Zhengyuan Tu and Snehashis Choudhury, of the Archer Group, publish in Nature Energy

Appearing in Nature Energy this month is an article published by Zhengyuan Tu and Snehashis Choudhury, et al. from Prof. Lynden Archer’s lab. It reports the invention of a designed interphase on alkali metal anodes which significantly promotes the efficient and long-lifetime operation of high energy metal-based batteries. The article, titled ‘Fast ion transport at solid–solid interfaces in hybrid battery anodes’ is also highlighted in the News & Views of the same journal.

Metal anodes in batteries, such as lithium, sodium, aluminum, zinc, etc., can intrinsically store more energy than the currently adopted anodes such as graphite. Thus, batteries equipped with metal anodes can in principle offer significantly higher energy density than the state-of-art battery technology, and have been regarded as important next-generation devices for energy storage. However, two key challenges so far prevent the large-scale deployment of metal-based batteries, namely, uneven electrodeposition and poor efficiency. The former occurs during the charging stage of the battery when ions reduce to form metal. Instead of forming a smooth metal layer, they generate tree-like structures loosely termed as ‘dendrites’, partially due to the interphase inhomogeneity. Dendrites are known to be hazardous, as they proliferate in the battery and will eventually cause the short-circuit if not other serious consequences such as fire or explosion. The second issue comes from the high reactivity of the metal electrodes, which promotes parasitic side reaction between the anode interphase and the electrolyte. This process gradually depletes the active species in a battery and thus significantly limits the battery lifetime. The two challenges have been understood to be highly related, as the poorly defined interphase serves as the root to both.

Researchers in Archer lab adopt a facile and effective ion-exchange approach to form a thin layer of tin on the metal anode surface as the protective interphase. It offers high ionic conductivity and homogeneity that allow efficient cycling of the battery. The structure of the protective interphase can be carefully investigated at nanometer scale, thanks to the advanced electron microscopic technology developed in Prof. Lena Kourkoutis’s lab, with the help of Michael Zachman, a graduate student in her group. Uneven electrodeposition of metal is found to be largely suppressed as observed in both light and electron microscopes.

As opposed to conventional inert protective coatings, the tin-based protective interphase also actively participate in the electrochemistry to store additional energy. It has been known that tin also exhibits high energy density in a battery. Here, a thin layer of tin provides a bi-functionality of both surface regulation and energy storage. This concept, known as the hybrid energy storage, is found effective in both lithium and sodium metal anodes. The flexible plug-in approach behind it, which can be implemented in various stages of battery manufacturing, further offers a promising opportunity towards the high energy batteries in future.

The paper can be found at:
https://www.nature.com/articles/s41560-018-0096-1

The News and Views can be found at:
https://www.nature.com/articles/s41560-018-0114-3