Na _0.9 Ni _0.45 Ti _0.55 O ₂ as novel bipolar material for sodium ion batteries

Because of low cost, low toxicity and simple synthesis method, transition metal oxides have been regarding as promising candidate materials for sodium ion batteries (SIB). In this work, O3-type layered oxide of Na _0.9 Ni _0.45 Ti _0.55 O ₂ was synthesized and evaluated as a novel bipolar material for SIB. It is found that, as a cathode material, the initial discharge capacity can reach around 109.6 mAh g ⁻¹ at 0.05C. When severing as anode material, it displays a reversible capacity of 44.5 mAh g ⁻¹ . The bipolar character is attributed to two different redox active substances in Na _0.9 Ni _0.45 Ti _0.55 O ₂ with the high-voltage redox couple Ni ⁴⁺ /Ni ²⁺ and the low-voltage redox couple Ti ⁴⁺ /Ti ³⁺ . This study provides new insights into the design and synthesis of novel electrode materials for SIBs and some other applications.