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

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(NbOPO) nanosheet assembled twodimensional composite material(NbOPO/rGO) is firstly fabricated and presented as a promising highperformance 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 NbPOand Nb which contributes to the reversible capacity in the subsequent cycles.Meanwhile,the lithiation-generated Li3 PO,behaving as a good lithium ion conductor,facilitates ion transport.The rGO support further regulates the structural and electron/ion transfer properties of NbOPO/rGO composite compared to neat NbOPO, resulting in greatly enhanced electrochemical performances.As a result,NbOPO/rGO as a new-type LIB anode material achieves a high capacity of 502.5 mAh gafter 800 cycles and outstanding rate capability of 308.4 mAh gat 8 A g.This work paves the way for the deep understanding and exploration of phosphate-ba sed high-efficiency anode materials for LIBs.