Evaluation of commercial 18650 and 26700 sodium-ion cells and comparison with well-established lithium-ion cells

Recently, the first sodium-ion cells have been commercialized and have become available for consumers. Given,
moreover, the exciting announcements by several producers of such battery cells, it is of great interest to analyze
these first commercial cells in order to understand which materials are used and how these cells are designed.
Herein, two types of commercially available sodium-ion battery cells (cylindrical 1.5 Ah 18650 and 3.5 Ah
26700 cells) are investigated regarding (i) their electrode chemistry, (ii) their thermal properties upon discharge
as a function of the applied C rate, (iii) the available specific energy, and (iv) their cell impedance. The data are
correlated with the electrode thickness and electrode area obtained from an ex situ (ante-mortem) analysis of the
18650 cells, and discussed in comparison with the performance metrics reported for commercial lithium-ion cells. This comparison reveals that the herein studied 18650 sodium-ion cells (hard carbon⎪⎪Na$_x$Ni$_y$Fe$_z$Mn$_{1-y-z}$O$_2$) provide a comparable or even higher specific energy (~128 Wh kg$^{-1}$) than that of graphite⎪⎪LiFePO$_4$ lithium-ion cells.