Researchers at the University of Texas at El Paso (UTEP) and Sandia National Laboratories have produced gel polymer electrolytes (GPEs) — semi-solid materials that sit between liquid and fully solid electrolytes in lithium-ion batteries — using the light-based 3D printing process vat photopolymerization (VPP).

The study, published in Communications Engineering, systematically examined how solvent choice within the electrolyte affects both ionic conductivity and the ability to print usable parts.

The team formulated composite resins by combining a UV-curable poly(ethylene glycol) diacrylate (PEGDA) base with a liquid electrolyte containing 1 M lithium perchlorate (LiClO₄) dissolved in one of two solvent systems: ethylene carbonate/diethyl carbonate (EC:DEC) or ethylene carbonate/propylene carbonate (EC:PC), each at a 1:1 volume ratio. 

Five resin-to-electrolyte ratios were tested, from 1:1 to 1:5 by volume, with the 1:4 ratio identified as the point at which ionic conductivity and mechanical handleability were best balanced.

Printing in open air and cycling performance

Interestingly, the printing was carried out outside a controlled-atmosphere glovebox, in a laboratory environment at 22% relative humidity. Despite exposure to ambient air, the printed GPEs retained ionic conductivity on par with their tape-cast counterparts, a result the researchers attributed in part to the low hygroscopicity of LiClO₄ compared to more commonly used lithium salts. 

Electrochemical stability was maintained up to approximately 4.5 V versus Li⁰/Li⁺, a range sufficient for low-voltage cathode materials such as lithium iron phosphate (LiFePO₄). Symmetric cell testing — in which lithium metal serves as both electrodes — confirmed stable lithium plating and stripping behavior over 100 cycles.

Geometry and UV blocker trade-offs

The team also printed complex geometries using PC-based GPE, including simple discs and a hexagonal honeycomb lattice structure. While disc geometries were printed with high fidelity, the resin’s optical transparency caused overcuring in the lattice, partially filling pores with solidified material. 

Adding allura red — a food dye — as a UV-blocking additive resolved the overcuring issue, allowing well-defined lattice features and a 1 cm³ solid cube to be produced. Cyclic voltammetry testing indicated that allura red did not produce a faradaic reaction within the tested voltage window, though the researchers cautioned that UV absorbers warrant careful evaluation before use in battery applications, as they may affect the solid electrolyte interphase (SEI) and ion transport behavior.

The research was funded in part by the University of Texas System Regents’ Research Excellence Program and Sandia National Laboratories’ Laboratory-Directed Research and Development program.