Electrode composition for lithium ion batteries

Abstract

To provide an electrode composition for a lithium ion battery that yields an electrode for a lithium ion battery with excellent cell performance (electrical resistance, coulombic efficiency, and capacity retention rate).SOLUTION: An electrode composition for a lithium ion battery includes an electrode active material, a binder resin, a conductive assistant, and a dispersant, the dispersant is an alkylene oxide adduct of a phenol compound, and the total weight of carbon atoms constituting an aromatic ring skeleton and hydrogen atoms bonded to carbon atoms in the dispersant is 55 wt.% or less based on the weight of the dispersant.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to an electrode composition for a lithium ion battery. [Background technology]

[0002] Lithium-ion batteries, with their high voltage and high energy density, are widely used in the field of portable information devices and have established themselves as the standard battery for mobile phones, laptop computers, and other portable devices. While their applications continue to expand, their use in hybrid and electric vehicles, in addition to their traditional applications, is also being considered, and some applications have already been put into practical use. To further popularize these applications, secondary batteries with higher capacity and power output are required, and various technologies are being attempted.

[0003] To increase the capacity of lithium-ion batteries, it is necessary to increase the proportion of active material in the electrodes, and it is preferable to use less of the other components, such as binder resin and conductive additives. However, simply reducing the amount of these components used will not ensure the strength and electronic conductivity of the resulting electrode, resulting in a deterioration in battery performance. Therefore, additives (mainly dispersants) that can reduce the amount of binder resin and conductive additives used while maintaining battery performance have been investigated.

[0004] For example, Patent Document 1 uses methyl cellulose, polyvinyl pyrrolidone, polyvinyl alcohol, etc. as polymer dispersants. However, these dispersants, particularly polyvinyl pyrrolidone, may undergo a decomposition reaction in the positive electrode potential range (3 to 5 V), which may reduce battery performance. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-181140 Summary of the Invention [Problem to be solved by the invention]

[0006] The present invention has been made in view of the above-described circumstances, and an object of the present invention is to provide an electrode composition for a lithium ion battery, which can provide an electrode for a lithium ion battery having excellent cell performance (electrical resistance value, coulombic efficiency, capacity retention rate). [Means for solving the problem]

[0007] The present inventors have made extensive studies and arrived at the present invention. The present invention provides an electrode composition for lithium ion batteries, which comprises an electrode active material, a binder resin, a conductive additive, and a dispersant, wherein the dispersant is an alkylene oxide adduct of a phenol compound, the total weight ratio of carbon atoms constituting an aromatic ring skeleton and hydrogen atoms bonded to the carbon atoms in the dispersant is 55 wt % or less based on the weight of the dispersant, the weight ratio of the electrode active material is 78 to 97 wt % based on the solid content weight of the electrode composition for lithium ion batteries, the weight ratio of the binder resin is 1 to 20 wt % based on the solid content weight of the electrode composition for lithium ion batteries, the weight ratio of the conductive additive is 1 to 5 wt % based on the solid content weight of the electrode composition for lithium ion batteries, and the weight ratio of the dispersant is 2 to 20 wt % based on the weight of the conductive additive. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide an electrode composition for a lithium ion battery that can provide an electrode for a lithium ion battery having excellent cell performance (electrical resistance value, coulombic efficiency, capacity retention rate). DETAILED DESCRIPTION OF THE INVENTION

[0009] The electrode composition for a lithium ion battery of the present invention is an electrode composition for a lithium ion battery that contains an electrode active material, a binder resin, a conductive additive, and a dispersant. The electrode composition for a lithium ion battery of the present invention contains an electrode active material. The electrode active material may be a positive electrode active material or a negative electrode active material. When the electrode active material is a positive electrode active material, the electrode composition for a lithium ion battery of the present invention can be used as a positive electrode composition for a lithium ion battery, and when the electrode active material is a negative electrode active material, it can be used as a negative electrode composition for a lithium ion battery.

