3D Carbon-Silicon Composite Structure for Silicon Expansion Control
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Solution Overview
Problem
Existing silicon-based electrode materials face issues with volume expansion leading to cracking and collapse of the electrode structure, along with decreased capacity and cycle life due to side reactions with the electrolyte.
Innovation Solution
A carbon-silicon three-dimensional structural composite material is prepared by embedding silicon spheres between layers of graphene using a mixed emulsifier formed with graphene quantum dots and graphite oxide, enhanced by a hydrothermal reaction and drying process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If silicon-carbon composite materials are prepared by assembling or mixing silicon and carbon materials to relieve volume expansion, then the volume expansion of silicon is reduced, but the conduction of electrons and ions is hindered, increasing polarization and affecting cycle life and rate performance
Solution Approach 1:
The patent embeds silicon particles within the three-dimensional network structure of graphene and carbon nanotubes, creating a nested configuration where silicon is contained within the carbon matrix. This nesting approach allows silicon to expand volumetrically during lithiation while the surrounding carbon structure provides mechanical confinement and maintains electrical conductivity pathways, thus resolving the contradiction between volume expansion control and conduction performance.
Solution Approach 2:
The patent creates a composite material system consisting of silicon particles integrated with a three-dimensional network of graphene and carbon nanotubes. This composite structure combines the high capacity of silicon with the mechanical flexibility and electrical conductivity of carbon materials, enabling simultaneous achievement of volume expansion management and maintained conduction performance for improved cycle life and rate capability.
2Quantity of substance
If silicon material is used as electrode material due to high capacity, then capacity is improved, but volume changes greatly during charging and discharging leading to cracking and collapse of electrode material structure
Solution Approach 1:
The patent employs a three-dimensional network structure composed of graphene and carbon nanotubes that forms a flexible matrix surrounding silicon particles. This flexible carbon network can accommodate the large volume changes of silicon during lithiation and delithiation cycles, providing mechanical support that prevents cracking and collapse of the electrode structure while maintaining electrical conductivity throughout the cycle.
Solution Approach 2:
The patent creates a composite material system where silicon particles are integrated within a three-dimensional network of graphene and carbon nanotubes. This composite structure combines the high capacity of silicon with the mechanical flexibility and structural strength of carbon materials, enabling the electrode to maintain structural integrity despite the large volume changes of silicon during charging and discharging.
3Quantity of substance
If SEI film on the surface of silicon material is formed, then initial capacity is achieved, but side reaction with electrolyte occurs resulting in decrease of capacity and service life
Solution Approach 1:
The patent introduces a three-dimensional carbon network structure as an intermediary layer between the silicon particles and the electrolyte. This carbon matrix acts as a protective interface that allows initial capacity utilization of silicon while preventing direct and continuous side reactions with the electrolyte. The SEI film forms on the carbon surface rather than directly on silicon, reducing ongoing parasitic reactions and improving long-term service life while maintaining initial capacity.
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 material effectively alleviates volume expansion, improves electrical conductivity, and enhances cycle life and rate performance by maintaining structural integrity and increasing electron transport channels.
Implementation Method 1
the graphene quantum dots are utilized with their surface activity for the first time to be mixed and react with transition metal chloride to prepare an emulsifier
Implementation Method 2
the prepared mixed emulsifier plays an emulsifying role in the reaction between the graphite oxide aqueous solution and the nanosilicon sphere solution
Implementation Method 3
the graphite oxide (graphene oxide) is reduced into graphene by using a reducing agent, and enters an oil phase from the aqueous phase
Implementation Method 4
performing a hydrothermal reaction to obtain a reduced emulsion
Implementation Method 5
a fourth step of freeze-drying the reduced emulsion obtained in the third step
Data Source
AI summary
Provided are a carbon-silicon three-dimensional structural composite material and a preparation method thereof. The preparation method includes: dissolving graphene quantum dots in ultrapure water, dropwise adding a CuCl2 or ZnCl2 solution, and performing oscillation to generate a mixed emulsifier; mixing the mixed emulsifier with a graphite oxide aqueous solution and a cyclohexane solution containing nanosilicon spheres, and performing homogenization to form a uniform oil-in-water emulsion; adding hydrazine hydrate into the obtained emulsion for reduction, and performing a hydrothermal reaction to obtain a reduced emulsion; and freeze-drying the reduced emulsion, performing washing with a washing liquid, and performing vacuum drying to obtain a carbon-silicon three-dimensional structural composite material.