Bi-Modal Separator Coating for Lithium-Ion Electrode Expansion
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Solution Overview
Problem
Existing lithium ion batteries face issues with electrode expansion during charging, leading to deformation and potential short circuits due to lack of internal space for expansion, which can cause accidents such as explosions or fires.
Innovation Solution
A separator coating with a bi-modal polymer particle distribution, comprising smaller particles less than 1.5 microns and larger particles greater than 1.5 microns, creates an uneven surface to accommodate expansion without increasing the battery's outer dimensions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a separator coating is applied to prevent short circuits and improve heat stability, then safety is improved, but the internal space for electrode expansion is reduced
Solution Approach 1:
The separator coating is designed with a porous structure containing voids and cavities that provide expansion space for electrodes during charging cycles. The coating includes pore-forming agents that create interconnected porous networks, allowing electrolyte penetration and electrode expansion without compromising the separator's safety functions.
Solution Approach 2:
The separator coating is formulated as a composite material system comprising polymer binders, pore-forming agents, and functional additives. This composite structure combines the mechanical strength and thermal stability of polymers with the space-providing capability of porous architectures, achieving both safety and expansion accommodation.
2Productivity
If the battery components are allowed to expand during charging, then performance is improved, but the battery outer dimensions increase
Solution Approach 1:
The expansion space is created within the separator coating's internal porous structure (three-dimensional voids) rather than increasing the battery's external dimensions. The porous coating acts as an internal expansion chamber that accommodates electrode volume changes without affecting the battery's outer envelope.
Solution Approach 2:
The porous coating structure is nested between the separator and electrode, creating internal voids that are contained within the existing battery architecture. This nested arrangement allows electrode expansion to occur within the separator-co electrode assembly without requiring additional external space.
3Reliability
If polyolefin-based separators are used to prevent short circuits, then safety is improved, but heat resistance deteriorates due to melting at high temperatures
Solution Approach 1:
The separator system is designed as a composite structure combining polyolefin base material with heat-resistant ceramic coatings and/or aramid layers. The polyolefin provides excellent short circuit prevention through its shutdown mechanism, while the ceramic or aramid components maintain structural integrity at elevated temperatures, preventing thermal runaway.
Solution Approach 2:
Different regions of the separator structure are assigned different functional properties: the polyolefin matrix provides shutdown functionality for short circuit prevention, while ceramic coatings or aramid reinforcement layers provide heat resistance in high-temperature zones. This local differentiation allows each material to optimize its specific function.
Data Source
Figure 1
Figure 2~3
AI summary
The invention relates to a separator for non-aqueous-type electrochemical devices that has been coated with a polymer binder composition having polymer particles of two different sizes, one fraction of the polymer particles with a weight average particle size of less than 1.5 micron, and the other fraction of the polymer particles with a weight average particle size of greater than 1.5 microns. The bi-modal polymer particles provide an uneven coating surface that creates voids between the separator and adjoining electrodes, allowing for expansion of the battery components during the charging and discharging cycle, with little or no increase in the size of the battery itself. The bi-modal polymer coating can be used in non-aqueous-type electrochemical devices, such as batteries and electric double layer capacitors.