Study On The Preparation And Performance Of Electrode Materials For Lithium Secondary Batteries Based On Carbon Materials

With the development of the protable instruments and electronic cars,it has a high requirement on the power density and energy density of the energy storage devices.Li secondary batteries are regarded as the most potentials ones,which include Lithium-ion batteries?LIBS?,Lithium-sulfur batterries?Li-S batteries?and Li-O2 batteries.The commercial LIBs,which use carbon materials as the anode,can not meet the demands of high power devices due to its low power density.It is the key to develop new electrodes to resolve this problem.Fe₂O₃,as one of promising LIBs anode materials,shows high theoretical capacity,environmental friendly and ease of the morphology and structure control.However,the low conductivity and pulverization restrict its partical applications.To solve these problems,we prepared porous Fe₂O₃ nanosheets on conductive carbon cloth by the electrodeposition methods.The strong interaction between the Fe₂O₃ nanosheets and carbon fiber not only reduces the charge transfer resistance,but also improve the structural integrity of electrode.Meanwhile,the ?-Fe₂O₃ nanosheets with tremendous meso-porous faciliate the ion transport,leading the composites to exhibit excellent electrochemical performance.By contrasting the electrodes with different Fe₂O₃ mass loading,we found that the Fe₂O₃@CC electrode which is prepared with deposition time of 4 hours show best performance.The capacity is 2970 mAh g-1 at 0.1 A g-1,and the retention is 85%after 60 cycles.As the current density increases to 10 A g-1,it still remains at 567 mAh g-1.Futhermore,the ratio of the capacity reaches 92%of its initial value,when the density is restored to 0.1 A g-1.Li-S batteries is considersed to be one of the most promising energy storage devices owing to their high specific capacity and energy density.Futhermore,sulfur is naturally abundant,low cost and environmental friendlly.However,utilization of Li-S batteries is still hindered for some problems,including the low conductivity,shuttle effect and volume expansion.To overcome the drawbacks of sulfur cathode,including the poor conductivity and the soluble intermediate products,we use mesoporous carbon CMK-5 to load S.Then we use the melt-diffusion method to combine CMK-5 and sulfur.Through hydrothermal method,the composite was coated by reduced graphene oxide?rGO?later.The rich channel structure provides a high specific area and suitable pore volume,which is benefit for the storage of sulfur and the electron and ion transpotation.Simultaneously,CMK-5 and rGO could enhance the conductivity of sulfur and restrain the shuttle effect,leading to higher capacity and better cycle performance.When the sulfur content is 68 wt%,the composite shows a superior performance.Discharge capacity reaches 1304.9 mAh g-1 at 0.1 C,and maintains 591 mAh g-1 after 50 cycles.The electrode material coated by rGO presents a capacity of 1169.3 mAh g-1 at 0.5 C,and remains at 608.5 mAh g-1 after 50 cycles,which demonstrates that rGO is able to improve the electrochemical performance of CMK-5@S.