Preparation Of Graphene Composite Materials And Its Application In Supercapacitors

As a new type of energy storage device,supercapacitor with advantages such as high rate of charge/discharge,high power density,long cyclic life,and good operational safety,has attracted tremendous attentions recently.The most used electrode materials for supercapacitors include carbon materials,metal oxides/hydroxides,and conductive polymers.Carbon materials have high power density and superior cyclic stability,due to rapid ion absorption and desorption.However,this kind of rapid process only occurs at the interface of the materials,the bulk of materials cannot be used,resulting low active material utilization,so the capacitance is very limited(usually below 200 F g^-1).On the other hand,metal oxides/hydroxides and conductive polymers usually exhibit higher capacitance than carbon materials,due to redox reactions,but it also limits their charge and discharge efficiency at high rates.Therefore,composite materials such as carbon-metal oxide/hydroxide or carbon-conductive polymer have become the research hotspot,in order to obtain high-performance electrode materials with both high energy density and power density.This thesis mainly includes the following three parts:（1）A graphene/nickel-cobalt hydroxide ternary hydrogel（G-Ni-Co）with superior electrochemical performances was prepared by a simple hydrothermal method using Ni（NO₃）₂?6H₂O,Co（NO₃）₂?6H₂O,and graphene oxide as the starting materials.The mass fraction and the p H value of the reaction system were optimized.The prepared G-Ni-Co was assembled into a symmetric supercapacitor and its electrochemical performance was estimated.In a symmetric supercapacitor,the specific capacitance of G-Ni-Co is 551.3 F g^-1 at the scan rate of 10 m V s^-1 and 646.1 F g^-1 at the current density of 0.5 A g^-1,respectively.The specific capacitance still retains 70.8%after 5000 cycles at the scan rate of 100 m V s^-1.The energy density reaches 108.6 W h kg^-1 at a power density of 550.0 W kg^-1 and remains 72.4 W h kg^-1 at 7600.0 W kg^-1,respectively.（2）A facile one-step co-exfoliation method has been constructed to prepare the water-processable all-carbon composites（PG/GO）made of pristine graphene（PG）and graphene oxide（GO）using ultrasonic cell disruptor.The application of these PG/GO composites to supercapacitor has been also explored.As a result,the PG/GO composites deliver more excellent electrochemical performance compared to most all-carbon composites reported.The composite synthesized under the optimized experimental condition(PG/GO_10:1)exhibits a specific capacitance of 293.6 F g^-1 at the scan rate of 10m V s^-1 and 326.3 F g^-1 at the current density of 0.5 A g^-1,respectively.The cycling stability of these PG/GO composites is quite good.The specific capacitance of PG/GO_10:1 increases with increasing the cycle number and even breaks through 126.9%of the initial value after10000 cycles at the scan rate of 100 m V s^-1.（3）A new graphene oxide/pristine graphene/polyaniline（GPP）ternary composite is successfully prepared by an easy method.The GPP exhibits higher specific capacitance than binary composites.The specific capacitance of GPP reaches 1231.8 F g^-1,measured by galvanostatic charge-discharge method at a current density of 1.0 A g^-1 using a three-electrode system,and still keeps as high as 598.1 F g^-1 in a sandwich type symmetric supercapacitor at a current density of 1.0 A g^-1.The specific capacitance of the composites retains approximately 71.2%and 55.1%after 10000 cycles at the scan rate of 100 m V s^-1in the three-electrode and two-electrode systems,respectively.