| Lithium ion battery have the advantages of green,environmental,recyclable and so on.However,the electronic equipments require high capacity and protable in our life and the traditional graphite lithium ion batteries can not meet the requests.So more researcher have been widely study for the high capacity and electric conduction materials.GeO2,as a promising anode material for lithium ion batteries because of their high specific capacity,low operating voltage and fast Li+ diffusion.However,the design of GeO2 based anodes with satisfactory cycling ability and high capacity still presents a big challenge because of strict requirements in the need for a special type of solvent,a complicated preparation process,high energy and material costs,and/or difficulty in process upscaling.In this article,the GeO2 was used as anode material,we through a lot of methods to change the structure and morphology of the GeO2,dispersed nano-GeO2 particles load on the reduced graphene oxide surface,and change space of GeO2 via Kirkendall Effect.The detail results are as follows:First,in this work,porous nano-structured GeO2 has been successfully synthesized by a hydrothermal deposition and low temperature annealing method.The sample exhibits high specific capacity and excellent rate capacity.Porous nano-structured GeO2 showed a higher storage capacity of 1000 m Ahg-1 after 10 cycles at a current of 0.1 Ag-1 and a flat capacity plot remained above 500 m Ahg-1 even after 100 cycles at 1 Ag-1.The good electrochemical performance is attributed to the superior porous nano-structure of GeO2,which can provide a high specific surface area and a large number of channels for Li+ transportation,and mitigation of huge volume variation during discharge/charge processNext,GeO2/RGO nanocomposite is successfully synthesized as an anode material by a simple,green and in-situ reactive method,which stacked the GeO2 nanoparticles directly on the reduced graphene oxide sheets in an in situ process.The sample exhibits high specific capacity and enhanced rate capacity as an electrode material for lithium ion batteries.GeO2/RGO nanocomposite shows a higher storage capacity of 1020.4 mAhg-1(theoretical capacity 1125 mAhg-1)after 30 cycles with a current density of 0.1 Ag-1,and a long-term cycle capacity of 464 mAhg-1 even after 100 cycles at 1 Ag-1.This good electrochemical performance is due to the superior properties of non-aggregated graphene sheets and homogeneously dispersed GeO2 nanoparticles in GeO2/RGO nanocomposite,and the RGO in hybrid materials not only could buffer drastic volume change upon Li+ insertion/extraction matrix,but also as electrically conductive additives to improve the electrochemical performance.Finally,the germanium dioxide(GeO2),undergo an irreversible conversion reaction in discharge/charge process.This restricts the maximum capacity of such batteries to 1126 m Ahg-1(the equivalent of storing 4.4 Li+).However,it should be noted that the theoretical capacity of GeO2 based on the theoretical maximum(8.4 Li/Ge)is 2152 m Ahg-1 if the first step is reversible reaction in GeO2 lithium ion battery and the GeO2 can be reoxidized completely according to the reversible reaction.In this work,porous GeO2/Ge nanostructures(GeO2 in the outer part and Ge in the inner part)were successfully fabricated and used as a lithium-ion battery anode,giving a high capacity of 1333.5 mAhg-1 at a current density of 0.1 Ag-1 after 30 cycles and a stable long-time cycle performance after 100 cycles at a current density of 0.5 Ag-1.We relate the excellent battery performance to the unique GeO2/Ge nanostructure fabricated via a novel process utilizing the Kirkendall effect and the accompanying presence of Ge as the catalyst.This GeO2/Ge nanostructure with an extra metal component to promote the kinetics of conversion reaction,in which the elemental Ge co-existing with GeO2 act as an electrocatalyst for Li2O decomposition and provide a conductive network for electron transport between metal and Li2O to facilitate the reoxidation reaction. |
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