Improving conductivity in Na2Ti3O7 for Na-Ion anodes through Ti reduction

Na2Ti3O7 is a promising anode material for use in sodium ion batteries, however it suffers from low total conductivity, which is critical for conversion anode performance. Here we employ a reduction strategy, removing oxygen from the crystal structure during synthesis, aiming to increase the total conductivity through reduction of Ti ions. Using impedance spectroscopy, we show that the room temperature conductivity can be increased from 9.7 × 10–8 S.cm−1 to 4.0 × 10–7 S.cm−1 in the reduced NTO. Using cyclic voltammetry, we show that the reduced material shows a modest increase in specific capacity and rate capability, which we attribute to improved sodium ion mobility due to wider Na-ion channels, and decreased activation energy (170 meV in the reduced sample vs 250 meV at room temperature). This demonstrates that using reduction during synthesis is a viable method to simultaneously improve multiple key electrochemical properties in Na2Ti3O7.