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Manganese Compounds Composited With Graphene For Electrochemical Energy Storage

Posted on:2018-06-24Degree:MasterType:Thesis
Country:ChinaCandidate:B L LiuFull Text:PDF
GTID:2322330533457840Subject:Electronic Science and Technology
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Most of metal oxides/sulfides are important semiconductor materials.Generally,they have relatively wide energy gap and low electronic conductivity.They have been widely applied in many fields due to their special thermal,electrical and magnetic properties.Many metal oxides/sulfides can reversibly storage lithium ion and act as anode materials of lithium ion batteries(LIBs),and their theoretical capacity of metal oxides/sulfides is 2~3 times higher than traditional graphite anode.Moreover,they are abundant,cheap and facile preparation,have become the potential candidate of anode materials for the new generation LIBs.However,the huge volume changes in lithiation and delithiation process lead the loss of active materials,which induce the capacity fade of lithium ion battery.This thesis mainly focuses on manganese compounds.In order to improve their electrochemical performance when acted as anode materials of lithium ion batteries,we prepared MnO/rGO and MnS/rGO nano-composites and systematically studied their electrochemical performance.Nano-composites not only shorten Li+ transport distance in active materials,suppress the active materials agglomeration,alleviate the stress derived from huge volume changes of active materials,and also improve the electrode electrical conductivity,and maintain the electrode integrity,ultimately,improve the electrode cycle stability.The main research contents and conclusions are as follows:1.Fabrication of the composites of carbon-wrapped MnO nanodendrites and rGO(C-MnO/rGO)and used as an anode for LIBs.Different mass ratios of C-MnO/rGO composites were prepared on nickel foam by a facile vacuum filtration and a subsequent thermal treatment.As a binder-free anode of lithium ion battery,components optimized C-MnO/rGO composites(quality ratio of precursors for MnO2 and GO is 3:1)have excellent rate capability,which show discharge capacities of 930.3,799.3,646.9,513.0,360.3,and138.9 mAh g-1 at current densities of 100,200,500,1000,2000,and 5000 mA g-1,respectively,and finally recovers to 1357.8 mAh g-1 when the current density goes back to 100 mA g-1.It still maintains reversible capacity of 577.8 mAh g-1 at 1000 mA g-1 after 250 cycles.In addition,The MnO nanodendrites become much smaller nanoparticles embeded in graphene sheets after several lithiation/delithiation cycles,which is beneficial to further increasing specific capacity and life span of the electrode.2.Preparation of the composits of nanoscale ?-MnS particles/nitrogen and sulfur co-doped rGO(NSG)(?-MnS/NSG)for long-life lithium-ion batteries.The honeycomb ?-MnS/NSG composites were prepared by one pot hydrothermal synthesis and a heat treatment process.?-MnS/NSG anodes show excellent cyclability,which keep a high capacity of 763.5mAh g-1 at a current density of 100 mA g-1 after 100 cycles and a reversible capacity of 576.7 mAh g-1 at 1000 mA g-1 after 2000 cycles.More interestingly,the ?-MnS/NSG electrodes also display superior cyclability(450 cycles)at an asymmetrical charge/discharge current density.Furthermore,nanoscale ?-MnS become ultrafine MnS particles embeded in NSG framework during the charge/discharge process,which not only endow the good electronic contact,but also provide more active sites reaction,and further enhance electrochemical performance.
Keywords/Search Tags:Lithium ion battery, manganese oxide, manganese sulfide, reduced graphene oxide, structural stability
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