Preparation And Electrochemical Properties Of Heteroatom Doped Polymer-based Carbon Materials

With the linear rise of the technological level,the demand for high-efficiency energy storage devices is imminent.The reason why supercapacitors(SCs)have become highly competitive electrochemical energy storage devices is mainly due to their superior power density,fast charge and discharge rate,stable cycle life,and higher safety.In addition,zinc ion hybrid capacitors(ZHSs)can well make up for the shortcomings of traditional supercapacitors with low energy density,so many recent studies have focused on ZHSs devices.In this article,the target polymer will be obtained through a simple polymerization reaction,and then used as a precursor to obtain polymer-based carbon materials through pre-oxidation and high-temperature activation.During the carbonization process,the polymer will undergo degradation reactions,resulting in a pore structure.In addition,the polymer as a precursor is easy to control the molecular weight and structure,which is one of the main reasons for the design of polymer-based carbon materials in this thesis.At the same time,through various structural characterization methods and electrochemical tests,the carbon materials are deeply explored.Finally,the prepared carbon material and the designed hydrogel electrolyte were assembled into SCs or ZHSs,and the device performance was studied and the device application evaluation was carried out.The main conclusions of this paper are as follows:(1)Using melamine and formaldehyde solution as raw materials,the nitrogen-containing polymer(MF)precursor was obtained through polycondensation reaction.Then the precursor is carbonized and activated to prepare N/O co-doped porous carbon materials(AMFCs).The effect of changing the melamine content on the morphology of the polymer and the 2D porous network carbon sheet was studied,and in-depth exploration of the electrochemical properties of AMFCs.The conclusions were as follows:in the three-electrode system,the specific capacitance of the best sample AMFC-2 is as high as 281.1 Fg^-1 when the current density is 0.5 Ag^-1;when the current density is increased to 100 Ag^-1,the specific capacitance retention rate is 92.5%,showing excellent electrochemical performance.When the active material loading of the working electrode is increased to 25 mg cm^-2,it shows higher area capacitance at low current density(0.5 Ag^-1)and high current density(10Ag^-1),respectively 3.56 F cm^-2 and 2.68 F cm^-2.The superior electrochemical performance was attributed to its large specific surface area(1853.7 m² g^-1)and abundant pore structure(0.77 cm³ g^-1).The AMFC-2 electrode and the neutral double cross-linked polymer hydrogel electrolyte are assembled into quasi-solid supercapacitors(QSSCs).The potential window can be expanded to 2.0 V,the energy density can reach 28.3 Wh kg^-1,and it has good cycle stability.This new strategy for preparing high-performance 2D carbon and its combined use with polymer hydrogel electrolytes has a good application prospect in future flexible electronic devices.(2)Using melamine,formaldehyde solution,and sodium alginate as raw materials,the polymer(MA)precursor was successfully prepared through polycondensation reaction.The precursor is pre-oxidized and activated at high temperature to obtain a continuous three-dimensional frame porous carbon material(AMACs)co-doped with N/O.The effect of activation temperature on the morphology,structure and performance of the material was studied,and the electrochemical performance of AMFCs was deeply explored.The following conclusions are drawn as follows:as the activation temperature increases,the internal defects of the carbon material increase.When the activation temperature is 700?,the carbon material has a larger specific surface area(1282.82 m² g^-1)and a rich microporous structure(0.56 m L g^-1).The AMAC-700 positive electrode,Zn negative electrode and Zn(CF₃SO₃)₂ electrolyte are assembled into button ZHSs,and the electrochemical performance test is carried out.The results show that the capacity is92.1 m Ah g^-1 when the current density is 0.25 Ag^-1,and the capacity retention rate is as high as 40.2%when the current density is increased to 20 Ag^-1.The designed flexible double cross-linked polymer hydrogel electrolyte is applied to quasi-solid ZHSs,and its energy density is as high as 71.4 Wh kg^-1.Moreover,after 10000 cycles of the quasi-solid device,the capacity retention rate was 89.5%,showing superior cycle stability.This research proves that ZHSs devices have obvious advantages in energy density compared with traditional SCs.(3)Using melamine,formaldehyde solution,PVA,and boric acid as raw materials,N/O/B triple-doped porous carbon materials were prepared through freeze-drying,pre-oxidation and activation.The influence of the change of PVA content on the morphology of the polymer and the morphology and performance of the 2D porous carbon sheet was studied and in-depth exploration of the electrochemical properties of APMCs.After testing,the main conclusions are as follows:The best sample APMC-2 is used as the cathode material for liquid ZHSs.When the current density is 0.25 Ag^-1,the capacity is 110.2 m Ah g^-1,the current density is increased to 20 Ag^-1,and the capacity retention rate is as high as 40.0%.The highest energy density of the device is 91.4 Wh kg^-1.The designed flexible PBG₁/SCG₂/Zn anti-freeze polymer gel electrolyte and the quasi-solid ZHSs device assembled with APMC-2 also showed excellent electrochemical performance.The results show that at room temperature,the capacity is 95.6 m Ah g^-1 when the current density is 0.25 Ag^-1,and the capacity retention rate when the current density is increased to 20 Ag^-1 is as high as 58.3%.At the same time,the device can still operate normally in a low temperature environment(-20?).When the current density is 0.25 Ag^-1,the capacity is as high as 62.1 m Ah g^-1,and it has good electrochemical stability.This research proves that the ZHSs devices have the potential of practical application.