JP-7856093-B2 - Coated carbon material, negative electrode, and secondary battery

Inventors

• 長谷川 辰弥
• 志藤 慶治
• 加藤 波奈子
• 椋木 一詞
• 畠山 宏毅
• 関 敬一

Assignees

• 三菱ケミカル株式会社

Dates

Publication Date

20260511

Application Date

20220329

Priority Date

20210330

Claims (16)

1. A coated carbon material in which a carbon material is coated with a film, The carbon material is graphite, The true density of the carbon material is 2.2 g/cm³ or more and 2.26 g/cm³ or less. A coated carbon material wherein the coating comprises at least one selected from the compounds (X) and crosslinked compounds of the group of compounds (Y) below. (X): Acetoacetyl group-containing resin (Y): Polyvinyl alcohol-based resin and silicon-containing compound
2. A coated carbon material in which a carbon material is coated with a film, The carbon material is graphite, The coating comprises at least one selected from the following compounds (X) and crosslinked compounds of the group of compounds (Y), A coated carbon material having a true density of 2.2 g/cm³ or more and 2.26 g/cm³ or less. (X): Acetoacetyl group-containing resin (Y): Polyvinyl alcohol-based resins and silicon-containing compounds
3. The coated carbon material according to claim 1 or 2, wherein the pore volume in the range of 10 nm to 1000 nm of the carbon material is 0.05 mL/g or more and 0.3 mL/g or less.
4. The coated carbon material according to claim 1 or 2, wherein the pore volume in the range of 10 nm to 1000 nm of the coated carbon material is 0.01 mL/g or more and 0.3 mL/g or less.
5. The coated carbon material according to any one of claims 1 to 4 , wherein the coating is applied to the basal surface of the carbon material.
6. The coated carbon material according to any one of claims 1 to 5 , wherein the coating comprises the compound of (X).
7. The coated carbon material according to claim 6 , wherein the acetoacetyl group-containing resin contains a hydroxyl group.
8. The coated carbon material according to claim 6 or 7 , wherein the acetoacetyl group-containing resin is a polyvinyl alcohol-based resin containing acetoacetyl groups.
9. The coated carbon material according to any one of claims 1 to 5 , wherein the coating comprises a crosslinked compound of the group of compounds (Y) mentioned above.
10. The coated carbon material according to claim 9 , wherein the polyvinyl alcohol-based resin contains an acetoacetyl group.
11. The coated carbon material according to claim 9 or 10 , wherein the coating further comprises a boron-containing compound.
12. The coated carbon material according to claim 11, wherein the boron element-containing compound is at least one compound selected from boron oxide, metaboric acid, tetraboric acid, borate, and alkoxide having 1 to 3 carbon atoms bonded to boron.
13. A method for manufacturing a coated carbon material in which a carbon material is coated with a film, The carbon material is graphite, The true density of the carbon material is 2.2 g/cm³ or more and 2.26 g/cm³ or less. A method for producing a coated carbon material, comprising the step of mixing a carbon material with the compound (X) and/or the group of compounds (Y) described below. (X): Acetoacetyl group-containing resin (Y): Polyvinyl alcohol-based resin and silicon-containing compound
14. A method for manufacturing a coated carbon material in which a carbon material is coated with a film, The carbon material is graphite, The process includes a step of mixing a carbon material with the compound (X) and/or the group of compounds (Y) below, The true density of the aforementioned carbon coating material is 2.2 g/cm³. 3 2.26g/cm or more 3 The method for manufacturing a coated carbon material is as follows: (X): Acetoacetyl group-containing resin (Y): Polyvinyl alcohol-based resins and silicon-containing compounds
15. The device comprises a current collector and an active material layer formed on the current collector, A negative electrode wherein the active material layer includes a coated carbon material according to any one of claims 1 to 12 .
16. A secondary battery comprising a positive electrode, a negative electrode, and an electrolyte, A secondary battery wherein the negative electrode is the negative electrode described in claim 15 .

