Improved Compatibility of α‐NaMnO2 Cathodes at the Interface with Ionic Liquid Electrolytes

Abstract The behaviour and compatibility of monoclinic sodium manganite, α‐NaMnO 2 , cathodes at the interface with electrolytes based on the 1‐ethyl‐3‐methylimidazolium bis(fluorosulfonyl)imide (EMIFSI) and N ‐trimethyl‐ N ‐butylammonium bis(fluorosulfonyl)imide (N 1114 FSI) ionic liquids is presented and discussed. The Na + insertion process was analysed through cyclic voltammetry tests combined with impedance spectroscopy measurements and the cell performance was tested by charge‐discharge cycles. XPS and FIB‐SEM measurements allowed analysis of the surface composition and the morphology of post‐mortem cathodes. Overall, the α‐NaMnO 2 cathode showed high reversibility in N 1114 FSI‐based electrolyte, delivering 60 % of the initial capacity after 1200 cycles in conjunction with a Coulombic efficiency above 99 %. To our knowledge, these very promising results are the best result obtained till now for monolithic α‐NaMnO 2 cathodes, are ascribable to the formation of a stable passive layer onto the electrode surface, as confirmed by spectroscopic analysis.