[0010] There are no particular limitations on the positive electrode active material as long as it can be used as a positive electrode active material for a lithium ion battery. For example, composite oxides of lithium and transition metals {composite oxides containing one type of transition metal (e.g., LiCoO2, LiNiO2, LiAlMnO4, LiMnO2, and LiMn2O4), composite oxides containing two types of transition metal elements (e.g., LiFeMnO4, LiNi 1-x Co x O2, LiMn 1-y Co y O2, LiNi 1 / 3 Co 1 / 3 Al 1 / 3 O2 and LiNi 0.8 Co 0.15 Al 0.05 O2) and composite oxides containing three or more metal elements [e.g., LiM a M' b M'' c O2 (M, M' and M'' are different transition metal elements, and a + b + c = 1 is satisfied. For example, LiNi 1 / 3 Mn 1 / 3 Co 1 / 3 O2), etc.}, lithium-containing transition metal phosphates (for example, LiFePO4, LiCoPO4, LiMnPO4, and LiNiPO4), transition metal oxides (for example, MnO2 and V2O5), transition metal sulfides (for example, MoS2 and TiS2), and conductive polymers (for example, polyaniline, polypyrrole, polythiophene, polyacetylene, poly-p-phenylene, and polyvinylcarbazole), and two or more of them may be used in combination. The lithium-containing transition metal phosphate may have some of the transition metal sites substituted with other transition metals.

[0011] From the viewpoint of the electrical characteristics of the battery, the volume average particle diameter of the positive electrode active material is preferably 0.01 to 100 μm, more preferably 0.1 to 35 μm, and even more preferably 2 to 30 μm.

[0012] In this specification, the volume average particle diameter refers to the particle diameter at 50% of the cumulative value (Dv50) in the particle size distribution determined by the Microtrac method (laser diffraction / scattering method). The Microtrac method is a method for determining particle size distribution by irradiating particles with laser light and utilizing scattered light obtained. The volume average particle diameter can be measured using a Microtrac manufactured by Nikkiso Co., Ltd.

[0013] The negative electrode active material is not particularly limited as long as it can be used as a negative electrode active material for a lithium ion battery. Examples of materials constituting the negative electrode active material include carbon-based materials and silicon-based materials. Among these, the negative electrode active material is preferably made of a carbon-based material.

[0014] Examples of carbon-based materials include graphite, non-graphitizable carbon, amorphous carbon, baked resins (e.g., phenolic resins, furan resins, etc., baked and carbonized), and cokes (e.g., pitch coke, needle coke, and petroleum coke). Mixtures of carbon-based materials with conductive polymers (e.g., polyacetylene and polypyrrole), metal oxides (titanium oxide and lithium-titanium oxide), and metal alloys (lithium-tin alloys, lithium-aluminum alloys, aluminum-manganese alloys, etc.) are also possible. Materials that do not contain lithium or lithium ions internally may be pre-doped to incorporate lithium or lithium ions into part or all of their interior.

[0015] Examples of silicon-based materials include silicon oxide (SiO x ), a Si-C composite, a Si-Al alloy, a Si-Li alloy, a Si-Ni alloy, a Si-Fe alloy, a Si-Ti alloy, a Si-Mn alloy, a Si-Cu alloy, and a Si-Sn alloy. Examples of Si-C composites include silicon carbide and carbon particles whose surfaces are coated with silicon and / or silicon carbide, as well as silicon particles and silicon oxide particles whose surfaces are coated with carbon and / or silicon carbide. The particles made of a silicon-based material may be single particles (also referred to as primary particles), or may form composite particles obtained by agglomeration of primary particles (i.e., secondary particles obtained by agglomeration of primary particles made of a silicon-based material). Composite particles may be formed when primary particles made of a silicon-based material are agglomerated by their adsorptive power, or when primary particles are agglomerated by adsorption via another material. An example of a method for forming composite particles by binding primary particles via another material is a method of mixing primary particles made of a silicon-based material with a polymer compound that constitutes a coating film.

[0016] From the viewpoint of the electrical characteristics of the battery, the volume average particle diameter of the negative electrode active material is preferably 0.1 to 100 μm, more preferably 1 to 50 μm, and even more preferably 2 to 20 μm.

[0017] The lithium ion battery electrode composition of the present invention contains a binder resin. The binder resin is not particularly limited as long as it has a binder function (adhesive strength). Examples of binder resins include starch, polyvinylidene fluoride (PVdF), polyvinyl alcohol, polyvinylpyrrolidone, polytetrafluoroethylene, tetrafluoroethylene, polyacrylic acid, sodium polyacrylate, polyacrylic acid ester, polymethacrylic acid ester, styrene-butadiene rubber (SBR), polyethylene, and polypropylene. The binder resin broadly includes thickeners, and examples of the thickener include carboxymethyl cellulose (CMC).

