During the past two decades, the demand for the Electrical Energy Storage systems has increased for both portable and stationary applications, predominantly in the form of batteries [1]. In this sense, lithium-ion batteries have dominated the market as they offer the highest gravimetric capacity. However, owing to concerns over lithium cost and sustainability of resources, there is a growing interest in sodium-ion batteries since sodium chemistry is considered as an attractive alternative to LIBs in terms of cost, safety, and sustainability [2].

Current research into cathode materials for sodium ion batteries encompasses a wide range of different chemistries. Amongst them, polyanionic compounds exhibit a very stable framework that enables facile low-energy alkali migration pathways leading to long-term structural stability. In this sense, theoretical calculations have recently suggested that N-based polyanionic compounds might be the next frontier in electrode design for Li-ion and Na-ion batteries [3-4]. Partial substitution of O by N lowers the voltage at which the transition metal is oxidized, which could permit to operate more than one redox couple per transition metal. In addition, nitrogen could also participate to the alkali de‑intercalation through a reversible oxidation of the N^III- anions. This kind of compounds could thus open the path to new attractive multi-electron materials, combining high energy with the safety and cost advantages of the polyanionic frameworks.

In this context, our group is exploring the synthesis and the electrochemical performances of a series of new lithium- and sodium-based N‑substituted polyanionic compounds. Among them, we will present the attractive reversible redox activity at medium and high voltage showed by some members of the family of CUBICON compounds Na_xM_y(PO₃)₃N. [5-7]

Acknowledgements

This work is financially supported by the Spanish Ministero de Economía y Competitividad (MINECO) through the projects ENE2013-44330-R, ENE2016-81020-R and ENE2016-75242-R and the post-doctoral grants FPDI-2013-17329 and FJCI-2014-19990. The authors would also like to thank the Basque Government for financial support through ELKARTEK project CICE17.

References

[1] J. M. Tarascon and M. Armand, Nature 414 (2001) 359-367

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[3] M. Armand and M. E. Arroyo y de Dompablo. J. Mater. Chem. 21 (2011) 10026-10034.

[4] B. Rousseau, V. Timoshevskii, N. Mousseau, M. Côté and K. Zaghib. Mater. Sc. Eng. B. 211 (2016) 185-190.

[5] J. Liu, X. Yu, E. Hu, K.W. Nam, X.Q Yang and P. Khalifah. Chem. Mater. 25 (2013) 3929-3931.

[6] J. Liu, D. Chang, P. Whitfield, Y. Janssen, X. Yu, Y. Zhou, J. Bai, J. Ko, K-W. Nam, L. Wu, Y. Zhu, M. Feygenson, G. Amatucci, A. Van der Ven, X.Q. Yang and P. Khalifah. Chem. Mater. 26 (2014) 3695-3305.

[7] M. Reynaud, A. Wizner, M. Galceran, L. Loaiza, T. Rojo, M. Armand and M. Casas-Cabanas, 84 (2017) 14-18.