Morphology-controlled Synthesis Of Nickel-cobalt Sulfide And MXene/manganese Dioxide Composites And Research On Supercapacitors

Supercapacitors,i.e.,electrochemical capacitors,are widely used alone because of their high power density,long cycle life and wide working temperature range in energy storage systems,or in combination with rechargeable batteries to improve the overall performance of energy storage systems,i.e.,the combination of batteries and supercapacitors makes it possible to charge and discharge large energy quickly.As a new device,supercapacitor still has a lot of room for development,mainly in the improvement of energy density.There are two improvement directions of influencing factors,namely the specific capacitance of electrode material and the working voltage of the device.This work focuses on the morphology design of electrode materials and its influence on specific capacitance,mainly including the following two aspects.1.NiCo₂S₄ electrode material with hollow sea urchin-like morphology was synthesized by two-step hydrothermal method and intermediate annealing treatment,and its electrochemical properties as supercapacitor electrode material were tested.The results show that:Due to Ostwald Ripening mechanism,the precursor undergoes a process of change from rod,needle,straw bundle,broccoli,sea urchin to hollow sea urchin for the sustaintially releasing effect of urea resulted in a continuous increasing p H.By the Kirkendall effect,when the inner ions diffuse outward faster while the outer ions cannot fill in in time,a hole is created in the center of the nanorod that makes up the sea urchin ball.Thus,compared with s-NiCo₂S₄ that directly vulcanized by the precursor,there are some improvements for h-NiCo₂S₄ with a hierarchical structure:(i)the crystallinity of h-NiCo2S4 is higher than that of s-NiCo₂S₄;(ii)BET specific surface area of h-NiCo2S4 is higher than that of s-NiCo₂S₄;(iii)the conductivity of h-NiCo₂S₄is higher than that of s-NiCo₂S₄;(iv)h-NiCo₂S₄ has a higher mass specific capacitance than s-NiCo₂S₄.At a current density of 1 A g^-1,h-NiCo₂S₄//AC asymmetric supercapacitor exhibits a specific capacitance of 41.08 F g^-1,an energy density of 12.84Wh kg^-1,and a power density of 732.97 W kg^-1,which shows good performance compared with reported literatures.2.MXene and?-MnO₂with layered structure were synthesized respectively and simply physically mixed to obtain the composite material,and its electrochemical properties were tested as supercapacitor electrode material.The results show that:The two materials have a synergistic effect on improving the specific capacitance,from a63.60 F g^-1 of single MXene material and a 44.73 F g^-1of single?-MnO₂material to a121.23 F g^-1of MXene@?-MnO₂,showing the rationality of this design.