Preparation Of Sub-nano Porous Carbon Materials And Electrochemical Energy Storage Research

Double electric layer supercapacitor（EDLC）,which has received much attention for its advantages of high-power density,fast charging and discharging rate and good cycling stability,has become the most promising energy storage device.Electrode material,as the core component of EDLC,is the key factor affecting its performance.Based on the special physical electrostatic accumulation energy storage mechanism of EDLC,electrode materials with high specific surface area and specific pore structure need to be prepared.Therefore,for porous carbon materials,most of the research focus is on the design of pore structure.Several studies have confirmed that ion storage in sub-nano pores depends on the size of the solvated ions,and that the surface of sub-nano pores is barely accessible to ions when the pore size is smaller than the solvated ions.Sub-nano pores possess the ability to increase the specific surface area,but only those with a specific range of pore sizes are able to increase the specific capacitance.In order to better investigate the"constitutive relationship"between sub-nano pores pore structure and electrochemical properties,in this paper,a new strategy of interpenetrating polymer networks（IPNs）carbonization was adopted to tune the relevant parameters of the pore structure by controlling the relative content of the two phases,a series of sub-nano porous carbons with monodisperse pore size and located at 0.6 nm were prepared.The relationship between pore structure and electrochemical properties was reasonably explained.The main research of this paper is as follows:（1）In this section,porous carbon materials with rich sub-nano pores were prepared by direct carbonization of dimethylamine formaldehyde resin（DF）and sodium polyacrylate（PAAS）interpenetrating polymers.It was demonstrated that the IPN direct carbonization strategy successfully achieved precise control of the material pore size（0.6 nm）and could tune the pore ratio of sub-nano pores.Among them,C-IPN3 sub-nano porous carbon has a partially graphitized structure with a maximum total specific surface area of 575 m² g^-1.The C-IPN3 electrodes for aqueous-based supercapacitors maintained 82%of the initial capacity value when the current density was increased by a factor of 20(0.5～10 A g^-1)and exhibited a high specific capacitance of 239.1 F g^-1 at 0.5 A g^-1.More importantly,the aqueous-based supercapacitor device assembled with a two-electrode system exhibited a high energy density of 7.57 Wh Kg^-1 at 62.5 W Kg^-1 power density.（2）To further validate the advantages for the application of sub-nano porous carbon materials prepared by direct carbonization of IPNs in the field of supercapacitors.This section was designed through the replacement of carbon precursor structural units to dissolve the dicyandiamide formaldehyde（CD）resin prepolymer into the interior of the PAAS molecular structure under osmotic pressure,initiate the post-polymerization section and first synthesize the CD/PAAS IPNs.Then a series of sub-nano porous carbon materials with different pore structures were prepared by high temperature carbonization.The obtained results demonstrate that the pore size of the carbon material is perfectly regulated at 0.6 nm,the pore size distribution is monodisperse,and C-IPN1 and C-IPN3 are distinguished by locally graphitized structure.C-IPN1 exhibits excellent specific capacitance value of 238.5 F g^-1 at 0.5 A g^-1 current density,and the capacitance retention rate is as high as 79.5%relative to the initial capacitance value even when the current density is expanded to20 times.More importantly,at the current density of 5 A g^-1,the coulombic efficiency and capacitance retention are consistently maintained at 100%during 8000charge/discharge cycles.This indicates that C-IPN1 has good cycle stability and reversibility of charging/discharging.In addition,the symmetrical two-electrode device based on C-IPN1 electrode material was assembled to obtain 7.31 Wh Kg^-1energy density at 62.5 W Kg^-1 power density in alkaline electrolyte,and 6.1 Wh Kg^-1energy density was maintained at power densities up to 1500 W Kg^-1.（3）The first two chapters confirmed that the porous carbon prepared by the direct carbonization strategy of IPNs can not only precisely control the pore size,but also regulate the pore structure,interpreting that sub-nanometer micropores have an important role in the charge storage process.In order to obtain porous carbon electrode materials with higher energy storage properties,ethylenediamine-formaldehyde（EF）resin was chosen as the carbon precursor to form IPNs with no covalent bonding to each other at the molecular level and only physical entanglement with PAAS.During the carbonization process,EF strips off unstable heteroatoms and functional groups to form a carbon framework,while PAAS pyrolysis produces small molecules that escape leaving abundant pores in the carbon framework.The BET results showed that C-IPN2exhibited the highest specific surface area of 1514.873 m² g^-1,in which the contribution of sub-nanometer micropores reached 91.7%.The results show that the specific capacitance value of C-IPN2 can reach up to 271.5 F g^-1 at 0.5 A g^-1 current density.Meanwhile,when the current density was 5 A g^-1,12,000 cycles of charging and discharging process were performed,and the capacitance retention and Coulomb efficiency were stable at about 100%.In view of the excellent electrochemical properties of the C-IPN2 electrode material,a symmetrical two-electrode device based on an aqueous alkaline electrolyte was assembled,and the device can provide a high specific capacitance of 61.7 F g^-1 at 0.25 A g^-1 and a high energy density of 8.45 Wh Kg^-1 at a power density of 125 W Kg^-1.Thus,the direct carbonization of IPNs can combine good electrochemical properties with flexible and tunable pore structures to provide new opportunities for realizing high-performance electrochemical energy storage devices.