Enhanced performance of the electrolytes based on sulfolane and lithium difluoro(oxalate)borate with enhanced interfacial stability for LiNi0.5Mn1.5O4 cathode

Abstract

The electrolytes based on lithium difluoro(oxalate)borate (LiODFB) and sulfolane (SL) including LiODFB-ethylene carbonate (EC)/dimethyl carbonate (DMC) and LiPF6-EC/DMC as the references have been studied on electrochemical performance and interfacial stability in Li/LiNi0.5Mn1.5O4 cells. LiODFB-containing electrolytes show outstanding electrochemical stability within 5.5V due to the passivation phenomenon on the cathodes, while LiPF6-containing electrolytes undergo continuous decomposition beyond 4.5V. The initial charge/discharge profiles and cyclic voltammetry (CV) curves prove that the cell with LiODFB-SL/DMC(2:1 by vol.) electrolyte has lower degree of polarization and better reversibility. The cathode with LiODFB-SL/DMC(2:1 by vol.) electrolyte displays the best cycling performance and the cathode with LiPF6-EC/DMC(1:1 by vol.) electrolyte displays the worst cycling performance. AC impedance shows that the cell cycling with LiODFB-SL/DMC(2:1 by vol.) electrolyte has much smaller resistance of charge transfer on cathode/electrolyte interface than the cell cycling with LiODFB-EC/DMC(1:1 by vol.) electrolyte. The characterization of the cathode surfaces indicates that a more homogeneous and compact passivation layer forms on the cathode cycling with LiODFB-SL/DMC(2:1 by vol.) electrolyte to greatly improve the interfacial stability for the reason that SL motivates the passivation reaction of LiODFB and itself participates the formation of the passivation layers. Therefore, LiODFB-SL/DMC(2:1 by vol.) is a promising electrolyte for LiNi0.5Mn1.5O4 cathode.