Design,Preparation And Properties Of Carbon-Based Cathode For Lithium-Oxygen Batteries

Rechargeable lithium-oxygen(Li-O2)batteries are considered to be one of the most promising candidates to replace conventional lithium-ion(Li-ion)batteries as energy storage mediums.The theoretical specific energy density of Li-O2 batteries can be as high as 3485 Wh kg-1,which is almost ten times higher than that of Li-ion batteries(387 Wh kg-1).Currently,the realization of Li-O2 batteries with high capacity have to adopt carbon or carbon-based materials as cathodes due to their large surface area and pore volume,which offer more catalytic active sites for oxygen reduction reaction(ORR)and storage space of the discharge product,lithium peroxide(Li2O2).However,the Li-O2 batteries based on carbon cathodes face several serious challenges,including large polarization and low round-strip efficiency due to the poor catalytic performance for ORR and oxygen evolution reaction(OER).Therefore,the development of a porous carbon-based cathode combined with a high-efficiency and low-cost difunctional catalyst(spinel metallic oxide: Co3O4,NiCo2O4)is a promising strategy for improving the performance of Li–O2 batteries.In the paper,the economic spinel-type metal oxides(Co3O4,NiCo2O4)with high catalytic activity are grown on different porous carbon substrate.With the suitable design of electrode structure,four kinds of carbon-based cathodes are prepared and work as the cathode in the lithium oxygen batteries.The detailed discussion on the relation among the electrode structure,morphology and catalytic performance are systematically explored:1.The Co3O4 nanoparticles are loaded on the nitrogen doping ordered mesoporous carbon(named Hollow Co3O4/NOMC)through the solvent evaporation induced self-assembly method,combining a two-step heat treatment,where the composites are oxygenized at 300 ? and carbonized in the N2 at 800 ?.The Hollow Co3O4/NOMC delivers the large specific surface area(650 m2 g-1)with ordered mesostructure.What's more,the high heat treatment ensures the graphitization degree and the crystallinity of Co3O4 nanoparticles.The electrochemical test demonstrates that Hollow Co3O4/NOMC have more positive onset potentials,half wave reduction potential,and higher limit diffusion current density,exerting the superior catalytic performance for ORR(Oxygen Reduction Reaction).In the lithium oxygen batteries,the Hollow Co3O4/NOMC cathode shows a high specific discharge capacity(3472 mAh g-1)and the narrow cell polarization.To further increase the electrochemical performance in the batteries,the precursor was directly composited with carbon paper by the spin-coating method.The obtained non-binder cathodes have the outstanding rate performance due to the increased electronic transmission and the plenty of open hole lead to the higher capacity(4190 mAh g-1).Moreover,the abandon of binder also minimize many side reaction,thus making the batteries cycle for 72 times at the current density of 200 mA g-1 with the cut-off capacity of 1000 mAh g-1.2.We in-situ fabricated a three-dimensional(3D)hierarchical porous hybrid film composed of metallic oxide(Fe2O3,Co3O4,NiCo2O4)nanoparticles(NPs)-decorated mesoporous N-doped carbon nanofibers(Fe2O3@NCF,Co3O4@NCF,NiCo2O4@NCF),using electrospinning combined with annealing treatment.Thereinto,NiCo2O4@NCF possesses the best catalytic activities for oxygen reduction reaction(ORR)and oxygen evolution reaction(OER)This hybrid film can serve directly as a binder-free self-supported cathode for Li–O2 batteries that exhibit high specific capacity(5304 mAh g-1),excellent rate capability,and outstanding cycling stability(close to 100 cycles),benefiting from structural and material superiority.Its hierarchical porous structure not only can facilitate O2 diffusion and enhance electrolyte infiltration but also promises abundant Li2O2 storage.In addition,crisscross N-doped carbon nanofibers with high graphitization form the perfect conductive network,which ensures the fast transmission of electrons and avoids binder-induced adverse side reactions.Moreover,the homogenously distributed NiCo2O4 NPs possess the efficient contact of both Li+ and O2 and supply numerous catalytic active sites,thus leading to high-efficiency difunctional catalytic activities for ORR and OER.Therefore,these encouraging results suggest an effective approach to obtaining high-performance nonaqueous Li–O2 batteries by optimizing the electrode structures and catalyst properties.3.The NiCo2O4 nanoparticles are firmly anchored onto the surface of the N-doped reduced graphene oxide(N-rGO)by the hydrothermal method followed by low temperature calcination.Compaed with the pure metallic oxide,the introduction of the rGO can create the high surface area,which provides plenty of catalytic active sites for ORR,and improve the electrical conductivity between the NiCo2O4 nanoparticles.The high-loading NiCo2O4 nanoparticles also ensure the material to have great catalytic activity for OER and the rGO can protected by the nanoparticle coating against the side reaction with the Li2O2.The as-synthesized NCO@N-rGO composites have a specific surface area(about 242.5 m2 g-1),exhibiting the three-dimensional(3D)porous structure,which provides large passageway for the diffusion of the oxygen and the electrolyte and the storage of the discharge products.Owing to these special architectures features and intrinsic materials,the NCO@N-rGO cathode delivers a high specific capacity(6716 mAh g-1),great rate performance and excellent cycling stability(112 cycles)for lithium-oxygen batteries.The improved electrochemical catalytic activity and the special 3D porous structure make the NCO@N-rGO composites be a promising candidate for Li-O2 batteries.4.An effective binder-free cathode with high capacity for Li-O2 batteries,needle-like mesoporous NiCo2O4 nanowire arrays uniformly coated on the flexible carbon textile have been in-situ fabricated via a facile hydrothermal process followed by low temperature calcination.Due to the material and structural features,the needle-like NiCo2O4 nanowire arrays(NCONWAs)served as a binder-free cathode exhibits high specific capacity(4221 mAh g-1),excellent rate capability,and outstanding cycling stability(200 cycles).This cathode based on nonprecious mesoporous metal oxides nanowire arrays has large open spaces and high surface area(90 m2 g-1),providing numerous catalytically active sites and effective transmission pathways for lithium ion and oxygen,and promises the abundant Li2O2 storage.The fast electron transport by directly anchoring on the substrate ensures fast electrochemical reaction process involved with the every nanowire.Furthermore,a bendable Li-O2 battery assembled by using the flexible NCONWAs as the cathode,can be able to light an LED and shows good rate capability and cyclic stability.