Controllable Synthesis And Electrochemical Energy Storage Application Of Carbon-Based Electrode Materials

The continuous consumption of fossil energy has stimulated the development and utilization of sustainable energy resources,greatly compelling the change of energy structure.At present,the limited lithium reserve,uneven distribution,and high cost of lithium resources impede the development of lithium ion batteries.Sodium ion batteries,potassium ion batteries and metal ion hybrid capacitors(K+,Zn2+,etc.)have attracted increasing attention due to the abundant natural resources,wide distribution,and low cost.For these electrochemical energy storage devices,the electrode materials are the key factors affecting their electrochemical performance.Carbonaceous based materials have been used in the field of energy storage owing to its unique features,including low cost,abundance resources,high electronic conductivity,and good chemical stability.In this thesis,we developed various synthetic methods for preparing heteroatom-doped carbon materials,which were applied to new electrochemical energy storage systems,including sodium ion batteries,potassium ion batteries,potassium ion hybrid capacitors and aqueous zinc ion hybrid capacitors.Meanwhile,the energy storage mechanisms of carbon materials were systematically investigated.The main contents are as follows:(1)A sample bifunctional template method was developed to realize the controllable preparation of P/N codoped carbon mesoporous nanotubes(PNC-MeNTs).Then,we investigated the sodium/potassium ions storage performances and corresponding reaction mechanisms of the PNC-MeNTs materials.When PNC-MeNTs were used as anode materials for sodium ion batteries and potassium ion batteries,both exhibiting high specific capacities and long cycling life.More importantly,potassium-ion hybrid capacitors were assembled using PNC-MeNTs anode and activated carbon cathode with a mass ratio of 1:1.5,which could deliver high energy/power density of 175.1 Wh kg-1/160.6 W kg-1,as well as a long cycle life exceeding 3000 cycles.The possible origins and storage mechanisms were investigated with combined characterization methods including in situ Raman spectroscopy and a galvanostatic intermittent titration technique(GITT).(2)A performance optimization strategy for heteroatom doped carbon-based anode materials was proposed to reveal the potassium storage mechanism of hierarchical carbonaceous nanotubes with simultaneous ultrasmall Sn cluster incorporation and nitrogen doping(u-Sn@NCNTs)and its potential for practical application.When the u-Sn@NCNTs anodes were applied in potassium/sodium ion half-cells,the potassium/sodium ion storage performances of u-Sn@NCNTs anodes were significantly improved compared with the only nitrogen-doped carbon nanotubes.The potassium storage mechanism and kinetics of the u-Sn@NCNTs anode were explored by ex situ X-ray photoelectron spectroscopy,in situ Raman spectrum and GITT.Finally,the mass ratio of activated carbon cathode to u-Sn@NCNTs anode was optimized to be 1:1,the potassium ion hybrid capacitor displayed a high current density of 181.4 Wh kg-1 at a power density of 185 W kg-1,and a capacity retention of 93%after 3000 cycles,indicating good potential for practical applications.(3)We elucidated the relationship between P,N dual-doped and the electrochemical performance of carbon-based cathode materials for aqueous zinc ion hybrid capacitors,and the energy storage mechanism of P,N dual-doped hollow nanospheres(PN-CHoNS)cathode was investigated.The zinc ion hybrid capacitors with the PN-CHoNS cathode achieved an exceptional energy density of 116.0 Wh kg-1 at a power density of 141 W kg-1,an extremely high power density of 21660 W kg-1 under a decent energy density of 36.1 Wh kg-1,as well as ultra-long cycling stability up to 12000 cycles.In addition,the energy storage mechanism of PN-CHoNS cathode material was investigated by combination of the systematic characterization and density functional theory calculation,which deciphered that P,N dual-doping could promote the chemical absorption/desorption kinetics of zinc ions to boost the electrochemical charge storage of carbon materials.(4)A facile and controllable synthesis method was developed to successfully incorporated sulfur atoms into nitrogen-rich porous carbon nanotubes(SN-PCNTs),elucidated the relationship between S/N heteroatom doping and the energy storage performance of carbon cathode materials for aqueous zinc ion hybrid capacitors,and unveiled the action mechanism of heteroatom.Benefitting from the synergistic effect of porous feature,hollow structure and heteroatom doping,the SN-PCNTs cathode based aqueous zinc ion hybrid capacitors could deliver a high energy density of 95.9 Wh kg-1 at a power density of 125 W kg-1,a superb power density of 19170 W kg-1 at a decent energy density of 21.3 Wh kg-1,along with an ultralong lifespan up to 25000 cycles with a capacity retention of 93.5%.Then,the energy storage mechanism of SN-PCNTs cathode was deeply studied by using in situ Raman spectrum and ex situ tests.Furthermore,the density function theory simulations revealed the conformational relationship between heteroatom doping and their electrochemical performances,showing that sulfur incorporation can significantly improve the absorption kinetics of zinc ion and modulate the electron transfer behavior.This study not only synthesized carbon-based materials with different structures and morphologies,but also successfully applied them to a variety of electrochemical energy storage devices.This work provides a unique route to design carbon-based electrode materials,which is expected to push forward the development of carbon materials in energy storage and conversion systems.