Tuning the electrochemical kinetics of bismuth-based conversion-alloying anodes with anion modulation for sodium-ion storage

Sodium-ion batteries (SIBs) have great application potential in large-scale energy storage devices due to their abundant sodium resources and economic effectiveness, whereas the unavailability of graphite and silicon makes it urgent to develop high-performance anode materials to promote the commercialization of SIBs. In this work, a series of bismuth-based conversion-alloying anode materials are comprehensively studied to decouple the electrochemical kinetics essence through modulating the anions. It's confirmed that bismuth telluride reveals the lowest band gap (E_g), moderate Na-ion adsorption energy (E_a) and Na-ion diffusion barrier (E_b), thereby contributing the optimal electron and Na-ion transfer kinetics behavior. Therefore, Bi₂Te₃ anode delivers superior rate capability with high specific capacity of 108.4 mAh·g⁻¹ at 5000 mh·g⁻¹ and ultra-long lifespan over 4000 cycles with low-capacity fading rate of 0.015 % per cycle. High angle annular dark field scanning transmission electron microscopy results visually illustrate from the atomic scale that Na-ion insertion and extraction is carried out through conversion-alloying dual-mechanism, in which Bi-ion is responsible for charge compensation verified by X-ray absorption spectroscopy. The assembled Na-ion full batteries demonstrate the practicality of Bi₂Te₃ anode, exhibiting high energy density of 230.4 Wh·kg⁻¹, great rate property and excellent cycling stability with long lifetime over 600 cycles.