Rational design of high reversible capacity in Li-rich disordered rocksalt cathodes

Abstract

The Li-excess rocksalt materials have opened a vast new chemical space to develop low-cost and high-energy-density cathode materials for satisfying the rising market demand of rechargeable batteries. However, those materials suffer from capacity and voltage decay on cycling due to irreversible structural rearrangement. Quantitatively characterizing reversible capacity are decisive to collaboratively improve capacity and cycling stability, but very challenging to predict for experiencing complicated redox. A “state-accumulated charge-transfer gap” model is introduced to continuously accumulate electrochemical reversibility effect during the whole redox process. This is demonstrated through rational design and preparation of several representative compositions in the cation-disordered Li-Mn-Ti-O-F chemical space. Based on electrochemical tests and first-principles studies, we found that Li1.2Mn0.6Ti0.2O1.67F0.33 with almost complete Mn4+ oxidation states and a little anionic redox in the end of charge could achieve high capacity of 330 mAh g−1 in first cycle and 225 mAh g−1 after 20 cycles, which reaches the best comprehensive electrochemical performance in reported Li-rich materials. The present study opens a new avenue to design Li-rich cathode materials with high reversible capacity.