Silicon–Germanium bilayer sputtered onto a carbon nanotube sheet as anode material for lithium–ion batteries

Abstract

In this work, multiwalled carbon nanotube-silicon/germanium (MWCNT-Si/Ge) electrodes were prepared by layer-by-layer deposition of Si and Ge films onto an MWCNT sheet using RF magnetron sputtering. The MWCNT-Si/Ge composites were characterized by spectroscopy and microscopy techniques, which confirmed the deposition of amorphous Si and Ge films. The as-prepared Si/Ge@MWCNT composites were tested as an anode material in a half cell using Li metal as counter and reference electrodes, and in a full cell using LiFePO4 as a cathode. MWCNT-Si/Ge showed a greater charge capacity retention (88% capacity retention) than MWCNT-Si (72% capacity retention) and Cu–Si/Ge (12% capacity retention) after 50 GCD cycles, confirming the important roles of the Ge layer and MWCNT substrate in the enhancement of the performance of Si-based anodes. The results confirmed that the lithium storage performance of the Si film was enhanced by the deposition of the Ge film on the surface. Si/Ge@MWCNT composites exhibited stable electrochemical performance during the first 50 cycles at 500 mA/g, with a reversible specific capacity greater than 1580 mAh/g. The MWCNT-Si/Ge composite anode exhibited a specific charge capacity of 1975 mAh/g at a current density of 200 mA/g, 1725 mAh/g at 500 mA/g, 1635 mAh/g at 1000 mA/g, 1580 mAh/g at 2000 mA/g, and 1472 mAh/g at 3000 mA/g. The MWCNT-Si//LiFePO4 full cell displayed satisfactory cycling performance.