The exploration of a CuNb3O8 Li+-storage anode compound

Niobates are regarded as prospective Li+-storage anode candidates due to the rich chemistry of niobium and crystal-structural openness. However, the exploration of niobates is still insufficient. In this study, we explore CuNb3O8 with a large theoretical capacity is 341.9 mAh g(-1) as a high-performance anode compound. The reversible redox reaction among Nb5+, Nb4+ and Nb3+ during lithiation/delithiation is confirmed by ex-situ XPS, and a large reversible capacity of 231.8 mAh g(-1) and safe lithiation potential of 1.53 V are achieved at 0.1 C. An intercalation-type Li+-storage mechanism is confirmed by in-situ XRD after the first lithiation process, guaranteeing the good cyclability from the second discharge-charge cycles. The Li+ diffusivity in CuNb3O8 is systematically and carefully studied. The galvanostatic intermittent titration technique tests show large Li+ diffusion coefficients of 1.2 x 10(-12)/1.5 x 10(-12) cm(2) s(-1) during lithiation/delithiation, and the corresponding values obtained through the cyclic voltammetry technique are similar (2.2 x 10(-12)/3.0 x 10(-12) cm(2) s(-1)). Additionally, CuNb3O8 is successfully coupled with LiFePO4, and the resultant CuNb3O8//LiFePO4 full cell also exhibits good electrochemical properties, demonstrating the practicability of CuNb3O8 for large-scale energy-storage applications.