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EP-3790079-B1 - SECONDARY BATTERY SEPARATOR COMPRISING DISPERSANT, AND MANUFACTURING METHOD THEREFOR

EP3790079B1EP 3790079 B1EP3790079 B1EP 3790079B1EP-3790079-B1

Inventors

  • KIM, MYEONG SOO
  • YOON, SU JIN

Dates

Publication Date
20260506
Application Date
20200417

Claims (6)

  1. A separator for a secondary battery comprising: a porous separator substrate comprising a polyolefin-based material; and a coating layer coated on at least one surface of the separator substrate, wherein the coating layer is a dry form of a slurry comprising a binder, an inorganic material, a mixed solvent comprising at least two solvents, and a dispersant, wherein the inorganic material is a metal hydroxide, and the dispersant is tannic acid, an amount of the dispersant is 0.1 wt% to 0.3 wt%, the mixed solvent comprises an alcohol, wherein the alcohol is an alcohol having 1 to 5 carbon atoms, and an amount of the alcohol is 5 wt% to 20 wt% based on a total amount of the mixed solvent.
  2. The separator for a secondary battery according to claim 1, wherein the metal hydroxide is represented by the following formula (1), M(OH) x (1) wherein, in formula (1), M is B, Al, Mg, Co, Cu, Fe, Ni, Ti, Au, Hg, Zn, Sn or Zr, and x is an integer of 1 to 4.
  3. A method of manufacturing the separator for a secondary battery according to claim 1 or 2, the method comprising: (a) preparing a primary slurry by adding and mixing the inorganic material and the dispersant in the mixed solvent comprising at least two solvents; (b) preparing a secondary slurry by adding and mixing the binder to the primary slurry; and (c) coating and drying the secondary slurry on the porous separator substrate comprising the polyolefin-based material, wherein the inorganic material is a metal hydroxide, the dispersant is tannic acid, an amount of the dispersant is 0.1 wt% to 0.3 wt%, the mixed solvent comprises an alcohol, wherein the alcohol is an alcohol having 1 to 5 carbon atoms, and an amount of the alcohol is 5 wt% to 20 wt% based on a total amount of the mixed solvent.
  4. The method according to claim 3, wherein step (c) comprises a vapor-induced phase separation (VIPS) process.
  5. The method according to claim 4, during the vapor-induced phase separation process, liquid-induced phase separation (LIPS) occurs simultaneously.
  6. An electrochemical device comprising the separator for a secondary battery according to claim 1 or 2.

Description

[Technical Field] This application claims the benefit of priority to Korean Patent Application No. 2019-0054480 filed on May 9, 2019. The present invention relates to a separator for a secondary battery comprising a dispersant and a method of manufacturing the same, and particularly, a separator for a secondary battery comprising a dispersant having improved adhesion force due to a binder concentrated on a surface of a separator coating layer and a method of manufacturing the same. [Background Art] Since lithium secondary batteries have high output compared to conventional secondary batteries, there is a high interest in securing stability of lithium secondary batteries. In order to increase the safety of a separator, a safety-reinforced separator (hereinafter referred to as 'SRS separator') has been developed and used. The SRS separator is configured to have a structure in which a coating layer including inorganic particles and a binder is formed on a polyolefin-based substrate, thereby providing high safety against high temperatures. The coating layer of the SRS separator forms a porous structure by the inorganic particles and a volume in which a liquid electrolyte solution is placed is increased by virtue of the porous structure. Therefore, lithium ion conductivity and an electrolyte impregnation rate of the SRS separator are increased, whereby both the performance and the stability of an electrochemical device using the SRS separator may be improved. In the past, alumina (Al2O3) was used as the inorganic particles constituting the coating layer of the SRS separator, but aluminum hydroxide has been proposed as an alternative inorganic material for solving the flame retardancy problem. When preparing a slurry for forming the coating layer of the SRS separator, a cyano-based resin or the like is used to secure a dispersion force of the inorganic particles. However, the aluminum hydroxide is not well dispersed in cyano-based resins. Therefore, various attempts have been made to develop an inorganic material with improved dispersibility while solving the flame retardancy problem. Patent Document 1 relates to a coating separator for a secondary battery comprising that an organic-inorganic composite coating layer is applied on one or both surfaces of a polyolefin-based porous base film, the organic-inorganic composite coating layer comprising 1 to 20 parts by weight of polyvinylidene-fluoridene-based resin based on 100 parts by weight of cellulose-based resin, 1,000 to 6,000 parts by weight of an inorganic filler, and 1 to 10 parts by weight of a dispersant. Patent Document 1 discloses the separator coated with the organic-inorganic composite coating layer on the base film, but fails to disclose a technology for improving the dispersion force depending on the type of inorganic particles. Patent document 2 relates to a battery cell including a porous polymer substrate and an organic-inorganic porous coating layer formed on at least one surface of the porous polymer substrate, the porous polymer substrate including a PVdF-HFP polymer binder in which an amount of hexafluoropropylene (HFP) is high, and a PVdF-HFP in which an amount of HFP is low. Patent Document 2 improved adhesion force to an electrode by forming the organic-inorganic porous coating layer including two kinds of binders. However, Patent Document 2 fails to disclose a technology capable of improving the dispersion force of inorganic particles in the organic-inorganic porous coating layer. Patent Document 3 relates to a method of manufacturing a separator for an electrochemical device comprising the steps of obtaining a porous polyolefin film by extracting a plasticizer from a polyolefin film, coating a slurry for forming a porous flame-retardant coating layer on at least one surface of the porous polyolefin film, and heat-setting the porous polyolefin film coated with the slurry to obtain a composite separator having a porous flame-retardant coating layer. Patent Document 3 has a feature of having a self-extinguishing function by forming the flame-retardant coating layer including flame-retardant particles, but fails to disclose a technology for improving adhesion force. There is a need to improve the technology capable of securing adhesion force to an electrode while exhibiting uniform physical properties by improving dispersion force of inorganic materials used to form a coating layer of a separator with improved safety, but a clear solution has not yet been proposed. US 2017/0338460 A1 describes a separator for a rechargeable battery including a porous substrate and an adhesive layer on at least one surface thereof. WO 2018/128484 A1 concerns a binder in a separator that comprises a porous polyolefin substrate and an organic-inorganic composite porous coating layer which includes a mixture of a binder compound with inorganic particles formed on at least one surface of the substrate; and a separator comprising the same. CN 109037551 A concerns a