Silicon Anode Binder Crosslinking for Cycle Life
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Solution Overview
Problem
Conventional lithium secondary batteries using silicon or silicon alloy as negative-electrode active material face issues with binder adhesion to the active material and current collector, leading to poor charge-discharge cycle characteristics due to volume changes during lithium storage and release.
Innovation Solution
A lithium secondary battery design incorporating a negative-electrode active material layer with a polyimide resin binder containing a crosslinked structure formed by imidization of hexavalent or higher-valent carboxylic acids or anhydrides with diamines, which enhances mechanical strength and adhesion to prevent binder breakage and peel-off, thereby improving cycle characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a polyimide binder is used to achieve high current collecting performance, then the charge-discharge cycle characteristic is improved, but the adhesion of the binder to negative electrode members becomes unsatisfactory
Solution Approach 1:
The patent uses a composite binder system comprising polyimide resin combined with polyacrylonitrile or polyacrylamide. This composite structure leverages the electrochemical stability and charge-discharge cycle performance of polyimide while incorporating the adhesive properties of polyacrylonitrile or polyacrylamide, thereby resolving the contradiction between cycle characteristic and adhesion strength
Solution Approach 2:
The patent modifies the binder composition by introducing additional polymer components (polyacrylonitrile or polyacrylamide) with specific functional properties. This parameter change in binder chemistry enhances adhesion to negative electrode members while preserving the electrochemical benefits of polyimide, thus improving both adhesion and cycle characteristic simultaneously
2Ease of manufacture
If conventional binders are used, then the manufacturing process is simple, but the binder breaks and peels off during volume changes of silicon active material
Solution Approach 1:
The patent creates a composite binder system that combines polyimide resin with polyacrylonitrile or polyacrylamide. This composite structure provides both mechanical flexibility to accommodate silicon volume changes and sufficient adhesion strength, preventing binder breakage and peel-off while maintaining ease of manufacturing through established coating processes
Solution Approach 2:
The binder composition is designed beforehand to include polymers with high flexibility and elasticity (polyacrylonitrile or polyacrylamide) that can preemptively accommodate the volume expansion and contraction of silicon active material during charge-discharge cycles, preventing binder failure before it occurs
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 crosslinked polyimide resin binder provides increased mechanical strength and adhesion, preventing degradation of the negative electrode's electronic conductivity and resulting in an excellent charge-discharge cycle characteristic.
Implementation Method 1
the binder contains a polyimide resin including a crosslinked structure formed by imidization of a hexavalent or higher-valent carboxylic acid or an anhydride thereof with a diamine
Implementation Method 2
crosslinked structure formed by imidization of a hexavalent or higher-valent carboxylic acid or an anhydride thereof with a diamine
Implementation Method 3
the polyimide resin has many imide bonds in the crosslinked structure and, therefore, can develop high adhesion. Because the imide bond has a high polarity, it exhibits high adhesion to silicon active material particles and metal foil serving as a current collector
Data Source
AI summary
Provided is a lithium secondary battery in which negative-electrode active material particles containing silicon and/or a silicon alloy are used and which prevents the occurrence of breakage of a binder itself and peel-off of the binder at the interfaces with the negative-electrode active material and the negative-electrode current collector and has a high energy density and an excellent cycle characteristic. The lithium secondary battery includes: a negative electrode in which a negative-electrode active material layer including negative-electrode active material particles containing silicon and/or a silicon alloy and a binder is formed on a surface of electrically conductive metal foil serving as a negative-electrode current collector; a positive electrode; and a nonaqueous electrolyte, wherein the binder contains a polyimide resin including a crosslinked structure formed by imidization of a hexavalent or higher-valent carboxylic acid or an anhydride thereof with a diamine.