Aqueous slurry for electrodes for electrochemical devices, electrodes for electrochemical devices, and non-aqueous electrolyte secondary batteries

Abstract

The present invention provides: an electrode for electrochemical devices, said electrode being able to be obtained by an aqueous process, which uses water as a solvent, even in cases where an electrode active material that is very likely to be hydrolyzed is used; and a nonaqueous electrolyte secondary battery.　An electrode for electrochemical devices, said electrode containing a neutralizing dispersant and a composite oxide (A) that is capable of absorbing and desorbing lithium ions, and said electrode being characterized in that: the neutralizing dispersant contains a water-soluble compound (B') that contains a group 13 element (B) of the periodic table and at least one water-soluble polymer (C) that is selected from the group consisting of alkali metal salts, alkaline earth metal salts or ammonium salts of alginic acid, methylcellulose, carboxy methylcellulose, carboxymethyl starch or carrageenan, pullulan, guar gum and xanthan gum; a film of the water-soluble polymer (C) is formed on the surface of the composite oxide (A); and the group 13 element (B) of the periodic table is present in the film of the water-soluble polymer (C).

Description

[Technical Field]

[0001] The present invention relates to an electrode for an electrochemical device and a non-aqueous electrolyte secondary battery. [Background technology]

[0002] In recent years, power storage devices such as electrochemical capacitors and lithium-ion secondary batteries have been developed as electrochemical devices to be installed in mobile phones, electric vehicles, and the like. Among these, lithium-ion secondary batteries enable devices to be made smaller and lighter, have good charge / discharge efficiency, and have high energy density, and are therefore used as power sources for, for example, mobile devices, notebook PCs, home appliances, and even hybrid and electric vehicles. They are also attracting new attention as power storage devices for storing generated electricity in combination with natural energy systems such as solar power generation and wind power generation.

[0003] The electrodes that make up electrochemical devices are composed of electrode active materials that are directly involved in storing electrical energy, conductive additives that provide the conductive paths between the active materials, binders, current collectors, etc. The characteristics of electrochemical devices are highly dependent on the electrodes, and are greatly influenced by the characteristics of each material itself and how the materials are combined.

[0004] In recent years, with the expansion of applications of lithium-ion secondary batteries and the like, there has been an increasing demand for increased electrode capacity. Active materials containing high concentrations of nickel (hereinafter sometimes referred to as "high-nickel active materials") have attracted attention as active materials that can meet this demand, and their use is expected to increase in the future. Meanwhile, higher-capacity nickel-containing positive electrode materials are known to be more reactive with water than conventional iron- or manganese-based positive electrode materials. Therefore, currently, electrode slurries containing the high-nickel active materials are prepared using organic solvents and fluororesin-based binders.

[0005] The organic solvents used to prepare the slurry are often hydrophilic. Therefore, when moisture from the air gets mixed into the organic solvent, the positive electrode material undergoes hydrolysis, generating alkali, which extracts the fluorine from the fluororesin binder, potentially causing the slurry to gel. This necessitates the need for manufacturing in a special humidity-controlled environment, such as a low-dew-point dry room. Furthermore, the organic solvent is dried and removed at high temperatures during electrode manufacturing. Because the organic solvent is dried and removed in a dry environment requiring careful handling of open flames, the process requires strict monitoring of the lower explosive limit.

[0006] Furthermore, because the use of organic solvents is undesirable from the standpoints of safety, environmental impact, and ease of handling, studies have been conducted on methods for producing positive electrodes using aqueous processes, using aqueous dispersants and aqueous binders when producing electrode slurries. Aqueous processes eliminate the need for low-dew-point dry rooms and are easier to manage, which is expected to lead to cost reductions. However, as mentioned above, positive electrode active materials are highly reactive with water and undergo hydrolysis in the presence of water. Furthermore, regardless of whether they are positive or negative electrodes, electrode materials, particularly lithium-containing metal oxides, are particularly susceptible to hydrolysis. As a result, electrode slurries tend to be strongly alkaline (pH 10.5 or higher) and gel-like, making them difficult to apply. Furthermore, the strong alkaline nature of the electrode slurries can corrode the aluminum foil current collector. On the other hand, degradation of the electrode active material can lead to problems such as a decrease in the capacity and charge / discharge cycle characteristics of electrochemical devices and a loss of high-temperature durability.

[0007] Therefore, in order to suppress the deterioration of the electrode active material, the use of a binder mainly composed of an acid form of alginic acid (Alg-H) has been investigated (see, for example, Patent Document 1). It has been proposed that the use of such a binder can be used to neutralize the base in the electrode slurry, thereby suppressing the deterioration of the electrode active material. Furthermore, in order to obtain a positive electrode slurry that is stable against moisture, the use of a pH adjuster and carboxymethyl cellulose has been attempted (see, for example, Patent Document 2). [Prior art documents] [Patent documents]

[0008] [Patent Document 1] International Publication No. 2016 / 052715 [Patent Document 2] Japanese Patent Application Laid-Open No. 2009-64564 Summary of the Invention [Problem to be solved by the invention]

[0009] However, when these conventional aqueous technologies were tested, it was found that the period during which pH and viscosity could be maintained stably was short, and it was not possible to achieve maintenance for more than 24 hours. In mass-production battery manufacturing, given the possibility of factory shutdowns due to holidays or disasters, it is considered difficult to introduce slurries into the manufacturing process unless they maintain a stable pH and viscosity for at least 72 hours. Furthermore, from the perspective of storage stability, even slurries using the conventional organic solvent NMP can become contaminated with water during the 72-hour storage period if humidity control is interrupted, for example, due to a power outage. This raises concerns about ensuring pot life, particularly for slurries containing high-nickel active materials.

[0010] Furthermore, when the high-temperature life characteristics of the conventional aqueous system were examined, it was confirmed that the performance was inferior to that of a battery including a positive electrode fabricated using a conventional organic solvent process. Therefore, from the viewpoint of the pot life of the slurry and the high-temperature life characteristics of the fabricated battery, there is still room for improvement in the techniques described in Patent Documents 1 and 2.

[0011] The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide an electrode for an electrochemical device and a nonaqueous electrolyte secondary battery that can be obtained by an aqueous process using water as a solvent, even when an electrode active material that is very susceptible to hydrolysis is used. [Means for solving the problem]

[0012] As a result of intensive research into solving the above-mentioned problems, the inventors have found that the above-mentioned problems can be solved by using a material technology that can suppress an increase in pH and maintain viscosity over a long period of time, even in the case of an electrode slurry produced using water as a solvent, and have thus completed the present invention.

[0013] In order to achieve the above object, the electrode for an electrochemical device of the present invention comprises: An electrode for an electrochemical device containing a neutralizing dispersant and a composite oxide (A) capable of absorbing and desorbing lithium ions, The neutralizing dispersant is a water-soluble compound (B′) containing a Group 13 element (B) of the periodic table; and at least one water-soluble polymer (C) selected from the group consisting of alkali metal salts, alkaline earth metal salts, or ammonium salts of alginic acid, methyl cellulose, carboxymethyl cellulose, carboxymethyl starch, or carrageenan, pullulan, guar gum, and xanthan gum; a film of the water-soluble polymer (C) is formed on the surface of the composite oxide (A); The water-soluble polymer (C) film is characterized in that the Group 13 element (B) of the periodic table is present in the film.

[0014] In the electrode for electrochemical devices of the present invention, the Group 13 element (B) of the periodic table preferably includes boron.

[0015] In the electrode for electrochemical devices of the present invention, it is preferable that the electrode for electrochemical devices further comprises a conductive additive and a binder, the neutralizing dispersant, the composite oxide (A), the conductive additive, and the binder constitute an electrode mixture, and the boron content in the electrode mixture is in the range of 0.001% by weight or more and 5% by weight or less.

[0016] In the electrode for electrochemical devices of the present invention, when the content of the water-soluble compound (B') containing the Group 13 element (B) of the periodic table is taken as 100 parts by weight, it is preferable that the content of the water-soluble compound containing boron be in the range of 51 parts by weight to 100 parts by weight.

[0017] In the electrode for electrochemical devices of the present invention, the composite oxide (A) has a composition of Li a Ni b Co c Mn d M 1-b-c-d O2 or Li 4+x Ti5O 12 and Li 2+x Preferably, the composite oxide is represented by any one of the following formulas: Ti3O7, where M is one or more elements selected from the group consisting of Al, Mg, Ti, Fe, V, Cr, Nb, Mo, W, Cu, Zn, Ga, In, Sn, Zr, Ru, and La; 0.8≦a≦1.0 0 <b≦1.0 0≦c≦0.4 0≦d≦0.35 0 <b+c+d≦1.0 0≦x≦3 is.

[0018] The nonaqueous electrolyte secondary battery of the present invention comprises a positive electrode and a negative electrode, and contains an electrolyte between the positive electrode and the negative electrode, and at least one of the positive electrode and the negative electrode is the electrode for electrochemical devices of the present invention. [Effects of the Invention]

[0019] The present invention makes it possible to obtain an electrode slurry by an aqueous process that can suppress a long-term increase in pH (alkalinization) and a decrease in viscosity, even when using an electrode active material that is highly susceptible to hydrolysis, such as a lithium-containing metal oxide, and to provide an electrode for an electrochemical device that can be suitably used in an electrochemical device using the slurry.The use of this electrode for an electrochemical device makes it possible to provide a nonaqueous electrolyte secondary battery with excellent high-temperature durability. DETAILED DESCRIPTION OF THE INVENTION

[0020] Hereinafter, embodiments of the present invention will be described in detail, but the scope of the present invention is not limited to these descriptions, and other than the examples below, modifications and implementations can be made as appropriate within the scope that does not impair the spirit of the present invention. In this specification, unless otherwise specified, "A to B" representing a numerical range means "A or more, B or less." Furthermore, "mass" and "weight," "mass %" and "weight %" are treated as synonyms.

[0021] The electrode for electrochemical devices of the present invention contains a neutralizing dispersant and a composite oxide (A) capable of absorbing and desorbing lithium ions. The neutralizing dispersant contains a water-soluble compound containing a Group 13 element (B) of the periodic table and a water-soluble polymer (C). The water-soluble compound containing a Group 13 element (B) of the periodic table acts as a neutralizing agent, and the water-soluble polymer (C) acts as a dispersant.

