Variable Porosity Battery Separators for Current Uniformity
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Solution Overview
Problem
Battery constructions with internal terminals often result in non-uniform current density and temperature distribution across electrodes, leading to uneven electrode decay, mechanical stresses, and accelerated cell failure.
Innovation Solution
The development of variable porosity separators with controlled pore size and distribution, created through a solvent exchange process and selective densification, to ensure uniform ionic flow and current distribution by varying porosity along the separator's width, with higher porosity regions further from electrode tabs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If internal terminals are used to connect multiple electrodes, then electrical connection between electrodes is achieved, but non-uniform current density and temperature distribution occur across electrodes
Solution Approach 1:
The separator is designed with variable porosity distribution, where different regions of the separator have different pore sizes and densities. Specifically, the separator has higher porosity in regions farther from electrode tabs and lower porosity near tabs, creating localized differences in ionic conductivity that compensate for the non-uniform current distribution caused by internal terminals
2Ease of manufacture
If internal terminals are used to connect multiple electrodes, then electrical connection between electrodes is achieved, but temperature distribution becomes non-uniform across electrodes
Solution Approach 1:
The variable porosity separator creates regions with different thermal and ionic properties. The higher porosity regions farther from tabs provide enhanced ionic transport pathways that reduce local resistance and heat generation, while lower porosity regions near tabs provide structural stability, collectively promoting more uniform temperature distribution
3Ease of manufacture
If internal terminals are used to connect multiple electrodes, then electrical connection between electrodes is achieved, but electrode decay becomes uneven
Solution Approach 1:
The separator's variable porosity creates optimized local environments at different positions. Regions with higher porosity enhance ionic access and reduce concentration polarization, while regions with lower porosity provide mechanical support, ensuring more uniform electrochemical reactions and preventing localized degradation that would lead to uneven electrode decay
4Ease of manufacture
If internal terminals are used to connect multiple electrodes, then electrical connection between electrodes is achieved, but mechanical stresses increase
Solution Approach 1:
The variable porosity separator provides differentiated mechanical support across different regions. The lower porosity regions near electrode tabs offer enhanced mechanical strength and structural stability to withstand connection stresses, while higher porosity regions maintain ionic conductivity, collectively reducing overall mechanical stresses on the electrode structure
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 approach achieves a more uniform current and temperature profile across the battery cell, reducing electrode decay and mechanical stresses, and enhancing the overall performance and lifespan of the battery.
Implementation Method 1
a porous or microporous polymeric separator... absorb liquid electrolyte into its porous structure
Implementation Method 2
the pores permit liquid electrolyte flow and ion conduction through the separator
Data Source
AI summary
A porous polymer battery separator is provided that includes variable porosity along its length. Such battery separators can increase the uniformity of the current density within electrochemical battery cells that may normally experience higher current density and higher temperatures near their terminal ends than they do near their opposite ends. By disposing a variable porosity separator between the electrodes of an electrochemical cell such that its terminal end has a lower porosity than its opposite end, the transport of ions, such as lithium ions, through the separator can be more restricted in normally high current regions and less restricted in normally low current regions, thereby increasing the overall uniformity of current density within the battery cell. Variable porosity battery separators may be produced by a modified solvent exchange process. The process may include forming a polymer-containing film having a non-uniform thickness, selectively densifiying the film so that it has a non-uniform polymer concentration, and inducing variable porosity in the film.