A Low Self-Discharge Lithium−Sulfur Cell for the Evaluation of the Long Battery Shelf Life
Authors: Wu Cheng-Che , Ho Yun-Chung , Chung Sheng-Heng 
Published: December 2024

The pursuit of high-energy-density charge storage has driven significant research into next-generation energy-storage systems, with lithium–sulfur cells emerging as a promising candidate. Lithium–sulfur batteries, with the high theoretical capacity of sulfur (1,675 mA·h g–1), coupled with its abundance and eco-friendly nature, are potential post-lithium-ion battery system for commercialization in energy-storage technology. However, the polysulfide diffusion during cell cycling and resting is still the major and remained challenge hindered the development of lithium–sulfur batteries. To address this problem, many studies have introduced novel electrode designs, polysulfide adsorbents, and electrolyte additives to hinder the polysulfide diffusion while enhancing the lithium–sulfur cell performances for the accomplishment of high energy density rechargeable battery systems.

However, although great improvements in the dynamic electrochemistry, cycling performance, and energy densities of the batteries have been shown in recent studies, the measurements of the static electrochemistry of the self-discharge behavior and battery shelf life of the lithium–sulfur cells have rarely been discussed. Moreover, the discussion of long-term effect of the extreme self-discharge of lithium–sulfur cell is even less. The self-discharge caused by the reaction between active material and liquid electrolyte and polysulfide diffusion is more serious when raising the active-material loading to achieve high energy density. The severe self-discharge effect reduces the battery charge-storage performance and may further causes cell heating and thermal runaways due the non-electrochemical reactions during long-term storage.

To understand and subsequently resolve the self-discharge effect of the lithium–sulfur cell, in this study, we present an evaluation method to measure both electrochemistry of long-term static storage and dynamic cycling of self-discharge effect of the lithium–sulfur cells. Through cell measurements and quantitative analyses, the comprehensive study and analysis reveal the self-discharge behavior in the lithium–sulfur battery chemistry. Furthermore, to address the critical issue of self-discharge of lithium–sulfur cells to achieve long shelf life, a low-self-discharge lithium–sulfur cell is introduced. The low-self-discharge lithium–sulfur cell, having a cathode combining polysulfide active material and carbonized electrospun nanofiber, can achieve a high sulfur content (66.7 wt%) and a high sulfur loading (4.03 mg cm–
2). With strong hindrance of the polysulfide diffusion and great stability as a conductive network, the designed cell can maintain low time-dependent capacity-fade rate of 0.26 % per day while reaching a long shelf life of 90 days. The low-self-discharge lithium–sulfur cells also retain high lithium-ion diffusion rate with both freshly made and cycled conditions after long resting periods (7–28 days). This study has demonstrated a comprehensive study into the self-discharge behavior of the lithium–sulfur batteries and introduced a well-designed cell with low-self discharge and stable electrochemistry (Figure).

References:

Y.-C. Ho and S.-H. Chung, Chem. Eng. J., 2021, 422, 130363.

C.-C. Wu and S.-H. Chung, J. Power Sources, 2023, 566, 232944.

C.-C. Wu, Y.-C. Ho and S.-H. Chung, J. Mater. Chem. A, 2023, 11, 24651–24660.

Figure 1