[0018] The electrode composition for a lithium ion battery of the present invention contains a conductive additive. The conductive additive is not particularly limited as long as it is a material having conductivity. Examples of conductive additives include metals [aluminum, stainless steel (SUS), silver, gold, copper, titanium, etc.], carbon [graphite (flaky graphite (UP)), carbon black (acetylene black, ketjen black, furnace black, channel black, thermal lamp black, etc.), carbon nanofibers (CNF), carbon nanotubes (CNT), etc.], and mixtures thereof. These conductive additives may be used alone or in combination of two or more. Furthermore, alloys or metal oxides thereof may also be used. From the viewpoint of electrical stability, acetylene black is preferred.

[0019] Carbon-based materials are used both as negative electrode active materials and as conductive additives, but in this application, those with a volume average particle diameter of 15 μm or more are considered to be negative electrode active materials, and those with a volume average particle diameter of less than 15 μm are considered to be conductive additives.

[0020] The electrode composition for a lithium ion battery of the present invention contains a dispersant. The dispersant is an alkylene oxide adduct of a phenol compound. Examples of phenolic compounds include monocyclic phenolic compounds (such as phenol and cresol), bisphenol compounds (such as bisphenol A, bisphenol F, and bisphenol S), and polycyclic phenolic compounds (such as tribenzylphenol, dibenzylphenol, benzylphenol, 2,4-bis(α,α-dimethylbenzyl)phenol, and phenolphthalein). Of these, from the viewpoint of dispersibility of the conductive additive, etc., bisphenol compounds and polycyclic phenol compounds are preferred, and polycyclic phenol compounds are particularly preferred.

[0021] Examples of the alkylene oxide (hereinafter abbreviated as AO) to be added to the phenol compound include AOs having 2 to 4 carbon atoms, such as ethylene oxide (hereinafter abbreviated as EO), 1,2-propylene oxide (hereinafter abbreviated as PO), 1,3-propylene oxide, 1,2-, 1,3- or 2,3-butylene oxide, and tetrahydrofuran (hereinafter abbreviated as THF). Of these, EO or PO is preferred from the viewpoint of dispersibility of the conductive additive.

[0022] The total weight ratio of carbon atoms constituting the aromatic ring skeleton and hydrogen atoms bonded to carbon atoms in the dispersant is 55% by weight or less based on the weight of the dispersant. From the viewpoint of dispersibility of the conductive additive, the total weight ratio of the carbon atoms constituting the aromatic ring skeleton and the hydrogen atoms bonded to the carbon atoms in the dispersant is preferably 52% by weight or less, and more preferably 35% by weight or less, based on the weight of the dispersant.

[0023] In the present invention, the ratio of the total weight of the carbon atoms constituting the aromatic ring skeleton and the hydrogen atoms bonded to the carbon atoms in the dispersant can be calculated from the weight of the phenol compound used in the reaction for synthesizing the alkylene oxide adduct of the phenol compound that is the dispersant and the number of moles of the added alkylene oxide. 1 It can also be calculated by measuring H-NMR. 1 When measuring by H-NMR, specifically, it can be determined by the following measurement conditions and analysis method.

