Researchers at Boise State University have developed a new method for making novel lithium-ion battery materials. Starting from amorphous (ie, a material lacking long-range order) niobium oxide, the team found that cycling the material with lithium induced transformation to a novel crystalline Nb2O5 anode with exceptional Li accumulation and fast cycling. This process could potentially be used to make other lithium-ion battery materials that cannot be easily made by conventional methods.
The study, jointly led in the labs of Hui (Claire) Xiang, professor of materials science and engineering at Boise State University, and Xu Ping Ong, professor of nanoengineering at the University of California, San Diego, is published in Nature. Materials.
The discovery of new materials for lithium-ion batteries has gained renewed urgency. Fueled by rising gas prices, there has been a surge in demand for electric vehicles (EVs), and with it, for the lithium-ion batteries that power them. However, today’s lithium-ion batteries are still very expensive and charge very slowly.
“Lithium-ion batteries are a key technology for the rechargeable battery market, but there is an increase in demand for batteries to have more power and faster charging times,” said Pete Barnes, Ph.D. an alumnus of Xiang’s Electrochemical Energy Materials Lab in the Micron School of Materials Science and Engineering and lead author of the paper. “If you want to charge your EV for 15 minutes and then go on the road for the next 200 or 300 miles, you need new battery electrodes that can charge at a much faster rate without much loss in performance.”
One of the biggest obstacles to charging in today’s lithium-ion batteries is the anode. The most common anode is made of graphite, which is very energy dense, but cannot be charged quickly due to the risk of fire and explosions by a process known as lithium metal plating. Intercalation metal oxides like the rock salt Nb2O5 material the team discovered are promising anode alternatives as they reduce the risk of lithium plating at low voltages.
To create the new anode material, Xiang’s group developed an innovative new technique called electrochemically-induced amorphous-to-crystalline transformation. The new electrode can achieve a high lithium storage of 269 mAh/g at a charging rate of 20 mA/g, and more importantly, continues to retain a high capacity of 191 mAh/g at a high charging rate of 1 A/g.
“The maximum thrilling factor of this paintings is the invention of a totally new technique for developing novel lithium-ion battery electrodes,” stated Xiang. “The trick is to start with a high-energy phase, such as an amorphous material. Simply cycling the material with lithium allows us to create new crystalline systems that exhibit improved properties beyond those made through traditional methods such as solid-state reactions.”
The exceptional rate performance of the anode is due to its disordered rock salt or DRX structure, which is like regular table salt but with Li and Nb atoms arranged in a random fashion. Although DRX cathode materials are well known, DRX anodes are relatively rare. Using computational techniques, Yunxing Zuo, Ph.D. Alumnus of the Ongs Materials Virtual Lab at UC San Diego, showed that the process of adding Li to amorphous Nb2O5 allows materials scientists to access metastable materials. The team developed a metric to identify other metal oxides that could potentially be synthesised in a similar fashion. Calculations show that the DRX structure has pathways for fast lithium diffusion, leading to higher rate performance.
“We accept as true with this paintings is the begin of a totally new manner of considering substances synthesis,” stated Ong. “Atoms like to arrange themselves in certain ways. When we make things the traditional way, we often get the same arrangements over and over again. This new method opens up a promising way to create other unconventional metal oxides.”
The team Dr. Sungsik Lee, Justin Connell, Hua Zhou and Yuji Liu from Argonne National Laboratory, Prof. Paul Davis, Paul Simmonds, and Dr. Darin Schwartz from Boise State, and Dr. Ying Du and Zhihua Zhu from the Pacific Northwest National Laboratory.