Nano Silicon-Carbon Composite for Li-Ion Battery Cycle Stability
Solution Overview
Problem
Existing nano silicon-carbon composite materials for lithium ion batteries suffer from poor cycle stability due to the huge volume effect of silicon during lithium ion insertion and extraction, leading to separation of silicon and carbon materials and loss of electric contact, which limits their long-term cycle performance.
Innovation Solution
A nano silicon-carbon composite material is developed with a carbon matrix, nano silicon dispersed on the carbon matrix, nano silicon carbide at the interface, and silicon oxide coating on the nano silicon, along with a preparation method involving silica sol, carbon particles, and electrochemical reduction in a molten salt electrolyte to control porosity, density, and resistivity, enhancing bonding between silicon and carbon.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If silicon nanocrystallization is adopted to reduce particle size and volume change, then the internal stress of the electrode is reduced, but the nanosize material is easily aggregated during cycling, resulting in insufficient performance improvement
Solution Approach 1:
The patent applies composite materials by combining silicon with carbon to form a silicon-carbon composite material. The carbon component serves as a buffer skeleton that accommodates the volume expansion and contraction of silicon during lithium insertion and extraction, preventing aggregation while maintaining structural integrity. This composite structure resolves the contradiction by providing both volume stability and cycle reliability.
Solution Approach 2:
The patent employs a flexible carbon buffer skeleton that acts as a shell or matrix surrounding the silicon particles. This flexible structure can expand and contract with the silicon during cycling, maintaining physical contact and preventing aggregation. The carbon buffer layer absorbs internal stress while keeping the silicon particles dispersed, thereby improving cycle performance without sacrificing volume stability.
2Stability of the object's composition
If nanosize silicon-carbon composite material is adopted with carbon as buffer skeleton, then the structure stability is improved, but the electric conductivity deteriorates due to poor conductive performance of silicon material
Solution Approach 1:
The patent creates a silicon-carbon composite material where carbon serves dual functions: as a buffer skeleton for structural stability and as a conductive network for electrical conductivity. The carbon component compensates for the poor conductivity of silicon while maintaining the structural benefits of the buffer skeleton, thereby resolving the contradiction between structure stability and electric conductivity.
Solution Approach 2:
The carbon component in the composite material performs multiple functions simultaneously: it acts as a buffer skeleton to accommodate volume changes, provides a conductive network to improve electrical conductivity, and maintains structural stability during cycling. This multi-functionality resolves the contradiction by making the carbon component serve both structural and electrical roles.
3Ease of manufacture
If physical combination of silicon and carbon is used, then the material can be prepared simply, but the bonding becomes weaker after repeated cycling, resulting in loss of electric contact and poor cycle stability
Solution Approach 1:
The patent changes the bonding parameter from physical combination to chemical combination. By forming chemical bonds between silicon and carbon atoms, the composite material achieves strong bonding that withstands repeated cycling. This chemical bonding maintains electric contact and prevents separation, resolving the contradiction between preparation simplicity and cycle stability while still maintaining relatively simple preparation processes.
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 achieves improved cycle stability by preventing silicon and carbon separation during lithium insertion and extraction, maintaining electric contact, and allowing for continuous production with abundant, low-cost raw materials and a simple, pollution-free process.
Implementation Method 1
silica is electrochemically reduced into the nano silicon
Implementation Method 2
electrochemical reduction in a molten salt electrolyte
Implementation Method 3
nano silicon carbide dispersed on the interface of the carbon matrix and the nano silicon
Data Source
Figure 1~2
Figure 3(a)~4c
Figure 5
AI summary
The invention relates to a nano silicon-carbon composite negative material for lithium ion batteries and a preparation method thereof. A porous electrode composed of silica and carbon is taken as a raw material, and a nano silicon-carbon composite material of carbon-loaded nano silicon is formed by a molten salt electrolysis method in a manner of silica in-situ electrochemical reduction. Silicon and carbon of the material are connected by nano silicon carbide, and are metallurgical-grade combination, so that the electrochemical cycle stability of the nano silicon-carbon composite material is improved. The preparation method of the nano silicon-carbon composite material provided by the invention comprises the following steps: compounding a porous block composed of carbon and silica powder with a conductive cathode collector as a cathode; using graphite or an inert anode as an anode, and putting the cathode and anode into CaCl2 electrolyte or mixed salt melt electrolyte containing CaCl2 to form an electrolytic cell; applying voltage between the cathode and the anode; controlling the electrolytic voltage, the electrolytic current density and the electrolytic quantity, so that silica in the porous block is deoxidized into nano silicon by electrolytic reduction, and the nano silicon-carbon composite material for lithium ion batteries is prepared at the cathode.