(Nanowerk News) A research group led by Professor Minoru Osada at the Institute of Materials and Systems for Sustainability (IMaSS), Nagoya University in Japan, in collaboration with NIMS, has developed a nanosheet device with the highest ever energy storage performance. Their results are published in Nano Letters (“Very High Energy Storage in 2D High-κ Perovskites”).
Innovations in energy storage technologies are essential for the effective use of renewable energy and the mass production of electric vehicles. Current energy storage technologies, such as lithium-ion batteries, are subject to long charging times and problems, including electrolyte degradation, service life, and even unwanted ignition.
One promising alternative is the dielectric energy storage capacitor. The basic structure of a capacitor is a sandwich-like film made of two metal electrodes separated by a solid dielectric film. Dielectrics are materials that store energy through a physical charge transfer mechanism called polarization. When an electric field is applied to a capacitor, the positive charge is attracted towards the negative electrode. The negative charge is attracted towards the positive electrode. Then, storing electrical energy relies on polarizing the dielectric film by applying an external electric field.
“Dielectric capacitors have many advantages, such as short charge times of only a few seconds, long life, and high power density,” said Osada. However, the current dielectric energy density is far from meeting the increasing demand for electrical energy. Increasing energy density will help dielectric capacitors compete with other energy storage devices.
Since the energy stored in a dielectric capacitor is related to the number of polarizations, the key to achieving a high energy density is to apply the highest possible electric field to a high dielectric constant material. However, the materials present are limited by the amount of electric fields they can handle.
To go beyond conventional dielectric research, the group used nanosheet coatings made of calcium, sodium, niobium, and oxygen with a perovskite crystal structure. “The perovskite structure is known as the best structure for ferroelectrics, because it has very good dielectric properties such as high polarization,” explained Osada. “We found that using this property, high electric fields can be applied to dielectric materials with high polarization and converted into electrostatic energy without loss, achieving the highest energy density ever recorded.”
The findings from the research group confirmed that nanosheet dielectric capacitors achieve 1-2 orders of magnitude higher energy density while maintaining the same high output density. Interestingly, nanosheet-based dielectric capacitors achieve high energy densities which maintain their stability over multiple cycles of use and are stable even at high temperatures up to 300 °C.
“This achievement provides a new design guide for the development of dielectric capacitors and is expected to be applied to all solid-state energy storage devices that take advantage of the nanosheet features of high energy density, high power density, short charge time. seconds, long life, and high temperature stability,” said Osada. “Dielectric capacitors have the ability to release stored energy in a very short time and create intense pulsed voltages or currents. These features are useful in many pulse discharge and power electronics applications. As well as hybrid electric vehicles, they are also useful in high-power accelerators and high-power microwave devices.”