Preparation And Capacitive Performance Of Mixed Transition Metal Oxide With Multi-shelled Hollow Sphere Structure

Mixed transition metal oxides have attracted tremendous interest for their excellentredox activity and large natural abundance.They could achieve distinct electrochemical properties by engineering special hollow structures.In this paper,multi-shelled Ni₆MnO₈ hollow spheres and multi-shelled nickel-cobalt-manganese oxide hollow spheres were successfully prepared by template method.The morphology,structure and electrochemical properties of the samples were also studied.The main contents are as follows:1. Triple-shelled Ni₆MnO₈ hollow spheres with nanosheet shells（Ni₆MnO₈-NS）were successfully synthesized through step by step adsorption of the corresponding metal ions on carbon spheres followed by calcination in air.And triple-shelled Ni₆MnO₈hollow spheres with nanoparticle shells（Ni₆MnO₈-NP）were also prepared through one-step adsorption of the corresponding metal ions on carbon spheres.The as-prepared Ni₆MnO₈-NS hollow microspheres have a high surface area of 145.011 m² g^-1.And they demonstrate more outstanding capacitive performance as electrode materials for supercapacitors,including high specific capacitance of 1380 F g^-1 at current density of 1 Ag^-1,distinguished rate capability with a retention rate of 68%at a current density of 100 Ag^-1 and stable cycle performance with a retention rate of 98%after 5000 cycles at 10 Ag^-1.Moreover,the assembled Ni₆MnO₈-NS//AC asymmetric supercapacitor exhibits a high energy density of 31.8 Wh kg^-1 at a power density of 750 W kg^-1 and the capacitance loss is only 7%at a current density of 10 Ag^-1after 10000 charge-discharge cycles.The distinguished performances can be attributed to the synergy of binary metals and the unique hollow structure.2. Based on carbon sphere template,double-shelled and quadruple-shelled nickel- cobalt-manganese oxide hollow nanospheres were successfully synthesized through direct adsorption of Ni²⁺,Co²⁺,Mn²⁺ternary transition metal ions on carbon spheres followed by calcination in air at different heating rates.The results show that quadruple-shelled nickel-cobalt-manganese oxide hollow nanospheres have better capacitive performance.The specific capacitance was 952 F g^-1at current density of 1 Ag^-1.When the current density is up to 40 Ag^-1,the specific capacitance still reaches 696 F g^-1,with capacitance retention rate of 73%.The capacitance retention is as high as 89%even after 3200 cycles at 10 Ag^-1 current density.In short,quadruple nickel-cobalt-manganese oxide hollow nanospheres have good rate performance and cycle performance.The reason is that multi-shelled hollow structures have larger specific surface area and pore volume,which can increase the contact area between electrode material and electrolyte and provide abundant active sites for Faraday reaction.In addition,hollow structures can shorten the diffusion/transport pathways of ions from exterior to interior and accelerate the reaction kinetics.It is beneficial to improve the capacitive performance of electrode materials.