Synthesis And Electrochemical Li-storage Performance Of Core-shell Structured G-C₃N₄/C@S And Porous MnO/g-C₃N₄/C Spheres

As electrode materials for lithium-ion batteries,sulfur and manganese monoxide have theoretical capacities of 1675 and 755 mAh/g,respectively.Furthermore,they are abundant and environmental friendly.However,they both have poor electrical conductivity,drastic volumetric variation during discharge/charge cycling,and“shuttle effect”of soluble polysulfides in sulfur cathode leading to poor cyclic performance.To address these issues,in this thesis,core-shell structured g-C₃N₄/C@S cathode and porous MnO/g-C₃N₄/C spherical anode have been prepared by aerosol-pyrolysis route.and many kinds of structures and electrochemical analysis methods were used in this paper.The microstructure,pore structure and electrochemical Li-storage properties of the two electrode materials have been investigated through combined microstructural and electrochemical methods,and the main conclusions are as follows:?1?During aerosol-pyrolysis synthesis,sodium chloride precipitates at the center of the composite spheres,while manganese compounds precipitate in the shell of the composite sphere.After pickling with hydrochloric acid,g-C₃N₄/C porous hollow spheres are obtained,which have high sulfur loading.?2?At 0.2C current density,the first discharge capacity of core-shell structured g-C₃N₄/C@S is 1517 mAh/g,which reaches 90%of the theoretical capacity?1675mAh/g?of sulfur.When the current density increases to 2.5C,the reversible capacity remains 794.6 mAh/g.The reversible capacity of 636 mAh/g is maintained after 400 charge/discharge cycles at 1C,correspondingly,an average capacity fading rate of 0.09%per cycle has been achieved.?3?The porous MnO/g-C₃N₄/C composite spheres with 8.6 wt.%carbon and g-C₃N₄ have the largest pore volume and specific surface area,and the electrochemical Li-storage performance is the best.At 0.5C current density,the discharge/charge capacities can maintain 607.7/600.2 mAh/g after 150 cycles,and the reversible capacity retention is 99%.Even at 5C?3.775 A/g?current density,the reversible capacity remains 400 mAh/g,which is ca.53%of the theoretical capacity of MnO.?4?The capacity of MnO/C₃N₄/C-0.4 consists of diffusion-controlled battery-type capacity and pseudocapacitance.At a CV scanning rate of 2 mV/s,the proportion of pseudocapacitance is ca.33%.