Composition for lithium-ion battery cathode

Abstract

A lithium-ion battery cathode composition and a method for manufacturing a lithium-ion battery cathode composition are provided. An electrode is also provided which includes an active material layer formed from the lithium-ion battery cathode composition on a current collector.

Description

Technical Field

[0001] The present disclosure generally relates to a lithium-ion battery cathode composition. The present invention relates, without limitation, in particular to a lithium-ion battery cathode composition comprising at least one cathode active material, at least one electrical conductivity improving additive, at least one viscosity modifier, and at least one water-insoluble binder. The present disclosure further relates to an electrode for a lithium-ion battery comprising a current collector and an active material layer formed from the composition on the current collector.

Background Art

[0002] In this section, no technology described herein is admitted to represent the state of the art, and useful background information is exemplified.

[0003] Lithium-ion battery (LiB) cathodes typically consist of an active material (e.g., lithium nickel manganese cobalt oxide (NMC) or lithium iron phosphate (LFP, LiFePO4)), an electrical conductivity improving additive (e.g., carbon nanotubes, graphene, or carbon black), and a binder that binds the electrode components together to an aluminum current collector.

[0004] Currently, polyvinylidene fluoride (PVDF) is a well-established cathode binder in LiBs. PVDF is thermally stable and chemically inert over the potential range used. However, halogenated PVDF requires an environmentally harmful organic N-methylpyrrolidone (NMP) solvent and is reactive towards lithiated graphite.

[0005] Due to these drawbacks, other binder chemistries have been investigated as alternatives to PVDF. Polyacrylic acid (PAA) has been identified as a potential binder for LiB electrodes. PAA can be in an acidic form or can be partially or fully neutralized with, for example, sodium, lithium, or potassium.

[0006] However, there is still a need for new and improved lithium-ion battery cathode compositions. [Overview of the Initiative]

[0007] In a first aspect, the present invention provides a lithium-ion battery cathode composition comprising at least one cathode active material, at least one electrical conductivity improving additive, at least one viscosity modifier, and at least one water-insoluble binder.

[0008] In a second aspect, the present invention provides an electrode for a lithium-ion battery comprising an aluminum current collector and at least one active material layer on at least one surface of the aluminum current collector, wherein the at least one active material layer is formed from a positive electrode composition according to the present invention.

[0009] In a third aspect, the present invention provides a method for producing a lithium-ion battery cathode composition, the method comprising the steps of: mixing water with at least one viscosity modifier; subsequently adding at least one electrical conductivity improving additive; subsequently adding at least one cathode active material; and adding at least one water-insoluble binder.

[0010] In a fourth aspect, the present invention provides a method for manufacturing an electrode for a lithium-ion battery positive electrode, the method comprising the steps of: mixing water with at least one viscosity modifier; subsequently adding at least one electrical conductivity improving additive; subsequently adding at least one positive electrode active material; subsequently adding at least one water-insoluble binder; subsequently coating an aluminum current collector with the composition; and drying the coated aluminum current collector.

[0011] In a fifth aspect, the present invention provides a lithium-ion battery comprising an electrode for a lithium-ion battery according to the present invention.

[0012] In a sixth aspect, the present invention provides the use of the lithium-ion battery cathode composition according to the present invention for electrodes of lithium-ion batteries.

[0013] Surprisingly, lithium-ion battery cathode compositions comprising at least one cathode active material, at least one electrical conductivity enhancing additive, at least one viscosity modifier, and at least one water-insoluble binder such as an acrylic copolymer were found to provide excellent flexibility and adhesion to aluminum current collectors.

[0014] Furthermore, it was found that using poly(styrene acrylate), such as butyl acrylate-styrene copolymer, as a non-water-soluble binder with a high solid content speeds up film formation during drying, and the small particle size of the dispersion ensures uniform dispersion of the binder in the composition. The hydrophobicity, flexibility, and strength of the film can be adjusted by selecting the ratio of styrene to acrylate such as butyl acrylate in the composition.

