N- and F-Co-Doped Carbon Quantum Dots Coated on a Ni Foam Substrate as Current Collector for Highly Stable Li-Air Batteries

Because of their high theoretical density, Li-air batteries (LABs) are expected to be critical components of future energy storage devices. However, the commercial use of LABs is limited by their low charge-discharge efficiency, high overpotential, and low cyclic stability. Therefore, to improve the cyclic stability of LABs, we manufactured N- and F-co-doped carbon quantum dots (NF-CQDs), thinly coated them on the surface of a Ni foam current collector via ultrasonic spray coating, and used the as-fabricated NF-CQD/Ni as the current collector of an LAB cathode. The NF-CQD/Ni-based cathode maintained remarkable cycling stability over 42 cycles (with a limited capacity was 1000 mAh/g) and exhibited a superior specific discharge capacity of approximately 5121.91 mAh/g (at 100 mA/g). NF-CQD/Ni-based cathode exhibits superior electrochemical properties, including its high cycling stability and high discharge capacity, primarily contributed by the NF-CQD coating layer, which prevented the oxidation of the Ni foam substrate and increased the electrical conductivity and electrocatalytic activity of the cathode. Therefore, NF-CQD/Ni can serve as an excellent current collector for LAB cathodes.