[0022] <Composite oxide (A) that can absorb and release lithium ions> The composite oxide (A) capable of absorbing and releasing lithium ions (hereinafter also referred to as composite oxide (A)) functions as an electrode active material. In the case of a positive electrode, the composite oxide (A) is LiCoO2, LiFePO4, LiNi 0.5 Mn 1.5 O4, LiMnO4, and a Ni b Co c Mn d M 1-b-c-dMaterials selected from complex oxides represented by O2 can be used. In the above, even if the ratio of the constituent elements deviates slightly from the ratio described in the exemplified chemical formula, they can be used. Here, M is one or more elements selected from the group consisting of Al, Mg, Ti, Fe, V, Cr, Nb, Mo, W, Cu, Zn, Ga, In, Sn, Zr, Ru and La, 0.8 ≦ a ≦ 1.0 0 < b ≦ 1.0 0 ≦ c ≦ 0.4 0 ≦ d ≦ 0.35 0 < b + c + d ≦ 1.0 is preferred. In the case of the negative electrode, Li 4+x Ti5O 12 and compounds represented by Li 2+x Ti3O7 can be used. Here, x is a real number satisfying 0 ≦ x ≦ 3. Also, silicon-based inorganic compounds and transition metal oxides such as CuO, Cu2O, MnO2, MoO3, V2O5, CrO3, MoO3, Fe2O3, Ni2O3, CoO3 can be used.

[0023] Examples of the silicon-based inorganic compound include SiO z (0.5 ≦ z ≦ 1.6), LiSiO2, M q SiO w , (M = Na, Mg, Ca, 0.1 ≦ q ≦ 4, 0 < w ≦ 4), etc. silicon oxides, or silicon oxides composed of an equilibrium phase containing any two or more selected from Si, SiO2, Li2Si2O5, Li2SiO3 and Li4SiO4.

[0024] Here, SiO zIn this case, if z is 0.5 or greater, the cycle characteristics are improved, volume expansion can be alleviated, and pulverization can be suppressed. If z is 1.6 or less, the resistance of the silicon oxide can be kept low. From the viewpoint of cycle characteristics, z = 1 shows the best cycle characteristics. Such silicon oxides can be either single-phase types manufactured without applying heat, or separated-phase types that are disproportionated by applying heat during production, separating them into an amorphous SiO2 matrix and microcrystalline or amorphous silicon dispersed within the matrix. Furthermore, trace amounts of impurity elements can be present without causing any problems.

[0025] The silicon-based inorganic compound preferably has an average particle size (D50) of 0.1 to 20 μm, more preferably 1 to 15 μm. When the silicon-based inorganic compound has such a particle size range, it is easy to prevent the compound from being pulverized and the specific surface area is sufficient, which is advantageous in ensuring output characteristics. These compounds may be composited with or coated on a carbon material to enhance conductivity. Composite methods include mechanical alloying, carbonization, and surface chemical vapor deposition.

[0026] SiO z The particles can be prepared by a conventional method. For example, SiO z In most manufacturing methods, SiO z Gas is generated and deposited on the deposition substrate to form lumpy SiO z This is then crushed to produce particles.

[0027] Typical methods for lithium pre-doping include direct pre-doping, in which a lithium source is directly contacted, and electrochemical methods (electrochemical pre-doping), but other methods may also be used. Direct pre-doping involves contacting a silicon-based inorganic compound with a lithium source. The lithium source is preferably in the form of a metal foil sheet or liquid. The contacting step can be performed before or after the electrode is completed. Preferred examples of the present invention include a method in which a sheet electrode using a silicon-based inorganic compound (a silicon-based inorganic compound, a semi-inventive neutralizing dispersant, a binder, a conductive additive, etc., is applied and dried, and then processed into a predetermined shape) is attached to a metal lithium foil sheet and heated below the melting point of metallic lithium; a method in which a silicon-based inorganic compound powder and a lithium source powder are heated and mixed; and a method in which a sheet electrode using a silicon-based inorganic compound or a silicon-based inorganic compound powder is immersed in a lithium-containing liquid and contacted. Examples of lithium sources include lithium metal, organolithium compounds, lithium hydride, and lithium aluminum hydride.

[0028] In the electrochemical pre-doping method, lithium ions can be electrochemically doped into silicon oxide by passing current through an electrochemical cell that is composed of a sheet electrode using a silicon-based inorganic compound and a counter electrode made of metallic lithium or a substance containing lithium, to which a lithium ion conductive non-aqueous electrolyte is added. Alternatively, these methods may be combined to perform pre-doping.

[0029] The composite oxide (A) may be one of the above materials, or two or more of them may be used in combination. When two or more of them are used in combination, at least two materials selected from the materials usable for the positive electrode and at least two materials selected from the materials usable for the negative electrode may be used in combination. The mixing ratio of the materials constituting the composite oxide (A) may be arbitrary.

[0030] The device used to mix multiple materials is not particularly limited, but for example, in the case of rotary mixers, cylindrical mixers, twin cylindrical mixers, double cone mixers, regular cube mixers, and hoe-shaped mixers can be used, and in the case of stationary mixers, spiral mixers, ribbon mixers, Muller mixers, helical flight mixers, pugmill mixers, fluidizing mixers, etc. can be used.

[0031] The composite oxide (A) is preferably granular, and in this case, the particle diameter is preferably about 400 nm to 40 μm, more preferably in the range of 200 nm to 20 μm. If the particle diameter is less than 400 nm, it is likely to be difficult to disperse the slurry, and if the particle diameter is more than 40 μm, cracks in the electrode plate are likely to occur. Here, the particle diameter refers to the primary particle diameter or secondary particle diameter. Furthermore, shapes other than granular shapes, such as scale shapes, are also preferred. In this case, the particle diameter is preferably such that the shorter dimension of the length or width is 40 μm or less.

[0032] According to the present invention, it is now possible to prepare aqueous slurries for higher-capacity ternary cathode materials and nickel-containing electrode materials containing the high-nickel active material, which currently require the use of organic solvents and fluororesin binders due to their higher reactivity with water compared to conventional iron-based and manganese-based electrode materials. Since the use of these electrode materials is expected to increase in the future, the ability to prepare electrodes using aqueous slurries has been eagerly awaited.

[0033] In addition, the composite oxide (A) may be doped with a small amount of elements such as fluorine, boron, aluminum, chromium, zirconium, molybdenum, or iron, or the particle surface of the composite oxide (A) may be surface-treated with carbon, MgO, Al2O3, SiO2, or the like.

[0034] Furthermore, the composite oxide (A) may contain a carbonaceous material in the surface layer. This can improve the electrical conductivity of the composite oxide (A), thereby improving the battery characteristics of a lithium-ion battery containing such composite oxide (A) as a cathode or anode material. The average thickness of the carbonaceous material is preferably 3 nm or more and 5 μm or less. When the average thickness of the coating carbonaceous material is 3 nm or more, the effect of improving electrical conductivity is exhibited. When the average thickness of the coating carbonaceous material is 5 μm or less, a decrease in electrode density can be suppressed, and a decrease in battery capacity can be suppressed.

[0035] In the nonaqueous electrolyte secondary battery of the present invention, at least one of the positive electrode and the negative electrode is the electrode for electrochemical devices of the present invention. When either the positive electrode or the negative electrode is not the electrode for electrochemical devices of the present invention, suitable electrode active materials for the electrode include metal chalcogenides such as TiS2, MoS2, and NbSe3; sulfur, sulfur-selenium composites, composites of sulfur or sulfur-selenium composites with porous carbon such as template carbon or activated carbon, or composites of sulfur or sulfur-selenium composites with modified polymers such as modified polyacrylonitrile; conductive polymer compounds such as polyacene, polyparaphenylene, polypyrrole, and polyaniline; silicon, zinc, bismuth, graphite, non-graphitizable carbon, and activated carbon.

[0036] <Water-soluble compounds containing Group 13 elements (B) of the periodic table> Examples of the Group 13 element (B) contained in the neutralizing dispersant include boron, aluminum, gallium, indium, and thallium. Among these, at least one element selected from boron and aluminum is preferred. Furthermore, a water-soluble compound containing a Group 13 element (B), i.e., a water-soluble compound containing at least one element selected from boron, aluminum, gallium, indium, and thallium, is hereinafter referred to as a "Group 13 element-containing compound (B')" (also referred to as a Group 13 element-containing compound (B')). Examples of the Group 13 element-containing compound (B') include oxides, sulfides, inorganic acids, and inorganic acid salts. Among these, compounds containing boron and aluminum are preferred due to their ease of availability, and boron compounds selected from boric acid, borates, and mixtures thereof, and aluminates, are more preferred. The Group 13 element-containing compound (B') acts as a neutralizing agent.

[0037] The boron compound selected from boric acid, borate salts, and mixtures thereof is not particularly limited as long as it is industrially available. For example, boric acid is H3BO3 (orthoboric acid) and / or HBO2 (metaboric acid), and borate salts include borax (sodium tetraborate, Na2B4O7·10H2O), anhydrous borax (Na2B4O7), its pentahydrate (Na2B4O7·5H2O), sodium pentaborate (NaB5O8), etc.

[0038] Among these boron compounds, boric acid (H3BO3), borax, sodium pentaborate, or a mixture thereof is particularly preferred. When the boron compound is a mixture of boric acid and a sodium salt of boric acid, the molar ratio (Na / B) of boron (B) to sodium (Na) is preferably greater than 0 and not greater than 0.3. Within this range, the pH value of the aqueous solution can be adjusted to 7 or less, thereby exhibiting a neutralizing and dispersing function. Furthermore, these mixtures of boric acid and a sodium salt of boric acid may contain polyborate ions. To obtain a mixture containing polyborate ions, the mixture is completely dissolved in hot water. Furthermore, the completely dissolved aqueous solution can be evaporated to dryness to obtain a powder.

[0039] <Example of polyborate ion production> 100g of water was heated to 80°C, and 42g of boric acid and 35g of borax were added and dissolved, then cooled to room temperature. The pH of the solution was 5.8. The solution was then evaporated to dryness using the spray-drying method in a 140°C environment. The spray-drying method involves turning a liquid into a fine mist, spraying it into hot air, and instantly drying it to obtain a powder.

[0040] The boron-containing compounds described above are preferred because they exhibit excellent properties in stabilizing the viscosity and pH of a slurry containing a composite oxide when used in combination with the water-soluble polymer (C) described below.

[0041] In the present invention, the mixing ratio of the Group 13 element-containing compound (B') to the composite oxide (A) is such that the content of the Group 13 element-containing compound (B') relative to the composite oxide (A) is 0.01% by weight or more, preferably 0.02% by weight or more, and 10% by weight or less, preferably 4% by weight or less. If the content of the Group 13 element-containing compound (B') is too low, the pH and viscosity stability of the slurry will be insufficient. If the content is too high, the resistance of the produced electrode will be high, and the internal resistance of the battery will become too high. As a result, the battery capacity will tend to decrease.

[0042] The boron content in the electrode mixture is preferably in the range of 0.001% by weight to 5% by weight, and the content of the water-soluble compound containing boron is preferably in the range of 51 parts by weight to 100 parts by weight, based on 100 parts by weight of the Group 13 element-containing compound (B').

[0043] <Water-soluble polymer (C)> The water-soluble polymer (C) contained in the neutralizing dispersant is preferably a polymer that dissolves completely in water, but even if the polymer is water-insoluble, it can be made dispersible in water by introducing a hydrophilic component to partially solubilize it in water. In other words, the water-soluble polymer (C) acts as a dispersant.

