Preparation Of Carbon-based Composites And Their Electrochemical Performance

Supercapacitor is a new type of energy storage device.Compared with traditional capacitor,it possesses high energy density,high power density and long cycle life.In this paper,the preparation and electrochemical properties of carbon matrix composites are studied,mainly involving nitrogen and phosphorus co-doped porous carbon-based materials,APC/MnO₂ composites and MWCNT/PANI/MnO₂ composites.The structure was characterized by SEM,XRD,FTIR and Raman spectra.The capacitive characteristics of three electrode materials were further studied by means of electrochemical technology such as CV,GCD and EIS.The main results are as follows:?1?Carbon black?CB?was used as conductive filler,and polyaniline containing phytic acid was loaded on CB by in situ oxidation polymerization.Nitrogen-phosphorus co-doped CB was prepared by pyrolysis at high temperature.CB was replaced by activated carbon?AC?,and the nitrogen and phosphorus co-doped AC was prepared by the same method as before.Thus,the optimal ratio n?aniline+phytic acid?:n?CB?is0.1(labeled NP/CB_0.1).NP/CB_0.1 has a higher electrical conductivity and a higher degree of graphitization than monatomic,with a specific capacitance of up to 165 F/g.After 20000 charge and discharge cycles,the capacity retention rate is 89.12%of the initial value.This is because CB is amorphous,and the disordered space channel formed is not easy to be destroyed.By calculating its specific capacitance,it is found that the composite has better electrochemical performance than other composites with fewer holes.Therefore,the porous structure carbon material can enhance the electrochemical performance to some extent.?2?Active porous carbon?APC?was prepared by electrostatic spinning and potassium hydroxide activation with PAN as precursor.MnO₂ was then generated on the porous carbon surface by electrodeposition.APC/MnO₂ composite electrodes with different MnO₂ content were prepared by different electrodeposition time.Under the three-electrode test system,APC/MnO₂-₅₀₀ electrodeposited at 500 s has the maximum specific capacitance of 280.8 F/g.It has good cyclic stability,and the capacitance retention rate after 20000 charge and discharge cycles is 83.90%.However,the conductivity of MnO₂ is poor,and the multiplier performance of the supercapacitor prepared by MnO₂ composite material needs to be improved.?3?MWCNT/PANI/Mn O₂ composites were prepared by two-step method.First,the loaded PANI was polymerized in situ on the MWCNT surface to obtain MWCNT/PANI.Secondly,KMnO₄ solution was mixed with MWCNT/PANI to obtain MWCNT/PANI/MnO₂ through redox reaction.The electrochemical test shows that the material has the properties of pseudocapacitance.The comparison of the electrochemical performance of MWCNT/PANI and MWCNT/PANI/MnO₂ shows that MWCNT/PANI/MNO₂-_0.34 has the maximum specific capacitance.When the current density is 0.2 A/g,the specific capacitance is 230 F/g,the constant current charges and discharges 20000 times,and the capacitance retention rate is 86.51%.Experimental results show that the PANI layer and MnO₂ thin layer are loaded on the MWCNT surface.MnO₂ thin layer grows in situ on PANI surface,which can not only effectively protect the structure of PANI layer,but also increase specific capacity.Therefore,MWCNT/PANI/MnO₂ is an excellent electrode material.