Negative Electrode Coating Profile for Edge Lithium Control
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Solution Overview
Problem
Secondary batteries face challenges in achieving good safety performance due to issues like local lack of active material and lithium precipitation at the edges, which can lead to cracking and reduced cycle life, exacerbated by the 'fat-edge phenomenon' during the manufacturing process.
Innovation Solution
A negative electrode plate with a specific thickness profile, where the edge regions have a continuously decreasing thickness from a uniform middle region, and a slurry composition including sodium carboxymethyl cellulose or starch with controlled molecular weight and polydispersity, along with styrene butadiene rubber, to prevent crimping, cracking, and lithium precipitation, while maintaining high solid component concentration for stability and processability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the negative film layer has uniform thickness across the entire surface, then the manufacturing process is simple, but edge regions accumulate excess active material causing 'fat-edge phenomenon' and subsequent cracking
Solution Approach 1:
The patent applies local quality by creating different thickness zones in the negative film layer: a first region with first thickness and a second region with second thickness different from the first. This non-uniform thickness distribution prevents active material accumulation at edges while maintaining manufacturing feasibility through controlled coating processes.
2Reliability
If the edge regions have large width to ensure sufficient active material, then local lack of active material is reduced, but the thickness non-uniform region expands increasing crimping risk
Solution Approach 1:
The patent changes the thickness parameter across different regions of the negative film layer. By controlling the thickness ratio and width ratio between the first and second regions within specific ranges, it achieves optimal balance between active material distribution and geometric stability, preventing both crimping and lithium precipitation.
3Quantity of substance
If the negative film layer thickness is increased to provide sufficient active material, then capacity is improved, but edge regions become more prone to lithium precipitation and safety issues
Solution Approach 1:
The patent applies local quality by creating different thickness zones in the negative film layer: a first region with first thickness and a second region with second thickness different from the first. This non-uniform thickness distribution prevents active material accumulation at edges while maintaining manufacturing feasibility through controlled coating processes.
4Stability of the object's composition
If the slurry has high solid component concentration for stability, then storage stability is improved, but the slurry becomes more difficult to process and coat uniformly
Solution Approach 1:
The patent uses composite materials by combining multiple binder types (first binder and second binder with different functionalities) in the slurry formulation. This composite binder system maintains high solid component concentration for stability while ensuring adequate flow and coating properties through synergistic interactions between different binder components.
Data Source
AI summary
A negative electrode plate includes a negative current collector and a negative film layer located on a surface of the negative current collector. The negative film layer has a length direction consistent with a length direction of the negative current collector and a width direction consistent with a width direction of the negative current collector. A cross section of the negative film layer perpendicular to the length direction includes a uniform thickness region located at a middle portion in the width direction and edge regions located at two ends in the width direction. Either of the edge regions has a thickness continuously decreasing in a direction from the uniform thickness region to the edge region. A width a of either of the two edge regions and an average thickness d of the uniform thickness region satisfy a/d≤1.5 and d≤300 μm.