Microporous Battery Separator Membranes with Controlled Heat Shrinkage
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Microporous membranes for battery separators face challenges in achieving a balance between low heat shrinkage, high meltdown temperature, and low shutdown temperature, particularly at elevated temperatures, which is crucial for preventing internal short circuits and ensuring battery safety.
Innovation Solution
The development of microporous membranes comprising polymethylpentene (PMP) in the range of 22.0 wt.% to 40.0 wt.% based on the weight of the layer, with a specific process involving extrusion, stretching, and diluent removal, which results in membranes with controlled heat shrinkage and air permeability, enhancing thermal stability and safety margins.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If polyethylene and polymethylpentene are mixed with solvent or third polymer to produce microporous membrane, then shutdown temperature is reduced, but heat shrinkage at elevated temperature increases
Solution Approach 1:
The invention changes the chemical composition parameters by using specific polyethylene (HDPE or LLDPE with defined molecular weights and comonomer content) and polymethylpentene in precise weight ratios (20-40 wt% PMP), eliminating the need for third polymers or solvents while achieving the desired balance between shutdown temperature and heat shrinkage resistance
Solution Approach 2:
The invention creates a composite microporous membrane material consisting of polyethylene and polymethylpentene in a specific composition range, where the composite structure provides both low shutdown temperature (from polyethylene) and low heat shrinkage (from polymethylpentene), achieving properties that neither component alone could provide
2Temperature
If polymethylpentene content is increased to improve meltdown temperature, then heat shrinkage at 105°C is reduced, but air permeability decreases
Solution Approach 1:
The invention optimizes the polymethylpentene content parameter within a specific range (20-40 wt%) to achieve the desired balance between meltdown temperature, heat shrinkage resistance, and air permeability, avoiding both excessive PMP content (which would reduce permeability) and insufficient content (which would not provide adequate thermal stability)
3Object-affected harmful factors
If microporous membrane has low heat shrinkage at 105°C, then battery safety is improved, but shutdown temperature increases
Solution Approach 1:
The invention adjusts the polyethylene molecular weight parameters (using HDPE with Mw ≥ 5.0 × 10^5 or LLDPE with specific Mw and comonomer content) and the PMP content ratio to simultaneously achieve low heat shrinkage at 105°C and low shutdown temperature, resolving the trade-off between these two critical safety parameters
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 membranes exhibit desirable air permeability, increased meltdown temperature, and reduced heat shrinkage, effectively addressing the safety and performance concerns in battery applications by maintaining mechanical strength and preventing heat-induced failures.
Implementation Method 1
Microporous membranes are useful as separators for primary and secondary batteries
Implementation Method 2
Microporous membranes having a heat shrinkage in the range of about 1.0% to 10.0% at 105°C have been made using polyolefin
Data Source
Figure 1~3
AI summary
The present invention relates to microporous membranes comprising polymer and having well-balanced permeability and heat shrinkage, especially heat shrinkage at elevated temperature. The invention also relates to methods for making such membranes, and the use of such membranes as battery separator film in, e.g., lithium ion secondary batteries.