By Michael Klein, The University of Texas at Austin, Electrochemical Energy Laboratory and MRS Student Chapter
The formation of a solid electrolyte interphase (SEI) plays a critical role in the operation and cyclability of lithium-ion batteries (LIBs). Without a stable SEI, the lithiated graphite anode will continually attack the electrolyte and lithium dendrite formation can be exacerbated. A good SEI layer enables the favorable kinetics (high rate performance) of LIBs while providing safety and cyclability to the system.
Characterizing the SEI layer remains problematic as it forms during battery cycling and its stability should ideally be characterized in situ in the relevant electrolyte solution. Scanning electrochemical microscopy (SECM) is a potential panacea for this problem, as it provides local electrochemical and topological characterization in an appropriate chemical environment. Its utility is hampered by the considerable experimental difficulty required to successfully apply the technique on a battery electrode surface.
Heinz Bülter of Professor Gunther Wittstock’s group at the University of Oldenburg and coworkers have successfully applied SECM to garner some insight into the stability of the SEI formed on composite graphite anodes after cycling using DBDMB as a redox mediator. Their work, published this year in the Angewandte Chemie International Edition showed evidence of spontaneous changes in the SEI, with the authors suggesting the possibility of damage from volume changes, re-dissolution of parts of the SEI, or even gas bubble formation and evolution. The difficulty in analyzing the simultaneous influence of the surface morphology, local electrochemistry, and other possible changes (i.e. gas formation) is readily apparent in the research. However, this approach is admirable, and continued work with this technique should afford currently unattainable insight into the operation of lithium-ion batteries.