[0044] The water-soluble polymer (C) preferably has a functional group containing an ionic cation or anion, and / or a functional group containing a hydrogen bond donor (hydrogen donor atom) or acceptor (hydrogen acceptor atom). Alternatively, the polymer is preferably one to which these functional groups can be added by chemical modification. Specific examples include oxygen-containing functional groups such as carboxyl, hydroxyl, carbonyl, ether, and ester groups; sulfur-containing functional groups such as sulfo, sulfonyl, and sulfinyl groups; nitrogen-containing functional groups such as amino, amide, and imide groups; phosphorus-containing functional groups such as phosphate groups; and substituents containing highly electronegative halogens. Among these, those containing carboxyl, hydroxyl, carbonyl, amino, amide, and imide groups are preferred. Specific examples include water-soluble thickening polysaccharides, acrylic resins, vinyl alcohol resins, and polyethers.

[0045] Among these, water-soluble thickening polysaccharides are preferred because they have suitable water solubility and viscosity, and can provide long-term slurry stability. They also provide excellent smoothness to the electrode coating surface, can be dried at relatively low temperatures, and can achieve both high battery capacity and improved cycle characteristics.

[0046] Polysaccharides are compounds formed by the polymerization of one or more monosaccharides, such as polyhydroxyaldehydes or polyhydroxyketones, via glycosidic bonds. Specific examples of water-soluble thickening polysaccharides include alkali metal salts, alkaline earth metal salts, or ammonium salts of compounds such as alginic acid, methylcellulose, carboxymethylcellulose, carboxymethyl starch, and carrageenan, as well as pullulan, guar gum, and xanthan gum. Among these, alkali metal salts, alkaline earth metal salts, or ammonium salts of carboxymethylcellulose, alginic acid, and carrageenan are more preferred in terms of excellent dispersibility.

[0047] The viscosity of the water-soluble polymer (C) is preferably 250 cP to 78,000 cP when prepared as a 1 wt% aqueous solution. This range ensures water solubility and provides stable slurry viscosity. If the viscosity is too low, maintaining the dispersion state over a long period of time becomes difficult, resulting in rapid sedimentation of the active material. If the viscosity is too high, a large amount of water is required to increase the fluidity of the slurry, lowering the solids concentration of the slurry. This results in longer drying times and longer cycle times for the coating process during production. Regarding carboxymethyl cellulose, there are no particular limitations on the degree of etherification, but a value of 0.4 to 1.6 is preferred. Regarding alginic acid, there are no particular limitations on the ratio of mannuronic acid to guluronic acid (referred to as the M / G ratio), but a value of 0.5 to 1.5 is preferred.

[0048] In the present invention, the mixing ratio of the water-soluble polymer (C) to the composite oxide (A) is such that the content of the water-soluble polymer (C) relative to the composite oxide (A) is 0.3 wt% or more, preferably 0.5 wt% or more, and 7 wt% or less, preferably 5 wt% or less. If the proportion of the water-soluble polymer (C) is too high, the amount of the composite oxide serving as the active material decreases, which tends to reduce the battery capacity. If the proportion is too low, dispersibility decreases, the slurry settles, and it becomes difficult to obtain long-term storage properties.

[0049] When the total content of the compound (B') containing a Group 13 element of the periodic table and the water-soluble polymer (C) in the electrode is 2% by weight, the content of the compound (B') containing a Group 13 element of the periodic table is preferably 0.2% by weight or more and 1.6% by weight or less, and more preferably 0.5% by weight or more and 1.5% by weight or less.

[0050] In addition, when the pH stabilizing effect is insufficient or the slurry stability due to thickening is insufficient, the neutralizing dispersant of the present invention may further contain at least one of a neutralizing agent (auxiliary) and a dispersing agent (auxiliary). Examples of neutralizing agents (auxiliary) include disodium phosphate (NaH2PO4) and Alg-H. Examples of dispersing agents (auxiliary) include Alg-H, methylcellulose, carboxymethyl starch, carrageenan, PVP (polyvinylpyrrolidone), PVA (polyvinyl alcohol), and PAA (sodium polyacrylate). Only one type of neutralizing agent (auxiliary) and / or dispersing agent (auxiliary) may be used, or two or more types may be used in combination. It is preferable to add the neutralizing agent (auxiliary) in an amount not exceeding the content of the neutralizing agent, and the dispersing agent (auxiliary) in an amount not exceeding the content of the dispersing agent.

[0051] <Binder composition> An electrode binder composition is preferably used for the electrodes (positive electrode, negative electrode) constituting the nonaqueous electrolyte secondary battery of the present invention. The binder composition may contain a water-soluble polymer (C) pre-mixed therewith, or may contain a compound (B') containing a Group 13 element of the periodic table pre-mixed therewith. There are no particular restrictions on the types or combinations of the water-soluble polymer (C) and the compound (B') containing a Group 13 element of the periodic table when mixed, but types or combinations that are highly compatible when mixed with the binder composition are preferred.

[0052] When mixing, the binder composition, water-soluble polymer (C), and compound (B') containing a Group 13 element of the periodic table are mixed in such a ratio that the total content of the water-soluble polymer (C) and compound (B') containing a Group 13 element of the periodic table relative to the binder composition is 10% by weight or more, preferably 25% by weight or more. Also, the total content is 800% by weight or less, preferably 500% by weight or less. If the content is too low, dispersibility becomes insufficient, making it difficult to maintain the long-term storage stability of the slurry. Furthermore, the electrode plate resistance may increase, resulting in a deterioration in battery performance. If the content is too high, the electrode plate strength may decrease.

[0053] The binder composition can be an emulsion or a polymer aqueous dispersion. As the emulsion, synthetic resin emulsions such as "polyacrylic acid copolymer resin emulsion," "conjugated diene polymer emulsion," and "fluorine-containing copolymer emulsion," and as the polymer aqueous dispersion, resin-based emulsions developed for battery applications such as "fluorine-containing copolymer aqueous dispersion" can be preferably used.

[0054] By using a binder composition containing such an emulsion or polymer aqueous dispersion in combination with the water-soluble polymer (C) and the compound (B') containing a Group 13 element of the periodic table, the strength of the electrode plate can be increased. High electrode plate strength increases durability over long periods of use and resistance to expansion and contraction due to charge and discharge, thereby extending the life of the device. Furthermore, electrode plates with high adhesive strength are expected to prevent the problem of the active material layer peeling off from the current collector when a battery is wound.

[0055] The term "polyacrylic acid copolymer resin emulsion" refers to an emulsion of a copolymer resin obtained by emulsion polymerization of acrylic acid monomers and other reactive monomers in water. Examples of the other reactive monomers include vinylidene fluoride monomers; styrene monomers; ethylenically unsaturated monomers containing nitrile groups, such as acrylonitrile, methacrylonitrile, α-chloroacrylonitrile, crotonnitrile, α-ethylacrylonitrile, α-cyanoacrylate, vinylidene cyanide, and fumaronitrile; monofunctional monomers, such as methacrylic acid and acrylic acid; fumaric acid, maleic acid, itaconic acid, citraconic acid, mesaconic acid, glutaconic acid, 1,2,3,6-tetrahydrophthalic acid, 3-methyl-1,2,3,6-tetrahydrophthalic acid, 4-methyl-1,2,3,6-tetrahydrophthalic acid, and methyl-3,6-endomethylene-1,2,3,6-tetrahydrophthalic acid. Examples of the other reactive monomers include ethylenically unsaturated monomers containing a carboxylic acid, such as trihydrophthalic acid, exo-3,6-epoxy-1,2,3,6-tetrahydrophthalic acid, and himic acid; anhydrides of the above ethylenically unsaturated monomers containing a carboxylic acid; saponification products of the above anhydrides; ethylenically unsaturated monomers containing a ketone group, such as methyl vinyl ketone, ethyl vinyl ketone, isopropyl vinyl ketone, isobutyl vinyl ketone, t-butyl vinyl ketone, and hexyl vinyl ketone; and ethylenically unsaturated monomers containing an organic acid vinyl ester group, such as vinyl acetate, vinyl propionate, vinyl butyrate, trimethyl vinyl acetate, vinyl caproate, vinyl caprylate, vinyl laurate, vinyl palmitate, and vinyl stearate. One type of the other reactive monomer may be used, or two or more types may be used in combination.

[0056] Furthermore, by substituting the terminals of the polyacrylic acid copolymer resin with specific functional groups, it is possible to obtain a modified product that can react with specific monomers, etc. Examples of modified products include epoxy modified products, carboxy modified products, isocyanate modified products, and hydrogen modified products.

[0057] As the "conjugated diene polymer emulsion", an emulsion of styrene butadiene copolymer rubber can be suitably used. The styrene butadiene copolymer rubber emulsion is a particle of a copolymer of styrene and butadiene, and has a copolymer component derived from styrene and a copolymer component derived from butadiene. The content of the copolymer component derived from styrene is preferably 50 to 80 mol % based on the total copolymer components constituting the styrene butadiene copolymer. The content of the copolymer component derived from butadiene is preferably 20 to 50 mol % based on the total copolymer components.

[0058] The styrene-butadiene copolymer may contain other reactive monomers in addition to the copolymerization components derived from styrene and butadiene, such as those mentioned above as components of the emulsion of the polyacrylic acid copolymer resin.

[0059] When the styrene-butadiene copolymer contains the other reactive monomer, the content of the other reactive monomer is preferably 1 to 30 mol% based on the total copolymerization components constituting the styrene-butadiene copolymer. The styrene-butadiene copolymer may be any of a random copolymer, a block copolymer, and a graft copolymer. In addition, the styrene-butadiene copolymer may be carboxy-modified.

[0060] The styrene-butadiene copolymer rubber emulsion is an emulsion of rubber particles obtained by emulsion polymerization of styrene monomers, butadiene monomers, and, if necessary, other reactive monomers in water, and is also sometimes called latex or synthetic rubber latex.

[0061] Instead of styrene-butadiene copolymer rubber, butadiene rubber (BR), isoprene rubber (IR), chloroprene rubber (CR), nitrile rubber (NBR), butyl rubber (IIR), ethylene propylene rubber (EPDM), natural rubber (NR), etc. can also be used.

[0062] A "fluorine-containing copolymer" is a copolymer containing a polymer of at least one fluorine-containing monomer in its molecule. Examples of fluorine-containing copolymers include copolymers of polyvinylidene fluoride (PVDF) and polyvinyl alcohol (PVA), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), polyvinylidene fluoride-hexafluoropropylene (PVdF-co-HFP), ethylene-tetrafluoroethylene copolymer (ETFE), polychlorotrifluoroethylene (PCTFE), propylene-tetrafluoroethylene copolymer, and ethylene-chlorotrifluoroethylene copolymer (ECTFE).

[0063] The term "fluorine-containing copolymer emulsion" refers to an emulsion of a copolymer resin obtained by emulsion polymerization in water of one type of fluorine-containing monomer and another reactive monomer, or two or more types of fluorine-containing monomers, etc. The term "aqueous dispersion of a fluorine-containing copolymer" refers to an aqueous solution of a copolymer resin obtained by copolymerizing one type of fluorine-containing monomer and another reactive monomer, or two or more types of fluorine-containing monomers, etc., or a dispersion in which the copolymer resin is dispersed in water.

