Composite Heat Spreader Mitigates Battery Thermal Runaway
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Solution Overview
Problem
Lithium ion battery packs face a high risk of thermal runaway due to tight spacing, which exacerbates heat transfer and safety risks, especially in electric vehicle applications where energy density targets require minimal unused space.
Innovation Solution
A composite heat spreader comprising a first and second flexible graphite layer with a gas evolving layer in between, which reduces thermal conductivity by at least a factor of five when a threshold temperature is reached, effectively acting as a thermal fuse to shield adjacent cells from heat and potentially disconnect overheated cells from the electrical system.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If lithium ion cells are packaged with tight spacing to meet energy density targets, then energy density is improved, but thermal runaway risk increases due to enhanced heat transfer between cells
Solution Approach 1:
A composite heat spreader is positioned between adjacent battery cells to act as an intermediary thermal management component. The heat spreader includes a gas evolving layer that remains thermally conductive at normal operating temperatures to dissipate heat, but evolves gas when threshold temperature is reached to create thermal isolation and prevent thermal runaway propagation to neighboring cells
Solution Approach 2:
The thermal conductivity parameter of the gas evolving layer changes dynamically with temperature. At normal operating temperatures, the layer maintains high thermal conductivity for effective heat dissipation. When the threshold temperature is reached, the layer evolves gas which reduces thermal conductivity by at least a factor of five, transforming the thermal management behavior from heat conduction to thermal isolation
2Volume of moving object
If tight spacing is used between battery cells, then space utilization is improved, but heat transfer between cells is exacerbated increasing safety risks
Solution Approach 1:
The composite heat spreader serves as an intermediary component inserted between closely spaced battery cells. It provides a controlled thermal interface that facilitates heat dissipation under normal conditions while preventing thermal runaway propagation through gas evolution and thermal isolation when threshold temperatures are reached
Solution Approach 2:
The gas evolving layer undergoes a phase transition or chemical decomposition when threshold temperature is reached, evolving gas that fills the space between battery cells and transforms the thermal management regime from conductive heat transfer to convective and radiative heat transfer with significantly reduced thermal conductivity
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 composite heat spreader mitigates thermal runaway by reducing heat transfer between battery cells and can electrically disconnect overheated cells, enhancing safety and reducing the risk of chain reactions during thermal events.
Implementation Method 1
When a threshold temperature is reached, the thermal conductivity of the gas evolving layer is reduced by at least factor of five
Implementation Method 2
a first flexible graphite layer, a second flexible graphite layer, and a gas evolving layer positioned between the first flexible graphite layer and the second flexible graphite layer
Data Source
AI summary
A composite heat spreader includes a first flexible graphite layer, a second flexible graphite layer, and a gas evolving layer positioned between the first flexible graphite layer and the second flexible graphite layer. The gas evolving layer is temperature sensitive and when a threshold temperature is reached, the thermal conductivity of the gas evolving layer is reduced by at least factor of five.