What's in the Life of a Battery?
Researchers can now observe the life of batteries to find a cure to their short life cycle
Results: Notice that your cell phone battery keeps its charge longer when it's new versus when it's a year or two older? Scientists at Pacific Northwest National Laboratory are researching the reason capacity fading happens to batteries, like in our cell phones or our electric vehicles. Scientists believe that capacity fades because of irreversible changes in the microstructure of the active materials, anode and cathode, in the battery. The PNNL team observed how the negative poles inside a battery—tin oxide anode, for example—change, which is featured by twisting and contorting during charging and discharging.
Why It Matters: Many ideas to reduce the nation's oil addiction require an effective battery. For example, electrical vehicles need better batteries to drive longer distances. Lithium-ion batteries, used in cell phones and other devices, are a popular option, because pound for pound, they are some of the most energetic rechargeable batteries available. One of the greatest challenges facing lithium-ion battery development is solving the gradual capacity fading that accompanies each charge and discharge. This study answers important questions on how the microstructure evolves during charging and discharging of a battery, giving scientists important data to look into new strategy of designing a better battery.
Methods: Scientists at PNNL designed a tiny battery and used advanced diagnostic tools to see the battery operation in real time under vacuum. The team constructed the battery containing a single tin oxide nanowire, the negative electrode, and an ionic-liquid-based electrolyte, a special liquid that has properties similar to regular electrolytes, but does not evaporate under a vacuum.
This tiny battery can be charged and discharged, while scientists study how the microstructure changes and falls apart. The team used electron microscopy and other surface- and bulk-sensitive tools, located in EMSL, to probe the structural evolution of active materials. This in situ testing within the electron microscopy excluded other artifacts, such as would have been obtained if it was done by ex situ methods. They noticed that upon initial charging, the tin oxide is subject to lithiation-induced solid-state armorphization, followed by nucleation and growth of lithium tin alloy particles dispersed in the lithium oxide matrix. This composite structure provides key information on how the structure evolves upon initial charging.
What's Next: Continued collaboration with industry, other laboratories, and universities will allow scientists to gain more answers about capacity fading and other battery issues in real-world batteries. Scientists will broaden the research to include different materials. For example, many electrodes are not made of nanowires; instead, they may be made of nanoparticles with additives to hold them together. Researchers would like to put those materials to the test and investigate how they behave with the help of a high-power electron microscope, eventually solving the issue of capacity fading during a battery's life.
Acknowledgments: This work was supported by the Materials Sciences and Engineering Division, Office of Basic Energy Sciences and the Office of Biological and Environmental Research, U.S. Department of Energy and PNNL's Transformational Materials Science Initiative, and Chemical Imaging Initiative, funded by the Laboratory Directed Research and Development effort. The observations were performed on the microscopy in the Environmental Molecular Sciences Laboratory, a national scientific user facility at PNNL.
Research Team: Chong-Min Wang, Wu Xu, Jun Liu, Ji-Guang Zhang, Lax V. Saraf, Bruce W. Arey, Daiwon Choi, Zhen-Guo Yang, Jie Xiao, Suntharampillai Thevuthasan, and Donald R. Baer, Pacific Northwest National Laboratory.
Reference: Wang CM, W Xu, J Liu, J Zhang, LV Saraf, BW Arey, D Choi, Z Yang, J Xiao, S Thevuthasan, and DR Baer. 2011. "In Situ Transmission Electron Microscopy Observation of Microstructure and Phase Evolution in a SnO2 Nanowire during Lithium Intercalation." Nano Letters 11(5):1874-1880.