Layered Electrode Mixture Structure for Fast-Charging Secondary Batteries
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Solution Overview
Problem
When the tortuosity of the mixture layer in a secondary battery is reduced, the rate characteristics improve, but this leads to a decrease in active material particle packing density and capacity, resulting in degraded cycle characteristics during high-rate charging and discharging.
Innovation Solution
A secondary battery design featuring a positive electrode and negative electrode with a multi-layer mixture structure, where the tortuosity of the second mixture layer is smaller than the first, maintaining high packing density and 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 the capacity per mixture material volume decreases
Solution Approach 1:
The mixture layer is divided into multiple sub-layers with different tortuosity values. The first sub-layer has higher tortuosity (better packing density) while the second sub-layer has lower tortuosity (better rate characteristics). This segmentation allows each sub-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 according to their functional requirements. The first sub-layer (closer to the current collector) has higher tortuosity for maximum packing, while the second sub-layer (outer region) has lower tortuosity for rapid ion transport. This local differentiation resolves the global contradiction.
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 of the mixture layer, which leads to degradation of the cycle characteristics
Solution Approach 1:
The mixture layer is segmented into sub-layers where the first sub-layer provides high packing density and stable conductive paths for cycle stability, while the second sub-layer provides low tortuosity for rapid ion transport. This segmentation prevents particle isolation while maintaining rate characteristics.
Solution Approach 2:
The mixture layer is constructed as a composite structure with different tortuosity characteristics in different sub-layers. This composite approach combines the advantages of high packing density (first sub-layer) and low tortuosity (second sub-layer), achieving both rate characteristics and cycle stability.
3Quantity of substance
If the packing density of the mixture layer is increased, then the capacity per mixture material volume is improved, but the rate characteristics during high-rate charging and discharging are degraded
Solution Approach 1:
The mixture layer is divided into sub-layers with different packing densities. The first sub-layer has high packing density for maximum capacity, while the second sub-layer has lower packing density but lower tortuosity for rapid ion transport during high-rate charging/discharging. This segmentation resolves the contradiction between capacity and rate characteristics.
Solution Approach 2:
Different regions of the mixture layer are optimized for different functions: the first sub-layer (inner region) is optimized for high packing density and capacity, while the second sub-layer (outer region) is optimized for low tortuosity and rapid ion transport. This local quality differentiation resolves the global contradiction between capacity and rate characteristics.
Data Source
AI summary
A secondary battery according to one embodiment of the present invention is provided with: a positive electrode that has a positive electrode core and a positive electrode mixture layer formed on said core; a negative electrode that has a negative electrode core and a negative electrode mixture layer formed on said core; and an electrolyte. The positive electrode mixture layer and the negative electrode mixture layer each includes a first mixture layer and a second mixture layer arranged on the first mixture layer. The curve ratio (τ2) of the second mixture layer is less than the curve ratio (τ1) of the first mixture layer.