Gaussian 16, a molecular orbital calculation software manufactured by Gaussian, USA, was used as the quantum chemical calculation program, and calculations were performed using density functional theory (DFT).

[0098] [Method for calculating proton dissociation energy] The most stable structure of the target molecule (HA) in the ground state under vacuum was calculated using the B3LYP functional and the 6-31+G(d) basis set, and its total energy E(HA) was calculated. Furthermore, the target molecule (HA) was decomposed into a dissociative proton (H + ) dissociated into one anion (A - ) is calculated using the functional B3LYP and the basis set 6-31+G(d) to find the most stable structure in the ground state under vacuum. The total energy E(A -) is calculated to obtain the proton dissociation energy ΔE defined by the following equation (a) pd (unit: kJ / mol) was calculated. (a) ΔE pd =[E(A - )+E(H + )]-E(HA) However, protons (H + ) has no electrons, so the total energy cannot be evaluated by quantum chemical calculations. Therefore, the total energy of the proton here, E(H + For molecules with multiple dissociative protons, only the first stage of proton dissociation is considered, and the total energy E(A - The proton dissociation energy was calculated for the proton dissociation position where the σ is minimized.

[0099] [HOMO calculation method] The most stable structure of the target molecule in the ground state under vacuum was calculated using the B3LYP functional and the 6-31+G(d) basis set, and the energy level of the highest occupied molecular orbital (HOMO) (unit: atomic unit (au)) was calculated.

[0100] The apparatus used in this example is as follows: (1) Rotation-revolution type mixer: Thinky Corporation, Awatori Mixer, atmospheric pressure type ARE-310 (2) Dry Booth: Manufactured by Nihon Spindle Manufacturing Co., Ltd. (3) Rheometer (condition 1): Anton Paar, MCR302, jig: CP40-1, measurement gap: 0.08 mm, measurement temperature: 25°C, measurement conditions: 0.01 → 1000 sec -1 The shear viscosity was measured by sweeping the shear rate from 100 s -1 The values ​​at were adopted. (4) Rheometer (condition 2): Anton Paar MCR302e, jig: PP50, measurement gap: 0.08 mm, measurement temperature: 25°C, measurement conditions: 0.01 → 1000 sec -1The shear viscosity was measured by sweeping the shear rate from 100 s -1 The values ​​at were adopted. (5) Roll press machine: SA-602, manufactured by Takumi Giken Co., Ltd. (6) X-ray diffractometer: PANaltical, X'Pert Pro MPD

[0101] [X-ray diffraction measurement] X-ray diffraction patterns of the positive electrode active material were collected using an X'Pert Pro MPD (PANaltical) with a CuKα radiation source (45 kV, 40 mA) emitting at a wavelength of 1.5418 Å. The instrument configuration was a 0.02 rad Soller slit, a 10 mm automatic variable divergence slit, and a 1 / 2° anti-scatter slit on the incident side, and an 8 mm anti-scatter slit and a 0.02 rad Soller slit on the receiving side. The goniometer radius was 240 mm. For XRD, diffraction patterns were acquired from 10 to 100° (2θ) with a step size of 0.013° / scan and a step time of 250 seconds.

[0102] The crystallite size of the positive electrode active material was calculated using the known Scherrer equation from the diffraction angle of the (104) plane peak obtained from the X-ray diffraction pattern and the full width at half maximum (FWHM) obtained by subtracting the device-specific full width at half maximum.

