Lithium-Sulfur Batteries: State of the Art and Future Directions

Sulfur remains in the spotlight as a future cathode candidate for the post-lithium-ion age. This is primarily due to its low cost and high discharge capacity, two critical requirements for any future cathode material that seeks to dominate the market of portable electronic devices, electric transportation, and electric-grid energy storage. However, before Li-S batteries replace lithium ion batteries, several technical challenges need to be solved. Among these challenges are polysulfide containment, the increase of sulfur loading (which must be ≥4-6 mg cm ^-2), the increase of sulfur fraction to ≥70%, the increase of sulfur utilization to ≥80%, the decrease of the electrolyte/sulfur weight ratio (which must be in the range of 3:1 or lower), and the stability of lithium anode material. Besides traditional carbon coating strategies, recent novel strategies addressing each of these challenges have been reported. The main purpose of this work is to review the state of the art and summarize and shed light on the most promising recent discoveries related to each challenge. This review also addresses the role of the electrolyte systems and electrocatalytic additives.