Electrodeposition Of Gallium,Silicon Nanoparticles And Germanium Nanostructures From Ionic Liquids And Their Applications In Lithium-ion Batteries

Lithium ion batteries have become the most important power supply of energy for portable equipment and industrial energy storage systems because of long cycle life,low self-discharge rate and high working voltage.As graphite has a low reversible capacity of only 372 mAh/g,it is challenging to meet the needs of mobile devices in the future.There is a world-wide interest in developing high capacity lithium alloy anodes using materials such as Ga,Si and Ge to replace graphite.However,the common disadvantages of these electrode materials are pulverization and cracking caused by huge volume expansion during Li insertion/deinsertion,which affects the performance of the battery.Therefore,based on the above strategies,two experimental equipment were designed,and Ga,Si nanoparticles and Ge nanowires were prepared.The growth mechanism and the lithium ion battery performance of these nanomaterials were studied.A set of equipment for pulsed laser assisted ionic liquid electrodeposition of nanomaterials at room temperature was designed.It is found that laser irradiation can slow down the decomposition of[EMIm]⁺cations of[EMIm]Tf₂N ionic liquids.Laser irradiation also affects the reaction process between Ga and Si on the electrode surface,making the reduction peak potential positive shifted in CV curve,and the increase of reduction peak current.The shift of peak is due to the thermal effect of laser.Ga nanospheres and Si clusters were prepared.The laser irradiation makes the diameter of Ga nanospheres more than 1000 nm,and showed a cluster state and an upright growth trend.The surface morphology of Si deposits changed coarsely and granularity compared with those without laser irradiation.The influence of laser irradiation on the morphology of deposits has been studied.It is found that the thermal effect of laser enhanced the uneven discharge of ions during the deposition process,and changed the morphology of deposits obviously.Ge nanostructures with different morphologies were prepared by pulsed laser assisted ionic liquid electrodeposition.When the laser energy increased from 30 to 50 mJ/pulse,the deposits changed from nanoparticles to nanowire structures.When the laser energy was 60mJ/pulse,the growth of small branches on the trunk of nanowires is achieved.The deposits transformed from amorphous films in the absence of laser irradiation to polycrystalline nanowires under laser irradiation.The Ge nanowire anode deposited on Cu had an initial discharge and charge capacity of 1646 and 1278 mAh/g,and retained a charge capacity of884 mAh/g after 50 cycles at 0.2 C.Moreover,the Ge nanowire showed good rate capability performance,and the charge capacity was 730 mAh/g cycled at 2 C.The Ge branched nanostructures were prepared.When the laser energy increased from 70 to 90mJ/pulse,the deposits grow from a partially branched nanostructure to a uniform branched nanostructure.Ga-doped Ge?Ge-Ga?nanowires array anodes have been prepared at a low temperature?60°C?via a two-step ionic liquid electrodeposition.The nanowires with diameters ranging from 100²00 nm,most of the nanowires are kinked and taper significantly along the axial direction.When the nanowires were deposited on Cu substrates,nanowire arrays with finer and more uniform size distribution were obtained,which could be directly used as anode materials for lithium ion batteries.The Ge-Ga nanowire arrays anode has an initial discharge and charge capacity of 1730 and 1537mAh/g,and retains a discharge capacity of 1146 m Ah/g after 150 cycles at 0.32 A/g,with a coulombic efficiency in excess of 95%after the second cycle.Even at a current density of16 A/g,it still delivers a capacity of 574 mAh/g.The higher cycling stability and rate capability can be attributed to the formation of a porous network structure during the charge/discharge process.