[0024] <Sample preparation method> 100 mg of the measurement object and 10 mg of an internal standard (for example, tetramethylsilane) are weighed into an NMR tube, and 0.45 ml of a deuterated solvent (for example, deuterated chloroform) is added to dissolve them, and measurement is performed under the following measurement conditions. < 1 H-NMR measurement conditions> Equipment: Bruker BioSpin "AVANCE III HD400" Number of times accumulated: 4 times <Analysis method> The weight percentage (wt%) of hydrogen atoms bonded to carbon atoms constituting the aromatic ring skeleton is calculated from the integral ratio of the peaks derived from the carbon atoms and hydrogen atoms bonded to the carbon atoms constituting the aromatic ring skeleton to the peak of the proton derived from the methyl group of the internal standard. That is, the total weight percentage (wt%) of the carbon atoms and hydrogen atoms bonded to the carbon atoms constituting the aromatic ring skeleton is calculated from the integral ratio of the protons derived from the hydrogen atoms bonded to the carbon atoms constituting the aromatic ring skeleton around the chemical shift of 6.5 to 7.5 ppm, the integral ratio of the protons derived from the methyl group of the internal standard at a chemical shift of 0 ppm, and the charged weights of the sample and internal standard. Total weight ratio of carbon atoms constituting the aromatic ring skeleton and hydrogen atoms bonded to carbon atoms (% by weight) = Aa / (Ai / Pi) × Ma / Mi × Wi / Ws × 100 where Aa is the integral ratio of the peak of the proton derived from the hydrogen atom bonded to the carbon atom constituting the aromatic ring skeleton, Ai is the integral ratio of the peak of the proton derived from the methyl group of the internal standard substance, Pi is the number of protons of the internal standard substance, Ma is the molecular weight of the dispersant, Mi is the molecular weight of the internal standard substance, Wi is the charge weight (mg) of the internal standard substance, and Ws is the charge weight (mg) of the sample. The total weight ratio of the carbon atoms constituting the aromatic ring skeleton and the hydrogen atoms bonded to the carbon atoms in the dispersant can be adjusted by the molecular weight and number of moles of the alkylene oxide to be added.

[0025] The hydroxyl group concentration of the dispersant is preferably 0.5 to 10% by weight, more preferably 1 to 7% by weight, based on the weight of the dispersant. In the present invention, the hydroxyl group concentration of the dispersant can be determined from the weight of the phenol compound used in the reaction for synthesizing the alkylene oxide adduct of the phenol compound serving as the dispersant and the number of moles of the alkylene oxide added. In addition, with respect to the dispersant, 1 It can also be calculated by measuring H-NMR. 1 When measuring by H-NMR, specifically, it can be determined by the following measurement conditions and analysis method.

[0026] <Sample preparation method> 100 mg of the measurement object and 10 mg of an internal standard (for example, tetramethylsilane) are weighed into an NMR tube, and 0.45 ml of a deuterated solvent (for example, deuterated chloroform) is added to dissolve them, and measurement is performed under the following measurement conditions. < 1 H-NMR measurement conditions> Equipment: Bruker BioSpin "AVANCE III HD400" Number of times accumulated: 4 times <Analysis method> The concentration of hydroxyl groups (wt%) is calculated from the integral ratio of the peak derived from hydroxyl groups to the peak derived from the protons of the methyl groups of the internal standard. That is, the concentration of hydroxyl groups (wt%) is calculated from the integral ratio of the protons derived from hydroxyl groups at a chemical shift of around 3.5 to 4.5 ppm, the integral ratio of the protons derived from the methyl groups of the internal standard at a chemical shift of 0 ppm, and the charged weights of the sample and internal standard. Hydroxyl group concentration (wt%)=Ab / (Ai / Pi)×Ma / Mi×Wi / Ws×100 where Ab is the integral ratio of the peak of protons derived from hydroxyl groups, Ai is the integral ratio of the peak of protons derived from methyl groups of the internal standard substance, Pi is the number of protons of the internal standard substance, Ma is the molecular weight of the dispersant, Mi is the molecular weight of the internal standard substance, Wi is the charge weight (mg) of the internal standard substance, and Ws is the charge weight (mg) of the sample. The content of hydroxyl groups can be adjusted by appropriately adjusting the composition and charge equivalent of the raw materials constituting the dispersant.

[0027] From the viewpoint of dispersibility of the conductive assistant, the weight average molecular weight of the dispersant is preferably 1,000 to 10,000, and more preferably 1,000 to 3,000. The weight-average molecular weight of the dispersant can be determined by GPC (gel permeation chromatography) measurement under the following conditions: A sample dispersant is dissolved in a solvent such as orthodichlorobenzene, N'-dimethylformamide (DMF), or tetrahydrofuran (THF) to prepare a 0.25 wt% solution, and the insoluble matter is filtered through a PTFE filter with a pore size of 1 μm to prepare the sample solution. Apparatus: Alliance GPC V2000 (Waters) Solvent: orthodichlorobenzene, DMF, THF Standard: Polystyrene sample Concentration: 3mg / ml Column stationary phase: PLgel 10um, MIXED-B, two columns in series (Polymer Laboratories) Column temperature: 135℃

[0028] The dispersant can be produced by carrying out an addition reaction of an alkylene oxide to the phenol compound by a known method.

