Plasma-Enhanced Atomic Layer Deposition of Ultrathin Oxide Coatings for Stabilized Lithium-Sulfur Batteries

Abstract

One of the most challenging problems in the development of lithium-sulfur batteries is polysulfide dissolution, which leads to cell overcharge and low columbic efficiency. Here, we propose the formation of a thin conformal Li-ion permeable oxide layer on the sulfur-carbon composite electrode surface by rapid plasma enhanced atomic layer deposition (PEALD) in order to prevent this dissolution, while preserving electrical connectivity within the individual electrode particles. PEALD synthesis offers a fast deposition rate combined with a low operating temperature, which allows sulfur evaporation during deposition to be avoided. After PEALD of a thin layer of aluminium oxide on the surface of electrode composed of large (ca. 10 mu m in diameter) S-infiltrated activated carbon fibers (S-ACF), significantly enhanced cycle life is observed, with a capacity in excess of 600 mAhg(-1) after 300 charge-discharge cycles. Scanning electron microscopy (SEM) shows a significant amount of redeposited lithium sulfides on the external surface of regular S-ACF electrodes. However, the PEALD alumina-coated electrodes show no lithium sulfide deposits on the fiber surface. Energy dispersive spectroscopy (EDS) studies of the electrodes' chemical composition further confirms that PEALD alumina coatings dramatically reduce S dissolution from the cathodes by confining the polysulfides inside the alumina barrier.