Development Of Electrode And Electrolyte Materials For All-organic Rechargeable Batteries

Rapid development of electric vehicles, smart grids and renewable power stations puts forward a great challenge for battery chemistry. However, it is very difficult to enhance the electrochemical performance and reduce cost of electrode materials. The all-organic secondary batteries are pursed as one of the most promising candidates for large scale energy storage, because of their advantages of structure diversity, abundant resources, sustainability and environmental friendliness. Therefore, in this thesis, we were aimed at developing new organic cathode and anode materials for Li-ion and Na-ion batteries with higher energy and power density, good cycling stability and sustainability, thereby to realize all-organic rechargeable batteries. The main results and new findings are summarized as follows:1. Two typical conjugated carbonyl compounds:3,4,9,10-perylenetetracarboxylic acid lithium salt (Li4C24H8Og) and3,4,9,10-perylenetetracarboxylic acid sodium salt (Na4C24H8O8) were prepared as anode materials for Li-ion and Na-ion battery, respectively, due to the increased chemical stability and decreased dissolubility in organic electrolytes with larger conjugated perylene ring. It was found that Li4C24H8O8anode displays a quite high capacity of～200mAh g-1with a charge/discharge plateaus at1.3/1.05V, an excellent cycling stability with100%capacity retention after100cycles, and superior rate capability with128mAh g"1reserved at400mA g"1current density. Moreover, Na4C24H8O8anode gives a relative lower capacity of102mAh g-1at0.6V/0.4V and remains its initial capacity after1000cycles. The mechanism of lithium/sodium storage is found to go through enolation reaction of carbonyl double bonds and carbonylation reaction of enolate with the association/disassociation of Li+/Na+.2. Development of conductive polymer with higher electrode potential by the introduction of strong electron-withdrawing groups as lithium/sodium storage cathode materials. The copolymer of aniline and ortho-nitroaniline (P(AN-oNA)) was prepared by means of oxidized polymerization based on the considerations that the-NO2owns strong electron-withdrawing ability and can form conjugated structure with aniline. P(AN-oNA) cathode demonstrates a quite high capacity of195mAh g’1at an average discharge voltage at3.34V, a good cycling stability with93mAh g’1reserved after500cycle, which is the best results reported in the literature. Meanwhile, this cathode can also gives a reversible capacity of195mAh g-1at3.2V in Na+electrolyte,173mAh g-1reserved after50cycles, an excellent rate capability with almost no capacity fading at a current density below200mA g-1, which is comparable or even superior to the electrochemical performances of the Na-ion batteries with inorganic electrode materials. Overall, the conductive polymers can realize high capacity, good cycling stability and excellent rate capability and be considered as a promising cathode for secondary batteries.3. Development of self-doping conductive polymers:TEMPO-grafted polydiphenylamine (PDPA-TTEMPO) and carboxylic-grafted polypyrrole (1-PPYM,3-PPYM). Also, these polymers were in situ doped by redox-active dopant (NQS) in electrolyte. PDPA-TEMPO cathode displays a capacity of70.4mAh g-1at an average voltage of3.65/3.63V, while PDPA-TEMPO in situ doped by NQS can delivers a quite high capacity of188.7mAh g-1, suggesting a electrochemical activation between NQS and PDPA-TEMPO. Similarly,1-PPYM cathode displays only a pseudocapacitive response giving a small capacity of55.1mAh g-1, while1-PPYM in situ doped by NQS can give a much higher capacity of158.1mAh g-1, and remain137.7mAh g-1after450cycles. Compared with1-PPYM, the3-PPYM cathode in situ doped by NQS displays a higher capacity (202.2mAh g-1and227.4mAh g-1) and higher discharge voltage (AE=200mV), an excellent rate capability with113.2mAh g-1capacity retention at a current density of800mA g-1and good cyclability with133.5mAh g-1capacity reserved after150cycles. This work provides a new insight for the development of new organic electrode materials. 4. An organic plastic crystalline electrolyte (Na+-SCNs) was prepared and used to construct an all-organic Na-ion battery using polymeric P(AN-NA) cathode and PAQS anode.5mol%NaClO4-SCN electrolyte deliveries high solid-state conductivity of≥10"3S cm-1at10-47℃, and a wide electrochemical window of>3.5V. P(AN-oNA)/5mol%NaC104-SCN/PAQS cell gives a capacity of200mAh g-1at a current density of50mA g-1at an average voltage of-1.5V, an excellent rate capability with60%theoretical capacity at a current of800mA g-1, realizing a specific energy and rate performance even higher than the organic solvent Na-ion batteries currently developed. Overall, this work proves the feasibility of the plastic crystalline electrolyte for Na-ion batteries, which offers a new avenue for the development of solid state electrolytes for safer Na-ion batteries.