Cathode composite composition, cathode, lithium-ion secondary battery, and mobility

Abstract

To provide a secondary battery with good initial capacity and cycle characteristics of a lithium-ion secondary battery, further suppressing outgas generation and having high safety. 【Solution means】It contains a positive electrode active material (A), a conductive material (B), and a resin (C). The positive electrode active material (A) is a compound represented by the following general formula (1), and it is solved by the positive electrode composite material composition. Li w Fe x M y O z General formula (1) (In general formula (1), w, x, y, and z are respectively 3 ≤ w ≤ 5, 0.5 ≤ x < 1, 0

Description

[Technical Field]

[0001] The present invention relates to a positive electrode composite composition containing a positive electrode active material made of lithium iron oxide containing group 13 to 16 elements, a conductive material, and a resin. More specifically, the present invention relates to a positive electrode suitably used in lithium-ion secondary batteries installed in mobility devices such as automobiles and aircraft. [Background technology]

[0002] This invention relates to the development and improvement of lithium-ion secondary batteries used in mobility devices such as electric vehicles. A lithium-ion secondary battery is a type of rechargeable battery in which lithium ions move from the negative electrode to the positive electrode during discharge and return from the positive electrode to the negative electrode during charging. Lithium-ion batteries are widely used in portable electronic devices, automobiles, aircraft, and the like because they have a high energy density, a low memory effect, and the stored electricity is lost very slowly when not in use.

[0003] However, the major challenges facing the use of lithium-ion batteries in electric vehicles are the limitations of driving range and battery life (cycle characteristics). The driving range of an electric vehicle refers to the distance the vehicle can travel on a single battery charge. This directly impacts the practicality and convenience of electric vehicles in everyday use, and is therefore a crucial factor in the widespread adoption of electric vehicles. Battery life is the ratio of the capacity that can be charged on the first charge to the capacity that can be charged after a certain number of charge-discharge cycles.

[0004] Several methods have been proposed to extend the range of electric vehicles. One method is to increase the amount of energy that can be stored in a given space, i.e., the initial capacity. This can be achieved by changing the materials used in the battery, such as the cathode active material. Lithium metal oxide has been proposed as a promising material due to its high capacity.

[0005] Furthermore, various metal-containing positive electrode active materials have been proposed as a way to extend battery life. For example, lithium iron phosphate, nickel-manganese-cobalt, and positive electrode active materials with small amounts of other elements added to these have been proposed.

[0006] As examples of these, Patent Document 1 relates to a lithium-ion battery equipped with a positive electrode active material containing a lithium transition metal composite oxide. Patent Document 2 introduces a lithium-ion secondary battery equipped with a positive electrode active material containing a lithium transition metal oxide. Patent Document 3 discloses a lithium-ion battery equipped with a positive electrode active material containing a lithium composite oxide. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] European Patent No. 4283712 Brochure [Patent Document 2] Japanese Patent Publication No. 2023-083719 [Patent Document 3] European Patent No. 4167314 Brochure [Overview of the project] [Problems that the invention aims to solve]

[0008] While these prior technologies have contributed to advancements in the field of lithium-ion batteries for electric vehicles, they have not adequately addressed the issues of initial capacity and battery life (cycle characteristics). Furthermore, cathode active materials capable of storing many lithium ions in a single molecule, such as lithium iron oxide, have safety concerns, as repeated charging and discharging cycles lead to oxygen desorption, reducing capacity and generating outgassing.

[0009] Therefore, the present invention aims to provide a lithium-ion secondary battery that has good initial capacity and cycle characteristics, and further suppresses outgassing, resulting in high safety. [Means for solving the problem]

[0010] As a result of intensive studies in view of the above problems, the inventors have found that the above problems can be solved by combining a cathode active material having a specific composition with a conductive material, and have thus arrived at the present invention.

[0011] That is, the present invention includes the following embodiments. The embodiments of the present invention are not limited to the following. [1] A composite material composition for a positive electrode, comprising a cathode active material (A), a conductive material (B), and a resin (C). The cathode active material (A) is a compound represented by the following general formula (1), and is a composite material composition for a positive electrode. Li w Fe x M y O z General formula (1) (In the general formula (1), w, x, y, and z are each in the range of 3 ≤ w ≤ 5, 0.5 ≤ x < 1, 0 < y ≤ 0.5, and 3 ≤ z ≤ 5. Also, 0.9 ≤ x + y ≤ 1.1. M is any one of Group 13 to Group 16 elements other than oxygen.) [2] The composite material composition for a positive electrode according to [1], wherein in the general formula (1), M is any one of elements in the 3rd to 6th periods. [3] The composite material composition for a positive electrode according to [1] or [2], wherein in the general formula (1), M is at least one selected from the group consisting of aluminum, silicon, phosphorus, sulfur, gallium, and germanium. [4] The composite material composition for a positive electrode according to any one of [1] to [3], wherein the conductive material (B) is a carbon nanotube. [5] The composite material composition for a positive electrode according to any one of [1] to [4], wherein the carbon nanotube has an outer diameter of 1 to 20 nm and a length of 0.1 to 100 μm. [6] The positive electrode composite material composition according to any one of [1] to [5], wherein the resin (C) is at least one selected from nitrile butadiene rubber, hydrogenated nitrile butadiene rubber, polyvinyl alcohol, polyvinyl butyral, polyvinyl pyrrolidone, and polyvinylidene fluoride. [7] A positive electrode formed from the positive electrode composite material composition according to any one of [1] to [6]. A lithium-ion secondary battery comprising the positive electrode described in [8] [7]. A mobility comprising the lithium-ion secondary battery described in [9] [8].

