Zn Makes a Difference: Cubic ZnBi₃₈O₆₀ as a Durable and High-Rate Anode for Rechargeable Na-Ion Batteries

A stoichiometric cubic phase of zinc bismuth oxide ZnBi₃₈O₆₀ (ZBO) is introduced as an anode for rechargeable Na-ion batteries. ZBO is synthesized using a coprecipitation method and characterized by various physicochemical techniques. Pristine ZBO shows a high cyclability in an ether-based electrolyte due to the formation of a robust interphase coupled with high Na⁺ conductivity. Fast charge-transfer kinetics and high chemical compatibility between the electrolyte and electrode result in a high reversible stable capacity of ∼300 mA h/g at 100 mA/g and ∼180 mA h/g at 1000 mA/g for the as-synthesized ZBO. Using in situ diffraction (XRD) experiments, both conversion and alloying reactions are found to be responsible for the observed good performance. A robust, multilayered SEI composed of an inner bismuth-rich inorganic layer and an outer polyether layer with high ionic conductivity is observed using X-ray photoelectron spectroscopy analysis. The battery characteristics are found to be superior to the individual binary oxides, Bi₂O₃ and ZnO, thus bringing out the advantages of the addition of zinc and the ternary system studied. Preliminary full cell studies with the ZBO anode and Na₃V₂(PO₄)₃ cathode show good performance with high energy density and stability. The present investigations reveal a great potential for the anode, ZBO, comprising earth-abundant elements, and will likely lead to an alternate anode material for rechargeable batteries.