Binary Si-Ge Alloys as High-Capacity Anodes for Li-Ion Batteries

Herein, Si-Ge binary alloy films are prepared by deposition on rough copper (Cu) foil and multiwalled carbon nanotube (MWCNT) sheets using radio frequency (RF) magnetron sputtering. The as-prepared SiGe@Cu and SiGe@MWCNT thin films are then characterized by spectroscopy and microscopy techniques. Scanning electron microscopy (SEM) shows that SiGe nanosheets are deposited on the Cu foil, whereas amorphous SiGe spherical nanoparticles are deposited on the MWCNT surface and incorporated inside its pores. Raman and X-ray diffraction (XRD) confirm an amorphous structure for the sputtered films. SiGe film thicknesses of 201, 386, and 582 nm are measured by topography after 0.5, 1, and 2 h RF sputtering, respectively. The electrochemical performance of SiGe@Cu and SiGe@CNT is assessed by cyclic voltammetry (CV) and galvanostatic charge-discharge (GCD) in half cells using Li metal as the counter and reference electrode and 1 m LiPF6 in organic carbonates electrolyte. SiGe@Cu exhibits a very stable cyclability during the first ten cycles. The specific charge capacity retention decreases from 97.7%, 94.5%, 88.7%, and 81.2% after 20, 30, 40, and 50 cycles, respectively. A higher specific capacity of SiGe@MWCNT is measured due to deeper lithiation/delithiation reactions. Thus, more investigations are needed to improve the performance of SiGe during long cycling.