Advantages of the Invention

[0012] According to the present invention, it is possible to provide a secondary battery having an increased initial capacity, good cycle characteristics, further suppressed outgas generation, and high safety.

Modes for Carrying Out the Invention

[0013] The present invention will be described below. Note that the present invention is not limited to the following embodiments, and embodiments implemented within the scope of not changing the gist of the present invention are also included.

[0014] Aspects of the present invention are best understood by referring to the descriptions set forth herein. All aspects described herein will be better recognized and understood when considered in conjunction with the following description. However, it should be understood that the following description shows preferred aspects and many specific details thereof for illustrative purposes only and should not be treated as limiting. Within the scope of this specification, changes and modifications can be made without departing from the spirit and scope of the present invention, and the present invention herein includes all such modifications.

[0015] In addition, the numerical range specified using "~" in this specification is assumed to include the numerical values described before and after "~" as the range of the lower limit value and the upper limit value. In this specification, carbon nanotubes may be denoted as "CNT" and N-methyl-2-pyrrolidone may be denoted as "NMP". In this specification, the carbon nanotube dispersion may be referred to as "CNT dispersion" or "conductive material dispersion", and the lithium-ion secondary battery may be referred to as "secondary battery" in some cases. Unless otherwise noted, the various components appearing in this specification may each be used alone or in combination of two or more. In addition, the numerical values specified in this specification are values obtained by the methods disclosed in the embodiments or examples.

[0016] ≪Composite Composition for Positive Electrode≫ The present invention relates to a composite composition for a positive electrode, and includes a positive electrode active material (A) which is a compound represented by the general formula (1), a conductive material (B), and a resin (C).

[0017] <Positive Electrode Active Material (A)> The positive electrode active material is a compound represented by the following general formula (1). Li w Fe x M y O z General Formula (1) (In the general formula (1), w, x, y, and z are each in the ranges of 3 ≤ w ≤ 5, 0.5 ≤ x < 1, 0 < y ≤ 0.5, and 2 ≤ z ≤ 5. Also, 0.9 ≤ x + y ≤ 1.1. M is any one of Group 13 to Group 16 elements other than oxygen.)

[0018] The compound represented by the general formula (1) is preferably obtained by a method of manufacturing the positive electrode active material (A) by mixing a lithium iron oxide, which will be described later, and a compound containing a Group 13 to Group 16 element other than oxygen.

[0019] Since the lithium iron oxide can hold 3 to 5 lithium ions in one molecule, the capacity becomes large when used as a lithium ion secondary battery. On the other hand, since oxygen is easily desorbed during charge and discharge, the cycle characteristics are extremely poor and the safety due to outgas generation is low. Here, by adding a Group 13 to Group 16 element other than oxygen to the lithium iron oxide, the oxygen desorption from the lithium iron oxide is suppressed, the cycle characteristics are improved, and the safety is improved.

[0020] In general formula (1), M is preferably an element of the 3rd to 6th periods. Preferably, it can be selected from the 3rd period or the 4th period. More preferably, it can be selected from aluminum, silicon, phosphorus, sulfur, gallium, and germanium. These elements can form strong bonds with oxygen contained in lithium iron oxide, suppress the oxygen desorption reaction during charging, and improve the cycle characteristics of the battery. From the perspective of cost, aluminum, silicon, phosphorus, and sulfur are more preferable. M can be used alone or in combination of two or more.

[0021] In general formula (1), w is preferably 4 ≤ w ≤ 5. x is preferably 0.7 ≤ x < 1. y is preferably 0 < y ≤ 0.3. z is preferably 3 ≤ z ≤ 5. x + y is preferably 0.95 ≤ x + y ≤ 1.05. By setting the above ranges, the number of lithium ions in one molecule increases, the initial capacity increases, the oxygen desorption reaction is suppressed, and the cycle characteristics become good, so it is preferable. When M is two or more kinds, y for M1, M2, M3,..., Mk is y1, y2, y3,..., yk, and y = y1 + y2 + y3 +... + yk. The positive electrode active material (A) is preferably contained in an amount of 80 to 99.8% by mass, more preferably 90 to 99.5% by mass, based on the total mass of the positive electrode composite material composition (100% by mass). Increasing the content of the positive electrode active material (A) is preferable because the initial capacity increases.

[0022] The median diameter of the positive electrode active material (A) is preferably 0.1 to 100 μm, more preferably 0.1 to 20 μm. Appropriately reducing the median diameter is preferable because the packing ratio increases and the initial capacity increases. The median diameter (D 50 ) is the particle diameter corresponding to a cumulative frequency of 50% on a volume basis in the particle diameter distribution, and can be measured, for example, using the laser diffraction method.

