Multilayer Porous Membrane Structure for Thin Battery Separator Safety
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional multilayer porous membranes used in lithium ion secondary batteries for on-vehicle applications face challenges in ensuring safety and heat shrinkage resistance, particularly when subjected to nail penetration testing, due to their thickness and structure, which can lead to short circuiting.
Innovation Solution
A multilayer porous membrane with specific pore structure and composition, including a polyolefin resin base and porous layers containing inorganic particles and a binder polymer, is developed. The membrane has a controlled thickness, high inorganic particle content, and optimized pore distribution to enhance ion permeability and heat resistance, with a 400°C solder test to determine suitable design parameters.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If the thickness of the inorganic porous layers is reduced to decrease separator thickness, then the weight and thickness of the battery are reduced, but the heat shrinkage resistance is significantly impaired
Solution Approach 1:
The patent uses a composite porous layer comprising inorganic particles (such as alumina, silica, or boehmite) dispersed in a binder polymer matrix. This composite structure provides both mechanical strength and heat resistance in a thin layer, allowing the separator to maintain safety performance while reducing overall thickness. The inorganic particles form a heat-resistant skeleton that prevents shrinkage even when the layer is thin.
Solution Approach 2:
The patent optimizes specific parameters of the porous layer including particle size distribution (D50 between 0.03-1.0 μm, D90 ≤ 3.0 μm), inorganic particle content (30-90 wt%), and layer thickness (1-10 μm). By carefully controlling these parameters, the separator achieves adequate heat shrinkage resistance with minimal thickness, resolving the contradiction between thinness and safety.
2Reliability
If the porous layer thickness is increased to improve heat shrinkage resistance, then safety is enhanced, but the battery thickness and weight increase
Solution Approach 1:
The patent employs a porous layer with controlled porosity (30-70%) that provides high surface area and heat resistance in a thin configuration. The porous structure allows ion permeability while the inorganic particle framework maintains dimensional stability at high temperatures. This enables achieving heat shrinkage resistance without proportionally increasing thickness.
Solution Approach 2:
The patent transitions from relying on thickness for heat resistance to relying on the three-dimensional network structure of inorganic particles dispersed throughout the binder polymer. The spatial arrangement and connectivity of particles create a heat-resistant framework that functions effectively at minimal thickness, moving the solution from a one-dimensional (thickness-based) to a three-dimensional (structural network) approach.
3Ease of manufacture
If conventional multilayer porous membranes are used, then manufacturing process is simple, but safety in nail penetration tests is insufficient leading to short circuiting
Solution Approach 1:
The patent applies a porous layer with specific local properties (high inorganic particle content, controlled porosity, optimized particle size) only where needed on the separator surface. This localized enhancement of heat resistance and mechanical strength at the porous layer provides improved nail penetration safety without requiring changes to the entire separator structure or complex manufacturing processes.
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 provides a highly safe and effective multilayer porous membrane that maintains battery characteristics while improving safety in nail penetration tests and reducing heat shrinkage, ensuring reliable performance in on-vehicle lithium ion secondary batteries.
Implementation Method 1
the heat shrinkage-inhibiting functions of the conventional multilayer porous membranes described in PTLs 1 and 2 have been insufficient for the demands of high safety and high capacity for on-vehicle purposes
Implementation Method 2
Separators are generally required to have ion permeability and to also exhibit safety
Data Source
AI summary
Provided is a multilayered porous membrane that comprises a porous membrane containing polyolefin resin as the main component thereof, and that comprises a porous layer layered on at least one surface of the porous membrane and containing inorganic particles and a binder polymer. The total thickness of the porous layer is 0.5-3.0 μm; the number of pores in the porous layer having an area for the individual pore of at least 0.001 μm2 is 65-180 per 10 μm2 of the field of observation; of the pores in the porous layer that have an area of at least 0.001 μm2, the proportion therein of pores in the range from 0.001 μm2 to 0.05 μm2 is at least 90%; the proportion taken up by the inorganic particles in the porous layer is from 90-99 mass %; and the aspect ratio of the inorganic particles is from 1.0-3.0.