Rapid microwave-assisted refluxing synthesis of hierarchical mulberry-shaped Na3V2(PO4)2O2F@C as high performance cathode for sodium & lithium-ion batteries

Abstract

Unique hierarchical mulberry-shaped Na 3 V 2 (PO 4 ) 2 O 2 F@C nanocomposite was fabricated by a rapid microwave-assisted low-temperature refluxing strategy. The V(acac) 3 reverse micelle systems in the water-in-oil microemulsions played key roles in forming the self-assembly architectures. The prepared Na 3 V 2 (PO 4 ) 2 O 2 F@C nanoparticles with the anisotropic growth along the [002] direction were in-situ encapsulated in carbon shells, which greatly contribute to fast Na + /e − transfer in electrodes. And the self-assemblies with high structure stability help to improve the cycle performance and mitigate voltage fading. The initial discharge capacity of Na 3 V 2 (PO 4 ) 2 O 2 F@C as cathode for sodium ion batteries is about 127.9 mA h g −1 at 0.1 C. Besides, a high rate performance with a capacity of 88.1 mA h g −1 at 20 C has been achieved, and the capacity retains 82.1% after 2,000 cycles. In addition, the reaction kinetics and Na + transportation mechanism of Na 3 V 2 (PO 4 ) 2 O 2 F@C were preliminarily investigated by the ex situ X-ray diffraction, X-ray photoelectron spectroscopy and galvanostatic intermittent titration technique. More interestingly, when coupled with Li, the fabricated hybrid Li/Na-ion batteries also exhibit excellent rate and cycling performances. The proposed rapid refluxing strategy to synthesize mulberry-shaped Na 3 V 2 (PO 4 ) 2 O 2 F@C opens up a new opportunity to develop high-performance electrode materials for the energy storage systems.

Effect of the Particles Morphology on the Electrochemical Performance of Na3V2(PO4)2F3‐yOy

“…For instance, dealing with this last approach, it was shown that nanosizing carbon coated‐NVPF by mechanical activation improves high rate capacity and cycling stability [22] . Although it is well known that particle's size and morphology influence the energy storage performance and a lot of particle shapes can be obtained, such as nano or microspheres, [23–25] hollow spheres, [19,26,27] nano or microcubes, [28–30] nano‐flowers, [31,32] platelets [33] and other special morphologies, [34–40] it is still unclear which particle's morphology allows to reach the best high‐rate performance and if the synthesis method influences the electrochemical properties. Indeed, different electrode formulations, nature of electrolytes, active mass loadings, carbon coatings or conductive additives make very complicated a simple comparison between all the studies reported in the literature.…”

Designing Advanced Vanadium‐Based Materials to Achieve Electrochemically Active Multielectron Reactions in Sodium/Potassium‐Ion Batteries

“…Other researchers also put tremendous effort into further improving the electrochemical performance of this oxyfluorophosphate material by various strategies, such as transition metal element doping, carbon matrix designs unique morphologies control, etc. [ 185–195 ] Very recently, Ceder's group tried to utilize the V 4+ /V 5+ redox couple by inserting additional sodium into the vanadium oxyfluorophosphate solid solution Na 3 V 2 (PO 4 ) 2 F 3‐ y O 2 y (0 ≤ y ≤ 1). [ 176 ] Na 4 V 2 (PO 4 ) 2 FO 2 was observed upon discharging at ≈1.6 V with extended capacity up to 165 mAh g −1 (Figure 14h).…”

Fluorophosphates: Next Generation Cathode Materials for Rechargeable Batteries

“…[ 180 ] Full cell with hard carbon anode delivered a specific capacity of 120 mAh g −1 at a working voltage of 3.1 V. [ 181 ] Recently carbon encapsulated N3VOPF was synthesized by rapid microwave‐assisted technique and delivered a capacity of 127.9 mAh g −1 with 82.1% retention after 2000 cycles at 20 C rate. [ 182 ] It also led to good rate kinetics and cycling performances of N3VOPF in lithium half‐cell configuration. Zhang et al.…”