Oxygen Vacancy Engineering in Na₃V₂(PO₄)₃ for Boosting Sodium Storage Kinetics

Abstract

Improving Na‐ion diffusion kinetics is an effective strategy to boost the sodium storage performance of electrode materials for sodium ion batteries (SIBs). Herein, an oxygen vacancy engineering is reported to evidently enhance Na‐ion diffusion kinetics of Na3V2(PO4)3 and accordingly boost sodium storage performance. Na3V2(PO4)3/C with different molar contents of Cu doping (0%, 2.5%, 4%, 5%, and 6%) are synthesized using a simple sol–gel method followed by an annealing treatment. The experimental results show that Cu2+ successfully replaces the V3+ sites of Na3V2(PO4)3 and that does not change its phase composition. The introduction of Cu2+ not only results in the formation of V4+ to maintain charge balance, leading to a shorter VO bond, but also promotes the generation of oxygen vacancies and accordingly facilitates Na‐ion diffusion kinetics. As expected, the optimal sample displays a stable capacity of 111.4 mA h g−1 with capacity retention of 90.4% over 300 cycles at 1 C and a high rate capacity of 83.8 mA h g−1 at 20 C. The studies demonstrate that the Cu doping is favorable for the electrochemical enhancement of Na3V2(PO4)3, which provides a promising prospect for Na3V2(PO4)3 as a cathode for SIBs.

Facilitating reversible transition metal migration and expediting ion diffusivity via oxygen vacancies for high performance O3-type sodium layered oxide cathodes

“…20–23 Nonetheless, only a handful of reports shed light on the effect of oxygen vacancies in Na x TMO 2 cathodes for SIBs and the relevant interplay between oxygen vacancies and stable high-voltage operation is still in an infant stage. 24…”

“…[20][21][22][23] Nonetheless, only a handful of reports shed light on the effect of oxygen vacancies in Na x TMO 2 cathodes for SIBs and the relevant interplay between oxygen vacancies and stable high-voltage operation is still in an infant stage. 24 Within this scope, O3-type layered NaCrO 2 is chosen as the model system in the present work, which is known to reect strong effect of irreversible TM migration when charged above 3.6 V. Mere half of its theoretical capacity (∼250 mA h g −1 ) can be achieved, corresponding to less than 0.5 mol Na + reversibly inserted into the layered structure. 25,26 To tackle this issue, we innovatively adopt a hydrogen reduction method assisted by spray-drying to in situ construct adequate oxygen vacancies into host materials with no need for harsh chemical conditions or extra multi-step reactions (Fig.…”

Mnx+ Substitution to Improve Na3V2(PO4)2F3-Based Electrodes for Sodium-Ion Battery Cathode

“…In recent times, transition metal oxides [ 8 , 9 , 10 ], polyanionic compounds [ 11 , 12 ], Prussian blue analogues [ 13 , 14 ], and organic compounds [ 15 , 16 ] make up the mainstream of cathode materials for SIBs [ 17 ]. Among them, Na 3 V 2 (PO 4 ) 2 F 3 (NVPF) and Na 3 V 2 (PO 4 ) 3 (NVP) with the NASICON type phosphates are considered to be the most favorable cathode materials owing to their three-dimensional open frameworks, which can boost sodium ion transport by delivering large interstitial spaces [ 18 ].…”

“…Among them, Na 3 V 2 (PO 4 ) 2 F 3 (NVPF) and Na 3 V 2 (PO 4 ) 3 (NVP) with the NASICON type phosphates are considered to be the most favorable cathode materials owing to their three-dimensional open frameworks, which can boost sodium ion transport by delivering large interstitial spaces [ 18 ]. NVPF has also been demonstrated to possess a higher average working potential of ~3.9 V, and an ideal theoretical capacity of 128 mAh g −1 , which is higher than that of NVP (~3.4 V, 117.6 mAh g −1 ) [ 17 , 19 , 20 ].…”

Substituting inert phosphate with redox-active silicate towards advanced polyanion-type cathode materials for sodium-ion batteries

“…In terms of the chemical and crystal structure of NVP, the building blocks include tetrahedral [PO 4 ], octahedral [VO 6 ] and inserted Na + -ions. [33][34][35][36] While Na + and V 3+ components are the sites responsible for Na + -ion storage capability, anionic phosphate (PO 4 3− ) is electrochemically inactive during battery cycling and inert for providing capacity. [37][38][39] Substituting inert PO resulting in an improved Na-storage capacity, but also decreases the bandgap of the NVP lattice, leading to enhanced electroconductivity.…”