Electrochemical Performance And Mechanism Of Lithium-organic Primary Batteries

Lithium primary batteries are widely used in military,medical,aerospace and civilian fields due to their high energy density and long service life.Currently,the commercialized lithium primary batteries mainly are lithium-manganese dioxide,lithium-fluorinated carbon(Li-CFx),lithium-thionyl chloride and lithium-sulfur dioxide primary batteries.Among them,Li-CFx battery promises the highest theoretical energy density of 2180 Wh/(kg of CFx).However,CFx has to be synthesized by fluorinating graphite with fluorine under extreme conditions,leading to its prohibitively high cost.Other primary battery systems have much lower theoretical specific capacities or are extremely toxic,corrosive and present severe safety concerns.In contrast to inorganic electrode materials,organic electrode materials have been extensively explored for rechargeable lithium batteries due to their advantages in facile synthesis,low toxicity,high-abundance and sustainability.However,organic electrode materials are mainly based on single-electron electrochemical reactions of active groups,which have a low specific capacity and are difficult to meet the needs of social development.In this thesis,a new organic battery chemistry is introduced,which enables a 4-electron reduction reaction of carbonyl groups and delivers capacities comparable with these inorganic cathode materials.We also conduct a systematic study of the reaction mechanism,and the results are of great significance for the development of high specific energy lithium-organic batteries.The main work is as follows:(1)A new chemistry is based on AQ and activated by the presence of an electrolyte additive,fluoroethylene carbonate(FEC).The single-electron reaction of the carbonyl group disappears and is replaced by a new carbonyl four-electron reaction,which significantly increases the specific capacity.Differing from its electrochemistry behavior in the absence of FEC,AQ delivers a much higher discharge capacity(575m Ah/g)at a stable discharge plateau of 2.4 V,corresponding to an energy density of1030 Wh/kg.The mechanism of this new battery chemistry is systematically investigated using electrochemical and spectroscopic,which reveals that AQ is eventually reduced to 9,10-dihydroanthracene(DHAN),corresponding to a theoretical capacity of 1204 m Ah/g,much higher than the theoretical specific capacity of AQ in secondary lithium ion battery(257 m Ah/g)where AQ is reduced to the enol structure.The theoretical specific energy is not only higher than all reported organic electrode materials,but also higher than commercial inorganic electrode materials.The discovery of such a new lithium-organic battery chemistry opens up a new avenue to the next generation primary batteries of high energy density,high safety,low cost as well as environmental sustainability.(2)Furthermore,1,4-benzoquinone(BQ),an organic electrode material with a smaller organic molecule,is adopted as the active cathode material.Since BQ has a high solubility in organic electrolytes,BQ is dissolved in the electrolyte as a catholyte when assembling batteries,and a graphene electrode is used.In presence of FEC,BQ delivers a high discharge capacity of up to 1.87 m Ah,and the discharge voltage is up to 3.0 V.The carbonyl group in BQ undergoes a 4-electron reduction reaction.The results further prove that this new reaction mechanism can greatly improve the discharge specific capacity of the organic electrode,and lay the foundation for the realization of ultra-high specific energy lithium batteries.