Composition for electrode formation, 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

Electrode-forming composition, additive, and gelation inhibitor

[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.

[0002] Lithium-ion secondary batteries have a high energy density per unit 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 mainstream method for manufacturing a negative electrode is to coat a copper foil current collector with the negative electrode slurry and dry it, while the mainstream 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] As positive electrode active materials for lithium ion secondary batteries, inorganic compounds such as transition metal oxides and transition metal chalcogens containing alkali metals are known as materials capable of obtaining a battery voltage of around 4 V. Among these, highly alkaline positive electrode active materials containing large amounts of nickel and manganese are used in order to obtain high-capacity lithium ion secondary batteries.

[0005] For example, Li ｘ NiO ２ High nickel positive electrode active materials, such as those listed above, have a high discharge capacity and are attractive positive electrode materials. However, on the surface, there are proton exchange reactions with the residue of the raw material or moisture, and LiOH and Li ２ O, LiHCO ３ , Li ２ CO ３There are alkaline components such as

[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, in the process of producing the positive electrode, alkaline components present on the surface of the positive electrode active material, in the presence of a trace amount of moisture, promote the dehydrofluorination reaction of the fluorine-based binder, such as polyvinylidene fluoride (PVdF) having a vinylidene fluoride structure, 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 an electrode slurry (cathode material slurry) so that it does not exhibit strong alkalinity even when dispersed in water. However, preparing an electrode slurry so that it 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 from the dispersion to extract the cathode active material, and then dried. As a result, this process leads to cumbersome operations and 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 high-concentration solution. Furthermore, because the above-mentioned ultra-high molecular weight polymers have a high water-binding ability, 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. Furthermore, there is a problem 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 of 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, and LiF produced as a by-product increases the internal resistance of the battery, reducing capacity. Furthermore, 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 are removed by washing with an aqueous solution containing a lithium salt. However, there are issues with this method, such as increased environmental load due to wastewater generated during washing and the cost associated with treating the wastewater.

[0015] JP 2000-90917 A JP 2019-121471 A JP 9-306502 A JP 10-79244 A JP 2006-286240 A International Publication No. 2017 / 034001

[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.

[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, wherein the compound has a dissociative proton in the molecule, the proton dissociation energy of the compound is less than 1484.2 (kJ / mol), and the highest occupied molecular orbital (HOMO) of the compound is greater than -0.27736 (a.u.). [2] The electrode-forming composition according to [1], wherein the positive electrode active material comprises a first positive electrode active material that is a polycrystalline body and a second positive electrode active material that is a single crystal. [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 diameter, 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 a lithium-containing transition metal oxide particle having a layered rock salt structure, and the crystallite size determined by Scherrer's formula based on the diffraction peak of the (104) plane obtained from an X-ray diffraction pattern of the lithium-containing transition metal oxide particle using a CuKα radiation source is 50 nm or more and less than 800 nm. [5] The lithium-containing transition metal oxide particle having the layered rock salt structure in the first positive electrode active material is a compound 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 ２represents 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 [3] or [4], wherein the lithium-containing transition metal oxide particles having a layered rock salt structure in the second positive electrode active material are crystalline metal oxide particles 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 ２represents at least one element 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. [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 the electrode-forming composition according to any one of [1] to

[13] , 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 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, the additive having a dissociative proton in a 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.).

[19] A gelation inhibitor for 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, the gelation inhibitor having a dissociative proton in its molecule, a proton dissociation energy of less than 1484.2 (kJ / mol), and a highest occupied molecular orbital (HOMO) of greater than -0.27736 (a.u.).

[20] A method for inhibiting 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, the method comprising causing the electrode-forming composition to contain a compound having a dissociative proton in its molecule, a proton dissociation energy of less than 1484.2 (kJ / mol), and a highest occupied molecular orbital (HOMO) of greater than -0.27736 (a.u.).

[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.

[0020] 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.

[0021] (Electrode-forming composition) 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), and the highest occupied molecular orbital (HOMO) of the specific compound is greater than -0.27736 (a.u.).

