Electrodeposition Of Ge Based Materials From Ionic Liquids And Their Electrochemical Properties

Germanium has a perfect electrochemical performance,which means that Ge may be an attractive electrode material for Li ion batteries.However,the large volumetric change for Ge results in cracking and pulverization of particles,which causes capacity reduction.Furthermore,all these reported Ge materials are synthesized using very expensive instrument and with environmental pollution.In this dissertation,to overcome the problems,we designed different morphological Ge materials that can buffer the volume change,including nanofilm,nanowire,Ge-Ni foam,Ge-Ni nanocone arrays,Ge/CNT,Ge/RGO and Ge/PEDOT.We prepared Ge materials by ionic liquid electrodeposition.Ge based materials synthesized using this method did not require any catalyst nanoparticles.Ionic liquid electrodeposition is a low energy processing method.As well all the materials gain from this method are binder free and electrochemically active.The improved cycle stability and rate performance characteristics make these anodes highly attractive for the most demanding Li-ion applications.The electrochemical performance of Ge and Ge composite materials were systematically investigated,and the related charge/discharge performance and morphology were discussed and analyzed.The main contents are summarized as following.Ge films can be prepared by ionic liquid electrodepositon at room temperture.3D ordered macroporous(3DOM)Ge films have been made by a simple method,which utilized self-assembled polystyrene colloidal crystals as templates.The 3DOM Ge films obtained from [EMIm]FAP are well-ordered.Water is an important factor to form the 3DOM structure,as with a little H2 O in electrodeposition process,we just can get 2D nano-architecture from [BMIm]TFSA.Ionic liquid electrodepositon compared with thermal evaporation method and solvothermal method,it does not require catalyst,which is a simple and green method for prepare semiconductor Ge elements.Porous Ge films were electrodeposited from ionic liquid by the potentiostatic method.The optimal electrolyte composition and process conditions were as follows: 1.5 mol/L Al Cl3 + 0.1 mol/L Ge Cl4/[EMIm]Tf2N solution,depostion potential of-1.3~-1.4 V,electrodeposition temperature of room tempreture or 60 oC.The nucleation mechanism of Ge4+ in 1.5 mol/L Al Cl3 + 0.1 mol/L Ge Cl4/[EMIm]Tf2N solution on Ni electrode was studied.Cyclic voltammetry and chronoamperometry showed that the deposition of Ge4+ was an irreversible electrode process controlled by the diffusion step and followed the mechanism of progressive nucleation and three-dimensional growth.During annealing followed with Lifshitz-Slyozov-Wagner theory(LSW),Ge nanoparticles agglomerated to porous inland.Finally,sticklike Ge nanowires covered on the surface of collector.The obtained Ge NWs can directly be used as the electrode.The Ge nanowires anodes retain capacities of 1200 m A h/g after 200 cycles at 0.1 C(1 C=1600 m Ah/g),with an initial Coulombic efficiency of 81.3%.The Ge nanowires exhibits a high capacity of 620 m A h/g at rate of 5 C.The electrochemical performance of Ge films anode materials prepared by ionic liquid electrodeposition on different 3D current collector has been studied.The electrochemical performance of all the 3D electrodes are better than that of 2D electrodes.The 3D Ni foam Ge exhibits a high capacity of up to 871 m Ah/g after 100 cycles at 0.1 C.Ultrathin and freestanding 3D Ge nickel nanocone arrays(NCAs)anode materials shows a better cycling capability of over 500 m Ah/g after 100 cycles.Even at 5 C the capacity of 3D Ge anode is above 200 m Ah/g,the capacity of 2D Ge anode is just about 100 m Ah/g.The preparation of 3D acetylene black/germanium materials is by the method of electrophoresis and ionic liquid electrodeposition.The carbon films are shown to provide a network structure that is not only highly conductive but also sufficiently flexible to accommodate the volume change in the Ge particles during Li insertion/extraction.This material exhibits a high capacity of up to 924 m Ah/g after 100 cycles at 0.1 C.The electrochemical performance of Ge composite materials(sush as Ge/CNT,Ge/RGO and Ge/PEDOT)prepared by ionic liquid electrodeposition has been studied.Ge/CNT materials exhibits a high capacity of up to 851 m Ah/g after 200 cycles at 0.1 C and a high rate capability at 5 C rates of 880 m Ah/g.The excellent electrochemical performance of the Ge/CNT sample is because the interconnected carbon nanotubes provide a network of electronic pathways,which could increase the reaction rate of lithium ion.The freestanding Ge/RGO anode exhibits a high capacity of up to 1213 m Ah/g after 200 cycles at 0.1 C and a high rate capability at 5 C rates of 540 m Ah/g.The excellent electrochemical performance of the Ge/RGO anode is because the RGO films provide a network of electronic pathways.Flower-like grading structure Ge/PEDOT electrode exhibits a high capacity of up to 1329 m Ah/g after 200 cycles at 0.1 C rate and a high rate capability of 1137 m Ah/g at 5 C rates.