An innovative multiphase electrode/electrolyte composite is proposed here, which is obtained by a fast, versatile and easily scalable UV-induced free-radical photo-polymerisation technique. This novel configuration consists of a methacrylic-based polymer electrolyte directly formed in situ at the interface of different electrode films (i.e. commercial graphite and hydrothermally synthesized LiFePO4). Conformal coatings are confirmed by SEM analysis which indicates an intimate interfacial adhesion between the electrode material particles and the polymer electrolyte. Laboratory-scale lithium pouch cells assembled by contacting a lithium metal counter electrode over the as-prepared electrode/electrolyte composites display good ambient temperature charge/discharge characteristics, at the level of the corresponding lithium cells in liquid electrolyte, along with very stable cyclability even at high current rates. In addition, preliminary results of a laboratory-scale Li-ion polymer cell, assembled by contacting the LiFePO4 cathode with the graphite anode, both in situ coated with the polymer electrolyte, are presented. The obtained findings outline the practical relevance of the novel procedure adopted which leads to the preparation of composite films with interesting performance, particularly for the next generation of flexible all-solid-state Li-ion microbatteries.