VdF/TFE Copolymer Binder for Stable Li-Ion Battery Slurry
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Solution Overview
Problem
Lithium-containing complex oxides with nickel or manganese tend to cause gelation in positive electrode mixture slurries, leading to instability and poor battery performance due to their basic nature, and existing binders like PVdF and VdF copolymers swell in organic solvents, resulting in adhesion issues and reduced flexibility.
Innovation Solution
A positive electrode mixture slurry using a VdF/TFE copolymer as the binder, with specific molar ratios and low water content in the organic solvent, stabilizes the slurry and provides flexibility, preventing gelation and maintaining adhesion to the current collector.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If PVdF is used as a binder for positive electrode active materials containing nickel or manganese, then adhesion is provided, but gelation occurs due to the basic nature of these materials
Solution Approach 1:
The invention changes the chemical composition parameters of the binder by using a copolymer containing vinylidene fluoride and tetrafluoroethylene units instead of pure PVdF. This compositional change allows the binder to resist gelation with basic positive electrode materials while maintaining adhesion properties.
Solution Approach 2:
The invention uses a composite binder system comprising a copolymer of vinylidene fluoride and tetrafluoroethylene, combining the advantages of both monomer units to achieve both adhesion and resistance to gelation with basic electrode materials.
2Strength
If PVdF is used as a binder in lithium ion secondary batteries, then binding is provided, but swelling occurs in organic solvents leading to adhesion deterioration
Solution Approach 1:
The invention modifies the binder's chemical structure by incorporating tetrafluoroethylene units alongside vinylidene fluoride units, changing the polymer's swelling characteristics in organic solvents and preventing adhesion deterioration during battery cycling.
3Strength
If PVdF is used as a binder, then binding is achieved, but the electrode sheet has poor flexibility causing peeling during folding or rolling
Solution Approach 1:
The invention changes the physical properties of the binder by using a copolymer with specific vinylidene fluoride and tetrafluoroethylene content, which provides both binding strength and flexibility, preventing peeling during electrode sheet folding or rolling operations.
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 solution results in a homogeneous, stable positive electrode with improved flexibility and enhanced battery characteristics, including reduced internal resistance and increased cycle durability.
Implementation Method 1
a positive electrode mixture slurry which comprises a positive electrode active material (A), a binder (B), and an organic solvent (C), wherein the positive electrode active material (A) is a lithium-containing complex metal oxide... and the binder (B) comprises a fluorine-containing polymer... has homogeneous stability and prevents gelation
Implementation Method 2
the adhesion of the PVdF to the metal foil current collector deteriorates with repeated charge-discharge cycles... the binder (B) comprises a fluorine-containing polymer... maintains adhesion to the current collector
Implementation Method 3
PVdF is more likely to swell in an organic solvent for the nonaqueous electrolyte... the binder (B) comprises a fluorine-containing polymer... with specific molar ratios... prevents gelation and maintaining adhesion
Implementation Method 4
a slurry of the positive electrode mixture is prepared by dispersing a positive electrode active material together with a binder... in an organic solvent... the binder (B) comprises a fluorine-containing polymer... and an organic solvent (C)
Data Source
AI summary
The invention provides a stable positive-electrode mixture slurry that is not subject to gelation, a positive electrode with abundant flexibility, and a lithium secondary battery with excellent battery characteristics. The slurry comprises a positive-electrode active material, a binder, and an organic solvent, the positive-electrode active material is a lithium-containing complex metal oxide represented by Formula: Lix M1yM21-yO2 (wherein 0.4≦x≦1; 0.3≦y≦1; M1 is at least one selected from Ni or Mn; and M2 is at least one selected from Co, Al, or Fe); and the binder comprises a fluorine-containing polymer represented by Composition Formula: (VDF)m(TFE)n(HFP)l (wherein VDF is a structural unit from vinylidene fluoride; TFE is a structural unit from tetrafluoroethylene; HFP is a structural unit from hexafluoropropylene; and 0.45≦m≦1; 0≦n≦0.5; and 0≦l≦0.1, and m+n+l=1).