UNIVERSITY PARK, Pa. — Chao-Yang Wang, William E. Diefenderfer Chair in Mechanical Engineering and professor of mechanical engineering, of chemical engineering and of materials science and engineering at Penn State, has received a three-year award from the Toyota Research Institute (TRI) through the institute’s University Research Program (URP). The award will support Wang’s research on redesigning liquid electrolytes to prevent lithium-ion (Li-ion) batteries from catching fire.
Launched in 2016, URP “brings together TRI researchers and university teams to tackle major societal challenges, including aging society, climate change and human understanding,” according to the TRI website. This year marks the introduction of URP 3.0, the next phase of URP, which will support 69 research projects across 31 universities in the largest cohort since the program’s inception.
Wang will be one of 88 TRI researchers and 104 faculty members participating in URP 3.0 and “working on technologies to advance [artificial intelligence (AI)], robotics, driving and material science,” according to the announcement from TRI. Wang conducts research on fuel cells and advanced batteries for electric propulsion, stationary power generation and portable electronics.
“The overall goal for the upcoming project is to develop a new generation of safer liquid electrolytes and additives that work with today’s advanced battery materials,” Wang said. “These innovations will help enable the production of lithium-ion batteries that are far less likely to catch fire.”
A typical Li-ion battery is filled with a liquid electrolyte containing lithium salt. An anode and a cathode are positioned at opposite ends of the electrolyte, each connected through an external circuit to the device being powered. When the battery is in use, lithium ions flow from the anode to the cathode through the electrolyte, while electrons flow toward the cathode through the external circuit. A similar process occurs in the opposite direction while the battery is being charged, with an external power source driving lithium ions and electrons from the cathode back to the anode.
If the battery is crushed, overheated or otherwise damaged, a series of chemical reactions occurs in rapid succession, building heat and pressure in a cycle known as thermal runaway. At a high enough temperature, an oxide-based cathode releases oxygen, which reacts with either the liquid electrolyte or a lithium-containing anode. Following this reaction, the battery combusts, causing fire or explosion.
Thermal runaway has been associated with burning of the flammable liquid electrolyte. As a result, it’s often assumed that using non-combustible electrolytes, such as ionic liquids and solid electrolytes, would guarantee a reduction in the risk of runaway fires. However, Wang said his team previously identified a more serious factor that could drive thermal runaway in both solid and liquid electrolytes.
“When oxygen is released from the cathode, it can combine with highly reactive lithium at the battery’s anode and generate intense heat,” Wang said. “We aim to make lithium-ion batteries safer by redesigning the liquid electrolyte inside them, so that it can either capture this oxygen before it reaches the lithium or block the oxygen from traveling across the battery in the first place.”
With support from TRI, Wang said he plans to build on findings published by his research team in Nature Energy, which investigated the mechanisms underlying thermal runaway. Wang's team set up liquid-electrolyte, mock-solid and ionic-liquid cells to replicate the structures of different Li-ion batteries. Upon inducing internal short circuiting in a precisely controlled manner, the researchers observed that the mock-solid and ionic-liquid cells, which had no capacity for removing oxygen released by the cathode, caught fire more rapidly and violently than the liquid-electrolyte cells.
“We found that the safest electrolytes were those that could protect lithium anodes from oxygen while releasing low heat in the process,” Wang said. “Going forward, we aim to identify and synthesize liquid electrolytes that can efficiently scavenge oxygen while still working with modern materials like graphite, silicon-based and lithium metal anodes. These would help enhance the safety of many applications for lithium-ion batteries, from electric vehicles to AI data centers.”