Preparation And Electrochemical Performance Of Transition Metal Sulfides-Based Electrode Materials For Hybrid Supercapacitors

Global energy transition and decarbonization pose greater demands on energy storage technologies.It is imperative to develop new energy storage devices that are safe,stable and efficient.Hybrid supercapacitors are one of the most promising electrochemical energy storage devices due to their high energy density compared to supercapacitors,high power density compared to batteries,as well as long cycling life,high safety and low cost.Unfortunately,the commercialization of hybrid supercapacitors is limited by their insufficient energy density.Featuring high theoretical specific capacity,high redox activity,diversified structures,and high electrical conductivity,transition metal sulfides as battery-type electrodes for hybrid supercapacitors can increase the energy density of devices effectively.However,the substantial volume effects and sluggish kinetics of transition metal sulfides in electrochemical reactions lead to poor cycling stability and rate performance.In this dissertation,the electrochemical properties of transition metal sulfides are improved through strategies such as optimizing composition,regulating structure,and constructing composites.The relationships between the composition,structure,morphology and electrochemical properties of materials have been investigated.In addition,the energy storage mechanism of electrodes has been studied.The electrochemical performance of hybrid supercapacitors assembled from transition metal sulfides-based positive electrodes and reduced graphene oxide-based negative electrodes is evaluated.The main contents of the study are as follows:(1)NiCo-MOF@PBA nanosheets grown on nickel foam were prepared by a two-step mild room-temperature reaction.Subsequently,sandwich-like Co-Ni3S2 nanosheet arrays were obtained by calcination and hydrothermal sulfuration.Sandwich-like structure endows the CoNi3S2 electrode with a higher specific surface area,more abundant ion diffusion channels,and better structural stability.In addition,Co doping improves the electrochemical activity and the binder-free in-situ growth process enhances the mechanical stability of the electrode.The ingenious designs enable the Co-Ni3S2 electrode to exhibit an excellent rate performance and a high specific capacity(1102 C g-1 at 1 A g-1).In the energy storage process,the capacity contribution of the diffusion-controlled is comparable to that of the surface-controlled process.The Co-Ni3S2//RGO hybrid supercapacitor offers excellent electrochemical performance,achieving a maximum energy density of 66.1 Wh kg-1,a high capacity retention rate of 100.1%after 10,000 cycles,and a coulombic efficiency up to 98.8%.(2)Hetero-structured NiS2/CoS2 nanoparticles embedded on carbon nanocage with ultrathin nanosheets composites were synthesized by room temperature co-precipitation,cation exchange etching,high-temperature carbonization,and annealing sulfuration.Electrochemical reactivity and charge transfer rates of the electrode are facilitated by multi-dimensional nanostructures and multi-level pore characteristics.The conductivity and structural stability are enhanced by three-dimensional N/S co-doped carbon nanocage substrates.Meanwhile,the hetero-structured NiS2/CoS2 nanoparticles enrich the redox reactions of the electrode.The NiS2/CoS2@C electrode demonstrates outstanding electrochemical performance,with a specific capacity as high as 1373 C g-1 at 1 A g-1,and capacity retention of more than 100%after 10,000 cycles.Electrochemical reactions of NiS2/CoS2@C electrode are dominated by diffusion-controlled.The NiS2/CoS2@C//RGO hybrid supercapacitor delivers an ultra-high energy density(63.3 Wh kg-1),power density(16 kW kg-1),and cycling stability(98%,13,000 cycles).In this paper,transition metal sulfides-based electrode materials with controllable morphology and structure were obtained by optimizing the preparation process,demonstrating the feasibility of transition metal sulfides as high-performance electrode materials,and providing an effective way for the development of high energy density hybrid supercapacitors.