Yolk-Shell Silicon-Carbon Composite for Silicon Expansion Buffering
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Solution Overview
Problem
Existing silicon-based negative electrode active materials in secondary batteries suffer from significant volume expansion during charge and discharge cycles, leading to mechanical instability and deterioration in battery performance, which existing methods using strong acids to form voids are not environmentally friendly or efficient.
Innovation Solution
A silicon-carbon composite with a yolk-shell structure is manufactured using a polymer layer as a sacrificial layer, formed through initiator-based chemical vapor deposition (iCVD) to create uniform voids without strong acids, by polymerizing a monomer on silicon particles and forming a carbon thin film with controlled thickness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a polymer layer is used as a sacrificial layer formed through iCVD, then uniform voids can be formed without strong acids and the thickness can be precisely controlled, but the manufacturing process complexity increases
Solution Approach 1:
A polymer layer is introduced as an intermediary sacrificial material that can be precisely deposited through iCVD and then removed to create uniform voids. This intermediary layer enables controlled void formation without requiring strong acid etching, resolving the contradiction between precision and process simplicity.
Solution Approach 2:
The invention changes the physical and chemical parameters of the sacrificial layer by using a polymer material with controllable deposition parameters in iCVD. By adjusting polymerization conditions such as monomer flow rate, initiator concentration, and deposition temperature, uniform voids can be formed with precise thickness control while avoiding strong acid processes.
2Reliability
If the carbon thin film thickness is precisely controlled, then carbon film peeling is suppressed, but the manufacturing precision requirements increase
Solution Approach 1:
The invention uses a carbon thin film with precisely controlled thickness as a flexible shell around the silicon particles. The controlled thickness ensures the film is thin enough to accommodate silicon expansion without peeling, while still providing sufficient mechanical strength and adhesion, resolving the contradiction between reliability and manufacturing precision.
Solution Approach 2:
The carbon thin film is designed with precise thickness control to act as a cushioning layer before silicon expansion occurs during battery operation. This pre-designed film thickness provides adequate stress distribution and adhesion, preventing carbon film peeling during subsequent charge-discharge cycles.
3Volume of stationary object
If the polymer layer thickness is increased to accommodate more volume expansion, then the void space increases, but the carbon film may peel off due to excessive stress
Solution Approach 1:
The invention optimizes the polymer layer thickness parameters to achieve the right balance between void volume and stress distribution. By precisely controlling the polymer layer thickness through iCVD parameters, sufficient void space is created to accommodate silicon expansion while maintaining adequate carbon film adhesion strength.
Solution Approach 2:
The polymer sacrificial layer creates localized void spaces with specific thickness distribution around the silicon particles. This local quality control ensures that voids are formed where needed to accommodate expansion, while the carbon film maintains sufficient adhesion in regions where stress concentration could cause peeling.
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 method allows for precise control of the sacrificial layer thickness, accommodating volume expansion and suppressing carbon film peeling, thereby enhancing battery performance and lifespan.
Implementation Method 1
activating the initiator to polymerize the monomer, thereby forming a polymer thin film on the surface of the silicon particles
Implementation Method 2
performing heat treatment at a temperature of 400 to 1,400°C
Data Source
Figure 1~2
Figure 3(a)~4(b)
Figure 5A~5B
AI summary
The present invention relates to a silicon-carbon composite having a yolk-shell structure, a manufacturing method therefor, and a negative electrode active material comprising same. The silicon-carbon composite having a yolk-shell structure according to an embodiment of the present invention may be manufactured without an etching process using a strong acid and may have uniform voids formed therein by using a polymer layer having a uniform thickness as a sacrificial layer. Accordingly, the silicon-carbon composite, when used as a negative electrode active material, may accommodate the volume expansion of silicon and thus may suppress the phenomenon in which the outermost carbon thin film is peeled off. As a result, the degradation of battery performance and life span may be suppressed.