Multi-Layer Battery Electrode Tortuosity for Fast Charging and Cycle Life
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Solution Overview
Problem
When the tortuosity of the mixture layer in a secondary battery electrode is reduced, the rate characteristics improve, but this leads to a decrease in active material packing density and capacity, resulting in degraded cycle characteristics during high-rate charging and discharging.
Innovation Solution
A multi-layer electrode structure is implemented, where the tortuosity of the second mixture layer is smaller than the first mixture layer, maintaining high packing density while improving cycle characteristics during high-rate charging and discharging.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the tortuosity of the mixture layer is reduced, then the rate characteristics are improved, but the packing density of active material particles decreases and capacity per mixture material volume decreases
Solution Approach 1:
The mixture layer is divided into multiple layers with different tortuosity values. The first mixture layer has higher tortuosity (better packing density) while the second mixture layer has lower tortuosity (better rate characteristics). This segmentation allows each layer to optimize for its specific function, resolving the contradiction between packing density and rate characteristics.
Solution Approach 2:
Different regions of the mixture layer are assigned different tortuosity values to perform different functions. The first layer (closer to the current collector) has higher tortuosity for maximum packing, while the second layer (outer layer) has lower tortuosity for rapid ion transport. This local differentiation resolves the global contradiction by optimizing each region for its specific role.
2Speed
If the tortuosity of the mixture layer is reduced, then the rate characteristics are improved, but the active material particles are isolated from a conductive path which leads to degradation of cycle characteristics
Solution Approach 1:
The mixture layer is segmented into multiple layers where the first layer maintains high tortuosity for excellent cycle characteristics through good particle connectivity, while the second layer has lower tortuosity for improved rate characteristics. This segmentation allows simultaneous optimization of both cycle stability and charging/discharging speed.
Solution Approach 2:
The conductive network is optimized locally in different layers. The first layer provides a robust conductive path for long-term stability, while the second layer facilitates rapid ion transport. This local quality differentiation ensures that cycle characteristics are not degraded even as rate characteristics improve.
3Speed
If the tortuosity of the mixture layer is reduced, then the rate characteristics are improved, but the capacity per mixture material volume decreases
Solution Approach 1:
The electrode structure is segmented into multiple mixture layers with different tortuosity values. The first layer maximizes capacity density through high packing, while the second layer enhances rate capability through lower tortuosity. This segmentation resolves the contradiction by distributing different functional requirements across separate layers.
Solution Approach 2:
The solution moves from a single-layer structure to a multi-layer structure, adding a dimensional aspect to the mixture layer design. By controlling the thickness and tortuosity of each layer independently, the patent achieves both high capacity density and excellent rate characteristics that cannot be obtained in a single uniform layer.
Data Source
AI summary
An electrode for secondary batteries according to one embodiment of the present invention is provided with a core body and a mixture layer that is formed on the core body. The mixture layer comprises a first mixture layer and a second mixture layer that is arranged on the first mixture layer. The tortuosity (τ2) of the second mixture layer is lower than the tortuosity (τ1) of the first mixture layer. The ratio (τ2/τ1) of the tortuosity (τ2) to the tortuosity (τ1) satisfies, for example, 0.3≤(τ2/τ1)<1.