LiFePO ₄ cathode fabricated by pulsed laser deposition for all-solid-state thin-film batteries

Abstract Lithium iron phosphate (LiFePO ₄ , LFP) is one of the main cathode materials for lithium-ion batteries on the market; however, its implementation in all-solid-state thin-film batteries remains challenged by transport and interfacial limitations, as well as by compatibility and reactivity issues arising from thin film fabrication processes. In this work, carbon-free LiFePO ₄ thin films with thicknesses between 120 and 300 nm were deposited by pulsed laser deposition and investigated as cathodes in LFP/ lithium-phosphorus oxynitride (LiPON)/Li all-solid-state thin-film batteries. Structural and morphological analyses confirm the growth of phase-pure, crystalline LiFePO ₄ films without post deposition annealing. Electrochemical measurements reveal reversible lithium insertion and extraction, yet the theoretical capacity of LiFePO ₄ is not fully accessed under most operating conditions. When cycled at elevated temperature (50 °C), the full cells show a clear enhancement in capacity utilization, with the 200 nm-thick cathode delivering an areal capacity of 7.2 µ A·h·cm ⁻² (100 mA·h·g ⁻¹ ) at 5 µ A·h·cm ⁻² . The limited utilization of the active material may originate, in part, from interfacial phenomena at the LFP/Pt current-collector interface. From an application perspective, the achieved areal capacities and current densities fall within the operational range required for low-power autonomous microsystems, highlighting the potential relevance of LFP/LiPON thin-film batteries for internet-of-things applications.