(735as) Advancing High Energy Dense Li-S Pouch Cell through Form Factor Optimization

The success of lithium-ion batteries (LIBs) has been the catalyst for a revolution in electrochemical energy storage and the main driving force for widespread adoption of mobile devices. Sulfur is abundant, low-cost, and environmentally friendly, making it a promising alternative to LIBs. Battery technology with high energy density is being driven by the shift to renewable energy sources and the electrification of the transportation sector. The high energy density of lithium-sulfur (Li-S) batteries¹ (2,600 Wh kg^-1) makes them a viable prospect for the next generation of energy storage. However, the practical energy yield is lower than theoretically predicted because of problems like lithium polysulfide (LiPS) shuttling and Li dendrite growth. Advanced mitigation strategies are needed because these problems result in rapid capacity fade, reduced coulombic efficiency, and potential safety hazards.

Recent advancements in Li-S technology have led to an increase in sulfur content within electrodes, highlighting the positive impact of carbon materials on enhancing electrochemical performance. However, challenges persist, including the considerable 'dead weight' from inactive components² that significantly detracts from the batteries' specific energy. Efforts to reduce the electrolyte volume are constrained by the reactive nature of lithium metal, the fragility of the solid electrolyte interface (SEI), and the necessity for conductive carbon and sufficient electrolyte to support cathode functionality.³ The design parameters for Li-S batteries, especially in pouch formats, markedly deviate from those of coin cells, influencing their cycle life and overall stability. The endeavor to diminish the electrolyte volume relative to the sulfur load (E/S) and the negative to positive capacity (N/P) ratios⁴ for pouch cells introduces fresh challenges and highlights the complexity of producing stable, long-lasting Li-S batteries on a large scale.

Pouch cells of Li-S batteries with capacities ranging from 375 mAh to 1.4 Ah have been developed⁴. Our findings indicate that sulfur loading, and the electrolyte/sulfur ratio are essential form factors for achieving high energy density batteries in a pouch cell format. We have engineered a 1.45 Ah pouch cell with optimized sulfur loading and an electrolyte/sulfur ratio, attaining an energy density of 151 Wh/kg and a capacity retention rate of 70% for up to 100 cycles. Additionally, the developed 1Ah pouch cell exhibits a 68% capacity retention after 50 cycles, aiming for a higher energy density of 180 Wh/kg. Morphological analysis of cycled electrodes reveals that the primary cause of pouch cell failure⁴ is attributed to Li metal powdering and subsequent polarization, rather than LiPS shuttling. To prove real-world viability, Li-S pouch cells have been successfully integrated into a functional drone.⁴

References

1. W. Weng, V. G. Pol, K. Amine, "Ultrasound Assisted Design of Sulfur/Carbon Cathodes with Partially Fluorinated Ether Electrolytes for Highly Efficient Li/S Batteries," Adv. Mater., 2013, 25, 1608–1615.

2. C. N. Hong, D. K. Kye, A. U. Mane, V. Etacheri, V. G. Pol, “Blocking Polysulfides in Graphene–Sulfur Cathodes of Lithium–Sulfur Batteries through Atomic Layer Deposition of Alumina”, Energy Technology, 2019, 1900621

3. A. D. Dysart, N. A. Cardoza, G. Mitchell, V. Ortalan, V.G. Pol, “Effect of Synthesis Method Using Varying Types of Micropore Level Sulfur Infiltration on Electrochemical Performance in Lithium–Sulfur Batteries,” Energy Technology, 2019, 1900194.

4. S. Das, MSA Bhuyan, K. N. Gupta, O. Okpowe, A. Choi, J. Sweeny, D. Olawale, V. G. Pol, Optimization of the Form Factors of Advanced Li-S Pouch Cells, Small 2024, 2311850