[0015] Furthermore, surprisingly, it was found that the half-cell (LFP / lithium metal) containing the composition of the present invention is extremely stable.

[0016] The attached claims define the scope of protection. [Brief explanation of the drawing]

[0017] [Figure 1] The specific discharge capacity (mAh / g) of the LFP electrode, obtained using an aqueous binder (sample and reference sample according to the present invention), is shown. [Modes for carrying out the invention]

[0018] [Detailed explanation] In a first aspect, the present invention provides a lithium-ion battery cathode composition comprising at least one cathode active material, at least one electrical conductivity improving additive, at least one viscosity modifier, and at least one water-insoluble binder.

[0019] In one embodiment, the cathode active material is lithium nickel manganese cobalt oxide (NMC LiNi x Mn y Co z O2), lithium iron phosphate (LFP, LiFePO4), carbon-coated LFP, lithium cobalt oxide (LCO, LiCoO2), lithium manganese oxide (LMO, LiMn2O4), lithium nickel cobalt aluminum oxide (LiNiCoAlO2), lithium titanate (LTO, Li2TiO3), or a mixture thereof, preferably including lithium iron phosphate (LFP, LiFePO4), carbon-coated LFP, or a mixture thereof.

[0020] In one embodiment, the amount of the cathode active material is 70 to 95% by weight, preferably 80 to 95% by weight, based on the total dry weight of the composition.

[0021] In one embodiment, the electrical conductivity improving additive includes carbon nanotubes, graphene, carbon black, activated carbon, or a mixture thereof.

[0022] In one embodiment, the amount of the electrical conductivity improving additive is 1 to 15% by weight, preferably 2 to 10% by weight, more preferably 2 to 5% by weight, based on the total dry weight of the composition.

[0023] In one embodiment, the viscosity modifier includes carboxymethyl cellulose (CMC), water-soluble polysaccharides, water-soluble anionic polysaccharides, polyvinyl alcohol, water-soluble acrylic polymers, or a mixture thereof, preferably the viscosity modifier is CMC. The viscosity modifier is used in the composition to increase or decrease the viscosity of the composition. The amount of the viscosity modifier in the composition is selected such that the composition has a predetermined viscosity.

[0024] In one embodiment, the amount of the viscosity modifier is 0.1 to 1.5% by weight, preferably 0.5 to 1.5% by weight, more preferably 0.5 to 1% by weight, based on the total dry weight of the composition.

[0025] In one embodiment, the water-insoluble binder is in the form of an aqueous dispersion (i.e., a water-insoluble binder dispersion or an aqueous binder), preferably essentially free of organic solvents, and more preferably free of organic solvents.

[0026] In one embodiment, the composition is an aqueous composition.

[0027] In one embodiment, the composition is essentially free of organic solvents, and more preferably free of organic solvents.

[0028] In one embodiment, the water-insoluble binder is polymerized from a combination of monomers selected from alkyl acrylates, alkyl methacrylates and / or optionally substituted styrenes. The monomers may also contain water-soluble monomers such as (meth)acrylic acid in a low ratio.

[0029] The monomers and the ratio of the monomers can be selected such that the composition has a film-forming temperature and a glass transition temperature under process conditions such that the flexibility of the film is obtained and maintained.

[0030] In one embodiment, the water-insoluble binder is formed by polymerizing monomers selected from alkyl acrylates, alkyl methacrylates and / or optionally substituted styrenes, water-soluble monomers such as (meth)acrylic acid, and combinations thereof.

[0031] In one embodiment, the water-insoluble binder is selected from acrylic copolymers, preferably poly(styrene acrylate), more preferably butyl acrylate-styrene copolymer.

[0032] In one embodiment, the water-insoluble binder dispersion contains a stabilizer.

[0033] In one embodiment, the stabilizer is a polymer stabilizer or a surfactant. The stabilizer is anionic, cationic, and / or nonionic. The amount of stabilizer is preferably <15% by weight, more preferably <5% by weight, and even more preferably <2.5% by weight of the dry content of the water-insoluble binder dispersion.

