Self-Improving Anode for Lithium-Ion Batteries Based on Amorphous to Cubic Phase Transition in TiO₂ Nanotubes

We report an electrochemically driven transformation of amorphous TiO2 nanotubes for Li-ion battery anodes into a face-centered-cubic crystalline phase that self-improves as the cycling proceeds. The intercalation/deintercalation processes of Li ions in the electrochemically grown TiO2 nanotubes were studied by synchrotron X-ray diffraction and absorption spectroscopies along with advanced computational methods. These techniques confirm spontaneous development of a long-range order in amorphous TiO2 in the presence of high concentration of Li ions (>75%). The adopted cubic structure shows long-term reversibility, enhanced power with capacity approaching the stochiometry of Li2Ti2O4. The anode shows also superior stability over 600 cycles and exhibits high specific energy (~200 W h kgelectrode–1) delivered at a specific power of ~30 kW kgelectrode–1. The TiO2 anode in a full Li-ion cell with a LiNi0.5Mn1.5O4 cathode operates at 2.8 V and demonstrates the highest (~310 mA h/g) reversible specific capacity reported to date. Our conceptually new approach fosters the ability of amorphous nanoscale electrodes to maximize their capacity in operando , opening a new avenue for synthesis of safe and durable high-power/high-capacity batteries.