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CN-122011272-A - Soap-free emulsion polymerization method, polymer emulsion and application thereof

CN122011272ACN 122011272 ACN122011272 ACN 122011272ACN-122011272-A

Abstract

The invention relates to the technical field of battery materials, in particular to a soap-free emulsion polymerization method and application of a polymer emulsion prepared by the method in a battery. The soap-free emulsion polymerization method provided by the invention is not applicable to an extra emulsifier, the polymerization step is divided into two steps, and the characteristic that the reaction monomer simultaneously contains a hydrophilic monomer and a lipophilic monomer is utilized to form an amphiphilic polymer emulsifier in the first step, and then the polymer emulsion required by the second step is formed. And during the process, the weight average molecular weight of the high molecular emulsifier obtained in the first step is controlled, so that the stability of the polymer emulsion is ensured.

Inventors

  • Xu Chunzi
  • YANG QINGYUN
  • WANG HUI
  • WU JING
  • CHANG XIAOLONG

Assignees

  • 重庆硕盈峰新材料科技有限公司

Dates

Publication Date
20260512
Application Date
20231229

Claims (10)

  1. 1. A soap-free emulsion polymerization process comprising the steps of: Step 1, preparing a high molecular emulsifier, namely dividing total reaction monomers into two parts, and carrying out polymerization reaction on a first part of monomers under the atmosphere of inert gas to form the high molecular emulsifier; Wherein the first part of monomers account for 10% -30% of the total reaction monomer molar quantity; the total reaction monomer comprises 25% -45% of acrylic monomers, 10% -30% of acrylic monomers and 35% -55% of nitrile monomers according to mole percentage, wherein the mole ratio of the acrylic monomers, the acrylic monomers and the nitrile monomers in the first part of monomers, the second part of monomers and the total reaction monomer is the same; And step 2, dropwise adding a second part of monomers into the reaction system in the step 1, and reacting to obtain the white stable emulsion.
  2. 2. The soap-free emulsion polymerization method according to claim 1, wherein in step 1, the neutralization degree of the acrylic monomer is 10% to 60%.
  3. 3. The soap-free emulsion polymerization method according to claim 2, wherein in step 1, the degree of neutralization of the acrylic monomer is 30% -40%.
  4. 4. The soap-free emulsion polymerization method according to claim 1, wherein the weight average molecular weight of the high molecular emulsifier obtained in the step 1 is 8775-17867 g/mol.
  5. 5. The soap-free emulsion polymerization method according to claim 1, wherein in step 1, the initiator is persulfate, and the amount of the initiator is 0.2% -0.4% of the total reaction monomer mass.
  6. 6. The soap-free emulsion polymerization method according to any one of claims 1 to 5, wherein in the step 2, carboxymethylcellulose salt accounting for 0.01 to 0.2% of the total reaction monomer mass is added in the process of dropwise adding the second part of monomers.
  7. 7. The soap-free emulsion polymerization method according to claim 6, wherein the weight average molecular weight of the carboxymethyl cellulose salt is 10700-50900 g/mol.
  8. 8. The soap-free emulsion polymerization method according to any one of claims 1 to 5, characterized in that: The acrylic monomer is at least one selected from acrylic acid and methacrylic acid; the acrylic ester monomer is selected from one or more of butyl acrylate, butyl methacrylate, isooctyl acrylate, isooctyl methacrylate, propyl acrylate, propyl methacrylate, dodecyl acrylate, dodecyl methacrylate, tetradecyl acrylate, tetradecyl methacrylate, hexadecyl acrylate, hexadecyl methacrylate, octadecyl acrylate and octadecyl methacrylate; the nitrile monomer is one or more selected from acrylonitrile, 3-pentenenitrile, 2-pentenenitrile, 4-pentenenitrile, 2-furan acrylonitrile, 5-capronitrile, 6-heptenenitrile and citronellonitrile.
  9. 9. A polymer emulsion prepared by the soap-free emulsion polymerization method of any one of claims 1 to 8.
  10. 10. Use of a polymer emulsion according to claim 9 as a negative electrode binder for lithium batteries.

