Preparation And Energy Storage Properties Of Three-dimensional Porous Self-supported Transition Metal Sulfides

Transition metal sulfides show a potential application in electrochemical energy storage battery fields due to their high specific capacity,easy preparation,low cost and friendly environment.However,transition metal sulfides suffer large volumetric changes during repeated electrochemical cycling,leading to poor cyclability and high-rate capacities,which seriously hinders their large-scale apllication.It is found that the electrochemical performance of electrode materials can be improved through designing and building unique morphology.In this thesis,three-dimensional?3D?porous self-supported transition metal sulfides?MoS₂ and Ni₃S₂?are constructed.This structure can enhance Li/Na ions transport,and buffer their volumetric changes during charging/discharging as well.The electrochemical test result indicates they have high specific capacities,long cycle life and large high-rate capacities.The main research work contents the following aspects:?1?Electrochemical construction of 3D porous self-supported MoS₂ and its lithium/sodium storage.3D porous self-supported MoS₂ electrodes are constructed by electrodepositing coupled with high temperature heat treatment using 3D porous Cu prepared via electroless plating as the substrate,and directly used as anode of lithium/sodium ion battery.In the case of lithium storage,the influence of current density of electrodeposition and heat treatment temperatures on the lithium storage performance of MoS₂ electrode were investigated.The electrochemical test result shows that the 3D porous self-supported MoS₂electrode were constructed by electrodepositing at 6.2 mA cm^-22 coupled with heat treated at350?has the best electrochemical performance.It demonstrates a high first reversible capacity of 1296.3 mAh g^-1at 200 mA g^-1with a high first coulombic efficiency of 87%,and a good capacity retention of 1228.7 mAh g^-11 after 400 cycles at 200 mA g^-1.The reversible capacity at 3.2 A g^-1shows high value of 868.9 mAh g^-1,which is 61%of that at 0.05 A g^-1.In the case of sodium storage,the influence of heat treatment temperatures on the sodium storage performance of MoS₂ electrode were also investigated.The electrochemical test result shows that the 3D porous self-supported MoS₂ electrode heat treated at 350?has the best electrochemical performance.It demonstrates a high first reversible capacity of 714.1 mAh g^-1at 50 mA g^-11 with a high first coulombic efficiency of 84%,and a good capacity retention of306.8 mAh g^-1after 100 cycles at 2 A g^-1.The reversible capacity at 3.2 A g^-1shows high value of 286.2 mAh g^-1,which is 37%of that at 0.05 A g^-1.The outstanding electrochemical performance of 3D porous self-supported MoS₂ electrode can be also attributed to its unique micro-nanostructure.The 3D porous structure can accommodate the volumetric expansion/shrinkage and alleviate the stress caused from the large volumetric changes of MoS₂ electrodes during electrochemical cycling.Meanwhile,large surface area of this unique also can provide fast Li/Na ion transportation path.?2?3D porous self-supported Ni₃S₂ and its sodium storage.3D porous self-supported Ni₃S₂ electrodes are constructed by one-pot hydrothermal route using 3D porous Ni foam prepared via electroless plating as the substrate and Ni source,and directly used as anode of sodium ion battery.The cyclic performance of 3D porous self-supported Ni₃S₂ electrodes obtained from the reaction solution with different concentrations were studied.When the reactant concentration is medium concentration?0.0025M?,3D porous self-supported Ni₃S₂electrode exhibits the best cycle life.It remains a high reversible capacity of 307.4 mAh g^-1after 120 cycles at 100 mA g^-1.The improved electrochemical performance of 3D porous self-supported Ni₃S₂ electrode can be also attributed to its unique morphology.High specific surface area increases the contact area between the electrolyte and active material to ensure efficient electrolyte penetration.Meanwile,3D porous structure can effectively accommodate the volumetric changes and retard active material pulverization during electrochemical cycling.