The Preparation Of Self-standing Electrode And Its Electrochemical Performance In Lithium-oxygen Battery

Rechargeable lithium-oxygen?Li-O₂?battery,as a new type of battery system,has attracted worldwide attention due to its high theoretical energy(3600 Wh kg^-1).Its appearance was considered as a revolutionary event in the electrical energy storage field.However,the development of Li-O₂ battery is still in its infancy stage,and there are still numerous key scientific and technological problems that must be overcome before its commercial application could come true.These problems include the volatilization of liquid electrolytes,the corrosion and chalking of lithium anode,the poor stability of cathodes and so on.Additionally,the involvement of electrochemically inactive polymer binders in the traditional cathode fabrication,such as polytetrafluoroethylene?PTFE?and polyvinylidene fluoride?PVDF?,would concurrently occupy the porous channels,thus blocking the diffusion of oxygen and electrolyte and limiting the specific capacities of Li-O₂ batteries.And the organic binders would also be survived nucleophilic attack of high-sensitive intermediated radicals and decompose to Li F,LiOH and Li₂CO₃,which may passivate the surface of the electrode.In response to these above problems,a serious of works about binder-free porous electrodes have been carried out.Cerium dioxide?ceria?,as an effect redox catalyst,has the ability to catalyse the oxygen reduction reaction?ORR?and oxygen evolution reaction?OER?in Li-O₂ battery.In addition,ceria is an active catalyst that enhances the reactivity of other materials.In this article,CeO₂ nanoparticles was successfully loaded on the NiCo₂O₄ nanowires via the water-bathing method?CeO₂@NiCo₂O₄?.Due to its good catalytic performance and unique nanowire arrays structure,CeO₂@NiCo₂O₄ electrode in Li-O₂ battery has great electrochemical performances,including lower discharge-charge voltage gap,larger discharge capacity and longer cycle life.The discharge product Li₂O₂ was also investigated via SEM.Different from the sludge-like products on the NiCo₂O₄ cathode,the nanosheet-like discharge products are uniformly and loosely dispersed on the surface of CeO₂@NiCo₂O₄ cathode.This arrangement helps to maintain active sites of CeO₂@NiCo₂O₄ electrode,supporting the electrochemical reaction during subsequent discharge and thus improving the electrochemical performance of the Li-O₂ battery.Mo₂C nanoparticles modified carbon nanofibrous electrodes?MCNFs?are successfully prepared via electrospinning technique and high temperature carbonization.The choice of high temperature carbonization temperature is crucial for the synthesis of Mo₂C nanoparticles during the preparation.The three-dimensional network structure of the MCNFs electrode would promote the rapid diffusion of electrolyte and oxygen and provide sufficient space for the deposited discharge products.In addition,well dispersed Mo₂C nanoparticles on the carbon nanofibers provide enough catalytic active sites for the cell,which can effectively promote the formation/decomposition of the discharge product Li₂O₂.As a result,Li-O₂ batteries with MCNFs electrodes have good electrochemical performance,including high specific capacity(10,509 mAh g^-1 at 100mA g^-1),low discharge-charge voltage gap?1.0 V?,and long cycle life(124 cycles at200 mA g^-11 with a specific capacity limit of 500 mAh g^-1).Activated cobalt-nitrogen-doped carbon-nanotube/carbon-nanofiber composites as cathodes for Li-O₂ batteries have been successfully prepared via a novel in situ chemical vapour deposition.The unique three-dimensional network structure of Co-N-CNT/CNF electrode could improve the rapid oxygen diffusion and electrolyte penetration.Meanwhile,the Co-N-C composites and Co/CoN_x exhibites good ORR and OER properties,respectively.These active sites would promote the reversible formation/decomposition of discharge product Li₂O₂.Therefore,Li-O2 batteries with Co-N-CNT/CNF electrodes have good electrochemical performances,including lower overpotential,higher discharge capacity,better capacity rate and longer cycle life.In addition,benefitting from the excellent flexibility of Co-N-CNT/CNF electrode,the assembled flexible battery can work normally and hold better discharge potentials under various shapes.