[0103] [Scherrer equation]

number

[0104] The raw materials used in this example are as follows: <Cathode active material> The first positive electrode active material was S-800, which was a polycrystalline material, and the second positive electrode active material was T81RS, which was a single crystal material. S-800: Lithium nickel manganese cobalt oxide (LiNi 0.8 Co 0.1 Mn 0.1 O2, polycrystalline type, manufactured by Ningbo Ronbay New Energy Technology Co., Ltd., Ni ratio: 50% by mass, crystallite size determined by X-ray diffraction: 97 nm) T81RS: Lithium nickel manganese cobalt oxide (LiNi 0.8 Co 0.1 Mn 0.1 O2, single crystal type, manufactured by Hunan Shanshan Energy Technology Co., Ltd., Ni ratio: 50% by mass, crystallite size determined by X-ray diffraction: 296 nm)

[0105] <Binder> Solef-5130: Polyvinylidene fluoride (PVdF), manufactured by SOLVAY <Conductive additive> AB: Denka Black (registered trademark) Li100 (high-purity acetylene black), manufactured by Denka Co., Ltd. <Solvent> NMP: N-methyl-2-pyrrolidone, manufactured by Nippon Refine Co., Ltd. <Additives A1 to A28 and a1 to a26> The additives used were those listed in Tables 1-1 and 1-2 below. The additives listed in Table 1-1 are the additives used in the examples. The additives listed in Table 1-2 are the additives used in the comparative examples. The presence or absence of dissociative protons, proton dissociation energies, and HOMOs of these additives are shown in Tables 1-1 and 1-2. Furthermore, Figure 1 shows a diagram in which the proton dissociation energies are plotted on the horizontal axis and the HOMOs are plotted on the vertical axis for additives A1 to A28 and a1 to a26.

[0106] [Table 1-1]

[0107] [Table 1-2]

[0108] The manufacturer names listed in Tables 1-1 and 1-2 are as follows: Company F: Fujifilm Wako Pure Chemical Corporation Company T: Tokyo Chemical Industry Co., Ltd. Company S: Shin-Etsu Chemical Co., Ltd. Company C: Nippon Carbide Industries Co., Ltd. Company B: BASF AD Company: ADEKA Corporation Company A: Aldrich It should be noted that X-12-1214A (trade name) of A6 is a silane coupling agent having a benzotriazole structure manufactured by Shin-Etsu Chemical Co., Ltd. A22, Irganox 3114 (trade name), is 1,3,5-Tris(3,5-di-tert.-butyl-4-hydroxybenzyl)-1,3,5-triazine-2,4,6(1H,3H,5H)-trione manufactured by BASF. A23, Irganox MD1024 (trade name), is 2',3-Bis[[3-[3,5-di-tert.-butyl-4-hydroxyphenyl]propionyl]]propionohydrazide manufactured by BASF. A24, ADK STAB AO-40 (trade name), is 6,6'-di-tert-butyl-4,4'-butylidenedi-m-cresol manufactured by ADEKA Corporation. A25, ADK STAB AO-80 (trade name), is 3,9-Bis{2-[3-(3-tert-butyl-4-hydroxy-5-methylphenyl)propionyloxy]-1,1-dimethylethyl}-2,4,8,10-tetraoxaspiro[5.5]undecane manufactured by ADEKA Corporation. The water-soluble methylol melamine a7 (Nikaresin S176: trade name) is a water-soluble methylol melamine manufactured by Nippon Carbide Industries Co., Ltd.

[0109] Preparation of positive electrode composition (electrode slurry) [Examples 1 to 16, Comparative Examples 2 to 25] For each of Additives A1 to A16 and Additives a1 to a24, a 5% by mass NMP solution (additive solution) was prepared. Subsequently, the positive electrode active material, binder powder, conductive additive, additive solution, NMP, and water were mixed in a dry mixer to obtain the composition ratios shown in Tables 2-1 to 2-4, and mixed using a rotation-revolution mixer to obtain electrode slurries. The total amount of each slurry prepared was 100 g, with a solid content of 73% by mass. The solvent composition of the slurry was adjusted to NMP / HO (mass ratio) = 95 / 5. The water was added to intentionally create a high moisture content in the slurry.

[0110] [Examples 17 to 20, Comparative Examples 26 to 27] The positive electrode active material, binder powder, conductive additive, additive, NMP, and water were mixed in a dry mixer to obtain the composition ratios shown in Tables 2-2 and 2-4, and then mixed using a rotation-revolution mixer to obtain electrode slurries. The total amount of the prepared slurries was 100 g each, with a solid content of 73 mass% and a solvent composition of NMP / HO (mass ratio) = 95 / 5. The water was added to intentionally create a high moisture content in the slurry.

