Solid Polymer Wax Coated Separator for Lithium-Ion Battery Safety
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Solution Overview
Problem
Lithium-ion batteries face safety hazards due to thermal shrinkage and short circuits when overheated, as existing separators fail to effectively cut off lithium ion channels during overcharge, leading to potential fires or explosions.
Innovation Solution
A lithium-ion battery separator with a substrate membrane coated with ceramic particles, solid polymer wax, and an adhesive, where the solid polymer wax melts at a temperature below the shutdown point of the polyethylene layer to capillary-enter and block lithium ion channels, preventing overcharge and thermal runaway.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a polyethylene separator is used to provide thermal shutdown protection, then the separator can shut down micropores at high temperature, but the shutdown temperature is too high (130°C) to effectively prevent safety hazards that occur at lower temperatures (90-100°C)
Solution Approach 1:
The patent changes the shutdown temperature parameter by using a solid polymer wax with melting point of 85-120°C instead of polyethylene with 130°C melting point. This parameter change allows the separator to shut down at temperatures matching actual safety hazard occurrence (90-100°C), making the thermal protection effective rather than theoretical.
Solution Approach 2:
The patent creates a functional copy of the thermal shutdown mechanism using solid polymer wax that replicates the micropore closure function but at the correct temperature. The wax coating layer copies the shutdown function while operating at the appropriate temperature range, solving the mismatch between shutdown temperature and actual hazard temperature.
2Reliability
If the temperature of the lithium-ion battery rises to 90°C or above, then thermal shrinkage occurs causing short circuits, but conventional polyethylene or polypropylene separators cannot prevent this shrinkage and subsequent short circuits
Solution Approach 1:
The patent applies beforehand cushioning by coating the separator with solid polymer wax before any thermal event occurs. This pre-applied coating acts as a protective layer that will melt and cushion the thermal shrinkage effect when temperature rises to 90-100°C, preventing the separator from shrinking and causing short circuits between electrodes.
Solution Approach 2:
The solid polymer wax coating serves as an intermediary layer between the separator and the thermal shrinkage force. When temperature rises, the wax melts first and absorbs the thermal stress, mediating the interaction between heat and the separator structure, thereby preventing direct thermal shrinkage of the separator and subsequent short circuits.
3Reliability
If ceramics are coated onto the separator to reduce thermal shrinkage, then thermal shrinkage is reduced, but this does not work for overcharge situations where large heat generation occurs from electrode-electrolyte reactions
Solution Approach 1:
The patent achieves universality by making the solid polymer wax coating perform multiple functions: it reduces thermal shrinkage like ceramics, but additionally provides overcharge protection through shutdown at appropriate temperatures. The single wax coating layer serves both thermal management and charge protection functions, adapting to different failure modes (thermal runaway and overcharge) that single-material separators cannot handle.
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 solution significantly reduces thermal shrinkage and prevents short circuits, ensuring the safety of lithium-ion batteries by effectively cutting off lithium ion channels during overcharge, thereby preventing overheating and potential explosions.
Implementation Method 1
a melting point of the solid polymer wax is 85 ̃120° C.
Implementation Method 2
the solid polymer wax melts at a temperature below the shutdown point of the polyethylene layer to capillary-enter and block lithium ion channels
Data Source
AI summary
The present disclosure relates to a separator of a lithium-ion battery and a preparation method thereof, the separator comprises a substrate membrane and a coating provided on a surface of the substrate membrane, the coating comprises ceramic particles, an adhesive and a solid polymer wax which has a melting point of 85˜120° C., a molecular weight of 1,000˜25,000 and a particle size of 0.5˜10 μm. When the lithium-ion battery is heated due to overcharge and the like to make the interior temperature reach the melting point of the solid polymer wax, the solid polymer wax can be melt and enter among the ceramic particles and into the micropores of the substrate membrane by capillarity so as to function as electrical disconnection, which can effectively cut off the channel of the lithium ions and stop the overcharge, and ensure the safety performance of the lithium-ion battery under the situation of overcharge.