A Lifetime Evaluation Method for Lithium-Sulfur Batteries

Abstract

Lithium-sulfur (Li-S) batteries are attracting significant attention because of their high capacity and high energy density. For Li-S batteries using highly concentrated sulfolane-based electrolytes (i.e., sparingly solvating electrolytes for Li2S x ) and S8 active materials, we developed a method of lifetime testing to evaluate the dynamic and static degradation behavior. Short- to medium-term discharge/charge tests and long-term storage tests were conducted. The capacity degradation after cycling in the medium term was attributed to changes in the utilization of long- and short-chain Li2S x due to the incomplete recovery to S8. Storage tests were conducted under different temperature and state-of-charge (SOC) conditions. The discharge capacity at SOC70% decreased significantly more than that at SOC100%, demonstrating the difference in degradation behavior compared to that of typical lithium-ion batteries. The capacity retention rate decreased linearly with storage time up to approximately 9 months, revealing that degradation was accelerated by 2 times at SOC100% compared with that at SOC0%, from a simple liner analysis. The capacity also decreased with increasing storage temperature, exhibiting ∼2.4 times more degradation at 333.1 K than at 303.2 K. This may be due to the enhanced dissolution of the Li2S x reaction intermediates in the electrolyte and the redox-shuttle effect.