[0023] Also, the positive electrode active material (A) has a median diameter (D 50It is also preferable to use a combination of a positive electrode active material with a large particle size and a positive electrode active material with a small particle size, where the particle size difference is more than twice. This is preferable because the small particle size positive electrode active material fills the gaps in the larger particle size positive electrode active material, resulting in a full-fill positive electrode active material and thus a larger initial volume.

[0024] Median diameter (D) of positive electrode active material with large particle size 50 The diameter is preferably 2 to 20 μm. Median diameter (D) of positive electrode active material with small particle size 50 The particle size is preferably 0.1 μm to 1 μm. The ratio of positive electrode active material with large particle size to positive electrode active material with small particle size is preferably 100:1 to 2:1 by weight.

[0025] <Conductive material (B)> As the conductive material (B), carbon materials such as carbon black, graphene, and carbon nanotubes can be used. The role of the conductive material is to promote the flow of electrons during the charging and discharging process of the battery. Using carbon nanotubes as the conductive material is particularly preferable due to their excellent electrical conductivity and mechanical strength. Furthermore, it is preferable because carbon nanotubes form conductive paths by connecting positive electrode active materials to each other or to the positive electrode active materials and the substrate, thereby improving conductivity. The carbon material may be used by coating the surface of the positive electrode active material with a carbon film.

[0026] The carbon nanotubes used in this invention preferably have an outer diameter of 1 to 20 nm. The fiber length is preferably 0.1 to 100 μm. In particular, when the outer diameter is 1 to 20 nm and the length is 0.1 to 100 μm, the carbon nanotube is thin and long. Therefore, it is preferable because it can efficiently connect positive electrode active materials to each other, or positive electrode active materials to the substrate. The outer diameter is preferably 1 to 10 nm. The length is preferably 0.1 to 10 μm. The outer diameter and length can be calculated by observing 100 carbon nanotubes with a scanning electron microscope and taking the arithmetic mean.

[0027] The conductive material (B) is preferably present in an amount of 0.1 to 5% by mass, and more preferably 0.3 to 3% by mass, based on the total mass of the positive electrode composite composition (100% by mass). Including the conductive material (B) within the above range is preferable because it connects the positive electrode active materials (A) to each other and to the substrate, thereby forming conductive paths.

[0028] <Resin (C)> The positive electrode composite composition contains resin (C). Resin (C) can be any of the conventionally known resins. Specifically, examples include nitrile butadiene rubber, hydrogenated nitrile butadiene rubber, polyvinyl alcohol, polyvinyl butyral, polyvinylpyrrolidone, or polyvinylidene fluoride. Among these, hydrogenated nitrile butadiene rubber is particularly preferred. Hydrogenated nitrile butadiene rubber can uniformly disperse carbon nanotubes and, when mixed with the positive electrode active material, easily provides a uniform coating to its surface, thereby improving the cycle characteristics. The residual double bond ratio (RDB) in hydrogenated nitrile butadiene rubber is preferably low, and more preferably 1% or less. The residual double bond ratio is calculated using the following formula (2). RDB(mass%)=(BD / (BD+HBD))×100 (In equation (2), BD is the mass ratio of structural units derived from conjugated dienes having unsaturated bonds to the total mass of structural units derived from conjugated dienes, and HBD is the mass ratio of structural units derived from conjugated dienes with hydrogenated unsaturated bonds to the total mass of structural units derived from conjugated dienes.) Resin (C) can be used alone or in combination of two or more types.

[0029] The resin (C) is preferably present in an amount of 0.1 to 19.9% ​​by mass, and more preferably 0.2 to 10% by mass, based on the total mass of the positive electrode composite composition (100% by mass). Including resin (C) within the above range is preferable because it allows the positive electrode active material (A), conductive material (B), and substrate to adhere closely together, making it usable as a positive electrode.

[0030] <Solvent> The cathode composite composition preferably further contains a solvent. The solvent may be water or an organic solvent. The solvent helps dissolve, disperse, and mix the components in the cathode composite, thereby enabling uniform coating when the cathode composite composition is applied to a substrate. Various conventionally known organic solvents can be used. Specifically, N-methyl-2-pyrrolidone is one example. N-methyl-2-pyrrolidone is preferred because it can dissolve and disperse electrochemically stable resins such as nitrile butadiene rubber.

[0031] The solvent content is preferably 10 to 1,000 parts by mass, and more preferably 20 to 200 parts by mass, per 100 parts by mass of the total solid content of the positive electrode composite composition. This solvent content range is preferable because it imparts appropriate fluidity to the positive electrode composite composition, allowing for uniform coating onto the substrate.

[0032] <Other ingredients> The cathode composite composition of the present invention may optionally contain other components. Specifically, these include basic compounds, acidic compounds, surfactants, and dye derivatives.

[0033] Other components can be added to improve the initial viscosity and viscosity over time of the positive electrode composite composition, and within a range that does not drastically reduce the characteristics when used as a secondary battery. For example, they can be contained in an amount of 0.01 to 10% by mass, based on the total mass of the positive electrode composite composition (100% by mass).

[0034] (Basic compounds) Examples of basic compounds include inorganic bases such as sodium hydroxide, potassium hydroxide, and ammonia; organic bases such as alkylamines and alkanolamines; and basic dye derivatives, which will be discussed later.

