Microporous membrane separators for lithium ion rechargeable batteries and related methods

Patent metadata

Field	Value
Publication number	US-2016149181-A1
Application number	US-201514950478-A
Country	US
Kind code	A1
Filing date	Nov 24, 2015
Priority date	Nov 26, 2014
Publication date	May 26, 2016
Grant date	—

Abstract

The present invention relates in at least selected embodiments to novel or improved microporous battery separators for lithium rechargeable batteries and/or related methods of making and/or using such separators. A particular inventive dry process battery separator or membrane separator exhibits a thickness that is less than about 14 μm and has increased strength performance as defined by reduced splittiness. The mode of splitting failure has been investigated, and the improvement in splittiness quantified by a novel test method known as the Composite Splittiness Index (CSI).

First claim

We claim:

1 . An improved separator, membrane or base film for a lithium battery having a CSI of at least 29.

2 . The separator of claim 1 wherein the separator is a monolayer separator, membrane or base film.

3 . The separator of claim 1 wherein the separator is a multilayer separator, membrane or base film.

4 . The separator of claim 1 wherein the separator is a trilayer separator, membrane or base film.

5 . The separator of claim 1 wherein the separator is made by a dry stretch process.

6 . The separator of claim 1 wherein the separator is made by a lamination process.

7 . The separator of claim 1 wherein the separator has a puncture strength (PS) first load peak of at least 130 gf.

8 . The separator of claim 1 wherein the separator has a puncture strength (PS) first load peak of at least 130 gf and has a thickness of at least 7 um.

9 . The separator of claim 1 wherein the separator has a porosity of at least 25%.

10 . The separator of claim 1 wherein the separator has a porosity of at least 27%.

11 . The separator of claim 1 wherein the separator has a porosity of at least 31%.

12 . The separator of claim 1 wherein the separator has a porosity in the range of about 30% to 50%.

13 . The separator of claim 1 wherein the separator has a porosity in the range of about 31% to 40%.

14 . The separator of claim 1 wherein the separator is especially well suited for energy cells, such as used in consumer electronics.

15 . The separator of claim 1 wherein the separator has an ER of 1.5 ohm-cm 2 or less, has a porosity of at least 25%, and is adapted for a high energy cell or battery.

16 . The separator of claim 1 wherein the separator has a TD tensile strength of at least 150 kgf/cm 2 .

17 . The separator of claim 1 wherein the separator has a CSI of higher than 30.

18 . The separator of claim 1 wherein the separator has a CSI of at least 50.

19 . The separator of claim 1 wherein the separator has a CSI of at least 100.

20 . The separator of claim 1 wherein the CSI is based on an inventive test method known as Composite Splittiness Index (CSI) where the CSI value is defined by Equation 1 (noted below) where CSI is a function of the first load peak, the second load peak, TD tensile strength, MD tensile strength, and TD elongation measured during puncture strength testing:
CSI=( A−|B−A| 1.8 )× C ×( D×E )/10 6   Equation 1

where:
A=First Load Peak/Thickness×(1−% Porosity)
B=Second Load Peak/Thickness
C=TD Elongation
D=MD Tensile Strength
E=TD Tensile Strength

where First and Second Load Peak are in units of gram-force, thickness values are in microns, MD and TD tensile strength are in gram-force, and TD elongation is expressed as percentage, and where a high CSI value may be predictive of a microporous membrane that may have excellent strength performance in a secondary lithium battery.

21 . The separator of claim 1 wherein the separator includes at least one microporous polyolefin membrane produced according to a dry process in which a polyolefin resin is extruded to form said membrane, said resin having a melt flow index (MFI) of less than or equal to about 0.8 grams/10 minutes.

22 . The separator of claim 1 wherein the separator includes at least one microporous polyolefin membrane produced according to a dry process in which a polyolefin resin is extruded to form said membrane, said resin having a melt flow index (MFI) of less than or equal to about 0.5 grams/10 minutes.

23 . An improved multilayer separator or base film comprising:
at least one microporous membrane produced according to a dry stretch process in which a polyolefin resin, mix or blend is extruded to form said membrane, said resin having a melt flow index (MFI) of less than or equal to about 0.8 grams/10 minutes; and wherein said separator having a thickness of greater than or equal to about 7 μm, a porosity in the range of about 30% to about 50%, and an electrical resistance (ER) value of less than or equal to about 1.5 ohm-cm 2 , and optionally wherein the separator is a monolayer, multilayer, bilayer or trilayer separator or base film, is made by a dry stretch process, is made by a lamination process, has a puncture strength (PS) of at least 130 gf and has a thickness of at least 7 μm, has a puncture strength (PS) of at least 200 gf and has a thickness of at least 7 μm, has a puncture strength (PS) of at least 390 gf and has a thickness of at least 13 μm, has a puncture strength (PS) of at least 200 gf and has a thickness of about 7 has a porosity of at least 25%, has a porosity of at least 27%, has a porosity of at least 31%, has a porosity in the range of about 30% to 50%, has a porosity in the range of about 31% to 40%, is especially well suited for energy cells, such as used in consumer electronics, has an ER of 1.5 ohm-cm 2 or less, has a porosity of at least 25%, and is adapted for a high energy cells or batteries, includes at least two microporous polyolefin membranes produced according to a dry process in which a polyolefin resin is extruded to form said membrane, said resin having a melt flow index (MFI) of less than or equal to about 0.8 grams/10 minutes, includes at least three microporous polyolefin membranes produced according to a dry process in which a polyolefin resin is extruded to form said membrane, said resin having a melt flow index (MFI) of less than or equal to about 0.8 grams/10 minutes, includes at least one polyethylene or polypropylene membrane, includes at least two polypropylene membranes, and/or having an improved puncture strength or TD tensile strength over prior separators, multilayer separators, or trilayer separators of the same thickness.

Assignees

• Celgard Llc

Inventors

• Zhang Xiaomin
• Xiao Kang Karen
• Nark Robert A
• Smith Ron E

Classifications

• H01M50/449 Primary

  having a layered structure · CPC title

• H01M10/052

  Li-accumulators · CPC title

• H01M50/494

  Tensile strength · CPC title

• H01M50/491

  Porosity · CPC title

• H01M50/489 Primary

  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