Non-aqueous Electrolyte Quantum Chemical Research And In The Lithium-ion Battery Applications

The lithium salts are the important part of lithium ion containing electrolyte. So we have to develop new lithium salts to save the necessary of manufacturing lithium ion batteries. The focus on the development of the novel lithium salts has been placed on seeking proper anions for coordination with lithium cation to obtain desired species with appropriate chemical and electrochemical property.Getting the quantitative structure-property relationships(QSPR) to guide experimental scientists research and to save their time and costs, Quantum chemistry calculation can in many cases be a successful method applied to lithium salts. Because the anion-cation interaction within the lithium salts plays an important role in determining to the solubility, ionic conductivity, electrochemical windows and thermal stability, a thorough computational investigation on the electronic structures, energies, and orbitals of the lithium salts would be desirable to better our understanding their properties at a quantum chemistry level.The main concerns of the present work are as follows: more systematic research of the quantitative structure-property relationships for electrolytes; the research on design, synthesis, and the experimental results of lithium salts guided by the theoretical results.In chapter 1, 2 and 3 of thesis, reviewed the present research situation of lithium salt. Including the classification of lithium salt, methods of synthesis, experimental results of thermal- and electro-chemistry. Also it is included that the theoretical research by the quantum chemistry's method in molecular structure and quantitative structure-property relationships, particularly in the aspect of IR, NMR, thermal stability, electric conductivity and electrochemistry window.In the thesis chapter 4, it was put forward that research method of this work, research object and main research contents. We also carried on a total design to the follow-up research work in this chapter.Looking for the suitable quantum chemistry calculation method and the structure common feature of novel lithium salts, the gas-phase acidity and aromaticity of nitrogen squaric acid and its dimeric derivative were studied in the thesis chapter 5. The study included judge of acidity and aromaticity according to the criteria. According to the results, the suitable calculation method and the structure common feature for the lithium salt with a higher electric conductivity were gotten.For systematically studying the quantitative structure-property relationships for electrolytes, the thesis chapter 6, 7 and 8 systematically studied molecular(anions) structure and quantitative structure-property relationships, including the relationship between molecular structure and conductivity, anions structure and electrochemistry stability, on anions of 1,2-Dihydroxycyclo-pentenetrione (croconic acid, H₂C₅O₅) and the whole series of dicyanomethylene derivatives, anions of 1,2-dihydroxycyclobuten- 3,4-dione (squaric acid, H₂C₄O₄) and the whole series of dicyanomethylene derivatives, and anions of 1,2-Dihydroxy-cyclobuten- 3,4-dione (squaric acid, H₂C₄O₄) and the whole series of dicyanomethylene derivatives.Using of the above relevant research methods in the thesis chapter 9, we carried on detailed theoretical researches to lithium salt LBBB and its derivatives, which have already been synthesized and reported, and analyzed molecular structure and electronics structure of this kind of lithium salt. We also elaborated the essence of the relationships between the property (thermal stability, solubility, electric conductivity, and electrochemical stability window) and the structure.Under the instruction of above-mentioned theoretical results, in the thesis chapter 10, the strongly electron-withdrawing anion, C₅O₅^2-[dianion of croconic acid (4,5-dihydroxycyclopent-4- ene-1,2,3-trione)], was chosen as the chelator to coordinate with boron to form lithium salt, which will yield high ionic conductivity solutions, and exhibit wide electrochemical stability windows and high thermal stability. As described in the chapter, two new lithium salts containing C₅O₅^2-, lithium bis[croconato]borate (LBCB) and its novel derivative, lithium [croconato salicylato]borate (LCSB) for Li-ion battery electrolytes were synthesized. Their thermal and electrochemical stabilities, conductivities in solvent mixtures were studied and compared with those in the LBSB electrolyte. The results proved from the experiment the above theoretical study of accuracy.For better explaining quantitative structure-property relationships of the lately synthesized lithium salts (LBCB and LCSB), in the thesis chapter 11, we studied these new lithium salts with the above theoretical method. The results were completely consistent with the foregoing theoretical results.Finally, in the 12^th chapter, the author gives a general overview on the achievements and the deficiency in this thesis. Some prospects and suggestions of the possible future research directions are pointed out.