Graphite Heat Spreaders for Prismatic Battery Thermal Uniformity
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Solution Overview
Problem
Lithium ion battery packs face reduced capacity and performance due to temperature variations within the battery pack, leading to uneven charge and discharge efficiency among cells, which can shorten the battery's life cycle and reduce its operational temperature range.
Innovation Solution
Incorporating graphite heat spreaders with high in-plane thermal conductivity (>300 W/mK) in thermal communication with lithium polymer cells and heat sinks to manage temperature evenly across the battery pack, reducing thermal gradients and maintaining optimal operating conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If conventional thermal management is used without high thermal conductivity spreaders, then the battery pack structure is simpler and lighter, but temperature uniformity across cells deteriorates leading to reduced performance
Solution Approach 1:
The patent changes the thermal conductivity parameter of the heat spreader material from conventional values to greater than 300 W/mK (such as graphite or diamond-like carbon), which dramatically improves temperature uniformity across cells without requiring complex active thermal management systems
Solution Approach 2:
The patent uses thin film heat spreaders that can be replicated and applied to multiple cells uniformly, creating consistent thermal pathways across the battery pack while maintaining simplicity
2Productivity
If high thermal conductivity heat spreaders are used to improve temperature uniformity, then charge/discharge efficiency improves, but the weight of the battery pack increases
Solution Approach 1:
The patent employs thin film heat spreaders with thicknesses typically ranging from 1-50 micrometers, which provide the necessary thermal conductivity while maintaining extremely low weight, thus improving charge/discharge efficiency without significantly increasing battery pack weight
Solution Approach 2:
By selecting materials with exceptionally high thermal conductivity (greater than 300 W/mK), the patent achieves efficient heat distribution with minimal material thickness, thereby maintaining low weight while improving productivity
3Adaptability or versatility
If the battery operates outside the optimal temperature range, then adaptability to various environments improves, but the life cycle and capacity are reduced
Solution Approach 1:
The patent implements passive thermal management through high conductivity heat spreaders that proactively distribute heat throughout the battery pack before hot spots can develop, preventing thermal runaway and extending battery life while enabling operation in broader temperature ranges
Solution Approach 2:
The high thermal conductivity heat spreaders enable the battery pack to self-regulate temperature distribution without external intervention, automatically maintaining optimal operating conditions across cells even when ambient temperatures vary, thus improving both adaptability and 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 use of graphite heat spreaders enhances thermal management, maintaining peak performance and extending the battery pack's life cycle by ensuring consistent charge and discharge rates across cells, even at varying temperatures, thus improving the overall energy storage capacity and efficiency.
Implementation Method 1
Each heat spreader is in thermal communication with the heat sink and each heat spreader has an in-plane thermal conductivity of greater than about 300 W/mK at about room temperature
Data Source
AI summary
A lithium ion battery pack includes a plurality of prismatic lithium polymer cells and one or more graphite heat spreaders. Each spreader has at least two major surfaces and is made of one of a sheet of a compressed mass of exfoliated graphite particles, a graphitized polyimide sheet, or combinations thereof.