Shutdown Layer with Low Melting Point Wax for Battery Thermal Runaway Prevention
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Solution Overview
Problem
Lithium-ion batteries in electric vehicles face thermal runaway due to internal short circuits, which existing solutions like automatic shutdown separators and external fuses fail to effectively address, as they either allow continued ionic current transport or permanently deactivate the battery.
Innovation Solution
A shutdown layer comprising a low melting point wax material and conductive particles is introduced between the separator and electrodes, forming a conductive network that becomes non-conductive at elevated temperatures, effectively disconnecting internal short circuits and preventing thermal runaway while maintaining battery functionality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If automatic shutdown separators are used to prevent thermal runaway, then battery safety is improved, but ionic current transport continues and self-discharge is not effectively prevented
Solution Approach 1:
The shutdown layer is constructed as a composite material combining low melting point wax material with conductive particles (such as conductive carbon). This composite structure allows the layer to be electrically conductive during normal operation, preventing self-discharge, while the low melting point wax component enables thermal shutdown functionality when temperature exceeds the melting point, thus resolving the contradiction between preventing self-discharge and enabling thermal runaway protection.
2Reliability
If external fuses are used to address internal short circuits, then thermal runaway prevention is improved, but the battery is permanently deactivated
Solution Approach 1:
The shutdown layer employs a dynamic response mechanism based on temperature-dependent phase change. During normal operation below the melting point, the conductive particles maintain electrical conductivity, allowing the battery to function normally. When thermal runaway occurs and temperature exceeds the melting point, the wax material melts and the conductive network breaks, electrically isolating the short circuit. This dynamic behavior allows the battery to remain operational under normal conditions while providing automatic protection during thermal events, avoiding permanent deactivation.
Solution Approach 2:
The electrical conductivity parameter of the shutdown layer changes with temperature. At normal operating temperatures, the conductive particles provide sufficient conductivity to prevent self-discharge. At elevated temperatures above the melting point, the phase change of the wax material causes a dramatic change in conductivity, isolating the short circuit. This parameter change approach allows the system to adapt its electrical properties based on thermal conditions, preventing thermal runaway while maintaining battery functionality.
3Strength
If the shutdown layer uses high melting point material for structural stability, then mechanical strength is improved, but thermal runaway prevention capability deteriorates
Solution Approach 1:
The shutdown layer combines low melting point wax material with conductive particles to create a composite structure. The conductive particles (such as conductive carbon) provide structural integrity and electrical conductivity, while the wax material provides the thermal response function. This composite approach allows the layer to maintain mechanical strength and electrical conductivity during normal operation, while the low melting point wax enables thermal runaway prevention when temperature exceeds the melting point, resolving the contradiction between structural stability and thermal protection capability.
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 shutdown layer effectively limits or eliminates self-discharge and prevents thermal runaway by electrically isolating short circuits, allowing the battery to remain operational with reduced capacity, unlike previous solutions that shut down all ionic transport or did not address the short circuit issue.
Implementation Method 1
At a melting point temperature of the LMP material, the conductive network is reduced such that at least a portion of the shutdown layer is substantially electrically non-conductive
Data Source
AI summary
In at least one embodiment, a battery is provided comprising an anode and cathode, a separator between the anode and cathode, and a shutdown layer between the separator and the anode or cathode. The shutdown layer may include low melting point material and a conductive material within the low melting point material forming a conductive network within the shutdown layer. At a melting point temperature of the low melting point material, the conductive network is reduced such that at least a portion of the shutdown layer is substantially electrically non-conductive. The shutdown layer may be a free-standing layer or may be coated one or both of the electrodes.