The Research Of Catalytic Mechanism Of Redox Mediator In Lithium Air Batteries

With the ever-growing for the new energy revolution,the demand for next-generation energy storage technology with superior energy density have increased.Li–Air batteries with the extremely high theoretical specific energy(ca.3500Wh kg^-1)have attracted enormous researcher attention.However,the practical application of Li–O₂technology is severely hindered by low round-trip efficiency and poor cycle life,which can be ascribed to the passivation of the cathode surface by the insulated discharge product.Soluble redox mediators（RM）,are considered as an efficient tool to effectively reduce discharge or charge overpotential of Li-Air battery because of its homogeneously dissolved in the electrolyte,resulting in providing more catalytic site.The RM has the issues of poor chemical stability,unknown mechanism and inherent shuttle effect,which is due to oxidized RMs molecules easily migrated from the cathode side and to react with the Li metal anode.Based on the reaction mechanism and research obstacles of the redox mediators,the following studies have been carried out:（1）First of all,the ZnO-decorated/nitrogen-doped carbon frameworks on reduced graphene oxide（ZC-rGO）are presented for preventing shuttle effect.During discharging,the sheet-like rGO as the support provides ample space for discharge products growth.Upon charging,the uniformly distributed dodecahedral framework can capture of the Br₃^-ions,which originates at the cathode surface.This hierarchical and detached structure design guarantees effective reaction between the Br₃^-and Li₂O₂,fundamentally prevent shuttle effect.Even though at high concentration of 1M LiBr,the cells with ZC-rGO cathode exhibit low charge voltage,highly rate performance,and appreciable cycle stability.（2）Then,we carried out mechanism reaserch that the use of different concentrations LiBr as redox mediators applied in rechargeable Li-CO₂ batteries.We conducted a series of tests to prove that the mediator can promote the reversible decomposition of discharge products（Li₂CO₃ and C）.In the cell with low concentration mediators,it is confirmed that the Br₃^-ion can decompose lithium carbonate with a rather low charging platform（<4.2V）.Mediators can be applied as an effectual catalyst for the design of rechargeable Li-CO₂ batteries.