Electrochemical characteristics of amorphous silicon carbide film as a lithium-ion battery anode

The electrochemical reactions of SiC film with Li⁺ have been investigated by electrochemical characterization and X-ray photoelectron spectroscopy. The SiC film is prepared by inductively-coupledplasma chemical-vapor-deposition (ICP-CVD) technique and displays an amorphous state due to the low processing temperature (∼350 °C). An irreversible reaction of SiC with Li+ occurs with the formation of lithium silicon carbide (Li_xSi_yC) and elemental Si, followed by a reversible alloying/dealloying reaction of the elemental Si with Li⁺. The 500 nm SiC film shows an initial reversible specific capacity of 917 mA h g^-1 with a capacity retention of 41.0% after 100 cycles at 0.3C charge/discharge current, and displays much better capacity retention than the Si film (5.2%). It is found that decreasing the SiC thickness effectively improves the specific capacity by enhancing the reaction kinetics but also degrades the capacity retention (for 250 nm SiC, its initial capacity is 1427 mA h g^-1 with a capacity retention of 25.7% after 100 cycles). The better capacity retention of the 500 nm SiC anode is mainly because residual SiC exists in the film due to its incomplete reaction caused by its lower reaction kinetics, and it has high hardness and can act as a buffer matrix to alleviate the anode volume change, thus improving the mechanical stability and capacity retention of the SiC anode.