[0111] [Example 21] A 5% by mass NMP solution (additive solution) of Additive A2 was prepared. The positive electrode active material, binder powder, conductive additive, additive solution, NMP, and water were mixed in a dry mixer to obtain the composition shown in Table 2-2, and the mixture was mixed using a rotation-revolution mixer to obtain an electrode slurry. The total amount of the prepared slurry was 100 g, with a solids content of 71% by mass, and the solvent composition of the slurry was adjusted to NMP / HO (mass ratio) = 95 / 5. The water was added to intentionally create a high moisture content in the slurry.

[0112] [Example 22] A 5% by mass NMP solution (additive solution) of Additive A2 was prepared. The positive electrode active material, binder powder, conductive additive, additive solution, NMP, and water were mixed in a dry mixer to obtain the composition shown in Table 2-2, and the mixture was mixed using a rotation-revolution mixer to obtain an electrode slurry. The total amount of the prepared slurry was 100 g, the solid content was 73.5% by mass, and the solvent composition of the slurry was adjusted to NMP / HO (mass ratio) = 95 / 5. The water was added to intentionally create a high moisture content in the slurry.

[0113] [Examples 23 to 29] A 5% by mass NMP solution (additive solution) was prepared for each of Additives A21 to A27. Next, the positive electrode active material, binder powder, conductive additive, additive solution, NMP, and water were mixed in a dry mixer to obtain the composition ratios shown in Table 2-2, and mixed using a rotation-revolution mixer to obtain electrode slurries. The total amount of each slurry prepared was 100 g, the solid content was 73.5% by mass, and the solvent composition of the slurry was adjusted to NMP / HO (mass ratio) = 98.5 / 1.5. The water was added to intentionally create a high moisture content in the slurry.

[0114] [Example 30] The positive electrode active material, binder powder, conductive additive, additive, NMP, and water were mixed in a dry mixer to obtain the composition shown in Table 2-2, and then mixed using a rotation-revolution mixer to obtain an electrode slurry. The total amount of the prepared slurry was 100 g, with a solids content of 73.5 mass %, and the solvent composition of the slurry was adjusted to NMP / HO (mass ratio) = 98.5 / 1.5. The water was added to intentionally create a high moisture content in the slurry.

[0115] [Comparative Example 1] The positive electrode active material, binder powder, conductive additive, NMP, and water were mixed in a dry mixer to obtain the composition shown in Table 2-3, and then mixed using a rotation-revolution mixer to obtain an electrode slurry. The total amount of the prepared slurry was 100 g, with a solid content of 73 mass%, and the solvent composition of the slurry was adjusted to NMP / HO (mass ratio) = 95 / 5. The water was added to intentionally create a high moisture content in the slurry.

[0116] [Comparative Example 28] The positive electrode active material, binder powder, conductive additive, NMP, and water were mixed in a dry mixer to obtain the composition shown in Table 2-4, and then mixed using a rotation-revolution mixer to obtain an electrode slurry. The total amount of the prepared slurry was 100 g, with a solid content of 71 mass %, and the solvent composition of the slurry was adjusted to NMP / HO (mass ratio) = 95 / 5. The water was added to intentionally create a high moisture content in the slurry.

[0117] [Comparative Example 29] The positive electrode active material, binder powder, conductive additive, NMP, and water were mixed in a dry mixer to obtain the composition shown in Table 2-4, and then mixed using a rotation-revolution mixer to obtain an electrode slurry. The total amount of the prepared slurry was 100 g, the solid content was 73.5 mass%, and the solvent composition of the slurry was adjusted to NMP / HO (mass ratio) = 95 / 5. The water was added to intentionally create a high moisture content in the slurry.