[0034] In one embodiment, the stabilizer includes an anionic surfactant.

[0035] In one embodiment, the amount of water-insoluble binder is 1 to 15% by weight, preferably 2 to 8% by weight, and more preferably 2 to 5% by weight, based on the total dry weight of the composition.

[0036] In one embodiment, the water-insoluble binder has a high solid content, preferably 20-65, more preferably 35-60, and more preferably 46-59. Due to the high solid content, film formation is accelerated during drying.

[0037] In one embodiment, the water-insoluble binder has a small particle size. Due to the small particle size, uniform dispersion of the water-insoluble binder in the composition is ensured.

[0038] In one embodiment, the particle size D50 of the polymer particles in the water-insoluble binder dispersion is in the range of 20 to 400 nm, preferably 40 to 300 nm, more preferably 50 to 200 nm, and even more preferably 55 to 180 nm.

[0039] In one embodiment, the particle size D90 of the polymer particles in the water-insoluble binder dispersion is in the range of 50 to 500 nm, preferably 70 to 400 nm, more preferably 80 to 300 nm, and even more preferably 90 to 280 nm.

[0040] All particle sizes are measured using Malvern's Zetasizer Nano ZS. In relation to this invention, particle size D50 refers to the value relative to the 50th percentile of the volume-based distribution, and particle size D90 refers to the value relative to the 90th percentile of the volume-based distribution.

[0041] In a second aspect, the present invention provides an electrode for a lithium-ion battery comprising an aluminum current collector and at least one active material layer on at least one surface of the aluminum current collector, wherein the at least one active material layer is formed from a positive electrode composition according to the present invention.

[0042] In one embodiment, the aluminum current collector is a carbon-coated aluminum current collector.

[0043] In a third aspect, the present invention provides a method for manufacturing a lithium-ion battery cathode composition, the method being (i) A step of mixing water with at least one viscosity modifier, (ii) A step of adding at least one electrical conductivity improving additive, (iii) A step of adding at least one positive electrode active material, (iv) The step of adding at least one water-insoluble binder.

[0044] In one embodiment, the viscosity modifier, the electrical conductivity improving additive, the positive electrode active material, and the water-insoluble binder are preferably added sequentially in the order of steps (i), (ii), (iii), and (iv). In one embodiment, after the addition of each component, the resulting mixture is mixed.

[0045] Viscosity modifiers, electrical conductivity enhancing additives, positive electrode active materials, and water-insoluble binders may also be added in any other order, or two or more components may be added simultaneously.

[0046] In one embodiment, water is first mixed with at least one viscosity modifier, followed by the addition of at least one water-insoluble binder, then at least one electrical conductivity improving additive, and finally at least one positive electrode active material.

[0047] In one embodiment, the viscosity modifier, the electrical conductivity improving additive, the positive electrode active material, and the water-insoluble binder are the same as those defined above.

[0048] In a preferred embodiment, the lithium-ion battery cathode composition according to the present invention is manufactured by the method of the present invention.

[0049] In a fourth aspect, the present invention provides a method for manufacturing an electrode for a lithium-ion battery positive electrode, the method being: (i) A step of mixing water with at least one viscosity modifier, (ii) A step of adding at least one electrical conductivity improving additive, (iii) A step of adding at least one positive electrode active material, (iv) A step of adding at least one water-insoluble binder, (v) A step of coating the aluminum current collector with the composition, (vi) a step of drying the coated aluminum current collector, including

[0050] In one embodiment, the viscosity modifier, the electrical conductivity improving additive, the positive electrode active material, and the water-insoluble binder are preferably added sequentially in the order of steps (i), (ii), (iii), and (iv). In one embodiment, after the addition of each component, the resulting mixture is mixed.

[0051] Viscosity modifiers, electrical conductivity enhancing additives, positive electrode active materials, and water-insoluble binders may also be added in any other order, or two or more components may be added simultaneously.

