Harnessing Cold Sintering to Fabricate Composite Polymer Electrolytes - A Paradigm Shift in Organic-Inorganic Material Assembly

Abstract

The development of composite electrolytes for all-solid-state batteries is an emerging field, but the creation of predominantly inorganic electrolytes remains challenging. In this study, Li6.25Al0.25La3Zr2O12 (Al-LLZO), a ceramic material selected for its high ionic conductivity (1 × 10−4 S.cm−1 at ambient temperature) was shaped by the cold-sintering process (CSP). The organic phase was synthesized by free-radical polymerization of two poly(ethylene oxide) methacrylate derivatives in the presence of lithium bis(trifluoromethanesulfonyl)imide salts (LiTFSI). The polymethacrylate network with dangling poly(ethylene oxide) (PEO) chains was thus obtained. This in situ polymerization allows the one-pot synthesis of the composite electrolyte during CSP. Remarkably, the ionic conductivity of the CSP pellet varied with the nature of the organic phase, ranging from 1 × 10−4 to 1 × 10−5 S.cm−1 for non-grafted and grafted TFSI anion on the PEO-based network, respectively. Additionally, the transport of Li+ remained unaffected by the inorganic material’s nature as long as it contained Li species. Furthermore, a significant enhancement of the ionic conductivity was observed in the composite pellet compared to the TFSI grafted network (10−5 to 10−7 S.cm−1, respectively). Electrochemical impedance spectroscopy measurements revealed changes in the Al-LLZO||PEO-based polymer interface during CSP with the formation of an interphase, confirmed by a low activation energy value (0.1 eV).