T. T. Fister, P. Fenter, M. Balasubramanian, N. Karan, M. Chan, and J. Greeley

Researchers at Argonne National Laboratory’s Center for Electrochemical Energy Science (CEES) are developing a new approach for studying lithium and oxygen spectroscopy in a working battery environment. Inelastic x-ray scattering (IXS) uses the energy lost by high energy x-rays to measure excited state spectroscopy from core electrons of light elements, such as a lithium. IXS is an element-specific probe of bonding and chemical structure. Unlike traditional methods (e.g., electron energy-loss spectroscopy [EELS] and x-ray absorption spectroscopy [XAS]), IXS uses high energy x-rays that can penetrate the in-situ conditions of a working battery.

IXS is particularly useful in the study of decomposition products in lithium-ion batteries. Early research within CEES has been devoted toward characterizing the well-known solid electrolyte interphase (SEI) compounds and lithium-oxygen reaction products. Both the lithium and oxygen IXS spectra are extremely sensitive to the differences of bonding and structure in these materials (Figure 1).[1] Theoretical calculations systematically agree with the measured spectra and, in the case of lithium peroxide, were used to distinguish between two inconsistent crystal structures that had been proposed (Figure 2).[2] Ongoing and future studies in CEES will build on these results to break down the composition of the SEI and to decouple decomposition reactions from actual discharge products in a Li-air battery.

Figure 1 caption:  Experimental (a) and theoretical (b) lithium IXS from common SEI compounds is plotted both as function of x-ray energy loss and momentum transfer (q). Such q-dependence is unique to IXS and was used to quantify the s-p hybridization of each material.

Figure 2 caption: Analogous IXS was measured (a) and theoretically predicted (b) by members of CEES. Two candidate structures were calculated for lithium peroxide (Li₂O₂); the ​“Foppl” structure was found to systematically agree with Li and O IXS.

References

[1] T. T. Fister, M. Schmidt, P. Fenter, C. S. Johnson, M. D. Slater, M. K. Y. Chan, and E. L. Shirley, J. Chem. Phys. 135, 224513 (2011).

[2] M. K. Y. Chan, E. L. Shirley, N. K. Karan, M. Balasubramanian, Y. Ren, J. P. Greeley, and T. T. Fister, J. Phys. Chem. Lett. 2, 2483 (2011).