[0052] In one embodiment, water is first mixed with at least one viscosity modifier, followed by the addition of at least one water-insoluble binder, followed by the addition of at least one electrical conductivity improving additive, followed by the addition of at least one positive electrode active material.

[0053] In one embodiment, the viscosity modifier, the electrical conductivity improving additive, the positive electrode active material, and the water-insoluble binder are the same as those defined above. In one embodiment, the aluminum current collector is a carbon-coated aluminum current collector.

[0054] The coating of aluminum current collectors can be carried out by any suitable method known to those skilled in the art. Such methods include, for example, slot die, blade, roll-to-roll, and gravure coating techniques.

[0055] Drying of coated aluminum current collectors can be carried out by any suitable method known to those skilled in the art. Such methods include, for example, industrial dryers, oven drying, and vacuum drying.

[0056] In a preferred embodiment, the lithium-ion battery positive electrode according to the present invention is manufactured by the method of the present invention.

[0057] In a fifth aspect, the present invention provides a lithium-ion battery comprising an electrode for a lithium-ion battery according to the present invention.

[0058] In a sixth aspect, the present invention provides the use of the lithium-ion battery cathode composition according to the present invention for electrodes of lithium-ion batteries. [Examples]

[0059] material Cathode active material: Carbon-coated LFP Conductive additive: Carbon black Viscosity modifier: CMC Reference binders: Water-based binders and NMP Binder in the composition of the present invention: Butyl acrylate-styrene copolymer

[0060] Method according to the present invention for producing lithium-ion battery compositions First, the electrode composition was prepared by mixing CMC and deionized water, followed by the addition of a conductive additive. Next, the positive electrode active material was added to the mixture, followed by the addition of an aqueous binder dispersion. The amount of conductive additive was 2% by weight, and the total amount of CMC and aqueous binder was 3.5% by weight (percentages are based on the weight of LFP, for example, the amount of LFP is 100% by weight). The components were mixed at a speed of 4000 rpm using a disperser (IKA Ultra-Turrax T-25 digital). The final solid content of the composition was between 37% and 58% by weight, depending on the binder used.

[0061] Covering for aluminum current collector The prepared composition was coated onto carbon pre-coated aluminum foil using an automatic film applicator (BYK) and a film casting blade (Mitutoyo). 2 mAh / cm² 2 Volume loading and 12.5 mg / cm³ 2 To achieve the desired active mass loading, wet film thicknesses of 225–275 μm were used, depending on the solid content of the slurry. After casting, the aqueous coating was dried in an oven at 60°C for approximately 20 minutes. The electrodes were cut with an EL-Cell cutter (18 mm diameter) and pressed using a hydraulic press (Specac Atlas 25t manual hydraulic press) at 1.2 t / cm². 2 It was then pressed / calendered.

[0062] Electrochemical properties Half-cells were constructed using EL cells, and the stability of the half-cells was evaluated. Figure 1 shows the discharge capacity of LiB half-cells comprising aluminum current collectors coated with the composition of the present invention or the reference composition. In Figure 1, dotted lines represent lab coatings, and solid lines represent pilot coatings. Half-cells comprising aluminum current collectors coated with the composition of the present invention are very stable over 100 to 200 cycles.

[0063] Various embodiments have been shown. It should be understood that, in this specification, the words comprise, include, and contain are used as open-ended expressions not intended to be exclusive.

[0064] The foregoing description provides a complete and useful description of the best mode currently intended by the inventors to carry out the invention, as non-limiting examples of specific implementations and embodiments. However, it will be apparent to those skilled in the art that the invention is not limited to the details of the embodiments shown above and can be carried out in other embodiments using equivalent means or in various combinations of embodiments without departing from the features of the invention.

[0065] Furthermore, some of the features of the embodiments disclosed in advance may be used to their advantage without corresponding use of other features. Therefore, the foregoing description is merely illustrative of the principles of the present invention and is not intended to limit it. Accordingly, the scope of the present invention is limited only by the appended claims.

Claims

1. A lithium-ion battery cathode composition comprising at least one cathode active material, at least one electrical conductivity improving additive, at least one viscosity modifier, and at least one water-insoluble binder.

