MIT Uses Neutrons in Drive to Improve Energy Storage in Supercapacitors

At Oak Ridge National Laboratory, researchers at the Massachusetts Institute of Technology used neutrons to study MOF materials that could one day be used as durable supercapacitors and potentially powered vehicles. Image Credit: ORNL/Jill Hemman

Compared with capacitors, the chemicals contained in batteries store and release electrical energy at a relatively low rate. Capacitors are often used in applications that require rapid power delivery.

Capacitors can quickly charge and release energy by using electric fields to store charge on the negative and positive plates. The plates are separated by electrolytes, solid or liquid materials that conduct ions. Applying a positive or negative potential to the capacitor causes ions to flow in one direction or the other.

The new type of capacitor is called a supercapacitor, which is made of advanced composite materials and nanomaterials, which can provide higher energy storage capacity and higher power, and has an infinite cycle life. However, even higher energy density is required to make supercapacitors the only power source in high-power applications such as electric vehicles within a day.

Scientists from the Massachusetts Institute of Technology conducted neutron research at the Oak Ridge National Laboratory (ORNL) of the Department of Energy (DOE) to study a new, highly porous nanomaterial that can be used as a durable high-energy super Capacitor. The research results are published in

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Mircea Dincă, WM Keck Energy Professor of the Department of Chemistry at MIT, said: “A metal-organic framework with excellent conductivity and energy storage capacity has been recently developed. “If we can better understand how MOF can store and store so quickly Release a lot of electricity, we may be able to turn it into a strong super capacitor material. "

The development of next-generation electrode materials requires an in-depth understanding of their energy storage mechanisms.

It is a crystalline material composed of metal ions and organic molecules, and has micropores, which makes it a good model for studying charge and discharge mechanisms.

In order to study the adsorption mechanism of ions in MIT's porous conductive MOF, the research team used this material to make electrodes, and then immersed them in a solvent containing sodium triflate electrolyte. When the researcher turns the voltage on or off and switches it to negative or positive and then back again, this allows positive and negatively charged ions to flow freely.

Through small-angle neutron scattering experiments conducted on ORNL’s High Flux Isotope Reactor (HFIR), the researchers found that when the applied voltage is zero, the sodium ions in the electrolyte form a thin layer on the rod-shaped structural unit of the MOF. The solvent molecules penetrate into the pores. Applying a positive voltage or a negative voltage will cause sodium ions or triflate ions to enter the pores, respectively. Subsequent reversal of the polarity causes the ions in the hole to switch positions with the ions outside.

The neutron data indicate that the charge storage mechanism in the micropores strongly depends on the electrode polarization. These findings provide new insights into the charge storage mechanism in nanomaterials.

Lilin He, a neutron scattering scientist at ORNL, said: “MOFs generally have high porosity but poor conductivity, which limits their use in high-power applications.” “When you consider all internal pores, gaps and surfaces, This conductive MOF is a highly porous nanomaterial with a very large total surface area.

He added: "As important as its electrical conductivity, even after 10,000 cycles, the MOF's capacitance has only lost 10% and its internal resistance has not increased. This may indicate that it has a good future in commercial applications. Durability."

Neutron scattering is an ideal tool for observing the ion activity inside MOF, because neutrons can penetrate deeply into almost any material. They are also very sensitive to the presence of light elements, such as deuterium (isotopes of hydrogen) added to the electrolyte by researchers. The deuterated hydrogen in the electrolyte provides contrast to help see where the ions are, even in the millions of holes in the MOF.

Scientists next plan to produce variants of MOF materials and use neutrons again to study their energy capacity and determine whether they are more efficient, faster, and perform at higher voltages.

References: "Observation of ion electrosorption in metal-organic framework micropores under the small-angle neutron scattering of Operando" published by Dr. He Lilin, Prof. Yang Luming, Prof. Mircea Dincă, Dr. Zhang Rui and Dr. Li Jianlin on March 11, 2020,

The U.S. Department of Energy’s Office of Science and ORNL’s laboratory-directed research and development program provided support for neutron research.

HFIR is the Office of Scientific User Facilities of the US Department of Energy. ORNL is managed by UT-Battelle LLC, the Office of Science of the U.S. Department of Energy, which is the largest supporter of basic research in physical sciences in the United States. The US Department of Energy’s Office of Science is working hard to meet the most pressing challenges of our time.

MIT once again led the trend and conducted outstanding research. I was impressed by how many thoughtful innovations MIT reported.

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