Reversible Multi-Electron Transfer of Cr2.8+/Cr4.4+ in O3-Type Layered Na0.66Fe1/3Cr1/3Ti1/3O2 for Sodium-Ion Batteries

Abstract

Na-deficient O3-type Na0.66Fe1/3Cr1/3Ti1/3O2 material is synthesized by a simple solid-state reaction and its electrochemical property as a cathode material for sodium ion battery is evaluated for the first time. It delivers an initial large discharge capacity of 135.5 mA h g(-1) in the voltage range of 1.5-4.1 V at 0.1C with a smooth discharge voltage profile. X-ray absorption technique indicates that the redox processes occur entirely at the chromium sites during the Na ion intercalation and deintercalation, while Ti4+ and Fe3+ remain as stabilizing spectators in layered Na0.66Fe1/3Cr1/3Ti1/3O2. Our results have demonstrated the new pathway to realize multi-electron transfer of Cr2+similar to 3+/Cr4.4+ redox in layered compounds. (C) The Author(s) 2018. Published by ECS.