Wet Modification with Oxygen Storage Material of NaFexPO4 as an electrode material for sodium-ion batteries
V. Koleva, T. Tushev, S. Harizanova and R. Stoyanova
Abstract: Sodium-ion battery (SIBs) technology is one of the best promising alternatives to the lithiumion batteries due to the low cost and abundance of sodium which are critical issues for large-scale application. One of the challenges facing SIBs is the exploration of new cheap electrode materials with efficient electrochemical performances suitable for practical applications. Among the sodium intercalation compounds, phosphate framework materials, and particularly these containing iron element (NaxFey(PO4)z) have attracted increasing attention due to their low cost, safety and being environmental friendly. The intercalation-based cathodes typically rely on the cationic redox activity of the transition metals. The activation of both cationic and anionic redox reactions in the electrodes has been found to increase drastically the reversible capacity of P3-Na2/3Ni1/2Mn1/2O2 cathodes by using CeO2 as an oxygen storage material. Moreover, first principle calculations have shown that anionic (O2-) redox processes in NaFePO4 are also visible.
Inspired by these data the main idea of the present contribution is to study the effect of Cemodification on the electrochemical properties of NaFexPO4 as cathode material in sodium and lithium half-cells. Ce-containing NaFexPO4 has been prepared by wet modification process. The electrochemical properties of the phosphate cathodes containing different amount of Ce are studied in galvanostatic and potentiostatic regimes at 20 and 40 C. The results show that the Cemodification generates the following effects: (i) A change in the phase composition of NaFePO4 with formation of NASICON and alluaudite type phases; (ii) Progressive increase in the redox potentials owing to the Fe2+/Fe3+ pairs with increase in the Ce amount; (iii) Strong polarization of both Na- and Li-ion cells which causes the capacity drop during the cycling; (iv) Ce-modification is beneficial for high-temperature operation (40 C) of the Li cells: the smaller Ce amount increases the specific capacity, while the larger amount is beneficial for the stable cycling. From these data one can conclude that further electrode optimization will enable to overcome the strong polarization of the ion cells and, hence to improve the electrochemical performance of the Ce-modified NaFexPO4 electrodes.
Acknowledgements: The authors thank to the financial support of projects CARiM (grant number № КП-06-ДB-6) and “National Center of Excellence Mechatronics and Clean Technologies“ (BG16RFPR002-1.014-0006) under “Research, Innovation and Digitization for Smart Transformation” program 2021-2027.
The authors from CARiM’s Research Team are bolded.
VIHREN-CARiM 2019 