Study On Potassiophilic Modification Of Carbon Cloth And The Stability Of Potassium Anode

Due to the uneven distribution of lithium resources on the earth and the extremely small reserves(0.0017%),lithium-ion batteries can no longer meet the needs of large-scale storage.Potassium-ion battery is considered as a promising energy storage battery because of its similar working mechanism with lithium-ion battery,abundant potassium resource and low price.At present,the anode materials(such as carbon and alloy)commonly used for potassium-ion batteries are not enough to meet the requirements of practical applications due to their limited capacity.In contrast,potassium is widely favored by researchers because of its high specific capacity(687 mAh g-1).However,the current research on potassium metal anode in liquid electrolyte is still limited by the formation of potassium dendrite,unstable SEI film and volume expansion in the process of continuous plating/stripping,which will shorten the cycle life of potassium metal battery and reduce coulombic efficiency.In recent years,the three-dimensional skeleton is an ideal choice for molten potassium support matrix by the advantages of high mechanical strength and high specific surface area.Among them,commercial carbon cloth as a common three-dimensional carbon-based skeleton,with the advantages of light weight,low cost,good flexibility and other advantages and has received wide spread attention.However,the surface inert carbon cloth has no kinetic regulation to the nucleation process of potassium,and has poor infiltration to molten potassium,so it is difficult to realize the uniform distribution of potassium in the skeleton.Therefore,surface modification of carbon cloth to achieve full infiltration of potassium is of great significance for the development of high-performance potassium metal anode.Based on the above analysis,in this paper,carbon cloth was selected as the skeleton,nano-metal oxides were modified on the three-dimensional carbon cloth skeleton by solution method,and the carbon-based potassium composite anode was obtained by potassium metal melting and infiltration,and the effect of metal oxide modified carbon cloth on the electrochemical performance of potassium composite anode was systematically studied.The specific research contents are as follows:(1)V2O5 nanofiber arrays were grown on the surface of carbon cloth by hydrothermal reaction and subsequent heat treatment,and CC@V@K composite anode was prepared by melting method on this basis.The reaction between V2O5 and molten potassium generates K2O,which provides a driving force for molten potassium to penetrate into the skeleton and realize the uniform distribution of potassium in CC@V2O5 skeleton.In addition,the high mechanical strength of skeleton can alleviate the volume expansion problem and ensure the integrity and stability of SEI film,thus improving the coulombic efficiency.Meanwhile,the high specific surface area of the threedimensional skeleton can effectively reduce the local current density and inhibit the dendrite growth,thus improving the cycle stability of the battery.Thanks to the advantages of the structure design,the CC@V@K symmetrical cell can cycle stably for 1200 h at a current density of 1 mAh cm-2,0.5 mA cm-2.The average coulombic efficiency of the half-cell assembled with CC@V2O5 skeleton as cathode and potassium plate as anode reaches 99.7%after 800 cycles.When CC@V@K and KVO were assembled into full cell,the capacity retention rate of the full cell was 85.1%after 200 cycles at a current density of 20 mA g-1,showing excellent cycle stability.(2)Cu-MOF precursors were modified on the surface of carbon cloth by solvothermal method with Cu(NO3)2 and H3BTC as solutes and ethanol as solvent,and CuO nanoparticles were grown in situ on the surface of carbon cloth after heat treatment.The uniform distribution of CuO nanoparticles promoted the uniform infiltration of molten potassium into the carbon cloth framework,so as to obtain a stable carbon-base potassium composite anode.CC@Cu skeleton can not only alleviate the volume expansion effect of potassium during the cycle,but also effectively reduce the local current density and inhibit the dendrite formation due to its high specific surface area.In addition,the excellent electrical conductivity and potassophilicity of the CC@Cu skeleton facilitate the rapid transport of electrons and ions.Thanks to the advantages of the CC@Cu skeleton,CC@Cu@K composite anode shows excellent cycle stability and rate performance in both symmetric and full cells.The CC@Cu@K symmetrical cell can cycle stably for 2000 h at a current density of 2 mAh cm-2,0.5 mA cm-2.Besides,a full cell assembled with the positive PTCDA/RGO electrode retains 80%of its capacity after 500 cycles.