Multi-layer Microporous Polyolefin Battery Separator
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Solution Overview
Problem
Current battery separator membranes face challenges with high heat shrinkage, leading to potential internal short circuits in batteries, especially at elevated temperatures, which existing technologies have not adequately addressed.
Innovation Solution
A multi-layer microporous polyolefin membrane with specific layer compositions and production methods is developed, featuring a heat shrinkage ratio of less than 3% in at least one planar direction and a rupture temperature of 180°C or higher, utilizing a combination of polyethylene and polypropylene with controlled molecular weights and diluents to enhance thermal stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional microporous polyolefin membranes are used as battery separators, then they provide basic separation function, but they exhibit high heat shrinkage at elevated temperatures causing internal short circuits
Solution Approach 1:
The membrane is divided into multiple layers with distinct functions: a first microporous layer containing polyethylene provides shutdown function, while a second microporous layer containing polypropylene with specific molecular weight provides heat shrinkage resistance. This segmentation allows each layer to optimize its properties for its specific role, resolving the contradiction between basic separation and thermal stability.
Solution Approach 2:
The invention uses a composite structure combining polyethylene and polypropylene with controlled molecular weights in a multi-layer configuration. The polypropylene layer with weight-average molecular weight of 6×10^5 or more provides exceptional heat shrinkage resistance while the polyethylene layer provides shutdown function, creating a composite material that simultaneously achieves both reliability and prevents harmful heat shrinkage effects.
2Stability of the object's composition
If polypropylene with high molecular weight is used to reduce heat shrinkage, then thermal stability improves, but manufacturing complexity increases due to specific molecular weight requirements
Solution Approach 1:
The invention specifies precise parameter ranges for the polypropylene, particularly weight-average molecular weight of 6×10^5 or more and molecular weight distribution Mw/Mn of 3.0 or more. By defining these specific parameter ranges, the patent transforms the manufacturing challenge into a controlled parameter specification, allowing manufacturers to achieve thermal stability through measurable and controllable material properties.
Data Source
AI summary
The invention relates to a microporous membrane having a relatively low heat shrinkage values along planar axes of the membrane. The invention also relates to a battery separator formed by such microporous membrane, and a battery comprising such a separator. Another aspect of the invention relates to a method for making the multi-layer, microporous polyolefin membrane, a method for making a battery using such a membrane as a separator, and a method for using such a battery.