Insights into the sodium storage mechanism of Bi 2 Te 3 nanosheets as superior anodes for sodium-ion batteries.

Although bismuth-based anode materials for sodium-ion batteries (SIBs) have attracted wide attention, their large volume variation hinders their actual applications, especially in Bi 2 Te 3 systems. In this study, Bi 2 Te 3 nanosheets (BT-Ns) are fabricated by a novel strategy via a solvent reductive reaction. The elements Bi and Te are spontaneously grown into ultrathin nanosheets because the hexagonal crystal of Bi 2 Te 3 has a strong tendency to grow horizontally. The crystal structure of the BT-Ns is well developed and the thickness is about 1.42 nm, which can not only offer more active sites but also promote electrical conductivity and the diffusion of Na ions and electrons. It exhibits excellent rate and long-term cyclic performance, delivering 364.0 mA h g -1 at 5 A g -1 after 1200 cycles. The high rate and long-term cyclic performance of the Bi 2 Te 3 anodes is attributed to the facile design of the 2D nanosheet structure, presenting an effective strategy to construct anodes for SIBs. The sodium storage mechanism of Bi 2 Te 3 follows a three-step crystallographic phase change of Bi 2 Te 3 , discovered by an in situ X-ray diffraction analysis. The applicability of BT-N anodes in full cells via pairing with Na 3 V 2 (PO 4 ) 3 cathodes delivers excellent performance (energy density of 107.2 W h kg -1 ) and satisfactory practical applied prospects.