Suppressed Degradation in Semiconducting Lithium-Rich Oxide Cathode Materials via Phase Structure Engineering

Owing to anionic oxygen redox (O redox), cathode materials containing lithium-rich oxides (LROs) exhibit a large discharge capacity exceeding 300 mAh·g^-1, in addition to a decent midpoint voltage (∼3.5 V). This makes them viable choices for the fabrication of cathode materials for future development of 500 Wh·kg^-1 lithium-ion batteries (LIBs). However, O redox is irreversible. This results in fast degradation of their voltage/capacity during cycling, in addition to a low initial Coulombic efficiency. In this work, we address the problem of degradation during cycling by phase structure engineering (PSE) of Li-rich C2/m and R3̅m through modification of the transition metal (TM) composition. Apart from NCM111, we intentionally incorporate NCM262, NCM523, NCM622, Ni_0.75Co_0.25, and NCM811 with the Li-rich Li₂MnO₃ phase domain, so that a series of composite-phase LRO nanocrystals (N20, N50, N60, N75, and N80, respectively) are fabricated, which exhibit an increased midpoint voltage (∼3.8 V) with improved cycling stability. For N75, the voltage fade is suppressed, with retention of 88.07% in voltage and a loss of 1.12 mV per cycle, which results in an increased retention of energy density (63.68%) after 400 cycles at 1C (RT, 2.0-4.8 V). This work provides routes to achieve lithium-rich oxides with high energy density and long lifespan.