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All‐solid‐sate Al‐air batteries with features of high theoretical energy density, low cost, and environmental‐friendliness are promising as power sources for next‐generation flexible and wearable electronics. However, the sluggish oxygen reduction reaction (ORR) and poor interfacial contact in air cathodes cause unsatisfied performance. Herein, a free‐standing Co3Fe7 nanoalloy and Co5.47N encapsulated in 3D nitrogen‐doped carbon foam (Co3Fe7@Co5.47N/NCF) is prepared as an additive‐free and integrated air cathode for flexible Al‐air batteries in both alkaline and neutral electrolytes. The Co3Fe7@Co5.47N/NCF outperforms commercial platinum/carbon (Pt/C) toward ORR with an onset potential of 1.02 V and a positive half‐wave potential of 0.92 V in an alkaline electrolyte (0.59 V in sodium chloride solution), which is ascribed to the unique interfacial structure between Co3Fe7 and Co5.47N supported by 3D N‐doped carbon foam to facilitate fast electron and mass transfer. The high ORR performance is also supported by in‐situ electrochemical Raman spectra and density functional theory calculation. Furthermore, the fabricated Al‐air battery displays good flexibility and delivers a power density of 199.6 mW cm−2, and the binder‐free and integrated cathode shows better discharge performance than the traditionally slurry casting cathode. This work demonstrates a facile and efficient approach to develop integrated air cathode for metal‐air batteries.

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Carbon dots (CDs) as new nanomaterials have attracted much attention in recent years due to their unique characteristics. Notably, structure and interface modification (carbon core, edge, defects, and functional groups) of CDs have been considered as valid methods to regulate their properties, which contain electron transfer effect, electrochemical activity, fluorescence luminescent, and so on. Additionally, CDs with ultrasmall size, excellent dispersibility, high specific surface area, and abundant functional groups can guarantee positive and extraordinary effects in electrical energy storage and conversion. Therefore, CDs are used to couple with other materials by constructing a special interface structure to enhance their properties. Here, diverse structural and interfacial modifications of CDs with various heteroatoms and synergy effects are systematically analyzed. And not only several main syntheses of CDs‐based composites (CDs/X) are summarized but also the merit and demerit of CDs/X in electrical energy storage are discussed. Finally, the applications of CDs/X in energy storage devices (supercapacitors, batteries) and electrocatalysts for practical applications are discussed. This review mainly provides a comprehensive summary and future prospect for synthesis, modification, and electrochemical applications of CDs.

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The oxygen reduction reaction (ORR) with sluggish kinetics on the cathode of aluminum–air (Al–air) batteries greatly limits their further development. Here, a new strategy is proposed to synthesize oxygen and nitrogen codoped carbon nanofibers loaded with manganese oxides (MnO/Mn2O3/ONCNF-n) as an efficient electrocatalyst for ORR by using oxygen plasma surface etching. The MnO/Mn2O3/ONCNF-3 exhibit superior ORR performance in an alkaline electrolyte, which is attributed to various active sites including N and O heteroatoms, vacancies, and manganese oxides. Additionally, the fabricated homemade Al–air battery (AAB) with MnO/Mn2O3/ONCNF-3 exhibits a maximum power density of 129.7 mW cm–2, demonstrating comparable performance to AABs based on the commercial Pt/C catalyst. This work provides a new approach of using O2 plasma for enhancing the ORR catalytic activities of carbon materials.

The increasing interests in flexible and wearable electronics stimulates the exploration of new energy storage systems. Flexible aluminum-air batteries with the features of high energy density, good safety, low cost and eco-friendly have attracted much attention. Herein, a sodium polyacrylate (PANa) based electrolyte with an optimized amount of sodium carboxymethyl cellulose (CMC) is prepared through free radical polymerization and employed to fabricate flexible Al-air batteries. The prepared PANa-5% CMC polymer electrolyte exhibits excellent ionic conductivity (0.324 S cm −1 ), mechanical strength and water uptake ability. This achieved properties can be attributed to the introduce of CMC, which not only decreases size of the pores but also forms the cobweb-like networks with a large amount of functional groups. The fabricated Al-air battery displays good flexibility and shows enhanced discharge performance with a higher voltage plateau and larger specific capacity, resulting in a maximum power density of 137 mW cm −2 . More importantly, the used gel polymer electrolyte can be recovered without any performance decay. Furthermore, the Al-air batteries are demonstrated to charge mobile phone and power smart watch in a flexible state, showing promising potential in flexible energy storage devices.

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