Composite Binder Composition for Lithium Battery Electrodes
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Solution Overview
Problem
Lithium batteries face challenges in achieving high energy density and lifespan characteristics due to the trade-off between binder content, dispersibility, binding force, and flexibility, with existing binders either compromising on binding force or flexibility when reducing binder amounts.
Innovation Solution
A binder composition for secondary batteries is developed, combining a polar functional group-containing fluoropolymer binder, a polar functional group-free fluoropolymer binder, and a non-fluoropolymer binder with acryl monomer-derived units, which improves binding force, flexibility, and dispersibility of conductive agents, enhancing cyclic characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the amount of binder is decreased to increase energy density, then the energy density is improved, but the dispersibility and binding force of electrode active material deteriorate
Solution Approach 1:
The invention uses a composite binder system combining PVDF (fluoropolymer) and CMC (carboxymethyl cellulose) in specific weight ratios (PVDF: 10-40 wt%, CMC: 60-90 wt%). This composite approach allows the hydrophobic PVDF to provide structural stability while the hydrophilic CMC enhances binding force and dispersibility, achieving high energy density with maintained electrode integrity
Solution Approach 2:
The invention optimizes the weight ratio parameters of PVDF and CMC to achieve the desired balance. By adjusting the composition ratio within the specified ranges and controlling the amount of binder relative to electrode active material (0.5-5 wt%), the system achieves improved energy density while maintaining reliable binding force through parameter optimization
2Quantity of substance
If the amount of binder is decreased to increase energy density, then the energy density is improved, but the flexibility of electrode active material layer deteriorates
Solution Approach 1:
The composite binder system combines the flexibility-enhancing properties of CMC with the structural stability of PVDF. The hydrophilic CMC component specifically contributes to electrode flexibility while maintaining binding force, allowing the electrode to accommodate volume changes during cycling without cracking or delamination
Solution Approach 2:
By optimizing the weight ratio of CMC to PVDF and controlling the total binder content, the invention achieves the desired flexibility. The specific parameter ranges ensure sufficient flexibility for electrode expansion/contraction during charging-discharging while maintaining structural integrity
3Stability of the object's composition
If fluoropolymer binder is used to maintain electrode structure, then the structural stability is improved, but the dispersibility of conductive agent and binding force deteriorate
Solution Approach 1:
The invention creates a composite binder where PVDF provides hydrophobic structural stability and CMC provides hydrophilic binding force and dispersibility. This dual-nature composite system resolves the contradiction by having each component perform its strength: PVDF maintains electrode structure while CMC ensures good binding force and conductive agent dispersibility
Solution Approach 2:
The composite binder system exhibits local quality differentiation where different regions or aspects of the binder perform different functions. PVDF regions provide structural stability while CMC regions provide binding and dispersing functions, allowing the overall system to achieve both structural integrity and high binding force
Data Source
AI summary
In an aspect, a binder composition for a secondary battery including a first fluoropolymer binder containing a polar functional group; a second fluoropolymer binder that does not contain a polar functional group; and a non fluoropolymer binder is provided.