Monoclinic vanadium diphosphide as a high-performance lithium-ion battery anode

Vanadium diphosphide (VP2) and its graphite-modified composite (VP2@G) were fabricated using a fast and simple solid-state manner, and evaluated as Li-ion battery (LIB) anodes. The electrochemical Li-mechanism of VP2 was investigated using various ex situ tools. During Li-insertion, VP2 underwent a topotactic-reaction by the formation of LixVP2 (x <= 1.5), and then was converted to Li3P and V phases with a partially unconverted LixVP2 phase at the Li-inserted state of 0 V via a partial conversion reaction. Conversely, during Li-extraction, Li3P, V, and unconverted LixVP2 phases recombined fully into VP2. First, when VP2 was used the topotactic-reaction between LixVP2 and VP2 (potential region: 0.3-2.0 V), stable cycling performance with a high volumetric-capacity (595 mAh cm(-3) after 100 cycles) and fast rate performance (similar to 555 mAh cm(-3) at 2 C and similar to 530 mAh cm(-3) at 3 C) were attained. Additionally, the graphite-modified composite VP2@G (potential region: 0-2.0 V) also exhibited stable cycling performance with a high gravimetric-capacity (602 mAh g(-1) after 100 cycles) and fast rate performance (similar to 530 mAh g(-1) at 1 C and similar to 470 mAh g(-1) at 2 C), which was attributed to the well-dispersed nanocrystalline (similar to 10-20 nm) VP2 in the Li-buffering graphite matrix. Therefore, the VP2 and VP2@G have high potential as a superior LIB anode. (C) 2021 Elsevier B.V. All rights reserved.