Solvent-free extrusion of polymer-based solid-state electrolytes: Formulation, processing and modeling

Solid-state batteries (SSBs), especially those paired lithium metal anodes with solid-state electrolytes (SSEs) and enabling high-voltage bipolar stacking architectures, promise higher safety and energy density than conventional Li-ion systems. Among candidate electrolytes, polymer-based solid-state electrolytes (PSEs) are attractive for their processability, interfacial compliance, low density, wide form-factor freedom (thin, flexible films), and better air handling than many sulfide/halide systems. Solvent-free extrusion of PSEs has emerged as a promising route for scalable solid-state battery manufacturing. First, we reviewed early foundational research before 2020, including pioneering melt-compounding and hot-pressing studies that established core processing principles and performance baselines, then we surveyed the rapid advances since 2020 in extruding both neat PSEs and composite PSEs. New polymer matrices, inert/ceramic fillers, and refined formulations have expanded the processing window and improved ionic conductivity and interfacial stability. We also detail the extrusion parameters, such as single and twin-screw setups, screw element design, barrel and die temperature profiles, screw speed, residence time distribution, and shear and cooling rates. These parameters determine polymer crystallinity, phase morphology, and ultimately performance. In parallel, we also focus on modeling and simulation approaches (e.g., CFD, SPH, DEM) that predict flow, mixing, and thermal behavior in extruders. Because most current extrusion simulations remain polymer-centric and do not yet encode lithium-salt identity, ion association, and transport closures with sufficient fidelity, the simulation discussion in this review is intended to quantify flow–mixing–thermal histories to guide screw/die and process-window design. So direct prediction of ionic conductivity and Li + transference number now still has to rely on experiments or on separate MD/DFT-type simulations of intrinsic ion transport that do not explicitly resolve the mixing process. Due to fidelity limitations, these tools serve as complementary guides rather than replacements for experiments completely. Key processing–structure–performance relationships are synthesized via comparative radar plots and other graphical summaries, highlighting critical trade-offs to inform design optimization. Finally, we outline future directions, including broadening the range of polymers and fillers, and establishing standardized extrusion protocols. By integrating materials innovation, process engineering, and modeling insights, solvent-free extrusion of PSEs is expected to accelerate the transition from lab-scale feasibility to robust, continuous, scalable production.