Comparative Study of High Voltage Spinel ║ Lithium Titanate Lithium‐ion Batteries in Ethylene Carbonate Free Electrolytes

Abstract

A persistent obstacle towards the realisation of high voltage cathodes is electrolyte instability where oxidation and transition metal dissolution manifest in rapid capacity failure with both issues connected to the presence of ethylene carbonate in the electrolyte. here, alternative electrolyte co‐solvents are investigated and compared, where the cyclic carbonate is replaced with sulfones ethyl methyl sulfone (EMS) and tetra methylene sulfone (TMS) and fluoroethylene carbonate (FEC). The best full cell performance was observed for cells cycled in a FEC/EMC (3/7) and FEC/EMC (1/1) electrolytes which exhibited 84‐85 % capacity retention after 500 cycles. TMS/EMC (3/7), was determined to be the best performing sulfone electrolyte and maintained 71% capacity after 500 cycles. Post‐mortem XPS analysis indicated different film forming mechanisms for the respective co‐solvent. A thicker cathode electrolyte interphase (CEI) on the LNMO was observed for the FEC containing electrolytes (relative to when TMS was used as the co‐solvent) indicating more effective passivation of the reactive cathode surface which correlated well with the enhanced cycling stability observed. For LTO, more evidence of transition metal migration and a thicker solid electrolyte interphase (SEI) layer was observed for the sulfone electrolyte suggesting more parasitic anode‐electrolyte interactions and an inability to mitigate Mn2+/Ni2+ crosstalk.