Synthesis Of Multicomponent Transition Metal Compound/Carbon Composites And Their Application As Anode Materials For Lithium-Ion Batteries

Environmental pressure and energy demand are increasing day by day in this world.Over the past centuries,fossil fuels which provide the power for human progress and development are dried up gradually.In addition,the exploitation and use of such non-renewable energy resources have caused a lot of irreversible damage to the earth's ecological environment.These problems are constantly pushing us to speed up for the development and promotion of clean renewable energy at a low cost and high efficiency.We are already in the era of new energy development.However,these new energy sources may be limited to different degrees by factors such as time and space.Therefore,in view of the efficient use of energy,efficient energy storage is no less important than energy development,which forces us to find a suitable energy storage device to meet their further development.Lithium-ion batteries?LIBs?have become a research hotspot for their long life cycle,high specific energy density and operating voltage than other storage devices.Because of the high theoretical lithium storage capacity,transition metal compounds have been widely used in the research of anode materials for LIBs.However,due to the low conductivity of metal compounds,and the serious volume strain and agglomeration effect during the process of intercalation and deintercalation,which reduces the contact area between electrolyte and electrode materials and the electrochemical activity of active materials,resulting in the degradation of the cycling and rate performance of metal compounds.Therefore,we design the corresponding improvement experiments,to a certain extent,to solve the shortcomings of the transition metal compounds as anode materials,and the cycling and rate performance of the electrode are improved.The main research contents are as follows:?1?ZnCo₂O₄/ZnO/carbon nanotubes?ZZCO/CNTs?nanocomposites are rapidly synthesized under microwave irradiation followed by annealing.The compounds are composed of ZnCo₂O₄/ZnO?ZZCO?nanocrystals?⁵ nm?coated on the ektexine of carbon nanotubes?CNTs?,and the introduction of CNTs can greatly improve the conductivity and stability of the hybrid material and effectively prevent the aggregation of ZZCO nanoparticles.When considered as anode material for LIBs,the as-synthesized ZZCO/CNTs nanocomposites exhibit a high reversible specific capacity of around 1433.0 mAh/g at 100 mA/g,great cycling stability up to 200cycles at a high current density of 500 mA/g,and superior rate performance.The outstanding performance of lithium storage is mainly attributed to the small size effect of ZZCO and the excellent electrochemical properties of CNTs.?2?The compounds of MnCo₂O₄/MnO₂/carbon nanotubes?MMCO/CNTs?are synthesized by hydrothermal method.The composites are composed of multiwalled carbon nanotubes and petal-like MnCo₂O₄/MnO₂?MMCO?nanosheets?5-8 nm in thickness;⁷5 nm in length?standing up and closely growing on the CNTs.Then the as-prepared MMCO/CNTs nanocomposites are made into the negative electrode for LIBs.The testing result shows that the intial discharing capacity is 1858.2 mAh/g at100 mA/g,and up to 100 cycles the capacity can still maintain at 1346.0 mAh/g.Meanwhile,superior capacity retention is exhibited,where the reversible capacity only slightly decays at different rates.When the current density restores to 100 mA/g after different high rates,the discharge specific capacity can finally reach to 1350.6mAh/g.And the MMCO/CNTs electrodes deliver a stable capacity up to 935.0 mAh/g after 500 cycles at 1600 mA/g.The enhanced electrochemical performance of MMCO/CNTs electrodes results from its unique structure,which accelerates the charge transfer rate and alleviates the volume change.?3?Core-shell porous Co₃S₄/Fe₃O₄/carbon?CoFe/C?nanocubes are synthesized by means of combination of precipitation and hydrothermal methods.These cubes with a side length of around 350 nm are composed of Co₃S₄/Fe₃O₄ nanocube and carbon cladding layer of about 50 nm in thickness.The existence of carbon shell not only enhances the electronic conductivity of the material,but also improves the structural strength of the cube.When exploring the CoFe/C as the anode material of LIBs for lithium storage test,galvanostatic charge-discharge test at 100 mA/g shows that the anodes deliver reversible capacity of 1124.2 mAh/g.And after testing at different current densities,back to 100 mA/g,the specific capacity can still achieve1125.4 mAh/g.The enhanced electrochemical performance of the CoFe/C electrode materials are significantly improved,compared to the pure CoFe,due to the carbon shell and porous material structure.