Sustainable, Dendrite Free Lithium‐Metal Electrode Cycling Achieved with Polymer Composite Electrolytes Based on a Poly(Ionic Liquid) Host
journal contributionposted on 18.01.2019, 00:00 authored by Gaetan Girard, Xiaoen WangXiaoen Wang, Ruhamah Yunis, Douglas MacFarlane, Aninda Bhattacharyya, Maria ForsythMaria Forsyth, Patrick HowlettPatrick Howlett
Polymer composite solid‐state electrolyte materials based on ionic liquids stand out as viable alternatives to flammable liquid electrolytes for solid state lithium‐metal batteries. They offer a compromise between favourable mechanical properties and stability against Li‐metal, coupled with favourable ion transport. However, insufficient Li+ transport properties for practical battery operation may result from the higher mobility of other ionic species from the ionic liquid (IL). Here, this issue was addressed by confining a highly concentrated IL electrolyte in a poly(ionic liquid) matrix with the addition of 5 wt % of alumina nanoparticles; these superconcentrated IL electrolytes favour Li+ ion transport. The composites are based on a poly(diallyldimethylammonium) bis(trifluoromethanesulfonyl)imide (PDADMA NTf2) matrix, and an electrolyte solution (ES) of high lithium concentration phosphonium IL, trimethyl(isobutyl)phosphonium bis(fluorosulfonyl)imide (P111i4FSI), with 3.8 mol kg−1 (3.8 m) LiFSI. The impact of ES content within the composite on Li+ transference number and electrochemical stability against Li‐metal is reported. For the 50 wt % ES and 50 wt % of PDADMA NTf2 composite, up to 0.5 mAh cm−2 of Li‐metal plating/stripping for over 20 days at 50 °C is shown. Scanning electron microscopy (SEM) confirmed that no Li dendrite formation was visible at the Li‐metal/polymer composite interface. Competitive performance of LiFePO4 electrodes (1.2 mAh cm−2) is also reported.