Niobium-Doped Titanosilicate Sitinakite Anode with Low Working Potential and High Rate for Sodium-Ion Batteries

Titanosilicate sitinakite compound with an ideal formula of Na(1.68)H(0.32)Ti(2)O(3)SiO(4)1.76H(2)O (NTSO) has been employed as a low intercalation potential anode for rechargable sodium ion batteries (SIBs), which exhibit low intercalation potential, low cost, and environmental friendliness. However, the NTSO suffers from shortcomings such as low electronic conductivity, which restricts its electrochemical performances. In this work, cation Nb-doped NTSO compounds have been synthesized and investigated systematically. The powder X-ray diffraction coupling with Rietveld refinement has been used to prove that the Nb has been successfully doped into the crystalline framework of NTSO. The electrochemical performances of Nb-doped NTSO (Na1.68H0.32(Ti1-xNbx)(2)O3SiO4.76H(2)O, 0 <= x <= 0.2) has been evaluated in SIBs. Compared to performances of pristine material, those of 10% Nb-doped samples exhibits enhanced electrochemical performances, which shows a stable capcaity of 124 mA h g(-1) at a current density of 0.05 A g(-1) and 55 mA h g(-1) under a current density of 2.0 A g(-1). First-principles calculations proved the formation of impurity bands and decrease of conductivity effective mass after Nb doped into the crystalline framework of NTSO with improvement in the electronic conductivity. These findings indicate that the cation doping is an effective way to modify the electrochemical performances of NTSO as an anode in SIBs.