Polyamide Binder Composition for Silicon Anode Volume Expansion
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Solution Overview
Problem
Commercial lithium-ion batteries using graphite negative electrodes have reached their theoretical limit, and silicon-based electrodes suffer from volume expansion and contraction during charging and discharging, leading to mechanical and electrical performance degradation.
Innovation Solution
A polyamide polymer binder with a specific mole ratio of repeating structural units A to B, formed by reacting diamine and polyamine with dibasic acid anhydride, provides a balanced hardness and softness to inhibit silicon particle expansion while maintaining flexibility, using a preparation method that includes solvent mixing and precipitation for large-scale production.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If aromatic polymer binders with strong π-π bonding interactions are used, then tensile strength to resist volume expansion is improved, but the binder becomes inelastic and loses flexibility
Solution Approach 1:
The patent employs a composite binder system combining aromatic polymer components (for strength via π-π interactions) with aliphatic polymer components (for flexibility). This composite approach allows the binder to simultaneously achieve high tensile strength to resist silicon expansion and sufficient elasticity to maintain flexibility during volume changes.
Solution Approach 2:
The binder design implements local quality differentiation by creating regions with different polymer characteristics. The aromatic segments provide localized strength where needed to counteract expansion forces, while aliphatic segments provide localized flexibility in other regions, achieving both properties within the same binder material.
2Strength
If polymer binders with strong intermolecular interactions are used to resist volume expansion, then mechanical strength is improved, but the binder becomes rigid and unable to accommodate volume changes
Solution Approach 1:
The binder is designed with dynamic characteristics through the incorporation of flexible aliphatic polymer segments that can adapt their conformation during volume changes. This dynamic structure allows the binder to transition between different states, maintaining mechanical strength while accommodating the dynamic volume expansion and contraction of silicon particles during cycling.
3Strength
If cross-linked polymer structures are used to inhibit silicon particle expansion, then resistance to volume expansion is improved, but the binder loses elasticity and bonding capability
Solution Approach 1:
The patent utilizes parameter changes by controlling the degree and type of cross-linking in the polymer structure. By optimizing cross-linking density and selecting appropriate cross-linking chemistry, the binder achieves sufficient structural resistance to expansion while preserving enough molecular mobility to maintain bonding capability and elasticity.
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 binder effectively suppresses silicon particle volume expansion, retains flexibility, and enhances the cycle performance of lithium-ion cells by maintaining adhesion and electrical performance.
Implementation Method 1
the aromatic polymers have a rigid and organized polymer backbone structure characterized by strong π-π bonding interactions between the polymers
Implementation Method 2
the binder mainly relies on intermolecular forces
Implementation Method 3
step 4: adding ether solvent, collecting precipitate to obtain the binder
Data Source
AI summary
A binder, including a polyamide polymer containing repeating structural units A shown in formula (I) and repeating structural units B shown in formula (II), in which R1 is an aryl group not containing amide groups and amino groups, R2 includes an aryl group containing at least one amide groups or at least one amino groups, and a mole ratio of the repeating structural units A to the repeating structural units B is (2: 1) to (6:1).