Self-assembly of Li single-ion-conducting block copolymers for improved conductivity and viscoelastic properties

Auteurs

Lozinskaya E.I., Ponkratov D.O., Malyshkina I.A., Grysan P., Lingua G., Gerbaldi C., Shaplov A.S., Vygodskii Y.S.

Référence

Electrochimica Acta, vol. 413, art. no. 140126, 2022

Description

Single-ion conducting polyelectrolytes (SICPs) with mobile Li cation have recently gathered significant attention as an “ideal” electrolyte for safe solid-state rechargeable lithium batteries, because they eliminate salt concentration gradients and concentration overpotentials, allowing transference number (tLi+) values close to unity. In this work, a series of single ion conducting block copolymers, namely [(LiM)n-r-(PEGM)m]-b-(PhEtM)k (A-b-B), is synthesized via reversible addition-fragmentation chain transfer (RAFT) copolymerization of 1-[3-(methacryloyloxy)propylsulfonyl]-(trifluoromethanesulfonyl)imide (LiM), poly(ethylene glycol)methyl ether methacrylate (PEGM) and 2-phenylethyl methacrylate (PhEtM) with controlled PEGM:LiM ratio, molecular weights (Mn = 25.8 ÷ 85.9 kDa) and narrow polydispersity (Mw/Mn = 1.12 ÷ 1.21). The bulk ionic conductivity, solid-state morphology and thermal properties of block copolymers are studied as a function of their composition. Block copolymers having molecular weights in the range of 46 ÷ 63 kDa and any ratio of PEGM:LiM (from 3:1 to 7:1) tend to evolve in quasi-hexagonally-packed cylinders, while copolymers with higher molecular weights (Mn > 74 kDa) and the ratio of PEGM:LiM = 5:1 and MA/MB ≤ 2.0 show lamellar phase separation. The lamellar long-range ordering in poly[(LiM17-r-PEGM86)-b-PhEtM131] and poly[(LiM17-r-PEGM86)-b-PhEtM194] results not only in the improved viscoelastic (mechanical) performance compared to parent copolymer poly[LiM17-r-PEGM86] (complex viscosity = 2.5 × 108 mPa s and 8.7 × 104 mPa s at 25 °C, respectively), but also in the demonstration of sufficiently high ionic conductivity despite the decrease in Li+ amount (σ = 3.8 × 10−7 and 4.1 × 10−7 S/cm at 25 °C, correspondingly). The selected poly[(LiM17-r-PEGM86)-b-PhEtM131] further shows high tLi+ (0.96 at 70 °C) and wide electrochemical stability (4.4 V vs. Li+/Li at 70 °C), which results in reversible and stable cycling at high specific capacities (up to 150 and 118 mAh g−1 at C/20 and C/5 rates, respectively) when assembled in lab-scale truly-solid-state Li metal cells with Li/copolymer/LiFePO4 configuration.

Lien

doi:10.1016/j.electacta.2022.140126