KR-20260065963-A - COMPOSITION FOR SECONDARY BATTERY

Abstract

A composition for a secondary battery is provided using a polymer having a structure derived from 1,2-difluoroethylene. The composition for a secondary battery comprises a fluorine-containing polymer and a solvent, wherein the fluorine-containing polymer is a polymer containing a structural unit represented by the following general formula (1).

Inventors

• 후루타니 다카히로
• 야노 료오이치
• 후쿠시마 간타

Assignees

• 다이킨 고교 가부시키가이샤

Dates

Publication Date

20260511

Application Date

20230314

Priority Date

20220323

Claims (8)

1. A composition for a separator of a secondary battery containing a fluorine-containing polymer and a solvent, A composition for a separator of a secondary battery, characterized in that the above-mentioned fluorine-containing polymer is a polymer containing a structural unit represented by the following general formula (1) and a structural unit represented by the following general formula (2). ( R1 is hydrogen, fluorine, a partially or wholly fluorinated hydrocarbon group with 5 or fewer carbon atoms, or an OR 5 group (the R5 group is a partially or wholly fluorinated hydrocarbon group with 5 or fewer carbon atoms). R2 , R3 , and R4 are each independently hydrogen or fluorine.)
2. A composition for a separator of a secondary battery, wherein, in claim 1, the structural unit represented by the general formula (2) is at least one structural unit selected from the group consisting of structural units represented by the following general formulas (3) to (8).
3. A composition for a separator of a secondary battery according to claim 1 or 2, wherein the weight average molecular weight of the fluorine-containing polymer is 50,000 to 50,000,000.
4. A composition for a separator of a secondary battery according to claim 1 or 2, wherein the ratio of structural units represented by general formula (1) in the fluorine-containing polymer is 0.1 mol% or more and 99.9 mol% or less.
5. A composition for a separator of a secondary battery according to claim 1 or 2, wherein the solvent is at least one compound selected from the group consisting of ester compounds, ketone compounds and amide compounds.
6. A method for forming a separator of a secondary battery having a process of applying a slurry onto a substrate and performing heat drying, wherein the slurry contains a composition for a separator of a secondary battery as described in claim 1 or 2.
7. A separator for a secondary battery containing a polymer containing a structural unit represented by the following general formula (1) and a structural unit represented by the following general formula (2). ( R1 is hydrogen, fluorine, a partially or wholly fluorinated hydrocarbon group with 5 or fewer carbon atoms, or an OR 5 group (the R5 group is a partially or wholly fluorinated hydrocarbon group with 5 or fewer carbon atoms). R2 , R3 , and R4 are each independently hydrogen or fluorine.)
8. A secondary battery characterized by having a separator for a secondary battery as described in claim 7.

Description

Composition for Secondary Battery The present disclosure relates to a composition for a secondary battery. Fluorine-containing polymers are polymers used in a wide variety of fields. Well-known monomers for manufacturing these polymers include tetrafluoroethylene, vinylidene fluoride, and hexafluoropropylene. In addition, the method of manufacturing 1,2-difluoroethylene is disclosed in Patent Document 1. In addition, Non-Patent Document 1 discloses the said compound and a polymer using the said compound. Meanwhile, it is known that fluorine-containing resins such as polyvinylidene fluoride are used as binders in electrodes of secondary batteries (Patent Document 2, etc.). The present disclosure will be described in detail below. The present disclosure is a composition for a secondary battery suitable for forming electrodes, electrolyte layers, or separators, mainly for secondary batteries. For example, in forming an electrode or electrolyte layer for a sulfide-based solid battery, a method is known in which a slurry containing sulfide-based solid electrolyte particles, a binder, and a solvent is applied and dried, and then pressed. When forming a good electrode or electrolyte layer by this method, the selection of the binder and solvent used in combination with the sulfide-based solid electrolyte particles becomes important. When using sulfide-based solid electrolyte particles, it is necessary to select one that does not react with the sulfide-based solid electrolyte particles, which limits the types of solvents that can be used. Furthermore, in order to prepare a slurry using such a solvent, it is necessary to select a binder that is soluble in the said solvent. Therefore, it is desirable to use a binder having suitable solubility in a solvent as a binder. However, most of the known binders had low solubility in solvents. Because of this, they could not be sufficiently dissolved in a slurry containing sulfide-based solid electrolyte particles, and thus could not fully perform their function as binders. In addition, if polyvinylidene fluoride, a relatively inexpensive and general-purpose polymer, is used as the above-mentioned binder, gelation may occur in the slurry. If the binder gels, a uniform slurry cannot be obtained, so it cannot perform its function as a binder. Such gelation is particularly likely to occur in slurries using positive electrode active materials containing lithium hydroxide. Some oxide-based solid electrolytes are susceptible to moisture and react with moisture in the air to transform into lithium hydroxide, which is presumed to become an alkaline component that causes gelation. Conventionally, it has been known that gelation occurs, particularly in the preparation of slurries used for manufacturing electrode materials, and many attempts have been made to improve this. In the present disclosure, a composition for a secondary battery suitable for manufacturing a battery is obtained by using a fluorine-containing polymer having a structure derived from 1,2-difluoroethylene, which has good solubility performance, as a binder. Furthermore, the composition for a secondary battery disclosed in this invention has excellent dispersibility, stability, gelation properties, and solid content improvement properties regarding viscosity. In addition, low resistance of the electrode surface can be expected. Furthermore, since a low boiling point solvent can be used, there are advantages such as lowering the drying temperature or shortening the drying time during the manufacturing process of electrodes, etc. The fluorine-containing polymer used in the present disclosure is a polymer having a structure represented by the following general formula (1), and may be a homopolymer or copolymer. The structure represented by the above general formula (1) is the following general formula (10) It is a structure obtained by polymerization using 1,2-difluoroethylene having a structure represented as shown as a monomer. Although 1,2-difluoroethylene is a known compound, conventionally, its use as a refrigerant has been mainly considered, and it has rarely been considered as a polymerization monomer. In addition, 1,2-difluoroethylene can be copolymerized with other monomers by a general method. Also, the copolymerization ratio can be easily changed. The above fluorine-containing polymer is a polymer consisting only of the structure represented by the above general formula (1), or a copolymer having a structural unit represented by the above general formula (1). In addition, 1,2-difluoroethylene exists as a trans body (E body) and a cis body (Z body). Therefore, when only the trans form is used as a raw material, when only the cis form is used as a raw material, or when a mixture thereof is used as a raw material, a difference in stereochemical configuration occurs. The above-mentioned fluorine-containing polymer may be any of these. In addition, it may be a mixture of any proportion thereof. When the above fluorin