Improving the charge storage capacity and lifetime and
charging/discharging
efficiency of battery systems is essential for large-scale applications
such as long-term grid storage and long-range automobiles. While there
have been substantial improvements over the past decades, further
fundamental research would help provide insights into improving the
cost effectiveness of such systems. For example, it is critical to
understand the redox activities of cathode and anode electrode materials
and stability and the formation mechanism and roles of the solid–electrolyte
interface (SEI) that forms at the electrode surface upon an external
potential bias. The SEI plays a critical role in preventing electrolyte
decay while still allowing charges to flow through the system while
serving as a charge transfer barrier. While surface analytical techniques
such as X-ray photoelectron (XPS), X-ray diffraction (XRD), time-of-flight
secondary ion mass spectrometry (ToF-SIMS), and atomic force microscopy
(AFM) provide invaluable information on anode chemical composition,
crystalline structure, and morphology, they are often performedex situ, which can induce changes to the SEI layer after
it is removed from the electrolyte. While there have been efforts
to combine these techniques using pseudo-in situapproaches
via vacuum-compatible devices and inert atmosphere chambers connected
to glove boxes, there is still a need for truein situtechniques to obtain results with improved accuracy and precision.
Scanning electrochemical microscopy (SECM) is anin situscanning probe technique that can be combined with optical spectroscopy
techniques such as Raman and photoluminescence spectroscopy methods
to gain insights into the electronic changes of a material as a function
of applied bias. This Review will highlight the potential of SECM
and recent reports on combining spectroscopic measurements with SECM
to gain insights into the SEI layer formation and redox activities
of other battery electrode materials. These insights provide invaluable
information for improving the performance of charge storage devices.