Expanded Graphite Heat Sink for Battery Thermal Management
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Solution Overview
Problem
Lithium-ion battery cells experience volume changes during charge-discharge cycles, leading to mechanical stresses and poor heat distribution due to the use of high-density graphite foils with limited compressibility, which hinders effective heat dissipation from hotspots.
Innovation Solution
A heat dissipator made of expanded graphite with a density of 0.6-1.4 g/cm³ and thermal conductivity of 120-240 W/(mK, combined with plastic particles, allowing for adaptability to volume changes and ensuring a permanent, conductive connection between battery cells and the heat sink.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If high-density graphite foils with density more than 1.5 g/cm³ are used to achieve strong anisotropy of thermal conductivity, then thermal conductivity in surface direction is improved, but compressibility and adaptability to volume changes deteriorate
Solution Approach 1:
The invention changes the density parameter of graphite from high-density (>1.5 g/cm³) to medium-density (0.6-1.4 g/cm³) by using expanded graphite. This parameter change simultaneously improves both thermal conductivity (120-240 W/(mK)) and compressibility (1-50%), resolving the contradiction between thermal performance and adaptability to battery cell volume changes.
Solution Approach 2:
The invention uses composite materials by combining expanded graphite with plastic particles (5-50% by weight). This composite structure maintains the excellent thermal conductivity of graphite while the plastic component enhances compressibility and elasticity, allowing the heat dissipator to adapt to battery cell volume changes during charge-discharge cycles.
2Temperature
If high-density graphite plates are used to provide strong thermal conductivity, then heat distribution is improved, but mechanical stress resistance deteriorates due to limited compressibility
Solution Approach 1:
By changing the density parameter from high-density to medium-density graphite, the invention achieves optimal balance between thermal conductivity and mechanical compliance. The expanded graphite structure provides sufficient thermal conductivity (120-240 W/(mK)) while enabling compressibility (1-50%) that reduces mechanical stresses during battery cell expansion and contraction.
Solution Approach 2:
The composite of expanded graphite with plastic particles creates a material that combines thermal conductivity with mechanical flexibility. The plastic component acts as a stress-absorbing matrix that allows the heat dissipator to deform elastically with battery cell volume changes, reducing mechanical stress concentration.
3Temperature
If high-density graphite foils are used to achieve anisotropic thermal conductivity, then thermal performance is improved, but contact quality with battery cells deteriorates due to poor adaptability
Solution Approach 1:
The invention optimizes the density parameter to medium-range (0.6-1.4 g/cm³), which provides the right balance between maintaining thermal conductivity and achieving sufficient compressibility. This allows the heat dissipator to conform to battery cell surfaces while maintaining effective thermal contact during charge-discharge cycles.
Solution Approach 2:
The expanded graphite-plastic composite provides both thermal conductivity pathways through the graphite structure and conformability through the plastic matrix. This composite enables reliable contact quality by allowing the heat dissipator to adapt to surface irregularities and volume changes while maintaining thermal performance.
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 enables uniform heat distribution and dissipation of excess thermal energy, avoiding mechanical stresses and ensuring continuous contact for efficient heat transfer, even during volume expansions and reductions of battery cells.
Implementation Method 1
the flat material has a thermal conductivity in the surface direction of 120-240 W/(mK)... good thermal conductivity in the surface direction can be provided
Implementation Method 2
with their considerable heat storage capacity... permanent heat input into the panels due to their limited heat storage capacity
Implementation Method 3
the flat material has a resilience of 0.5-15%... in the thickness direction, whereby the heat dissipator with a volume reduction of the battery cells in the released space can spread
Data Source
Figure 1~7c
AI summary
The invention relates to a heat sink (6-6'''''; 10-10''; 12; 14; 16; 18) having a flat graphite-containing material which is provided for bearing against one or more battery cells (5-5''; 15, 17, 19), and to an electrical energy storage means (1) having at least one battery cell (5-5''; 15, 17, 19) and a heat sink (6-6'''''; 10-10''; 12; 14; 16; 18), which is arranged on at least one outer face of the battery cell (5-5''; 15, 17, 19) and has a flat graphite-containing material, for dissipating heat from the battery cell (5-5''; 15, 17, 19). According to the invention, the flat graphite-containing material contains graphite expandate.