Construction Of Porous Spherical Transition Metal Compounds For Supercapacitor Performance

Transition metal sulfur and selenide are considered to be excellent energy storage materials due to their high electrical conductivity,low energy band,environmental friendliness,and tunable structure.The construction of electrode material structures with abundant active sites plays an important role in enhancing electrochemical performance.The rich internal cavity inside the structure can effectively alleviate the volume expansion caused by multiple redox reactions and improve the cycling stability.Therefore,in this thesis,porous spherical transition metal compounds were controllably synthesized from electrode materials and electrode structures by preferring substrate materials and template materials and optimizing reaction conditions.The supercapacitor performance of these materials was investigated,as follows:（1）Porous Mn-Co-S（MCSN）nanospheres were prepared by a simple hydrothermal method using negatively charged SiO₂ sol particles as a template and electrostatically adsorbed metal cations.The Mn S₂-Co S₂ nanosheets grown vertically on SiO₂ provided electron transport paths that facilitated rapid electron propagation.Furthermore,the construction of Mn S₂-Co S₂heterojunctions by density functional theory calculations demonstrated that the combination of both improved the activity of the electrode materials.The porous MCSN nanosphere electrode materials exhibited 1,158 F·g^-1 at 1 A·g^-1.An asymmetric supercapacitor device（ASC）was assembled with cathode activated carbon（AC）and anode MCSN.The MCSN//AC ASC exhibited capacitance retention of 90.4%after5,000 cycles at 10 A·g^-1 and an energy density of 34 Wh·kg^-1 at 775 W·kg^-1.（2）Porous yolk-shelled NiMnSe₃ nanospheres were prepared by the simple hydrothermal method and thermal treatment process under the presence of glycerol.Benefiting from the unique yolk-shelled structure and bimetallic synergy,NiMnSe₃ had abundant active sites and ion diffusion channels,which enhanced the charge transfer ability.Moreover,Ni Se₂-Mn Se heterojunctions were constructed,illustrating the synergy between Ni Se₂ and Mn Se components and the charge transfer paths at the heterogeneous interface by density functional theory calculations.NiMnSe₃ provided the high specific capacitance of1,093 F·g^-1 at 0.5 A·g^-1.The NiMnSe₃//AC ASC developed a maximum energy density of74.5 Wh·kg^-1 and a maximum power density of 8,259.3 W·kg^-1.Furthermore,99.5%capacitance retention was achieved after 12,000 cycles.（3）Porous multi-shelled MOF-derived N-doped N-CCS@NCS nanospheres were prepared with the CuCo-glycerol spheres synthesized under hydrothermal conditions as the substrate material.The number of shell layers,thickness,spacing,and shell densities was adjustable by the content of Ni.With the rich voids and open spaces in the porous multi-shelled structure,N-CCS@NCS had excellent energy storage capacity and cycling stability.N-CCS@NCS exhibited a high specific capacitance of 1,259 F·g^-1 at 0.5 A·g^-1.N-CCS@NCS//AC ASC had an energy density of 87.3 Wh·kg^-1 at 825 W·kg^-1 and a capacitance retention rate of 81.3%after 8,400 cycles.