Self-improving anode for lithium-ion batteries based on amorphous to cubic phase transition in TiO ₂ nanotubes

We report an electrochemically driven transformation of amorphous TiO ₂ 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 TiO ₂ 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 TiO ₂ 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 Li ₂Ti ₂O ₄. The anode shows also superior stability over 600 cycles and exhibits high specific energy (∼200 W h kg _electrode ^-1) delivered at a specific power of ∼30 kW kg _electrode ^-1. The TiO ₂ anode in a full Li-ion cell with a LiNi _0.5Mn _1.5O ₄ 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.