| With the development of the global economy and society,the excessive exploitation and utilization of traditional fossil energy lead to its rapid depletion,and the resulting energy crisis and environmental pollution are becoming more and more serious.To this end,the development of renewable energy to replace traditional fossil energy has become imminent,and the high-efficiency energy storage technology as an important part of the large-scale utilization of renewable energy is indispensable.Among the existing energy storage systems,lithium-oxygen batteries（LOBs）have aroused significant interest and attention due to their ultra-high theoretical energy density,which is expected to break through the energy density limit of current lithium-ion batteries（LIBs）and apply them in next-generation energy storage systems.Despite some progress has been made to LOBs through the unremitting efforts of researchers over the years,it is still a great challenge to obtain practical LOBs due to the evaporation,flammability,poor thermal stability,and low chemical/electrochemical stability of the traditional organic liquid electrolytes,as well as the dendrite growth and corrosion of Li metal anodes.These would lead to low discharge capacity,poor cycle performance,and severe safety hazards for LOBs.In order to solve the above problems,this thesis has explored and developed high-performance deep eutectic electrolytes（DEEs）for improving the electrochemical performance of LOBs,and designed high-performance solid-state electrolytes（SSEs）and battery structures for solid-state lithium-oxygen batteries（SSLOBs）to further improve the electrochemical performance and security.The main contents are as follows:1.To figure out the problems of poor chemical,electrochemical and thermal stability of traditional organic liquid electrolytes,we have pioneered the development of an amide-based DEE for LOBs.N-methylacetamide（NMA）was mixed with lithium bis（trifluoromethane）sulfonimide（Li TFSI）at a certain molar ratio,and the solid NMA and Li TFSI interacted with each other and transformed into a DEE.The NMA-based DEE comprehensively inherits the advantages of amide-based electrolytes,and also ionic liquids and molten salt-based electrolytes,while avoiding their disadvantages.Compared with the commonly used TEGDME-based electrolytes,NMA-based DEE exhibits higher lithium ion conductivity and thermal,electrochemical and chemical stability.Benefiting from these excellent properties,the electrochemical performance of NMA-based LOBs has been significantly improved,including a high discharge capacity of 8647 m Ah g-1 and a long cycle lifetime of 280 cycles at a limited specific capacity of 1000 m Ah g-1,which is about three times that of TEGDME-based LOBs.Even if the capacity is limited to 5000 m Ah g-1,the NMA-based LOBs could still run stably for 50 cycles.These indicate that the amide-based DEEs exhibit excellent stability and durability in the harsh operating environment of LOBs.In addition,the successful application of DEEs in LOBs has broadened the choice of high-performance electrolytes.2.Based on the above work,cheap urea was utilized as the raw material to synthesize a new kind of DEE electrolyte by mixing urea with lithium salt at a molar ratio of 3.6:1.With this molar ration,the two high melting point solids could form liquid urea-based DEE.Since urea is an industrially produced chemical and thus is easy to obtain,making the urea-based electrolyte have the characteristic of a simple synthesis.Moreover,this urea-based DEE possesses the abilities of non-flammability and high thermal resistance,which greatly improve the safety of LOBs.Importantly,the urea-based LOB presents a high discharge capacity(13698 m Ah g-1)and can operate stably for more than 500 cycles using Li Fe PO4 as the pseudo-anode and Super P as the cathode.The cycle performance of the urea-based LOBs is more than ten times that of TEGDME-based LOBs.Even at a deep depth of charge and discharge,the urea-based LOB could still exceed 50 cycles.The urea-based DEE,which is easy to prepare,resistant to high temperatures and non-flammable,enables the realization of LOBs with safe and excellent electrochemical performance to become possible,indicating that the urea-based DEE has great practical application potential.3.To further improve safety and address the issues existing in liquid LOBs and traditional SSLOBs,we designed a three-dimensional（3D）inorganic nanofiber framework-supported integrated electrolyte/electrode structure for advanced SSLOBs.On the upper layer of the integrated structure,a high-performance composite solid electrolyte（CSE）is formed,which effectively improves the lithium ion conductivity of the electrolyte,suppresses the growth of lithium dendrites,and protects the lithium metal anode from water and oxygen.In this integrated structure,the electrolyte and electrode share the same 3D ceramic nanofiber framework.Different from the mutually independent electrolyte/electrode structures in traditional SSLOBs,the integrated electrolyte/electrode structure effectively increases the interfacial contact and reduces the interfacial impedance.Therefore,the integrated SSLOB exhibits high discharge capacity and a long cycle lifetime.Benefiting from the flexible integrated electrolyte/electrode structure,the assembled pouch-type SSLOBs exhibit excellent flexibility and safety.The integrated composite solid electrolyte/electrode structure provides a new idea for designing novel SSLOBs. |
