Double-Layer Si Anode Structure for Cycle Life and Input Performance
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Solution Overview
Problem
Existing negative electrodes with Si-based active materials face challenges in maintaining satisfactory input characteristics, cyclic characteristics, and high-temperature storage characteristics due to particle isolation from conductive paths caused by volume changes during charging and discharging.
Innovation Solution
A double-layered structure for the negative electrode mixture layer, comprising a first layer with a Si-based active material, polyacrylic acid or its salt, and fibrous carbon, and a second layer with a carbon-based active material having higher tap density, is used to enhance contact and conductivity, thereby improving battery performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the amount of binder is increased to suppress isolation of negative electrode active material particles, then cyclic characteristics are improved, but input characteristics deteriorate
Solution Approach 1:
The negative electrode mixture layer is divided into a first region containing Si-based active material particles with binder and conductive agent, and a second region containing only carbon-based active material particles without binder or conductive agent. This segmentation allows the first region to maintain particle contact and conductivity (improving cyclic characteristics) while the second region provides high-capacity carbon material that does not deteriorate input characteristics when increased in amount.
Solution Approach 2:
Different regions of the negative electrode mixture layer have different compositions: the first region has binder and conductive agent to ensure particle contact and conductivity, while the second region has only carbon-based active material. This local quality differentiation allows each region to perform its specific function optimally - the first region maintains structural integrity during volume changes, while the second region provides high capacity without compromising input characteristics.
2Power
If carbon-based active material with high insertion rate is used to improve input characteristics, then input characteristics are improved, but cyclic characteristics deteriorate due to increased particle isolation
Solution Approach 1:
The negative electrode mixture layer is divided into a first region with Si-based active material particles surrounded by binder and conductive agent that maintain particle contact, and a second region with carbon-based active material particles. This segmentation ensures that the first region maintains good cyclic characteristics through proper particle contact, while the second region provides high input characteristics.
Solution Approach 2:
The first region has specific local quality with binder and conductive agent to ensure particle contact and prevent isolation, providing good cyclic characteristics. The second region has different local quality with only carbon-based active material particles, providing high input characteristics. This local quality differentiation allows both contradictory requirements to be satisfied in different regions.
Data Source
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AI summary
This negative electrode for a nonaqueous electrolyte secondary battery is configured such that a negative electrode mixture layer has: a first layer that is formed on a negative electrode collector and that contains a first carbonaceous active material, a Si-based active material, a polyacrylic acid or a salt thereof, and a fibrous carbon; and a second layer that is formed on the first layer and that contains a second carbonaceous active material which has a tap density higher than that of the first carbonaceous active material.