Revealing the lithium-ion storage mechanism and structural evolution of spinel (FeNiCoMnCu)3O4 high entropy oxide anode

Spinel high-entropy oxides (HEOs) have been studied as lithium battery anodes by reason of good thermodynamic stability. However, abnormal capacity fluctuations tend to occur during long cycles, with the capacity decreasing and then increasing, and the mechanism involved is still unclear. In this research, a spinel (FeNiCoMnCu) 3 O 4 materials was prepared by low-temperature hydrothermal method to study its lithium storage mechanism and structural evolution during long cycle process. In situ XRD results show that the anode undergoes an irreversible phase change during the first cycle, and part of the spinel phase transforms into an amorphous phase and transforms into nanocrystals with different crystal orientations. The amorphous phase closely connects each nanocrystal, which is conducive to the migration of lithium-ion. According to the capacity change, the long cycle of the (FeNiCoMnCu) 3 O 4 electrode is divided into four stages: first decay, activation, stability and secondary decay. Electrochemical and structural analysis show that the instability of the solid electrolyte interface film (SEI) formed by the active particles and the electrolyte is closely related to the capacity change. This study provides insight into long cycle structural changes in spinel HEOs. • The spinel phase transforms into an amorphous phase and nanocrystals with different crystal plane orientations. • The cycling performance of spinel HEO is closely related to the stability of the solid electrolyte interface film.