Preparation And Properties Of Phosphate Cathode Materials

The lithium-ion battery is a new generation of green high-energy rechargeable battery based on lithium battery and developed rapidly at the end of the last century.It has the advantages of high voltage,high specific energy,high cycle characteristics,small self-discharge,no memory effect and so on.It has gradually become the most important energy storage device for the development of the national economy and people’s livelihood.For lithium-ion batteries,the performance is mainly influenced by electrode materials and electrolyte materials.The choice of electrode materials determines the performance and price of lithium-ion batteries to a large extent.Compared with the anode materials,the research of cathode materials of lithium-ion batteries has been relatively backward,which is the bottleneck of its development.Therefore,the exploration of cathode materials has become the focus and hot spot of the related studies on lithium-ion battery materials.In this thesis,the preparation methods and electrochemical properties of cathode materials for lithium-ion batteries were studied.At present,the studies of cathode materials mainly includes transition metal oxides,polyanion compounds,and other materials.Based on the understanding of the advantages and disadvantages of the related materials and the research status,this thesis mainly studied the related phosphate cathode materials.Among them,the positive material lithium iron phosphate has certain research and application and has certain electrochemical performance,but it is used in the discharge voltage.There is still room for development in terms of conductivity and discharge rate;lithium vanadate phosphate not only has good safety but also has higher diffusion coefficient of lithium-ion,discharge voltage and energy density,which is regarded as the most promising cathode material for lithium-ion batteries of electric vehicles.Therefore,the research and preparation of lithium iron phosphate,lithium vanadium phosphate and other cathode materials with good performance,as well as the structure and performance research,will be conducive to the research,development,and application of new lithium-ion secondary batteries with good performance,low price,and environmental friendliness.The lithium iron phosphate materials were prepared by the solvothermal method and spray method respectively.The structure and morphology of the samples were characterized by means of X-ray diffraction and scanning electron microscopy.Then the button cells were assembled as cathode materials and lithium metal plates as negative electrodes,and the electrochemical performance was analyzed.Among them,the solvothermal method using ethylene glycol as a solvent not only acted as a reducing agent but also effectively improved the cycle performance of materials by making the particles evenly dispersed and uniform in size,while the materials prepared by spray method had higher charge-discharge capacity and charge-discharge efficiency.Lithium vanadium phosphate was prepared by the hydrothermal method and electrospinning technology.The structure and morphology of the samples were characterized,and the electrochemical properties of the samples were analyzed.Among them,the samples prepared by the hydrothermal method had higher initial specific capacity,while the samples prepared by electrospinning technology had higher lithium-ion diffusion coefficient and smaller charge transfer resistance.In this thesis,we tried to use different methods to prepare phosphate series anode materials and carry out structural characterization,performance research,and then comparative study through electrochemical performance analysis that might lay a good foundation for better exploration of preparation and application of phosphate anode materials with strong theoretical and practical significance.