Observation and Quantification of Nanoscale Processes in Lithium Batteries by Operando Electrochemical (S)TEM

Abstract

An operando electrochemical stage for the transmission electron microscope has been configured to form a "Li battery" that is used to quantify the electrochemical processes that occur at the anode during charge/discharge cycling. Of particular importance for these observations is the identification of an image contrast reversal that originates from solid Li being less dense than the surrounding liquid electrolyte and electrode surface. This contrast allows Li to be identified from Li-containing compounds that make up the solid-electrolyte interphase (SEI) layer. By correlating images showing the sequence of Li electrodeposition and the evolution of the SEI layer with simultaneously acquired and calibrated cyclic voltammograms, electrodeposition, and electrolyte breakdown processes can be quantified directly on the nanoscale. This approach opens up intriguing new possibilities to rapidly visualize and test the electrochemical performance of a wide range of electrode/electrolyte combinations for next generation battery systems.

Advanced analytical electron microscopy for lithium-ion batteries

“…When Gu et al 63 applied the liquid-cell configuration to study a battery with a Si nanowire electrode (Figure 6a), they not only observed phenomena that are consistent with the open-cell studies but also successfully unraveled the dynamics of the electrolyte, which is difficult to probe using the open-cell setup. 64 Following this pioneering work, Zeng et al 22 observed Li metal dendritic growth and SEI layer formation (Figures 6b and c) 65 used a similar configuration to determine the lithiation state of LiFePO 4 in real time with a relatively high spatial resolution. Beyond these discoveries, the liquid-cell configuration also holds potential for further improvements.…”

Low-Dose and In-Painting Methods for (Near) Atomic Resolution STEM Imaging of Metal Organic Frameworks (MOFs)

“…The downside to this ability to see small areas is that because the electron beam has a strong interaction with the sample, it can cause significant levels of electron beam damage. However, the last 40 years of protein crystallography and more recently the use of in-situ liquid stages to study chemical reactions in the (S)TEM [3], have shown that this beam damage effect can in most cases be mitigated by the use of extremely low-dose imaging (a dose rate of less than 0.1 electrons/angstrom 2 /s and a cumulative dose of less than 10 electrons/angstrom 2 ). In addition to simply lowering the dose through conventional means (changing the emission current and probe dwell time), more recent use of compressive sensing/in-painting methods for STEM has also been shown to lower the effective dose and dose rate [4].…”

Imaging Electrochemical Processes in Li Batteries by Operando STEM

“…Figure 1 shows the typical field distribution around the Protochips electrochemical stage that allows the fields to be quantified and the most probable location of the reaction to be identified [2]. To make sure that the electron beam does not have any effect on the electrochemistry being performed, the electron beam dose rate is carefully calibrated to be below the electrolyte damage threshold prior to operando electrochemical cycling (in this case all experiments use a dose  0.3 electrons/Å 2 /s) [3]. As such, typical beam effects such as the formation of bubbles and/or precipitates from the breakdown of the electrolyte are completely avoided.…”