| Lithium ion battery as a green energy storage device,having the advantages of high energy density,low self discharge,no memory effect,and long life,is widely used in portable electronic products,has a wide application prospect in the field of electric vehicles and other energy.Currently commercial lithium-ion battery carbon anode material has a low theoretical specific capacity,only 372 mAh g-1,which can not meet the demand of high performance lithium ion batteries.Metal Al and Si are abundant in nature and and have the high theoretical specific capacities of 2234 mAh g-1 and 4200 mAh g-1,respectively.However,in the process of intercalation/deintercalationof lithium ions both of Al and Si will produce a huge volume expansion,which results in the destruction of electrode’s structure and rapid decline in capacity.In this paper,the electrochemical performances of Al and Si electrodeshave been improved by astrategyof alloying and further pickling.Using micron-sized Al and Fe powders as the raw materials,methane(CH4)as the carbon source,Al-Fe/C composite nanopowderswereprepared through DC arc-discharge method.Characterization on the powders were carried out by means of XRD,XRF,TEM,elemental analysis,etc.It is indicated that the Al-Fe nanoparticles prepared in a carbon-free atmosphere are spherical in shapes,meanwhile,the carbon-containing atmosphere caused the nanoparticles columnar or chain-like in their morphologies as well,the compositions changed from Al4C3,FeAl2,and Fe2Al5 carbides in Al-Fe/C nanocomposite powders.The first discharge capacities of four kinds of nanoparticles’ electrodes were 348.8,193.3,275.5 and 628.8mAhg-1,at the current density of 100mAg-1,respectively.The presence of intermetallic Fe2Al5 in the powdersfavors to improvethe capacities and restrains the volume changes during the intercalation/deintercalation of lithium ions,thus the cycle stability of electrode has been greatly enhanced.To further improve the electrochemical performances of Al electrodes,Al-Si composite nanomaterialswerealso prepared by the DC arc-discharge method.XRD analysis revealed that Al and Si coexisted as an eutectic and no new alloy phases were formed.TEM analysis showed that the Al-Si composite nanoparticles were in irregular spherical shapes.The first discharge capacities of Al-Si nanopowders electrodes with mass ratios of Al:Si=8:2,Al:Si=7:3,Al:Si=6:4(wt.%)were 1573.4,2351 and 2936.1mAh g-1,respectively,at the current density of 100mAg-1.After 50 cycles,the capacitiesbecome 205.2,214.3 and 251.9mAh g-1,correspondingly.The electrochemical performance of Al-Si composite electrode has been greatly improved in comparision with that of Al-Fe/C nanocomposite,due to the contribution from active silicon.To further improve the cycling performance of Al-Si nanomaterialselectrode,the active component of nanopowders(Al:Si=6:4 in mass ratio)was treated with 8wt.% dilute hydrochloric acid to form the porous Si structure,through removing of the metal Al phase.It wasconfirmed by XRD and TEM analysis that the metallic Al was completely removed,a loose porous structurewas formed.The porous Si nanomaterial was used to fabricate an composite electrode,which exhibited the first discharge capacityof 3661 mAh g-1 at 100mAg-1current density,and 437 mAh g-1 after 50 cycles with Coulomb efficiency of 79.1%. |
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