Controllable Preparation And Energy Storage Performance Of Transition Metal Compound Composit Materials For Supercapacitor Electrodes

Since the ever-increasing interest in electric vehicles and portable electronic devices in our daily life,it has been highly essential to develop new energy storage devices to meet the practical requirements.Supercapacitors,also known as electrochemical capacitors,have been conceived as one of the most promising candidates owing to their high power density,fast charge-discharge capability,long lifespan,high safety and environmental compatibility,which is thus well complementary to the lithium-ion batteries and fuel cells.However,many of battery-type materials inevitably suffer from the low intrinsic conductivity,less satisfactory capacity,poor rate capability and stability,which greatly restrict their wide applications in supercapacitors.Therefore,in this thesis,we present several facile synthetic routes to fabricate new electrode materials with desirable structure and components,which ensures the full utilization of materials and the favorable kinetics of ion diffusion and electron transport in the electrode,to improve the material deficiency.The main contents of the dissertation are shown as follows:?1?Three-dimensional interconnected networks of ultrathin mesoporous Ni-Mo oxide nanosheet arrays are fabricated directly on Nifoam via a two-step approach.The results showed that the optimized Ni-Mo oxide nanosheets directly grown on Nifoam can deliver a high specific capacity of 138.7 m Ah/g at a current density of 1 A/g,which is substantially higher than that of pure NiO nanosheets?22.3 m Ah/g at 1 A/g?.Moreover,the ternary Ni-Mo oxide nanosheets exhibit a good rate capability and remarkable long-term cycling stability?77.7%?over 5000 cycles.?2?Three-dimensional hierarchical NiCo₂O₄@NiMoO₄ core–shell nanowire/nanosheet arrays are fabricated directly on Nifoam via a two-step approach.The results showed that the optimized NiCo₂O₄@NiMoO₄ hybrid electrode delivers a much enhanced areal capacity of 805.6 ?Ah/cm2 at 10 mA/cm2 with excellent rate capability?83.6% retention for current density increased from 10 to 80 m A/cm2?and remarkable cycling stability?81.8% retention over 5000 cycles?.In addition,an asymmetric supercapacitor was assembled by using the optimized NiCo₂O₄@NiMoO₄ can achieve a maximum areal capacitance of 1.54 F/cm2 and a high energy density of 5.64 m Wh/cm3.?3?Three-dimensional hierarchical NiCo₂S₄@Ni?OH?₂ core-shell hybrid nanosheet arrays are fabricated directly on Nifoam via a multi-step approach.The results showed that the optimized NiCo₂S₄@Ni?OH?₂ hybrid electrode demonstrates a high areal capacity of 680 ?Ah/cm2?240.3 m Ah/g in specific capacity?at 5 m A/cm2,with excellent rate performance?94.9% with current density increased to100 m A/cm2?and cycling stability?81.4% over 2000 cycles?.Moreover,an aqueous hybrid supercapacitor device has been successfully assembled with the NiCo₂S₄@Ni?OH?₂,exhibits high energy density?53.3 Wh/kg?,high power density?6420 W/kg?,as well as excellent cycling stability?98.8% over 2000 cycles at 20 m A/cm2?.