Ionic liquid functionalized electrospun gel polymer electrolyte for use in a high-performance lithium metal battery

Abstract

The ability to suppress the formation and proliferation of lithium dendrites is an important endeavour towards the successful commercialization of lithium metal batteries as high energy storage devices. The use of gel polymer electrolytes is one of the most promising pathways to solving this problem and obtaining high performance. Here, we propose a novel gel polymer electrolyte (GPE), in which a nanostructured ionic liquid (IL), silica nanoparticle-tethered 1-methyl-1-propylpiperidinium bis(trifluoromethanesulfonyl)imide (SiO₂PPTFSI), is first introduced into a gel polymer electrolyte matrix based on poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF–HFP) prepared by electrospinning, followed by plasticization in a fluoroethylene carbonate (FEC) electrolyte. After being incorporated with the nanostructured IL, this novel GPE exhibits good mechanical properties, an enhanced electrolyte uptake (552 wt%) and a high ionic conductivity (0.64 mS cm⁻¹) and lithium ion transference number (t_Li⁺ = 0.60). In addition, it suppresses lithium dendrite formation and exhibits stable plating/striping cycles over 1200 hours in a symmetric lithium cell. More importantly, it is electrochemically stable up to 5.1 V (vs. Li/Li⁺), making it practical for use in LiNi_0.5Mn_1.5O₄ systems with a much better cycle stability and rate capability relative to those of Celgard with a liquid electrolyte or GPE based on PVDF–HFP. The Li/LiNi_0.5Mn_1.5O₄ cell with the novel GPE exhibits an initial discharge capacity of 119 mA h g⁻¹ at 1C, a capacity retention of 92.1% after 460 cycles, and a high reversible capacity of 74 mA h g⁻¹ at 6C. Therefore, the use of a nanostructured IL-modified GPE presents a promising way to enhance the cycle performance and safety of lithium metal cells.