Fluoride-Free MXene-Polymer Composites for Li-Metal and Li-S Batteries: Comparative Synthesis Methods, Integration Rules, Challenges, and Future Directions.

MXene-polymer hybrids combine the high in-plane conductivity and rich surface chemistry of MXenes with the processability and mechanical tunability of polymers for lithium-metal and lithium-sulfur batteries. Most reported systems still rely on HF-etched MXenes, introducing F-rich terminations, safety and waste issues, and poorly controlled surfaces. This review instead centers on fluoride-free synthesis routes, benchmarks them against HF methods, and translates route-termination relationships into practical rules for choosing polymer backbones. We track the evolution from early linear hosts such as PEO- and PVDF-type polymers to polar nitrile or carbonyl matrices, crosslinked and ionogel networks, and emerging biopolymers and COF-type porous frameworks that are co-designed with MXene terminations to regulate ion transport, interfacial chemistry, and mechanical robustness. These chemistry-backbone pairings are linked to five scalable fabrication modes, including solution blending and film casting, in situ polymerization, surface grafting, layer-by-layer assembly, and electrospinning, and to roles as solid or quasi-solid electrolytes, artificial interphases, separator-like coatings, and electrode-facing architectures. Finally, we highlight key evidence gaps and reporting standards needed to de-risk scale-up of green MXene-polymer batteries.