Page 53 - Read Online

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

Keywords: Na-ion batteries, presodiation, recyclable ions, full cells, commercialization

INTRODUCTION
In the upcoming decades, the widespread adoption of clean and efficient energy storage systems will be
[6-9]
[1-5]
necessary to combat climate change . Metal-ion batteries , exemplified by lithium-ion batteries (LIBs),
have received extensive attention due to their high energy density and low self-discharge and have been
frequently applied in portable electronic devices, electric vehicles and grid-scale energy storage . However,
[6]
the limited and unevenly distributed lithium resources hinder the further development of LIBs [10,11] . It is
therefore necessary to search for other energy storage technologies to substitute for LIBs. As a result of their
significant abundance, high performance, low cost and similar physicochemical properties to LIBs,
sodium-ion batteries (SIBs) and capacitors (SICs) are viable alternatives to LIBs [12-17] . Recently, remarkable
research effort has been dedicated to the exploration of desirable electrode materials to meet the constantly
expanding demand for next-generation applications [1,18-22] . However, there are still a series of potential
problems that need to be further addressed. In addition to the inherent drawback of the energy density,
there is also a non-negligible capacity loss caused by the loss of recyclable ions and the irreversible
[23]
degradation of electrolytes to form the solid electrolyte interphase (SEI) . Generally, the cathode, as the
only sodium-ion source in the full cell, provides not only reversibly cyclic Na during charge and discharge
+
+
but also irreversible Na during the first cycle. The cell will inevitably experience capacity and energy density
decay due to the low initial Coulombic efficiency on the anode/cathode side and side reactions [24-30] . For
example, prior to the regular battery operation of sodium-ion insertion and desertion, partial sodium ions
are consumed and consolidated during the formation of the SEI layer on the active material surface,
particularly in the initial formation process owing to the low initial Coulombic efficiency. Generally,
presodiation technology is common for SIBs and SICs. For SICs, the reduction of Na ions in the electrolyte
can be prevented by pre-embedding Na in the anode material.

It is without a doubt that increasing the cyclable sodium-ion content in a full-cell system can directly and
efficiently improve its electrochemical performance by alleviating the sodium-ion loss in the initial cycle.
+
Presodiation, known as the pre-doping of Na , is an efficient method to prevent the capacity loss introduced
by constrained sodium sources in the cathode, which can also boost the operating voltage and elevate the
concentration of recyclable ions in SIBs [14,31-35] and SICs [36-38] . As indicated in Figure 1, under normal
conditions, the active sodium ions in the cathode material are partly responsible for Na loss; however, the
presodiated full cell can supply more active Na, which can compensate for the irreversibly recyclable Na,
preventing Na loss in the cathode and the corresponding capacity decay. On this basis, the presodiation
process is recognized as a practical method for bringing high-performance Na-ion full-cell manufacturing
to fruition in the future. Based on the research on prelithiation in LIBs [33,39-42] , several presodiation
strategies [33,35,43] have been reported containing physical, chemical and electrochemical approaches.
Considering the cathode side, mixing the suitable Na-containing additives and coupling them with
self-presodiation cathode materials are effective strategies to accomplish the presodiation process. For the
anode side, physical, chemical and electrochemical approaches are acceptable. It is crucial to deeply
consider and comprehend the various presodiation techniques for realizing the industrialization of SIBs and
SICs. In this review, we summarize the reported achievements and explore the fundamentals and challenges
of presodiation process from an industrial perspective, as well as state-of-the-art presodiation technologies.
This review will help researchers to gain a broad grasp of the presodiation procedure and hasten the
commercialization of SIBs and SICs.