Aromatic Molecules Based Organic Lithium Ion Batteries Cathodes/Anodes

In the past few decades,the lithium ion batteries?LIBs?have been the major energy storage device and widely applied to portable electronic devices and electric vehicles.Nowadays,LIB has encountered some bottlenecks.Firstly,the capacities of the commercial inorganic electrodes are limited.As very often used electrode materials in LIBs,LiFePO₄generally used as the cathode only has the theoretical capacity of 170 mAh g^-1 and graphite generally used as the anode only has the theoretical capacity of 372 mAh g^-1.Additionally,the commercial LIB cathodes are the inorganic transition metal compounds,and the large comsumpation of them has caused serious environmental pollution.Meanwhile,the limited mineral resources have obstructed their development.Therefore,the organic electrode materials have attracted increasing research attentions.Common organic cathodes including sulfides,radical compounds and carbonyl compounds and common organic anodes such as lithium carboxylate compounds have been the hotspot of the investigation on LIB due to the high natural abundance and tunable electrochemical behaviors in the molecular level and environmental friendliness.However,the types and quantities of organic LIB electrode materials are still very limited.It is urgent to explore new methods for synthesis and processing of organic electrode materials for the fabrication of novel LIB electrodes.In this thesis,we prepared organic cathode and anode materials for LIB with excellent rate performance and cycle stability.The detailed research contents are as follows:?1?Preparation of an integrated flexible lithium ion battery cathode material composed of the perylenetetracarboxylic diimide?PDI?and thermoplastic polyurethane?TPU?with solution method and its electrochemical properties:In this chapter,we used the solution method to make the PDI and conductive carbon black?CB?uniformly dispersed in the TPU solution?solvent:N,N-dimethylformamide?.Then,the integrated flexible conductive film was obtained by placing the mixture into water with a phase inversion method.The dried film can be used directly as the cathode of LIB.When the mass ratio of PDI:CB:TPU is 1:4:5,the electrochemical performance of the composite cathode is best.The capacity can reach the theoretical capacity value of 137 mAh g^-1 at 0.05 A g^-1,and it has better rate performance(118 mAh g^-11 at the current density of 5 A g^-1 and very stable cycling stability?capacity retention of 86%after500 cycles?.The PDI:CB:TPU?1:4:5?was used as the cathode and prelithiated carbon cloth as the anode to prepare the flexible pouch lithium ion cells,which exhibited excellent flexibility and stable electrochemical performance at different bending states.?2?Positively charged aromatic molecules for lithium storage:Compared to the organic cathodes,less attention was paid to the organic anodes,which would produce a"short board effect"and hinder the practical applications.For this reason,we prepared 4,4'-?1,4-phenylene?bis?2,6-diphenylpyraniumtetrafluoroborate??O-PDPP?,4'-?1,4-phenylene?bis?1,2,6-triphenylpyridinetetrafluoroborate??N-POTPP?and1,1'-?1,4-phenylene?)bis?2,4,6-triphenylpyridine boron tetrafluoride??N-PMTPP?by condensation reaction.O-PDPP,N-POTPP and O-PMTPP and the purchased 2,4,6-triphenylpyran tetrafluoroboron salts?O-TPP?were used as anodes for LIB to compare their electrochemical properties and O-PDPP shows the best electrochemical performance.The specific capacity of O-PDPP is as high as 1432 mAh g^-1 at a current density of 100 mA g^-1and 480 mAh g^-1 after 1500 cycles at 5000 mA g^-1.