Presented by Johanna Nelson,
Stanford Postdoctoral Scholar, SSRL MSD Hard X-ray Department
A key factor in the global move towards clean, renewable energy is the electrification of the automobile. Current battery technology limits EV (electric vehicles) to a short travel range, slow recharge, and costly price tag. Li-ion batteries promise the high specific capacity required for EVs to travel 300+ miles on a single charge with a number of possible earth abundant anode and cathode materials; however, set backs such as capacity fading hinder the full capability of these rechargeable batteries. In order to accurately characterize the dynamic electrochemical processes at the nanometer and atomic level, we have employed a set of complementary, in situ X-ray characterization techniques.
With X-ray diffraction (XRD) we have studied structural changes and the phase evolution of both anode and cathode materials during battery operation.1,2 This is especially critical in identifying and understanding metastable phases. Using transmission X-ray microscopy (TXM) we have tracked the morphological changes of sulfur in Li-S batteries2 and the crack formation in germanium anodes during cycling. Furthermore, with 3D TXM we are able to quantify the large volume changes known to occur in anode materials such as Si, Ge, and Sn. X-ray absorption spectroscopy (XAS) has allowed us to probe the changes in oxidation state during lithiation and delithiation of cathode materials. Finally, merging the TXM and XAS capabilities has allowed us to visualize the electrochemical reaction in a cathode during cycling to 30 nm resolution. By combining results from a number of different in situ X-ray characterization techniques we are able to form a more complete picture of the failure mechanism of Li-ion batteries
1. S. Misra, et al., ACS Nano, 6 (2012), 5465-5473.
2. J. Nelson, et al., JACS, 134 (2012), 6337-6343.
