Reversible Multi-Electron Transfer of Cr<sup>2.8+</sup>/Cr<sup>4.4+</sup>in O3-Type Layered Na<sub>0.66</sub>Fe<sub>1/3</sub>Cr<sub>1/3</sub>Ti<sub>1/3</sub>O<sub>2</sub>for Sodium-Ion Batteries
Journal of the Electrochemical Society