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Page 18 of 23 Zhou et al. Microstructures 2023;3:2023043 https://dx.doi.org/10.20517/microstructures.2023.38

In battery research, there is a continuous effort to develop new anode materials that can outperform
[87]
graphite, the current benchmark, while remaining cost-effective . In 1976, Lai et al. suggested that Si could
[88]
be a promising candidate for anodes, as it has the potential to store more lithium than graphite . However,
Si anode batteries suffer from poor charge-discharge cyclability due to significant volumetric changes
during cycling, leading to cracking and degradation. There has been a lack of analytical techniques with
sufficient spatial resolution to study the role of lithium in this degradation process, which hampers rational
material design to address the issue.

[89]
Recently, Kim et al. made significant progress by utilizing cryo-FIB, cryo-transfer, and cryo-APT , based
on the experimental method developed by El-Zoka et al. [Figure 5] . They applied the technique to analyze
[32]
the elemental distribution in a battery system comprising a liquid electrolyte and a single-crystal Si anode
after various charge-discharge cycles. In Figure 14A, the researchers successfully analyzed the frozen
pristine liquid electrolyte, which contains 1 M LiPF with a mixture of ethylene carbonate, (CH O) CO, and
2
6
2
diethyl carbonate, OC(OCH CH ) , in a 1:1 volume ratio, using cryo-APT. They also provided a reference
3 2
2
APT dataset of the single-crystal Si [Figure 14A]. After one cycle, a fragment consisting of Si and Si oxide
species (SiO ) was found in the frozen liquid electrode, indicating Si anode degradation [Figure 14B]. After
x
25 cycles, Figure 14C revealed a GB of Si nanocrystalline decorated with SiO , confirmed by transmission
x
electron microscope (TEM) analysis. These high-resolution elemental analyses of battery materials were
made possible through the use of cryo-APT, which is sensitive to light elements, in combination with cryo-
FIB, allowing the analysis of liquid samples. This breakthrough paves the way for more applications in
advancing other lithium-based energy storage devices using liquid electrolytes.
LIMITATIONS AND OUTLOOK
This article emphasizes the potential of cryo-APT and its combination with cryo-FIB specimen preparation
for providing nanoscale elemental mapping of materials. Several examples were presented to showcase its
applications in researching hydrogen in metals, liquid and organic specimens, and Li battery materials.
However, it is important to acknowledge the limitations of APT. Firstly, the cryo-APT and cryo-FIB
instrumentation is still under development and not yet optimal. Integrating temperature-tracking into
commercial LEAP and FIB systems for a complete thermal history of specimens remains challenging. This
affects the quantitative measurement of specimen temperature and precise control of ice sublimation for
high-quality biological specimen preparation .
[90]

Secondly, the data yield of APT experiments is limited by a high tip fracture rate. The success rate for
analyzing hydrogen-charged steel tips is currently lower than 10%, and it can be even lower for less
structurally robust specimens with heterogeneous interfaces or organic matter. Additionally, APT is a
destructive technique, making it impossible to reproduce measurements on the same specimen. This leads
to a comprehensive APT analysis being highly challenging and time-consuming. Thirdly, similar to other
high-resolution microscopy techniques such as TEM, APT has a limited field of view 50 × 50 × 300 nm .
3
Meaningful APT observations require more sampling compared to other imaging methods, further
complicated by the low data yield due to the high fracture rate.

Despite these challenges, the future of cryo-APT looks promising, with various potential applications that
can provide new insights in crucial scientific areas. For instance, a correlative imaging workflow can be
developed to combine APT with TEM, enabling a direct correlation of hydrogen location and its effects [91,92] .
It will also be interesting to correlatively apply imaging techniques that have wider fields of view than that of
APT, such as X-ray-related techniques. This is vital for understanding hydrogen embrittlement and
hydrogen storage. In analytical biology, cryo-FIB and cryo-APT can be utilized to study ionic transportation