When neutrons scatter, the future of energy is revealed
Materials science has a crucial role in the transition to renewable energy sources.
The world is shifting towards renewable energy. Some 17% of Australia’s electricity in 2016 was produced by solar, hydro, wind and bioenergy. That proportion will rise with five large-scale renewable energy projects started, under construction or completed in 2017.
While producing it is less of an issue today, storing electricity has become ever more crucial to reliable renewable energy.
Technology is still under development, and even lithium-ion batteries suffer performance difficulties – mostly due to their functional material components, according to Vanessa Peterson, leader of the Functional Materials for Energy Devices and Systems Project at ANSTO’S Australian Centre for Neutron Scattering.
“Fundamental research into battery function is therefore probably the biggest opportunity to address the global issue of energy storage,” she says. “Solving these challenges is likely to have high impact.”
Scientists with a possible new battery material need to know its fundamental structure and how that structure changes during use within a battery, when chargecarrying ions interact with it.
This is where ANSTO’S Australian Centre for Neutron Scattering (ACNS) comes in. The ACNS helps bring to light the crystal structure of materials, particularly those relevant for this age of new energy.
Just where energy technologies would be without neutron scattering is hard to say, Peterson says, but there would be major holes in what we know: “For example, the atomic structure of all commercially used electrode materials in lithium-ion batteries would be essentially unknown, and the crucial water management in fuel cells would be impossible.”
So exactly how does neutron scattering unveil a material’s atomic nuts and bolts?
Neutron scattering methods parallel older techniques of X-ray scattering – the earliest being X-ray diffraction, where a beam of X-rays hitting a material produces a pattern characteristic of the arrangement of atoms within that material. This happens because X-rays interact with the electron cloud enveloping each atom. The more electrons the atom has, the more X-rays scatter. Where the X-rays scatter is determined by the arrangement of layers of atoms within the material.this technique is used at ANSTO’S Australian Synchrotron in Melbourne.
At the ACNS in Sydney, though, instruments use neutrons instead of X-rays. It’s a similar concept, however, neutrons don’t interact with electron clouds. Their level of scattering depends on the strong nuclear force that glues protons and neutrons together in the atomic nuclei.
For its source of neutrons, the ACNS looks to ANSTO’S Open Pool Australian Lightwater (OPAL) multipurpose reactor next door. The OPAL reactor does this via a process called controlled fission. A neutron hitting the nucleus of a uranium-235 atom causes that atom to split, spitting out more neutrons. Some of these neutrons are used for more fission, while others are reflected and channelled
to any of the 14 neutron-beam instruments at the ACNS.
Each instrument has its strengths, not limited to energy materials. “Dingo” can non-invasively see through dense materials such as metal or ceramics. Another instrument called “Wombat” is particularlyuseful for studying magnetic materials, as well as materials that undergo rapid change in their atomic structure.
Max Avdeev, an instrument scientist at the ACNS, was part of an international collaboration to deduce where oxygen atoms sat in a new solid electrolyte, which held promise in applications such as oxygen separation membranes.
Working with other researchers and their instruments – including an X-ray diffraction instrument at ANSTO’S Australian Synchrotron – Avdeev’s “Echidna” instrument pinpointed where oxygen atoms sat in the electrolyte’s structure.
“The fact that the data from all the used techniques – neutron diffraction, X-ray diffraction, electron microscopy – are consistent gives confidence the oxygen atoms were located accurately,” he says.
The work appeared in the journal Advanced Functional Materials – one of about 180 published papers featuring ACNS scientists in 2017.
“Multi-instrument collaborations are very common,” Avdeev says. “Echidna typically contributes to studies involving groups from two to five countries.”
What excites Peterson about energy materials research is its interdisciplinary nature and its focus on energy issues.
“This fosters an environment ripe for scientific discovery and the commercial uptake of these discoveries in technologies,” she says. “Advances in energy materials are not independent of each other, and incremental progress will come from separate research areas, but major steps forward require integration of research fields.
“The increasing use of neutron scattering by researchers in the fields of battery and other energy technologies is testament to its significance.”