Microlayer membranes, battery separators, batteries, and related methods
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Solution Overview
Problem
Existing methods for manufacturing microporous multilayer battery separators do not fully optimize the balance of strength and performance properties required for advanced lithium-ion batteries, particularly in achieving thinner and stronger separators.
Innovation Solution
The development of microporous multilayer battery separators is achieved through a coextrusion process involving multiple polymer mixtures, followed by lamination, to create layers with improved properties such as enhanced elasticity, compressibility, elongation, and reduced high-temperature shrinkage, using additives like polysiloxanes and fatty acid salts to enhance performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional coextrusion or lamination methods are used to manufacture microporous multilayer battery separators, then the basic separator structure is formed, but the balance of strength and performance properties is not fully optimized
Solution Approach 1:
The separator is divided into multiple functional layers (first outer layer, first inner layer, second inner layer, second outer layer) with distinct polymer compositions and pore structures. Each layer is engineered to provide specific properties: the outer layers provide mechanical strength and stability, while the inner layers provide shutdown functionality and heat resistance. This segmentation allows optimization of puncture strength through the outer layers while maintaining safety functions in the inner layers.
Solution Approach 2:
The invention uses composite polymer structures combining different materials in each layer. The outer layers use polymers with high mechanical strength and thermal stability, while the inner layers use polymers with lower melting points for shutdown functionality. This composite approach enables the separator to simultaneously achieve high puncture strength and appropriate safety response characteristics that cannot be obtained with single-material separators.
2Length of moving object
If the separator is made thinner to improve battery energy density, then the space for electrolyte and electrodes increases, but the strength and durability of the separator decreases
Solution Approach 1:
The multilayer structure segments the thickness into functional zones where outer layers provide mechanical reinforcement and inner layers provide safety functions. This allows the overall separator to be thinner while maintaining strength through the optimized outer layer composition and structure, as the inner layers are designed for functionality rather than mechanical support.
Solution Approach 2:
Different regions of the separator have different properties optimized for their specific functions. The outer layers have higher crystallinity and thermal stability for mechanical strength, while the inner layers have lower melting points for shutdown functionality. This local differentiation allows thinning of the separator overall while concentrating strength properties in the outer layers where they are most needed for puncture resistance.
3Temperature
If high-temperature resistant materials are used to improve thermal stability, then the separator maintains structure at high temperatures, but the elasticity and compressibility decrease
Solution Approach 1:
The separator segments thermal response functions across different layers. The outer layers use high-temperature resistant polymers that maintain structural integrity and provide thermal stability up to high temperatures. The inner layers use polymers with lower melting points that provide shutdown functionality at moderate temperatures and maintain elasticity and compressibility for normal battery operation. This segmentation allows the separator to exhibit both high-temperature stability and appropriate mechanical flexibility.
Solution Approach 2:
The invention changes the thermal parameters of different layers to achieve complementary properties. The outer layers are designed with high melting points and thermal stability for structural maintenance, while the inner layers are designed with lower melting points for active shutdown response. This parameter differentiation across layers allows the overall separator to maintain both high-temperature resistance and operational elasticity.
4Reliability
If multiple layers are added to improve strength and performance, then the separator achieves better safety and durability, but the manufacturing complexity and production cost increase
Solution Approach 1:
The separator is segmented into four distinct layers with specific functions, where the multilayer structure achieves superior reliability through functional differentiation. While this segmentation increases manufacturing complexity compared to single-layer separators, it enables precise control over safety and durability properties that cannot be achieved with simpler structures.
Solution Approach 2:
The invention merges multiple manufacturing steps into an integrated coextrusion process where all four layers are formed simultaneously in a single production run. This merging approach, combined with lamination techniques, achieves the complex multilayer structure in one continuous process, reducing the overall manufacturing complexity that would result from assembling pre-made layers and enabling production scalability.
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 resulting microporous multilayer battery separators exhibit improved safety, strength, and durability, with increased puncture strength, elasticity, and reduced shrinkage, addressing the limitations of prior bi-layer or tri-layer separators.
Implementation Method 1
coextrusion process involving multiple polymer mixtures
Implementation Method 2
followed by lamination, to create layers with improved properties
Implementation Method 3
using additives like polysiloxanes and fatty acid salts to enhance performance
Data Source
AI summary
Described herein is a multilayer microporous film or membrane that may exhibit improved properties, including improved dielectric break down and strength, compared to prior monolayer or tri-layer microporous membranes of the same thickness. The preferred multilayer microporous membrane comprises microlayers and one or more lamination interfaces or barriers. Also disclosed is a battery separator or battery comprising one or more of the multilayer microporous films or membranes. The inventive battery and battery separator is preferably safer and more robust than batteries and battery separators using prior monolayer and tri-layer microporous membranes. Also, described herein is a method for making the multilayer microporous separators, membranes or films described herein.