US-12627001-B2 - Separator for lithium secondary battery, the method for manufacturing the same and lithium secondary battery including the same

US12627001B2US 12627001 B2US12627001 B2US 12627001B2US-12627001-B2

Abstract

A separator for a lithium secondary battery, a method for manufacturing the same, and a secondary battery including the same. The separator includes a porous coating layer including a top layer, an intermediate layer, and a bottom layer. An amount of a particle-type binder polymer present in the top layer is larger than an amount of the particle-type binder polymer present in the bottom layer. The porous coating layer also includes a dispersant having a carboxyl group and a glycol group.

Inventors

Hye-Jin KWON
Kyung-Ryun Ka
Seung-Hyun Lee

Assignees

LG ENERGY SOLUTION, LTD.

Dates

Publication Date: 20260512
Application Date: 20210929
Priority Date: 20200929

Claims (20)

1 . A separator for a lithium secondary battery, comprising: a porous polymer substrate; and a porous coating layer on at least one surface of the porous polymer substrate, wherein the porous coating layer comprises inorganic particles, a particulate binder polymer, and a dispersant, wherein the dispersant comprises a copolymer comprising a carboxyl functional group and a glycol functional group, wherein the porous coating layer comprises a top layer, an intermediate layer, and a bottom layer in a thickness direction, and wherein an amount of the particulate binder polymer present in the top layer is higher than an amount of the particulate binder polymer present in the bottom layer.
2 . The separator for the lithium secondary battery according to claim 1 , wherein the top layer is an outermost layer of the porous coating layer, when the porous coating layer is viewed in the thickness direction away from the porous polymer substrate; wherein the bottom layer faces the porous polymer substrate, when the porous coating layer is viewed in the thickness direction; and wherein the intermediate layer is between the top layer and the bottom layer in the porous coating layer.
3 . The separator for the lithium secondary battery according to claim 2 , wherein a concentration gradient of the particulate binder polymer increases from the bottom layer to the top layer in the thickness direction of the porous coating layer, and a concentration gradient of the inorganic particles increases from the top layer to the bottom layer in the thickness direction of the porous coating layer.
4 . The separator for the lithium secondary battery according to claim 1 , wherein the intermediate layer in the porous coating layer has a gradual concentration gradient of the particulate binder polymer, or has no concentration gradient.
5 . The separator for the lithium secondary battery according to claim 1 , wherein a weight ratio of the inorganic particles to the dispersant is from 99.5:0.5 to 95:5.
6 . The separator for the lithium secondary battery according to claim 1 , wherein the amount of the particulate binder polymer is 10 parts by weight to 50 parts by weight based on 100 parts by weight of the porous coating layer.
7 . The separator for the lithium secondary battery according to claim 1 , wherein the dispersant has a ratio of an equivalent number of glycol functional groups to an equivalent number of carboxyl functional groups of 0.05 to 0.25.
8 . The separator for the lithium secondary battery according to claim 1 , wherein the dispersant has a weight average molecular weight of 100 to 10,000.
9 . The separator for the lithium secondary battery according to claim 1 , wherein the dispersant is a copolymer of polyacrylic acid and polyethylene glycol.
10 . The separator for the lithium secondary battery according to claim 9 , wherein the dispersant is a block copolymer of polyacrylic acid and polyethylene glycol.
11 . The separator for the lithium secondary battery according to claim 1 , wherein the porous coating layer has a thickness of 2 μm to 10 μm.
12 . The separator for the lithium secondary battery according to claim 1 , wherein the inorganic particles are planar inorganic particles.
13 . The separator for the lithium secondary battery according to claim 12 , wherein the planar inorganic particles have an aspect ratio of 3.5 or more.
14 . The separator for the lithium secondary battery according to claim 12 , wherein the planar inorganic particles comprise at least one of Al(OH) 3 , AlO(OH), Mg(OH) 2 and BaTiO 3 .
15 . The separator for the lithium secondary battery according to claim 1 , wherein the separator satisfies at least three the following formulae: (i) increase in air permeation time≤100%, (ii) heat shrinkage≤10%, (iii) adhesion to electrode≥70 gf/25 mm, and (iv) viscosity of a slurry for forming the porous coating layer≤20 cp, wherein the increase in air permeation time is calculated by the formula of [(air permeation time of porous polymer substrate−air permeation time of separator)/(air permeation time of porous polymer substrate)]×100, and wherein the heat shrinkage is a smaller value of a heat shrinkage in the machine direction (MD) and the heat shrinkage in the transverse direction (TD) and is calculated by the formula of [(initial length−length after heat shrinking at 150° C./min for 30 minutes)/(initial length)]×100.
16 . A lithium secondary battery, comprising: a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode, wherein the separator is the same as defined in claim 1 .
17 . A method for manufacturing the separator for the lithium secondary battery as defined in claim 1 , comprising: a step of applying a slurry for forming the porous coating layer comprising a solvent, the inorganic particles, the particulate binder polymer and the dispersant to at least one surface of the porous polymer substrate, followed by drying, wherein the slurry for forming the porous coating layer has a viscosity of 200 cP or less, and wherein the slurry for forming the porous coating layer has a solid content of 10 parts by weight to 40 parts by weight based on 100 parts by weight of the slurry.
18 . The method for manufacturing the separator according to claim 17 , wherein the solvent is water, wherein the particulate binder polymer is in the form of particles dispersed in the solvent, and wherein phase separation is carried out in the drying step.
19 . A method for manufacturing the separator for the lithium secondary battery as defined in claim 1 , wherein the top layer is an outermost layer of the porous coating layer away from the porous polymer substrate in the thickness direction.
20 . A method for manufacturing the separator for the lithium secondary battery as defined in claim 1 , wherein the dispersant is a block copolymer of polyacrylic acid and polyethylene glycol, and wherein the dispersant has a ratio of an equivalent number of glycol functional groups to an equivalent number of carboxyl functional groups of 0.05 to 0.25.

