In Situ Investigation on Spatiotemporal Changes of SEI Properties By SECM

In our society Li-ion batteries are widely used, especially for small-scale devices. During the first charging process the solid-electrolyte-interface (SEI) between the electrode and electrolyte is established. This layer passivates the surface against electron transfer reaction but allows transfer of Li-ions. In order to realize high-energy Li-ion batteries in conventional carbonate-based electrolytes, the formation of the SEI is required.^[1]

Content and structure of the SEI are highly discussed.^{[2, 3]} The SEI represents a complex chemical system, where several solid, liquid and gaseous compounds establish interdependent equilibria. Characterization of the SEI is a difficult challenge, because of the similar chemical identity of SEI components and electrolyte molecules. Furthermore, ex situ analysis of the SEI requires separation and isolation of the SEI, which may change the content and the structure of the SEI.^[3] In situ analysis is highly sought after to circumvent this problem.

In our approach we use the scanning electrochemical microscopy (SECM) to investigate in situ the electron transport across the SEI. For this purpose, a redox mediator is added to the electrolyte, which communicates between the battery electrode and the positionable ultra-microelectrode (UME). Our results by SECM demonstrate the dynamic of SEI formation and dissolution. Furthermore, the swelling behavior of practical graphite anodes in standard battery electrolytes is characterized.

References

[1]        J. B. Goodenough, K.-S. Park, J. Am. Chem. Soc. 2013, 135, 1167.

[2]        V. Etacheri, R. Marom, R. Elazari, G. Salitra, D. Aurbach, Energy Environ. Sci. 2011, 4, 3243.

[3]        P. Verma, P. Maire, P. Novak, Electrochim. Acta 2010, 55, 6332.