Page 63 - Read Online

Page 12 of 16 Mu et al. Energy Mater 2022;2:200043 https://dx.doi.org/10.20517/energymater.2022.57

Table 1. Comparison of different presodiation strategies and possible research directions
Side Method Disadvantage Research direction
Cathode Self-sacrificed materials Residual materials, gas release Presodiation mechanism
In-situ characterization
Self-presodiation Limited materials
Theoretical calculation
Anode Direct contact Dangerous New self-presodiation cathode design
Chemical presodiation Air-sensitive, complex
Electrochemical presodiation Dangerous, disassembly

In comparison, self-presodiation cathode materials are regarded as superior materials due to their “zero
dead mass” and lack of gas release during the electrochemical process. Notably, the self-presodiation
method is strongly associated with the development of high-performance Na-rich cathodes. In addition to
presodiation for cathodes, presodiation for anodes has also attracted significant attention. Physical
presodiation based on direct contact with Na foil/powder is the most direct method but the handling of
high-risk Na foil/powder limits the industrialization of this method. In contrast, chemical presodiation
technique offers greater potential for application in the manufacture of commercial electrodes because of
the high feasibility. The presodiation reagent involves a THF or DME solution containing Na-Naph/Na-Bp,
which can maintain its stability in dry air. The Na storage mechanism during the chemical presodiation is
different from that during the electrochemical cycle, which may result in an additional side reaction during
the following electrochemical cycles in the full cell. Furthermore, the anion type in the presodiation solution
may also influence the formation of SEI film, which is necessary for further study. Different from chemical
presodiation, electrochemical presodiation by precycling in a half cell can make the anode presodiated in
real cell conditions. The Na storage mechanism and SEI film are in accordance with those in the normal
electrochemical process. It is easy to regulate the presodiation degree by controlling the cut-off voltage
during discharge. The greatest challenge is the complex procedure, including assembling the half cells,
disassembling the half cells and reconstructing the full cells, which is unfeasible for industrialization.

Although presodiation technology has been extensively investigated, there remain significant issues that
need to be resolved urgently, as shown in Table 1. In particular, the underlying mechanics of various
presodiation methods are still mysterious and need further investigation. In-situ characterization methods,
including in-situ XRD, spectroscopy, and TEM, need to be applied during the first charge and discharge to
understand the aforementioned mechanism. In addition, whether there is a difference between the
conventional SEI film and the SEI film formed after presodiation needs to be systematically evaluated,
especially considering the morphology and composition of the SEI film. As powerful tools, theoretical
calculations should be used to analyze the presodiation process, which can reveal the presodiation
mechanism from the electronic and atomic scales. To comprehend and grasp such crucial factors, in-depth
research should be conducted to promote the further development of Na-based energy storage devices.

Overall, the current presodiation technique for SIBs is still in its infancy due to it being quite different from
that of LIBs and therefore requires further exploration to pave the route from basic scientific research to
industrialization. The fundamental issues, such as the Na storage mechanism and SEI formation process
during chemical presodiation, should be intrinsically addressed, which benefits the development of
presodiation technique. This review provides feasible principles and strategies of presodiation to help
researchers to gain a comprehensive understanding of the presodiation process.

DECLARATIONS
Authors’ contributions
Conceived the idea, designed the manuscript: Gao XW