Ahn Su Mi, Kim Do Youb, Suk Jungdon, Kang Yongku, Kim Hwan Kyu, Kim Dong Wook
Advanced Materials Division, Korea Research Institute of Chemical Technology, Yuseong, Daejeon 34114, Korea.
Global GET-Future Laboratory & Department of Advanced Materials Chemistry, Korea University, 2511 Sejong-ro, Jochiwon, Sejong 30019, Korea.
ACS Appl Mater Interfaces. 2021 Feb 24;13(7):8159-8168. doi: 10.1021/acsami.0c17960. Epub 2021 Feb 15.
Excessive overpotential during charging is a major hurdle in lithium-oxygen (Li-O) battery technology. NO/NO redox mediation is an efficient way to substantially reduce the overpotential and to enhance oxygen efficiency and cycle life by suppressing parasitic reactions. Considering that nitrogen dioxide (NO) is a gas, it is quite surprising that NO/NO redox reactions can be sustained for a long cycle life in Li-O batteries with such an open structure. A detailed study with in situ differential electrochemical mass spectrometry (DEMS) elucidated that NO could follow three reaction pathways during charging: (1) oxidation of LiO to evolve oxygen, (2) vaporization, and (3) conversion into NO. Among the pathways, LiO oxidation occurs exclusively in the presence of LiO, which suggests that NO has high reactivity to LiO. At the end of the charging process, most of the volatile oxidized couple (NO) is stored by conversion to a stable third species (NO), which is then reused for producing the reduced couple (NO) in the next cycle. The dominant reaction of LiO oxidation involves the temporary storage of NO as a stable third species during charging, which is an innovative way for preserving the volatile redox couple, resulting in a sustainable redox mediation for a high-performance Li-O battery.
充电过程中过高的过电位是锂氧（Li-O）电池技术的一个主要障碍。NO/NO氧化还原介导是一种通过抑制寄生反应来大幅降低过电位、提高氧效率和循环寿命的有效方法。考虑到二氧化氮（NO）是一种气体，在具有如此开放结构的Li-O电池中，NO/NO氧化还原反应能够在长循环寿命中持续进行，这相当令人惊讶。一项采用原位差分电化学质谱（DEMS）的详细研究表明，在充电过程中NO可以遵循三条反应途径：（1）LiO氧化以释放氧气，（2）汽化，以及（3）转化为NO。在这些途径中，LiO氧化仅在LiO存在时发生，这表明NO对LiO具有高反应活性。在充电过程结束时，大部分挥发性氧化对（NO）通过转化为稳定的第三种物质（NO）而被储存起来，然后在接下来的循环中再用于生成还原对（NO）。LiO氧化的主要反应涉及在充电过程中将NO暂时储存为稳定的第三种物质，这是一种保存挥发性氧化还原对的创新方式，从而实现了高性能Li-O电池的可持续氧化还原介导。
