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US-20260128473-A1 - SEPARATOR, PREPARATION METHOD, SECONDARY BATTERY, AND ELECTRIC DEVICE

US20260128473A1US 20260128473 A1US20260128473 A1US 20260128473A1US-20260128473-A1

Abstract

A separator, a preparation method, a secondary battery, and an electric device. The separator includes a first porous base film, where the first porous base film is polyolefin, and a viscosity-average molecular weight of the first porous base film is greater than or equal to 1,200,000 g/mol, such that the separator has higher puncture strength; a degree of branching of the first porous base film is less than or equal to 5%.

Inventors

  • Quan Li
  • Jianrui YANG
  • Chengdong Sun
  • Chuying OUYANG
  • Siying HUANG
  • Yaohui Wang

Assignees

  • CONTEMPORARY AMPEREX TECHNOLOGY CO., LIMITED

Dates

Publication Date
20260507
Application Date
20260102
Priority Date
20230706

Claims (20)

  1. 1 . A separator, comprising a first porous base film, wherein the first porous base film is polyolefin, a viscosity-average molecular weight of the first porous base film is greater than or equal to 1,200,000 g/mol, and a degree of branching of the first porous base film is less than or equal to 5%.
  2. 2 . The separator according to claim 1 , wherein the viscosity-average molecular weight of the first porous base film is greater than or equal to 1,500,000 g/mol, and optionally 2,000,000 to 3,000,000 g/mol.
  3. 3 . The separator according to claim 1 , wherein the degree of branching of the first porous base film is less than or equal to 2%, and optionally less than or equal to 1%.
  4. 4 . The separator according to claim 1 , wherein a degree of polymerization of the first porous base film is greater than or equal to 50,000, and optionally 80,000 to 200,000.
  5. 5 . The separator according to claim 1 , wherein a crystallinity of the first porous base film is 40% to 90%, and optionally 75% to 85%.
  6. 6 . The separator according to claim 1 , wherein a puncture strength of the first porous base film is greater than or equal to 300 gf, and optionally 350 gf to 450 gf.
  7. 7 . The separator according to claim 1 , wherein a thickness of the first porous base film is 1 μm to 12 μm, and optionally 3 μm to 6 μm.
  8. 8 . The separator according to claim 1 , wherein: a porosity of the first porous base film is 20% to 50%, and optionally 30% to 40%; and/or an air permeability of the first porous base film is 100 sec/100 cc to 300 sec/100 cc, and optionally 200 sec/100 cc to 300 sec/100 cc; and/or a number-average molecular weight of the first porous base film is greater than or equal to 1,400,000, and optionally 1,600,000 to 2,400,000; and/or a weight-average molecular weight of the first porous base film is greater than or equal to 1,000,000 g/mol, and optionally 1,200,000 g/mol to 2,000,000 g/mol.
  9. 9 . The separator according to claim 1 , further comprising: a porous coating, the porous coating being disposed on at least one surface of the first porous base film, and the porous coating comprising a binder; optionally, the porous coating comprises a binder and filler particles.
  10. 10 . The separator according to claim 1 , further comprising: a porous coating and a second porous base film, the porous coating being located between the first porous base film and the second porous base film; optionally, the porous coating comprises a binder; more optionally, the porous coating comprises a binder and filler particles.
  11. 11 . The separator according to claim 10 , wherein: the binder comprises at least one of polyacrylate, polyacrylic acid, polytetrafluoroethylene, polyvinylidene fluoride, a vinylidene fluoride-trichloroethylene copolymer, polyvinylpyrrolidone, polyvinyl acetate, an ethylene-vinyl acetate copolymer, polyethylene oxide, polyarylate, carboxymethylcellulose, hydroxypropylcellulose, regenerated cellulose, cellulose acetate, cellulose acetate propionate, cellulose acetate butyrate, polyacrylonitrile, polyvinylalcohol, polyethylene, polypropylene, starch, and cyanoethyl branched starch; and/or the filler particles comprise at least one of inorganic particles, organic particles, and organo-metallic framework materials.
  12. 12 . The separator according to claim 11 , wherein the second porous base film comprises at least one of polyolefin, polytetrafluoroethylene, polyvinyl fluoride, polyethylene terephthalate, polyimide, and polyetheretherketone.
