Li-Salt Doped Single-Ion Conducting Polymer Electrolytes for Lithium Battery Application

Journal article, 2022

Traditionally solid polymer electrolytes (SPEs) for lithium battery application are made by dissolving a Li-salt in a polymer matrix, which renders both the Li+ cations, the charge carriers of interest, and the anions, only by-standers, mobile. In contrast, single-ion conductors (SICs), with solely the Li+ cation mobile, can be created by grafting the anions onto the polymer backbone. SICs provide the safety, mechanical stability, and flexibility of SPEs, but often suffer in ionic conductivity. Herein an intrinsically synergetic design is suggested and explored; one dopes a promising SIC, LiPSTFSI (poly[(4-styrenesulfonyl) (trifluoromethanesulfonyl)imide]), with a common battery Li-salt, LiTFSI. This way one both increases the Li+ concentration and transport. Indeed, systematically exploring doping, it is found that 50-70 wt% of LiTFSI renders materials with considerable improvements in both the (Li+) dynamics and the ionic conductivity. A deeper analysis allows to address connections between the ion transport mechanism(s) (Arrhenius/VTF), the charge carrier speciation and concentration, and the free volume and glass transition temperature. While no silver bullet is even remotely found, the general findings open paths to be further explored for SPEs in general and Li-salt doped SICs in particular.