Battery Separator Coating for Low-Temperature Thermal Shutdown
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Solution Overview
Problem
Thermal runaway and heat-related safety issues in lithium-based batteries, particularly in high-power applications like hybrid electric vehicles, necessitate a rapid shutdown mechanism at temperatures below 135°C to prevent catastrophic failure.
Innovation Solution
A separator for electrochemical cells comprising a porous substrate made of an olefin-based polymer with a melting point above 130°C and a porous coating layer composed of ethylene-based microparticles with a melting range of 80°C to 110°C, which transforms into a non-porous layer upon heating to halt ion transport and prevent further reactions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a separator with high melting point polymer is used to maintain structural integrity, then mechanical strength is improved, but rapid shutdown capability at low temperature deteriorates
Solution Approach 1:
The separator is divided into two functional layers: a porous substrate layer made of high melting point olefin polymer for mechanical strength, and a porous coating layer made of low melting point ethylene polymer for rapid shutdown. This segmentation allows each layer to perform its specialized function without compromise.
Solution Approach 2:
The separator uses a composite structure combining olefin-based polymer substrate with ethylene-based polymer coating layer. The composite material design integrates the high temperature stability of olefin polymers with the low temperature shutdown特性 of ethylene polymers, achieving both mechanical strength and rapid shutdown capability.
2Productivity
If a porous coating layer is applied to enable ion transport, then electrochemical performance is improved, but thermal runaway prevention capability deteriorates
Solution Approach 1:
The coating layer transitions from a porous state at normal operating temperatures (allowing ion transport) to a non-porous melted state at thermal runaway temperatures (blocking ion transport). This dynamic phase change enables the separator to adapt its properties based on temperature conditions, simultaneously achieving high ion transport efficiency and thermal runaway prevention.
Solution Approach 2:
The ethylene-based polymer coating layer undergoes a phase transition from solid porous structure to liquid melted state at temperatures between 90-120°C. This phase transition causes the coating layer to collapse and block pores, preventing thermal runaway while maintaining ion transport at lower operating temperatures.
3Reliability
If microparticles with small size are used to increase coating density, then shutdown reliability is improved, but manufacturing precision deteriorates due to particle distribution control
Solution Approach 1:
A binder material is introduced as an intermediary substance to hold the microparticles together and adhere them to the substrate. This binder facilitates uniform particle distribution and coating formation during manufacturing, reducing the difficulty of controlling microparticle placement while maintaining shutdown reliability.
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 effectively shuts down thermal runaway by transforming into a non-porous layer at elevated temperatures, preventing further reactions and ensuring safety in lithium-based batteries.
Implementation Method 1
The porous coating layer (B) has a Tm from 80° C. to 110° C.... transforms into a non-porous layer upon heating to halt ion transport
Data Source
AI summary
The present disclosure provides an electrochemical cell. In an embodiment, the electrochemical cell includes a separator disposed between an optional anode and an optional cathode. The separator includes (A) a porous substrate and (B) a porous coating layer on the substrate. The porous substrate (A) is composed of an olefin-based polymer having a melting point, Tm, greater than 130° C. The porous coating layer (B) has a melting temperature from 80° C. to 110° C. The porous coating layer (B) is composed of a plurality of microparticles, and an optional binding agent. The microparticles have an average particle size from 0.3 microns to 1.5 microns. The microparticles are composed of (i) an ethylene-based polymer, having (a) a density from 0.90 g/cc to less than 0.94 g/cc, (b) a Tm from 90° C. to 120° C., (c) a melt index from 30 g/10 min to 600 g/10 min. The microparticles also include (ii) a dispersant composed of a C14-C40 aliphatic fatty acid. The microparticles also include (iii) an optional acid functional wax.