Variable Impedance Lithium Battery Cells for Heat Sink Compensation
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Solution Overview
Problem
Lithium polymer batteries experience reduced discharge capacity due to uneven heat distribution within the battery casing, where electrochemical cells adjacent to the walls lose heat more rapidly, leading to lower operating temperatures and premature end-of-discharge.
Innovation Solution
The electrochemical cells adjacent to the heat sinks within the battery casing have a higher lithium salt concentration in their electrolyte and cathode, with a polymer/salt ratio of approximately 5:1 compared to those farther away, reducing impedance and enhancing discharge capability at lower temperatures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If electrochemical cells are arranged in a rigid casing with heat sink paths, then heat dissipation is improved, but cells adjacent to heat sinks experience excessive heat loss and reach end-of-discharge voltage prematurely
Solution Approach 1:
The patent applies local quality by differentiating the impedance characteristics of electrochemical cells based on their spatial location within the battery assembly. Specifically, cells positioned adjacent to heat sink paths are assigned lower impedance values compared to cells located in the center or away from heat sinks. This localized differentiation compensates for the uneven heat distribution, ensuring that all cells reach their end-of-discharge voltage simultaneously and maximizing overall battery discharge capacity.
2Ease of manufacture
If uniform impedance is assigned to all electrochemical cells, then manufacturing simplicity is maintained, but uneven temperature distribution causes premature discharge in cells near heat sinks
Solution Approach 1:
The patent implements local quality by assigning different impedance values to electrochemical cells based on their position relative to heat sink paths. Cells adjacent to heat sinks are configured with lower impedance to compensate for their higher heat loss rate, while cells in the center or away from heat sinks maintain higher impedance values. This position-dependent impedance differentiation ensures uniform discharge performance across all cells while maintaining practical manufacturability through a systematic configuration approach.
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
This configuration ensures that all electrochemical cells reach their end-of-discharge voltage simultaneously, maximizing the battery's discharge capacity by compensating for heat loss and maintaining optimal temperatures across the battery.
Implementation Method 1
excess heat generated by the plurality of electrochemical cells making up the battery is dissipated through the walls of the battery casing
Implementation Method 2
a solid electrolyte comprising a polymer and a lithium salt separating the positive electrode from the negative electrode and providing ionic conductivity between the electrodes
Data Source
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AI summary
A lithium battery comprising a plurality of electrochemical cells assembled together which are inserted in a rigid casing having side walls and upper and lower walls forming an enclosure; and at least one heat sink path to dissipate excess heat generated by the electrochemical cells; the electrochemical cells are assembled such that the electrochemical cells positioned adjacent to the heat sink path have a lower impedance than the other electrochemical cells of the battery.