Silicon Negative Electrode Holes for Cycle-Life and Fast Charging
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Solution Overview
Problem
Rechargeable lithium batteries face challenges with volume expansion of silicon-based negative electrode materials during charging and discharging, leading to reduced cycle-life and high-rate charging performance due to mechanical stress and capacity deterioration.
Innovation Solution
A negative electrode with a silicon-based active material layer incorporating holes that accommodate volume expansion, where the hole volume is limited to no more than five times that of silicon, enhancing mechanical strength and electrolyte impregnation, and strategically varying silicon content and hole distribution across the layer to manage expansion effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If silicon-based active material is used to increase capacity, then battery capacity is improved, but volume expansion occurs during charging and discharging leading to reduced cycle-life
Solution Approach 1:
The negative electrode active material layer is designed with a porous structure containing multiple voids or holes. These pores provide internal space to accommodate the volume expansion of silicon during lithiation, preventing mechanical stress and structural degradation. The porous structure allows silicon to expand into the void spaces rather than exerting outward pressure that would cause detachment from the current collector, thereby maintaining cycle-life stability while utilizing high-capacity silicon material.
Solution Approach 2:
The negative electrode active material layer is segmented into multiple regions with different silicon contents. By dividing the layer into zones with varying silicon concentrations, the structure can better manage localized expansion stresses. Regions with higher silicon content are distributed among regions with lower silicon content, creating a gradient structure that accommodates differential expansion and reduces overall mechanical stress on the electrode.
2Quantity of substance
If silicon content is increased to improve capacity, then battery capacity is improved, but mechanical strength is reduced due to volume expansion
Solution Approach 1:
The porous structure with controlled voids provides internal accommodation space for silicon expansion, preventing the formation of cracks and mechanical failure. The pores act as buffer zones that absorb expansion stresses, maintaining the structural integrity and mechanical strength of the negative electrode active material layer even with high silicon content.
Solution Approach 2:
The negative electrode employs a composite structure combining silicon-based active material with other materials in a porous matrix. This composite approach allows the integration of silicon's high capacity with the structural stability provided by the porous framework and other electrode materials, achieving both high capacity and maintained mechanical strength.
3Manufacturing precision
If uniform silicon distribution is used to simplify manufacturing, then manufacturing precision is improved, but volume expansion management is insufficient leading to detachment
Solution Approach 1:
The negative electrode active material layer exhibits non-uniform silicon distribution with different regions containing different silicon contents. This local variation in composition allows different zones to manage expansion differently, with higher silicon regions benefiting from the porous structure's expansion accommodation and lower silicon regions providing structural stability. This gradient structure prevents uniform expansion stresses that would cause detachment.
Solution Approach 2:
The silicon content parameter is deliberately varied across different regions of the negative electrode active material layer. By changing the silicon concentration parameter spatially, the electrode can manage volume expansion more effectively throughout its structure, preventing detachment while maintaining high overall capacity.
4Quantity of substance
If high silicon content is used to maximize capacity, then battery capacity is improved, but high-rate charging performance is reduced due to expansion stress
Solution Approach 1:
The porous structure with controlled voids facilitates rapid ion transport while accommodating expansion stresses during high-rate charging. The pores provide multiple pathways for lithium ion diffusion and reduce the kinetic barriers associated with silicon expansion, enabling the electrode to maintain high capacity utilization even at elevated charging rates.
Data Source
AI summary
A negative electrode for a rechargeable lithium battery and a rechargeable lithium battery including the same are described. The negative electrode includes a current collector; and a negative electrode active material layer on the current collector and including a negative electrode active material, wherein the negative electrode active material includes Si in an amount of greater than about 0 volume % and less than or equal to about 70 volume % based on the total 100 volume % of the negative electrode active material layer, and at least one hole is in the negative electrode active material layer, a volume of the at least one hole is about 5 times or less the total volume of Si.