Observing Lithium-Ion Battery Anodes in Action
Creating longer-life lithium-ion (Li-ion) batteries could help reduce our dependence on fossil fuels, affecting everything from vehicles to manufacturing. Current Li-ion batteries perform well, but over time the anode typically fails. A team of scientists from the Environmental Molecular Sciences Laboratory (EMSL), a DOE scientific user facility located in Richland, Washington, and users from Pacific Northwest National Laboratory (PNNL), Oak Ridge National Laboratory (ORNL), Applied Sciences Inc., and the General Motors Global Research & Development Center recently pinpointed the atomic-level changes that lead to anode failure in Li-ion batteries. The team created test anodes composed of hollow carbon nanofibers (CNFs) coated with a thin layer of amorphous silicon (Si). They then used EMSL’s in situ transmission electron microscope (TEM) to examine the performance of these anodes. Upon charging the anodes, the team observed a transformation of the amorphous Si into a crystalline state, and upon discharging, a return to a non-crystalline state. These results were further supported by performing theoretical calculations. Understanding the structural and phase transformation characteristics of CNFs with Si coatings provides Li-ion battery designers with the information they need to optimize silicon’s high storage capacity while maximizing the reliability of Li-ion batteries by manipulating coating layer thickness, CNF diameter, and the bonds between the coating layer and CNFs. For images of the transformation and for more information about this Si-carbon electrode research, see the news item “Silicon-carbon electrodes snap, swell, don’t pop.”
Wang, C.-M., X. Lin, Z. Wang, W. Xu, J. Liu, F. Gao, L. Kovarik, J.-G. Zhang, J. Howell, D. J. Burton, Z. Liu, X. Xiao, S. Thevuthasan, and D. R. Baer. 2012. “In Situ TEM Investigation of Congruent Phase Transition and Structural Evolution of Nanostructured Silicon/Carbon Anode for Lithium Ion Batteries,” Nano Letters 12(3), 1624-32. DOI: 10.1021/nl204559u.