Effect of organic solvent addition to PYR13FSI + LiFSI electrolytes on aluminum oxidation and rate performance of Li(Ni1/3Mn1/3Co1/3)O2 cathodes

• LiFSI is superior in suppressing Al oxidation in PYR13FSI electrolytes.
• Addition of EC:EMC to PYR13FSI ILs leads to higher t+, Li and σionic.
• IL-organic solvent mixtures enable high rate performance of Li(Ni1/3Mn1/3Co1/3)O2.

The superior suppression of aluminum current collector oxidation by a 1.2 M LiFSI in PYR13FSI ionic liquid electrolyte is demonstrated. Addition of EC:EMC (1:2 wt.) is shown to significantly increase the severity of parasitic aluminum oxidation. Despite leading to increased aluminum oxidation at high voltages (>4.2 V vs. Li/Li+), adding organic solvent to PYR13FSI based ionic liquids greatly enhances important electrochemical properties. The ionic conductivity and lithium ion transference number of the PYR13FSI + 1.2 M LiFSI electrolyte increase with increasing volumetric content of organic co-solvent (EC:EMC), resulting in significant improvements to high rate performance. The electrochemical benefits of organic co-solvent addition and the compatibility of the PYR13FSI + 1.2 M LiFSI electrolyte with Li(Ni1/3Mn1/3Co1/3)O2 demonstrated in this study substantiate the need to develop strategies to suppress aluminum oxidation during high voltage cycling of lithium-ion batteries in ionic liquid electrolytes.

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