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

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 5.5 V due to the passivation phenomenon on the cathodes, while LiPF6-containing electrolytes undergo continuous decomposition beyond 4.5 V. 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.