Lithium Aluminate Nanoflakes as an Additive to Sulfur Cathodes for Enhanced Mass Transport in High-Energy-Density Lithium-Sulfur Pouch Cells Utilizing Sparingly Solvating Electrolytes.

ABSTRACT

The utilization of sparingly solvating electrolytes has been reckoned as a promising approach to realizing high-energy-density lithium-sulfur batteries under lean electrolyte conditions through decoupling the electrolyte amount from sulfur utilization. However, the inferior wettability of high-concentration sparingly solvating electrolytes compromises mass transport, thereby impeding the maximum utilization of active material in sulfur cathodes. To address this issue, in this study, we incorporate lithium aluminate (LiAlO2) nanoflakes as an additive to sulfur cathodes to enhance the mass transport by improving the percolation and accessibility of sparingly solvating electrolytes to the bulk of the electrodes. The electrochemical kinetics of LiAlO2-containing sulfur cathodes are investigated using the galvanostatic intermittent titration technique. The Li+ self-diffusion coefficients of electrode materials were estimated through pulsed-field gradient nuclear magnetic resonance (PFG-NMR) spectroscopy. Finally, a 193 Wh kg-1 Li-S pouch cell (excluding the mass of the laminated Al pouch) is demonstrated by utilizing the LiAlO2-incorporated sulfur cathode with a high S-loading of 4.3 mg cm-2 in a low electrolyte/sulfur (E/S) ratio of 3 µL mg-1. The Li-S pouch cell retains 80% of its initial specific cell capacity after 50 cycles. Our comprehensive understanding of the role of LiAlO2 additives in enhancing the mass transport and Li+ self-diffusion coefficient of sulfur cathodes will contribute immensely toward the development of high-energy-density Li-S batteries under lean electrolyte conditions.