Mechanistically Novel Frontal‐Inspired In Situ Photopolymerization: An Efficient Electrode|Electrolyte Interface Engineering Method for High Energy Lithium Metal Polymer Batteries

The solvent‐free in situ polymerization technique has the potential to tailor‐make conformal interfaces that are essential for developing durable and safe lithium metal polymer batteries (LMPBs). Hence, much attention has been given to the eco‐friendly and rapid ultraviolet (UV)‐induced in situ photopolymerization process to prepare solid‐state polymer electrolytes. In this respect, an innovative method is proposed here to overcome the challenges of UV‐induced photopolymerization (UV‐curing) in the zones where UV‐light cannot penetrate, especially in LMPBs where thick electrodes are used. The proposed frontal‐inspired photopolymerization (FIPP) process is a diverged frontal‐based technique that uses two classes (dual) of initiators to improve the slow reaction kinetics of allyl‐based monomers/oligomers by at least 50% compared with the conventional UV‐curing process. The possible reaction mechanism occurring in FIPP is demonstrated using density functional theory calculations and spectroscopic investigations. Indeed, the initiation mechanism identified for the FIPP relies on a photochemical pathway rather than an exothermic propagating front forms during the UV‐irradiation step as the case with the classical frontal photopolymerization technique. Besides, the FIPP‐based in situ cell fabrication using dual initiators is advantageous over both the sandwich cell assembly and conventional in situ photopolymerization in overcoming the limitations of mass transport and active material utilization in high energy and high power LMPBs that use thick electrodes. Furthermore, the LMPB cells fabricated using the in situ‐FIPP process with high mass loading LiFePO 4 electrodes (5.2 mg cm ‐2 ) demonstrate higher rate capability, and a 50% increase in specific capacity against a sandwich cell encouraging the use of this innovative process in large‐scale solid‐state battery production.