Design And Electrochemical Performance Of Cu₂MoS₄-based Negative Electrode Materials

Supercapacitors have become one of important energy storage devices because of their fast charging and discharging rates,wide operating temperature range,and long cycle life.In order to improve energy density of supercapacitors,a lot of researches have been carried out on electrode,which is the core of energy conversion.However,the development of positive and negative electrode materials is not balanced,and there are few reports on high-performance negative electrode materials,so it is an important issue to explore new supercapacitor negative materials.Among them,bimetallic sulfide Cu₂Mo S₄（CMS）,which contains both P and I phase structures correspond to theP（?）2m and I（?）2m space groups.Its rich redox properties with various oxidation states of copper and molybdenum and tunable interlayer structure,it has great potential as a high-performance negative electrode material.In this thesis,new negative electrodes based on Cu₂Mo S₄ were prepared through phase composition design,morphology control and composite structure construction,respectively.And the application prospects of Cu₂Mo S₄ based supercapacitors in the energy storage field were also explored.（1）To investigate the effect of phase composition on the electrochemical performance of Cu₂Mo S₄,CMS-2,4,8,24 samples with corresponding phase composition of P,P+I,I+P,and I were synthesized using solvothermal method as supercapacitor negative electrode materials.P-CMS formed at the beginning,then gradually disappeared as reaction time progressed and transformed into I-CMS nanosheets under high temperature and pressure.The CMS-4 samples with dual-phase coexistence（P+I）exhibited better electrochemical performance compared to single P and I phases,which was attributed to the synergistic effect of the high electron transport efficiency of P phase and the high structural stability of I phase.The CMS-4@carbon cloth（CC）electrode yield the highest specific capacity of 33.9 m Ah g^-1 at a current density of 1 A g^-1,which is 12.6 and 4.0 times higher than that of the pure P and I phase,respectively.The kinetic analysis study indicated that Cu₂Mo S₄ is a battery-type material.The assembled Mn O₂@CC//CMS-4@CC hybrid supercapacitor exhibited a voltage window of 1.6 V and an energy density of 16.8 Wh kg^-1 at 800 W kg^-1power density.（2）In order to further improve the electrochemical performance of Cu₂Mo S₄,hollow tubular CMS was prepared by hydrothermal method,and different amounts of multi-walled carbon nanotubes（MWCNTs）were added to synthesize CMS/MWCNTs0.05,0.15,0.25 composite materials.The incorporation of MWCNTs could form a three-dimensional conductive network,which not only provided high-speed channels for electron transport,but also facilitated material transport due to the porous structure.The CMS/MWCNTs-0.15@CC electrode showed the best electrochemical performance,with a specific capacitance of 219 F g^-1 at 0.5 A g^-1,which was 2.45 times that of CMS@CC.The kinetic analysis showed that the smaller charge transfer resistance and ion diffusion impedance as well as the utilization of larger active area contributed to the best electrochemical performance of CMS/MWCNTs-0.15@CC.An asymmetric supercapacitor assembled with Ni-Co-S@CC positive electrode and CMS/MWCNTs-0.15@CC negative electrode exhibited an energy density of 24.5 Wh kg^-1 at a power density of 900 W kg^-1.