Improved Surface Stability of C+M_xO_y@Na₃V₂(PO₄)₃ Prepared by Ultrasonic Method as Cathode for Sodium-Ion Batteries

Abstract

Coated C+MO@NaV(PO) samples containing 1.5% or 3.5% wt. of MO (AlO, MgO or ZnO) have been synthesized by a two-step method including first a citric based sol-gel method for preparing the active material and second an ultrasonic stirring technique to deposit MO. The presence of the metal oxides properly coating the surface of the active material is evidenced by XPS and electron microscopy. Galvanostatic cycling of sodium half-cells reveals a significant capacity enhancement for samples coated with 1.5% of metal oxides and an exceptional cycling stability as evidenced by Coulombic efficiencies as high as 95.9% for ZnO@ NaV(PO). It is correlated to their low surface layer and charge transfer resistance values. The formation of metal fluorides that remove traces of corrosive HF from the electrolyte is checked by XPS spectroscopy. The feasibility of sodium-ion batteries assembled with C+MO@NaV(PO) is further verified by evaluating the electrochemical performance of full cells. Particularly, a Graphite//AlO@ NaV(PO) battery delivers an energy density as high as 260 W h kg and exhibits a Coulombic efficiency of 89.3% after 115 cycles.

Graphitic Carbon Materials for Advanced Sodium‐Ion Batteries

“…However, the capacity retention was only 70% after 250 cycles at 0.5 A g −1 , which may be attributed to the high cutoff voltage of 4.2 V inducing decomposition of the ether‐based electrolyte during charging. Other graphitic‐carbon‐based full cells, such as graphite//Al 2 O 3 @Na 3 V 2 (PO 4 ) 3 , porous graphite//Na 3 V 2 (PO 4 ) 3 , carbon nanotube@carbon black//Na 3.12 Fe 2.44 (P 2 O 7 ) 2 , and multiwalled carbon nanotube @graphite oxide nanoribbon//Na x MnO 2 have also been reported. However, none of these full cells exhibited output voltages above 3 V and a cyclic life beyond 1000 cycles, indicating that great efforts are needed to develop advanced Na‐ion full cells.…”

Na3V2(PO4)3/N‐doped Carbon Nanocomposites with Sandwich Structure for Cheap, Ultrahigh‐Rate, and Long‐Life Sodium‐Ion Batteries

“…This is because the proper carbon from SLS can effectively inhibit the growth of NVP grains in the synthesis, leading to fine crystallites (Table S2) and short ion diffusion distance in NVP. It can also regulated the structure of NVPUS/NHCUS nanocomposites, creating a stable sandwich framework structure and improving the insertion and extraction of Na ions . However, with the further increase of SLS, the excess carbon content resulted in a decreasing tendency for the Na‐ion diffusion coefficients of A4–A5, The effect of carbon content on Na‐ion diffusion and electronic conductivity is also affected by carbon structure.…”

“…Na 3 V 2 (PO 4 ) 3 (NVP) with the NASCION (Na super‐ionic conductor) structure is a very promising cathode material in SIBs . Many works have been done to enhance the cycling life and rate performances of NVP, mainly focusing on the improvement of the electronic conductivity by the NVP/carbon composite, cation doping,, fabricating novel structures to control particle size and morphology, and building a surface conductive layer . For instance, the honeycomb NVP/C microballs with hierarchical porous structure were prepared by in situ carbonization of hexadecyl trimethyl ammonium bromide surfactant, delivering a high reversible capacity of 80.2 mAh g −1 at 20 C corresponding to 71 % of the capacity .…”

Nonaqueous Sodium‐Ion Full Cells: Status, Strategies, and Prospects

“…Hence, the surface modification of the cathode has also attracted more and more attention. For example, after the presodiation process and surface coating, the electrochemical performance of the full cell has been greatly improved in terms of capacity, cycle stability, and rate capability. By coating NaPO 3 on Na 2/3 [Ni 1/3 Mn 2/3 ]O 2 , the cycle retention of the full cell was significantly increased from 22% to 73% (Figure b,c) .…”