[0064] Examples of the other reactive monomers include PVA, hexafluoropropylene, ethylene, and propylene.

[0065] The content (solid content concentration) of the polyacrylic acid copolymer resin, styrene-butadiene copolymer rubber, or fluorine-containing copolymer in the polyacrylic acid copolymer resin emulsion, styrene-butadiene copolymer rubber emulsion, fluorine-containing copolymer emulsion, or fluorine-containing copolymer aqueous dispersion is preferably 0.1 to 80 mass%, more preferably 0.5 to 65 mass%.

[0066] The solid content of the binder composition is preferably 0.5 to 95% by mass, more preferably 1.0 to 85% by mass, where the solid content is the total mass ratio of the polyacrylic acid copolymer resin, the conjugated diene polymer, or the fluorine-containing copolymer to the mass of the binder composition.

[0067] <Slurry> The slurry for producing an electrode for an electrochemical device of the present invention contains a binder composition, an electrode active material (composite oxide (A)), water, a Group 13 element-containing compound (B'), and a water-soluble polymer (C).

[0068] This slurry contains a Group 13 element (B) of the periodic table and a water-soluble polymer (C), which prevents the decomposition of the active material and also prevents an increase in pH, even though the slurry is aqueous. It is possible to suppress pH rise over the long term, and achieve long-term viscosity stability.

[0069] The electrode active material (cathode material) used for the positive electrode should not be added to water. Therefore, the manufacturing process using aqueous slurries has been studied only for materials that are resistant to pH changes when exposed to water. However, in the case of the electrode for electrochemical devices of the present invention, even if the slurry used to fabricate the electrode is aqueous, it can be applied to cathode materials that are susceptible to hydrolysis, such as nickel-based materials. When this slurry is applied to a current collector such as a current collector foil, a coated electrode can be manufactured without corroding the current collector. Therefore, no treatment to impart corrosion resistance to the current collector is required. Furthermore, because the slurry is aqueous, only water vapor is emitted during drying, which is preferable from the standpoints of safety and environmental impact. Furthermore, the equipment can be easily cleaned by simply washing with water.

[0070] The solids concentration of the slurry is preferably 65% ​​to less than 95% by mass. Outside this range, there is too much water, which can make drying take a long time, or the viscosity can be too low, causing the slurry to not stay on the foil, leading to concerns about the stability of the coating amount. If the solids content is too high, the coating amount will not be stable.

[0071] The slurry can be prepared, for example, by the following two methods. [Method 1] The composite oxide (A), the water-soluble compound (B') containing a Group 13 element (B) such as boron, and the water-soluble polymer (C) are mixed in powder form, and water is added and kneaded. Finally, the binder composition is added and kneaded. [Method 2] An aqueous solution containing a predetermined mass % of a water-soluble compound (B') containing a Group 13 element (B) such as boron and a water-soluble polymer (C) is prepared in advance. Next, the composite oxide (A) and the aqueous solution are mixed and kneaded, and then water is added to adjust the viscosity. Finally, a binder composition is added and kneaded.

[0072] These methods allow the Group 13 element (B) to be uniformly dispersed in the film of the water-soluble polymer (C). Furthermore, these methods allow the solid content of the slurry to be increased, even to a solid concentration of 80% or more. A higher solid concentration tends to improve the pH and dispersion stability, which is preferable. Furthermore, the drying time is faster, which shortens the process takt time and reduces the amount of heat required for drying, resulting in reduced manufacturing costs.

[0073] In the above, the mixing or kneading method can be, for example, mixing using various grinders, mixers, stirrers, etc., or dispersion using ultrasonic waves. Specific examples include processing methods using shear force or collision such as mixers, high-speed rotary mixers, shear mixers, blenders, ultrasonic homogenizers, high-pressure homogenizers, and ball mills; and methods using Waring blenders, flash mixers, turbulizers, etc. These methods can also be used in appropriate combination.

[0074] The slurry may contain a conductive additive to ensure electrical conductivity. Addition of a conductive additive reduces the internal resistance of the battery. The conductive additive is not particularly limited, and examples include metals, carbon materials, conductive polymers, and conductive glass. Among these, carbon materials are preferred, including nanocarbons such as carbon nanotubes, carbon nanofibers, carbon nanohorns, and fullerenes; acetylene black, furnace black, thermal black, channel black, Ketjen Black (registered trademark), Vulcan, graphene, vapor-grown carbon fiber (VGCF), and graphite. Acetylene black, Ketjen Black, VGCF, and carbon nanotubes are more preferred. Carbon nanotubes may be single-walled, double-walled, or multi-walled. The conductive additive may be used alone or in combination. Graphite can be used for active materials whose operating potential range does not fall below 0.15 V vs. lithium. The conductive additive may be acid- or alkali-treated to improve hydrophilicity.

[0075] The median diameter (also called "D50" or "50% particle diameter") of the conductive additive is preferably in the range of 10 nm to 1 μm. Within this range, the conductive additive can be stably and uniformly dispersed in the slurry. The median diameter can be calculated by measuring the particle size distribution by laser diffraction using a bulk density measuring instrument MT-3300 (manufactured by Microtrac).

[0076] The electrode active material layer may contain a conductive material to improve the conductivity of the electrode. The conductive material is not particularly limited as long as it can be mixed in an appropriate amount with the active material to impart conductivity. Typical examples include carbon powders such as acetylene black, carbon black, and graphite, as well as fibers, powders, and foils of various metals. Furthermore, non-oxide active materials commonly used in lithium-ion batteries, such as graphite, non-graphitizable carbon, easily graphitizable carbon, and activated carbon, may also be used in combination.

[0077] The water used for the slurry is not particularly limited, and commonly used water can be used. For example, tap water, distilled water, ion-exchanged water, pure water, ultrapure water, etc. can be used. Among them, ion-exchanged water, pure water, and ultrapure water are preferred.

[0078] The water may contain an organic solvent (hydrophilic organic solvent) that is uniformly miscible with water. Examples of hydrophilic organic solvents include N-methyl-2-pyrrolidone; dimethyl sulfoxide; alcohols such as methanol, ethanol, 2-propanol (IPA), isopropanol, n-butanol, and t-butanol; ketones such as acetone and methyl ethyl ketone (MEK); ethers such as 1,4-dioxane and tetrahydrofuran (THF); N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), dimethyl sulfoxide (DMSO), acetonitrile, and ethyl acetate. One or more hydrophilic organic solvents may be used. However, from the viewpoints of safety, environmental impact, and ease of handling, it is preferable to use only water without using an organic solvent.

[0079] The blending ratio of water to the organic solvent may be appropriately determined taking into consideration the type of organic solvent, the affinity between water and the organic solvent, and the like.

[0080] The ratio of each component in the solid content of the slurry is preferably 60 to 99 mass% for the electrode active material, 0.1 to 25 mass% for the binder composition, water-soluble polymer (C), and Group 13 element-containing compound (B'), and 0.1 to 10 mass% for the conductive aid, based on 100 mass% for the total amount of the electrode active material, binder composition, water-soluble polymer (C), and Group 13 element-containing compound (B'). More preferably, the ratio is 80 to 95 mass% for the electrode active material, 0.5 to 15 mass% for the binder composition, water-soluble polymer (C), and Group 13 element-containing compound (B'), and 0.5 to 5 mass% for the conductive aid.

[0081] <Method of manufacturing electrodes for electrochemical devices> The electrode for electrochemical devices of the present invention can be produced, for example, by applying the above-mentioned slurry to the surface of an electrode substrate (current collector), drying, and press-molding. This makes it possible to produce an electrode for electrochemical devices in which an electrode mixture layer is present on the surface of the electrode substrate. The electrode mixture is the electrode layer portion of the electrode after the slurry is applied to an electrode substrate such as foil and dried, and is a combination of an electrode active material (composite oxide (A)), a conductive additive, a neutralizing dispersant, and a binder.

[0082] Examples of the coating method include methods using a knife coater, comma coater, die coater, etc. As the electrode substrate (current collector), aluminum foil, copper foil, stainless steel foil, nickel foil, etc. For the purpose of improving conductivity, these foils coated with carbon can also be used as the electrode substrate.

[0083] The amount of the slurry applied to the electrode substrate can be set so that the thickness of the electrode mixture layer after drying is in the range of 0.02 to 0.40 mm, preferably 0.03 to 0.25 mm.

[0084] The temperature in the drying step can be appropriately set within the range of, for example, 35 to 150°C, preferably 40 to 135°C. The time for the drying step can be appropriately set within the range of, for example, 10 to 120 seconds, preferably 10 to 80 seconds. It is also preferable to carry out the drying step under reduced pressure. In this case, the reduced pressure condition is preferably a pressure of 10 Pa or less, and drying can be carried out for several hours.

[0085] The electrode for electrochemical devices thus obtained may be used as either a positive electrode or a negative electrode of an electrochemical device.

[0086] <Electrodes for electrochemical devices> The obtained electrode for electrochemical devices has the following properties. When the Group 13 element (B) of the periodic table is boron, the composite oxide (A) is coated with a water-soluble polymer (C), and the film of the water-soluble polymer (C) contains a specific amount of boron (B). In the electrode, the composite oxide (A) is protected by the coating of the water-soluble polymer (C) containing boron (B). This protection results in battery properties that are particularly excellent in heat resistance, as described below.

[0087] The reason for the improved heat resistance is thought to be the suppression of attack on the composite oxide (A) by hydrofluoric acid, a thermal decomposition product of the electrolyte. Furthermore, the protection of the composite oxide (A) by covering it with the water-soluble polymer (C) containing boron (B) suppresses the redox decomposition of the electrolyte, particularly suppressing gas generation. The suppression of gas generation is thought to be due to an increase in the reaction overvoltage of the electrolyte, and this effect is achieved by incorporating boron (B) into the water-soluble polymer (C) film. In contrast, electrodes that do not contain the water-soluble polymer (C) film containing boron (B) have poor heat resistance and may experience problems such as gas generation, overvoltage, low capacity, and inability to suppress metal elution.

[0088] In an electrode for electrochemical devices, the boron content in the electrode mixture is preferably in the range of 0.001% by weight to 5% by weight. This range ensures good battery characteristics at high temperatures and good cycle characteristics. To determine whether the boron content meets the requirements of the present invention, methods such as absorbance measurement or XPS (X-ray photoelectron spectroscopy) analysis can be used. If the boron content is higher than this range, the proportion of the composite oxide (A) that serves as the electrode active material decreases, which tends to reduce the battery capacity. If the boron content is too low, dispersibility decreases, making it more likely that sedimentation will occur in the slurry consisting of the electrode mixture and water, making it difficult to achieve long-term storage characteristics. Furthermore, it becomes difficult to achieve good battery characteristics at high temperatures.

