Surface Modification Of Low-cost Carbon Materials And Its Application In Supercapacitors

With the rapid development of science and technology,people have put forward new requirements for the portability and wearability of smart electronic products,which also impose high performance and safety requirements for energy storage devices of intelligent electronic products.Supercapacitors are considered the most feasible solution for flexible energy storage of electronics due to their high power density and good cycling stability.However,supercapacitors still fall short of industry requirements of energy density.In this thesis,low-cost carbon materials were modified by three surface modification methods,including co-activation,phytate phosphorylation-assisted activation,and polydopamine coating,respectively,for enhancing the energy density and stability of supercapacitors.（1）A flexible carbon was fabricated from commercial carbon felt by co-activation with potassium arginine and potassium hydroxide（KOH）as activators,and the resulting material was abbreviated as AKCF.Unlike the traditional KOH activation process,the addition of potassium arginine can produce a micro-graphitized carbon layer to be the outer layer of AKCF fibers for achieving better electronic transfer.Thanks to the thin micro-graphitized carbon layer imparting better electrical conductivity and lower charge transfer resistance,the capacitance of the optimized AKCF-0.1 electrode obtained by the co-activation process was elevated to a 1.8-fold higher value of 403 C·g^-1(2583 m C·cm^-2)relative to the AKCF-0 electrode prepared by KOH activation alone(222 C·g^-1 or 1369 m C·cm^-2).（2）A phosphorus-doped bamboo fiber-derived carbon material（P10-120-BFC）was obtained by phosphorus esterification,pretreatment of the precursor with bamboo fiber and phytic acid,followed by high-temperature calcination.The phosphorus esterification at low temperatures facilitated the homogeneous bonding of the two materials,and the activated P10-120-BFC had a porous structure and P-element doping.Benefiting from these advantages,the capacitance of the zinc ion hybrid capacitor（ZHSC）constructed with this P10-120-BFC electrode reached 109 m Ah g^-1.Furthermore,the assembled quasi-solid ZHSC exhibited a high energy density of 60 Wh kg^-1and a power density of 1653 W kg^-1.（3）A zinc（Zn）anode protective layer was constructed by a polydopamine（PDA）-coated carbon fiber（PCF）coating to inhibit the formation of Zn dendrites in ZHSC.Since PCF has a Zn-friendly functional group and three-dimensional structure,Zn was deposited parallel to the fiber surface of PCF,which thus served to inhibit the formation of Zn dendrites.The Zn anode with PCF-coated surface（PCF@Zn）displayed exceptional performance in corrosion resistance tests,being stabilized at current densities of0.5 m A cm^-2 and 5 m A cm^-2 for more than 400 h,which was higher than the unmodified Zn anode.