  13. 13 . The separator according to claim 10 , wherein: the viscosity-average molecular weight of the first porous base film is greater than a viscosity-average molecular weight of the second porous base film; optionally, the viscosity-average molecular weight of the second porous base film is 100,000 g/mol to 2,000,000 g/mol, and more optionally 300,000 g/mol to 800,000 g/mol; and/or the degree of branching of the first porous base film is less than a degree of branching of the second porous base film; optionally, the degree of branching of the second porous base film is less than or equal to 90%, and more optionally 10% to 40%; and/or the degree of polymerization of the first porous base film is greater than a degree of polymerization of the second porous base film; optionally, the degree of polymerization of the second porous base film is less than or equal to 8000, and more optionally 400 to 1000; and/or a melting point of the first porous base film is lower than a melting point of the second porous base film; optionally, the melting point of the second porous base film is 160° C. to 350° C., and more optionally 170° C. to 320° C.; and/or the crystallinity of the first porous base film is greater than a crystallinity of the second porous base film; optionally, the crystallinity of the second porous base film is 20% to 70%, and more optionally 30% to 45%; and/or the puncture strength of the first porous base film is greater than a puncture strength of the second porous base film; optionally, a ratio of the puncture strength of the first porous base film to the puncture strength of the second porous base film is greater than or equal to 2.5; optionally, the puncture strength of the second porous base film is greater than or equal to 70 gf, and more optionally 100 gf to 300 gf.
  14. 14 . The separator according to claim 1 , wherein the separator satisfies at least one of the following (1) to (4): (1) a transverse direction elongation at break of the separator is greater than or equal to 80%, optionally greater than or equal to 100%, and more optionally 100% to 300%; (2) a machine direction elongation at break of the separator is greater than or equal to 40%, optionally greater than or equal to 60%, and more optionally 60% to 200%; (3) a transverse direction tensile strength of the separator is greater than or equal to 1500 kgf/cm 2 , optionally greater than or equal to 2000 kgf/cm 2 , and more optionally 2000 kgf/cm 2 to 4000 kgf/cm 2 ; and (4) a machine direction tensile strength of the separator is greater than or equal to 1500 kgf/cm 2 , optionally greater than or equal to 2000 kgf/cm 2 , and more optionally 2000 kgf/cm 2 to 4000 kgf/cm 2 .
  15. 15 . A method for preparing the separator according to claim 1 , comprising: providing a polymer powder; mixing the polymer powder with lubricating oil, an antioxidant, and a crosslinking agent to obtain a mixture, and melting the mixture to obtain a melt; and casting and stretching the melt, and extracting the lubricating oil to obtain the first porous base film; wherein the first porous base film is polyolefin, the viscosity-average molecular weight of the first porous base film is greater than or equal to 1,200,000 g/mol, and the degree of branching of the first porous base film is less than or equal to 5%.
  16. 16 . The method according to claim 15 , wherein the method satisfies at least one of the following (1) to (4): (1) a mass fraction of the polymer powder in the mixture is 5% to 40%, and optionally 20% to 35%; (2) a mass fraction of the lubricating oil in the mixture is 50% to 90%, and optionally 60% to 75%; (3) a mass fraction of the antioxidant in the polymer powder is 0.3% to 1.0%, and optionally 0.5% to 1.0%; and (4) a mass fraction of the crosslinking agent in the polymer powder is 3% to 10%, and optionally 3% to 5%.
  17. 17 . The method according to claim 15 , wherein the method satisfies at least one of the following (1) to (3): (1) the polymer powder comprises a polyolefin powder; the lubricating oil comprises white oil and/or mineral oil; the antioxidant comprises at least one of 4,4-thiobis(6-tert-butyl-m-cresol), dibutylhydroxytoluene, phosphite esters, tert-butylhydroquinone, n-octadecyl β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, 1,1,3-tris(2-methyl-4-hydroxy-5-tert-butylphenyl) butane, 2-tert-butyl-6-methylphenol, N,N′-di-β-naphthyl-p-phenylenediamine, dilauryl thiodipropionate, tris(nonylphenyl) phosphite, and triphenyl phosphite; the crosslinking agent comprises a compound containing at least two unsaturated groups; (2) the polymer powder has a viscosity-average molecular weight of greater than or equal to 1,200,000 g/mol and a degree of branching of less than or equal to 5%; and (3) in the step of melting the mixture to obtain the melt, the mixture is mixed and melted within a temperature range of 160° C. to 250° C., and optionally 190° C. to 230° C.
  18. 18 . A secondary battery, comprising the separator according to claim 1 .
  19. 19 . The secondary battery according to claim 18 , further comprising: a positive electrode plate and a negative electrode plate wherein the separator is disposed between the positive electrode plate and the negative electrode plate, and the first porous base film faces the negative electrode plate.
  20. 20 . An electric device, comprising the secondary battery according to claim 18 .

