The Investigation On The Reversible Multi-electron Redox Chemistry In Organic Battery Cathode Materials Based On Phenothiazine-based Polymers

Battery technology is an advanced energy storage technology,which can efficiently store the electricity generated by renewable energy,and it is one of the solutions to solve energy problems.Traditional battery materials are inorganic materials and their development is hindered due to limited resources and high cost.In contrast,organic materials exhibit many advantages,such as low toxicity,abundant resources and low cost,hence showing great potential in energy storage technology,such as organic lithium ion battery and organic redox flow battery.However,the flammability of organic compounds brings in serious concerns on battery safety.The chance of burning or explosion of the battery will threaten the life of the user and cause serious consequences,which greatly hinders the further development of organic lithium-ion batteries.Moreover,the energy density of organic redox flow batteries is limited by voltage and solubility of the active materials,and its development has also been bottlenecked.Therefore,there is an urgent need to develop new active materials with high redox voltage and solubility,which is of great significance for the progress and development of China's new energy industry.Here in this paper,a series of organic cathode materials were designed,synthesized and applied to lithium ion battery or redox flow battery,providing ideas for solving the problems mentioned above.The main contents include two aspects as follows:(1)The safety issue of organic batteries has been improved by integrating flame-retarding unit into the polymer backbone of cathode materials.In this paper,a flame-retarding polymer,denoted as p-BrPhPT,was synthesized and applied to lithium ion batteries as cathode materials.Micro combustion calorimetry(MCC)test results showed that a remarkable improvement in flame retardancy could be achieved when the mass fraction of the flame-retarding unit reaches 3%.Compared with the blank sample,the one with p-BrPhPT exhibited a decrease of 33.05%,32.74%and 22.30%in heat release capacity,peak heat release rate and total heat release respective.Burning tests showed that the combustion time of the p-BrPhPT was greatly reduced.This strategy effectively improves the safety of the cathode materials without sacrificing the energy density.We believe that flame-retarding active materials would be essential for building a safer battery.(2)The energy density of organic redox flow batteries has been improved by optimizing the molecular structure,increasing the solubility and redox potential of the active materials.In this paper,based on the phenyl-phenoxazine,we introduced ether chain groups to increase the solubility of the active materials in the electrolyte.Moreover,we introduced electron-withdrawing groups,such as bromine-atoms,ester-groups and cyano-groups,in order to increase the redox potential of the active materials.The solubility and the redox potential of active materials could be improved by reasonable molecular design,such as introducing ether chain groups and electron-withdrawing groups.The results provide experimental basis and new design ideas for research on improving the energy density of organic redox flow batteries.