Ultrahigh energy storage in process-engineered NaNbO₃-based thin films with superior thermal and cyclic stability

Dielectric thin film capacitors are essential for miniaturized electronics and energy storage systems, offering ultrafast charge-discharge rates and high reliability. However, achieving high energy density, efficiency, and stability in lead-free systems remains challenging, particularly with scalable and cost-effective methods. Here, we demonstrate relaxor sodium niobate-based thin films with Bi and Mg substitution, synthesized via optimized chemical solution deposition. By tailoring crystallization temperature and heating rate, we achieved a recoverable energy density of 37 J cm^-3 and an efficiency of 80% at 2.45 MV cm^-1. The films exhibit exceptional thermal stability, with energy density variation below 10% up to 310 °C, and superior charge-discharge stability beyond 16 million cycles at high fields. Microstructural engineering, involving grain size reduction and enhanced granularity, was critical for achieving a high Weibull breakdown strength (2.29 MV cm^-1) and reliability. These films outperform previously reported sodium niobate systems, surpassing lead-based alternatives in environmental sustainability and scalability. Our approach highlights the potential of sodium niobate-based thin films for high-performance dielectric capacitors in harsh environments, offering a scalable pathway for environmentally sustainable energy storage technologies.