Layered Graphite Negative Electrode for Cycle Life and Low Swelling
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Solution Overview
Problem
Conventional graphite negative electrodes in lithium-ion batteries face challenges in achieving high cycle-performance and rate-performance while maintaining energy density and preventing volume swelling.
Innovation Solution
A negative electrode plate with two active material layers, where the first layer near the current collector has a small interlayer spacing and the second layer further away has a large interlayer spacing, optimizing the interlayer spacing ratio between 1.1 to 1.3 to enhance cycle and rate performance without compromising energy density or causing excessive swelling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the interlayer spacing of graphite is increased to improve cycle performance and rate performance, then the cycle performance and rate performance are enhanced, but the compacted density decreases causing volumetric energy density loss
Solution Approach 1:
The negative electrode active material layer is divided into multiple layers with different interlayer spacing values. The first layer has a first interlayer spacing value, the second layer has a second interlayer spacing value, and the third layer has a third interlayer spacing value, where the first < second < third. This segmentation allows different regions to serve different functions: the inner layer (first layer) with smaller spacing maintains high density and capacity, while the outer layers (second and third layers) with larger spacing improve ion transport and cycle performance.
Solution Approach 2:
Different interlayer spacing values are assigned to different positions within the active material layer. The layer closer to the current collector has smaller interlayer spacing for high energy density, while layers farther away have progressively larger spacing for improved kinetics and cycle stability. This local differentiation optimizes both energy density and performance characteristics in their respective regions.
2Productivity
If the interlayer spacing of graphite is increased to improve rate performance, then the rate performance is enhanced, but the volume swelling increases
Solution Approach 1:
The active material layer is segmented into multiple layers with progressively increasing interlayer spacing from the current collector outward. This segmentation creates a gradient structure where the third layer with the largest spacing facilitates rapid ion transport for high rate performance, while the first and second layers with smaller spacing provide structural stability and limit overall volume expansion.
Solution Approach 2:
The interlayer spacing parameter is varied systematically across different layers of the active material. By controlling the distribution of interlayer spacing values (first < second < third), the electrode achieves optimized ion transport pathways in outer layers for rate performance while maintaining structural integrity through smaller spacing in inner layers, thereby reducing volume swelling.
Data Source
AI summary
A negative electrode plate includes: a negative current collector; a first negative active material layer close to the negative current collector and disposed on at least one surface of the negative current collector, where the first negative active material layer includes a first negative active material; and a second negative active material layer. The second negative active material layer includes a second negative active material. The first negative active material layer is located between the second negative active material layer and the negative current collector. An interlayer spacing of the first negative active material is smaller than an interlayer spacing of the second negative active material.