| Aqueous zinc ion batteries(ZIBs)are one of the most promising energy storage systems for grid-scale applications due to the advantages of high theoretical capacity,suitable redox potential,low cost,high safety and environmental friendliness of zinc metal,and have received extensive attention from relevant researchers.V2O5 is a typical layered vanadium-based cathode with a theoretical specific capacity of up to 589 mAh g-1.However,V2O5 has limitations such as poor structural stability,irreversible vanadium dissolution and unsatisfactory cycle stability during continuous charge and discharge cycles.Therefore,this thesis revolves around the above mentioned problems of V2O5 as an cathode material for ZIBs to modify V2O5 in order to improve the electrochemical zinc storage performance and electrode reaction kinetics,and reveal the electrochemical zinc storage mechanism through characterisation analysis,which provides guidance for the design and optimisation of future cathode materials.The main research work of this thesis is as follows.(1)Sandwich-like V2O5/graphene composites(V2O5/XG)were controllably fabricated by tuning the amount of hydrophobic graphene.With the increase of graphene content,the corresponding electrochemical properties show a parabolic trend that increase first and then decrease.A maximum capacity of 270 mAh g-1 after 100 cycles at 0.1 A g-1 and a superior cycle stability with 82.4%capacitance retention after 6000 cycles at 10 A g-1 are achieved when the amount of graphene is about 10.4%(that is V2O5/5G).The addition of graphene has been proven not only to act as an effective conductive network to promote charge transfer and enhance the pseudocapacitance effect on the electrode surface;but also to increase the electrode hydrophobicity,effectively inhibiting the dissolution of vanadium,and promoting the desolvation and diffusion kinetics of hydrated zinc ions.(2)The V2O5 micro-flower was synthesized by a solvothermal method,and the interface is modified by coating with an AlF3 passivation layer(AlF3@V2O5).Impressively,AlF3@V2O5 exhibits excellent electrochemical and kinetic properties due to the special structure of V2O5 and the interfacial protection of AlF3.An excellent rate capability(325 mAh g-1 at 0.1 A g-1,188 mAh g-1 at 15 A g-1)and a superior cycle stability with 89.3%capacitance retention after 6000 cycles at 10 A g-1 are achieved when the amount of AlF3 is 2 wt%(that is AF-2@V2O5),which better than pure V2O5.The density functional theory(DFT)computation suggests that the AIF3 coating can weaken the interaction between V2O5 particles and Zn2+,thus facilitating the insertion/extraction process of Zn2+and enhancing the kinetic performance.(3)The polypyrrole-coated V2O5 nanobelts arrays grown on carbon cloth(PPy@V2O5/CC)are rationally designed and prepared by combination of solvothermal and vapor-phase polymerization process.The resultant flexible PPy@V2O5/CC electrode delivers a high specific capacity of 276 mAh g-1 at 0.1 A g-1,an excellent rate capability of 185 mAh g-1 at 10 A g-1,and extraordinary long-term cycling stability with 76%capacity retention after 8000 cycles at 5 A g-1,better than V2O5/CC.The significant enhancement can be attributed to the PPy protective layer,which can simultaneously achieve higher electronic conduction,suppressed vanadium dissolution,enhanced surface pseudocapacitive behavior,and faster Zn2+diffusion rate. |
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