Partially Fluorinated Electrolyte Formulations Enabling Safe Performance of Anode-Free Na-Based Batteries
Authors: Hinz Robert Tobias , Woelke Christian , Winter Martin , Cekic-Laskovic Isidora 
Published: December 2024

To reduce Europe's dependence on third-party countries during the transition to a green and digital economy, it's imperative to optimize existing and develop new battery technologies prioritizing lifetime, sustainability and safety. Next to exploring alternatives to lithium, creating safe batteries that don't rely on critical raw materials like cobalt, copper, and nickel is of vital importance. Sodium emerges as a strong contender due to its abundance, natural occurrence, and low cost, akin to lithium.[1] As a result, the momentum has shifted towards the development of sodium-based batteries (SBBs), especially to electrolyte optimization and development in recent years. In this way the risk of thermal runaway and prolonged electrolyte decomposition can be effectively addressed, ensuring enhanced safety and reliability in battery systems. Through systematic research and development efforts focused on electrolyte optimization, the quest for next-generation high-performance batteries capable of meeting the diverse demands of modern energy storage applications continues to advance.
Compared to traditional battery designs, anode-free battery cells typically boast higher energy density by eliminating the need for an anode material, allowing for greater energy storage capacity within the same volume or weight. This streamlined manufacturing process holds potential for cost savings and improved production efficiency. By utilizing aluminium as the current collector, the need for more expensive copper is avoided.[2] Prussian White as cathode material is an ideal candidate for battery applications, not only on account of its abundance and low cost, but also due to the absence of critical elements. The relatively high theoretical specific capacity of up to 150 mAh·g-1 is especially advantageous for applications requiring compact and lightweight battery systems, such as portable electronics or electric vehicles[3, 4].
In this study we demonstrated enhanced galvanostatic cycling performance of Prussian White || aluminium anode-free cells, achieved through the strategic utilization of a newly developed partially fluorinated electrolyte. In addition to its intrinsic non-flammability, the safety aspects of the cell are further enhanced by the inclusion of a flame-retardant additive in the electrolyte design. Detailed investigations into the physicochemical and electrochemical properties of the electrolyte in the resulting battery chemistry were conducted, encompassing as ionic conductivity assessment, self-extinguishing time (SET)and electrochemical stability determination, hand in hand with charge/discharge measurements. Performed study collectively underscores the flame-retarding capabilities and enhanced compatibility of the in situ plating of sodium metal on the aluminium current collector exhibited by the optimized electrolyte formulation. This multifaceted approach not only propels performance but also reinforces safety protocols, marking a significant stride forward in the realm of the emerging sodium-based battery technology.

References:

[1] Tapia-Ruiz, N.; Armstrong, A. R.; Alptekin, H.; Amores, M. A.; Au, H.; Barker, J.; Boston, R.; Brant, W. R.; Brittain, J. M.; Chen, Y.; et al. 2021 Roadmap for Sodium-Ion Batteries. J. Phys. Energy, 2021, 3 (3), 031503. https://doi.org/10.1088/2515-7655/ac01ef.
[2] Cohn, A. P.; Muralidharan, N.; Carter, R.; Share, K.; Pint, C. L. Anode-Free Sodium Battery through in Situ Plating of Sodium Metal. Nano Letters, 2017, 17 (2), 1296–1301. https://doi.org/10.1021/ACS.NANOLETT.6B05174
[3] Hasa, I.; Mariyappan, S.; Saurel, D.; Adelhelm, P.; Koposov, A. Y.; Masquelier, C.; Croguennec, L.; Casas-Cabanas, M. Challenges of Today for Na-Based Batteries of the Future: From Materials to Cell Metrics. Journal of Power Sources, 2021, 482, 228872. https://doi.org/10.1016/j.jpowsour.2020.228872.
[4] Xie, B.; Sun, B.; Gao, T.; Ma, Y.; Yin, G.; Zuo, P. Recent Progress of Prussian Blue Analogues as Cathode Materials for Nonaqueous Sodium-Ion Batteries. Coordination Chemistry Reviews, 2022, 460, 214478. https://doi.org/10.1016/j.ccr.2022.214478.