Structural characterization and electrochemical behavior of the medium-entropy spinel oxide (CrMnFeNi)3O4

A quaternary medium-entropy spinel oxide, (CrMnFeNi) 3 O 4 , was synthesized using a novel two-step metallurgical route comprising arc melting of an alloy precursor and oxidative annealing at 1000°C. Synchrotron X-ray diffraction and Rietveld refinement confirmed the formation of a single-phase spinel structure ( F d 3 ¯ m , a = 8.3694 Å). X-ray absorption near-edge structure (XANES) analysis revealed that Cr 3+ and Ni 2+ preferentially occupy octahedral sites, while Fe 3+ occupies tetrahedral sites, with manganese distributed across both sublattices to maintain charge neutrality. When evaluated as an anode material for lithium-ion batteries, cyclic voltammetry revealed a multi-step lithiation mechanism, while electrochemical impedance spectroscopy tracked the kinetic evolution and indicated dynamic surface restructuring that enhances active material utilization and facilitates ion transport. The material exhibits stable long-term cycling over 1000 cycles at moderate and high current densities. Post-mortem analysis confirmed the loss of long-range crystalline order of the active material, validating the conversion mechanism.