Battery Separator Thermal Shrinkage Control via Composite Structure
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Solution Overview
Problem
Current nonaqueous electrolyte batteries face safety issues due to thermal shrinkage of separators at high temperatures, leading to potential short circuits, as existing solutions either limit separator thickness or focus on thermal stability at temperatures below 120°C, failing to ensure safety at higher temperatures.
Innovation Solution
A battery separator incorporating heat-resistant fine particles and a thermoplastic resin, with specific particle size distributions and a multilayer structure, including a heat-resistant layer and a shutdown layer, to suppress thermal shrinkage and prevent short circuits at temperatures between 100°C to 150°C, and a positive electrode with a high heat generation starting temperature of 180°C or higher.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If a polyolefin microporous film separator is used to ensure basic separation function, then the separator can be made thin (20-30 μm) to improve battery energy density, but the separator easily shrinks at high temperatures causing short circuits
Solution Approach 1:
The patent uses a composite separator structure consisting of a heat-resistant base layer (polyester nonwoven fabric or heat-resistant resin) combined with a microporous film layer. This composite structure provides both the thin profile needed for high energy density and the thermal stability required to prevent shrinkage-induced short circuits at high temperatures.
Solution Approach 2:
The patent changes the material composition parameters of the separator by incorporating heat-resistant materials (polyester with high glass transition temperature, heat-resistant resins) and controlling the microporous structure parameters (pore size, porosity) to maintain separation integrity at elevated temperatures while keeping the separator thin.
2Quantity of substance
If the separator thickness is reduced to increase battery capacity, then energy density improves, but thermal shrinkage resistance decreases leading to safety issues
Solution Approach 1:
The composite separator combines a heat-resistant base layer that prevents thermal shrinkage with a microporous film layer that enables ion transport. This allows the separator to remain thin (maintaining high battery capacity) while the heat-resistant base layer counteracts thermal shrinkage forces at elevated temperatures.
Solution Approach 2:
The separator exhibits local quality differentiation where the base layer provides heat resistance and dimensional stability, while the microporous film layer provides ion permeability. This localized functional distribution allows thin overall thickness while maintaining thermal shrinkage resistance through the specialized base layer.
3Device complexity
If conventional separators are used to maintain simple battery structure, then manufacturing is easy, but safety at temperatures above 120°C cannot be ensured
Solution Approach 1:
The patent employs a composite separator structure with a heat-resistant base layer and a microporous film layer, providing both high-temperature safety and maintaining relatively simple manufacturing processes through established lamination techniques for battery separators.
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 solution effectively prevents short circuits and ensures the safety of nonaqueous electrolyte batteries in high-temperature environments by controlling thermal shrinkage and maintaining electrical integrity, enhancing safety and reliability.
Implementation Method 1
A battery separator incorporating heat-resistant fine particles and a thermoplastic resin, with specific particle size distributions and a multilayer structure, including a heat-resistant layer and a shutdown layer, to suppress thermal shrinkage and prevent short circuits at temperatures between 100°C to 150°C
Implementation Method 2
the proportion of particles with a particle size of 0.2 μm or less in the heat-resistant fine particles is 10 vol % or less and the proportion of particles with a particle size of 2 μm or more in the heat-resistant fine particles is 10 vol % or less
Data Source
AI summary
A nonaqueous electrolyte battery of the present invention includes a positive electrode having a positive active material capable of intercalating and deintercalating a lithium ion, a negative electrode having a negative active material capable of intercalating and deintercalating a lithium ion, a separator interposed between the positive electrode and the negative electrode, and a nonaqueous electrolyte. The heat generation starting temperature of the positive electrode is 180° C. or higher. The separator includes heat-resistant fine particles and a thermoplastic resin. The proportion of particles with a particle size of 0.2 μm or less in the heat-resistant fine particles is 10 vol % or less and the proportion of particles with a particle size of 2 μm or more in the heat-resistant fine particles is 10 vol % or less. The separator effects a shutdown in the range of 100° C. to 150° C.