| Lithium-ion batteries(LIBs)are the diminant portable energy storage devices in market,widely used in many mobile devices,such as smartphones,laptops,medical devices,digital cameras,and electric vehicles.Although the demand to LIBs is ever-increasing,the limited and cost Li resources make them difficult to satisfy their large-scale applications.Thus,it is highly necessary to develop potential alternatives for LIBs.Recently,potassium-based dual ion batteries(KDIBs)have attracted intensive interest from researchers wordwide,owing to their environmental friendliness,high safety performance,low cost,and high working voltage and abundant K resources.However,the sustainable development of KDIBs are greatly plagued by the lack of suitable electrode materials,which allows reversible reaction between the large-sized potassium ions and anion with the anode and cathode,respectively.Therefore,the lack of suitable electrode materials is the key limiting factor for the development of high-performance KDIBs.To address the problems of low specific capacity and poor cycling stability associated with the electrode materials for KDIBs,the thesis designed carbon anode,antimony(Sb)anode,and organic cathode materials and explored their energey storage behaviours when constructed into full battery of KDIBs.The main results achieved are outlined below:1.Hierarchically porous,free-standing,high N-doped carbon fibers(HPNCFs)as anode for high-performance KDIBs:Due to the poor cycling stability for graphite anode,Chaper 2 in this thesis fabricated HPNCFs via electrospinning as anode for high-performance KDIBs.HPNCFs has many structural advantages.1)Its hierarchical porous structure(micro/meso/macropores and nanochannels)furnishs sufficient free space to tolerate the volume expansion during cycling,and meanwhile shortens electron pathways.2)High-content nitrogen doping can not only improve conductivity of the electrode but also offer abundant active sites for the storage of potassium ions.3)Its free-standing nature allows using itself as the anode without the need of conductive agent,binder,and current collector,thereby greatly reducing the cost and weight of the battery.Hence,the KDIBs made using optimized HPNCFs anode and graphite as cathode delivers a high reversible capacity of 197 m A h g-1(normalized by the mass of the anode)at a current density of 50 m A g-1,and as wellshows excellent cycling stability(which can stably operate at least 346 cycles at a current density of 100 m A g-1).Therefore,the properly designed HPNCFs can effectively improve the capacity and cycling stability of the KDIBs,showing great potential for practical,high-performance energy-storage devices.2.High capacity of nanometer Sb thin film anode for KDIBs:Considering its excellent conductivity and high theoretical specific capacity(660 m A h g-1 in terms of K3Sb),Chapter 3 exlore the potential of using Sb metal as the anode for KDIBs.Sb was directly vapor deposited on a copper collector in a vacuum evaporater,which avoids the use of binder and conductive agent,lightening the weight of the battery.Consequently,KDIBs made using Sb thin film as anode and graphite as cathode delivers a high energy density(101.3 Wh kg-1)and also show long cycle life(tested upon 776 cycles at a current density of 300 m A g-1).3.Free-standing hierarchically porous composite architecture of antimony nanoparticles/carbon nanofibers for long cycling life of KDIBs:To break through short cycling life caused by serious volume expansion for Sb anode,chapter 4synthesized a free-standing hierarchically porous composite architecture of antimony nanoparticles/carbon nanofibers(HPSb CNFs)for high-performance KDIBs.The HPSb CNFs have the following tructural advantages.1)Its hierarchically porous structure not only offers sufficient free space to tolerate the repetitive volume expansion of Sb nanoparticles during long-term cycling but also greatly facilitates the transport of electrons and ions within electrode.2)The carbon capping layer on fiber further alleviates the volume expansion of Sb nanoparticles.These two methods can effectively improve the cycling performance of the KDIBs battery.3)High-content nitrogen doping can offer abundant active sites for the storage of potassium ions,thereby enhancing the specific capacity for the KDIBs battery.The KDIBs made using HPSb CNFs-700(in which 700 represent the calcination temperature of 700°C)as anode and graphite as cathode deliver a high reversible capacity of 440 m A h g-1(normalized by the mass of the anode)and a high discharge medium voltage of 4.5 V at a current density of 200 m A g-1,and show excellent cyclic life.Meawhile,KDIBs show excellent cyclic life(1440 cycles)at a current density of 500 m A g-1.These results suggest the as-designed HPSb CNFs-700 with high capacity and long-term cycling stability is a promising anode material for high-performance KDIBs.4.Organic polyparaphenylene anode for high performance KDIBs:To address the poor cycling stability and low reversible capacities associating with the widely used graphite cathode in KDIBs,Chapter 5.Hence,it is urgent to explore a neoteric cathode electrode material.Polyparaphenylene(PPP)is bipolar(p-and n-dopable)redoxactive polymers,which imply that it is used as both anode and cathode.Furthermore,PPP has high redox activities,suggesting its high capacity.The KDIBs made from PPP cathode and graphite anode delivers energy density of 105.6 W h kg-1 and a high discharge medium voltage of 3.91 V at a current density of 200 m A g-1.KDIBs have energy density of 90.0 W h kg-1and coulombic efficiency of 81.4%after 480 cycles at a current density of 500 m A g-1.At a current density of 1000 m A g-1,KDIBs stably operate at least 500 cycles,energy density of 84.7 W h kg-1and coulombic efficiency of 85.4%.Therefore,PPP is substitute for graphite as cathode material of KDIBs. |
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