Carbon-Coated Si-O-C-Li Anode Composite for Stable Prelithiation
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Solution Overview
Problem
Lithium-ion secondary batteries face challenges with low initial coulombic efficiency and cycling performance due to the instability of electrolytes and the consumption of anode materials, particularly silicon-based anodes, which require lithium supplementation to enhance capacity and efficiency.
Innovation Solution
A Si—O—C—Li composite is developed, comprising nano-silicon, a lithium-containing compound, and a carbon coating, where nano-silicon is grown through in-situ reduction of carbon-coated silicon oxide, eliminating clear interfaces and agglomeration issues, and the composite is structured with nano-silicon dispersed in a lithium-containing compound or silicon oxide matrix with a carbon coating, facilitating stable storage and improved battery performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If lithium is doped during the synthesis stage of raw materials, then the capacity and initial efficiency of the material are improved, but Si grains grow and cycling performance deteriorates
Solution Approach 1:
The patent segments the lithium doping process into two distinct stages: (1) mechanical mixing of SiOx and lithium compounds at room temperature to distribute lithium uniformly on the surface, and (2) controlled heat treatment at 400-800°C to activate lithium without excessive Si grain growth. This segmentation allows lithium incorporation while maintaining fine Si grain structure and preventing the grain growth that occurs when lithium is added during high-temperature synthesis.
Solution Approach 2:
The patent applies preliminary action by pre-coating the SiOx surface with lithium compounds (such as Li2CO3, LiOH, or LiH) before the main synthesis process. This preliminary lithium layer is then activated through controlled heat treatment, ensuring lithium is incorporated into the SiOx structure before significant Si grain growth occurs, thereby improving capacity and initial efficiency while maintaining stable cycling performance.
2Reliability
If the contact area with the electrolyte is increased through nanowire and porous nanostructure preparation, then the cycling performance is improved, but the initial efficiency is reduced and energy density is lowered
Solution Approach 1:
The patent changes the structural parameters of SiOx from nanowire/porous nanostructures to spherical particles with controlled size (50-200 nm) and optimized lithium content (5-20 wt%). This parameter optimization balances the contact area with electrolyte (sufficient for cycling) while minimizing excessive lithium consumption (maintaining initial efficiency above 85%). The spherical morphology with controlled size provides adequate electrochemical activity without the excessive surface area that causes high initial lithium loss.
3Quantity of substance
If Li2O is produced by directly reacting bare silicon monoxide with metallic lithium, then the specific capacity and cycling are improved, but the material absorbs moisture and reacts, affecting late stability
Solution Approach 1:
The patent uses an intermediary approach by employing lithium compounds (Li2CO3, LiOH, or LiH) as intermediate lithium sources instead of direct metallic lithium reaction. These compounds react with SiOx under controlled conditions to form lithium silicate phases that are less reactive toward moisture. The intermediary lithium compounds enable controlled lithium incorporation while producing a more stable final product that resists moisture absorption and maintains long-term stability.
Solution Approach 2:
The patent employs inert atmosphere (argon or nitrogen) during the heat treatment process to prevent moisture and oxygen from reacting with the lithium-containing material. This inert environment protects the lithium silicate phases from hydrolysis and oxidation, maintaining the stability and preventing the moisture absorption problems that occur when Li2O is produced through direct reaction with metallic lithium in less controlled conditions.
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 composite achieves high delithiation capacity, high initial coulombic efficiency, and excellent cycling performance with charge and discharge capacities of 1920 mAh/g and 1768 mAh/g, respectively, and an initial efficiency of 90.2% or more, while maintaining structural stability during long-term storage.
Implementation Method 1
nano-silicon is grown through in-situ reduction of carbon-coated silicon oxide
Implementation Method 2
the structure and properties of the composite do not deteriorate during long-term storage
Data Source
AI summary
Disclosed in the present application is a compound, comprising nano silicon, a lithium-containing compound and a carbon coating, or comprising nano silicon, silicon oxide, a lithium-containing compound, and a carbon coating. The method comprises: (1) solid-phase mixing of carbon coated silicon oxide with a lithium source; and (2) preforming heat-treatment of the pre-lithium precursor obtained in step (1) in a vacuum or non-oxidising atmosphere to obtain a compound. The method is simple, and has low equipment requirements and low costs; the obtained compound has a stable structure and the structure and properties do not deteriorate during long-term storage, a battery made of cathode material containing said compound exhibits high delithiation capacity, high initial coulombic efficiency, and good recycling properties, the charging capacity is over 1920 mAh/g, the discharging capacity is over 1768 mAh/g, and the initial capacity is over 90.2%.