Silicon-Graphite Negative Electrode Layers for Fast-Charge Cycle Life
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The use of silicon materials as negative electrode active materials in secondary batteries leads to disconnection of conductive paths during high-rate charging and discharging, resulting in degraded cycle characteristics due to reduced adhesion between active material particles and the conductive path.
Innovation Solution
A negative electrode with a multi-layer structure is developed, where the second mixture layer has a tortuosity ratio less than 1.1 compared to the first mixture layer, incorporating graphite and silicon materials, to enhance the packing density and maintain high-rate charging and discharging performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the tortuosity of the mixture layer is reduced to improve rate characteristics, then the charging and discharging speed is improved, but adhesion between active material particles decreases and conductive paths disconnect, leading to degraded cycle characteristics
Solution Approach 1:
The mixture layer is divided into a first mixture layer (near the collector) and a second mixture layer (outer layer), with different tortuosity characteristics. The first mixture layer has higher tortuosity to maintain adhesion and conductive path connectivity, while the second mixture layer has lower tortuosity to facilitate ion transport and improve rate characteristics. This segmentation resolves the contradiction by assigning different structural characteristics to different regions of the mixture layer.
Solution Approach 2:
Different regions of the mixture layer are given different local properties: the first mixture layer near the collector has higher tortuosity (τ1) to ensure strong adhesion and maintain conductive paths, while the second outer mixture layer has lower tortuosity (τ2) to enable fast ion diffusion and improve rate characteristics. The ratio τ2/τ1 is controlled to be 0.05 to 1.0 to optimize both cycle characteristics and rate performance simultaneously.
2Quantity of substance
If silicon material content is increased to improve energy density, then the energy storage capacity is improved, but volume change during charging and discharging increases, leading to disconnection of conductive paths
Solution Approach 1:
The mixture layer is segmented into two layers with different compositions and functions. The first mixture layer near the collector contains silicon material and provides structural stability with higher tortuosity to maintain conductive paths. The second outer mixture layer has lower tortuosity to accommodate volume changes and maintain connectivity. This segmentation allows high silicon content (≥0.5 wt%) to be used while preventing conductive path disconnection.
Solution Approach 2:
The mixture layer is designed as a composite structure containing graphite particles (average diameter 3 μm to 30 μm), silicon material particles (average diameter 0.3 μm to 3 μm), and conductive agent particles. The composite structure with controlled tortuosity ratio (τ2/τ1 = 0.05 to 1.0) allows the silicon material to expand and contract during cycling while maintaining continuous conductive paths through the hierarchical particle arrangement and controlled pore structure.
Data Source
AI summary
An electrode for secondary batteries according to one example of an embodiment is provided with a core body and a mixture layer that is formed on the core body. The mixture layer includes a first mixture layer and a second mixture layer disposed on the first mixture layer, and contains graphite and silicon material as active materials, and the content of the silicon material is greater than or equal to 0.5% by mass with respect to the active material. The ratio (τ2/τ1) of the tortuosity factor (τ2) of the second mixture layer to the tortuosity factor (τ1) of the first mixture layer is less than 1.1.