[0089] <Absorbance measurement> 2 mg of electrode mixture obtained by scraping from the electrode is dispersed in 10 ml of water to obtain an aqueous solution, which is then filtered to obtain an aqueous solution (filtrate). When the aqueous solution (filtrate) is measured using a spectrophotometer by azomethine H absorptiometry, the absorbance value in the range of 410 to 425 μm is measured. When boron is contained in the electrode mixture in a range of 0.001 wt% to 5 wt%, the absorbance is greater than 0 and less than 2.3.

[0090] To compare absorbance with boron concentration, prepare boron concentration standards (1 ppm, 2 ppm, 3 ppm, 4 ppm, etc.), measure the absorbance using a colorimeter, and plot the absorbance versus boron concentration. Because absorbance and boron concentration are proportional according to Lambert-Beer's law, a linear graph is obtained. This is used as a calibration curve, and the boron concentration is read from the absorbance. Absorbance is preferably measured at 410-425 nm, which is the maximum absorption wavelength of the complex formed by borate ions and azomethine H reagent (coloring solution). To measure the blank value, the same amount of azomethine H sample as used to form the complex in the filtrate is mixed with pure water and the absorbance is measured.

[0091] When the absorbance value of the aqueous solution was within the above range, a battery exhibiting good high-temperature durability and energy density could be obtained. In other words, when the absorbance value of the aqueous solution was outside the above range, it was confirmed that the high-temperature durability of the battery could not be obtained, or the resistance increased, resulting in a decrease in the energy density of the battery.

[0092] Here, absorbance is a dimensionless quantity that indicates the decrease in light intensity obtained when the filtrate of the aqueous solution in which the electrode mixture is dispersed is measured using a spectrophotometer. Azomethine H absorptiometry is a method for analyzing boron. It is a method for measuring a compound that is formed by reacting azomethine H with boron and that exhibits color in a specific range of visible light wavelengths using spectrophotometry.

[0093] In addition, when transition metals are mixed into the filtrate and it is difficult to develop color, it may contain a chelating agent for removing metal ions. Examples of the chelating agent include EDTA disodium salt (dihydrate), EDTA tetrasodium salt (tetrahydrate), CyDTA (trans-1,2-cyclohexanediaminetetraacetate), GEDTA (glycoletherdiaminetetraacetate), etc., and mixtures thereof. In particular, EDTA disodium salt (dihydrate), EDTA tetrasodium salt (tetrahydrate), and mixtures thereof are preferred because they can mask high-concentration metal ions. Examples of metal ions that can be masked by the chelating agent include iron ions, copper ions, aluminum ions, etc.

[0094] <XPS (X-ray Photoelectron Spectroscopy)> The measurement of the electrode sample (electrode binder) by XPS (X-ray Photoelectron Spectroscopy) is carried out using an X-ray photoelectron spectrometer (JEOL, JPS9030). The electrode sample to be measured is placed on the sample stage so as to be flat, and the spectra of O1s (530 - 533 eV) and boron (B1s) (189 - 195 eV) are measured using the Kα line of the aluminum X-ray source. The background is removed by the Tougaad method, and the peak area (S O ) of the O1s spectrum and the peak area (S B ) of the B1s spectrum are obtained. Further, by the relative sensitivity factor (RSF) method, the product of the peak area and the instrument sensitivity factor is taken to calculate the element concentration. The surface element ratio of boron (B element amount / O element amount) obtained by the following formula is defined as the surface element ratio of boron on the electrode surface.

[0095] (Formula) Surface element ratio of boron (B element amount / O element amount) = [Element concentration of boron calculated using the relative sensitivity factor method (RSF method) from S B ÷ [Element concentration of oxygen calculated in the same manner from S O × 100

[0096] When boron is contained in the electrode binder in the range of 0.001 wt% or more and 5 wt% or less, the surface element ratio of boron (B) at that time is greater than 0 and 15% or less.

[0097] It was confirmed that when the surface element amount ratio of boron (B) is outside the above range, the high temperature durability of the battery cannot be obtained, or the resistance increases, resulting in a decrease in the energy density of the battery.

[0098] <Electrochemical devices (non-aqueous electrolyte secondary batteries)> The nonaqueous electrolyte secondary battery of the present invention is an electrochemical device comprising a positive electrode and a negative electrode, and an electrolyte between the positive electrode and the negative electrode, and at least one of the positive electrode and the negative electrode is the electrode for electrochemical devices of the present invention.

[0099] In electrochemical devices, a separator is placed between the positive and negative electrodes to prevent short circuits between them. The positive and negative electrodes are each equipped with a current collector, and both current collectors are connected to a power source. Charging and discharging are switched by operating this power source.

[0100] Examples of electrochemical devices include non-aqueous electrolyte secondary batteries such as lithium ion secondary batteries, electrochemical capacitors, and also include non-lithium ion batteries, lithium ion capacitors, dye-sensitized solar cells, and the like.

[0101] The electrochemical device has high performance and can be used as a highly safe power storage device. Therefore, the electrochemical device may be installed in small electronic devices such as mobile phones, notebook computers, personal digital assistants (PDAs), video cameras, and digital cameras; transportation devices (vehicles) such as electric bicycles, electric automobiles, and trains; power generation devices such as thermal power plants, wind power plants, hydroelectric power plants, nuclear power plants, and geothermal power plants; natural energy power storage systems, and the like.

[0102] The nonaqueous electrolyte secondary battery of the present invention is more preferably a lithium ion secondary battery. High-nickel active materials are effective as electrode materials for lithium ion secondary batteries because they can increase the electrode capacity, but as mentioned above, they have the problem of being very susceptible to hydrolysis.

[0103] The nonaqueous electrolyte secondary battery of the present invention, which includes the electrode for an electrochemical device of the present invention, exhibits charge-discharge characteristics that are particularly superior in heat resistance compared to nonaqueous electrolyte secondary batteries including electrodes prepared from a slurry prepared using an organic solvent, as demonstrated in the Examples.

[0104] In the nonaqueous electrolyte secondary battery of the present invention, either the positive electrode or the negative electrode may be the electrode for electrochemical devices of the present invention, and if one of the positive electrode and the negative electrode is the electrode for electrochemical devices of the present invention, the other electrode (counter electrode) may be produced in an aqueous system or a nonaqueous system.

[0105] The nonaqueous electrolyte secondary battery of the present invention may be in the form of, for example, a cylindrical type in which a rectangular electrode and a separator are overlapped and wound up into a wound body, a laminate type in which electrodes are wrapped in separators and stacked and packaged in an aluminum laminate pouch, a coin type in which electrode pellets and a separator are stacked, etc. The exterior case may be made of stainless steel, aluminum, or the like.

[0106] <Electrolytes> Examples of electrolytes that can be used include non-aqueous electrolyte solutions in which lithium salts are dissolved in non-aqueous solvents, gel-like, rubber-like, or solid sheet-like electrolytes prepared by mixing non-aqueous electrolyte solutions with organic polymer compounds, and solid electrolytes prepared by solidifying solid compound particles (e.g., sulfides or oxides) with solid lithium ion conductivity using a press or the like.

[0107] Examples of non-aqueous solvents used in non-aqueous electrolyte solutions include cyclic carbonates such as propylene carbonate, ethylene carbonate, vinylene carbonate, and butylene carbonate; chain carbonates such as diethyl carbonate, dimethyl carbonate, and ethyl methyl carbonate; cyclic ethers such as tetrahydrofuran, 2-methyltetrahydrofuran, and 3-dioxolane; chain ethers such as diethoxyethane and dimethoxyethane; sulfone solvents such as sulfolane, ethyl isopropyl sulfone, dimethyl sulfone, and di-normal propyl sulfone; chain esters such as methyl formate, methyl acetate, and methyl propionate; cyclic esters such as γ-butyrolactone and γ-valerolactone; and acetonitrile.

[0108] These non-aqueous solvents may be used alone or in combination of two or more. When preparing a mixed solvent, a combination of a cyclic carbonate and a chain carbonate is preferred. The cyclic carbonate dissolves lithium salts at a high concentration, and the chain carbonate reduces the viscosity of the electrolyte without reducing the solubility of the lithium salt. This combination allows for the production of an electrolyte with high ionic conductivity. Furthermore, these mixed solvents are preferred because they have high oxidation-reduction resistance and are less susceptible to continuous electrolysis within the operating voltage range of lithium-ion batteries.

[0109] The non-aqueous solvent used in the non-aqueous electrolyte solution may be an ionic liquid. An ionic liquid is a molten salt formed by combining a cation and an anion, and refers to a salt that exists in a liquid state over a wide temperature range including room temperature. The ionic liquid can be formed by appropriately combining at least one of the following cations with at least one of the following anions.

[0110] The cation of this ionic liquid is not particularly limited as long as it allows the movement of lithium ions in the electrolyte solution and enables charging and discharging of the electricity storage device, and examples thereof include imidazolium, pyridinium, pyrrolidinium, piperidinium, tetraalkylammonium, pyrazolium, and tetraalkylphosphonium.

[0111] The imidazolium may, for example, be 1-ethyl-3-methylimidazolium [EMIm + ], 1-butyl-3-methylimidazolium, 1-ethyl-2,3-dimethylimidazolium, 1-allyl-3-methylimidazolium, 1-allyl-3-ethylimidazolium, 1-allyl-3-butylimidazolium, and 1,3-diallylimidazolium.

[0112] Examples of the pyridinium include 1-propylpyridinium, 1-butylpyridinium, 1-allylpyridinium, 1-ethyl-3-(hydroxymethyl)pyridinium, and 1-ethyl-3-methylpyridinium.

[0113] Examples of the pyrrolidinium include N-methyl-N-propylpyrrolidinium [MPPyr + ], N-methyl-N-butylpyrrolidinium, N-methyl-N-methoxymethylpyrrolidinium, N-allyl-N-methylpyrrolidinium, and N-allyl-N-propylpyrrolidinium.

[0114] Examples of the piperidinium include N-methyl-N-propylpiperidinium, N-methyl-N-butylpiperidinium, N-methyl-N-methoxymethylpiperidinium, and N-allyl-N-propylpiperidinium.

[0115] Examples of the tetraalkylammonium include N,N,N-trimethyl-N-propylammonium and methyltrioctylammonium.

[0116] Examples of the pyrazolium include 1-ethyl-2,3,5-trimethylpyrazolium, 1-propyl-2,3,5-trimethylpyrazolium, 1-butyl-2,3,5-trimethylpyrazolium, and 1-allyl-2,3,5-trimethylpyrazolium.

[0117] Examples of the tetraalkylphosphonium include P-butyl-P,P,P-triethylphosphonium and P,P,P-triethyl-P-(2-methoxyethyl)phosphonium.

[0118] The anions that are combined with these cations to form the ionic liquid may be any anions that allow the movement of lithium ions in the electrolyte and enable the charging and discharging of the power storage device. For example, BF4 - , PF6 - , SbF6 - , NO3 - , CF3SO3 - , (FSO2)2N - [Bis(fluorosulfonyl)imide anion; FSI - ], (CF3SO2)2N - [Bis(trifluoromethylsulfonyl)imide; TFSI - ], (C2F5SO2)2N - , (CF3SO2)3C - , CF3CO2 - , C3F7CO2 - , CH3CO2 - , (CN)2N - These anions may include two or more kinds.

