Collaborative Research: Material Simulation-driven Electrolyte Designs in Intermediate-temperature Na-K / S Batteries for Long-duration Energy Storage

Long-duration energy storage technology (>10 hours, LDES) is critical to the expansion of intermittent renewable energy (e.g., solar/wind). Conventional Na-S and K-S batteries are attractive for LDES due to their low cost and the use of earth-abundant elements. However, their deployment is severely hindered by their high operational temperature of 300-350oC and associated degradation and safety issues. This project will use materials design and simulation-driven approaches to develop innovative electrolytes to dissolve insoluble reaction products in Na-S and K-S batteries and advance knowledge on underlying dissolution mechanisms. Such novel electrolytes will enhance reaction kinetics so the operation temperature can be reduced to 60-120oC, which not only enhances thermal stability but also decreases operational costs. The new material systems from this project have the potential to be deployed for LDES, which enhances the economic competitiveness and sustainability of U.S. The project activities will integrate research and education, targeting students from K-12 to graduate school and promoting underrepresented communities' education through hands-on experiences, advising, and research integration across all levels. The primary challenge in traditional alkaline metal sulfur (AMS) batteries arises from the formation of solid M2S2 and M2S compounds during discharge (M = Na, K), which exhibit poor electrochemical kinetics. This limits the reversible redox range mainly to S/M2S3 reactions, reducing specific capacity and energy density. The goal of this project is to identify and develop new solvents that can dissolve M2S2/M2S readily to replace conventional ether electrolytes, which will in turn make M2S2/M2S electrochemically active. This will double the specific capacity of sulfur from 500 mAh/g in ether electrolytes to 1000-1500 mAh/g, along with a long cycle life. The project will utilize a simulation-driven approach to design electrolytes, such as combining molecular dynamics (MD) simulations and machine learning (ML). MD simulations calculate solvation free energy, and ML enables high-throughput screening for solvents with superior M2S2 and M2S solubilities. Promising candidates will be experimentally validated. After experimentally confirming the high-performance solvents, multi-scale/multi-modal characterizations will be used to understand the fundamental dissolution mechanisms, electrochemistry and transport in the proposed system comprehensively. An Ah-level prototype will be constructed and tested, and the cost of developed materials and devices will be analyzed for large-scale deployment. The advances in knowledge and research tools together will help develop next-generation batteries for long-duration energy storage.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.