High Entropy Fine-Tuning Achieves Fast Li+ Kinetics in High-Performance Co-Free High-Ni Layered Cathodes.

Co-free high-Ni layered cathode materials LiNixMeyO2 (Me = Mn, Mg, Al, etc.) are a key part of the next-generation high-energy lithium-ion batteries (LIBs) due to their high specific capacity and low cost. However, the hindered Li+ kinetics and the high reactivity of Ni4+ result in poor rate performance and unsatisfied cycling stability. This work designs a promising strategy for designing a high-performance high-entropy doping Co-free high-Ni layered cathode LiNi0.9Mn0.03Mg0.02Ta0.02Mo0.02Na0.01O2 (HE-Ni90-1.557) by elemental screening and compositional fine-tuning. Compositional fine-tuning optimizes the synergistic relationship between the high-entropy dopant elements, thereby significantly suppresses the kinetic hysteresis induced by Li+/Ni2+ mixing. The pillar effect significantly enhances the diffusion kinetics of Li+ at the high state of charge (SOC). Meanwhile, the high-entropy fine-tuning significantly postpones the H2-H3 phase transition and reduces the dissolution of transition metals and the loss of lattice oxygen in the cathodes. Consequently, the diffusion kinetics of Li+ at the atomic and electrode particle scales are significantly enhanced. The HE-Ni90-1.557 cathode exhibits an initial capacity of 225.1 mAh g-1 at 0.2 C and a full cell with a high capacity retention of 83.1% after 1500 cycles at 3C. This work provides a promising avenue for commercializing Co-free high-Ni cathodes for next-generation LIBs.