(84bc) Effects of Composite Sulfur Electrode Structures and Electrolyte Compositions on Rechargeable Aluminum-Sulfur Batteries

Aluminum-sulfur (Al-S) batteries are an emerging electrochemical energy storage technology with great promise due to the earth abundance, very low cost, high capacity, and safety of the electrode materials. Recently, we revealed by nuclear magnetic resonance (NMR) spectroscopy that soluble electrolyte-coordinated sulfur species form upon electrochemical discharge, resulting in loss of active mass that results in rapid specific capacity fade.¹ Pang et al. also showed that the large overpotential in Al-S batteries can be mitigated by operating the batteries at high temperatures (e.g. 100 °C) and by using a molten salt electrolyte instead of a room-temperature chloroaluminate ionic liquid electrolyte.² However, capacity fade associated with the dissolution of aluminum-polysulfides remains a challenge. Here, we study different carbon-sulfur composite electrode structures, characterize electrolyte speciation and ion transport properties, and investigate the effects of electrolyte additives to improve specific capacity retention and the energy efficiency of cycling over a range of operating temperatures. Composite sulfur electrodes were prepared with different sulfur contents, different carbon structures, and different preparation methods to study how they affect the presence of electrolyte-soluble polysulfide intermediates. Rechargeable Al-S batteries were studied using two different electrolytes: a molten salt consisting of a eutectic mixture of AlCl₃, NaCl, and KCl, and an ionic liquid consisting of a Lewis acidic mixture of AlCl₃ in 1-ethyl-3-methylimidazolium chloride ([EMIm]Cl). The species in the electrolyte were identified and their relative populations were quantified by liquid-state ²⁷Al, ¹H, and ¹³C NMR spectroscopy, while ion dynamics and diffusion were characterized by NMR relaxation and pulsed-field-gradient (PFG)-NMR diffusion measurements. The effects of electrolyte additives were studied on electrolyte properties and electrochemical interfaces. In aggregate, the results yield insights into how composite sulfur electrode compositions and structures, as well as electrolyte compositions and ion transport properties, influence the electrochemical properties of rechargeable Al-S batteries.

References:

1. “Soluble electrolyte-coordinated sulfide species revealed in Al-S Batteries by nuclear magnetic resonance spectroscopy,” Rahul Jay, Ankur L. Jadhav, Leo W. Gordon, Robert J. Messinger, Mater., 2022, 34, 4486-4495.
2. “Fast-Charging Aluminium–Chalcogen Batteries Resistant to Dendritic Shorting.,” Quanquan Pang, Jiashen Meng, Saransh Gupta, Xufeng Hong, Chun Yeun Kwok, Ji Zhao, Yingxia Jin, Like Xu, Ozlem Karahan, Ziqi Wang, Spencer Toll, Liqiang Mai, Linda Nazar, Mahalingam Balasubramanian, Badri Narayanan, Donald Sadoway, Nature., 2022, 608, 704-711.