Preparation And Electrochemical Properties Of Manganese-based Electrode Materials

Lithium-ion battery has experienced a long evolution since its discovery.In recent years,with the rapid development of technology and society,people put forward higher requirements on the performance of lithium-ion battery.Among these,high power density and energy density cause the attention of researchers particularly.At present,the commercial lithium-ion battery based on graphite anode and lithium cobaltate cathode suffers from serious problems of low energy density,it is therefore urgent and important to develop a next-generation lithium-ion battery electrode materials.Owing to the natural abundance,environmental friendliness,low cost and a high theoretical capacity,manganese oxides have been received great attention.However,there are some disadvantages in the process of lithium-ion storage,such as poor conductivity and volume expansion.In this paper,to address the problems of poor conductivity and volume expansion of manganese oxides,a novel technique of in situ carbon coating technology is developed to improve the cycle stability and rate performance.First of all,manganese dioxides were synthesized using a simple hydrothermal method.Then MnO₂/PPy intermediates were obtained via in situ interfacial polymerization.MnO/C nanocomposites were finally received after carbonization.X-ray diffraction,raman spectroscopy,thermogrammetric analyzer,X-ray photoelectron energy spectra,field emission scanning electron microscope and high resolution transmission electron microscope were used to characterize the chemical composition and microstructure.Cyclic voltammetry,galvanostatic charge-discharge and electrochemical impedance spectrum were employed to investigate the Li-ion storage performance.The main results include:?1?The MnO/C nanowire shows a distinct morphology of "bead chain" structure.When used as anode,the nanowire delivers a reversible specific capacity of 754 mAh g-1 at a current density of 100 mA g-1,and retains at 903 mAh g-1 after 100 cycles,indicating excellent cycling stability.The anode material still shows a reversible capacity of 521 mAh g-1 even at a high current density of 2000 mA g-1.In addition,the MnO/C anode exhibits good cycling stability and recoverability at different cut-off voltages,holding great promise in practical application of lithium-ion batteries.?2?Freestanding membranes consisting of ultralong MnO/C coaxial nanowires have successfully been fabricated using a hydrothermal method followed by in situ interfacial polymerization of PPy and a carbonization.When used as anode,the freestanding membrane MnO/C prepated at 600 oC shows the best Li-ion storage properties,including a first charge specific capacity of 683 mAh g-1 and a first discharge specific capacity of 1001 mAh g-1 at the current density of 100 mA g-1.More significantly,even after a long-term 600-cycle test at a high current rate of 1000 mA g-1,the anode retains a reversible capacity of 480 mA h g-1.?3?LiMn₂O₄ nanocrystalline particles was synthesized using a conventional solid state sintering.The products prepared at 750 oC shows the best electrochemical properties,including a high reversible specific capacity of 109 mAh g-1 at 100 mA g-1.The LiMn₂O₄ cathode was coupled with the afore-prepared MnO/C anode to constitue an all-manganese-based lithium ion batteries.The as-assembled LiMn₂O₄||MnO/C full battery exhibits excellent cycling performance with a capacity retention of 87 mAh g-1 at 200 mA g-1 after 1000 cycles.The results indicate that the new battery system manifests great potential application as a high-performance energy storage technology.