Nano microporous diaphragm of post-crosslinked rubber and polyolefin composite, and manufacturing method thereof

Patent metadata

Field	Value
Publication number	US-9991494-B2
Application number	US-201114442098-A
Country	US
Kind code	B2
Filing date	Jul 22, 2011
Priority date	Apr 22, 2011
Publication date	Jun 5, 2018
Grant date	Jun 5, 2018

Abstract

The present invention relates to a composite nano microporous diaphragm for use in lithium ion cells using polyolefin modified with post-crosslinked rubber and manufacturing method thereof. The microporous diaphragm at least comprises a nano microporous diaphragm A layer with a chemical gel content of more than 20%, the microscopic structure thereof is designed to be the rubber material that has been evenly dispersed and has subjected to a post-crosslinking treatment in polyolefin nano microfiber matrix, forming a nano microporous diaphragm of rubber-plastic composite. The nano microporous diaphragm with high strength, thermal cutoff, high temperature resistance, as well as good liquid absorption and swelling and compression elasticity can be applied to lithium ion power cells with high safety and long cycling life.

First claim

The invention claimed is:

1. A membrane based on a composite of a post-crosslinked rubber and a polyolefin plastic, the membrane comprising at least one membrane layer A having at least 20 wt. % of a chemical gel, the membrane and the membrane layer A both having a pore diameter of nano-scale, the membrane layer A comprising a nano microfiber matrix of polyolefin, and the post-crosslinked rubber, the post-crosslinked rubber being uniformly distributed in the matrix and being prepared by irradiating a raw rubber; wherein
a weight ratio of the raw rubber to the plastic is between (20:80) and (50:50);
the raw rubber is a liquid rubber or a waxy rubber selected from the group consisting of: an ethylene-propylene methylene copolymer (EPM), an ethylene propylene diene rubber (EPDM), an ethylene acrylic rubber, and a diene rubber; wherein the diene rubber is selected from the group consisting of a polyisoprene rubber (IR), a butadiene rubber (BR), a nitrile butadiene rubber (NBR) having less than 20 wt. % of an acrylonitrile, a styrene butadiene rubber (SBR) having less than 20 wt. % of a styrene, and a combination thereof;
the polyolefin plastic is a homopolymer selected from the group consisting of a high-density polyethylene (HDPE) having a weight average molecular weight of more than 500,000, a polypropylene (PP), a polybutene (PB), a linear low density polyethylene (LLDPE), an α-olefin copolymer, and a combination thereof;
and
the membrane has the following properties:
1) the membrane has a total thickness of 10-36 μm, an average pore size of less than 150 nm, a porosity of 35-70%, and a Gurley value of 50-500 S/100 CC;
2) imbibition and compressible elasticity: a thickness of the membrane after freely absorbing a DMC solution for one hour at the temperature of 30° C. is enlarged by (1.05-1.30) times; the membrane after DMC solution absorption is exerted with a 0.35 megapascal static compressive stress in a thickness direction for 5 minutes, and a compression deformation of the membrane in the thickness direction is approximately between 5% and 25% of that before the compression; and the thickness of the membrane five minutes after release of the compressive stress is recovered to be more than 85% of that before the compression;
3) the membrane has a longitudinal tensile strength of 50-200 megapascal, an elasticity modulus of larger than 800 megapascal, and a longitudinal elongation at break of larger than 30%; the membrane has a transverse tensile strength of 30-150 megapascal, an elasticity modulus of larger than 300 megapascal, a transverse tensile strength of larger than 50%, and an acupuncture strength of larger than 300 gf/20 μm; and
4) thermal shutdown and high temperature resistance: a 0.35 megapascal static compressive stress is exerted on the thickness direction, the membrane is heated from 90 to 200° C. at a heating rate of 1° C./min, and a thermal shutdown temperature is no higher than 145° C.; when the temperature is maintained at 200° C. for 5 min and then decreased to room temperature, a physical state of the membrane keeps intact, heat shrinkage rates in both the longitudinal direction and the transverse direction are smaller than 10%, and the Gurley value is larger than 2000 S/100 CC.

2. The membrane of claim 1 , wherein the polyolefin plastic comprises more than 10 wt. % of a maleic anhydride grafted polyethylene (MAH-PE).