[0119] The lithium salt used in the non-aqueous electrolyte is not particularly limited, and examples thereof include fluoride-based lithium salts such as LiPF6, LiBF4, and LiAsF6; halide-based lithium salts such as LiClO4, LiCl, LiBr, and LiI; and sulfonate-based lithium salts such as LiN(CF3SO2)2 (LiTFSI) and LiN(FSO2)2 (LiFSI). The lithium salt may be used alone or in combination of two or more. The concentration of the lithium salt in the non-aqueous electrolyte is 0.3 to 2.5 mol / dm 3 is.

[0120] When the nonaqueous electrolytic solution is mixed with an organic polymer compound and used as a gel-like, rubber-like, or solid sheet-like electrolyte, examples of the organic polymer compound that can be used include polyethylene oxide, polypropylene oxide, polyvinyl alcohol, polyvinyl butyral, polyvinyl pyrrolidone, polyvinylidene carbonate, polyacrylonitrile, and PVDF-HFP.

[0121] The nonaqueous electrolyte may contain an additive to suppress oxidative decomposition at the positive electrode or reductive decomposition at the negative electrode. Examples of additives include vinylene carbonate, fluoroethylene carbonate, ethylene sulfide, 1,3-propane sultone, 1,3-propene sultone, lithium bis(oxalato)borate, and lithium difluorooxalatoborate. The content of the additive is preferably in the range of 10 to 0.5 wt % of the nonaqueous electrolyte. An excessive content undesirably leads to an increase in the resistance of the electrochemical device. These additives form a strong coating on the electrode to protect the electrode surface, and this protective effect reduces damage to the electrode with each cycle, thereby effectively improving cycle characteristics.

[0122] The use of the neutralizing dispersant of the present invention can improve cycle characteristics even without the additive. The reasons for this are not definitive, but are thought to be, for example, as follows: Vinylene carbonate and the like form a strong coating on the electrode, protecting the electrode surface. This protective effect is thought to mitigate damage to the electrode with each cycle, leading to improved cycle characteristics. However, the additive itself decomposes during charging, forming a coating on the electrode. Since this consumes a small amount of lithium contained in the electrode, it is preferable to add a small amount within a range that does not impair cycle characteristics. The neutralizing dispersant of the present invention, for example, a combination of a boron compound and a natural polymer (water-soluble polymer), has the property of forming a coating that coats the electrode active material. This is thought to improve cycle characteristics by exhibiting a protective effect similar to that of vinylene carbonate and the like. According to the present invention, it is possible to improve cycle characteristics while suppressing lithium consumption.

[0123] <Separator> In the electrochemical device of the present invention, a separator is provided between the positive electrode and the negative electrode to prevent short-circuiting between them. Examples of separators include porous films containing polyethylene, polypropylene, cellulose, polyvinylidene fluoride (PVdF), polyimide, etc., cellulose nonwoven fabric, chitosan nonwoven fabric, and alginate nonwoven fabric. One or both sides of the separator may be provided with a coating layer. The coating layer may be a layer of inorganic fine particles with a particle size of several nanometers to several micrometers, such as alumina, zirconia, or silica, a layer of an organic material such as pulp, aramid, alginic acid, or chitosan, or a layer containing both of these, and is effective in improving heat resistance and preventing short-circuiting. [Example]

[0124] The present invention will be described in more detail based on examples and comparative examples, but the present invention is not limited thereto.

[0125] <Slurry Stability Evaluation (Production Examples A1 to A70, C1 to C70)> A slurry for obtaining an electrode for an electrochemical device according to the present invention was prepared by an aqueous process, and the stability of the obtained slurry was evaluated.

[0126] [Production of positive electrode mixture slurry using an aqueous production process (Production Examples A1 to A70)] 95 parts of the cathode material (composite oxide (A)), 2 parts of acetylene black as a conductive additive, 2 parts of a neutralizing dispersant, and 1 part of an acrylic emulsion as a binder were mixed, and 25 parts of water was added to this and kneaded using a planetary mixer (TK Hibismix, Primix Corporation) to prepare a cathode composite slurry. 0.6 CO 0.2 Mn 0.2 O2), NMC811(LiNi 0.8 Co 0.1 Mn 0.1 O2), NCA (nickel-cobalt-lithium aluminum oxide LiNi 0.8 Co 0.15 Al 0.05 Three types of neutralizing dispersants were used: 1.3 parts neutralizing agent and 0.7 parts dispersing agent. For Production Examples A1 to A30 and A32 to A34, 2 parts neutralizing dispersant was used, with 1.3 parts neutralizing agent and 0.7 parts dispersing agent. Regarding the neutralizing agent, for "boron oxide + sodium phosphate," the weight ratio of boric acid oxide to sodium phosphate was 7:3. For Production Examples A31 and A38, 1 part boric acid + Na2B4O7 (weight ratio 0.7:1) and 0.3 parts disodium phosphate were used. In Production Examples A32 to A34, multiple types of dispersants were used, with 0.5 parts (alkali metal salt, alkaline earth metal salt, or ammonium salt) and 0.2 parts (pullulan, guar gum, xanthan gum) being used, respectively. In Production Examples A35 to A38, 0.5 parts dispersing agent and 0.2 parts (auxiliary dispersing agent) were used. Here, the neutralizing agent is a water-soluble compound containing a Group 13 element (B) of the periodic table, and the dispersing agent is a water-soluble polymer (C).

[0127] [Production of negative electrode composite slurry using an aqueous production process (Production Examples C1 to C70)] Anode mix slurry was prepared in the same manner as in [Production of cathode mix slurry by aqueous production process], except that 95 parts of anode material, 2 parts of acetylene black as a conductive additive, 2 parts of a neutralizing dispersant, and 1 part of an acrylic emulsion as a binder were mixed and 25 parts of water was added. As shown in Tables 4 to 6, the anode material was a composite oxide (A) and a material selected from graphite, SiO, and SiOLi. The composite oxide (A) was Li4Ti5O 12 (LTO), LiNbO2 (LNO) were used. The materials shown in Tables 4 to 6 were used as neutralizing dispersants, and C1 to C70 correspond to the same numbers A1 to A70, respectively.

[0128] [Evaluation of long-term storage stability of slurry viscosity] The viscosity of the resulting slurry was measured using a Brookfield "Digital Viscometer HBDV-II+Pro" with a spindle CPE-41. 2.5 g of sample was placed in the attached cone and the mixture was stirred at 25°C and a shear rate of 40 s. -1 The viscosity of the slurry is defined as the viscosity measured when the spindle is rotated for 30 seconds. The rate of decrease in viscosity of the slurry after storage at 25°C for 5 days relative to the viscosity immediately after the slurry was prepared was calculated and evaluated according to the following criteria, with evaluations A and B being considered acceptable. The results are shown in Tables 1 to 6. Judgment A: Decrease rate is less than 10% Criterion B: Decrease rate is 10% or more but less than 15% Judgment C: Reduction rate is 15% or more

[0129] [Long-term storage stability evaluation of slurry pH] The obtained slurry was stored at 25°C for 3 days, and the pH was measured and evaluated according to the following criteria, with evaluations A and B being considered acceptable. The results are shown in Tables 1 to 6. Judgment A: pH less than 10.0 Classification B: pH 10.0 or higher but less than 10.5 Judgment C: pH10.5 or higher

[0130] [Table 1]

[0131] [Table 2]

[0132] [Table 3] [Table 4] [Table 5] [Table 6]

[0133] As shown in Tables 1 to 3, the positive electrode composite slurries of Production Examples A1 to A70 all met the acceptable levels for viscosity retention and pH retention, regardless of which positive electrode material was used. As shown in Tables 4 to 6, the negative electrode composite slurries of Production Examples C1 to C70 all met the acceptable levels for viscosity retention and pH retention, regardless of which negative electrode material was used.

[0134] <Output characteristics> 95 parts of NMC811 as the positive electrode material (composite oxide (A)), 2 parts of acetylene black as a conductive additive, 2 parts of a neutralizing dispersant shown in Table 7, and 1 part of an acrylic emulsion as a binder were mixed, and 25 parts of water was added to this mixture, followed by kneading using a planetary mixer (TK Hibismix, Primix Corporation) to prepare a positive electrode composite slurry.

[0135] The obtained positive electrode mixture slurry was applied to both sides of a 15 μm thick long aluminum foil (positive electrode current collector) in an amount of 12 mg / cm per side. 2 The coating weight was a value based on the positive electrode active material. That is, the coating weight was 12 mg / cm of the positive electrode active material per side. 2This means that the positive electrode composite slurry was applied so that the positive electrode composite layer was formed. The aluminum foil to which the positive electrode composite slurry was applied was then dried at 100°C for 120 seconds to form a positive electrode composite layer. This positive electrode composite layer was rolled using a roll press to adjust the positive electrode packing density to 3.0 g / cc, thereby obtaining positive electrodes for electrochemical devices of Examples 1 to 4 and Comparative Example 1.

[0136] Using the positive electrode for electrochemical devices obtained above, a lithium ion secondary battery for evaluating output characteristics was fabricated with the following configuration. The positive electrode was cut into a size of 12 mmφ, and the negative electrode was cut into a size of 13 mmφ. These were assembled in a glove box (dew point -60°C, argon atmosphere) using a CR2032-sized coin cell container. The materials used were as follows: Positive electrode: a positive electrode for the electrochemical device Negative electrode: metallic lithium Electrolyte: Ethylene carbonate (EC) and dimethyl carbonate (DM C) and a mixed solvent containing EC:DMC=1:1 (volume ratio), LiPF6 was dissolved as a supporting salt to a concentration of 1.0M. non-aqueous electrolyte (Hereafter referred to as "1.0MLiPF6+EC / DMC=1:1 (volume ratio)") Vinylene carbonate (VC) added at 2% Separator: Porous polyethylene film

[0137] [Measurement conditions] First, the lithium-ion secondary batteries for output characteristic evaluation were each charged using a constant current-constant voltage (CC-CV) charging method. In CV mode, charging was terminated when the current value reached one-tenth of the set current value in CC mode. Next, a charge-discharge test was performed on each battery at a voltage range of 3.0 to 4.3 V and 25°C at a 10-hour rate (0.1C rate) to measure the baseline capacity. Then, the discharge capacity was measured at a 1 / 3-hour rate (3C rate). The ratio of the 3C capacity to the 0.1C capacity was calculated and used as the capacity retention rate. The resulting capacity retention rate was evaluated according to the following criteria: A rating of "A" was considered a pass, and ratings B and C were considered "B" and "C" were considered "failures." The results are shown in Table 7. Judgment A: Capacity retention rate 80% or more Grade B: Capacity retention rate 70% or more but less than 80% Class C: Capacity retention rate less than 70%

[0138] [Table 7]

[0139] As shown in Table 7, Example 1, which used sodium carboxymethylcellulose (CMC-Na) as the dispersant, and Example 4, which used a mixture of CMC-Na and magnesium alginate (Alg-Mg), achieved favorable results with a capacity retention rate of over 80%. On the other hand, Comparative Example 1, which used only PVP, listed above as the auxiliary dispersant, achieved a capacity retention rate of less than 70%. When Alg-Na or Alg-Mg was used as the dispersant and PVP or PVA was used as the auxiliary dispersant (Examples 2 and 3), the capacity retention rate was improved compared to Comparative Example 1, which used only PVP. However, when the ratio of Alg-Mg to PVA was such that the PVA content exceeded the Alg-Mg content, as in Example 3, the capacity retention rate was improved compared to Comparative Example 1, but did not reach 70%. These results demonstrate that it is preferable to add the auxiliary dispersant in an amount that does not exceed the content of the dispersant.

