An Open‐Structured Matrix as Oxygen Cathode with High Catalytic Activity and Large Li₂O₂ Accommodations for Lithium–Oxygen Batteries

Abstract

However, several severe obstacles, particularly the large overpotential and the limited capacity far less than theory, have hindered the practical application of Li-O 2 batteries. [2] Many authors have revealed that the high overpotential of Li-O 2 batteries is mainly attributed to the sluggish oxygen redox kinetics, [2a,3] electrical passivation of the cathode by the poorly conducting Li 2 O 2 , [4] inferior Li 2 O 2 /cathode contact interface, [5] and undesired parasitic reactions. [6] As a gas electrode, two factors, structural factor and catalytic factor, are crucial in the electrochemical performance. Although the two factors are interrelated and interplayed, basically, the structural factor will determine the O 2 electrode capacities and the O 2 active species diffusions, while the catalytic factor will determine the oxygen redox kinetics. In the past few years, tremendous efforts have been devoted to developing effective oxygen cathodes for improving the electrochemical performance of Li-O 2 batteries. [7] A variety of carbon catalysts with well-designed architecture have been proposed to serve as frameworks for insoluble Li 2 O 2 storage mainly for improving the discharge capacity but with very limited overpotential improvement. [7a-e] On the other hand, different kinds of noble metals [7f-i] and transition metal oxides (TMOs) [7j-q] were widely used to reduce the large overpotential of Li-O 2 batteries but with relatively low capacity. In fact, these investigations which only focused on either the structural factor or catalytic factor are not The nonaqueous lithium-oxygen (Li-O 2 ) battery is considered as one of the most promising candidates for next-generation energy storage systems because of its very high theoretical energy density. However, its development is severely hindered by large overpotential and limited capacity, far less than theory, caused by sluggish oxygen redox kinetics, pore clogging by solid Li 2 O 2 deposition, inferior Li 2 O 2 /cathode contact interface, and difficult oxygen transport. Herein, an open-structured Co 9 S 8 matrix with sisal morphology is reported for the first time as an oxygen cathode for Li-O 2 batteries, in which the catalyzing for oxygen redox, good Li 2 O 2 /cathode contact interface, favorable oxygen evolution, and a promising Li 2 O 2 storage matrix are successfully achieved simultaneously, leading to a significant improvement in the electrochemical performance of Li-O 2 batteries. The intrinsic oxygen-affinity revealed by density functional theory calculations and superior bifunctional catalytic properties of Co 9 S 8 electrode are found to play an important role in the remarkable enhancement in specific capacity and round-trip efficiency for Li-O 2 batteries. As expected, the Co 9 S 8 electrode can deliver a high discharge capacity of ≈6875 mA h g −1 at 50 mA g −1 and exhibit a low overpotential of 0.57 V under a cutoff capacity of 1000 mA h g −1 , outperforming most of the current metal-oxide-based cathodes.

Hierarchical NiCo2S4@NiO Core–Shell Heterostructures as Catalytic Cathode for Long‐Life Li‐O2 Batteries

“…For example, Yan's group reported the embedded growth of large Li 2 O 2 aggregates on cathode surface with preferable OER polarization by virtue of different catalytic properties of α‐MnO 2 and Co 3 O 4 . Dong's group constructed an open‐structured Co 9 S 8 matrix realizing large hydrangea‐like Li 2 O 2 aggregations that could yield huge discharge capacity and exhibit lower charge overpotential simultaneously . However, trapped in the limited electrical conductivity and catalytic activity of metal oxide and single metal sulfide, the rate capability and long‐term cycling stability of these electrodes are still not good enough to satisfy the need of large‐scale commercial viability for Li‐O 2 batteries.…”

Metallic Co9S8 Coupled Hollow N‐Doped Carbon Sphere with Synergistic Interface Structure for Efficient Electricity Generation in Microbial Fuel Cells

“…As shown in Figure a, the Co 2p spectrum was described by the spin‐orbit doublets and shake‐up satellites with center peaks located at 781.3 and 796.8 eV, corresponding to the Co 2p 3/2 and Co 2p 1/2 electrons respectively, which could be further deconvoluted into two peaks. Given that the less binding energies of the transition metal 2p orbital always correspond to the lower oxidation state, the deconvoluted peaks at 778.4 and 793.9 eV anticipated the appearance of Co cta or Co tetra from Co−Co bonds, rather than Co 3+ . Since the ratio of peak area at 778.4 and 781.3 eV was determined about 0.044 instead of 0.125 (calculated from Table S1), the deconvoluted peak at 778.4 eV should be assigned to Co–Co bond, which was responsible for the metallic character of Co 9 S 8 owing to the bonding states occupying at the Fermi level, while the rest deconvoluted peaks at 781.3 and 796.8 eV were attributed to Co−S bonds.…”

Carbon‐Free Cathode Materials for Li−O2 Batteries

“…The property of the cathode material itself plays a significant role as well as the large surface area does. Lin et al . firstly reported an open‐structured Co 9 S 8 matrix with sisal morphology (Figure c).…”