RESUMEN
Inferior charge transport in insulating and bulk discharge products is one of the main factors resulting in poor cycling stability of lithium-oxygen batteries with high overpotential and large capacity decay. Here we report a two-step oxygen reduction approach by pre-depositing a potassium carbonate layer on the cathode surface in a potassium-oxygen battery to direct the growth of defective film-like discharge products in the successive cycling of lithium-oxygen batteries. The formation of defective film with improved charge transport and large contact area with a catalyst plays a critical role in the facile decomposition of discharge products and the sustained stability of the battery. Multistaged discharge constructing lithium peroxide-based heterostructure with band discontinuities and a relatively low lithium diffusion barrier may be responsible for the growth of defective film-like discharge products. This strategy offers a promising route for future development of cathode catalysts that can be used to extend the cycling life of lithium-oxygen batteries.
RESUMEN
A top-down method was developed to synthesize hierarchical composites consisting of NiCo2O4 nanocubes and graphene nanosheets through the electrostatic interaction of negatively charged graphene oxide nanosheets and positively charged NiCo2O4 spheres. Employed as anode materials for lithium-ion batteries, the hierarchical composites exhibit remarkably high electrochemical performance, including large reversible capacity, superior rate capability, and excellent cycling performance. Large reversible capacities of 1024 and 648 mA h g-1 are maintained at a current density of 500 and 3000 mA g-1, respectively, for over 200 cycles. The excellent electrochemical performance of the composite is attributed to the synergistic effect of the hierarchical structure, the well dispersed NiCo2O4 nanocubes and the uniform graphene coating. This work provides an effective and promising strategy for the rational structural design of the metal oxide electrode material.
RESUMEN
Free-standing macroporous air electrodes with enhanced interfacial contact, rapid mass transport, and tailored deposition space for large amounts of Li2 O2 are essential for improving the rate performance of Li-O2 batteries. An ordered mesoporous carbon membrane with continuous macroporous channels was prepared by inversely topological transformation from ZnO nanorod array. Utilized as a free-standing air cathode for Li-O2 battery, the hierarchically porous carbon membrane shows superior rate performance. However, the increased cross-sectional area of the continuous macropores on the cathode surface leads to a kinetic overpotential with large voltage hysteresis and linear voltage variation against Butler-Volmer behavior. The kinetics were investigated based on the rate-determining step of second electron transfer accompanied by migration of Li+ in solid or quasi-solid intermediates. These discoveries shed light on the design of the air cathode for Li-O2 batteries with high-rate performance.
RESUMEN
Sodium-ion batteries have attracted considerable attention in recent years. In order to promote the practical application of sodium-ion batteries, the electrochemical performances, such as specific capacity, reversibility, and rate capability of the anode materials, should be further improved. In this work, a Fe2O3/C composite with a well-ordered mesoporous structure is prepared via a facile co-impregnation method by using mesoporous silica SBA-15 as a hard template. When used as an anode material for sodium-ion batteries, the well-ordered mesoporous structure ensures fast mass transport kinetics. The presence of nano-sized Fe2O3 particles confined within the carbon walls significantly enhances the specific capacity of the composite. The carbon walls in the composite act not only as an active material contributing to the specific capacity, but also as a conductive matrix improving the cycling stability of Fe2O3 nanoparticles. As a result, the well-ordered mesoporous Fe2O3/C composite exhibits high specific capacity, excellent cycleability, and high rate capability. It is proposed that this simple co-impregnation method is applicable for the preparation of well-ordered mesoporous transition oxide/carbon composite electrode materials for high performance sodium-ion and lithium-ion batteries.
RESUMEN
To lower the overpotential of a lithium-oxygen battery, electron transport at the solid-to-solid interface between the discharge product Li2O2 and the cathode catalyst is of great significance. Here we propose a strategy to enhance electron transport property of the cathode catalyst by the replace of oxygen atoms in the generally used metal oxide-based catalysts with nitrogen atoms to improve electron density at Fermi energy after nitridation. Hierarchically porous CoN nanorods were obtained by thermal treatment of Co3O4 nanorods under ammonia atmosphere at 350 °C. Compared with that of the pristine Co3O4 precursor before nitridation, the overpotential of the obtained CoN cathode was significantly decreased. Moreover, specific capacity and cycling stability of the CoN nanorods were enhanced. It is assumed that the discharged products with different morphologies for Co3O4 and CoN cathodes might be closely associated with the variation in the electronic density induced by occupancy of nitrogen atoms into interstitial sites of metal lattice after nitridation. The nitridation strategy for improved electron density proposed in this work is proved to be a simple but efficient way to improve the electrochemical performance of metal oxide based cathodes for lithium-oxygen batteries.
RESUMEN
In this work, hydroquinone resin was used to grow carbon nanotubes directly on Ni foam. The composites were obtained via a simple carbonization method, which avoids using the explosive gaseous carbon precursors that are usually applied in the chemical vapor deposition method. When evaluated as cathode for Li-O2 batteries, the binder-free structure showed enhanced ORR/OER activities, thus giving a high rate capability (12690 mAh g(-1) at 200 mA g(-1) and 3999 mAh g(-1) at 2000 mA g(-1)) and outstanding long-term cycling stability (capacity limited 2000 mAh g(-1), 110 cycles at 200 mA g(-1)). The excellent battery performance provides new insights into designing a low-cost and high-efficiency cathode for Li-O2 batteries.
RESUMEN
A novel binder-free electrode for lithium-oxygen batteries has been prepared by electrodepositing a Co3O4 layer onto a pretreated TiO2 fiber mesh, formed on nickel foam by an electrospinning method. The Co3O4 depositing layer is composed of Co3O4 nanoflakes, forming a uniform flower-like porous structure. The Co3O4 nanoflakes within the depositing layer provide a large amount of catalytic active sites for oxygen evolution and reduction reactions. The three-dimensional porous network of the Co3O4 depositing layer can not only facilitate the transportation of ions and electrolyte within the electrode, but also provide plenty of space to accommodate Li2O2 species formed during the discharge process. The Co3O4 spheres embedded in the TiO2 fiber mesh, formed by the treatment of a suspension of cobaltammine precipitate, function as anchors to prevent the detachment of the Co3O4 layer from the current collector, resulting in excellent structural and cycling stability. Only a slight specific capacity decay is observed at full discharge/charge after 80 cycles. This work demonstrates the important factors in the preparation of binder-free cathodes for high performance lithium-oxygen batteries.