[0140] In the present invention, when the dispersant is a water-soluble polymer (C) derived from a natural product, such as CMC-Na, Alg-Na, or Alg-Mg, it is found that the presence of a neutralizing agent contributes to improving battery characteristics. Synthetic materials such as PVA and PVP do not achieve this effect. While the reason for this is not definitive, it is possible that synthetic materials have a weaker affinity for metal oxides and substances that exhibit strong alkalinity in water than natural materials. Therefore, it is thought that some kind of decomposition reaction occurs during prolonged contact with the electrode active material. Furthermore, water-soluble polymers derived from natural products have properties such as a higher thermal decomposition temperature and less susceptibility to softening due to heat than synthetic materials, which is likely to result in better battery characteristics at high temperatures.

[0141] <Cycle characteristics at room temperature 1A> Comparison with solvent-based systems [Example 5 (water-based) positive electrode mixture slurry] 95 parts of the positive electrode material (composite oxide (A)), 2 parts of acetylene black as a conductive additive, 2 parts of a neutralizing dispersant (boric acid: carboxymethyl cellulose sodium (CMC-Na) = 1.3:0.7), and 1 part of an acrylic emulsion as a binder were mixed, and 25 parts of water was added to this and kneaded using a planetary mixer (TK Hibismix, Primix Corporation) to prepare a positive electrode composite slurry. The positive electrode material was NCA (nickel-cobalt-lithium aluminum oxide LiNi 0.8 Co 0.15 Al 0.05 O2), NMC622(LiNi 0.6 CO 0.2 Mn 0.2 O2), NMC811(LiNi 0.8 Co 0.1 Mn 0.1 O2) were used.

[0142] [Comparative Example 2 (Solvent-Based) Positive Electrode Composite Slurry] A positive electrode composite slurry was prepared by mixing 95 parts of the positive electrode material (composite oxide (A)), 2 parts of acetylene black as a conductive additive, and 3 parts of polyvinylidene fluoride (EQ-Lib-PVdF, MTI), adding 25 parts of N-methyl-2-pyrrolidone as a non-aqueous solvent, and kneading the mixture using a planetary mixer (TK Hibismix, Primix Corporation). The positive electrode material was NCA (nickel-cobalt-lithium aluminum oxide LiNi 0.8 Co 0.15 Al 0.05 O2), NMC622(LiNi 0.6 CO 0.2 Mn 0.2 O2), NMC811(LiNi 0.8 Co 0.1 Mn 0.1 O2) were used.

[0143] The obtained positive electrode mixture slurry was applied to both sides of a 15 μm thick long aluminum foil (positive electrode current collector) in an amount of 12 mg / cm per side. 2 The coating weight was a value based on the positive electrode active material. That is, the coating weight was 12 mg / cm of the positive electrode active material per side. 2 This means that the positive electrode composite slurry was applied so that the positive electrode composite layer was formed. The aluminum foil to which the positive electrode composite slurry was applied was then dried at 100°C for 120 seconds to form a positive electrode composite layer. This positive electrode composite layer was rolled using a roll press to adjust the positive electrode packing density to 3.0 g / cc, thereby obtaining a positive electrode for electrochemical devices.

[0144] Using the positive electrode for electrochemical devices obtained above, a lithium ion secondary battery (for positive electrode evaluation) for cycle characteristic evaluation was fabricated with the following configuration. The positive electrode was cut into a size of 12 mmφ, and the negative electrode was cut into a size of 13 mmφ. These were assembled in a glove box (dew point -60°C, argon atmosphere) using a CR2032-sized coin cell container. The materials used were as follows: Positive electrode: a positive electrode for the electrochemical device Negative electrode: metallic lithium Electrolyte: 1.0MLiPF6 + EC / DMC = 1:1 (volume ratio) 2% 1,3-propane sultone (PS) added Separator: Porous polyethylene film

[0145] [Measurement conditions] First, the lithium-ion secondary batteries for cycle performance evaluation were charged using a constant current-constant voltage (CC-CV) charging method. In CV mode, charging was terminated when the current value reached one-tenth of the set current value in CC mode. Next, the batteries were discharged at 25°C at a constant current of 200 mA for NCA, 190 mA for NMC622, and 200 mA for NMC811, at a 1.0 C rate. The voltage range was 3.0 to 4.3 V. This process constituted one cycle, and was repeated 1,000 times.

[0146] The discharge capacity value at the first cycle and the discharge capacity value measured after 1000 cycles were substituted into the following formula to calculate the capacity retention rate for each battery. The results are shown in Table 8. Capacity retention (%) = (discharge capacity value after 1000 cycles) / (discharge capacity value at the first cycle) × 100 ... (formula)

[0147] [Table 8]

[0148] As shown in Table 8, it can be seen that, irrespective of which positive electrode material was used, the cycle characteristics of Example 5 (water-based) were superior to those of Comparative Example 2 (solvent-based).

[0149] <1C cycle characteristics at room temperature>Comparison with solvent-based systems [Example 6 (water-based) negative electrode mixture slurry] Anode material (composite oxide (A)) was mixed with 95 parts of conductive additive (acetylene black) (2 parts), neutralizing dispersant (boric acid: carboxymethyl cellulose sodium (CMC-Na) = 1.3:0.7), and 1 part of acrylic emulsion as binder. 25 parts of water was added and kneaded using a planetary mixer (TK Hibismix, Primix Corporation) to prepare anode composite slurry. The anode materials used were SiO, SiOLi, and LTO (Li4Ti5O 12 ), and LNO (lithium niobate LiNbO2).

[0150] [Comparative Example 3 (Solvent-Based) Negative Electrode Composite Slurry] Anode material (composite oxide (A)) was mixed with 95 parts of conductive additive acetylene black (2 parts), polyvinylidene fluoride (EQ-Lib-PVdF, MTI) (3 parts), and 25 parts of N-methyl-2-pyrrolidone (non-aqueous solvent) was added to the mixture. The mixture was kneaded using a planetary mixer (TK Hibismix, Primix Corporation) to prepare anode composite slurry. Four types of anode materials were used: SiO, SiOLi, LTO, and LNO.

[0151] The obtained negative electrode mixture slurry was applied in strips to both sides of a long negative electrode current collector having a thickness of 15 μm by a doctor blade method. When SiO or SiOLi was used as the negative electrode material, a copper foil was used as the negative electrode current collector, and the coating weight per side was 3 mg / cm. 2 When LTO or LNO was used as the negative electrode material, aluminum foil was used as the negative electrode current collector, and the coating weight per side was 10 mg / cm. 2 The weight per unit area is a value based on the negative electrode active material. That is, the weight per unit area is 3 mg / cm of the negative electrode active material per one side. 2 or 10 mg / cm 2This means that the negative electrode composite slurry is applied so that the negative electrode composite layer is formed. The copper foil or aluminum foil to which the negative electrode composite slurry was applied was then dried at 100°C for 120 seconds to form a negative electrode composite layer. This negative electrode composite layer was rolled using a roll press to adjust the negative electrode packing density to 1.5 g / cc, thereby obtaining a negative electrode for electrochemical devices.

[0152] Using the negative electrode for electrochemical devices obtained above, a lithium ion secondary battery (for negative electrode evaluation) for cycle characteristic evaluation was fabricated with the following configuration. The negative electrode was cut into a size of 12 mmφ, and the counter electrode was cut into a size of 13 mmφ. These were assembled in a glove box (dew point -60°C, argon atmosphere) using a CR2032-sized coin cell container. The materials used were as follows: Working electrode: a negative electrode for the electrochemical device Counter electrode: metallic lithium Electrolyte: 1.0MLiPF6 + EC / DMC = 1:1 (volume ratio) Vinylene carbonate (VC) added at 2% Separator: Porous polyethylene film

[0153] [Measurement conditions] First, the lithium-ion secondary batteries for cycle performance evaluation were charged using a constant current-constant voltage (CC-CV) charging method. In CV mode, charging was terminated when the current value reached one-tenth of the set current value in CC mode. Next, the batteries were discharged at 25°C at a constant current of 450 mA for SiO, 400 mA for SiOLi, 170 mA for LTO, and 190 mA for LNO anode materials at a 1.0 C rate. The voltage range was 1.5 to 0.01 V for SiO and SiOLi, 2.5 to 1.0 V for LTO, and 2.5 to 1.3 V for LNO anode materials. This process constituted one cycle, and was repeated 100 times.

[0154] The discharge capacity value at the first cycle and the discharge capacity value measured after 100 cycles were substituted into the following formula to calculate the capacity retention rate for each battery. The results are shown in Table 9. Capacity retention (%) = (discharge capacity value after 100 cycles) / (discharge capacity value at the first cycle) × 100 ... (formula)

[0155] [Table 9]

[0156] As shown in Table 9, it can be seen that the cycle characteristics of Example 6 (water-based) are superior to those of Comparative Example 3 (solvent-based) regardless of which negative electrode material is used.

[0157] <High temperature cycle characteristics>Comparison with solvent-based systems A lithium-ion secondary battery for evaluating output characteristics, which used the same positive electrode for an electrochemical device as that used in the room-temperature cycle performance evaluation, was used to evaluate cycle performance at high temperatures. The measurement conditions were the same as those at room temperature, except that the temperature during measurement was 70°C. The results are shown in Table 10.

[0158] [Table 10]

[0159] As shown in Table 10, even in a high-temperature (70°C) environment, the cycle characteristics of Example 5 (aqueous system) are superior to those of Comparative Example 2 (solvent system) regardless of which positive electrode material is used.