[0035] (acidic compound) Examples of acidic compounds include inorganic acids such as hydrochloric acid, nitric acid, sulfuric acid, and phosphoric acid, organic acids such as formic acid and acetic acid, and acidic dye derivatives, which will be discussed later.

[0036] (Surfactants) Various conventionally known surfactants can be added as surfactants. For example, sodium alkyl sulfates can be used.

[0037] (Dye derivatives) Various conventionally known dye derivatives can be added as dye derivatives. Examples of dye derivatives include acidic dye derivatives having acidic functional groups, basic dye derivatives having basic functional groups, amphoteric dye derivatives having both acidic and basic functional groups, and neutral dye derivatives having neither acidic nor basic functional groups.

[0038] As a dye derivative, for example, a dye derivative represented by the following formula can be used.

[0039] [ka] [In general formula (1), X1, X2, and X3 each independently represent -NH- or -O-, provided that at least one of X1, X2, and X3 is -NH-. Y1, Y2, and Y3 each independently represent a hydrogen atom, an optionally substituted phenyl group, an optionally substituted alkylene group, an optionally substituted arylene group, an optionally substituted cycloalkylene group, a phenyl group having a substituent containing at least -NHC(=O)-, a benzimidazole group, a benzimidazolinone group, an optionally substituted indole group or an optionally substituted pyrazole group, a benzimidazolinone group, or (CH2)mN((CH2)n)2. However, at least one of Y1, Y2, and Y3 is an optionally substituted phenyl group, and the substituent is selected from at least one of the following: a carboxyl group, a sulfo group, a phosphate group, or an amino group.

[0040] <Method for manufacturing a composite material composition for positive electrodes> The method for producing the cathode composite composition is not particularly limited, but it can be obtained, for example, by the following steps. First step: A lithium iron oxide is mixed with a compound containing group 13-16 elements other than oxygen to obtain the positive electrode active material (A). Second step: Mix the positive electrode active material (A), conductive material (B), and resin (C).

[0041] [First step] The first step involves mixing lithium iron oxide with a compound containing group 13-16 elements other than oxygen to obtain the positive electrode active material (A). One example is a method in which lithium iron oxide, Li5FeO4, is mixed with a compound containing group 13-16 elements other than oxygen, such as Al(OH)3, Li2SiO3, GeO2, Li3PO4, or Li2SO4, and then calcined at 500-1,500°C for 1-48 hours under an inert gas stream. Another example is a method of mixing lithium oxide as a lithium compound, iron oxide as an iron compound, and Al(OH)3, Li2SiO3, GeO2, Li3PO4, or Li2SO4 as a compound containing group 13-16 elements other than oxygen. The obtained positive electrode active material (A) can be ground to any desired particle size using yttria-stabilized zirconia beads with an outer diameter of 0.1 to 10 mm under an inert gas atmosphere.

[0042] [Second process] The second step involves mixing the positive electrode active material (A), the conductive material (B), and the resin (C). Mixing equipment can include planetary mixers, homogenizers, high-pressure homogenizers, and bead mills. One example is a method of mixing a positive electrode active material (A), a conductive material (B), a resin (C), and a solvent. Another example is a method in which a conductive material dispersion is prepared by first mixing and dispersing a conductive material (B), a resin (C), and a solvent, and then mixing it with a positive electrode active material (A).

[0043] ≪Positive electrode≫ The positive electrode composite composition of the present invention can be used as a positive electrode having an electrode film and a substrate by coating it onto a substrate.

[0044] There are no particular limitations on the method for coating the cathode composite composition onto the substrate, and known methods can be used. Specifically, examples include die coating, dip coating, roll coating, doctor coating, knife coating, spray coating, gravure coating, screen printing, or electrostatic coating. For drying after coating, methods such as standing drying, forced-air drying, hot-air drying, infrared heating, and far-infrared heating can be used, but are not limited to these. Furthermore, after coating the cathode composite composition, rolling treatment may be performed using a flatbed press, calender roll, etc. The thickness of the electrode film is, for example, 1 μm or more and 500 μm or less, preferably 10 μm or more and 300 μm or less.

[0045] <Base material> Various conventionally known substrates can be used. Examples of substrates include paper, wood, stone, film, and metal. When used as an electrode for a secondary battery, it is preferable that the substrate is conductive. Examples of such substrates include metals such as iron, aluminum, and copper, and conductive films.

[0046] ≪Secondary battery≫ The positive electrode of the present invention can be used as a component of a secondary battery. The secondary battery can be any of the various types of secondary batteries that are conventionally known, and is preferably a liquid electrolyte secondary battery, a semi-solid electrolyte secondary battery, or an all-solid electrolyte secondary battery, with a liquid electrolyte secondary battery being more preferred. Among these, a lithium-ion secondary battery is preferred.

[0047] [Lithium-ion rechargeable battery] A lithium-ion secondary battery consists of a positive electrode and a negative electrode capable of absorbing lithium ions, an electrolyte through which lithium ions can move, and a separator to prevent short circuits. The positive electrode and negative electrode contain an active material capable of absorbing lithium ions. The positive electrode can be the positive electrode described above.