Description

CROSS-REFERENCE TO RELATED APPLICATIONS The present application is a continuation of International Application No. PCT/CN2023/134840, filed on Nov. 28, 2023, which claims priority to Chinese Patent Application No. 202310826484.4 entitled “SEPARATOR, PREPARATION METHOD, SECONDARY BATTERY, AND ELECTRIC DEVICE” filed on Jul. 6, 2023, which are incorporated herein by reference in their entirety. TECHNICAL FIELD The present application belongs to the technical field of secondary batteries, and particularly relates to a separator, a preparation method, a secondary battery, and an electric device. BACKGROUND The secondary batteries have the outstanding characteristics of light weight, no pollution and negligible memory effect, and thus are widely applied to various consumer electronic products and electric vehicles. With the continuous development of new energy industries, users put higher use demands on the reliability of secondary batteries. Therefore, how to make the secondary batteries have better reliability is a problem to be solved urgently. SUMMARY In view of the technical problems in the background art, the present application provides a separator, a preparation method, a secondary battery, and an electric device, aiming to improve the reliability of the secondary battery. In order to achieve the above objective, a first aspect of the present application provides a separator including a first porous base film, where the first porous base film is polyolefin, a viscosity-average molecular weight of the first porous base film is greater than or equal to 1,200,000 g/mol, and a degree of branching of the first porous base film is less than or equal to 5%. Compared with the related art, the present application at least includes the following beneficial effects: In the separator provided by the present application, the first porous base film is polyolefin, and the viscosity-average molecular weight of the first porous base film is greater than or equal to 1,200,000 g/mol, such that the separator has higher puncture strength; because the degree of branching of the first porous base film is less than or equal to 5%, the molecular chain sequences in the first porous base film are easy to form ordered arrangement, and thus the regularity of the molecular chains is enhanced, thereby further improving the puncture strength of the separator. Therefore, the separator provided by the present application can reduce the risk that the separator is punctured by metal dendrites, prolong the cycle life of the secondary battery, and improve the reliability of the secondary battery. In any embodiment of the present application, the viscosity-average molecular weight of the first porous base film is greater than or equal to 1,500,000 g/mol, and optionally 2,000,000 g/mol to 3,000,000 g/mol, such that the separator has higher puncture strength, and can reduce the risk that the separator is punctured by metal dendrites, prolong the cycle life of the secondary battery, and improve the reliability of the secondary battery. In any embodiment of the present application, the degree of branching of the first porous base film is less than or equal to 2%, and optionally less than or equal to 1%, such that the molecular chain sequences in the first porous base film are easy to form ordered arrangement, and thus the regularity of the molecular chains is enhanced, thereby further improving the puncture strength of the separator. Therefore, the risk that the separator is punctured by metal dendrites can be reduced, the cycle life of the secondary battery is prolonged, and the reliability of the secondary battery is improved. In any embodiment of the present application, a degree of polymerization of the first porous base film is greater than or equal to 50,000, and optionally 80,000 to 200,000, such that the separator has higher puncture strength, can reduce the risk that the separator is punctured by metal dendrites, prolong the cycle life of the secondary battery, and improve the reliability of the secondary battery. In any embodiment of the present application, a crystallinity of the first porous base film is 40% to 90%, and optionally 75% to 85%, such that the separator has higher puncture strength, and can reduce the risk that the separator is punctured by metal dendrites, prolong the cycle life of the secondary battery, and improve the reliability of the secondary battery. In any embodiment of the present application, a puncture strength of the first porous base film is greater than or equal to 300 gf, and optionally 350 gf to 450 gf, such that the risk that the separator is punctured by metal dendrites can be reduced, the cycle life of the secondary battery is prolonged, and the reliability of the secondary battery is improved. In any embodiment of the present application, the thickness of the first porous base film is 1 μm to 12 μm, and optionally 3 μm to 6 μm, such that the risk that the separator is punctured by metal dendrites can b