Silicon Anode Composite With SiO2 Phases to Prevent Silicate Cracking
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Solution Overview
Problem
The use of silicon-based negative electrode active materials in non-aqueous electrolyte secondary batteries faces challenges due to the large irreversible capacity of silicon, leading to low initial charge-discharge efficiency and deterioration in cycle characteristics, primarily caused by stress-induced cracking in the lithium silicate phase.
Innovation Solution
Incorporating a crystalline phase of silicon dioxide with both β-cristobalite and quartz into the lithium silicate phase of composite particles, which increases the rigidity and flexibility of the silicate phase, thereby reducing stress and preventing cracking during lithium absorption and release.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If silicon particles are used as negative electrode active material, then theoretical capacity density is improved, but initial charge-discharge efficiency deteriorates due to large irreversible capacity
Solution Approach 1:
A lithium silicate phase is introduced as an intermediary material that hosts silicon particles within its structure. The lithium silicate phase acts as a buffer that accommodates the large irreversible capacity of silicon while maintaining structural integrity, thereby improving initial charge-discharge efficiency without sacrificing the high theoretical capacity density of silicon
2Ease of operation
If silicon phase absorbs and releases lithium during charge and discharge, then charge-discharge reaction is enabled, but stress is generated in silicate phase causing cracking
Solution Approach 1:
The chemical composition parameters of the silicate phase are modified by incorporating specific elements (such as Al, B, P, or rare earth elements) to optimize the balance between flexibility and strength. This allows the silicate phase to accommodate stress from silicon expansion/contraction while maintaining structural integrity and preventing cracking
3Stability of the object's composition
If silicate phase cracks due to stress, then newly exposed surface contacts non-aqueous electrolyte, but side reactions are facilitated and cycle characteristics deteriorate
Solution Approach 1:
The silicate phase is designed with built-in stress accommodation mechanisms through compositional optimization and structural design that anticipates and cushions against the stress generated during silicon expansion and contraction. This prevents cracking before it occurs, thereby preventing side reactions with the electrolyte and maintaining excellent cycle characteristics
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach effectively suppresses the deterioration in cycle characteristics and enhances the capacity retention of the battery by allowing the silicate phase to maintain its function as a lithium-ion conductive phase, leading to improved charge-discharge performance.
Implementation Method 1
Incorporating a crystalline phase of silicon dioxide with both β-cristobalite and quartz into the lithium silicate phase of composite particles, which increases the rigidity and flexibility of the silicate phase, thereby reducing stress and preventing cracking during lithium absorption and release
Implementation Method 2
a material containing silicon (Si) that forms an alloy with lithium has been expected to be utilized as a negative electrode active material having a high theoretical capacity density
Implementation Method 3
allowing the silicate phase to maintain its function as a lithium-ion conductive phase
Data Source
AI summary
A negative electrode active material for a non-aqueous electrolyte secondary battery includes composite particles containing a lithium silicate phase, a silicon phase dispersed in the lithium silicate phase, and a crystalline phase of silicon dioxide dispersed in the lithium silicate phase. The crystalline phase of silicon dioxide contains β-cristobalite and quartz.