Core-Shell SiOx Graphite Negative Electrode for Battery Life
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Solution Overview
Problem
Conventional lithium secondary batteries face challenges with low energy density due to the low theoretical capacity of graphite materials and the deteriorated battery life characteristics of Si-based materials, which experience large volume expansion during charge and discharge cycles, and SiOx materials have low initial coulombic efficiency and are difficult to apply practically.
Innovation Solution
A negative electrode active material is developed using a core-shell composite comprising silicon oxide (SiOx) with a lithium compound and a graphitic material, where the silicon oxide includes lithium silicate, and is coated with amorphous carbon to suppress lithium compound elution and enhance stability, improving initial efficiency and life characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If Si-based material is used to increase theoretical capacity, then energy density is improved, but volume expansion occurs during charge and discharge leading to deteriorated battery life
Solution Approach 1:
The patent embeds SiOx particles within a graphite matrix structure, creating a nested composite where the high-capacity SiOx is contained within the stable graphite framework. This nesting approach allows the SiOx to contribute its high theoretical capacity (3580 mAh/g) while the surrounding graphite provides structural stability and accommodates volume expansion, thereby maintaining battery life characteristics.
Solution Approach 2:
The patent creates a composite material combining SiOx and graphite in a core-shell or matrix structure. The composite leverages the high capacity of SiOx and the structural stability of graphite, achieving both improved energy density and maintained battery life through the synergistic combination of materials with complementary properties.
2Reliability
If SiOx material is used to reduce volume expansion, then battery life characteristics are improved, but initial coulombic efficiency decreases due to irreversible phase formation
Solution Approach 1:
The patent creates a heterogeneous structure where SiOx is distributed as discrete particles or phases within the graphite matrix, rather than using bulk SiOx. This local distribution allows regions of low volume expansion (graphite) to compensate for the irreversible phase formation in SiOx regions, maintaining overall structural integrity and improving initial coulombic efficiency while preserving life characteristics.
Solution Approach 2:
The patent modifies the composition parameters of the composite, specifically controlling the ratio of SiOx to graphite and the morphology of SiOx particles. By optimizing these parameters, the patent reduces the extent of irreversible phase formation while maintaining the volume expansion benefits, thereby improving initial coulombic efficiency without sacrificing life characteristics.
3Quantity of substance
If lithium compound is present on silicon oxide surface, then capacity is improved, but slurry pH increases causing side reactions with electrolyte
Solution Approach 1:
The patent introduces a surface coating or intermediate layer on the SiOx particles that contains the lithium compound in a controlled manner. This intermediate layer acts as a barrier between the lithium compound and the electrolyte, preventing harmful side reactions while still allowing lithium ion transfer for capacity enhancement. The coating may be a thin oxide layer or a protective polymer layer.
Solution Approach 2:
The patent applies a thin film coating on the SiOx surface that encapsulates the lithium compound. This flexible thin film allows lithium ion diffusion for capacity improvement while physically isolating the lithium compound from direct contact with the electrolyte, thereby preventing side reactions and maintaining slurry pH stability.
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
The solution effectively improves the initial efficiency and capacity of lithium secondary batteries while enhancing life characteristics by minimizing volume expansion and preventing lithium compound elution, leading to better stability and performance.
Implementation Method 1
coated with amorphous carbon to suppress lithium compound elution and enhance stability
Implementation Method 2
improving life characteristics by minimizing volume expansion
Data Source
AI summary
Provided is a negative electrode active material for a lithium secondary battery including a core-shell composite including: a core including a silicon oxide (SiOx, 0<x≤2) containing a lithium compound and a graphitic material; and a shell including amorphous carbon, positioned on the core. The silicon oxide (SiOx, 0<x≤2) includes at least one lithium silicate selected from Li2SiO3, Li2Si2O5, and Li4SiO4 in at least a part of the silicon oxide.