The Fabrication And Electrochemical Performance Of Noble-Metal-Free Catalyst For Li–O₂ Batteries

Aprotic Li–O₂ batteries have led to the emergence of a promising energy storage system owing to its extremely high theoretical storage capacity(3505 Wh kg^-1,based on Li₂O₂),which can meet the requirements for the long-range electric vehicles applications.However,the cathode product of Li₂O₂is the poor electrical conductivity and is also insoluble in aprotic Li–O₂ batteries,which results in the limited cathode reaction kinetics,high overpotential and poor cycle life.In response,it is highly desirable to rationally explore an optimal cathode catalysts involving highly active,stable in highly reactive oxygen species environment and well-defined hierarchical porous structure to efficiently catalyze ORR and OER as well as facilitating rapid diffusion of O₂ and electrolyte,which would improve the round-trip efficiency,initial discharge capacity and cycle life performance of the Li-O₂batteries.In this thesis,the electrochemical properties of non-noble metal cathode catalysts were analyzed.The details are as follows:?1?Porous Ni Co₂O₄ nanotubes have been successfully synthesized by a facile and cost-effective electrospinning method as noble metal-free catalysts for rechargeable Li-O₂ batteries.The as-synthesized Ni Co₂O₄ nanotubes with hollow cavity and porous wall is found to superiorly improve the electrochemical performance of the Li-O₂ batteries,including a high initial discharge capacity,reduced overpotential as well as good rate capability.Excellent cycle life over 110 cycles with the highly discharged voltage platform of 2.4 V at 200 m A g_c^–1 and limited capacity of 1000 m Ah g_c^–1was achieved.?2?Ultrathin Ni Co₂O₄ nanosheets directly supported on carbon nanofibers films?denoted as NCO/CNF?by solvothermal method is presented as a stable,noble metal-and binder-free cathode for Li–O₂ batteries.Combining well-defined hierarchical porous structure,enormous catalytic sites and remarkable electrolyte wettability on three-dimensional free-standing cathodes could be an efficient strategy for rechargeable Li–O₂ batteries,while simultaneously offering good stability in reactive oxygen radicals attack to prevent the formation of undesirable byproducts.Interestingly,the ultrathin Ni Co₂O₄ nanosheets result in continuous and well electrical contact Li₂O₂ layer on hierarchical NCO/CNF films,which may be responsible for the effective decomposition of Li₂O₂.The NCO/CNF air electrode exhibits greatly improved electrochemical performance with reduced overpotential and excellent cycling stability over 220 cycles at a limited capacity of 500 m Ah g_c^–1.?3?The stable and free-standing cathodes were combined with the nitrate anion electrolyte.The combination of Li NO₃ electrode illustrates outstanding electrochemical performance with reduced overpotential as low as 0.5 V at discharge 2000 m Ah g_c^–1,a high initial discharge capacity and excellent cycling stability of 130 cycles at a limited capacity of 1000 m Ah g_c^–1.