High performing ionanofluid electrolyte with higher lithium salt concentration for safer lithium metal batteries

Abstract: A new class of high-performance pyrrolidinium cation based ionanofluid electrolytes with higher lithium salt concentration are developed. The electrolytes are formed by dispersing imidazolium ionic liquid functionalized TiO2 nanoparticles in low conducting, 0.6 M lithium salt doped N-alkyl-N-butylpyrrolidinium bis(trifluoromethylsulfonyl)imide (Pyr14TFSI) ionic liquid (IL) hosted electrolyte. Viscosity, ionic conductivity and thermal properties of these electrolytes are compared with well studied 0.2 M salt doped Pyr14TFSI IL-based electrolyte. The highly crystalline 0.6 M lithium salt dissolved IL-based electrolytes gradually become amorphous with the increasing dispersion of surface functionalized nanoparticles within it. The ionic conductivity of the electrolytes shows unusual viscosity decoupled characteristics and at the 5.0 wt% nanoparticle dispersion it attains a maximum value, higher than that of pure IL host. As compared to pure IL-based electrolytes, the ionanofluid electrolyte also possesses a significantly higher value of lithium ion transference number. The Li/LiMn2O4 cell with the best conducting ionanofluid electrolyte delivers a discharge capacity of about 131 mAh g-1 at 25 degree C at a current density of 24 mA g-1, much higher than that obtained in 0.2 M Li salt dissociated Pyr14TFSI electrolyte (87 mAh g-1). Superior interfacial compatibility between ionanofluid electrolyte and electrodes as indicated by the excellent rate performance with outstanding capacity retention of the cell as compared to pure IL-based analogue, further establish great application potentiality of this optimized newly developed electrolyte for safer LMBs.