Studies On The Preparation Of Graphene-like Hollow Spheres And Their Electrochemical Properties

As a mainstream electrochemical energy storage system today,lithium-ion battery has a series of advantages such as high specific capacity,stable cycling performance,long service life,and easy portability.With the emphasis of society on green development,the development and utilization of clean energy is particularly important,especially for power batteries used in automobiles,which require higher energy density and cycling performance.Therefore,researching new electrode materials with simple preparation methods and good electrochemical performance is the main research direction at present.In this thesis,graphene-like hollow spheres were prepared by the high-voltage transient discharge method,and their electrochemical properties as anode materials for lithium-ion batteries and cathode materials for lithium-sulfur batteries were investigated.The Si O₂ solid spheres were prepared by the conventional St?ber method,and the Si O₂spheres were coated with dopamine hydrochloride as the carbon source according to its ability to self-polymerize under alkaline environment.15 nm in diameter,with a wall thickness of 15nm,and a specific surface area of 810 m²/g.The graphene-like hollow spheres were finally prepared.The best morphology of graphene-like hollow spheres（PDA 1-200-2）was also found to be prepared under the condition of two electric shocks at 1 capacitor and 200 V.Through electrochemical tests,it was found that the starting specific capacity of PDA 1-200-2 material was 574 m Ah/g at 1 A/g current density,and after continuous activation,the specific capacity increased continuously and stabilized at 731 m Ah/g after 800 cycles,which showed good cycling stability.m Ah/g,146 m Ah/g.The graphene-like hollow carbon spheres with a diameter of 220 nm,a wall thickness of19 nm,a specific surface area of 670 m²/g and good dispersion were prepared by transient discharge under hydrothermal conditions with the in situ coating of Si O₂ by the carbon source and the removal of the template.The best morphology of the material was obtained（RF 1-200-2）.The electrochemical tests showed that the specific capacity of RF 1-200-2 material was stable at 942 m Ah/g after 600 cycles at 1A/g current density,and the Coulomb efficiency was close to 100%,showing excellent cycling stability and high specific capacity.Using the above-prepared graphene-like hollow spheres as sulfur carriers,the effects of sulfur loading method and sulfur loading amount on the structure and electrochemical performance of the composite sulfur cathode material with graphene-like hollow spheres were investigated.It was found that the maximum specific surface area of the composite material was 24.7 m²/g and the actual sulfur content was 63.4%when the sulfur to carbon ratio was adjusted to S/C=7:3 by the melt sulfur infiltration method,and the sulfur in the material was uniformly distributed inside the graphene-like hollow spheres.The electrochemical tests show that the material has a high specific capacity of 1039 m Ah/g and 701 m Ah/g in the first cycle of charging and discharging at 0.2 C and 1 C multipliers,respectively,and the capacity retention rate is 60.8%and 59.2%after 200 cycles,respectively.It indicates that the prepared graphene-like hollow spheres can also exhibit good cycling performance when used as the cathode material for lithium-sulfur batteries.