Multi-layer Microporous Polyethylene Battery Separator with Heat-resistant Polymer
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Solution Overview
Problem
Existing microporous polyolefin membranes used in battery separators lack sufficient compression resistance, leading to inadequate battery capacity and cycle characteristics due to poor permeability variation and deformability under electrode expansion and contraction.
Innovation Solution
A multi-layer microporous polyethylene membrane is developed, comprising a first layer of ultra-high-molecular-weight polyethylene and a second layer with a heat-resistant polymer having a melting point or glass transition temperature of 170° C. or higher, dispersed as fine particles, enhancing shutdown properties, meltdown properties, permeability, mechanical strength, heat shrinkage resistance, and compression resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If polypropylene is used as the main component of microporous membranes, then heat shrinkage resistance is improved, but compression resistance deteriorates
Solution Approach 1:
The invention uses a composite structure consisting of a polypropylene layer and a polyethylene layer with heat-resistant filler. The polypropylene layer provides heat shrinkage resistance, while the polyethylene layer with heat-resistant filler (such as heat-resistant polyester or inorganic filler) provides compression resistance. This composite material approach allows both requirements to be satisfied simultaneously by combining materials with complementary properties.
2Strength
If polyethylene is used as the main component of microporous membranes, then compression resistance is improved, but shutdown temperature is too low
Solution Approach 1:
The invention creates a composite structure where the polyethylene layer is enhanced with heat-resistant filler (heat-resistant polyester or inorganic filler). This composite polyethylene layer maintains the compression resistance of polyethylene while the heat-resistant filler raises the effective shutdown temperature. The polypropylene layer further contributes to heat resistance, solving the low shutdown temperature problem of pure polyethylene.
Solution Approach 2:
The invention applies different functional properties to different layers: the polyethylene layer with heat-resistant filler provides local compression resistance and elevated temperature stability, while the polypropylene layer provides heat shrinkage resistance. This local differentiation of material properties allows each layer to optimize its specific function while contributing to overall performance.
3Strength
If polypropylene layers are used to improve strength, then mechanical strength is improved, but permeability deteriorates
Solution Approach 1:
The invention uses a composite structure where the polyethylene layer with heat-resistant filler provides high permeability due to polyethylene's inherent properties, while the polypropylene layer provides mechanical strength. The laminate structure allows both materials to contribute their advantageous properties without compromising either permeability or strength, as each layer performs its primary function independently.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The multi-layer membrane provides well-balanced properties, improving battery capacity, cycle characteristics, and safety by maintaining structural integrity and permeability under thermal stress and electrode expansion, while ensuring efficient shutdown and meltdown performance.
Implementation Method 1
fibrils are cleft with the fine particles as nuclei, thereby forming creased gaps constituting pores
Implementation Method 2
microporous polyethylene membrane... having well-balanced shutdown properties, meltdown properties, permeability
Implementation Method 3
shutdown properties... for stopping a battery reaction at the time of abnormal heat generation
Implementation Method 4
heat-resistant polymer other than polypropylene... heat shrinkage resistance... compression resistance
Data Source
AI summary
A multi-layer, microporous polyethylene membrane comprising (a) a first microporous layer made of a polyethylene resin, and (b) a second microporous layer comprising a polyethylene resin, and a heat-resistant polymer having a melting point or a glass transition temperature of 170° C. or higher, the heat-resistant polymer being dispersed in the form of fine particles in the polyethylene resin, and the second microporous layer having pores containing fine particles of the heat-resistant polymer as nuclei from which the cleavage of polyethylene resin fibrils starts, the multi-layer microporous polyethylene membrane having well-balanced shutdown properties, meltdown properties, permeability, mechanical strength, heat shrinkage resistance and compression resistance.