Preparation And Electrochemical Properties Of Manganese-based Materials And Their Composites

Lithium-ion batteries(LIBs) have been widely used as high-tech and highvalue-added products because of their high voltage, high specific capacity, highsecurity, low self-discharge, discharge stable, long repeat service life, no memoryeffect and environmentally benign features, etc. Nowadays, commercial lithium-ionbattery mainly use commercial graphite as anode materials owing to its strongconductivity, structural stability and low intercalation potential. However, lithium ionsare easily deposited on the negative electrode to generate lithium dendrites during thelithium insertion/extraction process, resulting in potential safety hazard. Furthermore,the specific capacity of commercial graphite electrodes is low. Therefore, it isimportant to find an anode materials with large-specific capacity and safetyperformance. Among them, MnO has attracted more and more attention recentlyowing to its high theoretical capacity, low voltage hysteresis, abundant, raw materialscheap, etc. However, the practical use of this material in LIBs has been seriouslyfrustrated due to their poor conductivity and severe pulverization caused by the drasticvolume variation during the process of charge/discharge. In addition, high theoreticalspecific capacity of MnO has never been achieved in practice. In this paper, weprepare manganese-based and graphene oxide composite material as electrodematerials to improve the cycle stability and rate properties. The main work is asfollows:(1) Novel composite of bi-component MnO/ZnO (denoted as MZO) hollowmicrospheres embedded in reduced graphene oxide (RGO) as a high performanceelectrode material for Lithium ion batteries (LIBs) is prepared via one-pothydrothermal method and subsequent annealing. The structures and morphologies ofas-prepared hybrid materials are characterized by X-ray diffraction, scanning electronmicroscopy, Raman spectra, FTIR and transmission electron microscopy. The resultsreveal that the MZO hollow microspheres with nanometer-sized building blocks arewell dispersed in the RGO support. The electrochemical tests show that the hybridmaterial has a reversible capacity of660mAh/g at a current density of100mA/g witha coulombic efficiency of98%after100cycles. Besides, a specific capacity of about207mAh/g is retained even at a current density as high as1600mA/g, exhibiting highreversibility and good capacity retention. Our results suggest that the composite ofbi-component MZO hollow microspheres embedded in RGO will be promising electrode materials for low-cost, environmentally friendly and high-performanceLIBs.(2) A simple co-precipitation method and post-annealing process are used toprepare composite material of RGO sheets and polyhedral MnO nanoparticles(p-MnO/RGO). The structure, morphology and composition of the p-MnO/RGO areanalysed. When evaluated as an anode material for LIBs, the p-MnO/RGO compositeexhibits a high specific discharge capacity, good rate capability and excellent cyclingstability at a current density of100mA/g. Besides, a specific capacity of about509mA h/g is obtained even at a current density as high as1600mA/g. The superiorelectrochemical performance is attributed to the robust composite structures, largequantity of accessible active sites, and synergistic effects between polyhedral MnOnanocrystals and RGO.