Full Exploitation of Charge Compensation of O3‐type Cathode Toward High Energy Sodium‐Ion Batteries by High Entropy Strategy

Abstract O3‐type cathodes with sufficient Na content are considered as promising candidates for sodium‐ion batteries (SIBs). However, these cathodes suffer from insufficient utilization of the active elements, restraining the delivered capacity. In this work, a high entropy strategy is applied to a typical O3 cathode NaLi 0.1 Ni 0.35 Mn 0.55 O 2 (NLNM), forming a high entropy oxide NaLi 0.1 Ni 0.15 Cu 0.1 Mg 0.1 Ti 0.2 Mn 0.35 O 2 (Na‐HE). Results show that the active elements are fully exploited in Na‐HE, with a two‐electron reaction by Ni 2+/4+ (further extended to Cu redox and even oxygen redox), vastly different from a one‐electron reaction of Ni 2+/3+ in NLNM. The full utilization of the active elements dramatically improves the output capacity of the cathode (122.6 mAh g −1 of Na‐HE versus 81 mAh g −1 of NLNM). Moreover, the detrimental phase transition is well suppressed in Na‐HE. The cathode exhibits high capacity retention of 88.7% after 100 cycles at 130 mA g −1 , compared to only 36.4% for NLNM. These findings provide new insight for the design of new cathode materials for SIBs with high energy density and robust stability.