With the fast rising global demand for advanced energy storage solutions in stationary (e.g. grid storage) and mobile (e.g. (hybrid) electric vehicles) application areas, Na-ion batteries (SIBs) are considered more as an addition than a replacement for the state-of-the art Li-ion related cell chemistry. Owing to the higher elemental abundance and therefore lowered mining cost of sodium over lithium, SIBs can offer distinct advantages of geographically independent and cost-efficient battery manufacturing.

While hard carbon is often used as an anode active material in SIBs, cathode chemistry is more diverse. Similar to LIBs, layered metal oxides (e.g. NFM) and polyanionic compounds (e.g. NVP) are widely accepted to be promising material classes. Sodium ferric phosphate pyrophosphate (NFPP, Na4Fe3(PO4)2(P2O7)), as a representative of the polyanionic compounds class, consists of only inexpensive, non-toxic elements. NFPPs robust 3D open framework crystal structure allows for highly-reversible Na storage, which enables both high rate and cycling stability. Previous studies have furthermore documented the pristine NFPPs moderate air stability for short-time exposure, which was found to be largely increased for carbon-coated NFPP/C nanosheets.[1,2]

In this study, cathodes, consisting of 94 % commercial NFPP/C active material with an areal capacity of approx. 2 mAh/cm2 (110 mAh/g), were manufactured by both conventional NMP-based as well as non-toxic and cost-efficient water-based slurry processing using upscalable dissolver technique. While in former medium, PVDF was used as binder, low-cost fluorine-free CMC/SBR was utilized in the aqueous approach. To ensure that pH 96 mAh/g. In full-cell configuration, both CMC/SBR/PAA- and PVDF-based electrodes allow for a respectable initial Coulombic efficiency of >87 % (0.05C). After 400 cycles at 1C/5C charge/discharge rate, a high capacity retention of 88.2 % reveals the aqueous-based cathode systems excellent cycling stability.

[1] X. Li, S. Dai, Q. Chen, H. Mao and H. Pan, J. Mater. Chem. A 2024, 12, 29726-29734, DOI: 10.1039/d4ta05262e
[2] M. Chen, W. Hua, J. Xiao et al., Nat. Commun. 2019, 10, 1480, DOI: 10.1038/s41467-019-09170-5