Preparation And Lithium Batteries Properties Of Manganese Oxide/Carbon Composites

Due to the limited specific capacity of conventional graphite anodes(372 mA h g^-1,the specific energy of conventional lithium-ion batteries is insufficient to meet the growing needs of society.Manganese-based oxides have attracted widespread attention due to their small voltage hysteresis,high theoretical specific capacity,and abundant reserves.However,its own poor conductivity,volume expansion and other defects will cause declination of battery performance in the actual applications.In order to solve this problem,a common strategy is to combine with carbon materials to prepare manganese-based oxides/carbon composites with different structures or crystal forms.In this study,cobalt-manganese oxide/carbon?MnCo₂O₄/C?composite samples with different morphology and structure,and amorphous manganese-base oxide/reductive graphene oxide?A-MnO_x/rGo?composite samples were prepared.The morphology of sample was analyzed by scanning electron microscope?SEM?and transmission electron microscope?TEM?.The structure of samples was tested with X-ray Diffraction?XRD?,X-ray photoelectron spectroscopy?XPS?and so on.The lithium-ion performance of the samples was also tested.The specific research contents and results are as follows:?1?The Mn-Co-C precursors were synthesized by a hydrothermal method using glucose,C₄H₆MnO₄·4H₂O and C₄H₆CoO₄·4H₂O as raw materials,and MnCo₂O₄/C composites with multilayer core-shell-like structure were obtained by subsequent high-temperature calcination.In this paper,the morphology and lithium properties of MnCo₂O₄/C samples prepared with different calcination temperatures were systematically explored,and experimental results show that the MnCo₂O₄/C-600 sample obtained via 600?calcination has the best lithium batteries performance.The initial discharge capacity of the first cycle at 1A g^-1 is 1001.6 mA h g^-1,and Coulomb efficiency is about 78.4%.The discharge capacity after 800 cycles still maintains at 978 mA h g^-1.Its excellent electrochemical properties can be attributed to the well-designed three-dimensional structure and good electrical conductivity.?2?Graphene oxide was synthesized by a modified Hummers method,and the amorphous manganese-base oxide?A-MnOx?was in-situ reduced on graphene layer with a chemical reduction method by using KMnO4 and oxalic acid as raw materials.This excellent structure can effectively relieve the volume change in the process of stripping lithium and also improve the conductivity of the material.The influence of graphene and crystallization on the electrochemical properties was investigated systematically.Results show that A-MnOx/rGo shows a better electrochemical property compared to the manganese oxide crystals.The initial capacity of the first cycle is 390 mA h g-1 at current density of 1A g-1,and the capacity increases gradually with cycling.After 500 cycles,the capacity increases to 800 mA h g-1 and the Coulomb efficiency close to 100%.Meanwhile,the A-MnOx/rGo presents a better Li-ion dynamic character compared to the samples without graphene.