A 4 V Na+ Intercalation Material in a New Na‐Ion Cathode Family. Issue 5 (6th October 2017) - Kim, Se Young
Abstract: Large‐scale electrochemical energy storage is a critical factor in the development of renewable energy sources to enable their intermittent power to become dispatchable. In this context, Na‐ion batteries are seen as promising alternatives to Li‐ion batteries, but their advancement requires the discovery of new materials, their electrochemical properties, and a better understanding of structure–property relationships that underpin the electrochemistry. This study presents a new class of Na + insertion materials for Na‐ion batteries. By virtue of its moderately inductive polyanionic framework, the air and moisture stable selenite Na2 Co2 (SeO3 )3 displays a highly suitable redox potential of ≈ 4 V versus Na/Na + based on the Co 2+ /Co 3+ couple, rendering it compatible with conventional liquid organic electrolytes. A microwave hydrothermal synthesis route is developed for the rapid synthesis of nanostructured Na2 Co2 (SeO3 )3 and its conductive graphene oxide composite. The electrochemistry and structural evolution of Na2 Co2 (SeO3 )3 determined on cycling the cathode in a Na battery was investigated by operando X‐ray diffraction, X‐ray photoelectron spectroscopy, and temperature dependent magnetic susceptibility measurements. These studies reveal good structural and electrochemical reversibility. Abstract : A transition metal selenite ‐ Na2 Co2 (SeO3 )3 ‐ is introduced as a new class of 4 V Na‐ion positive electrode materials. The moderately inductive polyanionic framework of SeO3 2− ensures a suitable potential for the Co 2+/ Co 3+ redox couple. A graphene oxide composite delivers a reversible capacity of ≈75 mA h g −1, while reversible structural transformation is observed during the charge/discharge process.