Researchers Unveil Mystery Inside Lithium-Oxygen Batteries
With a high power density, Li-O2 batteries have become a state-of-the-art battery Innovation. Inside the Li-O2 battery, the generation and disintegration of the discharged product solid lithium peroxide (Li2O2) have a significant impact on the battery’s performance.
Previous research has shed little light on Li2O2 form and distribution inside, leaving questions regarding the trend and contributing factors of internal Li2O2 change in form and size unanswered.
Recently, a group led by Prof. Tan Peng from the College of Science and Technology of China (USTC) of the Chinese Academy of Sciences designed a carbon-coated anodic aluminum oxide (C-AAO) air electrode with a highly-ordered, array-like structure. The group acquired new insights into the sudden death and reaction routes of Li-O2 batteries. The work was published in Nano Letters.
The research team designed a particular C-AAO electrode that breaks easily yet preserves its distribution of products, enabling Li2O2 observations throughout the entire electrode. The team used electrochemical impedance spectroscopy (EIS) to determine the contributing factor to sudden voltage drop and death at various current densities.
Research findings show that, at small currents, channel diameters restrict the growth of toroidal Li2O2, causing electrode blockage. So the sudden death in voltage is associated with a large charge transfer impedance and concentration polarization caused by electrode blockage. While at high currents, the sudden death is attributed to the less significant charge transfer impedance and concentration polarization from the fast electrochemical reactions.
Additionally, to find the mechanism of such reactions, the research team conducted a detailed analysis on the growth model of Li2O2 on the end surfaces and the interior of C-AAO electrodes. Li2O2 on the end surfaces is found in three toroidal model.
The most typicall one grows “hugging” the wall, creating an incomplete ring. The rest either grows laterally on the surface or in the form of nuclei, making on other Li2O2 surfaces. As current density amplifies, toroidal Li2O2 inside the electrode is likely to be covered by its flocculated counterparts, indicating that Li2O2 is produced along the electrode surfaces rather than from disproportionation inside channels.
The group proposed a new growth route for toroidal Li2O2, in which Li2O2 formed at the Li2O2/electrode interface throughout early growth is related to the surface route, followed by lithium peroxide (LiO2) in solution disproportionating around Li2O2 particles, covering the surface route and creating an incomplete ring.
This study offered answers to long-standing questions concerning the mechanism of Li-O2 batteries and insights into further electrode design.
More information:
Zhuojun Zhang et al, Reacquainting the Sudden-Death and Reaction Routes of Li–O2 Batteries by Ex Situ Observation of Li2O2 Distribution Inside a Highly Ordered Air Electrode, Nano Letters (2022). DOI: 10.1021/acs.nanolett.2c02516
Originally published by: PHYS.
