Porous yolk-shell structured Na3(VO)2(PO4)2F microspheres with enhanced Na-ion storage properties

Conductive Ti3C2Tx networks to optimize Na3V2O2(PO4)2F cathodes for improved rate capability and low-temperature operation

“…After fully charging to 4.30 V, the other two peaks at 518.1 and 525.4 eV are attributed to the partial electrochemical oxidation of V 4+ to V 5+ with the extraction of two Na ions per formula from NVOPF/Ti 3 C 2 T x . 43,58 Besides, Ti 2p XPS spectra of NVOPF/Ti 3 C 2 T x are almost identical at fully discharged/charged states, suggesting the good preservation of the local structure of Ti and the negligible capacity contribution of Ti 3 C 2 T x . To better reveal the Na + insertion/extraction mechanism, an illustration of the crystal structure transition of NVOPF/Ti 3 C 2 T x is shown in Fig.…”

“…3a provides the initial five cyclic voltammetry (CV) curves of the NVOPF/Ti 3 C 2 T x electrode at a scan rate of 0.1 mV s −1 . There are two pairs of distinct redox peaks located at 3.67/3.56 V (O1/R1) and 4.06/3.97 V (O2/R2), attributed to the (de)intercalation of two Na + ions from the host NVOPF structure using the following electrochemical eqn (1) and (2), corresponding to the valence change of V 4+ /V 5+ : 43 Na 3 V 2 O 2 (PO 4 ) 2 F ⇌ Na 2 V 2 O 2 (PO 4 ) 2 F + Na + + e − Na 2 V 2 O 2 (PO 4 ) 2 F ⇌ NaV 2 O 2 (PO 4 ) 2 F + Na + + e − …”

Interfacial Engineering of Na3V2(PO4)2O2F Cathode for Low-Temperature (−40 °C) Sodium-Ion Batteries

“…Most attention has focused on promising SIB cathode candidates, such as Prussian blue analogs, , transition-metal chalcogenides, − and Na + superionic conductor (NASICON) compounds. − Among various cathode materials for SIBs, NASICON-based electrode materials provoke tremendous interest and extensive investigation ascribing to their open three-dimensional (3D) ion channel, great structural stability, and excellent thermal stability. − As a member of the NASION-type materials, Na 3 V 2 (PO 4 ) 2 O 2–2 x F 1+2 x (NVPOF, 0 ≤ x ≤ 1) has emerged as a promising polyanionic compound for SIBs on account of its high theoretical specific capacity (130 mA h g –1 ), considerable average working voltage (∼3.8 V), and thereby a high energy density of ca. ∼500 W h kg –1 . ,− However, NVPOF has obvious disadvantages of intrinsically poor electronic conductivity (∼10 –12 S cm –1 ) and suppressed sodium-ion diffusion induced by the presence of highly electronegative fluorine, − which result in unsatisfactory rate capability and cycling stability. In view of inferior electron transport kinetics for the NVPOF cathode, extensive research efforts have focused on strategies of interfacial engineering, ,, ion doping, − composite architecture, , and nanostructural engineering , to achieve optimized electrochemical performances for NVPOF-based cathodes.…”

Multi-component surface engineering of Na3V2(PO4)2O2F for low-temperature (−40 °C) sodium-ion batteries

“…23,24 As a member of the NASION-type materials, Na 3 V 2 (PO 4 ) 2 O 2 F (NVPOF) with high working voltage (B3.8 V) and considerable theoretical capacity (130 mA h g À1 ) is very promising for high-energy SIBs. [25][26][27] The presence of highly electronegative F À , however, will lead to blockage of sodium ion diffusion, 28,29 demonstrating sluggish interfacial reaction kinetics in NVPOF. Moreover, its interface compatibility is relatively poor, which would cause irreversible loss of capacity.…”

“…The presence of highly electronegative F − , however, will lead to blockage of sodium ion diffusion, 28,29 demonstrating sluggish interfacial reaction kinetics in NVPOF. Moreover, its interface compatibility is relatively poor, which would cause irreversible loss of capacity.…”