[0023] The electrode-forming composition of the present invention is resistant to thickening and gelling and has high storage stability, making it suitable for use in forming positive electrodes for secondary batteries. When a secondary battery is manufactured using the composition, it is expected to offer 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, thereby contributing to reduced manufacturing costs and improved battery characteristics. 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-crystal) is more likely to thicken and gel. In one aspect of the electrode-forming composition of the present invention, 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-crystal) makes it possible to suppress thickening and gelling of a composition that is more prone to thickening and gelling. Although the mechanisms of thickening and gelation, and the mechanism by which their inhibitory effect is manifested, are unclear, the inventors believe that one of the reasons is that the addition of a specific compound to an electrode-forming composition inactivates radicals that are generated in the composition and promote thickening and gelation. When a compound has a dissociative proton and the proton dissociation energy of the compound is small, the compound is likely to release a proton, and the released proton is likely to undergo one-electron reduction and generate hydrogen radicals. When the highest occupied molecular orbital (HOMO) of a compound is high, the compound is likely to be radicalized and generate hydrogen radicals. This is illustrated below.

[0024] For example, hydrogen radicals react (e.g., radical coupling) with binder radicals that have been radicalized due to alkaline components present 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 is not limited to these mechanisms. Suppressing thickening and gelation of the electrode-forming composition enables the formation of a homogeneous positive electrode layer. It also makes it possible to increase the solids concentration in the electrode slurry, thereby reducing the cost and environmental impact of producing energy storage devices. Furthermore, corrosion of aluminum foil, which is commonly used as a current collector foil, and deterioration of battery characteristics due to reaction with the electrolyte, caused by alkaline components, can be suppressed.

[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 the specific compound is greater than -0.27736 (a.u.). Note that 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 achieved.

[0026] The ring structure of the specific compound may be an aliphatic ring or an aromatic ring. In addition, 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 heterocyclic ring. The specific compound may or may not have an aromatic ring.

[0027] The unsaturated bond possessed by the specific compound may be a double bond or a triple bond. The unsaturated bond possessed by the specific compound may be an unsaturated bond that constitutes a ring structure. For example, benzene is a compound that has a ring structure and three unsaturated bonds. Examples of double bonds include a carbon-carbon double bond, a carbon-oxygen double bond, a carbon-nitrogen double bond, a carbon-sulfur double bond, and a nitrogen-nitrogen double bond. Examples of triple bonds include a carbon-carbon triple bond and a carbon-nitrogen triple bond. 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 Group 14 to Group 17 elements. Examples of non-metallic elements selected from Group 14 to Group 17 elements include boron, carbon, silicon, nitrogen, phosphorus, oxygen, sulfur, and halogens. The specific compound may or may not contain heteroatoms. 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 contains heteroatoms, the heteroatoms contained in the specific compound are at least one of oxygen atoms, sulfur atoms, and nitrogen atoms. For example, when the specific compound contains 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, a 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 dissociative protons possessed by a specific compound is not particularly limited, and may be 1 or 2 or more. When the proton dissociation energy can be calculated, the compound is said to have dissociative protons.

[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 function, and its total energy E(HA) is calculated. Furthermore, dissociative protons (H ＋ ) dissociated into one anion (A － ) was calculated using the B3LYP functional and the 6-31+G(d) basis function to determine the most stable structure in the ground state under vacuum. － ) to calculate the proton dissociation energy ΔE defined by the following formula (a) ｐｄ (unit: kJ / mol) is calculated. (a) ΔE ｐｄ = [E(A － ) + E(H ＋ ) )]-E(HA) where proton (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 target molecules having 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 the proton dissociation energy is minimum.

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

[0034] Examples of specific compounds are shown below.

[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%. An even more preferable lower limit of the content of the specific compound is 0.01 mass% of the solid content. By keeping the content of the specific compound within this range, gelation of the electrode-forming composition can be effectively suppressed, and the battery characteristics of the resulting battery can be maintained. In the present invention, the solid content refers to the 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] <Positive Electrode 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, in order to further improve the battery capacity, reduce the amount of rare metal used, and reduce costs. In order to further reduce the amount of rare metal used and obtain a battery with a 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] An electrode-forming composition containing a positive electrode active material with a high nickel content has a strong tendency to thicken and gel. Therefore, in order to suppress thickening and gelling in an electrode-forming composition 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 mass% or more, and particularly preferably has a Ni content of 40 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 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 or lithium ion-containing chalcogen compounds capable of absorbing and releasing lithium ions, polyanionic compounds, elemental sulfur and its compounds, etc. can be used.

