Design Of Binary Transition Metal Composites And Study On Supercapacitor Performance

The rapid growth of electronic devices requires that energy storage devices demonstrate high charging and discharging rates to ensure high specific energy output.Supercapacitors（SCs）have higher specific power than batteries as well as much excellent specific energy than traditional capacitors.Moreover,compared with other types of energy storage devices,SCs have prominent specific power,higher charging and discharging rates,superior cycle life,wider application range,and lower environmental impact;however,the comparatively low specific energy of SCs,limit their application.Electrodes are key components determining the performance of SCs.Therefore,it is imperative to design electrode materials with superior electrochemical activity and high specific capacitance.The electrode materials,mainly carbon,transition metal oxygen/sulphide,etc.,have easily adjustable morphology and high energy density,but during the charging and discharging process,these materials have many drawbacks,such as rapid energy density decay and poor stability due to morphology collapse,electron/ion diffusion difficulties and volume expansion.Therefore,this thesis further explores the structure of the binary transition metal compound electrode material is reasonably optimised and designed in order to enhance its electrochemical performance,as described below:1.Three-dimensional flower-like polypyrrole-wrapped Zn Co₂S₄（Zn Co₂S₄@PPy）core-shell nanoclusters were successfully prepared by a combination of two-step hydrothermal and electrochemical deposition methods.The Zn Co₂S₄@PPy composite has an excellent specific capacitance of 1486 F·g^-1 at 1 A·g^-1,which suggested its potential use as a supercapacitor electrode material.Furthermore,the asymmetric supercapacitor containing a Zn Co₂S₄@PPy positive electrode demonstrated a high specific energy of 33.78 Wh·kg^-1 at800.05 W·kg^-1 and relatively long cycle life（5000 cycles-90%）.The excellent electrochemical performance of Zn Co₂S₄@PPy can be attributed to the synergistic effect of its main components and unique flower-like core-shell structure.The results reveal that the Zn Co₂S₄@PPy core-shell nanocluster array composites have important potential as electrodes for future energy-storage devices.2.The Ni-Mn LDH was grown on activated carbon nanofibers（ACNFs）and then phosphidated to obtain an electrode material with a three-dimensional core-shell structure（ACNFs@Ni-Mn-P）.This composite combines the electrochemical activity of the two-dimensional phosphidated nanosheets with the structural stability of the one-dimensional nanofibers.The resulting ACNFs@Ni-Mn-P electrode exhibits a high specific capacitance of 1077 F·g^-1 at 1 A·g^-1,which is 4.9 times higher than that of a non-phosphidated ACNFs@Ni-Mn LDH electrode,88.53%stability even after 5000 cycles at a high current density of 10 A·g^-1.Moreover,an asymmetrical supercapacitor featuring an ACNFs@Ni-Mn-P positive electrode achieves comparatively prominent specific energy of 56.25 Wh·kg^-1 at 806.13 W·kg^-1,respectively.Therefore,ACNFs@Ni-Mn-P as electrode material has great potential for application in supercapacitors.3.The Mn_xCo_yO₄@MoS₂ composites were obtained by coating flake MoS₂ arrays on the spherical Mn_xCo_yO₄ by hydrothermal and heat treatment methods.At x/y=1:2,the Mn_xCo_yO₄@MoS₂ electrode material has a high specific capacitance of 1422 F·g^-1 at 1 A·g^-1,which is higher than that at x/y=1:1 and 2:1.When assembled into an aqueous asymmetric supercapacitor,it was able to provide a specific capacitance of 131 F·g^-1 at 1 A·g^-1;the good cycle life of the electrode material is further illustrated by the fact that after 5000 cycles there is still 85%capacity retention.;the device existed at a power density of 794 W·kg^-1 with46.58 Wh·kg^-1.The design of this electrode material can therefore provide new ideas for the development of future electrodes.