[0029] The lithium-ion battery electrode composition of the present invention comprises an electrode active material, a binder resin, a conductive additive, and a dispersant, and the weight percentage of the electrode active material is 78 to 97 wt % based on the solid content weight of the lithium-ion battery electrode composition. If the weight percentage of the electrode active material is less than 78 wt % based on the solid content weight of the lithium-ion battery electrode composition, the capacity of the resulting battery will be reduced, and if it exceeds 97 wt %, the conductivity of the resulting electrode will be deteriorated. From the viewpoint of the balance between battery capacity and conductivity, the weight percentage of the electrode active material is preferably 89 to 92 wt % based on the solid content weight of the lithium-ion battery electrode composition. The "solids weight of the electrode composition for lithium ion batteries" means the weight of the materials excluding volatile components such as the organic solvent described below (the total weight of the electrode active material, binder resin, conductive additive, dispersant, etc.) Specifically, the weight of the solids weight is the weight of the residue when the electrode composition for lithium ion batteries is heated at 100°C for 8 hours.

[0030] In the lithium-ion battery electrode composition of the present invention, the weight proportion of the binder resin is 1 to 20 wt % based on the solid content weight of the lithium-ion battery electrode composition. If the weight proportion of the binder resin is less than 1 wt % based on the solid content weight of the lithium-ion battery electrode composition, the strength of the resulting electrode will be insufficient, and if it exceeds 20 wt %, the capacity of the resulting battery will be reduced. From the viewpoint of the balance between electrode strength and battery capacity, the weight proportion of the binder resin is preferably 3 to 10 wt % based on the solid content weight of the lithium-ion battery electrode composition.

[0031] In the lithium-ion battery electrode composition of the present invention, the weight proportion of the conductive additive is 1 to 5 wt % based on the solid content weight of the lithium-ion battery electrode composition. If the weight proportion of the conductive additive is less than 1 wt % based on the solid content weight of the lithium-ion battery electrode composition, the conductivity of the resulting electrode will deteriorate, and if it exceeds 5 wt %, the capacity of the resulting battery will be reduced. From the viewpoint of the balance between battery capacity and conductivity, the weight proportion of the conductive additive is preferably 2 to 5 wt % based on the solid content weight of the lithium-ion battery electrode composition.

[0032] In the electrode composition for lithium ion batteries of the present invention, the weight percentage of the dispersant is 2 to 20 wt% based on the weight of the conductive additive. If the weight percentage of the dispersant is less than 2 wt% based on the weight of the conductive additive, the conductivity of the resulting electrode will deteriorate, and if it exceeds 20 wt%, side reactions may occur, adversely affecting battery performance. From the viewpoint of battery performance, the weight percentage of the dispersant is preferably 5 to 20 wt% based on the weight of the conductive additive for lithium ion batteries.

[0033] The electrode composition for a lithium ion battery of the present invention may contain an organic solvent as needed. The organic solvent may, for example, be N-methyl-2-pyrrolidone (NMP).

[0034] The present specification discloses the following:

[0035] The present disclosure (1) is an electrode composition for a lithium ion battery, comprising an electrode active material, a binder resin, a conductive additive, and a dispersant, wherein the dispersant is an alkylene oxide adduct of a phenol compound, the total weight ratio of carbon atoms constituting an aromatic ring skeleton and hydrogen atoms bonded to the carbon atoms is 55 wt % or less based on the weight of the dispersant, the weight ratio of the electrode active material is 78 to 97 wt % based on the solid content weight of the electrode composition for a lithium ion battery, the weight ratio of the binder resin is 1 to 20 wt % based on the solid content weight of the electrode composition for a lithium ion battery, the weight ratio of the conductive additive is 1 to 5 wt % based on the solid content weight of the electrode composition for a lithium ion battery, and the weight ratio of the dispersant is 2 to 20 wt % based on the weight of the conductive additive.

[0036] The present disclosure (2) is the electrode composition for a lithium ion battery according to the present disclosure (1), wherein the hydroxyl group concentration of the dispersant is 0.5 to 10 wt % based on the weight of the dispersant.

