CN-122025991-A - Diaphragm, preparation method and battery cell

CN122025991ACN 122025991 ACN122025991 ACN 122025991ACN-122025991-A

Abstract

The application relates to the technical field of batteries, in particular to a diaphragm, a preparation method and a battery core, wherein the diaphragm comprises two outer layers and an intermediate layer, the materials of the outer layers comprise polypropylene, the intermediate layer comprises a cross-linked modified polyolefin elastomer, one outer layer, the intermediate layer and the other outer layer are sequentially bonded and fixedly connected, the crease resistance of the intermediate layer is greater than that of the outer layers, the hemming resistance of the intermediate layer is greater than that of the outer layers, and the rigidity of the outer layers is greater than that of the intermediate layer. According to the diaphragm, based on the arrangement of different materials of the middle layer and the outer layers, the crease resistance of the middle layer is larger than that of the outer layers, the hemming resistance of the middle layer is larger than that of the outer layers, and the rigidity of the outer layers is larger than that of the middle layer, so that the problems of easiness in wrinkling and poor hemming resistance of the diaphragm can be effectively solved.

Inventors

ZHANG YONG
ZHANG HENG
LIAO YULI
PENG YANQIU

Assignees

武汉亿纬储能有限公司

Dates

Publication Date: 20260512
Application Date: 20251231

Claims (13)

1. A separator for a cell, comprising: two outer layers (2), the material of each outer layer (2) comprising polypropylene, and, The middle layer (1), the middle layer (1) material comprises a polyolefin elastomer modified by crosslinking, and one outer layer (2), the middle layer (1) and the other outer layer (2) are sequentially attached and fixedly connected; Wherein the crease resistance of the middle layer (1) is greater than the crease resistance of each outer layer (2), the hemming resistance of the middle layer (1) is greater than the hemming resistance of each outer layer (2), and the rigidity of each outer layer (2) is greater than the rigidity of the middle layer (1).
2. The membrane according to claim 1, characterized in that the direction perpendicular to the stretching direction of the membrane is defined as the transverse direction, the transverse toughness of the intermediate layer (1) is greater than the transverse toughness of each of the outer layers (2), and/or, The intermediate layer (1) has a flexibility greater than the flexibility of each of the outer layers (2).
3. The separator according to claim 1, characterized in that the cell has a negative plate and a positive plate, the intermediate layer (1) has micropores for ion transfer between the negative plate and the positive plate, and the intermediate layer (1) is capable of closing the micropores when the temperature reaches a first temperature threshold; Wherein the first temperature threshold is less than or equal to 110 ℃.
4. A separator according to any one of claims 1 to 3, wherein the cross-linked modified polyolefin-based elastomer comprises a cross-linked modified ethylene-octene copolymer.
5. The separator of claim 4, wherein the cross-linked modified ethylene-octene copolymer has a cross-linking degree between 30% and 70%.
6. A membrane according to any one of claims 1-3, characterized in that the thickness of both outer layers (2) is the same, the ratio of the thickness of the intermediate layer (1) to the thickness of the outer layers (2) being between 1:1-2:1.
7. A method of preparation, comprising the steps of: melting and plasticizing polypropylene to obtain a melt forming two outer layers (2); Melting and plasticizing the polyolefin elastomer modified by crosslinking to obtain a melt forming the intermediate layer (1); Merging two sides of the melt of an intermediate layer (1) with the melt of two outer layers (2) respectively, and carrying out coextrusion casting to form a diaphragm; wherein the crease resistance of the intermediate layer (1) is greater than the crease resistance of each of the outer layers (2), the hemming resistance of the intermediate layer (1) is greater than the hemming resistance of each of the outer layers (2), and the rigidity of each of the outer layers (2) is greater than the rigidity of the intermediate layer (1).
8. The preparation method according to claim 7, characterized in that before melt plasticizing the cross-linked modified polyolefin-based elastomer to obtain a melt forming the intermediate layer (1), the preparation method further comprises: Mixing the polyolefin elastomer, the cross-linking agent and the cross-linking auxiliary agent, and carrying out cross-linking modification at a second temperature threshold value to obtain the cross-linked modified polyolefin elastomer.
9. The method of claim 8, wherein mixing the polyolefin elastomer, the cross-linking agent, and the cross-linking aid, and cross-linking modifying at a second temperature threshold to produce the cross-linked modified polyolefin elastomer comprises: taking dicumyl peroxide as a cross-linking agent, triallyl isocyanurate as a cross-linking auxiliary agent, taking an ethylene-octene copolymer as a polyolefin elastomer, mixing the ethylene-octene copolymer, the dicumyl peroxide and the triallyl isocyanurate, and carrying out cross-linking modification at a second temperature threshold value to prepare the cross-linked modified ethylene-octene copolymer; Wherein the second temperature threshold is between 140 ℃ and 170 ℃, and/or, The dicumyl peroxide is added in an amount of 0.5 to 1.5 parts by weight based on 100 parts by weight of the ethylene-octene copolymer, and/or, The triallyl isocyanurate is added in an amount of 0.2 to 1 part by weight based on 100 parts by weight of the ethylene-octene copolymer, and/or, The cross-linking degree of the cross-linked modified ethylene-octene copolymer is between 30% and 70%.
10. The method according to any one of claims 7 to 9, wherein melt plasticizing the cross-linked modified polyolefin-based elastomer to obtain a melt forming the intermediate layer (1) comprises: melt plasticizing the cross-linked modified polyolefin elastomer at a third temperature threshold to obtain a melt forming the intermediate layer (1); Wherein the third temperature threshold is between 150 ℃ and 170 ℃.
11. The method according to any one of claims 7 to 9, wherein joining the two sides of the melt of an intermediate layer (1) with the melt of the two outer layers (2), respectively, and performing coextrusion casting comprises: merging the two sides of the melt of an intermediate layer (1) with the melt of the two outer layers (2) respectively, and carrying out coextrusion casting at a fourth temperature threshold; wherein the fourth temperature threshold is between 170 ℃ and 190 ℃.
12. The method of preparation according to any one of claims 7 to 9, characterized in that in the formed separator the thickness of both outer layers (2) is the same, the ratio of the thickness of the intermediate layer (1) to the thickness of the outer layers (2) being between 1:1 and 2:1.
13. A cell comprising a separator according to any one of claims 1 to 6 or a separator prepared by a method according to any one of claims 7 to 12.