3. A method for manufacturing the membrane of claim 1 , the method comprising:
a) mechanically blending the polyolefin plastic, a compatibilizer, the raw rubber, and an antioxidant uniformly at a temperature of between 70 and 110° C. to yield a slurry, swelling the slurry for 8-24 hrs to produce a swelled slurry, introducing the swelled slurry after stable measurement to a twin screw extruder for continuous mixing, and performing sheet casting to produce a semi-finished gel sheet A; wherein the compatibilizer is selected from the group consisting of dioctyl sebacate (DOS), diisononyl phthalate (DINP), didecyl phthalate (DIDP), and a combination thereof;
b) biaxially hot stretching and strengthening the semi-finished gel sheet A;
c) performing in-line electron beam irradiation crosslinking; and
d) performing low temperature extraction, second hot stretching, and hot shaping.

4. The method of claim 3 , wherein the semi-finished gel sheet A is processed as follows:
the semi-finished gel sheet A is preheated, calendered and strengthened in a thickness direction with a thickness calendering ratio of between 1 and 2.5, followed by biaxially hot stretching and strengthening at a hot stretching temperature of 105-130° C. and hot stretching ratio of 3-7 in a machine direction (MD1) and 3-7 in a transverse direction (TD1);
the biaxially stretched membrane after the biaxial stretching is treated with in-line electron beam irradiation crosslinking with an irradiation dose of 50-250 KGy;
low temperature extraction is performed using an extraction solvent comprising alkanes and halogenated alkanes to selectively extract to remove the compatibilizer from a semi-finished membrane at a temperature of 0-55° C. under a normal pressure or a high pressure of 2-7 megapascal, whereby obtaining a semi-finished microporous membrane C1 based on polyolefin/rubber basically excluded from the high temperature compatibilizer; and
the semi-finished microporous membrane C1 after the extraction is performed with the second hot stretching and hot shaping to continuously regulate parameters comprising the pore size, the porosity, the thickness, and then cool rolled to yield the membrane.

5. The method of claim 3 , wherein the semi-finished gel sheet A is processed as follows:
the semi-finished gel sheet A is preheated, calendered and strengthened in a thickness direction with a thickness calendering ratio of 1-2.5, and biaxially hot stretched and strengthened at a hot stretching temperature of 105-130° C. and hot stretching ratio of 3-7 in a machine direction (MD1) and 3-7 in a transverse direction (TD1);
low temperature extraction is performed using an extraction solvent comprising alkanes and halogenated alkanes to selectively extract to remove the compatibilizer from the semi-finished membrane at a temperature of 0-55° C. under a normal pressure or a high pressure of 2-7 megapascal, whereby obtaining a semi-finished microporous membrane C2 based on the rubber/plastic composite material in the form of an analog interpenetrating polymer network (IPN);
the semi-finished microporous membrane C2 is performed with the second hot stretching and hot shaping to continuously regulate parameters comprising the pore size, the porosity, and the thickness to yield a basically finished microporous membrane D based on the rubber/plastic composite material in the form of the analog IPN; and
the basically finished microporous membrane D is treated by in-line electron beam irradiation crosslinking with an irradiation dose is 50-250 KGy, and then cool rolled to obtain the membrane.

6. A lithium ion battery comprising: a positive pole piece, a negative pole piece, an electrolyte, and the membrane of any one of claims 1 and 2 .

7. The membrane of claim 1 , wherein the membrane further comprises a layer B, wherein the layer B comprises the polyolefin plastic as a main body, and the post-crosslinked rubber, the post-crosslinked rubber being present at an amount of less than 20 wt. % of the layer B.

8. The membrane of claim 1 , wherein the membrane is prepared through a method comprising:
a) mechanically blending the polyolefin plastic, the raw rubber, a compatibilizer, and an antioxidant uniformly at a temperature of between 70 and 110° C. to yield a slurry, swelling the slurry for between 8 and 24 hrs to yield a swelled slurry, introducing the swelled slurry to

Assignees

• Li Xin
• Li Jianhua
• Chen Wei
• Jiao Yongjun
• Li Long
• Deng Xinjian
• Tianjin Dg Membrane Co Ltd

Inventors

• Li Xin
• Li Jianhua
• Chen Wei
• Jiao Yongjun
• Li Long
• Deng Xinjian

Classifications

• H01M10/0525 Primary

  Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries · CPC title

• H01M50/451

  comprising layers of only organic material and layers containing inorganic material · CPC title

• H01M50/494

  Tensile strength · 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