Unlocking anionic redox activity in O3-type sodium 3d layered oxides via Li substitution

Abstract

Sodium ion batteries, because of their sustainability attributes, could be an attractive alternative to Li-ion technology for specific applications. However, it remains challenging to design high energy density and moisture stable Na-based positive electrodes by implementing the anionic redox process that has recently boosted the capacity of Li-rich layered oxides.Here, we report the first anionic-redox active O3-NaLi1/3Mn2/3O2 phase obtained through a ceramic process by carefully controlling the delicate balance between synthesis conditions and stoichiometry. It shows a sustained reversible capacity of 190 mAh g −1 by redox processes on oxygen and manganese ions as deduced by combined HAXPES and mRIXS spectroscopy techniques. Remarkably, unlike any other anionic-redox layered oxides so far reported, O3-NaLi1/3Mn2/3O2 electrodes do not show voltage fade upon cycling. This finding is due to switching from the interlayer to intralayer migration of the Mn cations promoted by Li + displacement towards the alkali layer upon first Na + de-insertion. Another practical asset of this material stems from its moisture stability, hence facilitating its handling and electrode processing. Besides providing insightful fundamental findings pertaining to anion redox, this work offers future directions towards designing high energy density electrodes for advanced Na-ion batteries.

A New Approach to Stable Cationic and Anionic Redox Activity in O3‐Layered Cathode for Sodium‐Ion Batteries

“…Based on our findings, we can conclude that the Ni 2+ /Ni 3+ and O 2− /O 1− redox processes are responsible for the charge compensation mechanism in Na[Ni 2/3 Ru 1/3 ]O 2 , where the low plateaus are mainly governed by the cationic redox reaction and the higher plateau is mainly governed by the anionic oxygen redox reaction (Figure 10a). We compared the energy-density of O3-Na[Ni 2/3 Ru 1/3 ]O 2 with those of reported oxygen-redoxassisted O3-compounds, [38,40,41,[50][51][52][53][54][55] including the very recent work by Tarascon et al [56] (Figure 10b; and Table S3, Supporting Information). Apart from the high discharge capacity of about 190 mAh g -1 with an average operation voltage of 2.5 V (≈475 Wh (kg-oxide) −1 ) for the O3 type Na[Li 1/3 Mn 2/3 ]O 2 , the evolution of O 2 gas associated with migration of Li toward Na layers during the first charge is the urgent issue to be resolved, because such oxygen residue is inclined to form sodium carbonates as a CEI layer and may arise safety concern when overcharged in real systems.…”

Principles and Applications of Galvanostatic Intermittent Titration Technique for Lithium-ion Batteries

“…Inserting Equation ( 9) into Equation ( 8) yields Equation (10). Subsequently, expanding by dE yields Equation (11), and the diffusion coefficient can be expressed as Equation ( 12) by arranging Equation (11). This result implies that the diffusion coefficient is determined by the three variables of cell voltage, time, and stoichiometry deviation.…”

“…1(d), at the beginning of the relaxation period, mobile ions move to positions that minimize the total energy in a given structure to become a homogeneous or equilibrium state. In addition to the direct calculation of the diffusion coefficient, the time to reach an equilibrium state can be another parameter for investigating the transport kinetics of the material [11,32,33,51,52]. In the case of copper oxide (CuO), which is based on conversion reactions, Novák claimed that the CuO electrode needs two months to reach an equilibrium potential after applying a current pulse [51].…”

“…Additionally, the galvanostatic intermittent titration technique (GITT) has become a widely applied electroanalytical method for the kinetic analyses of LIBs [11][12][13][14][15][16][17][18]. The GITT measures the transient voltage change and open-circuit voltage (OCV) change during the charging and discharging processes using only a constant current supply and specified cut-off intervals [18].…”

Recent Advances in Electrode Materials with Anion Redox Chemistry for Sodium-Ion Batteries

“…In this part of the article, we will discuss the O3-type cathodes with anionic redox, in which sodium ions are located only in the alkali layer. [85]. The delivered first charge capacity was~250 mAh g −1 (0.…”