Ion coordination to improve ionic conductivity in polymer electrolytes for high performance solid-state batteries

Abstract

Polymer electrolytes with high ionic conductivity and good mechanical stability, which can be achieved by the incorporation of oxide ceramics into polymer electrolytes, are critical for solid-state batteries. However, it is challenging to obtain selectivity and efficiency of lithium-ion (Li+) transport enhancements in polymer electrolytes by oxide ceramic additives because the free volume increase in the polymer matrix by oxide ceramic-polymer interactions facilitates simultaneous Li+ and anion transport. Herein, cerium-zirconium oxide (ZrxCe(1−x)O2) nanoparticles are demonstrated to be an effective additive for ion coordination modification to selectively improve Li+ transport in poly (ethylene oxide) (PEO) electrolytes. By anion adsorption using ZrxCe(1−x)O2 nanoparticles, the ionic interaction between Li+ and bis(trifluoromethanesulfon)imide (TFSI-) is weakened, the proportion of PEO-TFSI- mixed coordination with Li+ is reduced, and Li+ coordination is modified. Therefore, after Li+ coordination modification, the PEO electrolyte with Zr0.5Ce0.5O2 nanoparticles achieves a high ionic conductivity of 7.3 × 10−5 S cm−1 and a high lithium transfer number of 0.42 at 30 ºC. Our work suggests that ion coordination modification by oxide ceramics can selectively improve the solid diffusion kinetics of Li+. This research provides new insights into the mechanism of Li+ transport.