[0048] Secondary batteries using the cathode composite material composition of the present invention can be installed and used in electronic devices such as smartphones and personal computers, as well as in mobility devices such as automobiles and aircraft. In particular, lithium-ion secondary batteries can be made to have a higher capacity than conventional batteries while also having good cycle characteristics, resulting in a longer driving range and longer lifespan. [Examples]

[0049] The present invention will be described in more detail below with reference to examples. The present invention is not limited to the following examples unless it exceeds the gist of the invention. Unless otherwise specified, "parts" refers to "parts by mass" and "%" refers to "percentage by mass".

[0050] Note that the weight-average molecular weight (Mw) of the fluororesin and the median diameter (D) of the positive electrode active material are also specified. 50 The outer diameter and length of the carbon nanotubes were measured by the following method. <Measurement of weight-average molecular weight (Mw) of fluororesins> The weight-average molecular weight (Mw) of the fluororesin was measured using gel permeation chromatography (GPC-900, JASCO Corporation; Shodex KD-806M column; temperature 40°C) on an NMP solution prepared by dissolving fluororesin powder at 0.1% by mass. The weight-average molecular weight was calculated based on the polystyrene equivalent.

[0051] <Median diameter of positive electrode active material (D) 50 ) Measurement > The positive electrode active material is dispersed in the dispersion medium to a concentration of 0.05% by mass, and the median diameter (D) is measured using a laser diffraction particle size distribution device (MALVERN Inst. MASTERSIZER 2000). 50 ) was measured.

[0052] <Method for measuring the outer diameter and length of carbon nanotubes> A conductive material dispersion was diluted 1,000 times with the solvent used for dispersion, coated onto a mica substrate, and after drying the solvent in an oven, the substrate surface on the coated side was platinum sputtered. This substrate was observed at 10,000x or 20,000x magnification using a scanning electron microscope (JEOL JEM-120i), and the outer diameter and length of 100 carbon nanotubes were calculated by arithmetic mean.

[0053] The materials used in the examples and comparative examples are listed below. <Conductive material (B)> Conductive material (B-1): TUBALL (single-walled carbon nanotube) manufactured by OcSiAl. Conductive material (B-2): JENOTUBE6A (thin-layer carbon nanotube) manufactured by JEIO Corporation Conductive material (B-3): Nanocyl NC7000 (multilayer carbon nanotube) Conductive material (B-4): Denka Black Li-435 (acetylene black) manufactured by Denka Co., Ltd.

[0054] [Manufacturing of conductive material (B-5)] Sixty parts of conductive material (B-2) were placed in a graphite crucible with an outer diameter of 10 cm and a height of 10 cm. The crucible containing the above CNTs was placed in a multi-purpose high-temperature furnace (High Multi 5000, manufactured by Fuji Denpa Kogyo Co., Ltd.) and subjected to heat treatment under reduced pressure and vacuum as follows. First, nitrogen gas was introduced into the multi-purpose high-temperature furnace, and the nitrogen gas substitution operation was performed twice. Next, the pressure was reduced using an oil rotary pump to adjust the furnace pressure to 9.8-9.5 Pa. Subsequently, the pressure was further reduced using an oil diffusion pump to adjust the furnace pressure to 0.03 Pa or less. Next, while maintaining reduced pressure using an oil diffusion pump, the temperature was raised to 1200°C at a heating rate of 20°C / min and held at 1200°C for 10 hours. After that, the furnace was allowed to cool naturally until the internal temperature dropped below 50°C to obtain conductive material (B-5).

[0055] <Resin (C)> Resin (C-1): Zetpol 2010L manufactured by Nippon Zeon Co., Ltd. (Hydrogenated nitrile butadiene rubber, solids content 100% by mass, RDB value 3.7% by mass) Resin (C-2): K-30 (polyvinylpyrrolidone) manufactured by Nippon Shokubai Co., Ltd. Resin (C-3): Kureha Corporation W#7300 (fluororesin; polyvinylidene fluoride, weight-average molecular weight of 100,000 or more)

[0056] <Cathode active material (A)> [Manufacturing of positive electrode active material (A-0)] 115 parts (5 mol) of lithium oxide and 89 parts (1 mol) of iron oxyhydroxide were mixed and formed into pellets. The mixture was calcined at 700°C for 8 hours under an argon gas atmosphere. Subsequently, using a Fritsch P-5 Classic Line planetary ball mill, argon gas was filled into a 250 mL zirconia container, and the mixture was dry-milled using 3 mmφ YTZ beads (Nikkatoh) to obtain the cathode active material (A-0). The composition formula is Li5FeO4, and the median diameter (D 50 The thickness was 5 μm.

[0057] [Manufacturing Example 1] [Manufacturing of positive electrode active material (A-1)] 139 parts (90 mol%) of positive electrode active material (A-0) and 8 parts (10 mol%) of aluminum hydroxide were mixed and formed into pellets. The pellets were fired at 700°C for 8 hours under an argon gas atmosphere. Subsequently, using a Fritsch P-5 Classic Line planetary ball mill, argon gas was filled into a 250 mL zirconia container, and dry grinding was performed using 3 mmφ YTZ beads (Nikkatoh) to obtain positive electrode active material (A-1). The composition formula is Li 5.0 Fe 0.9 Al 0.1 O4, median diameter (D 50 The thickness was 5 μm.