Description

This invention relates to a coated carbon material, a negative electrode using the coated carbon material, a secondary battery equipped with the negative electrode, and a method for manufacturing the coated carbon material. In recent years, with the miniaturization of electronic devices, the demand for high-capacity rechargeable batteries has been increasing. In particular, lithium-ion rechargeable batteries, which have higher energy density and superior high-current charge/discharge characteristics compared to nickel-cadmium and nickel-metal hydride batteries, have been attracting attention. While increasing the capacity of lithium-ion rechargeable batteries has been widely studied, in recent years, there has been a growing demand for even higher performance, requiring further increases in capacity, input/output capabilities, and lifespan. For lithium-ion secondary batteries, it is known that carbon materials such as graphite are used as the negative electrode active material. Among these, graphite with a high degree of graphitization is known to be preferable as a negative electrode active material for lithium-ion secondary batteries because, when used as such, it can achieve a capacity close to the theoretical lithium storage capacity of graphite (372 mAh/g), and also offers excellent cost and durability. On the other hand, increasing the density of the active material layer containing the negative electrode material to increase capacity has led to problems such as increased irreversible charge/discharge capacity during the initial cycle, decreased high-current charge/discharge characteristics, and decreased cycle characteristics due to material fracture and deformation. Furthermore, when the above-mentioned carbon materials are used as active materials for the negative electrode of lithium-ion secondary batteries, a protective film called SEI (Solid Electrolyte Interface) is usually formed on the surface of the carbon material through a reaction with polymer compounds used as binders and non-aqueous electrolytes. It is known that SEI prevents contact between the carbon material and the electrolyte, suppresses the decomposition of the electrolyte by the active carbon material, and maintains the chemical stability of the negative electrode surface. However, in lithium-ion secondary batteries using carbon materials as the negative electrode active material, the formation of SEI film and the generation of gases as by-reaction products increased the irreversible charge/discharge capacity during the initial cycle, resulting in a failure to achieve high capacity. Furthermore, the formation of a stable SEI film increased the interfacial resistance at the negative electrode, leading to a decrease in the battery's input/output characteristics. To solve the above problems, for example, Patent Document 1 describes a technology developed to produce spheroidized natural graphite by subjecting natural graphite to a spheroidization treatment (mechanical energy treatment), and further to use the spheroidized natural graphite as a core graphite and coat its surface with amorphous carbon. However, although the spheroidized natural graphite disclosed in Patent Document 1 can be obtained with high capacity and good rapid charge-discharge characteristics, excessive decomposition of the electrolyte occurs, resulting in insufficient initial irreversible capacity and charge-discharge cycle characteristics, as well as a large amount of by-reaction product gases, and further improvements were needed. On the other hand, a known technique for suppressing excessive decomposition of the electrolyte involves coating the carbon material, which is the active material for the negative electrode, with polymers or the like. For example, Patent Document 2 discloses a method for providing a coating layer on the surface of a carbon material, consisting of an ion-conducting polymer such as polyethylene oxide or a water-soluble polymer such as polyvinyl alcohol, with the aim of suppressing the decomposition of the non-aqueous electrolyte and the accumulation of its decomposition products on the negative electrode surface, thereby improving the initial charge-discharge efficiency and charge-discharge cycle characteristics. Furthermore, with the aim of suppressing the decomposition of the non-aqueous electrolyte and improving the initial charge-discharge efficiency, Patent Document 3 discloses a method for impregnating spheroidal natural graphite, which has surface oxygen functional groups to improve adhesion with water-soluble polymers, with a water-soluble polymer. Patent Document 4 discloses a method for impregnating the surface of a carbon material with a coating comprising boron atoms and a crosslinking portion having a C-O-C bond and interposed between the boron atoms and the negative electrode active material, with the aim of suppressing the increase in internal resistance after charge-discharge cycles and improving cycle characteristics.