Ti2Nb2O9/graphene hybrid anode with superior rate capability for high-energy-density sodium-ion capacitors

Abstract

Ti2Nb2O9/reduced graphene oxide (Ti2Nb2O9/RGO) hybrid anode is fabricated by flocculation of HTiNbO5 nanosheets and graphene oxide (GO) nanosheets, followed by annealing HTiNbO5/GO composite at 500 °C in Ar for 1 h, in which HTiNbO5 nanosheets are prepared by ion-exchange and followed by exfoliating process using KTiNbO5 as precursor. HTiNbO5 nanosheets are topotactically transformed into Ti2Nb2O9 nanosheets and GO is reduced into RGO by calcining the HTiNbO5/GO composite, causing enhanced Na+-intercalation pseudocapacitive behavior and significantly improved conductivity for Ti2Nb2O9/RGO hybrid anode. Ti2Nb2O9/RGO hybrid anode delivers superior rate capability (206 mAh g−1 at 4 A g−1) and excellent cycling performance with 95% capacity retention at 1 A g−1 over 1000 cycles. A hybrid device is assembled using Ti2Nb2O9/RGO as the anode and activated carbon (AC) as the cathode, it shows a maximum high energy density of 96 Wh kg−1 at a power density of 75 W kg−1, and the energy density still maintains 39 Wh kg−1 when the power density achieves as high as 10029 W kg−1. Moreover, the assembled device displays good cycling stability with a capacity retention of 79% after 10,000 cycles. This work can provide new insights on fabrication of Ti-Nb oxides-graphene based composite anode for sodium ion capacitors.