Abstract
In the pursuit of more sustainable, lower cost and higher performance battery technology, alkaline metal-air batteries (AMABs) are considered promising candidates for future electrical energy storage due to their cost effectiveness, natural abundance of electrode materials, high specific capacity, and safety [1-2]. It is also believed that this battery technology has the potential to help decarbonize our energy grid. However, our knowledge of the phase and compositional changes that occur on the electrode in a working AMAB is limited, and the degradation mechanism of AMABs during repeated cycling have yet to be fully elucidated. To fill these knowledge gaps, advanced operando imaging techniques capable of nanoscale resolution are required to monitor interfacial electrochemical reactions during battery operation [3]. Operando imaging techniques, including magnetic resonance imaging, nuclear magnetic resonance, diffraction, and microscopy methods, have developed dramatically in recent years. They have yielded considerable insights into battery failure, as well as electrode and electrolyte degradation mechanisms, information that is critical to the design of batteries with improved lifetime and performance [3]. Among the operando imaging techniques, electrochemical liquid cell transmission electron microscopy (EC-TEM) holds significant advantages. It offers unique capability to directly image material transformations at the electrode-electrolyte interface in real-time at the nanoscale, while also acquiring quantitative electrochemical signals [4]. However, the use of EC-TEM in battery research has been limited to aqueous battery systems with neutral and mildly acidic electrolytes, leaving its application to alkaline environments unexplored. This is mainly due to chemical incompatibility concerns between alkaline electrolytes and the EC-TEM hardware (e.g. the holder and silicon-based chips). Given the practical significance of AMABs and the scientific opportunities presented by this battery system, it is imperative to advance the frontiers of EC-TEM to include application to alkaline systems.Here we describe EC-TEM investigation of metal electrode behaviors in alkaline environments under realistic battery conditions. Using Fe, Al, and Zn negative electrodes in an alkaline solution as model systems, we assess the feasibility and potential benefits of performing EC-TEM experiments with a pH of up to 14. We outline our approaches to obtaining reproducible cyclic voltammograms within the liquid cell, across a variety of counter electrode designs, and compare the results to those from traditional benchtop experiments. Furthermore, we highlight the challenges associated with electrolyte depletion and ion diffusion limitations within the liquid cell during battery discharge. Finally, we present observations of redox product changes at the electrode as captured by EC-TEM, and discuss the potential effects of electron beams on EC-TEM results. Our work is expected to provide new opportunities for investigating electrochemical processes in other key alkaline systems [5].
Published Version
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