Application Of SnI₂ And Dual-functional Catalyst In Lithium-air Battery

Lithium-air battery is the electrochemical energy storage technology with the highest theoretical energy density and is the most ideal energy storage system in the future.It is considered to be the only battery technology that can break through 700Wh/kg and has attracted wide attention.Restricted by the reaction mechanism,the oxygen reduction reaction（ORR）and oxygen evolution reaction occurred at lithium-air battery air electrode necessitate the assistance of catalysts to improve the electrochemical reaction kinetics.After years of development,a variety of single-function catalysts have been developed to improve the ORR and OER kinetics.After years of development,a variety of single-function catalysts have been developed to improve the ORR and OER processes,respectively.However,high-efficiency bifunctional catalysts are still unavailable.Therefore,exploring new catalyst systems and developing bifunctional catalysts are the core challenges that must be addressed in Li-Air battery technology.In this dissertation,a rich variety of metal salts was adopted as the research objects,and SnI₂ was found to be an efficient metal salt catalyst,which,in combination with the charging catalyst TDPA,can further improve the discharge capacity and cycle life of the air electrode and exhibit the characteristics of a bifunctional catalyst.The main research of this thesis is as follows.（1）The addition of a tin iodide SnI₂ catalyst significantly enhanced the electrochemical performance of lithium-air batteries.The discharge capacity can reach 79015 m Ah/gcarbon（=7.69m Ah/cm²）at a current density of 100m A/gcarbon,which is 10 times higher than that of the comparison sample;the energy efficiency of the first cycle charge and discharge is as high as 96.9%,which exceeds the highest value reported so far,and the cycle time of 250cycles is also 11 times higher than that of the comparison sample,and the energy efficiency still reaches 91%.SEM images show that SnI₂ realized liquid-phase three-dimensional growth of the discharge product;the mechanism of the discharge product formation mediated by solution is proposed,and the discharge product undergoes two stages of transformation,first generating Sn²⁺（RO）_xO₂-solution-phase discharge product with increased solubility of the discharge product,which is transformed into Li₂O₂ through the second discharge step,and the ORR performance is significantly improved,as well as with better cycling stability.（2）The use of SnI₂together with the charging catalyst TDPA further improved the charge and discharge performance of the Li-air battery,exhibiting the characteristics of a bifunctional catalyst.The discharge capacity was increased to 95986 m Ah/gcarbon（=9.34m Ah/cm²）,which was 20%higher than that of the SnI₂ sample alone;in a cycle test at a fixed capacity of 500 m Ah/gcarbon at a current density of 100 m A/gcarbon,the charge/discharge energy efficiency was as high as 99.4%in the first cycle,and after 500cycles the energy efficiency After 500 cycles,the energy efficiency still reached more than90%,which is significantly better than 250 weeks for the SnI2 sample alone and 45 weeks for the TDPA alone.