[0058] [Manufacturing Examples 2-4] [Manufacturing of positive electrode active materials (A-2) to (A-4)] Positive electrode active materials (A-2) to (A-4) were obtained in the same manner as in Example 1, except that the raw materials and additive amounts were changed as shown in Table 1. The particle size of positive electrode active material (A) was adjusted by appropriately adjusting the rotation speed and processing time of the planetary ball mill.

[0059] [Manufacturing Example 5] [Manufacturing of positive electrode active material (A-5)] 139 parts (90 mol%) of positive electrode active material (A-0) and 12 parts (10 mol%) of Li3PO4 were mixed. Subsequently, using a Fritsch P-5 Classic Line planetary ball mill, argon gas was filled into a 250 mL zirconia container, and dry grinding was performed using 3 mmφ YTZ beads (Nikkatoh) to obtain positive electrode active material (A-5). The composition formula is Li 4.8 Fe 0.9 P 0.1 O4, median diameter (D 50 The thickness was 1 μm.

[0060] [Manufacturing Examples 6-8] [Manufacturing of positive electrode active materials (A-6) to (A-8)] Positive electrode active materials (A-6) to (A-8) were obtained in the same manner as in Example 1, except that the raw materials and additive amounts were changed as shown in Table 1. The particle size of positive electrode active material (A) was adjusted by appropriately adjusting the rotation speed and processing time of the planetary ball mill.

[0061] [Table 1]

[0062] [Table 2]

[0063] [Manufacturing Example 101] [Manufacturing of conductive material dispersion 1] A dispersion of resin (C-1) was prepared by adding 1.25 parts by mass of resin (C-1) and 96.25 parts by mass of NMP to a stainless steel container and dispersing it with a disperser. To this dispersion, 2.5 parts by mass of conductive material (B-1) were weighed and added while stirring with a disperser. Subsequently, a fine emulsifier screen was attached to a high-shear mixer (L5M-A, manufactured by Silverson), and batch dispersion processing was performed at a speed of 9,000 rpm. This batch dispersion processing was continued until the entire solution became uniform and the dispersion particle size was 200 μm or less as measured by a grind gauge. Next, a circulating dispersion treatment (80% bead filling, peripheral speed 12 m / s) was performed using a bead mill (Star Mill LMZ, manufactured by Ashizawa Finetech Co., Ltd.) filled with zirconia beads with an outer diameter of 1.0 mmφ, with a residence time of 10 minutes. Subsequently, the dispersion liquid was supplied to a high-pressure homogenizer via piping and subjected to a 15-pass dispersion treatment. Subsequently, the dispersion liquid was supplied to a high-pressure homogenizer (Star Burst Lab, manufactured by Sugino Machine Co., Ltd.) and subjected to a 15-pass dispersion treatment. This dispersion treatment was performed using a single nozzle chamber with a nozzle diameter of 0.25 mm and a pressure of 100 MPa. The solution after dispersion treatment was passed through a depth filter (3M, PP nonwoven fabric depth cartridge NT-T series, filtration accuracy 20 μm). Conductive material dispersion liquid 1 was obtained in this manner.

[0064] [Manufacturing Examples 102-105] [Manufacturing of conductive material dispersions 2-5] Conductive material dispersions 2 to 5 were obtained in the same manner as in manufacturing example 101, except that the conductive material (B) used was changed as shown in Table 3.

[0065] [Manufacturing Example 106] [Manufacturing of conductive material dispersion 6] A dispersion of resin (C-2) was prepared by adding 1.25 parts by mass of resin (C-2), 0.06 parts by mass of potassium hydroxide, and 96.25 parts by mass of NMP to a stainless steel container and dispersing it with a disperser. To this dispersion, 2.5 parts by mass of conductive material (B-5) were weighed and added while stirring with a disperser. Subsequently, a fine emulsifier screen was attached to a high-shear mixer (L5M-A, manufactured by Silverson), and batch dispersion processing was performed at a speed of 9,000 rpm. This batch dispersion processing was continued until the entire solution became uniform and the dispersion particle size was 200 μm or less as measured by a grind gauge. Next, a circulating dispersion treatment (80% bead filling, peripheral speed 12 m / s) was performed using a bead mill (Star Mill LMZ, manufactured by Ashizawa Finetech Co., Ltd.) filled with zirconia beads with an outer diameter of 1.0 mmφ, with a residence time of 10 minutes. Subsequently, the dispersion liquid was supplied to a high-pressure homogenizer via piping and subjected to a 15-pass dispersion treatment. Subsequently, the dispersion liquid was supplied to a high-pressure homogenizer (Star Burst Lab, manufactured by Sugino Machine Co., Ltd.) and subjected to a 15-pass dispersion treatment. This dispersion treatment was performed using a single nozzle chamber with a nozzle diameter of 0.25 mm and a pressure of 100 MPa. The solution after dispersion treatment was passed through a depth filter (3M, PP nonwoven fabric depth cartridge NT-T series, filtration accuracy 20 μm). In this way, conductive material dispersion liquid 6 was obtained.

