Si-C Composite Particles With Hollow Carbon for Electrode Swelling
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Solution Overview
Problem
Lithium-ion rechargeable batteries using silicon as a negative electrode active material face significant volume expansion issues due to silicon's electrochemical expansion and contraction, leading to poor cycle characteristics and detachment of silicon particles from the electrode.
Innovation Solution
The development of composite particles comprising porous carbon and silicon, with specific density and structural characteristics, including cavities and a thin coat layer, allows for uniform expansion and contraction, reducing stress and improving cycle durability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If silicon is used as a negative electrode active material to increase capacity, then the theoretical specific capacity increases from 372 mAh/g to 4200 mAh/g, but the volume expansion during charging reaches up to 3 to 4 times, causing particle self-destruction and detachment from the electrode
Solution Approach 1:
Silicon particles are embedded within hollow carbonaceous particles, creating a nested structure where the inner silicon can expand and contract within the confined space of the outer carbon shell. This nesting approach allows high-capacity silicon to be utilized while the outer carbon layer constrains excessive volume expansion and maintains structural integrity during charging cycles.
Solution Approach 2:
A thin coat layer of carbonaceous material is formed on the surface of the composite particles. This flexible shell accommodates the volume changes of silicon during lithiation and delithiation, preventing particle fracture and detachment from the electrode while maintaining electrical conductivity and structural stability.
2Manufacturing precision
If porous carbon material with small pores (5 to 1000 nm) is used for silicon filling, then the pores can be filled with silicon, but the Si-C composite material cannot achieve reduction in volume expansion of the electrode during charging
Solution Approach 1:
Hollow carbonaceous particles with controlled cavity structures are used as the base material. These porous structures provide sufficient internal volume for silicon filling while maintaining an overall particle morphology that can accommodate expansion. The hollow structure acts as a buffer space, allowing silicon to expand into the cavity without causing excessive external volume increase of the composite particle.
Solution Approach 2:
The pore size parameters are optimized to a specific range that balances silicon filling efficiency with volume expansion control. By carefully controlling the cavity diameter and pore volume of the carbonaceous material, the structure allows adequate silicon incorporation while maintaining the ability to reduce overall electrode volume expansion during charging cycles.
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 particles achieve a reduction in volume expansion during charging, enhancing the cycle characteristics and durability of lithium-ion rechargeable batteries.
Implementation Method 1
bringing a gas including a silicon-containing gas into contact with a porous carbon satisfying the following conditions at 300°C or more and 500°C or less to precipitate silicon in the pores of the porous carbon
Implementation Method 2
a step (C) for oxidizing the particles obtained in the step (A)
Data Source
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AI summary
The present invention provides composite particles consisting of a Si-C composite material capable of achieving a reduction in volume expansion of an electrode during charging in a lithium-ion rechargeable battery. The present invention includes composite particles including a carbon material and silicon, wherein a true density (He true density) by dry density measurement using helium gas is 1.30 g/cm3 or more and 2.00 g/cm3 or less, a true density (BA true density) by wet density measurement using 1-butanol is 1.00 g/cm3 or more and 1.64 g/cm3 or less, and the He true density is greater than the BA true density.