Construction And Performance Of Carbon-based Hybrid Capacitors

Hybrid capacitors(HCs),as a new type of electrochemical energy storage systems,combine the high energy density of rechargeable batteries and the high power density and long cycle life of supercapacitors.They show great application prospects in the fields of electric vehicles,aerospace,military medical and so on.However,the low specific capacity(especially volumetric capacity)of cathodes,together with the slow kinetics and unsatisfactory cycle life of anodes greatly prevents the further development of HCs.In this thesis,we carried out a series of investigation on materials design,electrode optimization and device construction,and made a great improvement in the electrochemical performance of HCs.The main results are as follows:(1)Electrode thickness matching for improving the volumetric energy density of lithium-ion hybrid capacitors(LIHCs).The structure-performance relationship that the electrode thickness is inversely proportional to the product of the density and gravimetric specific capacity of electrodes was determined.Then an electrode thickness matching strategy was proposed to construct high-volumetric-performance LIHCs.Guiding by this strategy,a facile method was developed to prepare a highly dense but porous activated carbon/graphene(AC/G)composite as the cathode of LIHCs.As a result,the volumetric energy density was increased by 62%to reach a high value of 98Wh L^-1.(2)Intercalation-type pseudocapacitive behavior for improving the specific capacity and kinetics of cathodes in LIHCs.Introducing a Faradic process to increase the specific capacity of cathodes in LIHCs was proposed.Through well controlling the number of layers,crystallinity,graphitization area and defects of graphene-based cathodes,we realized the kinetics transition from a slow intercalation-type battery behavior to a rapid intercalation-type pseudocapacitive behavior,as well as an increase of the gravimetric capacity(111.5 m Ah g^-1).At last,a novel cathode material with high voltage,high specific capacity,good rate performance and long cycle life was achieved.(3)Customized electrodes for constructing high-performance potassium-ion hybrid capacitors(KIHCs).According to the diverse requirements of cathodes and anodes based on different energy storage mechanisms,two kinds of graphene-based materials were customized for the cathode and anode of KIHCs by building three-dimensional interlinking and two-dimensional stacking constructions,respectively.As a result,a high-performance KIHC was achieved based on the cathode with high volumetric capacity(121 m Ah cm^-3)and the anode with high rate capability and good cyclability(2200 cycles).(4)Highly dense and oxygen-riched cathodes for high-volumetric-performance zinc-ion hybrid capacitors(ZIHCs).Influence of specific surface area(SSA)and surface chemistry on the electrochemical performance of cabon-based cathodes for aqueous ZIHCs was systematically investigated.It was confirmed that the surface chemistry has a more significant effect on improving the volumetric specific capacitance of cathodes than the SSA.As last,a highly dense and oxygen-riched graphene-based cathode with a high volumetric specific capacitance of up to 240 F cm^-3 was achieved.(5)Dual-functional protective layer for improving the stability of metallic Zn anodes.The self-corrosion of metallic Zn anodes in aqueous Zn SO₄ electrolyte was systematically investigated.A dual-functional protective metallic In layer,acting as both a corrosion inhibitor and a nucleating agent,was constructed to improve the stability of Zn anodes in aqueous electrolyte.This strategy significantly mitigates the corrosion and dendrite growth issues,thus resulting in a reduced overpotential of 54m V and an improved cycle life of up to 1500 h.