Amorphous TiO₂ Nanotube anode for rechargeable sodium ion batteries

Sodium ion batteries are an attractive alternative to lithium ion batteries that alleviate problems with lithium availability and cost. Despite several studies of cathode materials for sodium ion batteries involving layered oxide materials, there are few low-voltage metal oxide anodes capable of operating sodium ion reversibly at room temperature. We have synthesized amorphous titanium dioxide nanotube (TiO₂NT) electrodes directly grown on current collectors without binders and additives to use as an anode for sodium ion batteries. We find that only amorphous large diameter nanotubes (>80 nm I.D.) can support electrochemical cycling with sodium ions. These electrodes maximize their capacity in operando and reach reversible capacity of 150 mAh/g in 15 cycles. We also demonstrate for the first time a full cell all-oxide Na ion battery using TiO₂NT anode coupled to a Na_1.0Li _0.2Ni_0.25Mn_0.75O_δ cathode at room temperature exhibiting good rate capability.