Kinetic Rejuvenation of Li-Rich Li-Ion Battery Cathodes upon Oxygen Redox

Minimizing internal structural rearrangements upon oxygen redox is currently considered the chief guideline for designing high-performance Li-rich cathodes for Li-ion batteries. In contrast, our study of Li-rich layered- and disordered-rocksalt cathodes reveals that while global oxygen mobility promoted upon O-redox can be damaging, disruption of a local structural order [e.g., medium-range-order (MRO)] triggered by O-redox and associated volume expansion are highly beneficial as they reduce the Li-transport resistance in the materials, that is, the Li-rich cathodes become “rejuvenated” by this process. Furthermore, we use this knowledge to inform a molten-salt treatment to predisturb the MRO, expand crystal volume before cycling, and endow a surface gradient composition for highly Li-rich Co-free layered cathodes, such that the treated materials can achieve high capacity (>230 mA h/g) from the very first cycle with excellent rate capability (154 mA h/g at 2 A/g) and outstanding capacity/voltage-retention (∼4% capacity-loss, ∼140 mV voltage-loss after 200 cycles at 100 mA/g; >210 mA h/g). From these results, we explain the mechanism and universality of the rejuvenation process in various charge-ordered oxides and propose guidelines for designing advanced Li-rich cathode materials with combined transition-metal- and oxygen-redox activities.