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 materials (NbOPO4/rGO) is firstly fabricated and presented as a promising high-performance LIB anode material. In-depth electrochemical analyses and in-situ/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 high-output capacity in the subsequent cycles. Meanwhile, the lithiation-generated Li3PO4, behaving as a good lithium ion conductor, facilitates fast 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 capacity 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.