New spinel high-entropy oxides (FeCoNiCrMnXLi)3O4 (X = Cu, Mg, Zn) as the anode material for lithium-ion batteries

High-entropy oxides (HEOs) with numerous functional features such as high structure stability and superionic conductivity are considered as promising candidates of electrode materials for lithium-ion batteries (LIBs). In this study, a series of single-phase spinel-structured high-entropy oxides (FeCoNiCrMnXLi)3O4 (X = Cu, Mg, Zn) consisted of seven metal elements at equal molar ratio were synthesized by solid phase method. In-situ high-temperature XRD technique was used to investigate the structure evolution of (FeCoNiCrMnZnLi)3O4 and a single-phase HEO was acquired at 900 °C. As the anode of LIBs, all the HEOs (FeCoNiCrMnXLi)3O4 display excellent cyclic stability and rate capability owe to the expedite three-dimensional Li+ transport pathways of spinel structure, the entropy-dominated phase stabilization effect together with the abundant oxygen vacancies introduced by the incorporation of Li+. In comparison, the (FeCoNiCrMnZnLi)3O4 anode containing electrochemical active Zn with tetrahedral coordination structure shows better electrochemical lithium storage performances among the three samples. The ex-situ XRD of (FeCoNiCrMnZnLi)3O4 during the discharge/charge procedure shows an amorphous state structure after the first lithiation process and it retained for the de-lithiation process. This work provides a new strategy to design high-entropy energy-storage material and pave the way for understanding the storage mechanism of HEOs.