Toyota researchers are collaborating with the Center for Functional Nanomaterials (CFN) at the DOE’s Brookhaven National Laboratory to probe molecular structures and track chemical reactions in magnesium batteries.
“Issues related to cost, power, energy density, and durability of Li-ion batteries have slowed their implementation in large-scale applications, such as electric and hybrid vehicles,” said Toyota scientist Ruigang Zhang. “A rechargeable magnesium battery system is one interesting candidate that offers much greater earth abundance than lithium and higher storage capacity – but the necessary research remains a challenge.”
Magnesium ions carry twice the intrinsic charge of lithium ions, meaning they store and deliver more energy. But as those ions move during charge/recharge cycles, the nanostructure of the battery material degrades and transforms. The degradation rates and patterns must be probed in a variety of conditions so that scientists can design new atomic architectures to extend battery lifetimes and optimize performance.
“CFN possesses a full suite of powerful observational and analytical instruments,” said Brookhaven scientist Feng Wang. “With our newly developed imaging techniques, we are able to track the magnesium reactions in real time with nanoscale resolution, letting us understand how and why structural disorder emerges and impacts performance.”
Brookhaven Lab scientist Feng Wang of Brookhaven Lab’s Sustainable Energy Technologies Department, who will lead the collaboration with Zhang’s team at CFN.
The Toyota researchers plan to target a promising magnesium cathode composed of hollow carbon molecules called fullerenes. The compound offers consistent energy output, a rapid cycling rate, and extremely low voltage hysteresis, but the performance and ease of battery integration still need work, and scientists need a full understanding of structural evolution, crystallization mechanisms, and other factors influencing the electrochemical reactions.
“Unfortunately, our preliminary x-ray diffraction (XRD) results indicated material amorphization – a loss of crystalline structure – during operation that makes it challenging to follow the structural evolution,” Zhang said. “We now plan to use the advanced electron microscope facilities at CFN for local structural studies, particularly to track the reaction as it occurs rather than just before or after.”
The scientists will use CFN’s high-resolution transmission electron microscopy (TEM) and electron energy loss spectroscopy (EELS) techniques to identify morphologies and chemical elements as they emerge or transform. In these techniques, a focused beam of electrons strikes and interacts with the material’s atomic structure and then carries that information into highly sensitive detectors.
“Down the road, we also plan to use Brookhaven’s powerful new x-ray light source facility, the National Synchrotron Light Source II, to investigate battery properties and reaction evolutions in real time under real-world reaction conditions,” Zhang said.
Added Zhang, “Solving the magnesium challenges may open the door for other multivalent batteries such as cadmium or aluminum, thereby shedding light on the next generation of battery technology.”