[0037] The present disclosure (3) is the electrode composition for a lithium ion battery according to the present disclosure (1) or (2), wherein the weight average molecular weight of the dispersant is 1,000 to 10,000. [Example]

[0038] The present invention will now be described in detail with reference to examples, but the present invention is not limited to these examples as long as they do not depart from the gist of the present invention.

[0039] (Production Example 1: Production of Dispersant 1) Ethylene oxide (EO) was added to tribenzylphenol to produce alkylene oxide adducts of phenolic compounds. The average number of moles of EO added was 14. 500 parts of the alkylene oxide adduct and 98 parts of solid potassium hydroxide that had been crushed in advance under a nitrogen stream were placed in a sealed container and heated to 80° C. with stirring. Then, 74 parts of methylene chloride was added over about 30 minutes, and the mixture was reacted at 80° C. for about 3 hours. This reaction product was diluted with 500 parts of toluene, and the potassium hydroxide and potassium chloride were filtered off, and the volatile components were removed under reduced pressure to obtain Dispersant 1. The weight average molecular weight was 1,000. From the weight of the phenolic compound (tribenzylphenol) used in the reaction and the weight of ethylene oxide added to the phenolic compound (tribenzylphenol), the ratio of the total weight of the carbon atoms constituting the aromatic ring skeleton and the hydrogen atoms bonded to the carbon atoms to the total weight of the alkylene oxide adduct, and the hydroxyl group concentration in the alkylene oxide adduct were calculated and are shown in Table 1.

[0040] (Production Example 2: Production of Dispersant 2) Ethylene oxide (EO) was added to bisphenol A to produce alkylene oxide adducts of phenolic compounds. The average number of moles of EO added was 18. 500 parts of the alkylene oxide adduct and 98 parts of solid potassium hydroxide that had been crushed in advance under a nitrogen stream were placed in a sealed container and heated to 80° C. with stirring. Then, 74 parts of methylene chloride was added over about 30 minutes, and the mixture was reacted at 80° C. for about 3 hours. This reaction product was diluted with 500 parts of toluene, and the potassium hydroxide and potassium chloride were filtered off, and the volatile components were removed under reduced pressure to obtain Dispersant 2. The weight average molecular weight was 1,020. From the weight of bisphenol A used in the reaction and the weight of ethylene oxide added to bisphenol A, the ratio of the total weight of carbon atoms constituting the aromatic ring skeleton and hydrogen atoms bonded to the carbon atoms to the total weight of the alkylene oxide adduct, and the hydroxyl group concentration in the alkylene oxide adduct were calculated and are shown in Table 1.

[0041] (Production Example 3: Production of Dispersant 3) Propylene oxide (PO) was added to bisphenol A to produce an alkylene oxide adduct of a phenol compound. The average number of moles of PO added was 5. 500 parts of the alkylene oxide adduct and 98 parts of solid potassium hydroxide that had been crushed in advance under a nitrogen stream were placed in a sealed container and heated to 80° C. with stirring. Then, 74 parts of methylene chloride was added over about 30 minutes, and the mixture was reacted at 80° C. for about 3 hours. This reaction product was diluted with 500 parts of toluene, and the potassium hydroxide and potassium chloride were filtered off, and the volatile components were removed under reduced pressure to obtain Dispersant 3. The weight average molecular weight was 560. From the weight of bisphenol A used in the reaction and the weight of propylene oxide added to bisphenol A, the ratio of the total weight of the carbon atoms constituting the aromatic ring skeleton and the hydrogen atoms bonded to the carbon atoms to the total weight of the alkylene oxide adduct, and the hydroxyl group concentration in the alkylene oxide adduct were calculated and are shown in Table 1.

[0042] (Production Examples 4 to 10: Production of Dispersants 4 to 10) Dispersants 4, 5, 6, 7, 8, 9, and 10 were produced in the same manner as in Production Example 1, except that the type of starting material (phenol compound) and the number of moles of EO added were changed as shown in Table 1.

