Lee Donghoon, Park Hyeokjun, Ko Youngmin, Park Hayoung, Hyeon Taeghwan, Kang Kisuk, Park Jungwon
Center for Nanoparticle Research , Institute for Basic Science , Seoul 08826 , Republic of Korea.
J Am Chem Soc. 2019 May 22;141(20):8047-8052. doi: 10.1021/jacs.9b02332. Epub 2019 May 8.
Li-O battery is one of the important next-generation energy storage systems, as it can potentially offer the highest theoretical energy density among battery chemistries reported thus far. However, realization of its high discharge capacity still remains challenging and is hampered by the nature of how the discharge products are formed, causing premature passivation of the air electrode. Redox mediators are exploited to solve this problem, as they can promote the charge transfer from electrodes to the solution phase. The mechanistic understanding of the fundamental electrochemical reaction involving the redox mediators would aid in the further development of Li-O batteries along with rational design of new redox mediators. Herein, we attempt to monitor the discharge reaction of a Li-O battery in real time by liquid-phase transmission electron microscopy (TEM). Direct in situ TEM observation reveals the gradual growth of toroidal LiO discharge product in the electrolyte with the redox mediator upon discharge. Moreover, quantitative analyses of the growth profiles elucidate that the growth mechanism involves two steps: dominant lateral growth of LiO into disclike structures in the early stage followed by vertical growth with morphology transformation into a toroidal structure.
锂-氧电池是重要的下一代储能系统之一，因为在目前报道的所有电池化学体系中，它可能具有最高的理论能量密度。然而，要实现其高放电容量仍具有挑战性，并且受到放电产物形成方式的限制，这会导致空气电极过早钝化。氧化还原介质被用于解决这一问题，因为它们可以促进电荷从电极转移到溶液相中。对涉及氧化还原介质的基本电化学反应的机理理解，将有助于锂-氧电池的进一步发展以及新型氧化还原介质的合理设计。在此，我们尝试通过液相透射电子显微镜（TEM）实时监测锂-氧电池的放电反应。直接原位TEM观察揭示了在放电过程中，随着氧化还原介质的存在，电解质中环形LiO放电产物逐渐生长。此外，对生长曲线的定量分析表明，生长机制包括两个步骤：早期LiO主要横向生长成盘状结构，随后纵向生长并发生形态转变形成环形结构。
