Inert salt-assisted solvent-free synthesis of high-entropy oxide towards high-performance lithium-ion batteries

High-entropy oxide (HEO) is a promising anode material for lithium-ion battery (LIB) due to the synergistic effect of various metal species. Conventional HEO preparations typically involve a solid-state route or liquid-phase mixing followed by high-temperature calcination, leading to either a small surface area or environmental contamination. Herein, a novel, facile solvent-free preparation of HEOs is introduced, applying inert salt, NaCl, as an easily removable, eco-friendly and recyclable template. This approach realizes high-purity porous HEO (NPHEO) with specific surface area (28.1 m2 g-1) for high-performance lithium-ion batteries. With the enhanced electrochemical kinetics, the NPHEO anodes deliver a high reversible specific capacities of 1143.6 at 0.2 A/g. In addition, the NPHEO-based cells exhibit a desirable rate capability of 315.7 mAh/g at 5 A/g. At 1 A/g the cell delivers a good cyclability of 71.8 % capacity retention over 600 cycles, corresponding to an average coulombic efficiency of above 99.94 % per cycle. Ex-situ X-ray diffraction and in-situ electrochemical impedance spectroscopy experiments further probe the structural evolution and electrochemical behavior during lithiation/ delithiation, confirming the structural stability and fast electrochemical kinetics of NPHEO. The proposed advanced synthesis approach offers a new platform for the preparation of HEOs with high quality.