Research On The Preparation And Properties Of Nanosulfide/C Composites

As a new type energy storage device,supercapacitors combine the advantages of traditional capacitors and rechargeable batteries.Because of their high power density and long cycle life,and can meet the energy demand under specific occasions,so they have become a research hotspot of electrochemical energy storage devices.The electrochemical performances of supercapacitors are closely related to the electrode materials.Among them,transition metal sulfides have become popular materials in current research due to their high specific capacity and strong electrochemical activity.In particular,the bimetallic sulfides exhibit stronger redox activity due to the synergistic effect of the variable valence states between the bimetallic ions,and thus possess a higher specific capacitance and cycle stability.This dissertation focuses on the preparation method of the NiCo₂S₄/C composite electrode material and the influence of process parameters on the morphology and electrochemical performance of the material,in order to optimize the electrochemical performance of the material.The main research contents are as follows:1.Research on one-step hydrothermal method to prepare nano-NiCo₂S₄/C composites and their performances.Within the hydrothermal solvent system of water and glycol,the effects of different polyvinylpyrrolidone(PVP-K30)additions on the morphology and electrochemical performance of NiCo₂S₄ materials were studied.At the same time,the influences of different types of carbon materials on the electrochemical performance of the NiCo₂S₄/C composites were studied.The experimental results show that the addition of PVP can change the specific surface area of the NiCo₂S₄ material.When adding 0.1 g PVP,the obtained NiCo₂S₄ has the largest specific surface area(13.502 m²/g).When compounded with 0.12 g(14.2 wt%)high conductivity carbon nanotubes,the NiCo₂S₄/C composite electrode material has a high specific capacity(2055.04 F/g@0.2 A/g),good rate performance(the discharge capacity at 10 A/g is 79.2%of that at 0.2 A/g)and excellent stable cycle performance(the capacity retention rate of10000 cycles is 86.9%@20 A/g).2.Study on electrochemical deposition method to prepare NiCo₂S₄/C composite materials and their performance.The NiCo₂S₄/C composite materials were deposited by constant voltage method,and the effects of the initial deposition potential and deposition time on the micromorphologies and electrochemical performances of the materials were studied.The experimental results show that when the deposition potential is-0.9 V and the deposition time is 10 min,the prepared NiCo₂S₄/C composite has the highest specific capacity(2498.12 F/g@1 A/g),excellent rate performance(the discharge capacity at100 A/g is 61.1%of that at 1 A/g)and cycle stability(the capacity retention rate of 10000cycles is 98.53%@20 A/g).3.Assembly and performance testing of flexible supercapacitor devices.NiCo₂S₄/C composite electrode materials prepared by different methods,commercial activated carbon and polyvinyl alcohol/potassium hydroxide(PVA/KOH)gel electrolyte membrane are assembled into an asymmetric supercapacitor.The electrochemical and mechanical properties of the device were studied.The results show that the specific capacity of the device can reach 215.06 F/g@0.25 A/g,the highest energy density and power density can reach 76.47 Wh/kg and 201.01 W/kg,respectively,and the device can be cycled for 10,000 cycles at a current density of 5 A/g.Its capacity retention rate is89.03%,and it has good mechanical flexibility.