Variable Porosity Battery Separators for Uniform Current Distribution
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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 utilization, accelerated decay, and mechanical stresses, which can cause cell failure.
Innovation Solution
The development of variable porosity separators made from polymeric materials, where the porosity and pore size are controlled along the length of the separator to match the electrode configuration, allowing for more uniform ionic flow and current distribution by varying the size, number, and distribution of pores, particularly increasing porosity further from the electrode terminals.
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 spatially varying porosity, where different regions have different pore sizes and distributions. Specifically, the porosity increases from the terminal end toward the distal end of the separator, creating local variations in ionic conductivity that compensate for the non-uniform current density caused by internal terminal connections
Solution Approach 2:
The physical parameter of porosity is changed across different regions of the separator. By controlling the pore size, pore distribution, and overall porosity to vary spatially, the separator optimizes ionic flow paths and current distribution, transforming a uniform structure into a gradient structure that addresses the non-uniformity problem
2Ease of manufacture
If internal terminals are used to connect multiple electrodes, then electrical connection between electrodes is achieved, but accelerated decay and mechanical stresses occur
Solution Approach 1:
The separator exhibits local quality variations through its gradient porosity structure, with higher porosity regions positioned to reduce current density hotspots that would otherwise cause accelerated decay and mechanical stress concentrations at specific electrode locations
Solution Approach 2:
The variable porosity separator acts as a pre-designed compensatory structure that anticipates and mitigates the harmful effects of non-uniform current distribution. By embedding the porosity gradient during manufacturing, the separator proactively cushions against current hotspots and stress concentrations before they can cause electrode decay or failure
3Ease of manufacture
If uniform porosity separator is used, then manufacturing simplicity is maintained, but non-uniform ionic flow occurs due to internal terminal configuration
Solution Approach 1:
The separator transitions from uniform porosity to local quality variation, where specific regions have tailored porosity levels. The terminal end has lower porosity while distal regions have higher porosity, creating localized properties that optimize ionic flow distribution across the electrode surface
Solution Approach 2:
The porosity parameter is changed spatially across the separator structure. By controlling parameters such as pore size, pore density, and overall porosity to vary in a gradient manner from terminal to distal regions, the separator achieves uniform ionic flow despite the simplifying assumption of uniform manufacturing
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 helps to achieve a more uniform current and temperature profile across the electrodes, reducing the risk of uneven decay and mechanical stresses, thereby enhancing the performance and lifespan of electrochemical battery cells.
Implementation Method 1
a porous or microporous polymeric separator... to absorb liquid electrolyte into its porous structure
Implementation Method 2
the separator containing the liquid electrolyte facilitates ion transport through the pores of the separator and between electrodes
Data Source
AI summary
A porous polymer battery separator includes variable porosity along its length and 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 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 cell. The separators may be produced by a dry-stretching process or by a wet process. These processes may include forming a polymer-containing film, producing a uniform distribution of pore sites within the film, and reforming the polymer-containing film to a uniform thickness.