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Page 16 of 23 Zhou et al. Microstructures 2023;3:2023043 https://dx.doi.org/10.20517/microstructures.2023.38

the corroded glass substrate at the bottom and their presence in the top ice region from the alkaline
solution. Figure 11B presents the proximity histogram (proxigram) of local composition, confirming the
variance of Li + Na concentration (magenta) and distinguishing it from the concentration profiles of other
non-background elements such as Si and oxygen (O). In Figure 11C, the proxigram of the local composition
near the solution-glass interface confirms the high concentration of calcium (Ca), indicating the location of
the glass substrate. These results demonstrate the power of combining cryo-APT and cryo-FIB to site-
specifically capture microstructural features of interest in ice, thereby opening up new applications for these
techniques in biological specimens, such as cells that primarily consist of water.

Energy storage materials
The push to develop long-lasting and high-capacity energy storage materials in order to reduce reliance on
carbon-based fossil fuels has gained significant momentum. APT, with its ability to offer high-resolution
mapping of light elements such as Li, holds great promise in this research field for developing improved
[82]
battery materials .
However, when it comes to using APT for nanoscale Li mapping in battery materials, including anodes,
cathodes, and electrolytes, a major challenge arises from in-situ delithiation and Li redistribution during
APT experiments. The strong electrostatic field used in APT, along with the thermal migration caused by
the laser beam, often leads to Li loss and inaccurate distribution in measurements, as observed in previous
studies [83,84] . Since many battery materials are reactive to air or ambient moisture, using glovebox, vacuum
transfer, and cryo-transfer for accurate measurement of Li distribution has been considered. However,
Kim et al. found that neither vacuum nor cryo-transfer provided satisfactory APT measurements . In one
[85]
example dataset using a LiNi Co Mn O (NMC811) cathode material and laser-pulsed APT with a
2
0.1
0.8
0.1
specimen temperature of 60 K and low laser energy of 5 pJ, a nominally homogeneous distribution of Li was
expected. However, a non-homogeneous distribution was measured, with higher Li concentration at the top
and lower concentration underneath due to in-situ delithiation in APT [Figure 12A].
Interestingly, in Figure 12B, the authors observed contrasting results when the specimen was transferred in
air and at room temperature, leading to the measurement of a nominally homogeneous Li distribution.
They attributed this to the shielding effect of the surface layer, formed as a reaction with the ambient
environment. Moreover, they found that cryo-FIB was necessary to prepare specimens with pristine
compositions. In conclusion, Kim et al. emphasized the significance of electric-field shields and cryo-FIB,
[85]
rather than cryo-APT, for obtaining high-quality APT results in Li mapping experiments . These findings
highlight the importance of carefully considering the specimen preparation methods and environmental
factors in APT studies of battery materials.

Using the experimental cryo-FIB method developed by Singh et al. further used cryo-FIB for preparing
APT tips from NMC811 particles, which is a Li-containing cathode material . NMC811 particles are
[86]
susceptible to corrosion in air, limiting their application in high-performance batteries. Additionally,
similar to other lithium materials, NMC811 is also prone to electron beam damage during electron
microscope observation, posing significant challenges in specimen preparation for APT.

To overcome these challenges, Singh et al. utilized the cryo-FIB method to prepare APT tips that
[86]
incorporated the surface of an NMC811 particle [Figure 13A and B] . The particle was encapsulated in a
chromium (Cr) layer deposited through physical vapor deposition (PVD) (shown in orange in Figure 13B).
As a result, a layer consisting of Li, C, and O, representing corrosion products, was successfully captured in
the APT data, as shown in Figure 13C. To provide detailed information about the composition of the layer,