High-Entropy Doping Enables Ultrahigh-Ni Co-Free Layered Cathodes with Enhanced Thermal Stability

Layered Ni-rich cathode materials with high reversible energy densities are becoming prevalent. However, irreversible phase transitions and the associated severe strain propagation have long been reported as the major causes of their thermal decomposition during high-temperature cycling. Inspired by the entropy-stabilization effect and sluggish diffusion effect in conventional high-entropy alloys, here a compositionally complex (high-entropy) doping strategy was introduced to synthesize an ultrahigh-Ni Co-free layered cathode that has high thermal and cycling stability with negligible voltage decay. High-entropy doping simultaneously increases the energy barriers of Ni migrations and layer-spinel-rocksalt transitions by localizing charge density around Ni atoms, improving the covalency of the Ni–O bond, and optimizing local structure, resulting in suppressed surface reconstruction and postponed thermal decomposition. The design of high-entropy doping provides an innovative and variable pathway to resolve the thermal instability and safety concerns for ultrahigh-Ni Co-free layered cathode materials.