| As consequence of the rapid development and global urbanization,energy supply is much lower than its growing demands.Clean and efficient energy strategy is a key to solve the energy and environmental crisis.Energy storage and conversion technology has become an important research direction,including fuel cells,lithium-ion batteries and supercapacitors.Among energy storage devices,supercapacitors have their own unique advantages,for example,super high charge/discharge rate,super long cycling life and stability as wel as promised great potential in practical application,for instance,handcarts,buses,emergency doors and others.Although supercapacitors have achieved some encouraging efficiencies,however,their energy density is still beyond the values of flow batteries(20?80 Wh kg-1)and traditional batteries(80?200 Wh kg-1).The introduction of electrode materials with the potential of surface redox reaction can increase the energy density(10 times or higher),while the power density and cycling performance remain unaffected.Among them,the introduction of heteroatoms(nitrogen,boron,sulfur,fluorine,phosphorus,etc.)into carbon skeleton is an important research direction nowadays.Importantly,the N atoms can produce electrochemical synergy with oxygen and phosphorus.Based on these advantages,we plan to prepare heteroatoms doped carbon materials by blending polyimide and polyphosphonitrile matrix followed by the carbonization.We performed XRD,Raman,SEM,XPS and N2 adsorption/desorption isotherms to analyse the structure and surface composition of the as-synthesized materials.The capacitance performance was evaluated by cyclic voltammetry(CV),constant current charge-discharge(GCD),impedance spectroscopy.The main contents of the present work and its results are as follows:(1)Heteroatoms(N,P,O)doped carbon materials with high electrical properties were prepared by fine regulation of the doping ratio of polyimide(PI)and phenoxy polycyanonitrile(PZ).The incorporation of polyphosphonitrile is favorable for sintering and improving pore structure.We have investigated the effects of doping ratio of PI and PZ(1:0.2-1:5)on the morphology,structure and electrochemical properties of PI/PZ carbon materials.The carbon material having PI/PZ= 1:0.3 demonstrated the highest degree of graphitization and the best electrochemical performance with mass specific capacitance up to 528.4 F g-1.(2)We have selected the best proportion carbon materials,that is,of PI/PZ=I:0.3 as precursors for studying the effect of carbonization temperature on the morphology,crystal phase and heteroatoms content in carbon materials.We found that by increasing carbonization temperature the degree of graphitization of PI/PZ carbon material increased,while the heteroatom retention rate is decreased.Our results depicted that the PI/PZ= 1:0.3-900 has the highest degree of graphitization at 600 ? to 900 ?.(3)The influence of activation ratio(1/2-1/5)on specific surface area and electrochemical performance of PI/PZ=1:0.3 carbon materials was investigated on the basis of PI/PZ(1:0.3)and carbonization temperature(800?).When the activation ratio is 1/5,the specific surface area indexed to 1767.25 m2 g-1 while the specific capacitance value up to 435.6 F g-1.(4)We also have prepared hetroatoms(N,P,O)doped carbon materials by blending polyimide(PI)and cyclic phosphazene(HCCP).The structural morphology and electrochemical properties of PI/PZ(1:0.2-1:5)doped carbon materials with different mass ratios were investigated.PI/CP carbon materials have exhibited similar capacitance performance compared with PI/PZ carbon materials.When the ratio of polyimide and cyclic phosphazene is 1:0.5,the highest mass specific capacitance of 474.5 F g-1 is obtained. |
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