Ge-doped Li4Ti5-xGexO12 (x=0.05) as a fast-charging, long-life bi-functional anode material for lithium- and sodium-ion batteries

We explored the doping effect of Ge4+ on the Li4Ti5-xGexO12 (x = 0.0 and 0.05) anode material by looking at its electrochemical performance in both Li- and Na-ion batteries. Combined analysis using Rietveld refinement of high-resolution powder diffraction (HRPD) and transmission electron microscopy (TEM) unambiguously identified homogeneous Ge doping into the 16c octahedral Ti site of the Li4Ti5O12 (LTO) cubic spinel structure. This Ge doping leads to a much-reduced particle size, slightly expanded lattice and increased electrical conductivity due to the increased Ti3+ to Ti4+ ratio, these results were verified by HRPD, scanning electron microscopy (SEM), 4-point probe and x-ray photoelectron spectroscopy (XPS) analysis. The Li4Ti4.95Ge0.05O12 (Ge0.05-LTO) electrode shows much-improved capacity, high-rate capability and excellent cycling stability in a Li-half cell compared with an un-doped LTO electrode. This performance improvement is due to the reduced Li+ diffusion path and faster Li+ insertion/extraction kinetics that originate from Ge doping. In addition to these results, when tested as an anode for SIBs, the Ge0.05-LTO electrode exhibits enhanced capacity and cycling stability compared to un-doped LTO electrode, demonstrating its bi-functional, advantageous features in both LIB and SIB systems.