Flexible lead-free NBT-BT/PVDF composite films by hot pressing for low-energy harvesting and storage

• Published in: Journal of alloys and compounds Vol. 884; p. 161071
• Main Authors: Vijatovic Petrovic, M., Cordero, F., Mercadelli, E., Brunengo, E., Ilic, N., Galassi, C., Despotovic, Z., Bobic, J., Dzunuzovic, A., Stagnaro, P., Canu, G., Craciun, F.
• Format: Journal Article
• Language: English
• Published: Lausanne Elsevier B.V 05-12-2021; Elsevier BV
• Subjects: Anelasticity; Barium titanates; Bismuth; Composite materials; Electronic devices; Energy harvesting; Energy storage; Energy storage materials; Gamma phase; Hot pressing; Lead free; Modulus of elasticity; Piezoelectricity; Polymer matrix composites; Polymers; Polyvinylidene fluorides; Sodium titanate; Piezoelectricity; Composite materials; Energy storage materials; Polymers; Energy harvesting
• ISSN: 0925-8388; 1873-4669
• DOI: 10.1016/j.jallcom.2021.161071

•NBT-BT-PVDF flexible lead-free piezoelectric composite films were prepared by hot pressing.•Hot pressing method transforms PVDF α-phase into electro-active β and γ phases.•The dielectric permittivity increases with the active phase amount increase, up to 80.•Notable properties both for energy storage and energy harvesting application found.•Testing of force impact: up to 9 V and ~ 81 μW of output voltage and power obtained.
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The idea of this work is finding the way to efficiently and safely use mechanical energy released in small quantities around us to power up small-scale electronic devices used in everyday life. To this purpose, flexible lead-free piezoelectric composite films were prepared by hot pressing. Different amounts (30, 35 and 40 vol%) of lead-free piezoelectric material bismuth sodium titanate-barium titanate were embedded in the matrix of polyvinylidene fluoride under carefully optimized conditions of temperature and pressure, obtaining flexible films with quite homogeneous distribution of piezo-active filler. ATR-FTIR analysis revealed that hot pressing the flexible films caused a transformation of electro-inactive PVDF α-phase into electro-active β and γ phases. Dielectric measurements showed an increase of the permittivity up to 80 with the active phase increasing. Anelastic measurements showed that the elastic modulus increases as well with the fraction of active ceramic phase. Lastly, obtained flexible polymer-composites demonstrated notable properties both for energy storage and energy harvesting application, showing up to 74% of energy storage efficiency and, from testing of the force impact, up to 9 V and ~ 80 μW of output voltage and power.