Synergistic Combination of Cross-Linked Polymer and Concentrated Ionic Liquid for Electrolytes with High Stability in Solid-State Lithium Metal Batteries

Mingjie Zhang; Faezeh Makhlooghiazad; Urbi Pal; Mahin Maleki; Shinji Kondou; Giuseppe Antonio Elia; Claudio Gerbaldi; Maria Forsyth

doi:10.1021/acsapm.4c02520

Synergistic Combination of Cross-Linked Polymer and Concentrated Ionic Liquid for Electrolytes with High Stability in Solid-State Lithium Metal Batteries

ACS Appl Polym Mater. 2024 Dec 1;6(23):14469-14476. doi: 10.1021/acsapm.4c02520. eCollection 2024 Dec 13.

Authors

Mingjie Zhang¹, Faezeh Makhlooghiazad², Urbi Pal², Mahin Maleki², Shinji Kondou², Giuseppe Antonio Elia^{1

3}, Claudio Gerbaldi^{1

3}, Maria Forsyth²

Affiliations

¹ GAME Lab, Department of Applied Science and Technology (DISAT), Politecnico di Torino, Corso Duca degli Abruzzi 24, 10129 Torino, Italy.
² Institute for Frontier Materials (IFM), Deakin University, Burwood, Victoria 3125, Australia.
³ National Reference Center for Electrochemical Energy Storage (GISEL) - INSTM, Via G. Giusti 9, 50121 Firenze, Italy.

Abstract

Poly(ethylene oxide)-(PEO-based solid polymer electrolytes (SPEs) are regarded as excellent candidates for solid-state lithium metal batteries (SSLMBs) due to their inherent safety advantages, processability, low cost, and excellent Li+ ion solvation. However, they suffer from limited oxidation stability (up to 4 V vs Li⁺/Li). In this study, a crosslinked polymer-in-concentrated ionic liquid (PCIL) SPE consisting of PEO, N-propyl-N-methylpyrrolidinium bis(fluorosulfonyl)imide (C₃mpyrFSI) ionic liquid (IL), and lithium bis(fluorosulfonyl)imide (LiFSI) salt is developed. The adopted UV-crosslinking strategy synergistically reduces PEO crystallinity while increasing the amount of encompassed lithium salt and IL and improves PEO oxidative stability, therefore leading to enhanced electrochemical performance. The physical and electrochemical properties of both linear and crosslinked SPEs are explored and compared. The designed cross-linked SPEs exhibited a promisingly high oxidative stability of 4.9 V vs Li⁺/Li and high ambient temperature ionic conductivity of 4 × 10^-4 S cm^-1. Stable and reversible lithium plating/stripping is demonstrated in symmetrical Li||Li cells over hundreds of hours. High-loading solid-state lithium iron phosphate (LFP)||Li cells show favorable cycling with over 90% capacity retention at 0.1C over 100 cycles at 50 °C. High voltage solid-state lithium manganese oxide (LMO)||Li cells exhibit promising cycling with a 93% capacity retention at a 0.2 C rate over 50 cycles at 50 °C. Thus, the combination of concentrated ionic liquid electrolytes in a crosslinked PEO-based matrix enables a pathway for designing high-performing SPEs for high energy density solid-state LMBs.