Enhanced Li-Ion Diffusion and Cycling Stability of Ni-Free High-Entropy Spinel Oxide Anodes with High-Concentration Oxygen Vacancies.

High-entropy oxide (HEO) is an emerging type of anode material for lithium-ion batteries with excellent properties, where high-concentration oxygen vacancies can effectively enhance the diffusion coefficient of lithium ions. In this study, Ni-free spinel-type HEOs ((FeCoCrMnZn) 3 O 4 and (FeCoCrMnMg) 3 O 4 ) were prepared via ball milling, and the effects of zinc and magnesium on the concentration of oxygen vacancy (O V ), lithium-ion diffusion coefficient ( D Li + ), and electrochemical performance of HEOs were investigated. Ab initio calculations show that the addition of zinc narrows down the band gap and thus improves the electrical conductivity. X-ray photoelectron spectroscopy (XPS) results show that (FeCoCrMnZn) 3 O 4 (42.7%) and (FeCoCrMnMg) 3 O 4 (42.5%) have high O V concentration. During charge/discharge, the O V concentration of (FeCoCrMnZn) 3 O 4 is higher than that of (FeCoCrMnMg) 3 O 4 . The galvanostatic intermittent titration technique (GITT) results show that the D Li + value of (FeCoCrMnZn) 3 O 4 is higher than that of (FeCoCrMnMg) 3 O 4 during charge and discharge. All of that can improve its specific discharge capacity and enhance its cycle stability. (FeCoCrMnZn) 3 O 4 achieved a discharge capacity of 828.6 mAh g -1 at 2.0 A g -1 after 2000 cycles. This work provides a deep understanding of the structure and performance of HEO.