Research On The Novel Anode Materials For Lithium Ion Batteries

Rechargeable lithium ion batteries （LIBs）, which have been widely used in portableelectronics such as cell phones, laptop computers, digital cameras, etc., are believed to bepromising choices as energy-effective and environmentally friendly devices. The energydensities and performances of LIBs largely depend on the physical and chemical properties ofthe electrode materials. Thus, many research attempts have been made to design novelnanostructures and to explore new electrode materials. Graphene-based composites haveattracted special attention as high-capacity anode materials in LIBs.In the present work, graphene-based nanomaterials were synthesized through the modifiedHummers method, followed by the solid-phase method, liquid phase method, andmicrowave-assisted synthesis, respectively, including AB5-alloy oxide/graphene compositeand mesoporous SnO₂-graphene composite. The investigations of morphology andmicrostructure were performed by field emission scanning electron microscopy （FE-SEM）,transmission electron microscopy （TEM）, atomic force microscopy （AFM）, X-ray diffraction（XRD）, Infra-red spectrum（FT-IR）, Raman spectrum （Raman）, Thermogravimetricsanalysis（TGA）, energy-dispersive X-ray spectroscopy （EDS）, Brunauer-Emmett-Tellerspecific surface areas（BET）. The as-synthesized materials were used as anode for lithium ionbatteries. The electrochemical performances were evaluated through electrochemicalimpedance spectroscopy, cyclic voltammetry and constant current charge-discharge. Theas-synthesized materials exhibited excellent electrochemical performances, and the resultsshow that the unique graphene-contained composites are flexible enough to act as a buffer toaccommodate the strain associated with the volume variations of active material, prevents theagglomeration of pulverized active material and provides good electronic contact, thusextending the cycling life of the electrode. Details as below:（1） As SEM and TEM images shown that graphene displays a typical crinkly and rippledstructure, in which the ultrathin wrinkled structure represents a curled and corrugatedmorphology that graphene possesses intrinsically. The prepared graphene exhibits an initialdischarge capacity of1474.4mAh g^-1with a Coulombic efficiency of32.4%. After20cycles,the reversible capacity is still maintained at271.6mAh g^-1. （2） A novel AB5-alloy oxide/graphene nanocomposite was firstly fabricated through a facilemixing of commercially available oxidized AB5-alloy. Electrochemical measurements showthat the prepared composite anode exhibits an initial discharge capacity of1639.7mAh g^-1and maintains a high reversible capacity of418.2mAh g^-1up to180cycles with an averagecoulombic efficiency above98%.（3） AB5-alloy oxide nanoparticles are distributed randomly on the surface and edges of thegraphene. As anode material for lithium ion batteries, the composite exhibits enhancedelectrochemical lithium storage properties with the initial discharge and charge capacity of1520.4and1046.6mAh g^-1. In particular, at the higher current density (750mA g^-1), thereversible capacity of AB5-alloy oxide/graphene composite is still as high as377.9mAh g^-1.Remarkably, the reversible specific capacity of AB5-alloy oxide/graphene composite beginsincreasing from the80thcycle and reach to864.9mAh g^-1in the130thcycle, indicating moreevident the capacity retention and good cycling stability of this composite material.（4） Mesoporous SnO₂-graphene composite with a high specific surface area has beenprepared by an easy microwave-assisted synthesis. The well-dispersed SnO₂nanocrystals witha uniform particle size of3-5nm are homogeneously distributed on the surface of graphene.The as-synthesized SnO₂-graphene composite exhibits a high specific surface area (280.7m2g^-1). In comparison to bare SnO₂nanoparticles, the composite shows substantial enhancementin electrochemical lithium storage properties. More strikingly, the as-synthesizedSnO₂-graphene composite anode could deliver initial discharge and charge capacities of2445.7and1329.4mAh g^-1with a high initial Coulombic efficiency （54.4%）, as well as anexcellent cycling stability.