Fluorine Copolymer Binder for High Nickel Battery Electrodes
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Solution Overview
Problem
Conventional binders for secondary batteries, such as polyvinylidene fluoride (PVdF), have poor adhesion strength to metal substrates and limited flexibility, leading to issues like cracking and poor yield during electrode production, especially when high nickel content active materials are used, which cause alkaline conditions and viscosity issues in the electrode mixture.
Innovation Solution
A fluorine-containing polymer binder is developed, comprising polymerized units of vinylidene fluoride (VdF), tetrafluoroethylene (TFE), and a specific monomer, which provides excellent adhesion and flexibility, allowing for improved electrode density and reduced internal resistance, while maintaining fluidity and preventing gelation even with high nickel content active materials.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If PVdF binder is used in conventional lithium ion secondary batteries, then the electrode structure is maintained, but the adhesion strength to metal substrates is poor and flexibility is limited
Solution Approach 1:
The patent uses a copolymer binder composed of vinylidene fluoride (VdF) and hexafluoropropylene (HFP) monomers. This composite polymer structure combines the strong adhesion properties of PVdF with the flexibility and chemical resistance of HFP, achieving both high adhesion strength to metal substrates and excellent flexibility for electrode manufacturing processes including rolling and folding operations.
2Quantity of substance
If rolling is performed to densify the positive electrode mixture film, then the energy density is improved, but electrode sheets with PVdF binder easily suffer from cracking or removal
Solution Approach 1:
The patent changes the chemical composition parameters of the binder by using a copolymer of VdF and HFP with specific monomer ratios. This parameter change provides optimal balance between adhesion strength and flexibility, allowing the electrode film to be densely packed through rolling while maintaining integrity and preventing cracking or removal of the electrode mixture.
3Quantity of substance
If high nickel content active material is used, then the capacity is improved, but the slurry viscosity increases and gelation occurs
Solution Approach 1:
The copolymer binder acts as an intermediary substance between the high nickel content active material particles and the solvent. The HFP component provides excellent chemical resistance and compatibility with nickel-rich materials, preventing excessive viscosity increase and gelation while maintaining slurry processability for electrode fabrication.
Data Source
AI summary
The invention aims to provide a binder for a secondary battery excellent in both the adhesiveness to a current collector and the flexibility, and an electrode mixture for a secondary battery. The binder for a secondary battery of the invention contains a fluorine-containing polymer containing a polymerized unit based on vinylidene fluoride, a polymerized unit based on tetrafluoroethylene, and a polymerized unit based on a monomer (2-2) represented by the following formula (2-2): R5R6C=CR7R8CO2Y1 (2-2) wherein R5, R6, and R7 are each independently a hydrogen atom or a C1-C8 hydrocarbon group; R8 is a C1-C8 hydrocarbon group; and Y1 is an inorganic cation and/or an organic cation.