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

Co-free high-Ni layered cathode materials LiNiMeO (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 Ni 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 LiNiMnMgTaMoNaO (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/Ni 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 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.