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Page 10 of 32 Yan et al. Energy Mater 2023;3:300002 https://dx.doi.org/10.20517/energymater.2022.60

Figure 4. (A) Sequential SEM images during Li electrodeposition/dissolution processes based on a wolfram film with a thickness of
-2
90 nm and a LiPON electrolyte at 50 μA cm . (B) Schematic illustration of liquid confining cell. Reprinted with permission from Ref. [59] .
Copyright (2017) Elsevier. (C) Preserving and stabilizing Li by cryo-EM. (D) Atomic-resolution TEM images of Li metal and SEI.
Reprinted with permission from Ref. [62] . Copyright (2017) American Association for the Advancement of Science. (E) AFM
(two-dimensional, 2D) images of buckled surface topography from three RTIL electrolytes: no-salt P TFSI; 1.0 M Li TFSI in P TFSI; 1.0
14
14
M Li FSI in P TFSI. Reprinted with permission from Ref. [66] . Copyright (2018) American Chemical Society. (F) SECM cell for battery
14
electrodes including photograph, cross-sectional schematic, reactions at the microelectrode (ME) and sample during imaging (ME
radius and ME-sample distance are enlarged for clarity). (G) Sequence of SECM feedback images recorded at different
charge/discharge processes. Reprinted with permission from Ref. [67] . Copyright (2020) Wiley-VCH. (H) Sketch of X-ray tomography
setup. Reprinted with permission from Ref. [70] . Copyright (2013) American Association for the Advancement of Science. (I) X-ray
tomography slices showing cross sections of symmetric lithium cells cycled to various stages and magnified 3D reconstructed volumes
of cells. Reprinted with permission from Ref. [71] . Copyright (2014) Springer Nature.
In situ atomic force microscopy (AFM) has also been generally applied to obtaining surface information,
such as the analysis of the morphology of deposits and exploration of the Young’s modulus, which cannot
be detected by other microscopy techniques. Aurbach et al. studied the impact of the electrolyte component
on Li deposition behavior at low and high current densities via in situ AFM observation . Subsequently,
[64]
Kitta et al. employed in situ AFM combined with adhesion mapping to confirm that fresh Li protrusion
possessed a thinner SEI film and lower adhesion might grow rapidly . Yoon et al. used in situ AFM to
[65]
detect the plane strain modulus of an SEI that was formed in an ionic liquid at room temperature through a
[66]
mechanical analysis method . As exhibited in Figure 4E, under compressive stress, the SEI layer generates
surface buckling. According to the calculated results, the strain modulus of the SEI film for all the samples
ranges from 1.2 to 2.0 GPa. Based on an electrochemical reaction, scanning electrochemical microscopy
(SECM) is a kind of scanning technology that uses a small driving probe to scan samples and obtains
corresponding electrochemical information. The interfaces between measured liquid and solid samples,
which can be insulators, semiconductors and conductors, are effectively monitored, enabling SECM to
timely obtain the current on the electrode. Krueger et al. investigated the current evolution of the selected