Segmented Silicon Negative Electrode Plate for Battery Stress Management
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Solution Overview
Problem
Silicon-based materials in negative electrodes of electrochemical devices experience significant volume expansion during charge/discharge cycles, leading to mechanical stress, peel-off of the active material layer, and potential tearing of the current collector, which limits energy density and fast-charge performance.
Innovation Solution
A negative electrode plate design with a first active material layer closer to the current collector having a lower silicon content and smaller particle size, and a second active material layer farther away with higher silicon content and larger particle size, reducing stress on the current collector and enhancing lithium ion transmission and charging capabilities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If silicon-based material is used as negative active material to increase energy density, then theoretical specific capacity increases to 4200 mAh/g, but volume expansion rate reaches approximately 300% during charge/discharge cycles causing mechanical stress and structural failure
Solution Approach 1:
The negative electrode plate is divided into two distinct active material layers: a first layer closer to the current collector with lower silicon content and smaller particle size, and a second layer farther from the current collector with higher silicon content and larger particle size. This segmentation allows each layer to handle different mechanical stresses, with the first layer providing structural support and the second layer maximizing capacity utilization.
Solution Approach 2:
Different regions of the negative electrode are assigned different material compositions and particle size distributions. The first active material layer contains silicon-based material with weight percentage of 0.1%-30% and average particle size of 1-8 μm, while the second layer contains silicon-based material with weight percentage of 1%-100% and larger particle size. This local differentiation optimizes both mechanical stability near the current collector and capacity utilization in the outer layer.
2Quantity of substance
If uniform high silicon content is used throughout the active material layer to maximize energy density, then specific capacity increases, but peel-off of active material layer from current collector and tearing of current collector occurs due to huge mechanical stress
Solution Approach 1:
The active material layer is segmented into two sub-layers with different silicon contents. The first layer adjacent to the current collector has lower silicon content (0.1%-30% by weight), providing a stable foundation that adheres well to the current collector. The second layer has higher silicon content (1%-100% by weight), maximizing energy density while being supported by the first layer.
Solution Approach 2:
The silicon content is locally optimized: the first active material layer closer to the current collector contains less silicon (0.1%-30% weight percentage) to ensure strong adhesion and mechanical stability, while the second layer farther from the current collector contains more silicon (1%-100% weight percentage) to maximize specific capacity. This gradient distribution prevents peel-off and tearing.
3Quantity of substance
If fast-charge performance is improved by increasing silicon-based material content, then energy density increases, but lithium ion diffusion becomes slower due to larger particle size required for structural stability
Solution Approach 1:
The negative electrode is segmented into two layers with different particle size distributions. The first active material layer contains silicon-based material particles with smaller average size (1-8 μm), providing shorter diffusion paths for lithium ions and enabling faster charging. The second layer contains larger particles that provide high capacity while being supported by the first layer's rapid ion transport capability.
Solution Approach 2:
Particle size is locally optimized: the first active material layer closer to the current collector contains silicon-based material with smaller average particle size (1-8 μm) to facilitate rapid lithium ion diffusion and support fast-charge performance. The second layer contains larger particles that maximize energy density while benefiting from the ion transport infrastructure established by the first layer.
Data Source
Figure 1~2
AI summary
Embodiments of this application provide a negative electrode plate, an electrochemical device, and an electronic device. The negative electrode plate includes: a current collector; a first active material layer, where the first active material layer includes first silicon-based material particles; and a second active material layer, where the second active material layer includes second silicon-based material particles. The first active material layer is provided between the current collector and the second active material layer. A weight percentage of a silicon element based on a weight of the first active material layer is less than a weight percentage of the silicon element based on a weight of the second active material layer, and an average particle size Dv50 of the first silicon-based material particles is smaller than an average particle size Dv50 of the second silicon-based material particles. This application reduces defilming of the negative electrode plate containing silicon-based material particles in a cycle, deformation of an electrode assembly, and tearing of the current collector, and enhances charging capabilities of the negative electrode plate.