Ambient-Air Screen-Printable Poly(ethylene oxide)-Based Gel Polymer Electrolytes for Lithium-Ion Batteries: Role of Solvent-Salt-Polymer Interactions

This study reports a polyethylene oxide (PEO) based screen-printable gel polymer electrolyte (GPE) designed for lithium-ion battery applications. Through solvent and additive engineering, the electrolyte composition was tailored to modulate ionic transport and electrochemical stability. The GPE platform was formulated using LiTFSI, TEGDME as a plasticizing component, and either DIOX or ACN as volatile processing solvents. Succinonitrile (SN) was incorporated to examine its effects on ionic transport and electrochemical behavior. The optimized formulation (PEO-LiTFSI-TEGDME-DIOX; PEO-STD) exhibited a room-temperature ionic conductivity of (1.34 × 10-4 S cm-1) and an improved lithium-ion transference number (tLi+ = 0.57), reaching 0.65 upon SN addition. Linear sweep voltammetry on symmetric two-electrode cells indicated an apparent upper stability limit of 4.57 V, reported as an applied cell voltage rather than a Li/Li+-referenced oxidation potential. In half-cell tests, the optimized electrolyte delivered a high specific capacity (∼160 mAh g-1) and excellent coulombic efficiency (>99%) with LiFePO4 at 0.1 C. However, under prolonged cycling with the higher-voltage NMC622 cathode, PEO-STD retained 69.52% of its initial capacity after 50 cycles, while the incorporation of SN further accelerated capacity fading (30.26% retention), indicating that interfacial processes, rather than the intrinsic oxidative stability alone, govern long-term cell performance. In contrast, Li|GPE|Li symmetric-cell cycling showed that SN incorporation improved interfacial polarization stability at the lithium-metal anode, revealing an electrode-dependent trade-off in its effect on interfacial stability. Rheological analysis, including flow-curve and three-interval thixotropy tests (3ITT), confirmed pronounced shear-thinning behavior and rapid structural recovery, supporting their suitability for screen printing. These findings highlight the critical role of solvent-salt-polymer interactions in governing ionic transport, electrochemical stability, and printing performance. Furthermore, the developed GPEs were formulated under argon and successfully screen-printed and dried under ambient air, providing a practical route toward the fabrication of printable lithium-ion batteries.