Improvement of Cycling Performance of FeF3-Based Lithium-Ion Battery by Boron-Based Additives

Abstract

Two boron-based additives, tris(pentafluorophenyl)borane (TPFPB) and tris(1H,1H-heptafluorobutyl)borate (THFBuBO), are studied for their effects on the cycling performance of the FeF3/Li battery. When dissolved in the electrolyte consisting of LiPF6-ethylene carbonate/1,2-dimethyl carbonate, these compounds act as F− receptors to improve the electrochemical properties of the FeF3 cathode and cycling performance. The initial discharge capacity and voltage profile of FeF3/Li battery displayed little change with the additives. However, TPFPB and THFBuBO improved the capacity retention, with respective retention rates of 85.2% and 86.5% at the 10th cycle, while this value was 68.6% when no additive was used. Inductively coupled plasma atomic emission spectroscopy analysis showed that LiF was dissociated by TPFPB or THFBuBO in the electrolyte, and its solubility was higher with TPFPB. THFBuBO has the weak affinity for F− ions to allow reversible formation/dissociation of the [THFBuBO-F]− complex. Therefore, THFBuBO maintained the capacity of the FeF3/Li battery better than TPFPB.