Challenges and Solutions for Lithium-Sulfur Batteries with Lean Electrolyte

Lithium-sulfur (Li-S) batteries have high theoretical energy density and are regarded as next-generation batteries. However, their practical energy density is much lower than the theoretical value. In previous studies, the increase of the areal capacity of the cathode and the decrease of the negative/positive ratio can be well achieved, yet the energy density shows no corresponding increase. The main reason is the difficulty in decreasing electrolyte dosage because lean electrolyte inevitably causes the deterioration of reaction kinetics and sulfur utilization. Thus, the electrolyte/active material ratio in the reported works is usually higher than 10 mu L mg(-1), much higher than that in Li-ion batteries (usually lower than approximate to 0.3 mu L mg(-1) for cathode). Although many works have focused on this topic, a systematic discussion is still rare. This review systematically discusses the key challenges and solutions for assembling high-performance lean-electrolyte Li-S batteries. First, the key challenges arising from lean-electrolyte conditions are discussed in detail. Then, the approaches and the recent progress to reduce electrolyte usage, including optimization of electrode porosity and ion conduction, the introduction of electrocatalysis, exploration of new active materials, electrolyte regulation, and Li metal protection are reviewed. Finally, future research directions in lean-electrolyte Li-S batteries are proposed.