Battery Separator Z-Direction Stability via Inert Particulate
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Solution Overview
Problem
Lithium ion batteries face significant challenges with sudden thermal runaway, which is not effectively addressed by existing technologies, particularly due to the lack of Z-direction dimensional stability in battery separators, leading to potential hazardous situations during external force applications like nail penetration and crush tests.
Innovation Solution
A thermoplastic microporous membrane with inert, thermally non-deforming particulate dispersed within the separator is used to prevent physical contact between electrodes, enhancing Z-direction stability and preventing sudden thermal runaway.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a thin microporous membrane separator is used to prevent thermal runaway, then the separator can effectively shut down ionic flow at elevated temperatures, but the separator lacks Z-direction dimensional stability and shrinks under compression forces
Solution Approach 1:
The patent applies composite materials by combining a microporous membrane base material with dispersed inert particulate matter to create a separator that maintains both thermal shutdown capability and Z-direction dimensional stability. The composite structure allows the membrane to shrink in X and Y directions while preventing shrinkage in the Z direction through the particulate reinforcement.
Solution Approach 2:
The patent changes the physical parameters of the separator by incorporating inert particulate matter with specific properties (thermally non-deforming, puncture-resistant) to modify the Z-direction dimensional stability parameter while maintaining the thermal shutdown function at elevated temperatures.
2Reliability
If external forces are applied during safety tests like nail penetration or crush tests, then battery safety can be evaluated, but the forces compress the separator and cause anode and cathode to come into physical contact
Solution Approach 1:
The patent applies beforehand cushioning by incorporating puncture-resistant inert particulate matter into the separator structure in advance, creating a cushioning effect that prevents electrode contact when external compression forces are applied during safety tests like nail penetration or crush tests.
Solution Approach 2:
The inert particulate matter acts as an intermediary between the compression force and the electrodes, maintaining separator thickness and preventing direct contact between anode and cathode during external force applications while still allowing the separator to perform its thermal shutdown function.
3Volume of moving object
If the separator thickness is reduced to minimize internal forces, then the battery can be more tightly fitted into housing, but the separator becomes more susceptible to compression and electrode contact
Solution Approach 1:
The patent uses composite materials to create a separator with enhanced strength-to-thickness ratio by dispersing inert particulate matter throughout the microporous membrane, allowing the separator to maintain adequate compression resistance even at reduced thickness for tighter battery fitting.
Solution Approach 2:
The patent changes the mechanical parameters of the separator by incorporating particulate reinforcement, which increases compression resistance and puncture strength without significantly increasing thickness, enabling better space utilization while maintaining safety.
Data Source
AI summary
A battery separator is a microporous membrane. The membrane has a major volume of a thermoplastic polymer and a minor volume of an inert particulate filler. The filler is dispersed throughout the polymer. The membrane exhibits a maximum Z-direction compression of 95% of the original membrane thickness. Alternatively, the battery separator is a microporous membrane having a TMA compression curve with a first substantially horizontal slope between ambient temperature and 125° C., a second substantially horizontal slope at greater than 225° C. The curve of the first slope has a lower % compression than the curve of the second slope. The curve of the second slope is not less than 5% compression. The TMA compression curve is graphed so that the Y-axis represents % compression from original thickness and the X-axis represents temperature.