Challenges and promises of lithium metal anode by soluble polysulfides in practical lithium–sulfur batteries

The lithium–sulfur (Li–S) battery has raised great expectations as a next-generation high-energy-density energy storage system. The multielectron dissolution–precipitation redox conversion of S affords a great contribution to its high specific energy. Spontaneously, the highly reactive Li metal anode always confronts soluble Li polysulfides (LiPSs) in a working Li–S battery, and parasitically side reactions occur inevitably. The challenges of the Li metal anode induced by soluble LiPSs emerge as roadblocks for practical Li–S batteries with the development of the S cathode from its infancy into growth stage. Therefore, the fundamental understanding of Li anode in the electrolyte with LiPSs and the targeted protection strategies are urgently required. In this review, the challenges of the Li metal anode in the presence of LiPSs are systematically analyzed. Then, the preliminary advances in Li metal anode protection to deal with LiPSs are summarized. Finally, an insightful outlook is put forward through both a fundamental understanding and a practical exploration of the Li metal anode to promote the development of practical Li–S batteries.