Description

TECHNICAL FIELD The present disclosure relates to a separator applicable to an electrochemical device, such as a lithium secondary battery, a method for manufacturing the same, and a lithium secondary battery including the same. The present application claims priority to Korean Patent Application No. 10-2020-0127233 filed on Sep. 29, 2020 and Korean Patent Application No. 10-2020-0127237 filed on Sep. 29, 2020 in the Republic of Korea, the disclosures of which are incorporated herein by reference. BACKGROUND ART Recently, energy storage technology has been given an increasing attention. Efforts into research and development for electrochemical devices have been actualized more and more, as the application of energy storage technology has been extended to energy for cellular phones, camcorders and notebook PC and even to energy for electric vehicles. In this context, electrochemical devices have been most spotlighted. Among such electrochemical devices, development of rechargeable secondary batteries has been focused. More recently, active studies have been conducted about designing a novel electrode and battery in order to improve the capacity density and specific energy in developing such batteries. Among the commercially available secondary batteries, lithium secondary batteries developed in the early 1990's have been spotlighted, since they have a higher operating voltage and significantly higher energy density as compared to conventional batteries, such as Ni-MH, Ni-Cd and sulfuric acid-lead batteries using an aqueous electrolyte. Although such electrochemical devices have been produced from many production companies, safety characteristics thereof show different signs. Evaluation and securement of safety of such electrochemical devices are very important. For example, a separator prevents a short-circuit between a positive electrode and a negative electrode and provides a channel for transporting lithium ions. Therefore, such a separator is an important element affecting the safety and output characteristics of a battery. Such a separator frequently includes a polyolefin-based porous polymer substrate. In order to prevent the porous polymer substrate from heat shrinking and to enhance adhesion to an electrode, there has been frequently used a separator provided with a porous coating layer including inorganic particles and a binder polymer on at least one surface of a porous polymer substrate. The separators may be classified broadly into aqueous coating separators using an aqueous solvent and organic coating separators using an organic solvent, depending on the porous coating layer. Particularly, the aqueous coating separators allow uniform thin film coating and show high heat resistance. However, there is still a need for a separator showing increased adhesion (Lami strength) to an electrode, while maintaining high porosity in the porous coating layer. DISCLOSURE Technical Problem The present disclosure is designed to solve the problems of the related art, and therefore the present disclosure is directed to providing an aqueous coating separator which has excellent heat resistance, includes a porous coating layer having high porosity and shows improved adhesion to an electrode, a method for manufacturing the same, and a lithium secondary battery including the same. However, objects to be accomplished by the present disclosure are not limited to the above-mentioned problem, and other objects of the present disclosure may be understood from the following detailed description and will become more fully apparent from the exemplary embodiments of the present disclosure. Technical Solution In one aspect of the present disclosure, there is provided a separator for a lithium secondary battery, a method for manufacturing the same and a lithium secondary battery including the same according to any one of the following embodiments. According to the first embodiment, there is provided a separator for a lithium secondary battery, including: a porous polymer substrate; anda porous coating layer on at least one surface of the porous polymer substrate, wherein the porous coating layer includes inorganic particles, a particle-type binder polymer and a dispersant,wherein the dispersant includes a carboxyl group and a glycol group,wherein the porous coating layer includes a top layer, an intermediate layer and a bottom layer in the thickness direction, and wherein an amount of the particle-type binder polymer present in the top layer is higher than an amount of the particle-type binder polymer present in the bottom layer. According to the second embodiment, there is provided the separator for a lithium secondary battery as defined in the first embodiment, wherein the top layer is the outermost layer of the porous coating layer, when the porous coating layer is viewed in the thickness direction away from the porous polymer substrate; wherein the bottom layer faces the porous polymer substrate, when the porous coating lay