Nanofluid Reinforced Polymer Electrolytes for Safe and High Energy Density Secondary Lithium Batteries

Abstract

Using lithium metal anode comprising remarkably high theoretical capacity with lowest negative electrochemical potential is an attractive way to increase the low energy density of current lithium-ion batteries.However, the application of lithium metal in presence of conventional organic-solvent-based electrolytes is hindered by severe safety concerns such as leakage, electrode corrosion, flammability and the inevitable growth of lithium dendrite in the electrolytes during repeated Li deposition/dissolution processes. In this concern, gel polymer membranes as both separators and electrolytes have enabled tremendous recent research interest to achieve safer, high-energy density rechargeable batteries.Extending the research further, a novel class of nanocomposite gel polymer membrane electrolytes is prepared by blending poly(vinylidenefluoride-co-hexafluoropropylene) copolymer with a unique class of reinforcing agent, a highly conducting ionic liquid-based nanofluid, followed by soaking the resulted membranes into lithium salt dissolved liquid electrolyte. The conductivity of the nanofluids is optimized by dispersing different wt% of surface functionalized TiO2 nanoparticles in N-alkyl-N-butyl pyrrolidinium bis (trifluoromethylsulfonyl) imide (Pyr14TFSI) ionic liquid host. The best-conducting electrolyte containing 50wt% nanofluid shows excellent electrode/electrolyte interfacial stability when used in Li/LiFePO4 cell and delivers a discharge capacity of ~155 mAh g-1 at 25 °C at a considerably higher current density of 35 mAg-1. Excellent rate performance with superior capacity retention of the cell as compared to that comprising bare PY14TFSI ionic liquid reinforced gel polymer electrolyte indicates tremendous application potentiality of this novel class of electrolyte for safe and high energy density secondary lithium batteries.