Alkaline-earth Meltal Terephthalates As Organic Anode Materials For Lithium Ion Batteries

Carboxylate-based organic materials with the advantages of high theoretical specific capacity, ideal voltage platform(0.8 V vs. Li+/Li), low-cost, diverse structure, abundant raw materials, and enviormental benignity, which are catering for desire for sustainable materials, become popular as anode materials for lithium ion batteries. Howener, these materials have poor electronic conductivity and high solubility in electrolyte leading to unsatisfied rate capabilty and cycling performance. In this thesis, we reviewed the research background, including the working principle of lithium ion batteries, the state of the art of the elecrode materials, and the lithium storage mechanisms for terephthalate electrodes in lithium ion batteries. Displacement reaction can replace the cation of lithium terephthatlates with alkaline-earth metal cations, which leads to different physical chemical properties. The main contents are included as the following:(1) We prepare the alkaline earth metal terephthalates(calcium terephthalate, strontium terephthalate, barium terephthalate) via the cation exchange reaction. The difference in the crystal structure, microstrucutre, thermal stability, solubility in electrolyte, and electrochemical performance is studied.(2) Calcium terephthalate trihydrate(CaTPA·3H2O) and anhydrous calcium terephthalate(CaTPA) as anodes for lithium ion batteries are compared. Crystallography and local chemical bond analysis are combined to interpret the structure-property of calcium terephthalates. Results show that the anhydrous Ca TPA has a spacious ordered layer structure and a stronger Ca-O chemical bonding interaction, delivering a higher capacity, better cycling performance and rate performance than that of Ca TPA·3H2O.(3) Graphite is imported to improve the electronic conductivity of calcium terephthatle electrode. Calcium terephthalte/graphite composites are prepared via ball-milling and applied as anode materirals for lithium-ion batteries. We discuss the effect of graphite content on the capacity, electronic conductivity and electrochemical properties. It is found that ball-milling not only reduces the particle sizes of the composites, but also makes the graphite dispersed homogeniously. Moreover, graphite does not only improve the conductivity and specific capacity, but also alleviates the solubility of calcium terephthalate in the electrolyte. The composite CaTPA/C with the weight ratio of 100:10 delivers discharge capacity of 233 mAh/g at a current rate of 0.1 C and shows the smallest electrochemical polarization, largest Li+ diffusion coefficient, best rate capaicty and stable cycling property.(4) The mixture of calcium terephthalate and glucose aqueous solution are hydrothermally reacted at 180 oC for 12 hours, then is further annealed at 350 oC. The as-obtained carbon-coated calcium terephthalate exhibits the improved electronic conductivity and enhanced electrochemical property. It indicates that the surface carbon coating layer forms a conductive network, which not only effectively enhances the electronic conductivity but also alleviates the solubility of the active materials in the electrolyte as well as improves the reversible capacity.