Regulating solvent coordination enables non-flammable and durable potassium-ion batteries with all-aluminum current collectors

Potassium-ion batteries (PIBs) hold promise as affordable alternatives to lithium-ion batteries, but their development is hindered by safety issues, limited lifespan, and electrolyte incompatibility with high-capacity electrodes.

A team of materials scientists led by Dr. Lei Qin from Institute for Advanced Study (IAS), Shenzhen University (SZU), China, introduced a novel approach to electrolyte design by modulating the coordination of solvent molecules with potassium salts. By selecting fluorinated triethyl phosphate (FTEP)—a fluorinated phosphate with low solvating power—as the sole solvent, the researchers developed an electrolyte that is inherently fire-retardant while supporting high-performance electrodes. This electrolyte, at a moderate concentration of 1.0 mol/L potassium bis(fluorosulfonyl)imide (KFSI)/FTEP, enables the use of lightweight and inexpensive aluminum current collectors for both anode and cathode, addressing key barriers in PIB commercialization.

The team published their findings in Energy Materials and Devices on June 16, 2025.

“In this study, we provide molecular insights into solvation chemistry and interfacial behaviors to design compatible electrolytes for PIBs. By using FTEP, we create a solvation structure where FSI^- anions dominate the primary solvation shell, leading to a protective interphase that inhibits side reactions and aluminum corrosion,” said by Lei Qin, corresponding author of the paper and assistant professor at the IAS, SZU.

FTEP’s weak solvating ability stems from the electron-withdrawing effect of fluorine atoms, which reduces the coordination strength between solvent molecules and potassium ions. This results in a solvation shell dominated by FSI^- anions, promoting the formation of a robust, anion-derived solid electrolyte interphase (SEI) on the anode surface. Unlike traditional carbonate- or ether-based electrolytes, which often lead to flammable formulations and poor electrode stability, the FTEP-based electrolyte exhibits exceptional flame retardancy with a self-extinguishing time of zero seconds.

Raman spectroscopy and molecular dynamics simulations were used to characterize the solvation structure. Results reveal that over 90% of anions are coordinated in the FTEP electrolyte, compared to much lower ratios in non-fluorinated counterparts. This anion-dominant structure enhances the electrochemical window beyond 5.5 V (vs. K⁺/K), suppresses aluminum corrosion, and supports reversible potassium storage in graphite anodes with capacities of 273.8 mAh/g, which is close to the theoretical value of 279 mAh/g.

“Many challenges in PIBs arise from incompatible electrolytes that fail to passivate reactive anodes or prevent solvent decomposition. Our FTEP electrolyte addresses these by enabling flat potassium plating with high reversibility (~98.1% Coulombic efficiency over 600 cycles) and stable graphite cycling (~274 mAh/g after 300 cycles),” Qin said.

The electrolyte’s compatibility was proved by applying a high-voltage Prussian blue cathode with a K anode, demonstrating full-cell performance with an average voltage of ~3.2 V and capacity retention of 78.5 mAh/g over 200 cycles. The design avoids high salt concentrations or costly additives, making it cost-effective for scalable production.

The research team anticipates that this work would accelerate the adoption of non-flammable PIBs in applications like grid storage and electric vehicles. “Electrolytes like ours are expected to provide diversity and practicality for PIBs, integrating safety with high energy density.” said by Qin.

Other contributors include Yishuo Li, Xinyang Zhang, Wenjun Cai, Dexin Zhu, and Fei Xie from the IAS, SZU; and Xiaojuan Chen from the School of Chemical Engineering at Sichuan University.

This work was financially supported by the National Natural Science Foundation of China (Grant No. 52301280), the Shenzhen Science and Technology Program (Grant No.JCYJ20240813142526034), the Guangdong Basic and Applied Basic Research Foundation (Grant No. 2025A1515010810), and the Scientific Foundation for Youth Scholars of Shenzhen University (Grant No. 868-000001032171).