Search

JP-7856579-B2 - Asymmetric porous membrane

JP7856579B2JP 7856579 B2JP7856579 B2JP 7856579B2JP-7856579-B2

Inventors

  • イン，ウェンビン
  • アレクサンダー，ダニエル，アール．
  • ライナルツ，ステファン
  • シャオ，カン，カレン
  • 武田 久
  • ドン，アレン，エム．

Assignees

  • セルガード エルエルシー

Dates

Publication Date
20260511
Application Date
20210416
Priority Date
20200417

Claims (7)

  1. A secondary battery comprising a battery separator between the anode and the cathode, and having a liquid electrolyte, The aforementioned battery separator includes a porous membrane, consists of a porous membrane, or is essentially made of a porous membrane. The porous membrane comprises two outer layers and at least one inner layer. The ratio of the thickness of the thicker of the two outer layers to the thickness of the thinner of the two outer layers is 1.1:1 to 4:1, 1.1:1 to 3:1, or 1.1:1 to 2:1. The two outer layers mentioned above contain polypropylene, consist of polypropylene, or are essentially made of polypropylene. The at least one inner layer contains polyethylene, is made of polyethylene, or is essentially made of polyethylene. A secondary battery in which the thicker of the two outer layers faces the cathode and the thinner of the two outer layers faces the anode.
  2. A secondary battery according to claim 1, comprising inner layers 1 to 10.
  3. The secondary battery according to claim 1, wherein the porous membrane is formed by a method including laminating at least one of the two outer layers with at least one inner layer, or co-extruding at least one of the two outer layers with at least one inner layer.
  4. The secondary battery according to claim 1, wherein the total thickness of the porous membrane is 5 to 30 microns, 5 to 20 microns, 5 to 15 microns, or 5 to 10 microns.
  5. The secondary battery according to claim 1 , wherein the battery separator has an electrochemically stable voltage of 4.2 or more relative to Li/Li+, 4.5 or more relative to Li/Li+, or 5.0 or more relative to Li/Li+.
  6. The porous membrane includes a coating layer applied to the thinner of the two outer layers. The secondary battery according to claim 5 , wherein the coating is at least one of a ceramic coating, a polymer coating, and a shutdown coating, and/or the coating layer has a thickness of 1 to 5 microns.
  7. The secondary battery according to claim 6 , wherein the coating layer faces the anode.

Description

This application relates to improved porous membranes and battery separators, and to liquid electrolyte secondary lithium-ion batteries incorporating them. In particular, the improved porous membranes disclosed herein may be used to form thinner, safer battery separators and batteries. In the electric vehicle (EV and HEV) industrial market, the focus is on increasing the energy density of lithium-ion batteries while maintaining safety and lifespan. One development aimed at improving safety is the shutdown separator. For example, a three-layer shutdown separator is described in U.S. Patent No. 5,952,120, which is incorporated herein by reference. These shutdown separators typically have structures such as PP/PE/PP, PP/PE/PE/PP, or PP/PE/PE/PE/PP, where all layers are the same or substantially the same thickness. This symmetry was preferred because, for example, asymmetry in the separator can cause curling and other problems. Generally, shutdown separators improve safety at high temperatures by stopping ion transport and current flow across the separator. The PE layer, with its lower melting temperature, melts before the PP layer, and the molten PE fills the pores of the separator, blocking ion transport. It is generally accepted that thinner separators allow for the formation of batteries with higher energy density, and that more cells can be incorporated into a single battery with nearly the same weight and thickness. Therefore, a promising method for achieving high energy density without sacrificing safety is considered to be creating thin or ultrathin shutdown separators, such as three-layer shutdown products, by reducing the total weight and thickness of the three layers. However, simply reducing the symmetrical total thickness to create ultrathin or thin shutdown separators, such as three-layer shutdown separators, still presents application problems. For example, the rough surface of the cathode surface can easily break through and penetrate the outer layer of PP when used in liquid electrolyte lithium secondary batteries. Furthermore, high-voltage electrons can easily oxidize the PE layer, initiating side reactions and generating gases. In this case, energy density and safety are reduced. Figure 1 is a schematic diagram of an exemplary film described herein.Figures 2A and 2B are both FESM images of exemplary films described herein.Figure 2B is a FESM image of an exemplary film described herein.Figure 3 is a schematic diagram showing the difference between film thickness and pore length. The degree of flexibility is derived from these two measured values.Figures 4A, 4B, 4C, 4D, 4E, and 4F are schematic diagrams of exemplary embodiments described herein.Figures 4A, 4B, 4C, 4D, 4E, and 4F are schematic diagrams of exemplary embodiments described herein.Figures 4A, 4B, 4C, 4D, 4E, and 4F are schematic diagrams of exemplary embodiments described herein.Figures 4A, 4B, 4C, 4D, 4E, and 4F are schematic diagrams of exemplary embodiments described herein.Figures 4A, 4B, 4C, 4D, 4E, and 4F are schematic diagrams of exemplary embodiments described herein.Figures 4A, 4B, 4C, 4D, 4E, and 4F are schematic diagrams of exemplary embodiments described herein.Figures 5A and 5B are schematic diagrams of exemplary embodiments described herein.Figures 5A and 5B are schematic diagrams of exemplary embodiments described herein.Figures 6A, 6B, and 6C are schematic diagrams of exemplary embodiments described herein.Figures 6A, 6B, and 6C are schematic diagrams of exemplary embodiments described herein.Figures 6A, 6B, and 6C are schematic diagrams of exemplary embodiments described herein.Figure 7 shows the pore size distribution of an exemplary embodiment described herein. Asymmetric Porous Membrane Asymmetric porous membranes are described herein. An asymmetric porous membrane may include, consist of, or essentially consist of two outer layers and optionally at least one inner layer. There may be 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, or more inner layers. In some embodiments, the porous membrane may consist of, or essentially consist of, two outer layers, and may be without inner layers. The ratio of the thickness of one of the two outer layers to the thickness of the other of the two outer layers may be 1.1:1 to 10:1, 1.1:1 to 9:1, 1.1:1 to 8:1, 1.1:1 to 7:1, 1.1:1 to 6:1, 1.1:1 to 5:1, 1.1:1 to 4:1, 1.1:1 to 3:1, or 1.1:1 to 2:1. In some preferred embodiments, the total thickness of the porous membrane may be 2 to 30 microns, 2 to 25 microns, 2 to 20 microns, 2 to 15 microns, or 2 to 10 microns. In some embodiments, the total thickness of the porous membrane may be 3 to 12 microns, 4 to 12 microns, 5 to 12 microns, or 9 to 12 microns. In some embodiments, at least one of the outer layers has a thickness of 2 to 6 microns or 4 to 5 microns. In some embodiments, when the asymmetric porous membrane is used in a battery, the outer layer having a thickness of 2 to 6 microns or 4 to 5 microns is positioned facing the cathode. In som