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CN-121064461-B - Softening agent for adhesive, positive electrode plate and electrochemical device

CN121064461BCN 121064461 BCN121064461 BCN 121064461BCN-121064461-B

Abstract

The invention provides a softening agent for an adhesive, a positive electrode plate and an electrochemical device. The softening agent comprises a copolymer, the number average molecular weight of the copolymer is 200-100000, the glass transition temperature Tg of the copolymer is-50-10 ℃, the main chain of the copolymer comprises a first structural unit from a polyol monomer and a second structural unit from a carbonate monomer, and the end parts of the two ends of the copolymer comprise polar groups. The positive electrode plate prepared by the flexibilizer for the adhesive has good flexibility, can effectively inhibit the problems of coating cracking, rolling a rolled strip, winding light transmission and the like of the positive electrode plate, and can also improve the compaction density of the positive electrode plate, thereby improving the energy density of a lithium ion battery.

Inventors

  • ZHAN CHENGBO
  • ZHOU MING
  • JIA BAOQUAN
  • WANG JIAN

Assignees

  • 深圳好电科技有限公司

Dates

Publication Date
20260512
Application Date
20251110

Claims (6)

  1. 1. A softening agent for an adhesive is characterized in that the adhesive is at least one selected from polyvinylidene fluoride, polyacrylonitrile, polyimide, polyacrylic acid and polyacrylate, the softening agent comprises a copolymer, the number average molecular weight of the copolymer is 1000-12000, the glass transition temperature Tg of the copolymer is-50 to-20 ℃, the main chain of the copolymer comprises a first structural unit from a polyol monomer and a second structural unit from a carbonate monomer, and the end parts of two ends of the copolymer comprise polar groups; the mass ratio of the polyol monomer to the carbonate monomer is (40-85) (15-60); The polyol monomer comprises dihydric alcohol and an oligomer containing terminal hydroxyl groups, the mass ratio of the dihydric alcohol to the oligomer is (2-20): (20-83), the oligomer is selected from polyethylene glycol 400, polyethylene glycol 1000, polyester polyol 1000 or hydroxy silicone oil Mn-550, the dihydric alcohol is selected from butanediol, tetrafluorobutanediol, bisphenol A, diethanolamine, 1, 4-cyclohexanediol or 2,2' -dithiodiethanol, and the carbonate monomer is selected from at least one of dimethyl carbonate, dibutyl carbonate and diphenyl carbonate.
  2. 2. The softening agent for a binder according to claim 1, wherein the polar group is at least one selected from-OH, -COOH or a salt formed after neutralization, -PO 3 H or a salt formed after neutralization, -SO 3 H or a salt formed after neutralization, -NH 2 、-NHCH 3 、-NH 4 + 、-CN、-CONH 2 .
  3. 3. The softening agent for adhesives according to claim 2, wherein the polar group is at least one selected from the group consisting of-OH, -COOH, -NH 2 , the polar group is at least one selected from the group consisting of-CN, and the polar group is at least one selected from the group consisting of-COOH, -CONH 2 .
  4. 4. The positive electrode plate is characterized by comprising a positive electrode current collector and a positive electrode active material layer arranged on at least one side surface of the positive electrode current collector, wherein the positive electrode active material layer comprises a positive electrode active material, a binder, a conductive agent and a softening agent according to any one of claims 1-3, and the binder is at least one selected from polyvinylidene fluoride, polyacrylonitrile, polyimide, polyacrylic acid and polyacrylate.
  5. 5. The positive electrode sheet according to claim 4, wherein the mass of the softening agent is 2.5 to 50% of the mass of the binder.
  6. 6. An electrochemical device comprising the positive electrode sheet according to claim 4 or 5.

Description

Softening agent for adhesive, positive electrode plate and electrochemical device Technical Field The invention belongs to the technical field of battery materials, and particularly relates to a softening agent for an adhesive, a positive electrode plate and an electrochemical device. Background The positive electrode is an important component of a lithium ion battery. In order to improve the energy density of the positive electrode, three development directions are mainly that firstly, the specific capacity and working voltage platform of an active material are improved, secondly, the mass ratio of the active material in a pole piece is improved, the consumption of auxiliary materials such as a binder, a conductive agent and the like is reduced, and thirdly, the compaction density or the coating thickness of the pole piece is improved. The specific capacity of the active material and the improvement of the working voltage platform almost reach the bottleneck, and the application of the novel binder and the conductive agent enables the mass ratio of the active material in the pole piece to be gradually improved, but the current limit is also approached. Therefore, when a battery cell factory uses the improvement of the compaction density and the coating thickness of the pole piece as the key attack direction of the improvement of the energy density of the positive electrode. However, with the increase of the compaction density and the coating thickness, the brittleness of the positive electrode sheet is remarkably increased, and the problems of coating cracking, rolling of the belt, winding and light transmission and the like are difficult to solve in the process. The positive pole piece mainly comprises an active substance, a conductive agent, a binder and a dispersing agent. Wherein, the binder is usually polyvinylidene fluoride (PVDF) and the mass ratio of the binder in the pole piece is 1% -3%. The positive electrode binder is usually a semi-crystalline polymer, has higher modulus, thus having poorer flexibility and being a main source of brittleness of the pole piece. In order to reduce brittleness of the positive electrode binder and increase flexibility, one scheme is to modify the binder by copolymerization, grafting, blending, etc., but the cost is high, the process is complex, and other adverse effects may be brought, such as increased swelling of electrolyte, poor thermal stability, etc. The other proposal is that a softening agent is added into the pole piece, and the softening agent has the function of embedding between polymer chains of the binder, weakening the interaction between the chains and reducing the crystallinity of the binder. The second scheme has simple process and good compatibility. However, the softening agent disclosed in the prior art can improve the flexibility of the positive electrode plate and increase the compaction density or coating thickness of the electrode plate, but some materials are triphenylbenzene derivatives, the main structure rigidity is high, the effect of reducing the brittleness of the binder is limited, the material has fewer groups which interact with the binder, the interaction force with the binder is weak, and the effect of reducing the crystallinity of the binder is general. Disclosure of Invention In order to solve the problems of the existing softening agent, the invention provides a softening agent for an adhesive, a positive electrode plate and an electrochemical device. The aim of the invention is realized by the following technical scheme. In a first aspect, the invention provides a softening agent for an adhesive, the softening agent comprises a copolymer, the number average molecular weight of the copolymer is 200-100000, the glass transition temperature Tg of the copolymer is-50-10 ℃, the main chain of the copolymer comprises a first structural unit from a polyol monomer and a second structural unit from a carbonate monomer, and the end parts of two ends of the copolymer comprise polar groups. Further, the polar group is selected from at least one of-OH, -COOH or a salt formed after neutralization, -PO 3 H or a salt formed after neutralization, -SO 3 H or a salt formed after neutralization, -NH 2、-NHCH3、-NH4+、-CN、-CONH2. Further, the adhesive for polyvinylidene fluoride, polyacrylic acid and polyacrylate is characterized in that the polar group is at least one selected from-OH, -COOH and-NH 2, the adhesive for polyacrylonitrile is at least one selected from-CN, and the adhesive for polyimide is at least one selected from-COOH and-CONH 2. Further, the mass ratio of the polyol monomer to the carbonate monomer is (40-85): (15-60). Further, the polyol monomer comprises dihydric alcohol and an oligomer containing terminal hydroxyl groups, the mass ratio of the dihydric alcohol to the oligomer is (20-83), and the carbonate monomer is at least one selected from dimethyl carbonate, dibutyl carbonate and diphenyl carbonate. Further, the structure of