Synthesis of Fe3O4 nanocubes anchored in MgCo2O4 nanoneedle arrays for flexible all-solid-state asymmetric supercapacitor

The design of novel heterostructure with multifunctional characteristics is of great technical significance for the development of new energy storage devices. However, the lower conductivity of metal oxides and the accumulation caused by irreversible phase transition after multiple cycles are the main reasons for the low specific capacitance and cycle life. Herein, we synthesized bimetallic oxide MgCo2O4 nanoneedles with a spinel structure, and firmly anchored Fe3O4 nanocubes on MgCo2O4 nanoneedles by ion-exchange strategy. Thanks to the constructed heterostructure of nanoneedles/nanocubes, the introduction of Fe3O4 effectively improves the electron transport path in MgCo2O4 during repeated charging and discharging, and increases the effective activation sites involved in electron transfer. As a result, a higher specific capacitance of 1648 F g−1 at 1 A g−1 and an ultra-long cycle life of 78.6% capacitance retention after 6000 continuous charge/discharge cycles are obtained. A flexible all-solid-state asymmetric supercapcitor assembled with MgCo2O4-Fe3O4 as positive electrode and AC as negative electrode can deliver an ultra-high energy density of 78 Wh kg−1 and maximum power density of 1.2 kW kg−1, as well as extraordinary capacitive retention of 75.2% after 10,000 cycles. These excellent properties reveal the potential and application value of MgCo2O4-Fe3O4 in the development of high-performance supercapacitors.