For years, researchers have wanted to learn more about a group of metal oxides that hold promise as key materials for the next generation of lithium-ion batteries, as they can mysteriously store far more energy than should be possible. An international research team led by the University of Texas at Austin has cracked the code of this scientific anomaly and torn down a barrier to the construction of ultra-fast battery storage systems.
The team found that these metal oxides have unique possibilities to store energy beyond the classic electrochemical storage mechanisms. The research published in Natural materialsfound different types of metal compounds with up to three times the energy storage capacity compared to materials that are common in today’s commercially available lithium-ion batteries.
By deciphering this puzzle, the researchers are helping to unlock batteries with greater energy capacity. That could mean that smaller, more powerful batteries can quickly deliver charges for everything from smartphones to electric vehicles.
“For nearly two decades, the research community has been puzzled about the unusually high capacities of these materials, beyond their theoretical limits,” said Guihua Yu, associate professor in the Walker Department of Mechanical Engineering at the Cockrell School of Engineering and a leader on the project. “This work shows the first experimental evidence that the additional charge is physically stored in these materials via a space charge storage mechanism.”
To demonstrate this phenomenon, the team found a way to monitor and measure how the elements change over time. Researchers from UT, the Massachusetts Institute of Technology, the University of Waterloo In Canada, Shandong University of China, Qingdao University in China and the Chinese Academy of Sciences participated in the project.
At the heart of the discovery are transition metal oxides, which are compounds that contain oxygen bound to transition metals such as iron, nickel, and zinc. Energy can be stored in the metal oxides – in contrast to typical methods in which lithium ions move in and out of these materials or convert their crystal structures for energy storage. And the researchers show that additional charge capacity can also be stored on the surface of iron nanoparticles that were formed during a number of conventional electrochemical processes.
A wide range of transition metals can release this extra capacity, and they share a common thread – the ability to collect a high density of electrons. These materials are not yet ready for prime time, Yu said, mainly due to a lack of knowledge about them. However, the researchers said that these new findings should go a long way in unraveling the potential of these materials.
The key technique used in this study, referred to as in situ magnetometry, is a real-time magnetic monitoring method used to study the evolution of a material’s internal electronic structure. It is able to quantify the charging capacity by measuring fluctuations in magnetism. This technique can be used to study charge storage on a very small scale, beyond the capabilities of many conventional characterization tools.
“The main results came from a technique commonly used by physicists, but very rare in the battery community,” said Yu. “This is a perfect showcase for a beautiful combination of physics and electrochemistry.”
Reference: “Additional storage capacity in transition metal oxide lithium-ion batteries by in-situ magnetometry” by Qiang Li, Hongsen Li, Qingtao Xia, Zhengqiang Hu, Yue Zhu, Shishen Yan, Chen Ge, Qinghua Zhang, Xiaoxiong Wang, Xiantao Shang , Shuting Fan, Yunze Long, Guo-Xing Miao, Guihua Yu and Jagadeesh S. Moodera, August 17, 2020, Nature Materials.
DOI: 10.1038 / s41563-020-0756-y