Influence of cut-off voltage on the lithium storage performance of Nb12W11O63 anode

The niobium tungsten oxide Nb12W11O63 is synthesized by a simple solid-state method and studied as an anode for lithium-ion batteries. By comparing with graphite anode, Nb12W11O63 with orthorhombic structure has higher safe working voltage (˃1.70 V) and tap density (∼2.57 g cm−3). The effect of cut-off voltage on the electrochemical property is also analyzed in detail. X-ray diffraction results reveal the mechanism of performance deterioration in Nb12W11O63 under deep discharge, which is caused by the collapse of crystal structure due to the transformation of pentagonal bipyramid to octahedron induced by excessive Nb3+. At the cut-off voltage of 1.3 V, Nb12W11O63 electrode delivers excellent electrochemical performances with high initial coulombic efficiency of 94.7%, improved cycling stability of 146 mAh g−1 after 404 cycles at 113 mA g−1 (78.8% of capacity retention) and good rate capacity of 100 mAh g−1 at 4520 mA g−1. These results indicate that Nb12W11O63 is a promising anode for lithium-ion batteries, and also provide the insight into the performance optimization of such materials.