Negative Electrode Binder System for Lithium Battery Adhesion
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Solution Overview
Problem
Lithium secondary batteries face challenges in achieving high safety and capacity due to adhesion issues between the negative electrode mixture layer and the current collector, particularly when forming an inorganic particle layer, which can lead to poor coating quality and reduced adhesion strength.
Innovation Solution
Incorporating hydroxy group-modified polyvinyl pyrrolidone (PVP) and carboxymethylcellulose (CMC) in the negative electrode mixture layer, with a higher mass ratio of CMC to hydroxy group-modified PVP, to enhance adhesion strength and prevent swelling caused by solvents like NMP, thereby improving the quality and safety of the battery.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If NMP is used as the solvent for forming the inorganic particle layer, then the inorganic particle layer can be formed effectively, but NMP infiltrates into the negative electrode mixture layer causing SBR to swell and adhesion strength deteriorates
Solution Approach 1:
CMC acts as an intermediary substance between the inorganic particle layer and the negative electrode mixture layer. It prevents NMP from infiltrating into the SBR binder by forming a protective interface, thereby maintaining adhesion strength while allowing the inorganic particle layer to provide insulation performance
Solution Approach 2:
The negative electrode mixture layer uses a composite binder system consisting of both SBR and CMC. This composite material structure allows SBR to provide adhesion while CMC provides resistance to NMP infiltration, solving the contradiction between adhesion strength and insulation performance
2Strength
If CMC and SBR are used together in the negative electrode mixture layer, then adhesion strength is improved, but adhesion strength after forming the inorganic particle layer is still poorer than before
Solution Approach 1:
The invention changes the compositional parameters of the binder system by specifying that CMC content must be greater than SBR content. This parameter change optimizes the balance between adhesion strength and resistance to NMP infiltration, maintaining stable adhesion before and after inorganic particle layer formation
3Ease of manufacture
If a water-system slurry is used for the negative electrode mixture layer, then environmental load and costs are reduced, but the inorganic particle layer cannot be formed using the same solvent
Solution Approach 1:
The negative electrode mixture layer structure is designed to be compatible with multiple solvent systems. By using CMC as a key component, the layer can be formed with water-system slurry for cost-effectiveness, while simultaneously supporting the subsequent formation of an inorganic particle layer with solvent-system slurry, thus achieving multi-functionality
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
This configuration improves the adhesion strength between the current collector and the negative electrode mixture layer, maintains coating quality, and enhances the safety and capacity of lithium secondary batteries by reducing the risk of peeling and swelling, resulting in better insulation and performance.
Implementation Method 1
NMP infiltrates into the negative electrode mixture layer, causing SBR to swell
Implementation Method 2
the adhesion strength between the current collector and the negative electrode mixture layer becomes poor
Data Source
AI summary
A negative electrode mixture layer containing CMC and a hydroxy group-modified PVP. The mass ratio of CMC is greater than that of the hydroxy group-modified PVP. The hydroxy group-modified PVP has low affinity with a solvent for a solvent-system slurry that forms an inorganic particle layer. Adhesion strength is prevented from degrading after forming the inorganic particle layer on the negative electrode mixture layer.