| As a new generation of energy storage system,lithium-ion battery?LIB?has been widely used in consumer electronic products and electric vehicles in the past 20 years.However,because LIB is limited by the theoretical energy density of its electrode materials,it is difficult to meet people's demand for higher energy density energy storage device.Therefore,the development of the energy storage system with higher energy density has attracted widespread attention.Lithium-oxygen battery?LOB?,as potential next-generation energy storage system,has a theoretical energy density as high as 3458 Wh kg-1,which is10 times the energy density of lithium-ion battery.However,the lithium-air battery has its inherent problems that limit its development.Among them,one of the serious problems is the insolubility and insulation of the discharge product lithium peroxide.First of all,this causes the fact that discharge product in poor contact with cathode is hardly to be completely decomposed during the charging process,and it is difficult for the battery to contribute the full capacity.Secondly,due to its insulation,the charging overpotential will be very large when the contact between them is poor.Large overpotential may cause the instability of electrode material and electrolyte,and bring parasitic reactions,severely weakened the battery efficiency,stability,and safety.In addition,as the charge-discharge cycle progresses,the byproducts gradually accumulate at the electrode,clogging the diffusion channel of oxygen,and electrolyte,and will also passivate the electrode material surface,reducing the conductivity of the electrode material surface,seriously affecting the cycle life of the battery.There are many ways to improve the solubility and decomposition efficiency of discharge products from positive electrodes,additives,electrolytes,or the like,in order to improve the property of lithium-air battery.This thesis mainly focuses on the above problems,mainly in the following two aspects:?1?In order to solve the problem of poor solubility of lithium peroxide,a novel electrolyte,1,3-dimethyl-2-imidazolidinone?DMI?was used,in the discharge process help solvate lithium peroxide by interact with lithium peroxide and its intermediates,prompting liquid phase nucleation of lithium peroxide,thereby increasing its discharge capacity.Compared with the traditional aprotic electrolytes,the electrolyte can increase the discharge capacity about 1.5 times.At the same time,the use of solvents can reduce the charge overpotential of battery.For the nucleophilic attack of oxygen free radicals on the solvent,that causing poor battery cycling,the stability of the electrolyte and the cycling performance of the battery are effectively improved by adding the antioxidants to stabilize the oxygen free radicals in the solution.?2?In the experiment,we found that it is difficult to find a stable electrolyte in lithium-air battery,which is a complex and strong oxidizing environment.Therefore,we researched different types of electrolyte in lithium-air battery by rotating disk electrode?RDE?to explore the solvating efficiency of lithium peroxide and the mechanism of side reactions.The advantage of this method comparing with assembling batteries is that it can excludes the effects of electrodes,separators,and other components of the battery and allowing the study only focus on the effects and changes of electrolyte itself.Through the research,the solvating process of different solvents to lithium peroxide has a direct impact on the efficiency of solvating lithium peroxide and the degree of side reaction.The mechanism of the side reaction of different electrolytes are also presented,which is helpful to the better understand of the interaction between the electrolyte itself and lithium peroxide. |
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