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Synthesis And Performances Of LiMnPO4 As Cathode Materials For Li-ion Batteries

Posted on:2016-12-15Degree:MasterType:Thesis
Country:ChinaCandidate:Y L ShaFull Text:PDF
GTID:2321330464467502Subject:Applied Chemistry
Abstract/Summary:PDF Full Text Request
Li-ion batteries?LIBs?are attracting more and more attentions in terms of high energy/power density,environmental benignity and good safety.Comparied with LiFePO4,Li MnPO4 possesses a higher voltage plateau?4.1 V?and theoretical energy density,and hence is considered as a promising alternative.However,the low electronic conductivity(<10-1010 S cm-1)and Li+ion conductivity(10-7 cm2 s-1)seriously hamper its practical application.To overcome the shortcomings,great efforts focus on three issues:?i?adjusting particle size and morphology;?ii?doping with cations and/or anions;?iii?surface modification with high conductive materials.In this work,well-dispersed LiMnPO4 nanomaterial was synthesized using solvothermal method.Surface coating and dopping were further adopted to improve the electrochemical performances.X-ray diffraction?XRD?,scanning electron microscrope?SEM?,transmission electron microscope?TEM?,and energy dispersive spectroscope?EDS?were performed to characterize the composition,structure,and morphology.Galvanostatic charge-discharge,cyclic voltammetry?CV?,and electrochemical impedance spectroscope?EIS?were carried out to investigate the electrochemical performance.?1?Three strategies?solid-state method,sol-gel route,and solvothermal treatment?were used to fabricate LiMnPO4 nanomaterials.It showeded that obvious impurity existed in the product by solid-state method and was difficult to remove.The product from sol-gel method consisted of large microscale particles.By constrast,the sample derived from the solvothermal treatment was comprosed of uniform nanoparticles?50100 nm?.On this basis,the effects of Li:Mn:P ratios on the morphology and electrochemical performances were investigated.When the ratio was 2.5:1:1,the obtained LiMnPO4 nanoparticles exhibited good electrochemical performancewith an initial discharge capacity of 132.2mAh g-1??2?LiMnPO4 nanoparticles were further encapsulated by carbon nanolayers by a EG-assisted method to obtain ultrathin carbon coating LiMnPO4/C composites?ULMP/C?.The ULMP/C demonstrated much better cycling performances than pure LiMnPO4?LMP?and LiMnPO4/C?LMP/C?composites using the traditional hydrothermal coating.The initial discharge capacity of ULMP/C was 130.8 mAh g-1 and remained83%after 50 cycles.?3?LiMnxFe1-xPO4/C compound was synthesized using solvothermal method.The effect of different FeSO4 additionswas studied.It suggested that the product gain from Mn:Fe of 8?2.The initial discharge capacity was 123 mAh g-1 and kept 88%after 50 cycles.To sum up,the nanotechology,carbon coating,and Fe2+doping can effectively improve the lithium storage performance of LiMnPO4materials.
Keywords/Search Tags:lithium-ion battery, solvothermal, ultrathin carbon coating, LiMnPO4
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