Silicon Negative Electrode Binder for Lithium Battery Cycle Life
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Solution Overview
Problem
Rechargeable lithium batteries with silicon-containing negative active materials face issues of volume change during charging and discharging, leading to electrode breakage and reduced cycle-life and capacity, especially with rapid charging, which existing binders fail to adequately address.
Innovation Solution
A negative electrode for lithium batteries is developed using a silicon-based active material and an acryl-based copolymer binder composed of acrylic acid, acrylonitrile, and (meth)acrylate monomers, with lithium-substituted acrylic acid and a weight-average molecular weight of 300-600 g/mol, to minimize volume change and reduce resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If silicon-containing negative active material is used to improve capacity and current density, then battery capacity increases, but volume change during charging and discharging causes electrode breakage and reduced cycle-life
Solution Approach 1:
The invention changes the chemical composition parameters of the binder by incorporating acrylic acid units with lithium ions substituted at 40-80 mol%, creating a binder with optimized electrochemical properties that accommodates silicon volume expansion while maintaining electrode integrity over charge-discharge cycles
Solution Approach 2:
The invention uses a composite binder system comprising acryl-based copolymer with multiple monomer units (acrylic acid, acrylonitrile, and (meth)acrylate) that combines the benefits of each component: lithium-substituted acrylic acid for electrical conductivity and volume accommodation, acrylonitrile for binding strength, and (meth)acrylate for flexibility, creating a synergistic material that resolves the capacity-cycle-life contradiction
2Strength
If conventional binders are used to maintain electrode structure, then electrode integrity is maintained, but resistance increases and power characteristic deteriorates
Solution Approach 1:
The lithium ions substituted in the acrylic acid units act as intermediaries that facilitate charge transfer between the silicon active material and the current collector, reducing resistance while the copolymer structure maintains mechanical binding, thus improving power characteristic without sacrificing electrode integrity
3Speed
If rapid charging is implemented to improve charging speed, then charging time decreases, but cycle-life is reduced and capacity deteriorates
Solution Approach 1:
The binder's chemical composition with lithium-substituted acrylic acid units changes the electrochemical environment to enable faster lithium ion insertion/extraction kinetics, allowing rapid charging while the copolymer structure maintains electrode integrity to preserve cycle-life
Data Source
Figure 1
AI summary
Disclosed is a negative electrode for a rechargeable lithium battery and a rechargeable lithium battery including the same, and the negative electrode including a silicon-based negative active material and a binder, the binder is an acryl-based copolymer, the acryl-based copolymer including an acrylic acid first monomer, an acrylonitrile second monomer, and a (meth)acrylate third monomer, the acrylic acid first monomer includes acrylic acid substituted with lithium ions, the (meth)acrylate third monomer includes an ethylene glycol group, and a weight-average molecular weight (Mw) of the third monomer is less than about 900 g/mol.