Fluorine-Free Epoxy Copolymer Cathode Binders for Lithium-Ion Batteries
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Solution Overview
Problem
Current lithium-ion battery cathodes face challenges with fluorinated polymer binders, such as PVDF, which have low flexibility, leading to bond breakage during expansion/contraction cycles, and pose safety risks due to toxic gas emissions during high-temperature events, while lacking adequate polymer binders that provide electrochemical stability and high cycling stability.
Innovation Solution
An electrode composition using epoxy group-containing fluorine-free copolymers, specifically ethylene-vinyl acetate and nitrile rubber copolymers, which enhance peel strength, cycling stability, and capacity retention by improving binding properties between the cathode active material and the current collector.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If PVDF (polyvinylidene fluoride) is used as polymer binder, then electrochemical stability and bonding strength are improved, but flexibility is reduced leading to bond breakage during expansion/contraction cycles
Solution Approach 1:
The patent changes the chemical composition parameters of the polymer binder by introducing epoxy functional groups and using fluorine-free copolymers (ethylene-vinyl acetate and nitrile rubber) instead of conventional PVDF. This compositional parameter change provides both flexibility and adhesion, resolving the contradiction between electrochemical stability and bond strength during cycling.
Solution Approach 2:
The patent uses composite polymer binder systems combining epoxy-functionalized ethylene-vinyl acetate copolymer and epoxy-functionalized nitrile rubber copolymer. This composite material approach integrates the flexibility of rubber polymers with the adhesion enhancement from epoxy groups, simultaneously achieving electrochemical stability and maintained bond strength.
2Strength
If PVDF is used as polymer binder, then bonding strength is improved, but safety is worsened due to toxic gas emissions during high-temperature events
Solution Approach 1:
The patent extracts and removes the fluorine-containing PVDF component from the binder system, replacing it with fluorine-free copolymers. This extraction of the harmful fluorine element eliminates the source of toxic HF gas emissions during thermal events while preserving the necessary bonding strength through epoxy functional groups.
Solution Approach 2:
The patent converts the potential harm of using conventional binders by selecting fluorine-free alternatives that inherently avoid toxic emissions. The epoxy functional groups provide the necessary bonding strength without the harmful byproduct generation, turning a safety risk into a safe design.
3Ease of manufacture
If conventional polymer binders are used, then manufacturing simplicity is maintained, but cycling stability is insufficient due to bond breakage
Solution Approach 1:
The patent modifies the chemical parameters of the binder by incorporating epoxy functional groups and using specific copolymer compositions. These parameter changes enhance the binder's ability to withstand expansion/contraction cycles while maintaining adhesion, improving cycling stability without significantly complicating the manufacturing process.
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 use of epoxy group-containing fluorine-free copolymers in lithium-ion battery cathodes results in improved peel strength, cycling stability, and capacity retention, reducing the risk of bond breakage and toxic gas emissions, while maintaining electrochemical stability.
Implementation Method 1
The polymer binder is dispersed in the cathode slurry composition to improve adherence between the cathode active material and adhesion of the cathode active material with the current collector
Implementation Method 2
The polymer binder is dispersed in the cathode slurry composition to improve adherence between the cathode active material and adhesion of the cathode active material with the current collector. Simultaneously the polymer binder assists the dispersion of the conductive material.
Implementation Method 3
It is therefore highly desirable to use elastomeric materials as binder, for lithium-ion batteries, to enable flexible movement of the active material during use without delamination from the current collector or crack formation
Data Source
AI summary
The present invention relates to an electrode composition for a cathode of a cell of a lithium-ion battery comprising an epoxy group-containing fluorine-free copolymer, a cathode slurry composition comprising the electrode composition, a cathode, a process for manufacturing this cathode, and a lithium-ion battery having one or more cells incorporating this cathode.