Challenges and key parameters of lithium-sulfur batteries on pouch cell level

Application-relevant data such as cycle life, rate capability, and energy density are inaccessible via electrochemical standard tests in today's Li-S-lab cells due to electrolyte and anode excess masking major degradation mechanisms. Because of the gap of lab cell characterization and prototype cell development, misinterpretations and false expectations of material development are frequently reported, and electrode porosity as well as pressure on cell stack are neglected. Rapid transfer of new concepts on multilayer-pouch cell level is essential, especially for electrolytes working in lean electrolyte regime. Fundamental studies should concentrate on fundamental scientific questions related to the main bottlenecks of Li-S-cells: first, understanding anode and electrolyte degradation phenomena and realistic evaluation of stabilizing interfaces is crucial. Further, new analytical tools allowing electrochemical studies under lean electrolyte conditions and in situ studies of electrolyte and additive depletion pose tremendous chances for impactful research. In addition, tap density and the accompanied swelling and compaction behavior of cathodes in different electrolytes should be further addressed. Consequently, pressure distribution in pouch cells should be monitored and adapted to the respective mechanical properties of the cathode and anode. These guidelines help to realize a breakthrough of the Li-S technology as a sustainable, safe, and lightweight energy storage option in the near future.