Description

Soap-free emulsion polymerization method, polymer emulsion and application thereof Technical Field The invention relates to the technical field of battery materials, in particular to a preparation method of polymer emulsion used as a lithium battery binder. Background The lithium battery has the characteristics of high voltage platform, high energy density, long service life, no pollution and the like, and is widely used in the fields of new energy automobiles, aerospace, digital equipment, household appliances and the like. In lithium ion batteries, the binder, although not at a high ratio, uniformly disperses and adheres the active material and the conductive material to the current collector, allowing good connectivity therebetween. Meanwhile, the adhesive can influence the cycle performance and the quick charge and discharge capacity of the lithium battery, and the pole piece has good mechanical capacity and processability. It can be seen that the binder plays an important role in the lithium ion battery. Among the binders for batteries, polyvinylidene fluoride (PVDF), styrene-butadiene rubber (SBR), polyacrylonitrile (PAN), polyacrylic acid (PAA), polypropylene emulsion, polytetrafluoroethylene, and the like, and modified copolymers of the above polymers are commonly used. Among these binders, PAA, as a water-based binder, greatly reduces costs due to the solvent being water, and can realize non-toxic and harmless production. On the other hand, the PAA main chain contains rich carboxyl groups, so that the transmission performance of lithium ions can be greatly improved, and in addition, the PAA has lower expansibility in electrolyte, and the integrity of an electrode can be ensured. Methods for producing PAA are solution polymerization, bulk polymerization, suspension polymerization and emulsion polymerization. The emulsion polymerization reaction process mostly uses water as a solvent, avoids expensive or toxic solvents, meets the requirement of environment-friendly production, and has higher polymerization rate and higher molecular weight compared with other reactions. This is due to the large number of latex particles present during emulsion polymerization, which enclose a large number of free radicals, which results in a large polymerization rate for emulsion polymerization. On the other hand, because of the effect of electrostatic repulsion, different latex particles are difficult to agglomerate together, so that the free radical chains among the latex particles cannot collide, and the chain termination rate is basically equal to zero. However, the conventional emulsion polymerization method is complicated in process, high in cost and has a certain influence on the environment due to the use of a large amount of emulsifier. The use of the emulsifier affects the film forming property, water resistance, adhesiveness, and the like of the adhesive to some extent. Therefore, the development of the emulsifier-free synthetic polypropylene binder is of great significance. The use of soap-free emulsion polymerization can reduce cost, simplify process, avoid the post-treatment process of emulsifier and potential environmental hazard, and satisfy the current environmental protection trend. However, the polyacrylic emulsion obtained by the existing soap-free emulsion polymerization method is poor in stability, the polyacrylic emulsion is used as a lithium battery binder, the prepared slurry is easy to settle, demulsification is easy to occur under high-speed shearing, the slurry is settled, the coating of the pole piece is uneven, the adhesive force on the pole piece is unevenly distributed, the adhesion state between an active material and a current collector is affected, and the active material falls off on the current collector to further affect the battery performance and the cycle performance. Disclosure of Invention A first aspect of the present invention is directed to a soap-free emulsion polymerization process comprising the steps of: The preparation method comprises the steps of 1, dividing total reaction monomers into two parts, and carrying out polymerization reaction on first part of monomers in an inert gas atmosphere to form the high polymer emulsifier, wherein the first part of monomers account for 10% -30% of the total reaction monomers in terms of mole percent, the total reaction monomers comprise 25% -45% of acrylic monomers, 10% -30% of acrylic monomers and 35% -55% of nitrile monomers in terms of mole percent, and the mole ratios of the acrylic monomers, the acrylic monomers and the nitrile monomers in the first part of monomers, the second part of monomers and the total reaction monomers are the same. And step 2, dropwise adding a second part of monomers into the reaction system in the step 1, and reacting to obtain the white stable emulsion. Preferably, the weight average molecular weight of the high molecular emulsifier obtained in the step 1 is 8775-17867 g/mol. Optionally, in step 1,