Rechargeable aprotic lithium (Li)-O batteries with high theoretical energy densities are regarded as promising next-generation energy storage devices and have attracted considerable interest recently. However, these batteries still suffer from many critical issues, such as low capacity, poor cycle life, and low round-trip efficiency, rendering the practical application of these batteries rather sluggish. Cathode catalysts with high oxygen reduction reaction (ORR) and evolution reaction activities are of particular importance for addressing these issues and consequently promoting the application of Li-O batteries. Thus, the rational design and preparation of the catalysts with high ORR activity, good electronic conductivity, and decent chemical/electrochemical stability are still challenging. In this Review, the strategies are outlined including the rational selection of catalytic species, the introduction of a 3D porous structure, the formation of functional composites, and the heteroatom doping which succeeded in the design of high-performance cathode catalysts for stable Li-O batteries. Perspectives on enhancing the overall electrochemical performance of Li-O batteries based on the optimization of the properties and reliability of each part of the battery are also made. This Review sheds some new light on the design of highly active cathode catalysts and the development of high-performance lithium-O batteries.

8514 wileyonlinelibrary.com electrolyte, and an O 2 -penetrating cathode. Though the operation of the Li-O 2 battery is based on a simple reaction (2Li + + O 2 + 2e − → Li 2 O 2 , E 0 = 2.96 V vs Li/Li + ) consisting of oxygen reduction reactions (ORR) and oxygen evolution reactions (OER), the practical application of Li-O 2 batteries is constrained by their low coulombic efficiency, poor rate capability, and especially short cycle life. [2,3] The rational design of cathode catalysts with high ORR and OER activities is of particular importance for promoting the practical application of Li-O 2 batteries. Porous carbon materials are a desirable choice due to their advantageous properties such as a wide source of raw materials, good electronic conductivity, tuneable porous structures, and high specific capacity; as a result, they are a popular choice for ORR catalysts for Li-O 2 batteries. [2,4,5] However, their poor OER activity leads to high charging potentials of over 4.5 V. These charging potentials are high enough to cause decomposing of the electrolyte and the carbon electrode, thus deteriorating the performance of the Li-O 2 battery. [6] Noble metals such as Pt and Au, and metal oxides (particularly RuO 2 ) give new insight into the design of high performance Li-O 2 battery cathodes. [7][8][9][10][11][12] These cathodes usually exhibit much higher efficiency in the Li 2 O 2 decomposition than that of carbon materials. Consequently, low charging potentials are observed (less than 4.0 V) and high cycling stability (more than 100 stable cycles) is achieved. However, the expensive raw materials, poor specific capacity, and complicated preparation procedures limit the further application of these cathode catalysts. [13] Porous transition metal oxides, on the other hand, are characterized by their low cost and accessible porous structures. However, issues such as poor electrical conductivity, low OER activity, and limited specific capacity impact their general application in Li-O 2 batteries. [14][15][16][17][18][19][20] Recently, metal carbides, particularly Mo 2 C, have received considerable attention due to their multiple valence states, high electrochemical activity, low electrical resistivity, and affordable cost. [21][22][23][24][25] Inspiring results have been reported for Mo 2 C as a cathode in Li-O 2 batteries. [26,27] Mo 2 C nanoparticle catalysts are believed to promote the formation of well-dispersed Li 2 O 2 Cathode design is indispensable for building Li-O 2 batteries with long cycle life. A composite of carbon-wrapped Mo 2 C nanoparticles and carbon nanotubes is prepared on Ni foam by direct hydrolysis and carbonization of a gel composed of ammonium heptamolybdate tetrahydrate and hydroquinone resin. The Mo 2 C nanoparticles with well-controlled particle size act as a highly active oxygen reduction reactions/oxygen evolution reactions (ORR/ OER) catalyst. The carbon coating can prevent the aggregation of the Mo 2 C nanoparticles. The even distribution of Mo 2 C nanoparticles results in the homogenous...

Lithium–oxygen batteries with an exceptionally high theoretical energy density have triggered worldwide interest in energy storage system. The research focus of lithium–oxygen batteries lies in the development of catalytic materials with excellent cycling stability and high bifunctional catalytic activity in oxygen reduction and oxygen evolution reactions. Here, a hierarchically porous flower‐like cobalt–titanium layered double oxide on nickel foam with intercalated anions of bistrifluoromethane sulfonamide (TFSI) is designed and prepared. When used as a binder‐free cathode for lithium–oxygen batteries, this material exhibits low polarization (initial polarization of 0.45 V) and superior cycling stability (80 cycles at a current density of 100 mA g−1 at full discharge/charge). The high electrochemical performance of the cathode material is attributed to the good dispersion of binary elements in its host layer and good compatibility with lithium bistrifluoromethane sulfonamide electrolyte induced by intercalated guest anions of TFSI within its interlayer. This work provides a novel strategy for the fabrication of binder‐free cathodes based on layered double oxides for high‐performance lithium–oxygen batteries.

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Supercapacitors based on nitrogen-doped micro/mesoporous carbon nets exhibited excellent specific capacitance and energy density.

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.

Sn/SnO nanoparticles are incorporated in crumpled nitrogen-doped graphene nanosheets by a simple melting diffusion method. The resulting composite exhibits large specific capacity, excellent cycling stability and high rate capability as an anode for lithium-ion batteries.

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