Bilayer Negative Electrode Structure for Silicon Volume Change
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Solution Overview
Problem
Conventional carbonaceous materials in negative electrodes for lithium secondary batteries have limited capacity, while silicon-based materials offer higher capacity but suffer from volume changes causing conductive path disconnection during charge/discharge cycles, leading to poor cycle characteristics.
Innovation Solution
A bilayer structure negative electrode with a first layer of carbonaceous active material and a second layer of silicon-based active material and carbon nanotubes, where carbon nanotubes are used to maintain contact with the silicon-based material, forming a stable conductive path despite volume changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If silicon-based material is used as negative electrode active material, then theoretical capacity is improved (4010 mAh/g), but charge/discharge efficiency deteriorates (80%) and volume stability worsens (300% change)
Solution Approach 1:
The patent uses a composite structure where silicon-based particles are embedded in a carbonaceous matrix. The carbonaceous material serves as both the active material and the binding matrix that holds silicon particles together, preventing their dispersion and maintaining structural integrity during volume changes. This composite approach allows the electrode to achieve high theoretical capacity from silicon while maintaining sufficient charge/discharge efficiency through the carbonaceous component.
2Quantity of substance
If silicon-based material is used as negative electrode active material, then theoretical capacity is improved (4010 mAh/g), but volume stability deteriorates (300% change during charge/discharge)
Solution Approach 1:
The carbonaceous material forms a flexible matrix that can accommodate the large volume changes of silicon-based particles during charge and discharge cycles. This carbonaceous shell or matrix acts as a buffer that absorbs expansion and contraction, preventing particle disconnection and maintaining conductive paths despite the 300% volume change in silicon.
3Reliability
If conventional carbonaceous material is used as negative electrode active material, then charge/discharge efficiency is improved (92%), but theoretical capacity deteriorates (372 mAh/g limit)
Solution Approach 1:
The electrode uses a composite of silicon-based particles dispersed in a carbonaceous matrix. The carbonaceous material provides the high charge/discharge efficiency (92%) while the silicon-based particles contribute the high theoretical capacity (4010 mAh/g). The synergistic combination allows the electrode to achieve both high efficiency and high capacity simultaneously.
Data Source
AI summary
A negative electrode including: a current collector; a first negative electrode active material layer positioned on at least one surface of the current collector for a negative electrode and containing a first carbonaceous active material; and a second negative electrode active material layer positioned on a surface of the first negative electrode active material layer and containing a silicon-based active material and carbon nanotubes. A lithium secondary battery including the negative electrode is also disclosed.