Polysiloxane Binder for Silicon Anode Integrity
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Solution Overview
Problem
Lithium ion batteries face limitations due to the low capacity of graphite-based anode materials and safety concerns with lithium metal anodes, while alternative carbon-based electrodes like carbon nanotubes are costly and inefficient, and silicon or tin anodes suffer from volume changes that reduce cycle life.
Innovation Solution
The use of cross-linked polysiloxane polymers as binders for electrodes, which provide excellent adhesive strength, suppress volumetric changes, and enable efficient charge/discharge cycles, combined with a fast-cure method for polysiloxane-based gel polymer electrolytes to enhance battery performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional binders (PVdF or SBR) are used with silicon or tin anode materials, then the electrode can be assembled, but the electrode undergoes significant volume changes (200-300%) during charge/discharge, leading to separation from current collector and increased resistance
Solution Approach 1:
The patent changes the chemical composition parameters of the binder from conventional PVdF/SBR to polysulfone and polyacrylic acid polymers. This parameter change enables the binder to maintain adhesive strength while accommodating the 200-300% volume changes of silicon/tin anodes, resolving the contradiction between reliability and strength.
Solution Approach 2:
The patent uses a composite binder system combining polysulfone and polyacrylic acid polymers. This composite material leverages the mechanical strength of polysulfone and the adhesive properties of polyacrylic acid to simultaneously maintain structural integrity and adhesion during large volume changes, addressing both reliability and strength requirements.
2Reliability
If the amount of binder is increased to mitigate volume changes and prevent separation, then adhesive strength improves, but electrical resistance of the electrode increases, reducing battery capacity
Solution Approach 1:
The patent changes the chemical properties of the binder to achieve superior adhesive strength at lower concentrations. The polysulfone-polyacrylic acid composite binder provides adequate adhesion with only 5-15 wt% content, minimizing the harmful effect of binder on electrical conductivity while maintaining necessary adhesive strength.
3Strength
If polyvinyl alcohol or thermosetting plasticized polyvinyl alcohol is used as binder, then adhesive strength is good, but viscosity is low causing non-uniform application on copper foil and processing problems during thermal treatment
Solution Approach 1:
The patent employs a composite polymer system of polysulfone and polyacrylic acid that combines the advantages of both components. Polysulfone provides high viscosity for uniform application and thermal stability, while polyacrylic acid contributes adhesive strength, eliminating the processing problems of polyvinyl alcohol while maintaining good adhesion.
Solution Approach 2:
The patent changes the viscosity parameter of the binder by selecting polysulfone polymer with appropriate molecular weight and composition. This parameter adjustment ensures optimal flow properties for uniform coating on copper foil and stability during thermal treatment, while maintaining adequate adhesive strength through the composite formulation.
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 polysiloxane binders improve the charge/discharge efficiency and extend the service life of lithium ion batteries by maintaining electrode integrity and reducing electrical resistance, leading to superior battery performance.
Implementation Method 1
The binders exhibit superior adhesive strength between active materials and between the active materials and the current collectors
Implementation Method 2
the silicon and tin materials react with lithium. As a result of the reaction, the electrode undergoes significant changes in volume that can range from 200% to 300%. Due to such volume changes, repeated charge/discharge may result in separation of the anode active material from the current collector
Data Source
AI summary
An electrode includes a binder and an electroactive material, wherein the binder includes a polymer including a linear polysiloxane or a cyclic polysiloxane. The polymer may be generally represented by Formula I: