Controllable Preparation Of Carbon Nanosheet-based Composites And Their Supercapacitance Performance

As a new energy device,supercapacitors have the advantages of fast charging and discharging,high energy density and excellent cycling stability.Electrode materials play a key role in the electrochemical performance of supercapacitors.In this paper,a series of carbon nanosheet-based composites,including PC-Cs/Mn O₂,PC-Cs/CNTs,PC-Cs/PANI,PC-Cs/CNTs/PANI and PC-Cs/Mn O₂/Ni Co₂O₄,can be prepared by using potassium citrate-derived carbon sheets（PC-Cs）as the substrate,and the electrochemical performance of the composites are optimized by regulating the loading of metal oxides,PANI and micro struture,as follows:（1）PC-Cs/MnO₂ composites with sandwich structure were prepared by using PC-Cs as the reducing agent and sacrificial template.The optimal ratio of PC-Cs/Mn O₂-1/15（denoted as Cs/Mn-1/15）composites was obtained when PC-Cs/KMn O₄ ratio was 1/15,which exhibited the best electrochemical performance.The specific capacitance of the composite is 397 F/g at 1 A/g,and the capacity retention is 93.1%after 5000 cycles.The asymmetric supercapacitor assembled with PC-Cs/Mn O₂ composite as the positive electrode and PC-Cs as the negative electrode has a specific capacitance of 81.5 F/g at 0.5 A/g.When the power density is 143.8 W/kg,the energy density is 21.9 Wh/kg.（2）PC-Cs/CNTs composites were prepared by thermocatalytic growth of CNTs on PC-Cs substrate,and PANI was then grown by in-situ polymerization to prepare PC-Cs/PANI and PC-Cs/CNTs/PANI composites,respectively.Compared with PC-Cs/PANI composites,PC-Cs/CNTs/PANI composites have superior electrochemical performance.The maximum specific capacitance is 767 F/g at 1 A/g,and the capacitance retention is 87.5%after 5000 cycles.The asymmetric supercapacitors were assembled with PC-Cs/CNTs/PANI and PC-Cs/CNTs composites as positive and negative electrodes,respectively,it has a specific capacitance of 102.5F/g at 0.5 A/g.The specific capacitance is 70.1 F/g at 5 A/g.The maximum energy density is 56.9Wh/kg at a power density of 537 W/kg.（3）PC-Cs/MnO₂/NiCo₂O₄ was prepared by using the optimized PC-Cs/Mn O₂ as substrate,by loading with Ni Co₂O₄ nano-needles through hydrothermal reaction and followed by high temperature annealing treatment,and the optimized PC-Cs/Mn O₂/Ni Co₂O₄-0.1（Cs/Mn/Ni-0.1）composite had the best electrochemical performance when the template dosage of PC-Cs/Mn O₂was 0.1 g.The specific capacitance is 1254 F/g at 1 A/g,much higher than that of the PC-Cs/Mn O₂composite（397 F/g）and pure Ni Co₂O₄（430 F/g）.At a current density of 5 A/g,the specific capacitance retention rate is 81.9%after 5000 long-cycles tests.The asymmetric supercapacitor assembled with Cs/Mn/Ni-0.1 as the positive electrode and PC-Cs/CNTs as the negative electrode has a specific capacitance of 161 F/g at 0.5 A/g.The specific capacity is 101 F/g at a current density of 5 A/g.The energy density is 22.2 Wh/kg at a power density of 727.9 W/kg.This thesis has 42 figures,9 tables and 127 references.