US scientists are set to provide insights into battery materials that allow the rapid charging of electric vehicles after making observations on how ions move in lithium titanate (LTO) electrode material.
A team led by the U.S. Department of Energy’s Brookhaven National Laboratory and Lawrence Berkeley National Laboratory captured, in real time, how lithium ions move in the material (made of lithium, titanium, and oxygen).
The team discovered that distorted arrangements of lithium and surrounding atoms in LTO “intermediates” (structures of LTO with a lithium concentration in between that of its initial and end states) provides an “express lane” for the transport of lithium ions.
Their discovery was reported in the 28 February issue of Science Magazine.
Co-corresponding author Feng Wang, a materials scientist in Brookhaven’s Interdisciplinary Sciences Department said: “Lithium needs to ‘fight’ its way into LTO, which is not a completely open structure. To get lithium in, LTO transforms from one structure to another.
“Typically, such a two-phase transformation takes time, limiting the fast-charging capability. However, in this case, lithium is accommodated more quickly than expected because local distortions in the atomic structure of LTO create more open space through which lithium can easily pass.
“These highly conductive pathways happen at the abundant boundaries existing between the two phases.”
The discovery was made after the scientists designed an electrochemical cell to operate inside a transmission electron microscope (TEM) that allowed them to track the migration of lithium ions in LTO nanoparticles in real time.
They then conducted electron energy-loss spectroscopy (EELS) during battery cycling. In addition to being highly sensitive to lithium ions, EELS, when carried out inside a TEM, provides the high resolution in both space and time needed to capture ion transport in nanoparticles.
To decipher the gathered information, scientists from the Computational and Experimental Design of Emerging Materials Research (CEDER) group at Berkeley and the Center for Functional Nanomaterials (CFN) at Brookhaven simulated the spectra.
On the basis of these simulations, they determined the arrangements of atoms from among thousands of possibilities.
“Computational modelling was very important to understand how lithium can move so fast through this material. Computations were able to confirm that the crowding of lithium ions together makes them highly mobile,” said co-corresponding author and CEDER group leader Gerbrand Ceder, from UC Berkeley.
Next, the scientists will explore the limitations of LTO— such as heat-generation and capacity-loss associated with cycling at high rates— for real applications.
They will examine how LTO behaves after repeatedly absorbing and releasing lithium at varying cycling rates, which will inform the development of practically viable electrode materials for fast-charging batteries.
Image: Brookhaven scientists (left to right) Deyu Lu, Mehmet Topsakal, Yimei Zhu, Lijun Wu, and Feng Wang