Three-Layer Li-Ion Separator for Thin Strength and Thermal Stability
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Solution Overview
Problem
Existing lithium-ion battery separators struggle to balance high mechanical strength with excellent thermal dimensional stability, especially at thinner thicknesses, leading to potential short circuits due to heat deformation and mechanical failure.
Innovation Solution
A lithium-ion battery separator design featuring a core layer with higher molecular weight and a surface layer with lower molecular weight, along with specific melt index ratios, to achieve balanced thermal shrinkage and strength, combined with a manufacturing process that includes melting, molding, bi-directional stretching, and heat setting.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the separator is made thinner to improve energy density, then the energy density is improved, but the mechanical strength sharply decreases
Solution Approach 1:
The separator employs a three-layer structure with different molecular weights: high molecular weight core layer (1.5-3.0 million) for strength, and low molecular weight surface layers (0.5-1.5 million) for thermal stability. This local differentiation allows each layer to perform its specific function optimally while maintaining overall separator performance.
2Use of energy by moving object
If the separator is made thinner to improve energy density, then the energy density is improved, but the thermal dimensional stability deteriorates
Solution Approach 1:
The surface layers with low molecular weight (0.5-1.5 million) are specifically designed to provide excellent thermal dimensional stability with low thermal shrinkage rate, while the thin overall structure maintains high energy density.
3Strength
If the molecular weight is increased to improve mechanical strength, then the mechanical strength is improved, but the thermal shrinkage rate increases
Solution Approach 1:
The core layer uses high molecular weight polymer (1.5-3.0 million) to provide high mechanical strength and stretching strength, while the surface layers use low molecular weight polymer (0.5-1.5 million) to provide low thermal shrinkage rate, achieving a balance between these two properties.
Solution Approach 2:
The separator is constructed as a composite of polymer materials with different molecular weights, combining the advantages of high molecular weight (strength) and low molecular weight (thermal stability) materials in a single structure.
4Strength
If the stretching ratio is increased to improve mechanical strength, then the mechanical strength is improved, but the thermal dimensional stability control and tensile uniformity are adversely affected
Solution Approach 1:
The three-layer structure with high molecular weight core and low molecular weight surfaces allows for optimized stretching parameters (5-15 times) that achieve high mechanical strength while maintaining good tensile uniformity and thermal dimensional stability control.
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 separator exhibits improved mechanical strength, thermal dimensional stability, and gas permeability, with reduced thermal shrinkage and enhanced safety under high temperatures, even at thinner thicknesses.
Implementation Method 1
bi-directionally stretching the stretched stacked layer body to obtain a stretched stacked layer body
Implementation Method 2
performing heat setting on the separator precursor to obtain the separator
Implementation Method 3
removing the pore-forming agent from the stretched stacked layer body to obtain a separator precursor
Data Source
AI summary
Some embodiments relate to the technical field of lithium ion battery diaphragms. Provided are an ultrathin lithium ion battery diaphragm with high mechanical strength and excellent thermal dimensional stability, and a preparation method thereof.