Study On The Preparation And Electrochemical Properties Of Carbon-Based Bimetallic Oxide Composites

Transition metal compounds（TMC）have suprior electrochemistry performance due to redox reactions.Though various TMC have been intensively investigated so far,there are still problems such as structural collapse,partial irreversible redox reactions,and the poor conductivity,which restrict the energy storage performance of the materials.To address these thorny problems,an effective approach is to build more rational composite materials,such as combining TMC with conductive substrates.Among various substrate materials,carbon materials attract attention for their highly contactable surface and stable structure.Combining them with metal oxides can effectively enhance the overall electrical conductivity,accelerate electron transfer,improve the overall structural stability,and enhance cycling performance of electrode materials.Although notable progress has been made based on these theories,the previous preparation process is too tedious and the morphology is somewhat damaged after multiple calcinations,which undoubtedly affect the electrochemical performance partly.Based on the above considerations,the main research of this theses are as follows.（1）Preparation and energy storage of nitrogen-doped carbon capsule（N-Cc）@NiO/NiCo₂O₄composite electrode.The N-Cc_x@NiO/NiCo₂O₄composites were prepared in situ by one-step calcination.The structural characteristics of the composite were analyzed by SEM and BET,and the overall stability was increased by the firm bonding of N-Cc with NiO/NiCo₂O₄.Secondly,density flooding theory（DFT）calculations were performed to further verify that the addition of NiO increased the Fermi energy level of NiCo₂O₄and enhanced the electrical conductivity of the material.Finally,the electrochemical analysis shows that the specific capacitance（C_s）reaches 648.8 F g^-1at a current density of 1 A g^-1,and the energy density of the asymmetric supercapacitor device（ASC）assembled with AC as the negative electrode can easily reach 101.4 Wh kg^-1,showing a great prospect of application.（2）Preparation of N-Cc@NiPS₃-x composite electrode and energy storage study.The N-Cc@NiPS₃-x composites were obtained in situ by chemical vapor deposition（CVD）technique using a self-made N-Cc as the conductive substrate.The hollow N-Cc with large specific surface area provides more active sites and shorter transit paths for ion transport,and the CVD treatment enables thicker and rougher surfaces to be obtained,increasing the stability while giving more attachment sites.Electrochemical tests showed that high C_sof 1180 F g^-1was exhibited at a current density of 1 A g^-1.In addition,the present work was carried out to demonstrate that carbon-based NiPS₃electrode materials have a large potential for SCs applications.（3）Preparation and energy storage study of N-Cc@Ni₃S₂-x composites.The Ni₃S₂flakes were grown on the surface of N-Cc by one-step hydrothermal method.A reasonable ratio of Ni₃S₂to N-Cc was found by regulating the amount of Ni₃S₂production.Based on the enhanced overall structural stability and the reasonable ratio providing more active sites with a larger specific surface area,N-Cc@Ni₃S₂-1.0finally exhibited a high specific capacitance of 1502 F g^-1.In addition,the constructed ASC devices showed good cycle stability during five thousand charge/discharge cycles.