Sodium and Lithium Metal Nitridophosphates AxMy(PO3)3N as high-voltage positive electrode materials for Sodium-ion and Lithium-Ion batteries
Authors: Wizner Agnieszka , Reynaud Marine , Galceran Montse , Rojo Teófilo , Armand Michel , Casas-Cabanas Montse 
Published: February 2020

Lithium-ion batteries have become the dominant technology from portable electronics to mid-scale applications owing to their high-energy density and light weight. However, risks on cost fluctuations and resources scarcity have induced an intense search for alternatives. Sodium-ion batteries are considered to be effective energy storage devices, as well as promising candidates that may well replace Lithium-ion technology for stationary applications.1,2

Current research into cathode materials encompasses a wide range of different chemistries, amongst which polyanionic compounds stand out as attractive candidates due to their stable 3D framework.3
Furthermore, according to theoretical calculations, N-substituted polyanionic compounds should enable the use of more than one redox couple of transition metals due to the lowering their working voltage.4

On the example of Na3Ti(PO3)3N and Na2Fe2(PO3)3N,5,6 we first focused on sodium metal nitridophosphates, with the general formula NaxMy(PO3)3N, which crystallize in a cubic structure 7 where sodium cations occupy three independent crystallographic sites (see Figure 1a).8,9 This CUBICON structure is favorable to both electrochemical and ionic properties, resulting in facile ion migration at room temperature and a stable and reversible electrochemistry.
In particular, our research on sodium vanadium nitridophospate, Na3V(PO3)3N, has uncovered the remarkably high working voltage of this compound, which together with Na7V3(P2O7)4
is the sodium-based cathode with the highest operation voltage for the VIII+/VIV+ redox couple (4.0V vs. Na+/Na0, Figure 1b).10,11 Na3V(PO3)3N can be as well successfully applied in a hybrid Lithium-ion configuration. The reaction mechanism of this material vs. both Li and Na and the possibility to reach the VIV+/VV+ redox couple will be discussed.
Aiming to lower the cost and improve the electrochemistry we have further explored the family of nitridophosphates. Screening several compositions by the replacement of V with other transition metals we have discovered a new family of compounds which will be also shown.12

References

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10 M. Reynaud, A. Wizner, N. A. Katcho, L.C. Loaiza, M. Galceran, J. Carrasco, T. Rojo, M. Armand, and M. Casas-Cabanas, Electrochemistry Communications 84, 14 (2017).

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12 A. Wizner, M. Reynaud, J.X. Lian, F. Bonilla, J.-M. Lopez del Amo, J. Carrasco, and M. Casas-Cabanas, submitted.

Figure 1