Designs And Characterizations Of High Performance Electrode For Aqueous Rechargeable Ag-Bi Batteries

With the gradual depletion of global petrochemical energy and the increasing problem of environmental pollution,people are particularly concerned about the large-scale development and utilization of the new generation of green energy represented by solar energy.At present,these energy sources are mainly used in the form of electric energy conversion.Due to the intermittent problem of these energies,the research and development of high capacity,long life,safe and cheap electric energy storage equipment is urgent.Meanwhile,the vigorous development of electric vehicles and portable electronic equipment also puts forward higher requirements for the comprehensive performance of energy storage equipment.As an important branch of electrochemical energy storage equipment,aqueous rechargeable battery has higher conductivity,lower fabrication cost and higher safety performance compared with organic electrolyte system.However,the usage of aqueous electrolyte also limits its operating voltage within the decomposition voltage of water,which is much lower than the battery voltage of organic system,resulting in a large decrease in the energy density of the device.One of the effective ways to solve this problem is to improve the specific electrical capacity of electrode materials.In this paper,metal Ag with high capacity ratio was used as cathode active material,and it is combined with high conductivity three-dimensional Cu nanowire arrays by ingenious structural design to form an unbonded Ag@Cu nanowire arrays electrode(Ag@Cu NWAs)with core-shell nanostructures,in which the active material metal Ag exhibits an ultrathin nanoshell layer on the electrode surface.This electrode not only had the intrinsic advantages of Ag high specific capacity,but also improved the rate performance and cycling performance by the utilization of metal Cu conductive framework.Moreover,in order to match the Ag@Cu NWAs positive electrode,we selected metal Bi with high theoretical capacity and low potential as negative active materials.The nanobox Bi@C NC composite electrode materials with hollow porous nanostructures were prepared by using ZIF-67 templates for structural nanocrystallization.The details is as follows:(1)A three-dimensional Cu(OH)2 nanowire arrays precursor was grown on a copper foam substrate by solution etching,on which metal Ag was deposited by silver mirror reaction.Then,the three-dimensional core-shell structure Ag@Cu NWAs cathode material supported by copper foam was prepared by H2 reduction annealing.The hierarchical structure takes the porous metal Cu nanowires grown in situ as the core,which ensures the stability and good electrical conductivity of the electrode.As the main active material,the ultrathin thickness of the surface Ag shell is about 7 nm,which is beneficial to the penetration of electrolyte and the difusion of ions,improving the material utilization.According to the electrochemical testing results,the electrode exhibited an ultrahigh specific capacity of 1.79 mAh cm-2(458 mAh g-1)and maintained 83.6%of the initial capacity after 5000 cycles.The electrochemical behavior and energy storage mechanism of the Ag@Cu NWAs during electrochemical process were also explored by quasi-in situ analysis,which verified that the main chemical reactions is attributed to Ag0?Ag+and Ag2+mutual transformation,and proves that its electrochemical behavior is a diffusion-dominated kinetic process.(2)We used the ZIF-67 as the precursor,and replaced the matched Co ion with Bi ion by ion exchange method.After high temperature carbonization and reduction process,the Bi@C nanobox electrode material(Bi@C NC)with hollow structure was prepared.The characterization results show that the primary ZIF-67 organic framework was transformed into porous hollow carbon framework after high temperature carbonization process and the introduced Bi ions are reduced to metal Bi nanoparticles uniformly dispersing in the carbon framework.This nanostructure not only improves the utilization efficiency of metal Bi,but also greatly improves the overall conductivity and stability.As the negative electrode of aqueous rechargeable battery,Bi@C NC electrode exhibited the high specific capacity of 1.67 mAh cm-2 and the cycling stability of 5000 cycles.Moreover,an aqueous alkaline Ag-Bi battery device with Ag@Cu NWAs as positive electrode and Bi@C NC as negative electrode was assembled.The device exhibits high energy density and high power density as well as good cycling performance.