Niobium oxyphosphate nanosheet assembled two-dimensional anode material for enhanced lithium storage

Abstract The development of high-capacity and high-rate anodes has become an attractive endeavor for achieving high energy and power densities in lithium-ion batteries (LIBs). Herein, a new-type anode material of reduced graphene oxide (rGO) supported niobium oxyphosphate (NbOPO4) nanosheet assembled two-dimensional composite material (NbOPO4/rGO) is firstly fabricated and presented as a promising high-performance LIB anode material. In-depth electrochemical analyses and in/ex situ characterizations reveal that the intercalation-conversion reaction takes place during the first discharge process, followed by the reversible redox process between amorphous NbPO4 and Nb which contributes to the reversible capacity in the subsequent cycles. Meanwhile, the lithiation-generated Li3PO4, behaving as a good lithium ion conductor, facilitates ion transport. The rGO support further regulates the structural and electron/ion transfer properties of NbOPO4/rGO composite compared to neat NbOPO4, resulting in greatly enhanced electrochemical performances. As a result, NbOPO4/rGO as a new-type LIB anode material achieves a high capacity of 502.5 mAh g−1 after 800 cycles and outstanding rate capability of 308.4 mAh g−1 at 8 A g−1. This work paves the way for the deep understanding and exploration of phosphate-based high-efficiency anode materials for LIBs.