Lithium-Ion Battery Separator With Porous Polymer Layer
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Solution Overview
Problem
Lithium-ion batteries face safety issues due to thermal runaway during overcharge, as conventional separators like polyethylene fail to prevent short circuits and thermal runaway when their pores close and melt, leading to high temperatures, smoke, and potential explosions.
Innovation Solution
A lithium-ion battery design featuring a separator with a porous base material and a porous polymer layer coated on one side, where the polymer layer melts to form an insulating barrier during overcharge, preventing direct contact between the cathode and anode and thus mitigating thermal runaway. The porous polymer layer is strategically positioned adjacent to the cathode, ensuring effective coverage and preventing short circuits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a porous polyethylene separator is used, then the battery can operate at normal temperatures with good ion transport, but the separator will shrink and melt at elevated temperatures leading to short-circuit and thermal runaway
Solution Approach 1:
The separator is constructed as a composite structure combining a porous polyethylene base layer with a porous polymer coating layer having a lower melting point. This composite design allows the base layer to provide structural integrity and ion transport at normal temperatures, while the coating layer melts first at elevated temperatures to form an insulating barrier that prevents thermal runaway and short-circuits.
Solution Approach 2:
The invention changes the thermal parameters of the separator by applying a coating layer with different thermal properties (lower melting point) onto the base separator. This parameter modification enables the separator to undergo a controlled phase change at elevated temperatures, transforming from a conductive state to an insulating state to prevent thermal runaway.
2Object-affected harmful factors
If a PVDF-coating is applied on the separator, then the battery safety is improved, but the coating is insufficient to protect the battery from thermal runaway during overcharge
Solution Approach 1:
The invention applies a porous polymer coating specifically on one or both surfaces of the separator, creating a localized protective layer with tailored properties. This coating is positioned strategically to provide enhanced thermal protection where it is most needed, while maintaining the overall separator structure and ion transport properties.
Solution Approach 2:
The porous polymer coating is designed to undergo a phase transition from solid to liquid at a specific melting point range. During overcharge conditions, this phase transition creates a molten barrier that effectively blocks ion transport and prevents thermal runaway, providing superior overcharge protection compared to non-phase-changing coatings.
3Object-affected harmful factors
If the porous polymer layer thickness is increased, then the thermal protection is enhanced, but the battery energy density is reduced
Solution Approach 1:
The invention applies a porous polymer coating layer with a thickness in the range of 1-30 μm, which is sufficient to provide effective thermal protection and prevent thermal runaway, while avoiding excessive thickness that would unnecessarily reduce battery energy density. This optimized thickness represents the minimum effective action needed to achieve the safety goal.
Solution Approach 2:
The invention optimizes the thickness parameter of the porous polymer coating layer to achieve the best balance between thermal protection effectiveness and battery energy density. By carefully controlling this parameter within a specific range, the separator provides adequate safety protection while minimizing the impact on battery performance and energy storage capacity.
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 effectively prevents thermal runaway and associated hazards such as explosions and fires by creating an insulating barrier that restricts current flow and maintains battery safety during overcharge conditions, enhancing the safety performance of lithium-ion batteries.
Implementation Method 1
the polymer layer melts to form an insulating barrier
Implementation Method 2
creating an insulating barrier that restricts current flow
Data Source
AI summary
Provided herein is a lithium-ion battery comprising an electrode assembly, wherein the electrode assembly comprises at least one cathode, at least one anode, and a separator interposed between the at least one cathode and the at least one anode; and wherein the separator comprises a porous base material and a porous polymer layer coated on a surface of the porous base material and adjacent to the at least one cathode. The lithium-ion battery comprising the separator disclosed herein prevents thermal runaway during overcharge, thereby ensuring the safety of lithium-ion battery.