[0118] [Comparative Example 30] The positive electrode active material, binder powder, conductive additive, NMP, and water were mixed in a dry mixer to obtain the composition shown in Table 2-4, and then mixed using a rotation-revolution mixer to obtain an electrode slurry. The total amount of the prepared slurry was 100 g, with a solids content of 73.5 mass %, and the solvent composition of the slurry was adjusted to NMP / HO (mass ratio) = 98.5 / 1.5. The water was added to intentionally create a high moisture content in the slurry.

[0119] Immediately after preparation, the slurries obtained above were subjected to viscosity measurement using a rheometer (condition 1) or a rheometer (condition 2). After storage at 40°C for 24 hours, the presence or absence of gelation was confirmed visually. For those that did not gel, viscosity measurement was similarly performed using a rheometer (condition 1) or a rheometer (condition 2) to check for thickening and a tendency to gel, and the results were evaluated based on the following criteria. These evaluations are also summarized in each table. The viscosities of Examples 1 to 22 and Comparative Examples 1 to 29 were measured using a rheometer (condition 1), and the viscosities of Examples 23 to 30 and Comparative Example 30 were measured using a rheometer (condition 2). [Judgment criteria] A: The composition has not gelled and can be used to form electrodes. B: The composition gelled and could not be used to form electrodes. Viscosity change rate (%) = ((viscosity after storage - initial viscosity) / initial viscosity) x 100

[0120] The electrode slurries obtained in Examples 1 to 30 and Comparative Examples 1 to 30 were each uniformly applied to an aluminum foil current collector (15 μm thick, UACJ Corporation) using a doctor blade, dried at 80°C for 30 minutes to form an active material layer, and then pressed twice with a roll press at a linear pressure of 0.25 kN / cm, twice at 1 kN / cm, and twice at 3 kN / cm to produce electrodes. Four 10 mm diameter disk-shaped electrodes were punched out from the resulting positive electrodes, and the mass of the positive electrode layer (the mass of the punched electrode minus the mass of the uncoated electrode punched out to a diameter of 10 mm) and the electrode layer thickness (the thickness of the punched electrode minus the thickness of the substrate) were measured, and the electrode density was calculated from the average value. These evaluations are also summarized in each table.

[0121] [Table 2-1]

[0122] [Table 2-2]

[0123] [Table 2-3]

[0124] [Table 2-4] The "-" in the "Viscosity change rate (%)" results in Tables 2-3 and 2-4 indicates that the product gelled after storage at 40°C for 24 hours, and the viscosity could not be measured after storage at 40°C for 24 hours.

[0125] The results in Tables 2-1 to 2-4 above confirm that the electrode-forming composition of the present invention, which contains a specific additive having a proton dissociation energy of less than 1484.2 (kJ / mol) and a highest occupied molecular orbital (HOMO) of more than -0.27736 (au), suppresses thickening and gelation and improves storage stability. Therefore, the electrode-forming composition does not lose its coatability even after a long time has passed since its preparation, and can be suitably used in the industrial production of lithium-ion secondary batteries.

Claims

1. An electrode-forming composition comprising a compound having a ring structure and an unsaturated bond (excluding 2,6-di-t-butyl-4-cresol), a positive electrode active material, a binder, and a solvent, The compound has a dissociable proton in the molecule, The proton dissociation energy of the compound is less than 1484.2 (kJ / mol), the highest occupied molecular orbital (HOMO) of the compound is greater than −0.27736 (a.u.); the positive electrode active material includes a first positive electrode active material that is a polycrystalline body and a second positive electrode active material that is a single crystal body, The binder is a fluorine-based binder. Composition for forming electrodes.

2. 2. The electrode-forming composition according to claim 1, wherein the first positive electrode active material is lithium-containing transition metal oxide particles having a layered rock salt structure, and the crystallite size determined by Scherrer's equation based on a diffraction peak of a (104) plane obtained from an X-ray diffraction pattern of the lithium-containing transition metal oxide particles using a CuKα radiation source is 20 nm or more and less than 500 nm.

