The Study On Organic Electrode Materials For High Performance Lithium Batteries

With the fast development of social economy,the demand for high energy density storage systems is ever-increasing,particularly in the fields of portable electronics,electric vehicles,smart grids,military,aerospace,medical and civilian applications.Lithium-ion batteries（LIBs）have been extensively explored as high energy density storage devices.Commercial LIBs use crystalline transition metal oxide cathodes that store energy via insertion/extraction of Li ions,which highly depends on the crystal structure and limits their capacities and energy densities.Compared with LIBs,lithium primary batteries can provide much higher energy densities,such as Li-CF_xand Li-SOCl₂batteries.However,they suffer from serious issues related to the cathode materials,including strict synthesis conditions and environmental pollution.Therefore,it is highly desired to develop feasible and reliable battery systems with good cycling stability and high energy density.Organic electrode materials,featured by structural diversity,abundant raw materials,eco-friendliness as well as low cost,are a kind of promising electrode materials for lithium batteries.However,their practical applications have been hindered by the poor cycling stability and low energy density.In this thesis,a series of organic electrode materials were synthesized and applied for lithium-ion and lithium primary batteries.Their electrochemical performances and storage mechanisms were systematically investigated.The findings are summarized as following:（1）Organic electrode material of indeno[3,2-b]fluorene-6,12-dione（IFDO）was synthesized and used as cathode for LIBs.IFDO molecule has a larger conjugated molecular plane,which may enhance the intermolecular interaction and reduce the solubility in organic liquid electrolytes.As a result,improved cycling stability was obtained.Further performance enhancement was realized by compositing IFDO with mesoporous carbon of CMK-3 due to the confinement of porous carbon matrix.（2）The effects of electrolytes on the electrochemical performance and behaviors of IFDO were investigated.A reduction specific capacity of 652 m Ah g^-1was obtained,corresponding to an energy density of 1392 Wh kg^-1as the electrolyte with the additive of fluoroethylene carbonate（FEC）was used,which is much higher than the electrolyte without FEC.Interestingly,the reduction is irreversible,manifesting a primary behavior.It is found that the carbonyl groups of IFDO were transferred into methylene groups via a four-electron reduction,providing a four-times higher theoretical capacity compared with that based on single-electron reaction in the electrolyte without FEC.（3）1,5-dinitronaphthalene（1,5-DNN）was used as an organic electrode material for lithium batteries and achieved an ultra-high specific capacity of 1338 m Ah g^-1and ultra-high energy density of 3273 Wh kg^-1in the electrolyte with FEC additive.They are higher than all previously reported organic electrode materials and most inorganic electrode materials.The reaction mechanism was systematically investigated,and the results show that the nitro groups were transferred into amino groups through a six-electron reduction.This finding opens up a new way in terms of battery chemistry for ultra-high energy density Li-organic batteries.