The Studies Of Nitrogen-Doped Carbon Flexible Oxygen Electrode And Mn_xCo_3-xO₄-decorated Separator For Li-O₂ Batteries

Li-O₂ batteries have been attracting much attention as promising power sources for electric vehicles（EVs）due to their significantly higher theoretical energy densities.One big challenge for Li-O₂ batteries thus far is the large overpotential,which could lower the round-trip efficiency and decompose the cathode materials and electrolytes.Using solid electrocatalysts and redox mediators（RMs）can decrease the energy barrier and promote the reaction kinectic,which thus minimizes the polarization.Although the solid electrocatalysts have been investigated,the poor contact between Li₂O₂ and catalyst is the key bottleneck due to its inherent immobilized nature.At present,an alternative approach comprises the soluble RMs.However,it has been reported that the redox shuttle effect exists in the RM-based Li-O₂ system,which leads to an unexpected RM decomposition and a serious deterioration of Li metal.In attempts to alleviate the problems above,the research presented in this thesis covers two parts as following :1.NCNs/CTs was prepared by ball-milled and heat treatment,which was used as flexible O₂ electrode in Li-O₂ cell.The porous nanocage structure can accelerate the full electrolyte penetration,Li⁺ migration and O₂ diffusion,and can promote the electrochemical reaction rate.Compare to the cell with pure CTs and reference electrode of NCNsNPs+binder/CTs,the cell with NCNs/CTs exhibits a lower overpotential,a good cyclability and a considerable reversibility.These enhanced results can be attributed to the highly electrochemical activity of NCNs and the proper binder-free and flexible electrode design.2.We introduced a bifunctional Mn_xCo_3-xO₄-decorated separator for efficient Li-LiI-O₂ batteries,which was applied to inhibit the shuttling effect.This bifunctional Mn_xCo_3-xO₄-based separator can not only protect Li anode from corrosion,but also promote both I^-/I₃^-and I₃^-/I₂ redox conversions.In addition,the redox mechanisam and the contribution of LiI on battery performance were also investigated.The cells with Mn_xCo_3-xO₄-based separators can sustain 461 cycles at a constant current density of 200 mA g^-1under the limited capacity of 1000 mAh g^-1within a potential range of 2.3-4.0 V vs.Li/Li⁺.This work can contribute to the development of functional separator for RM-based Li-O₂ batteries.