Sn-Doping in a Sb2Se3 Conversion-cum-Alloying Material Renders Efficient Sodium-Ion Electrochemical Performance: Facile Kinetics Achieved by Active Metal Doping

Abstract

Conversion-cum-alloying anode materials have particularly been sought after as promising high-capacity Na+ anode materials owing to a double redox alkali-ion uptake offered by them. The addition of electrochemically nonactive conducting additives to enhance the sluggish kinetics of the conversion/deconversion step although instrumental in enhancing the kinetics ends up in a considerable decline in electrochemical capacity. Herein, we demonstrate an alternative strategy of doping an ultra-active Sn element in the well-known conversion-cum-alloying Na+ battery anode, Sb2Se3. The Sn-doped Sb2Se3 phase, Sn0.2Sb1.8Se3, besides depicting an enhanced capacity (reversible capacity of 520 mA h g–1) and cyclic stability, delivered an excellently improved rate performance (360 mA h g–1 at a current of 500 mA g–1) in comparison to pristine Sb2Se3 which delivers a capacity of 45 mA h g–1 at the same current density. Electrochemical techniques such as cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) lend support to improved kinetics of the conversion/deconversion process. The enhanced kinetics reflects in larger anodic peak currents (147 mA g–1 for Sn0.2Sb1.8Se3 against 32 mA g–1 for Sb2Se3) in CV plots and reduced charge-transfer resistance (RCT of 350 Ω for Sn0.2Sb1.8Se3 against 670 Ω for Sb2Se3) in EIS measurements. The electrochemical galvanostatic intermittent titration technique reveals a 3-order-magnitude increase in the diffusion coefficients (2.02 × 10–14–6.6 × 10–11 cm2 s–1) in the Sn0.2Sb1.8Se3 in comparison to pristine Sb2Se3 (2.5 × 10–17–4.2 × 10–14 cm2 s–1).