| Lithium-ion batteries?LIBs?have the advantages of long cycle life,high safety and no memory effect,and are the most mature energy storage technologie.Currently,the graphite is a commonly used anode materials,but it has a theoretical capacity of only 372 mAh·g-1,which is difficult to meet to the growing demand for energy density and power density by social development.It is urgent to develop more negative electrode material with high specific capacity,stable cycle performance,and adapt to high current charging and discharging.Manganese-based oxides can be used as anode materials for lithium-ion batteries,and exhibit many advantages,such as abundant resources,high theoretical specific capacity,safety and reliability.So it has been favored by researchers in recent years.However,manganese-based oxides also have some disadvantages,such as poor conductivity and serious volume expansion.Focusing on related issues,this paper has carried out the following research.Firstly,the MnO2 nanotubes were synthesized by hydrothermal method,and the C/MnO composites were prepared by liquid phase deposition combined with carbon source aniline.The structure,morphology and composition of the materials were analyzed by X-ray diffraction?XRD?,scanning electron microscopy?SEM?,transmission electron microscopy?TEM?and thermos gravimetric analysis?TGA?.The results show that the synthesized C/MnO composite is a rod-like core structure,consisting of the carbon shell and MnO core,and the mass fraction of the active material MnO is 85.4%.It was assembled into a button battery to study its cycle performance and rate performance.At a current density of 100 mA·g-1,after 100 cycles,the discharge specific capacity was maintained at 943.6 mAh·g-1,and its cycle retention rate is83.6%.when the current density is increased to 4000 mA·g-1,it can still exhibit a discharge capacity of 484 mAh·g-1.Furthermore,carbon source?glucose?and manganese source Mn?NO3?2 were directly hydrothermally reacted under alkaline conditions to synthesize the composite material,which contained the carbon material innerlocked with the MnOx particles.Then,the carbon source and the manganese source are changed,and five composite materials were synthesized.XRD results show that manganese is present in various manganese-based oxides in five composites.SEM observation shows that the morphology of the composites varies with the mass ratio of carbon source to manganese source.When the mass ratio of carbon source to manganese source is 3:1,C/MnOx-3 composite has a spherical morphology and uniform particle size.The TGA test shows that the carbon content of the five composite materials relates to the mass of carbon source.with the increase of mass ratio of carbon source and manganese source,the carbon content of C/MnOx is gradually increasing.The five composite materials were assembled into lithium half-cells.The electrochemical test results showed that the C/MnOx-3 composites with the best morphology and carbon content?25.8%?had the best cycle performance,at current density of 100 mA·g-1,a maximum discharge capacity of 1034.42 mAh·g-1 can be exhibited.In addition,a new method for electrode preparation of LIBs was further explored.The traditional method is to mix the binder into the electrode material.In contrast,in this study,the polyvinylidene fluoride?PVDF?is dissolved in NMP to obtain different concentrations solution.Then,added them to the surface of MnO2 electrode.The protective film is formed on the surface of MnO2.The electrodes with different thickness protective film were made into batteries.The charge-discharge test showed that when the PVDF concentration was between 20-40 mg·mL-1,the cycle retention rate of the battery was ideal;after 100 cycles,the discharge capacities were329.1,297.1 and 291 mAh·g-1,respectively,which were 248%,223%and 219%of the conventional electrode preparation methods.And more,when an equal amount of PVDF is used,the electrode prepared with multilayer films is less desirable than the single layer film in the cycle test. |
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