Tuning Ionic Potential of Metal Fluorides in Solid Polymer Electrolytes for High-Rate Lithium Batteries

Incorporating metal fluorides is an effective strategy for increasing Li⁺ transference number ( t_\rmLi^+ ) in solid polymer electrolytes (SPEs) through coordination of metal cations with migrating anions, allowing for alleviating concentrated polarization and improving rate performance in lithium batteries. However, a higher charge quantity of the metal cation can not translate into a more significant increase in t_\rmLi^+ . In this work, we utilize the ionic potential (Z/r, the ratio of charge quantity to ionic radius) to generalize the anoin trapping capability of metal fluorides. By incorporating MnF₂, FeF₃ or NbF₅ with metal ionic potential of 2.99 Å⁻¹, 4.65 Å⁻¹, and 7.81 Å⁻¹, respectively, t_\rmLi^+ of polymerized vinyl ethylene carbonate and 2,2,3,3,4,4,5,5-octafluoro-1,6-hexanediol diacrylate monomers increase from 0.35 to 0.52 for MnF₂, 0.61 for FeF₃, and 0.67 for NbF₅ at 25 °C. Correspondingly, the assembled LiCoO₂||Li batteries with a cutoff voltage of 4.45 V at 25 °C based on NbF₅-SPE delivers discharge capacity of 153.81 mAh·g⁻¹ at 5 C and capacity retention of 86% for 5 C/0.2 C, significantly higher than 146.59 mAh·g⁻¹, 81.5% based on MnF₂, and 143.95 mAh·g⁻¹, 83.6% based on FeF₃. This work provides a promising design guideline of high t_\rmLi^+ SPE as well as high-rate lithium batteries.