Effect of a Boron Based Anion Receptor on Graphite and LiFePO 4 Electrodes

The effect of a boron based anion receptor, tris (hexafluoroisopropyle) borate (THFIPB), on the electrochemistry of graphite was investigated in 1 M LiPF 6 in ethylene carbonate/dimethyl carbonate (EC/DMC, 1:1 by weight) electrolyte. A stable solid electrolyte interphase (SEI) and more porous SEI layer, as observed by SEM, was formed in the presence of THFIPB. The rate capability of the graphite electrode was improved due to THFIPB addition. Capacity measurements performed for more than 200 cycles showed that the capacity retention was significantly improved due to THFIPB addition. Cycling experiments at 0 °C and 50 °C demonstrated that THFIPB is compatible with operations in an extended temperature window, and improved practical specific charge was demonstrated. Improved performance was also demonstrated for LiFePO 4 (LFP) cathodes in combination with THFIPB containing electrolyte. However, in graphite-LFP full cells, the use of the THFIPB containing electrolyte resulted in a slightly lower capacity, attributed to the higher irreversible charge “loss” and corresponding limitations of the Li-inventory in the balanced cell.