Low electrical resistance microporous battery separator membranes, separators, cells, batteries, and related methods

Patent metadata

Field	Value
Publication number	US-2016359157-A1
Application number	US-201615172215-A
Country	US
Kind code	A1
Filing date	Jun 3, 2016
Priority date	Jun 3, 2015
Publication date	Dec 8, 2016
Grant date	—

Abstract

Novel or improved microporous battery separator membranes, separators, cells, batteries including such membranes, separators, or cells, and/or methods of making such membranes and/or separators, and/or methods of using such membranes and/or separators. In accordance with at least certain embodiments, an improved or novel battery separator for a secondary or rechargeable lithium battery may have low Electrical resistance of less than 0.95 ohm-cm 2 , or in some cases, less than 0.8 ohm-cm 2 . Furthermore, the inventive battery separator membrane may provide a means to achieve an improved level of battery performance in a rechargeable or secondary lithium battery based on a possibly synergistic combination of low Electrical resistance, low Gurley, low tortuosity, and/or a unique trapezoid shaped pore. In accordance with at least certain multilayer embodiments (by way of example only, a trilayer membrane made of two polypropylene layers with a polyethylene layer in between), the inventive microporous membrane or battery separator may have excellent onset and rate of thermal shutdown performance.

First claim

We claim:

1 . A novel, improved or modified polyolefin battery separator membrane, comprising:
a microporous separator membrane having an electrical resistance less than 0.95 ohm-cm 2 , having a Gurley less than 500 sec/100 cc, having a tortuosity less than 1.5, and wherein said microporous polyolefin separator membrane has a non-round, trapezoid shape pore.

2 . The invention of claim 1 wherein the microporous separator membrane having an electrical resistance less than 0.8 ohm-cm 2 ,
having a Gurley less than 150 sec/100 cc,
having a tortuosity less than 1.3, and/or wherein said microporous polyolefin separator membrane consists of a polypropylene, polyethylene, mixtures thereof, and co-polymers thereof.

3 . The invention of claim 1 where said microporous polyolefin separator membrane can be a monolayer membrane or a multilayer membrane with a thermal shutdown function.

4 . The invention of claim 1 where said microporous polyolefin separator membrane can be a multilayer membrane consisting of a trilayer of polypropylene/polyethylene/polyethylene.

5 . The invention of claim 1 wherein the said microporous polyolefin separator membrane has a thickness less than 25 μm.

6 . The invention of claim 5 wherein the said microporous polyolefin separator membrane has pores with a non-round, trapezoid shape on each surface of said membrane.

7 . A novel, improved or modified polyolefin battery separator membrane made by a process comprising:
extruding a polypropylene which has a melt flow index less than 1.0 g/10 minutes to form a monolayer nonporous precursor membrane and, machine direction stretching a nonporous polypropylene precursor membrane to form a semi-porous intermediate membrane having a puncture strength>350 gf and TD elongation>600%, transverse direction stretching a semi-porous intermediate membrane using a stretch ratio of 15 to 400%, and preferably stretching using a stretch ratio of 25 to100% to form a microporous separator membrane.

8 . The microporous membrane of claim 7 formed when said semi-porous intermediate membrane is transverse stretched at a temperature of 100 to 130 deg C., formed wherein said semi-porous intermediate membrane is transverse stretched at a temperature of 100 to 130 deg C. at a speed of 100 ft/minute, and preferably at a speed of 50 ft/minute, wherein membrane is thermally relaxed at 120 to 140 deg C., and/or wherein membrane is heat treated at a temperature of 60 to 100 deg C. for preferably 8 hours to 2 to 3 days.

9 . A novel, improved or modified polyolefin trilayer battery separator membrane made by a process comprising:
extruding a polyethylene which has a melt flow index less than 1.0 g/10 minutes to form a monolayer nonporous polyethylene precursor membrane and, extruding a polypropylene which has a melt flow index less than 1.0 g/10 minutes to form a monolayer nonporous polypropylene precursor membrane and, laminating two plies of polypropylene precursor membrane as outer plies (layers) sandwiching one inner ply (layer) of polyethylene precursor membrane to form a trilayer polypropylene/polyethylene/polyethylene nonporous precursor, machine direction stretching a nonporous polypropylene/polyethylene/polyethylene precursor membrane to form a semi-porous intermediate membrane having a puncture strength>350 gf and TD elongation>600%, transverse direction stretching a semi-porous intermediate membrane using a stretch ratio of 15 to 400%, and preferably stretching using a stretch ratio of 25 to100% to form a microporous trilayer separator membrane.

10 . The microporous membrane of claim 9 formed when said semi-porous intermediate membrane is transverse stretched at a temperature of 100 to 130 deg C., formed wherein said semi-porous intermediate membrane is transverse stretched at a temperature of 100 to 130 deg C. at a speed of 100 ft/minute, and preferably at a speed of 50 ft/minute, wherein membrane is thermally relaxed at 120 to 140 deg C., and/or wherein membrane is heat treated at a temperature of 60 to 100 deg C. for preferably 8 hours to 2 to 3 days.

11 . Novel or improved microporous battery separator membranes, separators, cells, or batteries including such membranes, separators, or cells, and/or methods including methods of making such membranes, separators, cells, and/or batteries, and/or methods of using such membranes, separators, cells, and/or batteries, a battery separator for a secondary or rechargeable lithium battery which may have low electrical resistance of less than 0.95 ohm-cm 2 , in some cases, less than 0.8 ohm-cm 2 , the battery separator membrane or separator providing a means to achieve an improved level of battery performance in a rechargeable or secondary lithium battery based on a possibly synergistic combination of low electrical resistance, low Gurley, low tortuosity, and/or a unique shaped pore, which pore, in some cases, approximates the shape of a trapezoid or is trapezoid-like in shape, and/or multilayer embodiments (by way of example only, a trilayer membrane made of two polypropylene layers with a polyethylene layer in between), wherein the microporous membrane or battery separator having excellent onset of thermal shutdown and/or excellent rate of thermal shutdown performance as shown or described herein.

12 . In an improved separator, the synergistic combination of low ER, low Gurley and low tortuosity, and having a porous structure which resembles a “knitted-like” structure where the polymer crystalline lamellae regions resemble small islands connected by a 3-D array of vertically and diagonally elongated fibrillar structures, a unique morphology as evidenced in Scanning Electron Micrograph (SEM) analysis, such as SEM images of the surface of the inventive monolayer Ex. 6 and Ex. 7 are shown in FIGS. 12 and 13 , respectively, the pores having a non-round pore shape.

13 . The membrane or separator as shown or described herein.

14 . The membrane or separator of claim 13 as shown or described in FIGS. 12 or 13 herein.

15 . The membrane or separator of claim 14 as shown or described in FIG. 13 herein.

Assignees

• Celgard Llc

Inventors

• Zhang Xiaomin
• Shi Lie

Classifications

• B32B27/08 Primary

  of synthetic resin · CPC title

• H01M50/457

  comprising three or more layers · CPC title

• H01M50/417 Primary

  Polyolefins · CPC title

• H01M50/491

  Porosity · CPC title

• H01M50/489

  Separators, membranes, diaphragms or spacing elements inside the cells, characterised by their physical properties, e.g. swelling degree, hydrophilicity or shut down properties · CPC title