Aliphatic Polyimide Binders for Lithium-Ion Electrodes
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Solution Overview
Problem
Conventional polyimide binders for lithium-ion cell electrodes exhibit high irreversible capacity loss during the first cycle due to electrochemical reduction, which reduces the cell's performance and cycle life.
Innovation Solution
The use of aliphatic or cycloaliphatic polyimide binders, which have reduced aromatic carbonyl content, is proposed to minimize this irreversible capacity loss by forming electrodes that can better facilitate lithiation and delithiation processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional aromatic polyimide binders are used, then good cycling properties are achieved, but first cycle irreversible capacity loss is unacceptably large
Solution Approach 1:
The patent changes the chemical structure parameter of the polyimide binder from aromatic to aliphatic or cycloaliphatic, which fundamentally alters the electronic properties and reduces the electron-withdrawing carbonyl group effects, thereby eliminating the first cycle capacity loss while preserving cycling stability
Solution Approach 2:
The patent creates a composite electrode material system combining aliphatic/cycloaliphatic polyimide binder with powdered metal or graphite materials, where the unique properties of the aliphatic polyimide component resolve the contradiction between cycling stability and first cycle capacity loss
2Strength
If aromatic polyimide binders are used, then electrode adhesion is maintained, but electrochemical reduction consumes electrons needed for lithiation
Solution Approach 1:
The patent changes the chemical composition parameter of the binder from aromatic polyimide to aliphatic or cycloaliphatic polyimide, which reduces the electron-withdrawing carbonyl group effects while maintaining the binder's adhesion function through the polyimide backbone 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 aliphatic or cycloaliphatic polyimide binders significantly decrease the first cycle irreversible capacity loss, enhancing the cycle life and capacity of lithium-ion cells, particularly when used with small particle alloy powders, and allowing for the use of novel alloy powders in rechargeable lithium-ion cells.
Implementation Method 1
the first cycle irreversible capacity loss may be caused by electrochemical reduction of the polyimide, facilitated by the presence of electron-withdrawing carbonyl groups on the polyimide aromatic rings
Data Source
AI summary
Irreversible first cycle capacity loss in lithium secondary cells having a cell electrode based on a powdered material and a binder may be significantly decreased or eliminated by using an aliphatic or cycloaliphatic polyimide binder. Compared to conventional polyimide binders prepared by reacting an aromatic dianhydride and a diamine, the disclosed polyimide binders have decreased aromatic carbonyl content, may be less likely to undergo electrochemical reduction, and may be less likely to consume electrons that might otherwise help lithiate the electrode.