Effects of Mg doping on the remarkably enhanced electrochemical performance of Na₃V₂(PO₄)₃ cathode materials for sodium ion batteries

Abstract

Na 3 V 2Àx Mg x (PO 4 ) 3 /C composites with different Mg 2+ doping contents (x ¼ 0, 0.01, 0.03, 0.05, 0.07 and 0.1) were prepared by a facile sol-gel method. The doping effects on the crystal structure were investigated by XRD, XPS and EXAFS. The results show that low dose doping of Mg 2+ does not alter the structure of the material, and magnesium is successfully substituted for the vanadium site. The Mg doped Na 3 V 2Àx Mg x (PO 4 ) 3 /C composites exhibit significant improvements on the electrochemical performance in terms of the rate capability and cycle performance, especially for the Na 3 V 1.95 Mg 0.05 (PO 4 ) 3 /C. For example, when the current density increased from 1 C to 30 C, the specific capacity only decreased from 112.5 mA h g À1 to 94.2 mA h g À1 showing very good rate capability. Moreover, even cycling at a high rate of 20 C, an excellent capacity retention of 81% is maintained from the initial value of 106.4 mA h g À1 to 86.2 mA h g À1 at the 50th cycle. Enhanced rate capability and cycle performance can be attributed to the optimized particle size, structural stability and enhanced ionic and electronic conductivity induced by Mg doping.batteries for large-scale energy storage system applications is very important. 7 Recently, sodium ion batteries have gained an increasing amount of attention due to their abundant reserves and relatively even geological distribution. 8 Actually, many electrode materials such as Na 4 Fe 3 (PO 4 ) 2 (P 2 O 7 ), 9 Na[Ni 0.25 Fe 0.5 Mn 0.25 ]O 2 / C, 10 Na[Li 0.05 (Ni 0.25 Fe 0.25 Mn 0.5 ) 0.95 ]O 2 , 11 Na x CoO 2 , 12 Na 2 C 8 H 4 O 4 , 13 Na 3 (VO 1Àx PO 4 ) 2 F 1+2x , 14 Prussian blue analogues, 15,16 phosphorus, 17,18 and TiO 2 19 have been studied as active materials in cathodes and anodes for sodium ion batteries. However, due to the bigger ionic radius of the sodium ion than the lithium ion (1.02Å for Na + vs. 0.76Å for Li + ), its storage performance and cycle performance are much poorer than its lithium counterpart. The larger Na + radius is proved to be a crucial obstacle for Na + diffusion. 20,21 Therefore, improving Na + diffusion is quite important in developing new electrode materials for sodium-ion batteries with good electrochemical performance.NASICON-type Na 3 V 2 (PO 4 ) 3 has recently been investigated as a prospective cathode material for sodium ion batteries. It is worth noting that Na 3 V 2 (PO 4 ) 3 possesses the highly covalent three dimensional framework that generates large interstitial spaces through which sodium ions may diffuse easily. [22][23][24][25][26][27] In addition, the electrochemical response of the Na 3 V 2 (PO 4 ) 3 electrode displays two at plateaus at 3.4 V and 1.6 V vs. Na + /Na; the voltage plateau located at 3.4 V is relatively higher than most other cathode materials for sodium ion batteries in recent reports. 28,29 However, Na 3 V 2 (PO 4 ) 3 also has an inherent deciency. The distorted VO 6 octahedral units in the NASICON † Electronic supplementary information (ESI) available: SEM images of Na 3 V 2Àx Mg x (PO 4 ) ...

Layer‐by‐Layer Na3V2(PO4)3 Embedded in Reduced Graphene Oxide as Superior Rate and Ultralong‐Life Sodium‐Ion Battery Cathode

“…(7 of 9) 1600389 wileyonlinelibrary.com than the state-of-the-art reported NVP cathodes [2,13,18,32,38,39,48,54] and exceeds most other rechargeable sodium batteries significantly. [22][23][24][25][26][27][28][29][30] Moreover, the SEM images of NVP@rGO after 10 000 cycles at 50 C were shown in Figure S17a,b of the Supporting Information.…”

“…The initial capacity is 110 mA h g −1 while a capacity of 99 mA h g −1 is left after 1000 cycles. In addition, representative charge-discharge curves and long-life cycling performance of NVP@rGO at high rate of 20 C are shown in Figure 5b [54] GO-supported NVP, [48] (C@NVP)@pC, [38] NVP@C@CMK-3, [39] Mg doping NVP, [32] and HCF-NVP [40] ).…”

“…[32,[38][39][40]48,54] The specific comparison data is shown in Table S3 of the Supporting Information. To the best of our knowledge, our designed NVP@rGO delivers almost the same high-rate capacity compared to the best reported results but with lowest carbon contents (3.5 wt%) and relatively narrow voltage window (2.5-4.0 V).…”

Na3V2(PO4)3/C nanorods as advanced cathode material for sodium ion batteries

“…Tremendous efforts have been made to overcome this shortcoming. Coating with conductive carbon [19] and doping with supervalent metal ions [20][21][22] have been adopted to improve the electronic conductivity. In addition, another approach to improve the electrochemical performances of Na 3 V 2 (PO 4 ) 3 is to reduce the particle size [23,24], which can shorten the diffusion distance for electrons and sodium ions, and also increase the effective reaction areas.…”

Recent Advances in Sodium-Ion Battery Materials

“…In situ XRD study indicates a typical two-phase reaction between Na 3 V 2 (PO 4 ) 3 and NaV 2 (PO 4 ) 3 during the sodium insertion/extraction [77]. Tremendous efforts have been made to improve the electrochemical properties of Na 3 V 2 (PO 4 ) 3 electrode, including carbon decoration [78][79][80][81], conductive polymer coating [82] and metal ion doping [83][84][85]. And high-performance Na 3 V 2 (PO 4 ) 3 electrodes are reported [86][87][88].…”