Synthesis methods effects on performance and aging of cobalt-free (CrMnFeNiAl)3O4 high-entropy oxide nanoparticles as lithium-ion battery anodes

High-entropy oxides (HEOs) are attracting increasing attention as promising anode materials for lithium-ion batteries, mainly because these compounds combine structural stability with relatively high ionic conductivity. In the present study, a cobalt-free High-entropy oxide anode, (CrMnFeNiAl)₃O₄, was synthesized by hydrothermal and mechanochemical routes. The effects of the synthesis method and aluminum content on the electrochemical behavior were systematically investigated. Structural and morphological features, including XRD, XPS, SEM, and TEM analyses, were employed to characterize the prepared materials. Among the hydrothermally synthesized samples, Al-H-N-0.5 showed the smallest particle size and delivered the highest reversible capacity of 850 mAh g⁻¹ at 0.5 A g⁻¹, whereas its mechanochemical counterpart, Al-M-N-0.5, exhibited 359 mAh·g⁻¹ under identical conditions. After 500 cycles, the capacities remained stable at 366 and 234 mAh g⁻¹, respectively. The aging behavior, analyzed by impedance spectroscopy, incremental capacity analysis, and post-mortem analysis, suggested that conductivity loss was the dominant degradation mechanism. In contrast, loss of active material was mainly observed at the beginning of cycling. These observations indicate that careful control of the synthesis route can significantly improve the long-term stability of cobalt-free HEO anodes.