Multi-layer, microporous polyolefin membrane, its production method, battery separator and battery

1. A multi-layer, microporous polyolefin membrane, comprising: a first layer material and a second layer material, the first and second layer materials comprising polyethylene and polypropylene, wherein

(i) the first layer material contains polyethylene in a first amount of at least 80 wt. %, based on the weight of the first material;

(ii) the second layer material contains polyethylene in a second amount of at least 50 wt. %, based on the weight of the second material;

(iii) the first amount is greater than the second amount on a weight percent basis,

(iv) the multi-layer, microporous polyolefin membrane contains polyethylene in a total amount of at least 61 wt. %, based on the combined weight of the first and second layer materials, and

(v) a content of polypropylene in the first layer material is less than a content of polypropylene in the second layer material on a weight percent basis, and

wherein the polypropylene is a propylene homopolymer, and

wherein the multi-layer membrane comprises:

a first microporous layer containing the first layer material, a third microporous layer containing the first layer material, and a second microporous layer containing the second layer material, the second microporous layer being located between the first and third microporous layers.

2. The multi-layer membrane of claim 1 , wherein the first amount ranges from 80 wt. % to 99.5 wt. %, the second amount ranges from 50 wt. % to 85 wt. %, the first layer material contains at least 5 wt. % more polyethylene than the second layer material based on the weights of the first and second layer materials, and the total amount ranges from 70 wt. % to 90 wt. %.

3. The multi-layer membrane of claim 1 , wherein the polyethylene comprises a first polyethylene and a second polyethylene, wherein

(a) the polyethylene in first layer material has at least one characteristic selected from:

(1) the polyethylene has a Mw in the range of 1×10 4 to 1×10 7 ;

(2) the first polyethylene has an Mw ranging from 1×10 4 to 5×10 5 ;

(3) the polyethylene comprises the first polyethylene and the second polyethylene, wherein the second polyethylene has an Mw of at least 1×10 6 ;

(b) the polypropylene in the first or second layer materials has an Mw ranging from 1×10 4 to 4×10 6 ;

(c) the polyethylene in the second layer material has at least one characteristic selected from:

(1) the polyethylene has an Mw in the range of 1×10 4 to 1×10 7 ;

(2) the polyethylene comprises the first polyethylene having an Mw ranging from 1×10 4 to 5×10 5 ;

(3) the polyethylene comprises the first polyethylene and the second polyethylene, wherein the second polyethylene has an Mw of at least 1×10 6 .

4. The multi-layer membrane of claim 3 , wherein the polyethylene in the first layer material has an Mw in the range of 2×10 5 to 3×10 6 .

5. The multi-layer membrane of claim 3 , wherein the polyethylene in the second layer material consists essentially of the first polyethylene, wherein the first polyethylene has an Mw in the range of 1×10 4 to 5×10 5 .

6. The multi-layer membrane of claim 3 , wherein the first polyethylene is high-density polyethylene and the second polyethylene is ultra-high-molecular-weight polyethylene.

7. The multi-layer membrane of claim 3 , wherein the polyethylene in the first layer material comprises 10 wt. % or less of polyethylene having a weight-average molecular weight of 1×10 6 or more and 90 wt. % or more of polyethylene having a weight-average molecular weight of 1×10 4 to 5×10 5 , and wherein the polyethylene in the second layer material polyethylene has a weight-average molecular weight of 1×10 4 to 5×10 5 .