Terephthalate As An Organic Anode Material For Sodium Ion Batteries

In recent years, lithium ion batteries have been widely utilized in portable electronics, because of their high voltage, high energy density, low self-discharge rate and excellent cycling stability. At present, the serious challenge for lithium ion batteries is high production cost of purified lithium compounds and shortage of lithium resources in the earth. Thus, developing advanced novel battery systems with low-cost and abundant raw materials is inevitable way for large-scale electrical energy storage. In order to achieve this goal, great attention is paid to sodium element in the same main group with lithium element. One of the reasons is that there are abundant and low-cost sodium resources. Another reason is that sodium intercalation potential is 0.3 V higher than lithium intercalation potential, which means sodium-ion battery can have more choices in liquid electrolyte system and the enhanced safety. If sodium ion battery can be commercialized, it should be the qualified candidate for large-scale energy storage with respect to lithium ion battery. Therefore, it has become a topic of concern for exploring the electrode materials of sodium ion battery with high specific capacity and excellent cycle performance. Organic electrode materials due to the advantage of cheap price, easy to extract, green characters comparing with inorganic electrode materials do attract much attention. Particularly, conjugated carbonyl organic is of intriguing interest considering its high specific capacity, fast reaction rate and great variety in chemical structure. However, the current research on conjugated carbonyl organic is still in its infancy. For instance, the correlation of carbonyl structure, crystal structure and the derivatives, etc. with electrochemical properties is unclear. Therefore, this thesis aims at discovering the relations between their structures and properties by investigating the effect of metallic cations, crystal water, and carbon coating on the sodium storage properties of several terephthalates.First of all, lithium terephthalate(PTALi2), magnesium terephthalate(PTAMg), calcium terephthalate(PTACa), barium terephthalate(PTABa) and aluminum terephthalate(PTAAl2/3) were prepared by neutralization reaction and/or precipitation reaction, and then the electrochemical properties of the terephthalates were explored. It was found that the charge and ionic radius of metallic cation can affect rate capability and cycle performance while taking PTALi2, PTACa, PTAMg, PTABa and PTAAl2/3 as the samples.The effect of crystal water on the electrochemical performance of the terephthalates was also discussed. Both of the terephthalate with crystal water(PTAMg·2H2O) and without crystal water(PTAMg) were prepared, where the crystal water is helpful to improve electrochemical performance in terms of specific capacity in the first cycle, rate property and cycling performance.Finally, the carbon coating technology was applied to improve electronic conductivity of PTAMg electrode material. Glycine was used as carbon source. The discharge capacity was increased by carbon coating, and the electrode with 15% of glycine mass percentage had the most excellent electrochemical performance.