Surface nitrided and carbon coated TiNb2O7 anode material with excellent performance for lithium-ion batteries

Owing to the five-electron transfer mechanism, titanium niobium oxide (TiNb2O7) possesses high energy density and is considered to be a promising anode candidate for Li-ion batteries. However, its practical application is severely limited due to the poor electronic conductivity and the low Li+ diffusivity. Here, we report a novel surface nitrided and carbon coated TiNb2O7 (N-TiNb2O7@C) via a facile modification process using dicyandiamide (DCDA) as both carbon and nitrogen sources. After a calcination process, TiNb2O7 was coated by a thin carbon layer, while part of the Nb5+ on the particle surface was reduced to form NbN simultaneously. The obtained N-TiNb2O7@C delivered the reversible capacities of 165 mAh·g−1 and 135 mAh·g−1 at the rates of 20 C and 50 C, respectively. Good cyclability at 10 C was also measured where the capacity remained at 109.6 mAh·g−1 after 1000 cycles, featuring a capacity retention of 82.7%. The excellent performance of N-TiNb2O7@C can be attributed to the carbon coating, surface nitridation and Nb5+ reduction during the calcining process, which together improve the electronic conductivity and Li+ diffusivity. This study demonstrates a facile modification process to effectively improve the electrochemical performance of TiNb2O7 for Li-ion batteries.