[0043] Examples of lithium ion-containing chalcogen compounds include LiNiO ２ , Li ｘ Ni ｙ M １－ｙ O ２ (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 O ２ (M １ is at least one selected from the group consisting of Mn and Al, M ２ represents at least one element selected from the group consisting of Zr, Ti, Mg, B, Zr, Si, W, and V, and 1.00≦a≦1.50, 0.00≦x≦0.50, 0.00≦y≦0.50, 0.000≦z≦0.020). Examples of polyanion compounds include LiFePO ４ , Li ａ Mn ｂ Fe ｃ D ｄ P.O.４ (wherein 1.00≦a≦1.15, 0.01≦b≦0.99, 0.01≦c≦0.99, 0.00≦d≦0.10, and D is selected from Co, Mn, Ti, Cr, V, Al, Sn, Pb, and Zn, and at least a part of the metal has an olivine structure). Examples of sulfur compounds include sulfur, Li, ２ S, FeS ２ , TiS ２ , MoS ２ , rubeanic acid, etc. 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 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 element selected from the group consisting of Zr, Ti, Mg, B, W, and V, and preferably 1.00≦a≦1.50, 0.00≦x≦0.50, 0.00≦y≦0.50, 0.000≦z≦0.020). x may be 0.01≦x≦0.30 or 0.03≦x≦0.20. y may be 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 O ２ The Ni content is preferably 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 first positive electrode active material, which is a polycrystalline body, 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, 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, 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 (X), where τ1 is the crystallite diameter (nm) of the first positive electrode active material, and τ2 is the 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] The X-ray diffraction pattern of the positive electrode active material is collected using an X'Pert Pro MPD (manufactured by PANaltical) with a CuKα radiation source (45 kV, 40 mA) emitting at a wavelength of 1.5418 Å. The instrument is configured with a 0.02 radian Soller slit, a 10 mm automatic variable divergence slit with an irradiation area of ​​10 mm, and a ½° anti-scatter slit on the incident side, and an 8 mm anti-scatter slit and a 0.02 radian Soller slit on the receiving side. The goniometer radius is 240 mm. In XRD, the diffraction pattern is obtained in the range of 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] τ: crystallite size (unit: nm) (Crystallite size refers to the average size of regular (crystalline) domains, which may be smaller than the crystal grain size.) K: Scherrer constant (K=0.9) λ: X-ray wavelength (CuKα=0.15418 nm) β: FWHM θ: ½ of the diffraction angle 2θ of the diffraction peak assigned to the (104) plane. The peak of the (104) plane assigned to a crystal structure having space group R-3m is observed at 44.5±1° in the X-ray diffraction pattern. The instrument-specific half-width of 47.3° obtained using Si powder (NIST, SRM640f) is used.

[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, polyimide, ethylene-propylene-diene terpolymer, 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 measured 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 %, still 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 have conventionally been used in preparing electrode-forming compositions, such as 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 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. Examples of other organic solvents include γ-butyrolactone, dimethyl sulfoxide (DMSO), dioxolane, and sulfolane.

[0063] The organic solvent may be a protic solvent or an aprotic solvent, but an aprotic solvent is preferred. The aprotic solvent may be, for example, polar or non-polar. Preferred aprotic solvents are amides, ketones, and carbonates, and more preferred are amides.

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

[0065] The binder may be used by dissolving or dispersing it 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 concentration 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 usually 60 to 92 mass %, preferably 65 to 90 mass %, and more preferably 70 to 85 mass %.

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

[0068] <<Conductive Aid>> The conductive aid is used, for example, to improve electrical conductivity. The conductive aid is not particularly limited, and 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 aid 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 %, more preferably 0.05 to 4 mass %, even more preferably 0.1 to 3 mass %, and even more preferably 0.2 to 2 mass % of the solid content. By setting the content of the conductive additive within the above range, good electrical conductivity can be obtained.

[0070] The electrode-forming composition does not contain graphene, for example. 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>> Dispersants are used to improve the dispersibility of substances such as positive electrode active materials and conductive additives. Dispersants can be appropriately selected from those conventionally used as dispersants for conductive carbon materials such as CNTs. Nonionic polymers are preferred from the perspective of stability within the battery. Examples of nonionic polymers include polyvinylpyrrolidone (PVP) and polymers containing at least one functional group selected from the group consisting of nitrile groups, hydroxy groups, carbonyl groups, amino groups, sulfonyl groups, and ether groups. Examples of functional group-containing polymers include polyvinyl alcohol, polyacrylonitrile, polylactic acid, polyester, polyimide, polyphenyl ether, polyphenylsulfone, polyethyleneimine, and polyaniline. Polymers containing a pyrrolidone structure or a nitrile group are preferred as dispersants, with polyvinylpyrrolidone and polyacrylonitrile being more preferred. Dispersants can be used alone or in combination.

