(398e) Understanding Electrochemical Reaction Mechanisms and Properties of Rechargeable Aluminum-Sulfur and Aluminum-Selenium Batteries | AIChE

(398e) Understanding Electrochemical Reaction Mechanisms and Properties of Rechargeable Aluminum-Sulfur and Aluminum-Selenium Batteries

Authors 

Messinger, R. - Presenter, The City College of New York
Jay, R., The City College of New York
Jadhav, A. L., The City College of New York
Rechargeable Al metal batteries have recently garnered significant interest due to its low cost, earth abundance, inherent safety, and high volumetric (8040 mAh cm -3) and gravimetric (2980 mAh g -1) capacities due to the trivalent nature of Al3+ ions (3-electron redox). Commercialization of rechargeable aluminum battery systems has been limited, however, due to the small number of (i) electrolytes that enable reversible electrodeposition of Al metal at room temperature and (ii) positive electrode materials that are compatible with the electrolytes while providing high capacity and cycle life. Sulfur (S) and selenium (Se) are promising positive electrode materials for rechargeable battery systems as they exhibit very high specific capacities during electrochemical conversion reactions. To date, there are few reports of Al-S, and Al-Sebattery systems. There is no clear consensus on the electrochemical reaction mechanism during the charge/discharge process, while capacity fade plagues both systems during galvanostatic cycling.

Here, aluminum-sulfur (Al-S) and aluminum-selenium (Al-Se) cells were investigated with a chloroaluminate ionic liquid electrolyte, AlCl3:[EMIm][Cl] (molar ratio of 1.5:1), whose electrochemical reaction mechanisms and ensuing reaction products were analyzed via a combination of bulk (XRD, NMR) and surface (XPS) analyzation techniques.For Al-S batteries, electrochemical experiments showed high initial capacity, where both capacity and cycle life exhibited a non-monotonic relationship with the galvanostatic cycling rate. A higher capacity was observed upon charge, compared to discharge, pointing towards unwanted side reactions and/or polysulfide-shuttle-like behavior. For the Al-Se batteries, the two different reaction mechanisms that have been previously reported were found to be dependent on (i) the applied current density and (ii) the crystallinity of the active material. We demonstrate that, with appropriate cycling conditions, both reaction mechanisms can occur during a single charge/discharge step, thus significantly increasing the capacity and the electrochemical window of the Al-Se cell.

To understand the reaction mechanisms of Al-S and Al-Se batteries at a molecular level, solid-state and liquid-state 27Al NMR and 77Se NMR measurements (on Al-Se systems) were acquired on the electrodes and electrolyte at different states-of-charge, respectively. XPS was also performed on cycled chalcogen electrodes to understand surface compositions. The data yield insights into the reaction mechanisms and products, including aluminum coordination environments and the quantitative relative populations of aluminum in these environments. Overall, this work establishes the potential of conversion-type aluminum-chalcogen batteries as high-energy-density energy storage systems and highlights the importance of molecular-level analytical tools like NMR spectroscopy in clarifying reaction mechanisms in emerging electrochemical systems.