02Ba03
Formation mechanism of Silicon Nanoparticles with Carbon coating inInduction Thermal Plasma with Controllable Temperature Distributions
Xiaoyu ZHANG, Byeongil MIN, Yiran WANG, Ririko HAYASHIDA, Manabu TANAKA,
Takayuki WATANABE
Kyushu Univ
1

Introduction

Silicon is a promising anode material for lithium
ion batteries due to high charge storage capacity of4200 mAh/g, which is approximately 10 times
higher than commercial graphite. However,crystalline silicon shows a 400% volume expansion
during lithiation and delithiation and leads toserious electrode failure mechanisms, which has
severely reduced its promise for applications.
Application of carbon coating on silicon
nanoparticles (SiNPs) is believed as a useful way toprevent electrode pulverization, and provides
continuous electronic conduction pathways during
cycling. A reliable and effective synthesis method
for such structure is proposed in this research on thebasis of induction thermal plasma. The formation ofcarbon coating is influenced significantly bytemperature distribution in reaction chamber as wellas SiNPs. Therefore, the plasma properties are
modified through the composition of plasma sheathgas, and the effect on products will be investigated.

24Conclusion

The value of T/R has a significant effect on thetemperature distribution as well as the products, andthe component of products is tunable in the current
work which is meaningful for practical applications.

References[1] X. Zhang et al., Powder Technology. 371 (2020)
26–36.

Experimental

The experimental setup mainly consists of torch,chamber and filter. Plasma is generated with a RF
power supply at 4MHz and 17.5 kW. The ratio oftangential and radial flow rates (T/R), which
compose plasma sheath gas, varies from 0.5 to 1 tounderstand the effect on plasma properties as wellas products. Silicon raw powders with a diameter of
5 μm are injected at 800 g/min with Ar carrier gas.
Methane is chosen as carbon source and injected
into chamber to form carbon coating, and the flowrate varies from 1.28 to 1.92 L/min. Particles werecharacterized by XRD, TEM and EDS mapping.

3CH4 molecules will be suppressed. Therefore, theformation of SiC is ignored with T/R value of 1.
Core-shell structure can be identified with EDS
mapping results as shown in Fig. 2. Carbon coating
is prepared successfully in this work with various
T/R values, while the shell thickness of T/R=1 ismuch thinner than the lower case. This further
proves the conclusions obtained with TEM images,
and reveal the temperature distribution can beaffected by sheath gas significantly.

Fig. 1 TEM images of particles at changed C/Si and T/R.

Results and Discussion

Morphology of particle with special conditions isshown in Fig. 1. Prepared SiNPs marked withbrown circles can be observed in all cases while
SiC marked with the hexagonal symbols can only
be obtained in the case of T/R=0.5. Taking into
account of the formation mechanism of SiC [1],possible reason is the effect of T/R values on theplasma temperatures. As the tangential gas flowrate is higher, the temperatures in the zones of CH4
injection will be lower and the decomposition ofFig. 2 EDS mapping results at C/Si ratio of 3: (a-c) show
the results at T/R=0.5; (d-f) are results with T/R=1.
Green and red mean silicon and carbon, respectively.