The advancement of dielectric composites exhibiting high energy storage density and superior discharge efficiency holds significant importance for the miniaturization and lightweight design of power devices. In comparison to energy storage solutions like fuel cells and lithium batteries, polymer capacitors offer numerous benefits, including excellent flexibility, high operational voltage, and rapid discharge rates, making them widely applicable in electronic systems, pulse technologies, and power systems. Each of traditional dielectric materials, such as dielectric ceramics, polymers, and glass-ceramics, presents unique strength and weakness. For instance, dielectric ceramics boast an ultra-high dielectric constant but suffer from brittleness, low breakdown resistance, and challenging processing requirements. Conversely, most polymers, including polyvinylidene fluoride (PVDF) and polypropylene, exhibit outstanding breakdown resistance, flexibility, and ease of processing, though their dielectric constants typically remain below 10, limiting their utility.
Currently, neither ceramic nor polymer dielectric materials alone can satisfy the demands of high-power and miniaturized capacitors. To address this, the work aims to propose a composite method, integrating inorganic ceramic powder fillers into a polymer matrix. This method combines the beneficial properties of both ceramics and polymers, yielding composites with enhanced dielectric properties and superior breakdown strength, thereby improving energy storage and power density. Through a molten salt process combined with a mixed alkali method, the two-dimensional (2D) flake SrTiO3 powder with a high aspect ratio as the inorganic ceramic filler was prepared. To enhance the compatibility between the two phases, a 3-aminopropyltriethoxysilane coupling agent was applied for surface modification. The 2D flake SrTiO3/PVDF flexible composites were then fabricated with a casting method, achieving a uniform thickness by adjusting the composite concentration. The microstructure, phase composition, and energy storage performance of these PVDF composites were systematically analyzed by varying the content of surface-modified 2D flake SrTiO3 powder. A correlation was established between the interfacial interactions and energy storage performance, elucidating the mechanism behind the enhanced energy storage capabilities of the 2D flake SrTiO3 powder/PVDF composites.
Experimental results indicated that the synthesized 2D flake SrTiO3 powder featured dimensions of 2-5 µm in length and width, with a thickness of 0.3-0.7 µm, and exhibited a uniform particle size distribution. The surface-modified 2D flake SrTiO3 powder was well-dispersed within the PVDF polymer matrix. As the content of 2D flake SrTiO3 powder increased, the dielectric constant of the PVDF composites gradually rose. At a 7.5vol.% filling level, the dielectric constant reached 23.2, which was 2.9 times that of pure PVDF. Additionally, the composites maintained high breakdown strength at low filler content. Specifically, with a 2.5vol.% content of 2D flake SrTiO3 powder, the energy storage density of the composite reached 6.9 J/cm³, which was 2.46 times that of pure PVDF. These improvements in dielectric properties and energy storage density were primarily due to the use of surface-modified 2D lamellar SrTiO3 with a large aspect ratio, offering a novel strategy for enhancing the energy storage performance of PVDF composites through the incorporation of such ceramic powders. This study provides a certain experimental reference for the preparation of high-performance dielectric energy storage capacitors.
Key words
composite materials /
SrTiO3 /
energy storage performance /
two-dimensional flake fillers /
surface modification /
dielectric properties
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Funding
The Programs for Tackling Key Problems in Science and Technology of Henan Province (252102231014); The Innovation Training Program for College Students in Henan Province (202511517015); Key Scientific Research Projects of Colleges and Universities in Henan Province (26A430004)
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