Self-Assembled Monolayer in Hybrid Quasi-Solid Electrolyte Enables Boosted Interface Stability and Ion Conduction

Complex interactions between the inorganic solid electrolyte (ISE) and the liquid electrolyte (LE) give rise to challenges of achieving durable interface stability in hybrid quasi-solid electrolytes (HQSE), and the influence on the involved ISE surface ionic conductivity also needs to be investigated. Here, 4-chlorobenzenesulfonic acid (CBSA) is utilized to establish a self-assembled monolayer (SAM) on the surface of Li_6.4La₃Zr_1.4Ta_0.6O₁₂ (LLZTO), which is then incorporated into PEGDA-based in situ polymerized HQSE. The results show that the introduction of CBSA significantly improves the LLZTO/LE interface stability with the optimized solvation structure, resulting in a favorable ionic conductivity (1.19 mS⋅cm^-1) and an increasing Li⁺ transference number (0.647). Mechanisms for the promotion of ionic conduction and interfacial stability of SAM-HQSE are unveiled through the density functional theory (DFT) combined with Raman spectra and ⁷Li solid-state nuclear-magnetic-resonance. There are no short-circuits in the Li|SAM-HQSE|Li cells after 1000 h. The LFP|SAM-HQSE|Li cells or LFP|SAM-HQSE|Graphite pouch cells respectively achieve the capacity retention of 91.2 % and 87.0 % with the 0.5.C-rate for 500 and 300 cycles. This facile and effective strategy proposed in this work make it accessible for constructing the stable surface micro-environments of LLZTO where boost and homogenize the Li⁺ conduction in a hybrid quasi-solid electrolyte system.