Sythesis Of 2D LiFePO₄ Nanosheets And Its Research On Electrochemical Properties

Energy is the lifeblood of the society,which tremendously promote the development of the economy.However,the energy crisis has been triggered by the overuse of oil,coal and other non-renewable energy,along with the serious environmental problems.It is urgently to develop renewable energy sources to solve the aforementioned problems.Among them,the development of new renewable clean energy such as wind energy,solar energy and tidal energy will inject new vitality into the energy field and become the main candidates to replace traditional energy.However,the characteristic of discontinuity obstructed their further applications.Hence,the development of energy storage device was the key factor to promote the energy utilization.Lithium-ion batteries are the most promising power supply system which could provide high operating voltage and energy density thus was being expected to be used for large-scale energy storage and battery storage for electric vehicles and plug-in hybrid vehicles.At present,commercial lithium ion battery cathode material is mainly LiCoO₂,but this material with too many defects,such as expensive,poor safety and so on.Compared with LiCoO₂,LiFePO₄ has become one of the most popular cathode materials due to its low raw material price,high theoretical capacity,good chemical stability,thermal stability and environmental friendliness.However,due to its own crystal structure constraints,its electronic conductivity and ionic conductivity is poor,which are the main factors that prevent the LiFePO₄ material to be used widely in power and energy storage areas.In this thesis,we used FeSO₄·7H₂O,H₃PO₄,and LiOH·H₂O to prepare the Lithium iron phosphate through the solvothermal synthesis.The structures and morphologies of the LiFePO₄ were characterized by XRD and SEM.Using the method of galvanostatic charge-discharge,cyclic voltammetry and electrochemical impedance spectroscopy to investigate the electrochemical properties of LiFePO₄.The effects of different water contents on the morphologies and electrochemical properties of LiFePO₄ were investigated.On the other hand,we also investigate the improvement of the electrochemical properties of LiFePO₄ by adjusting the contents of graphene.The experimental results showed that the different water content in the synthesis conditions had a great influence on the morphology of LiFePO₄,which formed lithium iron phosphate nanoplates with different thickness,and had different degree of agglomeration.In addition,the electrochemical performance of LiFePO₄ cathode material was optimized by adding different contents of graphene.The electrochemical performance of LiFePO₄ cathode material with the condition of 5 ml H₂ O and rGO?2% of LiFePO₄ mass?was the best.The first charge and discharge capacity of 165 mAh·g^-1 at 0.2 C.The rate of 30 C charge conditions,it can still maintain a high capacity of 118.6 mAh/g.