(Invited) Energy Storage at Ultra Low Temperatures through Electrolyte Innovation

Operating rechargeable batteries at ultralow temperatures (below -40 ℃) has been essential for various applications, especially in scenarios such as defense operations, space exploration missions, and scientific research in polar regions. In these environments, conventional lithium-ion batteries (LIBs) encounter significant challenges, suffering from severe performance degradation that can restrict their usability and reliability. The primary issues when operating batteries in such extreme conditions are typically related to electrolyte complications, such as electrolyte freezing and inefficient Li+ transport. These limitations in current LIBs require a comprehensive reevaluation and redesign of battery electrolytes to maintain optimal performance at ultralow temperatures. This study focuses on overcoming these challenges by developing innovative electrolytes, particularly aiming to enhance battery performance in cold climates. The emphasis is on adopting new electrolyte solvents, having low melting points and superior solvation capabilities. These properties facilitate better Li+ transference and reduce the Li+ desolvation energy during battery operation. Our research has explored various ether solvents, including dipropyl ether (DPE), 1 tetrahydrofuran (THF), 2 and cyclopentyl methyl ether (CPME). 3 We incorporate these solvents by utilizing strategies that involve weak solvation and high electrolyte concentration for effective Li+ transport and favorable formation of interphase layers between the electrode and electrolyte. The electrolyte designs effectively reduce polarization and the risk of Li plating/dendrite formation, thereby allowing facile Li+ transport during Li+ reaction process. Theoretical simulations, including density functional theory and molecular dynamics, validate the unique advantages of the specialized Li+ solvation approach. Notably, the electrochemical performance at low temperatures with high nickel cathodes maintains approximately 65% of room temperature capacity at -40 ℃1. Additionally, an electrolyte formulation centered on CPME supports repeated battery charging and discharging cycles, even at temperatures down to -100 ℃.4, 5 Additionally, our research extended to developing a ternary fluorinated electrolyte system, which proved capable of preserving 61% of its ambient temperature capacity at -50 ℃, alongside a notably low charge transfer activation energy of 55.71 kJ mol-1.6 By tackling the significant challenges that batteries face in cold climates, our comprehensive investigation not only aids in improving low-temperature battery performance but also establishes a foundation for their use in extreme environments, like defense, space exploration, and Arctic exploration. Future work will involve further exploration of alternative electrode materials and an in-depth examination of the fundamental mechanisms behind Li+ transport at low temperatures, which are vital for advancing energy storage technologies that can endure the severe conditions of extreme environments. References Z. Li, H. Rao, R. Atwi, B. M. Sivakumar, B. Gwalani, S. Gray, K. S. Han, T. A. Ajantiwalay, V. Murugesan, N. N. Rajput, V. G. Pol, “Non-polar Ether-based Electrolyte Solutions for Stable High-Voltage Non-aqueous Lithium Metal Batteries”, Nature Commun., 2023,14, 868. S. Kim, B. Seo, H. V. Ramasamy, Z. Shang, H. Wang, B. M. Savoie, V. G. Pol, “Ion-Solvent Interplay in Concentrated Electrolytes Enables Subzero Temperature Li-Ion Battery Operations”, ACS Appl. Mater. Interfaces, 2022, 14, 41934-41944. H. V. Ramasamy, S. Kim, E. Adams, H. Rao, V. G. Pol, “Novel Cyclopentyl Methyl Ether Electrolyte Solvent with Unique Solvation Structure for Room and Ultralow Temperature (-40 ℃) Lithium-ion Battery Cycling”, Chemical Commun., 2022, 58, 5124. C. M. Jamison, S. Kim, H. V. Ramasamy, T. E. Adams, V. G. Pol, “Lithium-ion Battery Testing Capable of Simulating 'Ultralow’ Lunar Temperatures”, Energy Technol., 2022, 2200799. S. Kim, Y. Zhang, H. Wang, T. E. Adams, V. G. Pol, “Enabling Extreme Low-Temperature (≤−100 ℃) Battery Cycling with Niobium Tungsten Oxides Electrode and Tailored Electrolytes”, Small, 2024, 2306438. E. Adams, M. Parekh, D. Gribble, T. E. Adams, V. G. Pol, “Novel ternary fluorinated electrolyte's enhanced interfacial kinetics enables ultra-low temperature performance of lithium-ion batteries”, Sustainable Energy Fuels, 2023, 7, 3134-3141.