Researchers Discover a Path Toward More Efficient Batteries
The University of Pennsylvania research team developed a high-quality single-crystal layer of niobium-titanium oxide, but the material faces challenges.
Many seek new technologies that improve lithium-ion batteries as the world wrestles with the growing need for more efficient, higher-capacity batteries. One such technology is niobium-titanium oxide (NTO), a material with exceptional ionic conductivity, theoretical capacity, and stability for future battery anodes.
Image used courtesy of Adobe Stock
But, to date, no one has successfully harnessed the material in a real battery. Recently, University of Pennsylvania researchers challenged this narrative with the successful growth of an NTO crystal.
The Promise of Niobium Oxide
Niobium, specifically niobium-titanium oxide (NTO), is emerging as a promising material in the lithium-ion battery landscape. Specifically, NTO is being analyzed as an anode material with major potential for improving battery efficiency and lifecycle.
One of the standout features of niobium-based anodes is their outstanding cycle life. Unlike carbon anodes, Niobium doesn't change volume during charge and discharge cycles. This stability prevents issues like cyclic strain and dendrite growth, which can lead to battery self-discharge and other safety concerns. For this reason, NTO anodes have demonstrated the ability to retain 90% of their initial capacity even after 5000 charge/discharge cycles.
NTO has a promising balance of capacity and long life. Image used courtesy of Toshiba
Another key attribute of niobium oxide is its ability to enable faster movement of lithium ions. With an ionic conductivity reaching 10^-6 S/cm, niobium oxide promises to enable high-efficiency ion transport in batteries. This property is particularly vital for high-speed charging and high-power charging.
Finally, NTO has roughly 3x higher theoretical volume capacity density than lithium-titanium oxide. This means that NTO batteries can theoretically have a much greater capacity than conventional lithium-ion solutions.
Niobium Oxide Roadblocks
Despite the promise of NTO anodes, a significant challenge lies in creating these materials. Specifically, growing these materials into thin, flat layers, or "films," of high enough quality to be used in real-world applications has yet to be demonstrated.
According to the researchers, this problem is rooted in T-Nb205's complex structure and the existence of similar forms, or polymorphs, of niobium oxide. The complexity of T-Nb2O5's structure makes it difficult to control the growth process to produce thin films. The process requires precise control of temperature, pressure, and other conditions to ensure the resulting film has the desired properties. Even slight deviations can lead to films with suboptimal properties or the formation of unwanted polymorphs.
Moreover, many polymorphs of niobium oxide add another layer of complexity. Each polymorph has unique properties, and controlling which polymorph forms during growth is a significant challenge. These polymorphs can also affect the properties of the resulting film, potentially limiting its usefulness in practical applications.
NTO Crystal Research
Recently, University of Pennsylvania researchers announced the first successful growth of a single layer of NTO crystal.
The researchers synthesized a specific form of niobium oxide called Nb12O29 and studied its electrochromic properties through advanced tools like X-ray diffraction and absorption to analyze the material's structure. With a better understanding of the material’s structure, the researchers used precise methods, controlling temperature, pressure, and other conditions to grow the material into the desired form. The researchers successfully demonstrated the epitaxial growth of high-quality single-crystalline T-Nb2O5 thin films for battery use.
A schematic showing Li-ion migration into T-Nb2O5. Image used courtesy of Han et al.
According to the researchers, the growth of single-crystalline T-Nb2O5 thin films represents a significant advancement in energy storage. By unraveling the complex structure of niobium oxide and optimizing its properties, the work holds the promise of transforming energy storage technologies with potential benefits for transportation, consumer electronics, and more.