Insight into the limited electrochemical activity of NaVP₂O₇

Abstract

Recently, LiVP 2 O 7 has been investigated as a possible high-voltage substitute for Li 2 FeP 2 O 7 . However, its Na-equivalent, NaVP 2 O 7 , as an economic replacement for Li 2 FeP 2 O 7 has not yet been well understood.Here, for the first time, we report the feasibility of NaVP 2 O 7 as a 3.4 V cathode material for Na-ion batteries. Having a theoretical capacity of 108 mA h g À1 , it shows an initial discharge capacity of 38.4 mA h g À1 at 1/20C (1C ¼ 108 mA g À1 ) in the voltage range of 2.5-4.0 V. Our study suggests that part of the sodium ions in the lattice structure exist as structural stabilizers and bring lattice distortion upon desodiation. This study also shows that the title compound, NaVP 2 O 7 , suffers from high intrinsic internal resistance, which limits the phase transition kinetics between pristine NaVP 2 O 7 and desodiated Na 1Àx VP 2 O 7 .

Vanadium‐Based Nanomaterials: A Promising Family for Emerging Metal‐Ion Batteries

“…NaVP 2 O 7 has a theoretical capacity of 108 mA h g −1 in SIBs. However, the experimental study by Kee et al found that the initial specific capacity was only 38.4 mAh g −1 at 1/20 C (1 C = 108 mA g −1 ) in 2.5–4.0 V. Through DFT calculations and electrochemical characterizations, the authors proposed that the limited electrochemical activity of this compound is not only attributed to sluggish Na + ion migration kinetics, but also intrinsically high resistance, which limits the phase transition kinetics between NaVP 2 O 7 and Na 1− x VP 2 O 7 . Barpanda et al reported a new Na 2 (VO)P 2 O 7 for SIB cathode, and a high redox potential of ≈3.8 V (V 5+ /V 4+ ) with a reversible capacity of ≈80 mAh g −1 was achieved.…”

Recent Progress in Electrode Materials for Sodium‐Ion Batteries

“…[205][206][207] Barpanda et al fi rst introduced tetragonal Na 2 (VO)P 2 O 7 , which yields a reversible capacity of 80 mA h g −1 involving the V 4+ /V 5+ redox reaction at 3.8 V vs Na + /Na. [ 205 ] More recently, Kim et al reported a new V-based pyrophosphate compound, Na 4 V 3 (P 2 O 7 ) 4 , as a cathode for NIBs.…”

Investigation of Al-doping effects on the NaFe0.5Mn0.5O2 cathode for Na-ion batteries

“…Unfortunately, most of these compounds show significantly inferior electrochemical performance to their Li-equivalents and require further improvement [1,2,3]. While Na is the most abundant alkali metal, Fe and Mn are the most widespread transition metals.…”