Polyimide Nanosheet Separator Coating for High-Temperature Li-Ion Cells
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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 risk of short circuits, and existing solutions like Ceramic Coating Separation face challenges with agglomeration and reduced energy density.
Innovation Solution
A separator with a porous base film and a functional coating of irregularly stacked polyimide nanosheets, where the thickness ratio of the coating to the base film is between 0.1 and 1.0, enhancing thermal and chemical stability, and preventing short circuits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional PE separator is used, then the separator has good basic performance and low cost, but the separator shrinks by more than 30% at 150°C causing short circuit hazards
Solution Approach 1:
The patent uses a composite structure consisting of a polyethylene base film combined with a silane-modified polyethylene crosslinked layer. The crosslinked layer is formed by introducing silane groups that undergo condensation reactions to create a three-dimensional network structure, combining the low melting point shutdown function of PE with the high temperature stability of crosslinked structures.
Solution Approach 2:
The patent changes the chemical structure parameter of the separator by introducing crosslinked bonds through silane modification. This transforms the linear polyethylene chains into a three-dimensional crosslinked network, fundamentally altering the thermal behavior from shrinkage above melting point to dimensional stability through the crosslinked structure.
2Reliability
If CCS (Ceramic Coating Separation) is used to improve high temperature resistance, then the separator has better thermal stability, but agglomeration occurs during production creating particles that pierce the separator
Solution Approach 1:
Instead of using expensive ceramic coatings that require complex processing, the patent employs a chemical modification approach using silane-modified polyethylene that crosslinks in situ. This eliminates the need for external ceramic particles and complex coating processes, achieving high temperature resistance through molecular-level crosslinking.
3Reliability
If heat resistant material is used to fabricate separator, then the separator has good high temperature resistance, but the specific gravity is relatively large reducing weight energy density
Solution Approach 1:
The patent changes the chemical composition parameters by introducing crosslinked bonds through silane modification rather than using dense ceramic materials. This creates a lightweight crosslinked polymer network that provides high temperature stability without the high density associated with ceramic materials, maintaining low specific gravity.
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 proposed separator significantly improves high temperature resistance, maintains pore structure integrity above 180°C, reduces self-discharge rates, and enhances safety and energy density of lithium ion batteries.
Implementation Method 1
the silane-modified polyethylene crosslinks, so that a three-dimensional network structure is formed
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
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.