Polyimide-Coated Battery Separator for Thermal Shrinkage Resistance
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Solution Overview
Problem
Conventional lithium ion battery separators lack sufficient high temperature resistance, leading to potential safety hazards due to shrinkage and particle agglomeration issues, and existing solutions like Ceramic Coating Separation (CCS) compromise weight energy density and are costly.
Innovation Solution
A separator with a porous base film coated irregularly with polyimide nanosheets forming a lamellar loose structure, combined with a binder, which improves thermal and chemical stability, and reduces self-discharge rates by preventing electrode short-circuits, while maintaining a lightweight design.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional PE separator is used, then the separator has basic separation performance, but it shrinks by more than 30% at 150°C causing short circuit and safety hazards
Solution Approach 1:
The patent applies composite materials by coating the PE separator with a silane-modified polyimide layer. This composite structure combines the good electrochemical properties of PE with the high thermal stability of polyimide, preventing thermal shrinkage at 150°C while maintaining basic separation performance. The silane modification enhances adhesion between the coating and substrate, ensuring the composite structure remains intact under thermal stress.
Solution Approach 2:
The patent changes the thermal and chemical parameters of the separator by introducing a polyimide coating layer with different thermal properties than the PE substrate. The coating layer has a much higher glass transition temperature and thermal stability, which fundamentally alters the separator's behavior at elevated temperatures, preventing the 30% shrinkage that would occur in pure PE separators.
2Reliability
If CCS (Ceramic Coating Separation) is used to improve high temperature resistance, then thermal stability improves, but particle agglomeration occurs during production and specific gravity of boehmite is large reducing weight energy density
Solution Approach 1:
The patent employs porous materials by using a silane-modified polyimide coating that forms a porous or microstructured layer on the separator. This porous structure provides high surface area for thermal stability without requiring heavy ceramic particles like boehmite. The low density of the polyimide coating maintains weight energy density while the porous structure allows ion transport and provides thermal barrier functions.
Solution Approach 2:
The patent changes the material parameters by replacing heavy ceramic coatings (boehmite) with a lightweight polyimide-based coating. This substitution fundamentally alters the density and weight characteristics of the separator, achieving high temperature resistance without the penalty of increased weight that would reduce energy density.
3Object-affected harmful factors
If a thick functional coating is applied to improve thermal resistance, then thermal shrinkage resistance improves, but the separator may become too thick affecting ion transport
Solution Approach 1:
The patent applies porous materials in the functional coating design, creating a coating layer with controlled porosity that allows ion transport. The porous structure provides thermal stability through the polyimide matrix while the void spaces and channels maintain ion conductivity, preventing the coating from becoming too dense or thick to the point of blocking ion transport.
Solution Approach 2:
The patent applies local quality by creating a functional coating with specific local properties - the polyimide coating is applied only where thermal stability is needed (on the separator surface), with controlled thickness and porosity. This localized approach provides thermal protection without uniformly increasing the overall separator thickness, maintaining ion transport pathways in the bulk separator structure.
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 enhances thermal shrinkage resistance, mechanical puncture resistance, and safety of lithium ion batteries, maintaining performance up to 300°C and reducing self-discharge rates, while optimizing energy density and weight.
Implementation Method 1
the thermal shrinkage resistance of the separator has also been significantly improved, so the pore structure of the separator may keep unchanged in an environment above 180°C
Implementation Method 2
the polyimide coating may isolate the internal conduction of electrons between positive and negative electrodes, and prevent the positive and negative electrodes of battery from being short-circuited
Implementation Method 3
the long-term service temperature of the separator may be increased to 300°C, and it will not cause the failure of a battery cell if it is kept in an environment of 150°C for 2 h
Data Source
AI summary
The present embodiments provide a separator, a process for preparing the same, a lithium ion secondary battery, a battery module, a battery pack and an apparatus. The separator provided by the present application comprises a porous base film and a functional coating disposed on at least one surface of the porous base film, wherein the functional coating comprises polyimide nanosheets, and the polyimide nanosheets are stacked irregularly to form a lamellar loose structure; and a thickness ratio of the functional coating to the porous base film is from 0.1 to 1.0. The present application also provides a process for preparing the separator, and a lithium ion secondary battery and an apparatus comprising the separator.