Progress, Outlook, and Challenges in Lead-Free Energy-Storage Ferroelectrics

For energy-storage materials, dielectric capacitors exhibit higher power density than fuel cells, Li ion batteries, and super capacitors, giving them potentional for application in hybrid electric vehicles, high-speed trains, and even spaceplanes. However, their low energy-storage density (ESD) has limited their commercialization, which has therefore fallen behind the other three named systems to some extent. Because of this, a key factor in the development of dielectric/ferroelectric capacitors is an increase in ESD. Optimizing electrical breakdown strength and dielectric constant are regarded as two promising ways to achieve this. Five-state dielectric energy-storage materials are introduced and their respective merits and demerits are summarized. Enormous efforts, including the modification of preparation techniques, have been made to improve energy-storage performances in the past two decades; the significance of interface engineering is discussed in this context. Energy-storage density, efficiency, thermal stability with polarization fatigue, and mechanical fatigue are all optimized, demonstrating promising potential for practical applications.