Nanosheet tech to enhance dielectric capacitors for energy storage

A research group led by Professor Minoru Osada at Nagoya University in Japan, in collaboration with NIMS, has developed a nanosheet device with high energy storage performance. The research findings were published in Nano Letters. Current energy storage technology, such as lithium-ion batteries, has long charging times and problems, including electrolyte degradation, lifetime and even unwanted ignition.

A promising alternative is dielectric energy storage capacitors. The structure of the 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 displacement mechanism called polarisation. When an electric field is applied to the capacitor, the positive charges are attracted towards the negative electrode. The negative charges are attracted towards the positive electrode. Then, storing electrical energy depends on the polarisation of the dielectric film by applying an external electric field.

Osada said dielectric capacitors have many advantages, such as a short charging time, long life and high power density. However, the energy density of current dielectrics falls short of meeting the rising demands for electrical energy. Enhancing the energy density would help dielectric capacitors compete with other energy storage devices. Since the energy stored in a dielectric capacitor is related to the amount of polarisation, the key to achieving high energy density is to apply as high an electric field as possible to a high dielectric constant material. However, existing materials are limited by the amount of electric field they can handle.

The researchers used layers of nanosheets made of calcium, sodium, niobium and oxygen with a perovskite crystal structure. “The perovskite structure is known as the best structure for ferroelectrics, as it has excellent dielectric properties such as high polarisation. We found that by using this property, a high electric field could be applied to dielectric materials with high polarisation and converted into electrostatic energy without loss, achieving the highest energy density ever recorded,” Osada said.

The research findings confirmed that nanosheet dielectric capacitors achieved higher energy density while maintaining the same high output density. The nanosheet-based dielectric capacitor achieved a high energy density that maintained its stability over multiple cycles of use and was stable at high temperatures up to 300°C.

“This achievement provides new design guidelines for the development of dielectric capacitors and is expected to apply to all-solid-state energy storage devices that take advantage of the nanosheet’s features of high energy density, high power density, short charging time of as little as a few seconds, long life and high temperature stability,” Osada said.

Dielectric capacitors can release stored energy in a short time and create an intense pulsed voltage or current; these features are useful in pulsed-discharge and power electronic applications. In addition to hybrid electric vehicles, they would also be useful in high-power accelerators and high-power microwave devices.

Image credit: iStock.com/Kuzmik_A