Lithium–Sulfur Solid-State Electrolyte (Polymers, Oxides and Sulfides) Batteries with a High-Loading Polysulfide Cathode
Authors: Chung Sheng-Heng 
Published: December 2024

Introduction

Since the introduction of lithium-ion batteries in 1990, the steady growth in volume and performance of lithium-ion cell components and batteries has demonstrated their strong demand in the high-energy-density energy-storage market. The commercial lithium-ion cells adopt the stable intercalation reaction to enable the reversible insertion of lithium ions between layered oxide cathodes and graphite anodes, resulting in the high energy density (100–350 Wh kg–1) and long-term cycling capability (1,000 cycles) that outperform other rechargeable batteries. However, after three decades of research, the charge-storage capacities of the electrode active materials are approaching their theoretical values (200–300 mAh g–1), while the cost of the electrode continues to increase. This limits the improvement of the energy density of lithium-ion cells, which has reduced the annual growth rate from 7% to 2%, making it difficult to supply the energy-storage market of more than 1,500 GWh in 2030. In response to these challenges, next-generation batteries are being developed, focusing on electrochemical cells to achieve high reversible energy storage and competitive prices and solid-state electrolytes for enhanced stability and improved energy density. Both developments aim at achieving new energy density records (300–500 Wh kg–1 and 700–800 Wh L–1) that would enable electric vehicles to surpass conventional vehicles in range, while reducing cell costs.

Results and Discussion

In this presentation, we will present the designs of the next-generation rechargeable cells aimed at overcoming the bottleneck faced by current commercial lithium-ion cells. From the materials science point of view, the lithium–sulfur battery is the most promising candidate because of its high energy density, low cost, and low toxicity. On the other hand, from the materials engineering point of view, the solid-state electrolytes with high ionic conductivity are proposed to increase the energy density, cyclability, and safety of the batteries through configuration modification. To adopt the advantages of these two novel battery technologies, we report an integrated design of the lithium–sulfur electrochemical cell with the solid-state electrolyte as a lithium–sulfur solid-state electrolyte cell. The lithium–sulfur electrochemical cell employs a high-sulfur-loading polysulfide cathode to achieve high energy density and to form a smooth ion-transfer interface between the catholyte and the solid-state electrolyte. On the other hand, the solid-state electrolyte provides excellent stability and safety to the cells by stabilizing the polysulfide cathode and protecting the lithium anode. The resulting cell design demonstrates the new battery materials and configurations, which include the development of a high-performance polysulfide cathode, the design and synthesis of solid-state electrolytes (i.e., polymer, oxide, and sulfide-based electrolytes), and the cell integration and interface analytical method. Our battery technologies enable the design of lithium–sulfur solid-state electrolyte batteries to achieve high sulfur loadings (4–16 mg cm–2) and high sulfur contents (50–80 wt%), which are better than those of current lithium–sulfur batteries that aim to be 5–10 mg cm–2 and 70 wt%. With the high sulfur loading, the lithium–sulfur solid-state electrolyte batteries exhibit high areal capacity (5–7 mA·h cm–2) and energy density (11–15 mW·h cm–2). Both values are higher than those of commercial lithium-ion cells for electric vehicles. Moreover, the cell has a long cyclability (100–200 cycles) and high rate capability (C/20 to 1C rate).

Conclusion

In summary, we report in the presentation a summary of our lithium–sulfur solid-state electrolyte batteries with a high-loading polysulfide cathode. The solid-state electrolytes stabilize the polysulfide cathode and the electrochemical reaction of lithium–sulfur batteries, while the stabilized polysulfide cathode forming a stable ionic conductive interface between the cathode and the solid-state electrolytes. Our lithium–sulfur solid-state electrolyte cells demonstrate outstanding battery-design parameters, excellent cell-performance values, and advanced interface analytical method. Both are essential for the commercial development of advanced next-generation rechargeable batteries.

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