2. The positive electrode active material is lithium nickel manganese cobalt oxide (NMC, LiNi x Mn y Co z O 2 ), lithium iron phosphate (LFP, LiFePO 4 ), carbon-coated LFP, lithium cobalt oxide (LCO, LiCoO 2 ), lithium manganese oxide (LMO, LiMn 2 O 4 ), lithium nickel cobalt aluminum oxide (LiNiCoAlO 2 ), lithium titanate (LTO, Li 2 TiO 3 ), or a mixture thereof, preferably, lithium iron phosphate (LFP, LiFePO 4 ), carbon-coated LFP, or a mixture thereof, the lithium ion battery positive electrode composition according to claim 1.

3. The lithium-ion battery cathode composition according to claim 1 or 2, wherein the electrical conductivity improving additive comprises carbon nanotubes, graphene, carbon black, activated carbon, or a mixture thereof.

4. The lithium-ion battery cathode composition according to any one of claims 1 to 3, wherein the viscosity modifier comprises carboxymethylcellulose (CMC), water-soluble polysaccharides, water-soluble anionic polysaccharides, polyvinyl alcohol, water-soluble acrylic polymer, or a mixture thereof, preferably the viscosity modifier is CMC.

5. The lithium-ion battery cathode composition according to any one of claims 1 to 4, wherein the water-insoluble binder is formed by polymerizing monomers selected from alkyl acrylates, alkyl methacrylates and / or optionally substituted styrene, water-soluble monomers such as (meth)acrylic acid, and combinations thereof.

6. The lithium-ion battery cathode composition according to any one of claims 1 to 5, wherein the amount of the positive electrode active material is 70 to 95% by weight, preferably 80 to 95% by weight, based on the total dry weight of the lithium-ion battery cathode composition.

7. The lithium-ion battery cathode composition according to any one of claims 1 to 6, wherein the amount of the electrical conductivity improving additive is 1 to 15% by weight, preferably 2 to 10% by weight, and more preferably 2 to 5% by weight, based on the total dry weight of the lithium-ion battery cathode composition.

8. The lithium-ion battery cathode composition according to any one of claims 1 to 7, wherein the amount of the viscosity modifier is 0.1 to 1.5% by weight, preferably 0.5 to 1.5% by weight, and more preferably 0.5 to 1% by weight, based on the total dry weight of the lithium-ion battery cathode composition.

9. The lithium-ion battery cathode composition according to any one of claims 1 to 8, wherein the amount of the water-insoluble binder is 1 to 15% by weight, preferably 2 to 8% by weight, and more preferably 2 to 5% by weight, based on the total dry weight of the lithium-ion battery cathode composition.

10. An electrode for a lithium-ion battery comprising an aluminum current collector and at least one active material layer on at least one surface of the aluminum current collector, wherein the at least one active material layer is formed from the lithium-ion battery positive electrode composition described in any one of claims 1 to 9.

11. The electrode for a lithium-ion battery according to claim 10, wherein the aluminum current collector is a carbon-coated aluminum current collector.

12. A method for manufacturing a lithium-ion battery cathode composition, (i) A step of mixing water with at least one viscosity modifier, (ii) A step of adding at least one electrical conductivity improving additive, (iii) A step of adding at least one positive electrode active material, (iv) A step of adding at least one water-insoluble binder, A method that includes this.

13. A method for manufacturing electrodes for lithium-ion batteries, (i) A step of mixing water with at least one viscosity modifier, (ii) A step of adding at least one electrical conductivity improving additive, (iii) A step of adding at least one positive electrode active material, (iv) A step of adding at least one water-insoluble binder, (v) A step of coating the aluminum current collector with the composition, (vi) A step of drying the coated aluminum current collector, A method that includes this.

14. A lithium-ion battery comprising an electrode for a lithium-ion battery according to claim 10 or 11.

15. Use of the lithium-ion battery cathode composition according to any one of claims 1 to 9 for electrodes for lithium-ion batteries.

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