[0072] The content of the dispersant in the electrode-forming composition is not particularly limited, but is preferably 0.001 to 0.5 mass %, more preferably 0.001 to 0.3 mass %, and even more preferably 0.001 to 0.2 mass % based on the solid content. An even more preferable lower limit of the dispersant content is 0.01 mass % based on 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 %, more preferably 0.01 to 1 mass %, based on the solid content.

[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 a value 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. Examples of methods for forming the electrode layer include a method in which the 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 case where the electrode layer is used solely as an electrode in a secondary battery, the thickness 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 serving as 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 comprises, for example, the electrode of the present invention. The secondary battery comprises, for example, at least one pair of a positive electrode and a negative electrode, a separator interposed between these 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] The electrolyte salt is, for example, LiPF ６ , LiBF ４ , LiN(SO ２ F) ２, LiN(C ２ F ５ SO ２ ) ２ , LiAsF ６ , LiSbF ６ , LiAlF ４ , LiGaF ４ , LiInF ４ , LiClO ４ , LiN(CF ３ SO ２ ) ２ , LiCF ３ SO ３ , LiSiF ６ , LiN(CF ３ SO ２ ), (C ４ F ９ SO ２ Lithium salts such as LiI, NaI, KI, CsI, and CaI ２ metal iodides such as those mentioned above; iodide salts of quaternary imidazolium compounds; iodide salts and perchlorates of tetraalkylammonium compounds; LiBr, NaBr, KBr, CsBr, and CaBr ２ These electrolyte salts may 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 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; linear esters such as methyl acetate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate; and nitriles such as acetonitrile. These solvents may 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 Li ２ S-SiS ２ - lithium compounds (wherein the lithium compounds are Li ３ P.O. ４ , LiI and Li ４ SiO ４ At least one selected from the group consisting of ２ S-P ２ O ５ , Li ２ S-B ２ S ５ , Li ２ S-P ２ S ５ -GeS ２ and the like.

[0087] As the oxide-based solid electrolyte, for example, Li, which is an oxide having a garnet structure, ５ La ３ M ２ O １２ (M=Nb, Ta) or Li ７ La ３ Zr ２ O １２ , γ-Li, collectively known as LISICON ３ P.O. ４ Oxygen acid salt compounds based on the structure, perovskite type, collectively known as LIPON ３．３ P.O. ３．８ N ０．２２ , sodium / alumina, etc.

[0088] Examples of polymer-based solid electrolytes include polyethylene oxide-based 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-based solid electrolyte may contain a supporting salt and a plasticizer. Examples of supporting salts include lithium (fluorosulfonylimide). Examples of plasticizers include succinonitrile.

[0089] A battery manufactured using the electrode-forming composition of the present invention has high battery characteristics even if it contains less binder (for example, fluorine binder) compared to a general secondary battery.

[0090] The form of the secondary battery and the type of electrolyte are not particularly limited, and any form 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. The lamination method and production method of the secondary battery are also not particularly limited.

[0091] 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 the negative electrode, placing the electrode (positive electrode) of the present invention on top of that with the electrode layer facing downwards, placing a case and a gasket on top, and sealing the battery with a coin cell crimping machine.

[0092] (Method for manufacturing electrode-forming composition) The method for manufacturing an electrode-forming composition of the present invention is a method for manufacturing an electrode-forming composition that manufactures the electrode-forming composition of the present invention. The method for manufacturing 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 in which these materials are mixed is not particularly limited. One embodiment of the method for manufacturing 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 in which these materials are mixed 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 Gelling 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 an electrode-forming composition containing a positive electrode active material, a binder, and a solvent to inhibit gelation of the electrode-forming composition. The additives and gelation inhibitors are the specific compounds described above, and examples and preferred examples thereof include the examples and preferred examples given in the description of the specific compounds described 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 of 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 of 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 of 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 the present invention is a method for inhibiting gelation of an electrode-forming composition containing a positive electrode active material, a binder, and a solvent. In the method for inhibiting gelation, the electrode-forming composition is made to contain a specific compound. The use of the present invention is the use of a specific compound to inhibit 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 inhibiting 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.

[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, Inc., 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 B3LYP as the functional and 6-31+G(d) as the basis function, and the total energy E(HA) was calculated. Furthermore, dissociative protons (H ＋ ) dissociated into one anion (A－ ) was calculated using the B3LYP functional and the 6-31+G(d) basis function to determine the most stable structure in the ground state under vacuum. － ) to calculate the proton dissociation energy ΔE defined by the following formula (a) ｐｄ (unit: kJ / mol) was calculated. (a) ΔE ｐｄ = [E(A － ) + E(H ＋ ) )]-E(HA) where proton (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 target molecules having 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 ...

