Silicon Anode Terpolymer Binder for Volume Expansion Control
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Solution Overview
Problem
Current lithium-ion batteries with silicon-rich anodes face limitations in cycle stability and capacity due to volume expansion issues, leading to reduced battery life and ineffective suppression of electrode expansion during charging and discharging.
Innovation Solution
A terpolymer binder composed of recurring units from an ethylenically unsaturated carboxylic acid monomer, a methacrylamide monomer, and a distinct monomer, obtained through radical copolymerization, is used to enhance the adhesion and electrochemical stability of silicon-rich anodes, allowing for improved cycle stability and reduced electrode expansion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If silicon is used as active material to increase capacity, then battery capacity is improved, but volume expansion during charging causes electrode destruction and reduced service life
Solution Approach 1:
The patent uses a flexible polymer binder matrix that can accommodate the volume expansion of silicon particles during lithiation. The binder forms a compliant shell around active material particles, allowing the structure to flex and expand without breaking electrical connections or separating from the current collector, thus maintaining reliability while enabling high capacity.
Solution Approach 2:
The patent employs a composite binder system combining carboxymethyl cellulose (CMC) and styrene-butadiene rubber (SBR) in specific ratios. This composite material leverages the water solubility and adhesion properties of CMC with the elasticity and mechanical strength of SBR, creating a binder that simultaneously provides structural integrity and flexibility to withstand silicon volume changes.
2Ease of manufacture
If conventional binders are used with silicon-containing anodes, then manufacturing is simple, but binder can only accommodate limited silicon loading (up to 10 wt. %) before battery lifetime is significantly reduced
Solution Approach 1:
The patent optimizes the molecular weight parameters of the polymer binder components and their ratio to achieve optimal performance. By controlling the weight average molecular weight of CMC (10,000-1,000,000 g/mol) and the ratio of CMC to SBR (1:9 to 9:1), the binder achieves both high silicon loading capacity and maintained ease of manufacture through standard slurry preparation methods.
3Reliability
If aqueous solution of crosslinked sodium polyacrylate copolymer is used to improve capacity retention, then cycle characteristics are improved, but cracks are generated in the electrode during coating and drying processes
Solution Approach 1:
The patent uses carboxymethyl cellulose, a water-soluble polysaccharide derivative, as a biodegradable and process-friendly binder component. This material provides adequate binding function during electrode assembly and initial cycling, then gradually degrades or redistributes to accommodate volume changes, avoiding the crack formation issues associated with crosslinked polyacrylate copolymers while maintaining good cycle characteristics.
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 terpolymer binder significantly improves the cycle stability and electrochemical performance of silicon-rich anodes, leading to higher discharge capacity retention and extended battery life by effectively managing volume changes during charging and discharging.
Implementation Method 1
There are multiple polycarboxylate binders and derivatives being pursued, including polyacrylic acids, polyamic acids, polyacrylamides, and other hydrogen bonding structures.
Implementation Method 2
since the volume of silicon expands by about four times when charged, during charging and discharging
Implementation Method 3
A terpolymer binder composed of recurring units from an ethylenically unsaturated carboxylic acid monomer, a methacrylamide monomer, and a distinct monomer, obtained through radical copolymerization
Data Source
AI summary
The present invention relates to a binder for a non-aqueous electrolyte rechargeable battery, a negative electrode slurry for a rechargeable battery, a negative electrode for a rechargeable battery, and a rechargeable battery comprising the same.