Construction Of High-performance Aqueous Zinc Ion Hybrid Capacitors Based On Porous Carbon Materials

Aqueous zinc ion hybrid capacitors?ZIHCs?have attracted wide attention because of their high energy density,high power density and excellent cycle stability by bridging the gap between rechargeable second ion batteries and supercapacitors.The main puzzle for developing high performance ZIHCs is seeking for high performance capacitor-type electrode materials and preparation strategies for Zn anode as well as the suitable electrolyte with wide potential window.Because of its non-toxicity,inexpensive,good cycle life and excellent power output,commercial activated carbon is widely used as the capacitor-type material for zinc ion hybrid capacitors.However,the improvement of device performance is limited due to the poor interoperability between the pores and relatively small specific surface area of commercial activated carbon.Therefore,the development of capacitive materials with high specific surface area,rich pore structure and good interoperability is an effective means to construct high-performance zinc ion hybrid capacitors.In this paper,biomass and polymers are used as carbon sources respectively,and porous carbon with high specific surface area,hierarchical porous structure and good capacitance performance is prepared controllably by chemical activation method.The porous carbon is used as a capacitor-type material,and metal zinc foil or polymer coated zinc foil and zinc vanadate?ZnVO?is used as a battery-type material,a series of zinc ion hybrid capacitors with high energy density,high power density and ultra-long cycle life were assembled.The main research contents and results of this thesis are as follows:?1?Olive leaves were used as carbon source.The relationship between micro-morphology,pore structure,specific surface area,elemental composition and capacitive properties of olive leaf-derived porous carbon were systematically investigated for optimizing the activator dosage and activation temperature.The olive leaf-derived porous carbon?OLDC-750-3?with high specific surface area and optimal capacitive properties was selected.The aqueous zinc ion hybrid capacitor was assembled with OLDC-750-3 as capacitor-type cathode and metal zinc foil as battery-type anode.The hybrid device exhibited a high energy density(136.3 W h kg^-1),a high power density(20 kW kg^-1)and ultra-long cycle stability(20 000 cycles at a high current density of 10 A g^-1,with a capacity retention rate of 94.5%).Compared with carbon-based electric double layer supercapacitors,zinc ion hybrid capacitors had significantly improved energy density without losing power density.?2?Capparis spinosa was used as the carbon source.The effects of the amount of activator on the micro-morphology,graphitization degree,specific surface area,pore structure,elemental composition and capacitive properties of the capparis spinosa-derived porous carbon were systematically investigated.The optimal activation ratio was determined,and the N,O co-doped capparis spinosa-derived hierarchical nanoporous carbon?CSDC-700-3?with the best capacitance was screened.A zinc ion hybrid capacitor was assembled by CSDC-700-3 as a capacitor-type cathode and a metal zinc foil as a battery-type anode.The device showed high energy density(153.94W h kg^-1),high power density(20 kW kg^-1)and ultra-long cycle stability(50 000 cycles at a high current density of 10 A g^-1,with a capacity retention rate of 93.2%),which was a considerable improvement in energy density compared with a carbon-based electric double layer super capacitor.In order to further explore battery-type materials that can be used as zinc ion hybrid capacitors,we use self-prepared ZnVO as battery-type cathode and CSDC-700-3 as capacitor-type anode to build high-performance zinc ion hybrid capacitors,and the device showed a high energy density of 19.56 W h kg^-1.?3?In order to solve the problem of the zinc dendrites in metal zinc electrode,we designed to coat a layer of PZS polymer on the surface of metal zinc foil,using N,P,S and O atoms in polymer materials to form uniform metal zinc nucleation sites to effectively prevent the formation of zinc dendrites.Meanwhile,using SiO₂ as template,poly?cyclotriphosphazene-and-4,4'-sulfonyl diphenol?-based hollow nanocarbon spheres?PZS-HNCS?with defined morphology were synthesized by simple chemical polymerization and high-temperature pyrolysis,and its capacitance performance was studied.Finally,PZS-HNCS was used as capacitor-type cathode,metal zinc and Zn@PZS were used as battery-type anode,and 2 M ZnSO₄ was used as the electrolyte to assemble the zinc ion hybrid capacitor.The test results showed that the cycle stability of the Zn@PZS-based zinc ion hybrid capacitor was significantly improved.SEM characterization shows that this method can effectively inhibit and control the growth of dendrites,providing an effective strategy for zinc anode protection.Meanwhile,this method is simple and easy to implement,and it is expected to be applied to the protection of other metal electrodes.