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

[0100] The devices used in this example are as follows: (1) Rotation / revolution type mixer: Thinky Corporation, Awatori Rentaro, atmospheric pressure type, ARE-310 (2) Dry mix: Nippon 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 sec to 100 sec. －１ (4) Rheometer (condition 2): MCR302e manufactured by Anton Paar, 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 sec to 100 sec. －１ (5) Roll press machine: SA-602 manufactured by Takumi Giken Co., Ltd. (6) X-ray diffraction device: X'Pert Pro MPD manufactured by PANaltical

[0101] X-ray diffraction measurements. 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 was configured with a 0.02 rad Soller slit, a 10 mm automatic variable divergence slit, and a ½° 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. XRD diffraction patterns were obtained in the range of 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] τ: crystallite size (unit: nm) (Crystallite size refers to the average size of regular (crystalline) domains, which may be smaller than the crystal grain size.) K: Scherrer constant (K = 0.9) λ: X-ray wavelength (CuKα = 0.15418 nm) β: FWHM θ: 1 / 2 of the diffraction angle 2θ of the diffraction peak assigned to the (104) plane. The peak of the (104) plane assigned to a crystal structure having space group R-3m is observed at 44.5 ± 1° in the X-ray diffraction pattern. The instrument-specific half-width was 47.3° obtained using Si powder (NIST, SRM640f).

[0104] The raw materials used in this example are as follows. <Positive electrode active material> S-800 was used as the first positive electrode active material, which was a polycrystalline material. T81RS was used as the second positive electrode active material, which was a single crystal material. S-800: Lithium nickel manganese cobalt oxide (LiNi ０．８ Co ０．１ Mn ０．１ O ２ T81RS: Lithium nickel manganese cobalt oxide (LiNi), manufactured by Ningbo Ronbay New Energy Technology Co., Ltd., Ni ratio: 50% by mass, crystallite size determined by X-ray diffraction: 97 nm) ０．８ Co ０．１ Mn ０．１ O ２ , single crystal type, manufactured by Hunan Shanshan Energy Technology Co., Ltd., Ni ratio: 50 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 listed in Tables 1-1 and 1-2 below were used. 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. Tables 1-1 and 1-2 also show the presence or absence of dissociative protons, proton dissociation energy, and HOMO of these additives. Furthermore, Figure 1 shows 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 and a1 to a26.

[0106]

[0107]

[0108] The names of manufacturers listed in Tables 1-1 and 1-2 are as follows: Company F: Fujifilm Wako Pure Chemical Industries, Ltd. Company T: Tokyo Chemical Industry Co., Ltd. Company S: Shin-Etsu Chemical Co., Ltd. Company C: Nippon Carbide Industries Co., Ltd. Company B: BASF Company AD: ADEKA Corporation Company A: Aldrich Note that X-12-1214A (trade name) of A6 is a silane coupling agent having a benzotriazole structure manufactured by Shin-Etsu Chemical Co., Ltd. Irganox 3114 (trade name) of A22 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. Irganox MD1024 (trade name) in A23 is 2',3-Bis[[3-[3,5-di-tert.-butyl-4-hydroxyphenyl]propionyl]]propionohydrazide manufactured by BASF. ADK STAB AO-40 (trade name) in A24 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. Also, a7 water-soluble methylol melamine (Nikaresin S176: trade name) is water-soluble methylol melamine manufactured by Nippon Carbide Industries Co., Ltd.

[0109] Preparation of Positive Electrode Forming Composition (Electrode Slurry) [Examples 1 to 16, Comparative Examples 2 to 25] A 5 mass % NMP solution (additive solution) was prepared for each of Additives A1 to A16 and Additives a1 to a24. 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 an electrode slurry. The total amount of the prepared slurries was 100 g, the solid content was 73 mass %, and the solvent composition of the slurries was NMP / H ２ The mass ratio of the water and the water content of the slurry was adjusted to 95 / 5. The water was added to intentionally create a state in which the water content in the slurry was high.

[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 so as to have the composition ratios shown in Tables 2-2 and 2-4, and mixed using a rotation-revolution mixer to obtain electrode slurries. The total amount of the prepared slurries was 100 g, the solid content was 73 mass%, and the solvent composition of the slurries was NMP / H ２ The mass ratio of the water and the water content of the slurry was adjusted to 95 / 5. The water was added to intentionally create a state in which the water content in the slurry was high.

