Preparation And Electrochemical Performances Of Carbon-based Composite Transition Metal Catalysts For Lithium Oxygen Battery

Lithium oxygen(Li-O2)batteries(LOBs)have a wide range of applications in the field of energy conversion and storage equipment because of their ultra-high theoretical energy density.LOBs undergo oxygen reduction reaction(ORR)and oxygen precipitation reaction(OER)during discharge/charging,however,due to its slow ORR and OER dynamics,resulting voltage polarization,poor cycle life and other problems.Therefore,the development of highperformance cathode catalysts is of great significance to solve these problems and promote the commercialization of LOBs.The cathode carbon-based composite transition metal catalyst material is applied to the LOBs to improve its electrochemical properties.Carbon materials such as carbon nanotubes and graphene with porous structures can not only provide sufficient pore structure for the charge transfer of batteries,but also can anchor the transition metal particles,effectively enhancing the exposure of the metal active center and the conductivity of the composite catalyst.The specific contents are as follows:(1)The precious metal of iridium(Ir)nanoparticles and amorphous cobalt oxide(CoO)coatings were successfully introduced on multi-walled carbon nanotubes(CNT)by using simple solvent thermal reaction and one-step reduction reaction.In the prepared Ir/CoO@CNT cathode material,the amorphous CoO is uniformly coated on the surface of the CNT,while anchoring the precious metal ir is uniformly dispersed in the form of nanoparticles.Ir/CoO@CNT cathode material provides more active sites for the formation and decomposition of lithium peroxide(Li2O2),catalyzes the formation and complete decomposition of toroidallike Li2O2 at the three-phase reaction interface on the cathode,improves the discharge specific capacity of CNT and greatly reduces the charging overpotential of LOBs.At the current density of 100 mA g-1,the Ir/CoO@CNT electrode of LOBs shows a discharge specific capacity of～7600 mAh g-1,and the charge-discharge overpotential is only 1.2 V.And at the current density of 100 mA g-1 with the limited capacity of 500 mAh g-1,the Ir/CoO@CNT electrode maintained continuous cycles over 170 cycles,showing good rate capacity,strong cycle stability and long cycle life.(2)The cathode material of manganese selenide(MnSe@S-rGO)loaded on the sulfur-doped reduced GO surface was obtained by using one-step reaction.α-MnSe between the layers of rGO play key role in avoiding the accumulation of reduced GO layer.Moreover,the continuous loose porous 3D structure provides high conductivity for the cathode material,provides sufficient three-dimensional space for the storage of Li2O2,and provides rapid diffusion channels for the rapid transfer of lithium ions.There is a phenomenon of a cycle of activation process for MnSe@S-rGO catalyst material,and α-MnSe is activated after first cycle.LOBs showed an excellent discharge specific capacity of over 10000 mAh g-1 on the second cycle,up to 11078 mAh g-1.LOBs with MnSe@S-rGO catalyst shows a stable charge and discharge polarization and a continuous cycle over 150 cycles,indicating MnSe@S-rGO material possess a good catalytic ability,at the current density of 100 mA g-1 and the fixed capacity of 500 mAh g-1.After charging,MnSe@S-rGO electrode shows a better trends of impedance changes,and Rct drops to a similar value as the original battery,indicating MnSe@S-rGO can catalyze the complete decomposition of Li2O2.