Voltage window-dependent electrochemical performance and reaction mechanisms of Na3V2(PO4)3 cathode for high-capacity sodium ion batteries

• Published in: Ionics Vol. 26; no. 5; pp. 2343 - 2351
• Main Authors: Wei, Congcong, Luo, Fakui, Zhang, Chi, Gao, Hui, Niu, Jiazheng, Ma, Wensheng, Bai, Yanwen, Zhang, Zhonghua
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer Berlin Heidelberg 01.05.2020; Springer Nature B.V
• Subjects: Cathodes; Chemistry; Chemistry and Materials Science; Condensed Matter Physics; Dimensional stability; Electric potential; Electrochemical analysis; Electrochemistry; Energy Storage; Optical and Electronic Materials; Original Paper; Reaction mechanisms; Renewable and Green Energy; Sodium-ion batteries; Voltage; Cathode material; Sodium ion batteries; In-situ X-ray diffraction; Sodium vanadium phosphate; Biphasic mechanism
• ISSN: 0947-7047; 1862-0760
• DOI: 10.1007/s11581-019-03363-0

Na 3 V 2 (PO 4 ) 3 owns stable three-dimensional open framework and delivers a theoretical capacity of 117.6 mAh/g with a voltage plateau at 3.4 V (vs. Na + /Na). However, the voltage plateau at 1.6 V (vs. Na + /Na) corresponding to the V 2+ /V 3+ redox couple can also deliver a theoretical capacity of 59 mAh/g. Herein, the operating voltage window of Na 3 V 2 (PO 4 ) 3 is extended to fully utilize V 2+ /V 3+ /V 4+ redox couples. In 1.0–4.0 V (vs. Na + /Na), Na 3 V 2 (PO 4 ) 3 shows a high initial capacity but an inferior cycling stability, which is different from the scenario (low capacity but high stability) of 2.5–4.0 V (vs. Na + /Na). In comparison, Na 3 V 2 (PO 4 ) 3 delivers an initial capacity of 140.3 mAh/g at 200 mA/g in 1.4–4.0 V (vs. Na + /Na) and maintains a reversible capacity of 106.2 mAh/g after 600 cycles. At 20 mA/g, Na 3 V 2 (PO 4 ) 3 shows a reversible capacity of 135 mAh/g in 1.4–4.0 V (vs. Na + /Na) after 100 cycles. Meanwhile, operando X-ray diffraction is utilized to explore storage mechanisms of Na 3 V 2 (PO 4 ) 3 in different voltage ranges. The results show that the cathode reactions follow a biphasic mechanism at both 3.4 and 1.6 V (vs. Na + /Na), associated with the reversible transformation of Na 3 V 2 (PO 4 ) 3 ↔ NaV 2 (PO 4 ) 3 and Na 3 V 2 (PO 4 ) 3 ↔ Na 4 V 2 (PO 4 ) 3 , respectively.