[0066] [Table 3]

[0067] [Example 1] [Manufacturing of cathode composite material (1)] Capacity 150cm 3In a plastic container, conductive material dispersion 5 and resin (C-3) which had been pre-mixed with NMP to a concentration of 8% by mass were added. Then, using a rotation / revolution mixer (Awatori Rentaro, ARE-310), the mixture was stirred at 2,000 rpm for 30 seconds. After adding the positive electrode active material (A-1), the mixture was stirred again at 2,000 rpm for 30 seconds using a rotation / revolution mixer (Sinky Awatori Rentaro, ARE-310). Subsequently, the clumps were broken up with a spatula, and then the mixture was stirred again at 2,000 rpm for 300 seconds using a rotation / revolution mixer (Sinky Awatori Rentaro, ARE-310) to adjust the non-volatile content to 73.5%, thereby obtaining the positive electrode composite composition (1). In the non-volatile portion of the positive electrode composite composition, the non-volatile content ratio of positive electrode active material (A-1): conductive material (B-5): resin (C-1): resin (C-3) is 98.1:0.4:0.2:1.3.

[0068] [Examples 2-9, 11-14] [Manufacturing of cathode composite compositions (2) to (9), (11) to (14)] Positive electrode composite compositions (2) to (9) and (11) to (14) were obtained in the same manner as in Example 1, except that the positive electrode composite composition (A), conductive material (B), and resin (C) used were changed as shown in Table 4. In all cases, the non-volatile content ratio of positive electrode active material (A-1): conductive material (B-5): resin (C-1) or resin (C-2): resin (C-3) is 98.1:0.4:0.2:1.3.

[0069] [Example 10] [Manufacturing of cathode composite material (10)] Capacity 150cm 3In a plastic container, conductive material dispersion 5 and resin (C-3), which had been pre-mixed with NMP to a concentration of 8% by mass, were added. Then, using a rotation / revolution mixer (Awatori Rentaro, ARE-310), the mixture was stirred at 2,000 rpm for 30 seconds. Next, positive electrode active materials (A-4) and (A-5) were added in a mass ratio of 19:1, and then the mixture was stirred at 2,000 rpm for 30 seconds using a rotation / revolution mixer (Sinky Awatori Rentaro, ARE-310). Subsequently, the clumps were broken up with a spatula, and then the mixture was stirred at 2,000 rpm for 300 seconds using a rotation / revolution mixer (Sinky Awatori Rentaro, ARE-310) to adjust the non-volatile content to 73.5%, obtaining the positive electrode composite composition (10). In the non-volatile portion of the electrode composition, the non-volatile content ratio of positive electrode active material (A-4) + (A-5): conductive material (B-1): resin (C-1): resin (C-3) is 98.1:0.4:0.2:1.3.

[0070] [Comparative Example 1] [Manufacturing of cathode composite material (15)] Capacity 150cm 3 In a plastic container, conductive material dispersion 4 and resin (C-3) which had been pre-mixed with NMP to a concentration of 8% by mass were added. Then, the mixture was stirred at 2,000 rpm for 30 seconds using a rotation / revolution mixer (Awatori Rentaro, ARE-310). After adding the positive electrode active material (A-0), the mixture was stirred at 2,000 rpm for 30 seconds using a rotation / revolution mixer (Sinky Awatori Rentaro, ARE-310). Subsequently, the clumps were broken up with a spatula, and then the mixture was stirred at 2,000 rpm for 300 seconds using a rotation / revolution mixer (Sinky Awatori Rentaro, ARE-310) to adjust the non-volatile content to 73.5%, obtaining the positive electrode composite composition (15). In the electrode composition, the non-volatile content ratio of positive electrode active material (A-0): conductive material (B-4): resin (C-1): resin (C-3) is 98.1:0.4:0.2:1.3.

[0071] [Table 4]

[0072] [Example 101] [Manufacturing of a secondary battery (1)] <Fabrication of the positive electrode> The cathode composite material composition (1) is applied using an applicator, and the basis weight per unit of the electrode film is 20 mg / cm². 2 The material was coated onto aluminum foil in the manner described above. After coating, the coating was dried in an electric oven at 120°C ± 5°C for 25 minutes to obtain electrode film (1). Subsequently, electrode film (1) was rolled using a roll press (Sankmetal, 3t hydraulic roll press) to obtain positive electrode (1). The density of the electrode film after rolling was 3.1 g / cc. <Manufacturing of secondary batteries> The positive electrode (1) and the standard negative electrode were punched out to 45mm x 40mm and 50mm x 45mm, respectively. These electrodes, along with the separator (porous polypropylene film) to be inserted between them, were placed in an aluminum laminate bag and dried in an electric oven at 60°C for 1 hour. Subsequently, 2 mL of electrolyte (non-aqueous electrolyte) was injected into a glove box filled with argon gas, and then an aluminum laminate was sealed to create a laminate-type lithium-ion secondary battery (1).