[0043] [Table 1]

[0044] (Examples 1 to 9 and Comparative Examples 1 to 3: Preparation of Positive Electrode Compositions for Lithium-Ion Batteries) The dispersant and binder resin were weighed out according to the weight parts shown in Table 2, and N-methyl-2-pyrrolidone (NMP) was added so that the resulting solution had a solids concentration of 60% by weight. The mixture was stirred at 2000 rpm for 4 minutes using a planetary stirring mixer (Awatori Rentaro [manufactured by Thinky Corporation]) to completely dissolve the binder resin and dispersant. The positive electrode active material and conductive additive were then added in the weight parts shown in Table 2, and the mixture was stirred at 2000 rpm for 4 minutes using the Awatori Rentaro to prepare a positive electrode composition for a lithium-ion battery. The positive electrode active material is LiNi 0.8 Co 0.15 Al 0.05 O2 powder "HED NCA 7050" (referred to as "NCA" in Table 2, manufactured by BTBM) was used. As the conductive additive, acetylene black "Denka Black Li100" (referred to as "AB(Li100)" in Tables 2 and 3, manufactured by Denka Co., Ltd.) was used. Polyvinylidene fluoride (referred to as "PVDF" in Table 2, manufactured by Kishida Chemical Co., Ltd.) was used as the binder resin. The blending amount of each material shown in Table 2 is expressed as weight (wt %) based on the solid content of the positive electrode composition for a lithium ion battery.

[0045] <Measurement of viscosity of electrode composition (electrode slurry)> The viscosity of the positive electrode composition and the negative electrode composition was measured using a rheometer [MCR302, [Anton Paar]] with a cone plate CP25 and a shear rate of 0.1 to 100 s -1 Measured at 25°C and a shear rate of 10 s -1 The viscosity at this point was recorded and is shown in Tables 2 and 3.

[0046] [Table 2]

[0047] (Preparation of battery for charge / discharge test: for positive electrode) The positive electrode composition for lithium ion batteries was applied to one side of a current collector (aluminum foil, manufactured by Hosen Co., Ltd.) using a wire bar in the atmosphere, pre-dried overnight, and then punched out to a diameter of 15 mm, further dried at 120°C under reduced pressure (1.3 kPa) for 4 hours, and pressed to the target electrode density (electrode thickness) using a press to prepare a positive electrode for evaluation. Starting from the positive electrode side, the positive electrode, a separator [product name "#3501", manufactured by Celgard Corporation], and lithium foil were stacked in this order, and an electrolyte (manufactured by Kishida Chemical, EC:DEC (1:1 v / v%), LiPF concentration: 1 mol / L) was poured into the stack, followed by vacuum lamination to prevent oxygen from entering, to prepare a battery for charge / discharge tests.

[0048] (Examples 10 to 18, Comparative Examples 4 to 6: Preparation of negative electrode compositions for lithium ion batteries) The dispersant was weighed out according to the blending amounts listed in Table 3, and water was added so that the resulting aqueous solution had a solids concentration of 45% by weight. The solution was then stirred for 2 minutes at 2000 rpm using a planetary stirring mixer / kneader called "Awatori Rentaro" (manufactured by Thinky Corporation). Sodium carboxymethylcellulose (CMCNa: manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was then weighed out according to the blending amounts listed in Table 3 and added. The solution was then stirred for 5 minutes at 2000 rpm using a planetary stirring mixer / kneader called "Awatori Rentaro" (manufactured by Thinky Corporation) to dissolve the CMCNa. The negative electrode active material and conductive additive were then added in the blending amounts listed in Table 3, and the solution was then stirred for 4 minutes at 2000 rpm using the Awatori Rentaro. Finally, styrene butadiene rubber (referred to as SBR in Table 3, manufactured by Zeon Corporation) was weighed out according to the blending amounts shown in Table 3, and the mixture was stirred at 2000 rpm for 10 seconds using a planetary stirring type mixer / kneader "Awatori Rentaro" (manufactured by Thinky Corporation) to prepare a negative electrode composition for a lithium ion battery. As the negative electrode active material, graphite particles "SNG-WXA1" (referred to as "graphite" in Table 3) were used. As the conductive additive, acetylene black "Denka Black Li100" (referred to as "AB" in Tables 2 and 3, manufactured by Denka Co., Ltd.) and / or carbon nanotubes "NC7000" (referred to as "CNT" in Tables 2 and 3, manufactured by Nanocyl Corporation) were used. The blending amount of each material shown in Table 3 is shown by weight (wt %) based on the solid content of the negative electrode composition for a lithium ion battery.

