Reverse coprecipitation synthesis of rock-salt-type high-entropy oxide (MgCoNiCuZn)O for high-performance asymmetric supercapacitors

Abstract

High-entropy oxides with disordered multi-cation rock-salt lattices have emerged as promising electrode candidates for supercapacitors (SCs); however, the facile synthesis of homogeneous single-phase (MgCoNiCuZn)O and a systematic investigation of its charge-storage mechanism remain insufficiently explored. Herein, we report a simple, low-cost, and scalable reverse coprecipitation strategy using sulfate metal precursors and pure Na2CO3 as the precipitant to synthesize rock-salt-type HEO, which avoids the high-energy ball-milling or prolonged high-temperature annealing typically required by conventional solid-state HEO synthesis. To the best of our knowledge, this is one of the first attempts to employ rock-salt-type (MgCoNiCuZn)O as a positive electrode material for aqueous asymmetric supercapacitors (ASCs). The effects of precipitant dosage and calcination temperature on particle size, phase purity, and elemental uniformity are systematically investigated. Electrochemical characterizations reveal that the optimized (MgCoNiCuZn)O electrode delivers a high specific capacitance of 660 F g−1 at 1 A g−1, with enhanced interfacial charge-transfer kinetics and the contribution of oxygen-defect-related active sites. When assembled into an ASC, the device operates within a wide 0–1.5 V voltage window, achieving a specific capacitance of 253 F g−1 at 1 A g−1. The ASC exhibits an energy density of 79 Wh kg−1 at a power density of 749 W kg−1, along with a peak power density of 7500 W kg−1. This work provides a low-cost, scalable reverse coprecipitation pathway for fabricating high-performance rock-salt HEO electrodes and demonstrates the great application potential of the five-component (MgCoNiCuZn)O in advanced SC devices.