Preparation Of Nanocatalysts For Lithium Air Batteries And Exploration Their Catalytic Mechanism

Rechargeable lithium-air?Li-O₂?batteries as a new type of energy battery system have widely researched due to its ultrahigh theoretical energy density of 3,600 Wh kg^-1.Nevertheless,the development of lithium air batteries is in its infancy and many key scientific and technical problems need to be solved.For example,the poor rate performance and slow cathode mass transfer kinetics;short cycle life and poor electrochemical stability;the poor safety performance,what?s worse,the lithium-metal anode is easy to produce dendrite,corrosion and other problems,which limits a further development of lithium air batteries.In view of the above problems,we mainly conducted a detailed synthesis and study on the important role of catalysts in lithium air batteries,and the main contents of the research works are as follows:1.A highly dispersed electrocatalyst with Ru nanoclusters inside the special organic molecular cage?RuNCs@RCC3?through a reverse double-solvent method for the Li-O₂ batteries has been proposed for the first time.The results showed that the RuNCs@RCC3 catalyst,which was highly dispersed in the electrolyte,showed excellent catalytic performance including round-trip efficiency,specific capacity,rate,and cycling stability compared with the conventional solid Ru nanoparticles on the cathodes.By the scanning electron microscopy?SEM?,we explored the discharge product at different stages of charge and discharge stages.We found that the RuNCs@RCC3 electrocatalyst,which was highly dispersed in the electrolyte,could directly generate and decompose on the surface of Li₂O₂,greatly reducing the reaction potential and improving the cycling performance of the baterries.More importantly,the catalyst exhibits superior stability and durability during the cycles.2.A single atom catalyst Co by the novel polymer encapsulation strategy was firstly synthesized and applied in the Li-O₂ batteries.The results showed that the uniformly distributed N-HP-Co SACs exhibited better catalytic performance and higher stability than the noble metal catalysts with the same content.We demonstrated that the uniform nucleation of the discharge products can be regulated by the synergistic effect of uniformly dispersed single atom and carbon support,thus forming flower-like discharge products by sheet assembly.During the charging process,DFT calculation showed that the adsorption energy of N-HP-Co SACs catalyst on LiO₂ was lower than that of the commercial Pt/C catalyst,thus increasing the concentration of LiO₂ in the electrolyte,as a result,the charging mechanism was changed from a two-electron process to a one-electron process.During the cycles,we further found that the catalyst had high durability and remained in the single atom state through high-angle annular dark field scanning transmission electron microscopy?HAADF-STEM?image and X-ray absorption fine structure?XAFS?measurments.