Experimental Research On Synthesis And Properties Of Lithium Borate Electrolyte Of Lithium-ion Batteries

The battery materials and manufacture technologies have developed quickly since the birth of lithium ion battery in 1990. The study of battery materials supports the increase and improvement of lithium ion battery performance. The improvements of battery rate performance, high-low-temperature performance, safety performance and cyclic performance make lithium ion battery application to be true in cell phone, notebook computer, audio product, power tool, backup power source and automobile power. The market requirement for lithium ion battery is increasing in the future 10 years along with the extending of application field, and the lithium ion battery is possible to be applied in more other fields. Battery performance depends critically on the used materials, so the development of new materials is important for advancing battery technology. One challenge is the development of electrode materials with increased energy density, faster discharge kinetics and better stability. Another challenge is the development of safer and more reliable electrolytes to replace the currently used organic carbonate liquid solutions. Since the electrolyte composition is one of the key factors in influencing the performance of lithium ion battery, it is important to develop the design of electrolyte for lithium ion battery. Searching and assembling new lithium electrolyte which should have novel structure and a good electrichemical property are the intentions of this research.The thesis is totally divided into four chapters.In the first chapter, it is introduced the sorts, composing, structures and performances of the salts of Li ion secondary cell. Comparing with the differences of the salts, it is specially introduced the supplement and development of them.In the second chapter, the lithium salts which including Lithium difluoro [1,2-benzenediolato(2)-O, O'] borate (LDFBDB), Lithium difluoro [3-fluoro-1,2-benzenediolato(2)-O,O'] borate (FLDFBDB), Lithium difluoro [3,4,5,6-tetrafluoro-1,2-benzenediolato(2)-O,O'] borate (PFLDFBDB) are synthesized. All of them are characterized by NMR analysis.In the third chapter, the solubility, ionic conductivity, electrochemical windows and thermal stability of the three electrolyte salts are characterized.the salts have higher conductivity and higher oxidized potential.In the fourth chaper, using methods of density functional theory (DFT) study on LDFBDB and its derivatives. Molecular structure and electronic structure of electrolyte salts are analyzed. Because the lithium salts structure plays an important role in determining to the solubility, ionic conductivity, electrochemical windows and thermal stability.In summary, three organic lithium salts are synthesized, their structures and properties have also been studied combining experimental results.