| Lithium-ion batteries are closely related to human life and have been widely used in electric vehicles,mobile phones,smart products and other fields.Therefore,it is imperative to develop basic research of high-performance lithium-ion batteries.Electrode materials used in the field of electrochemical energy storage are currently mainly divided into two categories:inorganic electrode materials and organic electrode materials.Organic electrode materials have attracted tremendous attention in the field of electrochemical energy storage because of their tunable structure,low cost,and environmental friendliness,and have become potential high-performance candidates.However,organic electrode materials have problems such as low conductivity,low utilization rate,high solubility,and poor stability,which restrain the development of current organic batteries.In this academic dissertation,we designed two types of porphyrin molecules as new organic cathode materials for electrochemical energy storage.The one type is of[5,15-bis（ethynyl）-10,20-bis（5-methylthiophen-2-yl）porphinato]copper（II）（CuDETMP）and[5,15-bis（ethynyl）-10,20-bis（5-methylthiophen-2-yl）porphinato]copper（II）（CuDETCP）,the electrochemical performance of electron donating and electron withdrawing groups of materials was investigated.The other type is[5,15-bis（2-thienyl）-10,20-bis（5-ethynyl-2-thienyl）porphinato]copper（II）（CuDET4P）and 5,15-bis（2-thienyl）-10,20-bis（5-ethynyl-2-thienyl）porphyrin（DET4P）,the effect of the introduction of copper ion on the solubility and electrochemical performance of the material was investigated.（1）Two porphyrin materials CuDETMP and CuDETCP were designed and synthesized as cathode materials for organic lithium batteries to study the electrochemical energy storage performance and mechanism.Results show that the solubility and electronic structure of porphyrin electrode materials can be improved by introducing electron-donating and electron-withdrawing groups,thus to realize the regulation of the cycle performance and redox potential of the electrode materials.When the voltage range is 1.0–4.5 V（vs.Li+/Li）,CuDETMP and CuDETCP cathodes exhibit first high discharge specific capacities of 299 and 553 mAh g-1 at a current density of 0.1 A g-1,respectively.CuDETMP and CuDETCP cathodes exhibit excellent cycling stability in the voltage range of 1.8–4.5 V（vs.Li+/Li）and high current densities(1 A g-1),with discharge capacity of 100 and 125 mAh g-1（capacity retention of 82.1and 81.3%）after 2000 cycles,respectively.Compared with methyl groups,electron withdrawing groups,like chloride atom can improve the discharge voltage of porphyrin electrodes,and lithium ions can store at chlorine atom to further improve the discharge specific capacity.The electrochemical energy storage mechanism is investigated through a series of ex situ characterization methods,and it is demonstrated that the charge storage of the two porphyrin materials mainly controlled by pseudocapacitive contribution.（2）The introduction of alkynyl functional groups can effectively restrain the solubility of materials in organic solvents and improve the electrochemical performance,and their electrochemical energy storage mechanism were studied.Two porphyrin-based materials of CuDET4P and DET4P were acted as cathodes materials for organic lithium batteries,and the effects of ethynyl functional groups and metal coordination on the electrochemical properties of porphyrin materials were systematically studied.At current density of 200 mA g-1,CuDET4P and DET4P cathodes showed the discharge capacity of 210 and 180 mAh g-1 after 100 cycles in the voltage range of 1.2-4.5 V（vs.Li+/Li）,respectively.CuDET4P and DET4P cathodes exhibits a discharge capacity of85 and 85 mAh g-1（capacity retention of 89.1 and 88.2%）after 500 cycles at 1 A g-1.Both materials exhibit excellent rate performance due to the contribution behavior of the pseudocapacitance.The research data show that metal ion coordination of thiophene-based porphyrin molecules can remarkably increase the cycling stability of the electrode material and improve the discharge specific capacity. |
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