[0073] The standard negative electrode and non-aqueous electrolyte were prepared as follows. (Standard negative electrode) Capacity 150cm 3In a plastic container, 0.5 parts by mass of acetylene black (Denka Black® HS-100, manufactured by Denka), 1 part by mass of MAC500LC (carboxymethylcellulose sodium salt, Sunrose special type MAC500L, manufactured by Nippon Paper Industries, 100% non-volatile content), and 98.4 parts by mass of water were added, and the mixture was stirred at 2000 rpm for 30 seconds using a rotation / revolution mixer (Sinky Awatori Rentaro, ARE-310). Furthermore, 92 parts by mass of artificial graphite (manufactured by Nippon Graphite Industry, CGB-20) and 5 parts by mass of silicon oxide (manufactured by Osaka Titanium Technology, SILICON MONOOXIDE SiO 1.3C 5μm, 100% non-volatile content) were added as negative electrode active materials, and the mixture was stirred at 3000 rpm for 10 minutes using a high-speed stirrer. Next, 3.1 parts by mass of styrene-butadiene rubber (SBR) (TRD2001, manufactured by JSR Corporation) were added, and the mixture was stirred at 2000 rpm for 30 seconds using the aforementioned rotation-revolution mixer to obtain the negative electrode composite composition. Subsequently, the negative electrode composite composition was measured using an applicator to determine the basis weight per unit of electrode film, which was 8 mg / cm². 2 After coating the copper foil in this manner, the coating was dried in an electric oven at 120°C ± 5°C for 25 minutes. Furthermore, it was rolled using a roll press (manufactured by Sankumetal Co., Ltd., 3t hydraulic roll press) to obtain a density of 1.6 g / cm³ of electrode film. 3 A standard negative electrode was fabricated.

[0074] (Non-aqueous electrolyte) First, a mixed solvent was prepared by mixing ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate in a 1:1:1 (volume ratio). Next, 2 parts by mass of VC (vinylene carbonate) was added as an additive to 100 parts by mass of this mixed solvent, and then LiPF6 was dissolved at a concentration of 1 M to obtain a non-aqueous electrolyte.

[0075] [Examples 102-114, Comparative Example 101] [Manufacturing of secondary batteries (2) to (15)] Secondary batteries (2) to (15) were obtained in the same manner as in Example 101, except that the composite material composition for the positive electrode used was changed as shown in Table 4.

[0076] Evaluation of secondary batteries Secondary batteries obtained using the cathode composite material composition of the present invention were evaluated by the following method. The results are shown in Table 4.

[0077] <Initial capacity and cycle characteristics test> The secondary batteries of the examples and comparative examples were charged and discharged, and their initial capacity (discharge capacity in the first cycle) and cycle characteristics (capacity retention rate) were evaluated. A higher value for both initial capacity and capacity retention rate indicates better battery performance. For the first and second cycles, charging and discharging were performed at 0.1C, and from the third to the 50th cycle, charging and discharging were performed at 0.5C. Charging conditions: CC (constant current) / CV (constant voltage), 5mV / 0.005C current cut-off Discharge conditions: CC (constant current) conditions, 1.5V cut-off The capacity retention rate was derived using the following calculation. Capacity retention rate (%) = (Discharge capacity at the 50th cycle / Discharge capacity at the 1st cycle) × 100

[0078] <Outgassing Test> For the secondary batteries used in the cycle performance test, after the 50th cycle, the deformation of the aluminum laminate bag was visually observed to determine whether or not outgassing occurred. ○: No deformation was observed in the aluminum laminated bag. ×: Deformation is visible in the aluminum laminate bag.

[0079] [Table 5]

[0080] The results in Table 5 confirm that the secondary battery formed from the positive electrode composite composition containing the positive electrode active material of the present invention exhibits good initial capacity and cycle characteristics, and furthermore, outgassing is suppressed. Therefore, it can be suitably used in mobility applications such as electric vehicles and aircraft, as well as in applications for small portable electronic devices such as notebook personal computers, smartphones, tablet devices, and digital cameras. In particular, when used in mobility applications, it is clear that it can extend the driving range.

Claims

1. It comprises a positive electrode active material (A), a conductive material (B), and a resin (C), The positive electrode active material (A) is a compound represented by the following general formula (1), and is a positive electrode composite material composition. Li ｗ Fe ｘ M ｙ O ｚ General form (1) (In general formula (1), w, x, y, and z are in the ranges of 3 ≤ w ≤ 5, 0.5 ≤ x < 1, 0 < y ≤ 0.5, and 3 ≤ z ≤ 5, respectively. Also, 0.9 ≤ x + y ≤ 1.

1. M is one of the elements from Group 13 to 16 other than oxygen.)

2. The cathode composite composition according to claim 1, wherein in general formula (1), M is any element from the 3rd to 6th period.

3. The cathode composite composition according to claim 1, wherein M is one or more selected from the group consisting of aluminum, silicon, phosphorus, sulfur, gallium, and germanium in general formula (1).

4. The cathode composite composition according to claim 1, wherein the conductive material (B) is a carbon nanotube.

5. The cathode composite composition according to claim 4, wherein the carbon nanotube has an outer diameter of 1 to 20 nm and a length of 0.1 to 100 μm.

6. The positive electrode composite composition according to claim 1, wherein the resin (C) is one or more selected from nitrile butadiene rubber, hydrogenated nitrile butadiene rubber, polyvinyl alcohol, polyvinyl butyral, polyvinylpyrrolidone, and polyvinylidene fluoride.

7. A positive electrode formed from the positive electrode composite composition described in any one of claims 1 to 6.

8. A lithium-ion secondary battery comprising the positive electrode described in claim 7.

9. A mobility device comprising the lithium-ion secondary battery described in claim 8.

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