[0160] <Room temperature / high temperature cycle characteristics full cell> Comparison with solvent system Using the positive electrode materials and neutralizing dispersants shown in Tables 11 to 19, aqueous positive electrode mixture slurries were prepared in the same manner as in Example 5, and positive electrodes for electrochemical devices were obtained. 0.33 CO 0.33 Mn 0.33 O2), NMC532(LiNi 0.5 Co 0.3 Mn 0.2 O2), NMC622(LiNi 0.6 CO 0.2 Mn0.2 O2), NMC811(LiNi 0.8 Co 0.1 Mn 0.1 O2), NCA (nickel-cobalt-lithium aluminum oxide LiNi 0.8 Co 0.15 Al 0.05 O2), LFP(LiFePO4), LCO(LiCoO2), LMO(LiMn2O4), LNMO(LiNi 0.5 Mn 1.5 O4). Furthermore, using the negative electrode materials shown in Tables 11 to 19, negative electrode composite slurries were prepared in the same manner as in Example 6 (water-based) and Comparative Example 3 (solvent-based), and negative electrodes for electrochemical devices were obtained. Using these positive and negative electrodes, lithium ion secondary batteries for cycle performance evaluation (for full-cell evaluation) having the following configuration were fabricated. Positive electrode: a positive electrode for the electrochemical device Negative electrode: the negative electrode for the electrochemical device Electrolyte: 1.0MLiPF6 + EC / DMC = 1:1 (volume ratio) 2% 1,3-propane sultone (PS) Vinylene carbonate (VC) added at 0.8% Separator: Porous polyethylene film, or cellulose nonwoven fabric

[0161] The separator used was a porous polyethylene film when the negative electrode material was graphite, graphite + various SiO, SiO, or SiOLi, and a cellulose nonwoven fabric when the negative electrode material was LTO, LNO, or various LTO + LNO.

[0162] [Measurement conditions] First, the lithium-ion secondary batteries for cycle performance evaluation were charged using a constant current-constant voltage (CC-CV) charging method. In CV mode, charging was terminated when the current reached one-tenth of the set current in CC mode. Next, the batteries were discharged at a constant current of 200 mA for NCA, 150 mA for NMC111, 160 mA for NMC532, 190 mA for NMC622, 200 mA for NMC811, 170 mA for LFP, 130 mA for LCO, 120 mA for LMO, and 130 mA for LNMO at 25°C. The voltage ranges for the combinations of cathode and anode materials were as shown in Table 11. This process constituted one cycle, and was repeated 1,000 times.

[0163] [Table 11]

[0164] The discharge capacity value in the first cycle and the discharge capacity value measured after 1000 cycles were substituted into the following formula to calculate the capacity retention rate for each battery. The results are shown in Tables 12 to 20. Capacity retention (%) = (discharge capacity value after 1000 cycles) / (discharge capacity value at the first cycle) × 100 ... (formula)

[0165] [Table 12]

[0166] [Table 13]

[0167] [Table 14]

[0168] [Table 15]

[0169] [Table 16]

[0170] [Table 17]

[0171] [Table 18]

[0172] [Table 19]

[0173] [Table 20]

[0174] It can be seen that, for the combinations of positive and negative electrode materials shown in Tables 12 to 20, the negative electrode composite slurries prepared using a water-based system have better cycle characteristics than the negative electrode composite slurries prepared using a solvent-based system, both at room temperature and at high temperatures (70°C).

[0175] <Discharge capacity> [Positive electrode mixture slurry using other neutralizing agents (comparative examples)] A mixture of 95 parts of the positive electrode material (composite oxide (A)), 2 parts of acetylene black as a conductive additive, 0.7 parts of sodium carboxymethyl cellulose (CMC-Na) "CMC Daicel 2200" (manufactured by Daicel Miraize Co., Ltd.) as a dispersant, 1.3 parts of a neutralizer, and 1 part of an acrylic emulsion as a binder was used. 25 parts of water was added to this mixture, and the mixture was kneaded using a planetary mixer (TK Hibismix, Primix Corporation) to prepare a positive electrode composite slurry. The positive electrode material was NCA (nickel-cobalt-lithium aluminum oxide LiNi 0.8 Co0.15 Al 0.05 O2), NMC622(LiNi 0.6 CO 0.2 Mn 0.2 O2), NMC811(LiNi 0.8 Co 0.1 Mn 0.1 Three types of neutralizing agents were used: boric acid (comparative example 4) and oxalic acid (comparative example 5). Except for changing the neutralizing agent from boric acid to sulfuric acid (comparative example 4) and oxalic acid (comparative example 5), positive electrodes for electrochemical devices and lithium ion secondary batteries for evaluating output characteristics were fabricated in the same manner as above.

[0176] The discharge capacity was evaluated using a lithium ion secondary battery for evaluating output characteristics, which includes the same positive electrode for electrochemical devices as that used in the evaluation of cycle characteristics at room temperature and a positive electrode for electrochemical devices prepared by changing the neutralizing agent from boric acid to sulfuric acid and oxalic acid.

[0177] [Measurement conditions] First, the lithium-ion secondary batteries for output characteristic evaluation were charged using a constant current-constant voltage (CC-CV) charging method. In CV mode, charging was terminated when the current value reached one-tenth of the set current value in CC mode. Next, the batteries were discharged at 25°C at a constant current of 200 mA for NCA, 190 mA for NMC622, and 200 mA for NMC811 cathode materials at a 1.0 C rate. The voltage range was 3.0 to 4.3 V. After discharge, the discharge capacity was measured by integrating the time required for discharge and the current value at that time to calculate the amount of electricity. The results are shown in Table 21.

[0178] [Table 21]

[0179] As shown in Table 21, regardless of the cathode material used, the lithium-ion secondary batteries for evaluating output characteristics using the electrochemical device cathode manufactured by the process of Example 5 (aqueous system) exhibited almost the same discharge capacity as those using the electrochemical device cathode manufactured by the conventional solvent-based process (Comparative Example 2), indicating that no capacity reduction due to hydrolysis of the positive electrode active material occurred. However, when other neutralizing agents not containing a Group 13 element (B) of the Periodic Table were used as the neutralizing agent (Comparative Examples 4 and 5), the discharge capacity was significantly lower than that when the electrochemical device cathode manufactured by the conventional solvent-based process (Comparative Example 2) was used.

[0180] <Cycle characteristics at room temperature 2> Capacity retention rate of electrolyte without additives, compared with solvent-based electrolyte The lithium ion secondary battery for evaluating output characteristics used in the evaluation of "Cycle characteristics 1 at room temperature" was subjected to the same evaluation for 1200 cycles, except that the electrolyte was changed to the following: The results are shown in Table 22. Electrolyte: 1.0MLiPF6 + EC / DMC = 1:1 (volume ratio) No addition of 1,3-propane sultone (PS)

[0181] [Table 22]

[0182] Table 22 shows that the electrode (Comparative Example 2) using a conventional solvent-based binder (PVdF) exhibits poor cycle characteristics when the electrolyte does not contain 1,3-propane sultone (PS), whereas the electrode (Example 5) manufactured by an aqueous process using the neutralizing dispersant of the present invention exhibits good cycle characteristics even without an additive added to the electrolyte to suppress oxidative decomposition at the positive electrode. To suppress oxidative decomposition of the electrolyte at the positive electrode, a common technique is to add additives such as VC (vinylene carbonate) or 1,3-propane sultone (PS) to suppress capacity loss with each cycle. However, the present invention makes it possible to eliminate or reduce the addition of such additives, thereby reducing costs and simplifying the manufacturing process.

[0183] In the present invention, for example, the neutralizing dispersant, which is a combination of a boron compound and a natural polymer or the like (water-soluble polymer (C)), has the property of forming a film that coats the electrode active material (composite oxide (A)). A film of the water-soluble polymer (C) is formed on the surface of the electrode active material, and the presence of boron in this film is thought to exhibit a protective effect similar to that of additives such as vinylene carbonate, leading to improved cycle characteristics. According to the present invention, it is possible to improve cycle characteristics while suppressing lithium consumption.

[0184] From the above examples and the like, it is understood that even a slurry produced from a lithium-containing metal oxide by an aqueous process can suppress an increase in pH and a decrease in viscosity over the long term, and that by incorporating an electrode made from such a slurry, it is expected to provide a nonaqueous electrolyte secondary battery having excellent high-temperature durability.

[0185] The embodiments disclosed herein should be considered to be illustrative in all respects and not restrictive. The scope of the present invention is defined by the claims, not by the above description, and is intended to include all modifications within the meaning and scope of the claims.

Claims

1. An aqueous slurry for an electrode for an electrochemical device, comprising a neutralizing dispersant and a composite oxide (A) capable of absorbing and desorbing lithium ions, The pH value measured after storing the slurry at 25°C for 3 days from the preparation thereof is less than 10.5, The neutralizing dispersant is at least one water-soluble compound (B') selected from oxides, sulfides, inorganic acids, and inorganic acid salts containing a Group 13 element (B) of the periodic table; and at least one water-soluble polymer (C) selected from the group consisting of an alkali metal salt, alkaline earth metal salt, or ammonium salt of alginic acid, methyl cellulose, carboxymethyl cellulose, carboxymethyl starch, or carrageenan, pullulan, guar gum, and xanthan gum.

2. 2. The aqueous slurry for an electrode for an electrochemical device according to claim 1, wherein the Group 13 element (B) of the periodic table includes boron.

3. the aqueous slurry for an electrochemical device electrode further comprises a conductive aid and a binder; an electrode mixture is composed of the neutralizing dispersant, the composite oxide (A), the conductive additive, and the binder; 3. The aqueous slurry for an electrode for an electrochemical device according to claim 2, wherein the boron content in the electrode mixture is in the range of 0.001% by weight to 5% by weight.

4. 4. The aqueous slurry for an electrochemical device electrode according to claim 2 or 3, wherein the water-soluble compound containing boron is contained in an amount of 51 parts by weight to 100 parts by weight, based on 100 parts by weight of the at least one water-soluble compound (B′) selected from an oxide, a sulfide, an inorganic acid, and an inorganic acid salt containing a Group 13 element (B) of the periodic table.

5. The composite oxide (A) has a composition of Li ａ Ni ｂ Co ｃ Mn ｄ M １－ｂ－ｃ－ｄ O ２ or a composite oxide represented by Li ４＋ｘ Ti ５ O １２ and Li ２＋ｘ Ti ３ O ７ The aqueous slurry for an electrode for an electrochemical device according to any one of claims 1 to 4, wherein the composite oxide is represented by any one of where M is one or more elements selected from the group consisting of Al, Mg, Ti, Fe, V, Cr, Nb, Mo, W, Cu, Zn, Ga, In, Sn, Zr, Ru, and La; 0.8≦a≦1.0 0<b≦1.0 0≦c≦0.4 0≦d≦0.35 0<b+c+d≦1.0 0≦x≦3.

6. An electrode for an electrochemical device produced using the aqueous slurry for an electrode for an electrochemical device described in any one of claims 1 to 5.

7. A film of the water-soluble polymer (C) is formed on the surface of the complex oxide (A), 7. The electrode for electrochemical devices according to claim 6, wherein the element (B) of Group 13 of the periodic table is present in the water-soluble polymer (C) film.

8. a positive electrode and a negative electrode, and an electrolyte is contained between the positive electrode and the negative electrode; A non-aqueous electrolyte secondary battery, wherein at least one of the positive electrode and the negative electrode is the electrode for electrochemical devices according to claim 6 or 7.

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