3. 2. The electrode-forming composition according to claim 1, wherein the second positive electrode active material is lithium-containing transition metal oxide particles having a layered rock salt structure, and the crystallite size determined by Scherrer's equation based on a diffraction peak of a (104) plane obtained from an X-ray diffraction pattern of the lithium-containing transition metal oxide particles using a CuKα radiation source is 50 nm or more and less than 800 nm.

4. The lithium-containing transition metal oxide particles having a layered rock salt structure in the first positive electrode active material are represented by the general formula Li ａ Ni (１－ｘ－ｙ) Co ｘ M １ ｙ M ２ ｚ O ２ (In the formula, M １ is at least one selected from the group consisting of Mn and Al, M ２ represents at least one selected from the group consisting of Zr, Ti, Mg, B, W, and V, and 1.00≦a≦1.50, 0.00≦x≦0.50, 0.00≦y≦0.50, and 0.000≦z≦0.

020.

5. The lithium-containing transition metal oxide particles having a layered rock salt structure in the second positive electrode active material are represented by the general formula Li ａ Ni (１－ｘ－ｙ) Co ｘ M １ ｙ M ２ ｚ O ２ (In the formula, M １ is at least one selected from the group consisting of Mn and Al, M ２ represents at least one selected from the group consisting of Zr, Ti, Mg, B, W, and V, and 1.00≦a≦1.50, 0.00≦x≦0.50, 0.00≦y≦0.50, and 0.000≦z≦0.

020.

6. The electrode-forming composition according to claim 1 , wherein the ring structure is an aromatic ring.

7. The electrode-forming composition according to claim 1 , wherein the compound has a heteroatom.

8. The electrode-forming composition according to claim 1 , wherein the positive electrode active material comprises a metal oxide containing Ni.

9. The electrode-forming composition according to claim 1 , wherein the positive electrode active material contains Ni, and the Ni content in the positive electrode active material is 30% by mass or more and 61% by mass or less.

10. The electrode-forming composition according to claim 1 , wherein the solvent is an aprotic solvent.

11. The electrode-forming composition according to claim 1 , further comprising a conductive assistant.

12. An electrode layer obtained from the electrode-forming composition according to claim 1 .

13. A secondary battery comprising the electrode layer according to claim 12.

14. A method for producing an electrode-forming composition, comprising the steps of: a first positive electrode active material that is a polycrystalline body; and a second positive electrode active material that is a single crystal.

15. 15. The method for producing an electrode-forming composition according to claim 14, wherein a mass ratio of the first positive electrode active material to the second positive electrode active material in the electrode-forming composition (first positive electrode active material:second positive electrode active material) is 2:8 to 8:

2.

16. An additive for an electrode-forming composition, comprising: a first positive electrode active material that is a polycrystalline body; a second positive electrode active material that is a single crystal body; a binder that is a fluorine-based binder; and a solvent, An additive (excluding 2,6-di-t-butyl-4-cresol) having a dissociable proton in the molecule, with a proton dissociation energy of less than 1484.2 (kJ / mol) and a highest occupied molecular orbital (HOMO) of greater than -0.27736 (au).

17. A gelation inhibitor for an electrode-forming composition, comprising: a first positive electrode active material that is a polycrystalline body; a second positive electrode active material that is a single crystal body; a binder that is a fluorine-based binder; and a solvent, A gelation inhibitor (excluding 2,6-di-t-butyl-4-cresol) having a dissociable proton in the molecule, a proton dissociation energy of less than 1484.2 (kJ / mol), and a highest occupied molecular orbital (HOMO) of more than -0.27736 (au).

18. A method for suppressing gelation of an electrode-forming composition including a first positive electrode active material that is a polycrystalline body, a second positive electrode active material that is a single crystal body, a binder that is a fluorine-based binder, and a solvent, the method comprising: A method for suppressing gelation, in which the electrode-forming composition contains a compound (excluding 2,6-di-t-butyl-4-cresol) having a dissociable proton in the molecule, a proton dissociation energy of less than 1484.2 (kJ / mol), and a highest occupied molecular orbital (HOMO) of more than −0.27736 (a.u.).

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