[0111] [Example 21] A 5 mass% NMP solution (additive solution) of Additive A2 was prepared. A 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 71 mass%, and the solvent composition of the slurry was NMP / H ２ The mass ratio of the water and the water content of the slurry was adjusted to 95 / 5. The water was added to intentionally create a state in which the water content in the slurry was high.

[0112] [Example 22] A 5 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 mass%, and the solvent composition of the slurry was NMP / H ２ The mass ratio of the water and the water content of the slurry was adjusted to 95 / 5. The water was added to intentionally create a state in which the water content in the slurry was high.

[0113] [Examples 23 to 29] A 5% by mass NMP solution (additive solution) was prepared for each of Additives A21 to A27. 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 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 NMP / H ２ The mass ratio of the water to the slurry was adjusted to 98.5 / 1.5. The water was added to intentionally create a state in which the slurry had a high water content.

[0114] [Example 30] A 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. The total amount of the slurry prepared was 100 g, the solid content was 73.5 mass %, and the solvent composition of the slurry was NMP / H ２ The mass ratio of the water to the slurry was adjusted to 98.5 / 1.5. The water was added to intentionally create a state in which the slurry had a high water content.

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

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

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

[0118] [Comparative Example 30] A 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. The total amount of the slurry prepared was 100 g, the solid content was 73.5 mass %, and the solvent composition of the slurry was NMP / H ２ The mass ratio of the water to the slurry was adjusted to 98.5 / 1.5. The water was added to intentionally create a state in which the slurry had a high water content.

[0119] Immediately after preparation, the slurries obtained above were subjected to viscosity measurement using a rheometer (condition 1) or a rheometer (condition 2). Furthermore, after storage at 40°C for 24 hours, the presence or absence of gelation was visually confirmed. For those that had not gelled, the viscosity was similarly measured using a rheometer (condition 1) or a rheometer (condition 2) to check for thickening and a tendency to gel, and the results were judged 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 did not gel, and could be used to form an electrode. B: The composition gelled, and could not be used to form an electrode. 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 an electrode. Four disk-shaped electrodes with a diameter of 10 mm were punched out from the obtained positive electrode, and the mass of the positive electrode layer (the mass of the punched electrode minus the mass of the uncoated portion of the 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]

[0122]

[0123]

[0124] In Tables 2-3 and 2-4, the "-" in the "Viscosity change rate (%)" results indicates that gelation occurred 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 (a.u.), 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, a positive electrode active material, a binder, and a solvent, wherein the compound has a dissociable proton in its molecule, the proton dissociation energy of the compound is less than 1484.2 (kJ / mol), and the highest occupied molecular orbital (HOMO) of the compound is greater than -0.27736 (a.u.).

2. The electrode-forming composition according to claim 1, wherein the positive electrode active material comprises a first positive electrode active material which is a polycrystalline body and a second positive electrode active material which is a single crystal body.

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

4. The electrode-forming composition according to claim 2, wherein the second positive electrode active material is a lithium-containing transition metal oxide particle having a layered rock salt structure, and the crystallite size determined by Scherrer's formula based on the diffraction peak of the (104) plane obtained from an X-ray diffraction pattern of the lithium-containing transition metal oxide particle 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 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 is a crystalline metal-based oxide particle represented by the formula (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 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 is a crystalline metal-based oxide particle represented by the formula (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 claim 1, wherein the ring structure is an aromatic ring.

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

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

10. 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.

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

12. The electrode-forming composition according to claim 1, wherein the binder is a fluorine-containing binder.

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

14. An electrode layer obtained from the electrode-forming composition according to any one of claims 1 to 13.

15. A secondary battery comprising the electrode layer according to claim 14.

16. A method for producing an electrode-forming composition, which produces the electrode-forming composition according to any one of claims 1 to 13, 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.

17. The method for producing an electrode-forming composition according to claim 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 which is a polycrystalline body, a second positive electrode active material which is a single crystal body, a binder, and a solvent, the 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 more than -0.27736 (a.u.).

19. A gelation inhibitor for an electrode-forming composition comprising a first positive electrode active material which is a polycrystalline body, a second positive electrode active material which is a single crystal body, a binder, and a solvent, the 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 more than -0.27736 (a.u.).

20. A method for suppressing gelation of an electrode-forming composition comprising a first positive electrode active material which is a polycrystalline body, a second positive electrode active material which is a single crystal body, a binder, and a solvent, the method comprising causing the electrode-forming composition to contain a compound having a dissociable proton in its 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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