Description

Diaphragm, preparation method and battery cell Technical Field The application relates to the technical field of batteries, in particular to a diaphragm, a preparation method and a battery cell. Background The PP (polypropylene) dry-method unidirectional stretching diaphragm has wide application in the energy storage battery core due to simple process and low cost. However, when the film is used for an iron-lithium laminated battery core, the film is limited by technology and materials and has the defects of transverse easy wrinkling and poor edge rolling resistance, and particularly, the film is high in longitudinal strength by dry unidirectional stretching, but is transversely fragile, permanent wrinkling and curling easily occur in frequent bending during lamination, the former can cause internal short circuit, and the latter can even cause fatal short circuit caused by direct contact of pole pieces. Disclosure of Invention The embodiment of the application provides a diaphragm, which is provided with an outer layer, an intermediate layer and another outer layer which are sequentially connected, wherein the intermediate layer material comprises a cross-linked modified polyolefin elastomer, the materials of the outer layers all comprise polypropylene, and the intermediate layer and the outer layers are arranged based on the matching of different materials of the intermediate layer so as to at least partially solve the technical problems. In order to achieve the above object, according to a first aspect of the present application, there is provided a separator for a battery cell, comprising: two outer layers, each of which comprises polypropylene, and, The middle layer material comprises a cross-linked modified polyolefin elastomer, and one outer layer, the middle layer and the other outer layer are sequentially bonded and fixedly connected; Wherein the interlayer has a wrinkle resistance greater than that of each of the outer layers, the interlayer has a hemming resistance greater than that of each of the outer layers, and each of the outer layers has a rigidity greater than that of the interlayer. According to the diaphragm, the middle layer material comprises the polyolefin elastomer modified by crosslinking, the materials of the outer layers comprise polypropylene, the crease resistance of the middle layer is higher than that of the outer layers based on the arrangement of the different materials of the middle layer and the outer layers, the hemming resistance of the middle layer is higher than that of the outer layers, and the rigidity of the outer layers is higher than that of the middle layer, so that the problems of easiness in wrinkling and poor hemming resistance of the diaphragm can be effectively solved. The interlayer has excellent wrinkle resistance, and can resist permanent deformation caused by frequent bending in the lamination process, so that the risk of internal short circuit caused by wrinkle accumulation is reduced, and meanwhile, the interlayer has higher hemmability, so that the edge of the diaphragm can be prevented from curling, and the fatal short circuit caused by direct contact of pole pieces is avoided. The higher rigidity of the outer layer provides necessary integral support and dimensional stability for the diaphragm, overcomes the transverse fragile defect brought by the dry unidirectional stretching process, and ensures that the diaphragm maintains flatness and structural integrity in the lamination process. Optionally, a direction perpendicular to the stretching direction of the separator is defined as a transverse direction, and the transverse toughness of the intermediate layer is greater than that of each of the outer layers. Based on the fact that the middle layer has higher transverse toughness than the two outer layers, the internal stress remained by the stretching process can be absorbed and dissipated in the transverse direction, when the diaphragm is heated, the middle layer can effectively buffer and restrain concentrated release of the internal stress, and the transverse shrinkage degree of the whole diaphragm is obviously reduced. The electrode plate is used for maintaining the dimensional stability of the diaphragm under the action of heat, avoiding the electrode plate from being pulled and the interface joint between the electrode plate and the diaphragm from being damaged due to excessive shrinkage of the diaphragm, maintaining the uniformity of the internal structure of the battery cell and relieving the distortion of a local thermal field. Optionally, the intermediate layer is more flexible than each of the outer layers. Based on the fact that the middle layer has higher flexibility than the two outer layers, the diaphragm can be elastically deformed more easily in the lamination process, so that the micro outline of the surface of the pole piece can be more tightly conformed and attached, and the interface gap between the diaphragm and the pole piece i