Enhanced Li+ Diffusion and Lattice oxygen Stability by the High Entropy Effect in Disordered-Rocksalt Cathodes

Cation-disordered Rocksalt oxides (DRXs) are a promising new class of cathode materials for Li-ion batteries due to their natural abundance, low cost and great electrochemical performance. High entropy strategy in Mn-based DRXs appears to be an effective strategy for improving the rate capability, but it suffers from challenges including capacity degradation. The present paper reports a new group of high entropy DRXs (HE DRX) based on Ni2+-Nb5+ pair; the structural and chemical evolution upon cycling of DRXs with an increasing transition metal (TM) species are systematically investigated. An explanation is proposed for how the crystal field stability energy determines that HE DRX could exist in single Rocksalt solid solution structures. We further reveal that the charge compensation mechanism in HE DRX is the result of various TM synergistic effect. More importantly, through various in situ and ex situ techniques and theoretical calculation, the effective integration of more TM cation species within the HE DRX framework promotes better Li+ diffusion and improves lattice oxygen stability, consequently increasing capacity upon cycling.

Automated summary

This paper reports on a new class of high entropy disordered rocksalt oxides (HE DRXs) based on the Ni2+-Nb5+ pair, and investigates the structural and chemical evolution of DRXs with increasing transition metal species. The study proposes an explanation for the existence of HE DRX in single rocksalt solid solution structures based on the crystal field stability energy, and reveals the charge compensation mechanism in HE DRX as a result of various transition metal synergistic effects. The effective integration of more transition metal cation species within the HE DRX framework promotes better Li+ diffusion and improves lattice oxygen stability, leading to increased capacity upon cycling.