Tuning ionic potential of metal fluorides in solid polymer electrolytes for high-rate lithium batteries

Incorporating metal fluorides is an effective strategy for increasing lithium transference number (tLi+) in solid polymer electrolytes (SPEs) through coordination of metal cations and migrating anions, allowing for alleviated concentrated polarization and improved rate performance in lithium batteries. However, the higher charge quantity of the metal cation can not translate into the more significant increasing in tLi+. In this manuscript, we utilize the ionic potential (Z/r, the ratio of the charge quantity to the 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, tLi+ of polymerized VEC and OFHDODA monomers increased from 0.35 to 0.52 for MnF2, 0.61 for FeF3, and 0.67 for NbF5 at 25℃. Correspondingly, the assembled LCO||Li batteries with a cutoff voltage of 4.45 V at 25℃ based on NbF5-SPE delivers discharge capacity of 153.81 mAh g−1 at 5C 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 tLi+ SPE as well as high-rate lithium batteries.