[0049] [Table 3]

[0050] (Preparation of battery for charge / discharge test: negative electrode) The negative electrode composition for a lithium ion battery was applied to one side of a current collector (copper foil) using a wire bar in the atmosphere, pre-dried overnight, and then punched out to a diameter of 16 mm, further dried at 100°C under reduced pressure (1.3 kPa) for 4 hours, and pressed to the target electrode density (electrode thickness) using a press to prepare a negative electrode for evaluation. The negative electrode, a separator [product name "#3501", manufactured by Celgard], and lithium foil were stacked in this order from the negative electrode side, and an electrolyte (manufactured by Kishida Chemical, EC:DEC (1:1 v / v%), LiPF concentration: 1 mol / L) was poured into the stack. The stack was then vacuum laminated to prevent oxygen from entering, thereby preparing a battery for charge / discharge tests.

[0051] <Positive electrode half-cell charge / discharge test> At 25°C, the initial performance of the charge / discharge test battery (for the positive electrode) prepared by the following method was evaluated using a charge / discharge measuring device "HJ-SD8" (manufactured by Hokuto Denko Corporation). Using the constant current constant voltage charging method (also known as CCCV mode), the battery was charged to 4.2V at a current of 0.05C, and then maintained at 4.2V until the current reached 0.0025C. After a 10-minute break, the battery was discharged to 2.5V at a current of 0.05C. The charged capacity was defined as [initial charge capacity (mAh)], and the discharged capacity was defined as [initial discharge capacity (mAh)].

[0052] <Negative electrode half-cell charge / discharge test> At 25°C, the initial performance of the charge / discharge test battery (negative electrode) was evaluated using a charge / discharge measuring device "HJ-SD8" (manufactured by Hokuto Denko Corporation) according to the following method. The battery was charged to 0V at a current of 0.05C using the constant current charging method (also known as CC mode), and after a 10-minute rest, it was discharged to 1.5V at a current of 0.05C. The charged capacity was defined as [initial charge capacity (mAh)], and the discharged capacity was defined as [initial discharge capacity (mAh)].

[0053] The initial coulombic efficiency was calculated using the following formula, and the results are shown in Tables 2 and 3. Initial coulomb efficiency (%) = [initial discharge capacity] / [initial charge capacity] x 100 In addition, the electrical resistance value (10sDCR) was calculated from the voltage at the start of discharge and after 10 seconds using the following formula. 10sDCR(Ω·cm 2 ) = ([Voltage before discharge (V)] - [Voltage 10 seconds after discharge (V)]) / [Discharge current (A)] × 1.77 (1.77 cm 2 )

[0054] The above charge / discharge cycle was repeated 10 times. The battery capacity at the first charge (initial discharge capacity) and the battery capacity at the 10th charge cycle (discharge capacity after 10 cycles) were used to calculate the discharge capacity retention rate according to the following formula. The results are shown in Tables 2 and 3. Note that a larger value indicates less battery degradation. Discharge capacity retention rate (%) = [Discharge capacity at 10th cycle] / [Discharge capacity at 1st cycle] x 100 [Industrial Applicability]

[0055] A lithium ion battery equipped with an electrode obtained from the lithium ion battery electrode composition of the present invention is particularly useful as a lithium ion battery for use in mobile phones, personal computers, hybrid vehicles, and electric vehicles.

Claims

1. An electrode composition for a lithium ion battery comprising an electrode active material, a binder resin, a conductive additive, and a dispersant, the dispersant is an alkylene oxide adduct of a phenol compound, the total weight ratio of carbon atoms constituting the aromatic ring skeleton and hydrogen atoms bonded to carbon atoms in the dispersant is 55% by weight or less based on the weight of the dispersant, the weight proportion of the electrode active material is 78 to 97% by weight based on the solid content weight of the lithium ion battery electrode composition, the weight proportion of the binder resin is 1 to 20% by weight based on the solid content weight of the lithium ion battery electrode composition, and the weight proportion of the conductive assistant is 1 to 5% by weight based on the solid content weight of the lithium ion battery electrode composition, The weight ratio of the dispersant is 2 to 20% by weight based on the weight of the conductive assistant; The electrode composition for a lithium ion battery is characterized in that the weight average molecular weight of the dispersant is 1,000 to 10,000.

2. 2. The electrode composition for a lithium ion battery according to claim 1, wherein the hydroxyl group concentration of the dispersant is 0.5 to 10% by weight based on the weight of the dispersant.

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