Electrolytes toward High‐Voltage Na₃V₂(PO₄)₂F₃ Positive Electrode Durable against Temperature Variation

Abstract

High power and energy density, long cyclability, and tolerance for wide temperature (seasonal and daily operational temperature differences) must be considered to construct large‐scale sodium secondary batteries. In this regard, Na3V2(PO4)2F3 (NVPF) has become a subject of interest as a high‐performance positive electrode material owing to its high energy density. However, the high operating voltage of NVPF causes continuous decomposition of electrolytes during cycles, resulting in significant capacity fading and low Coulombic efficiency. In this study, the electrochemical performance of the NVPF electrode in organic solvent electrolytes with and without additives and an ionic liquid is investigated at high voltage regimes over a wide temperature range (−20 °C to 90 °C). The results reveal that the performance of organic electrolytes is still insufficient even with additives, and the ionic liquid electrolyte demonstrates high electrochemical stability and cyclability with NVPF electrodes over a temperature range from −20 °C to 90 °C, achieving stable cycling over 500 cycles. The detailed electrochemical analysis combined with X‐ray photoelectron and energy dispersive X‐ray spectroscopy indicates that a sturdy cathode electrolyte interphase layer around the electrode protects it from capacity fading at high voltage and elevated temperature, resulting in high Coulombic efficiency.

Na3V2(PO4)2F3@bagasse carbon as cathode material for lithium/sodium hybrid ion battery

“…Fig. 3(e) is the XPS photoelectron spectrum of the Na 3 V 2 (PO 4 ) 2 F 3 /C-20% (650 °C), and it shows that the V element has two characteristic peaks near 516.95 and 523.95 eV, and these peaks can be attributed to the V 2p3/2 and V 2p1/2 spin-orbits of V 3+ , respectively, 36–38 which proved once again that the Na 3 V 2 (PO 4 ) 2 F 3 could be successfully prepared by spray drying and a high temperature calcination method. The carbon content of the Na 3 V 2 (PO 4 ) 2 F 3 /C-20% was measured using TGA under ambient conditions.…”

A β”‐Alumina/Inorganic Ionic Liquid Dual Electrolyte for Intermediate‐Temperature Sodium–Sulfur Batteries

“…There is no significant anodic current observed at the Al electrode due to the formation of robust passivation layer, indicating the Al corrosion has not been observed with the electrolyte, which is also consistent with the suppressed Al corrosion problem in organic ILs. [67] The thermal stability of the Na[OTf ]-Cs[TFSA] IL was examined through thermogravimetry analysis, as illustrated in Figure S3, Supporting Information. The electrolyte manifests negligible mass loss at temperatures below 400 °C, showing high thermal stability that is beneficial for Na/S IT operations.…”

“…There is no significant anodic current observed at the Al electrode due to the formation of robust passivation layer, indicating the Al corrosion has not been observed with the electrolyte, which is also consistent with the suppressed Al corrosion problem in organic ILs. [ 67 ]…”

Structure, Composition, Transport Properties, and Electrochemical Performance of the Electrode‐Electrolyte Interphase in Non‐Aqueous Na‐Ion Batteries

“…This excellent electrochemical performance is the result of the thin and robust CEI formed after the oxidation of FSA − in the ionic liquid electrolyte at different temperatures, as suggested by XPS and EDX measurements. [168] The influence of highly concentrated of its initial capacity while cycling at 1 A g −1 , almost full discharge capacity is obtained at 4 A g −1 , and 79% of the capacity is retained at 20 A g −1 . In the 25 to 90 °C temperature range, a very high Coulombic efficiency above 99.5% is found at 100 mA g −1 for more than 300 cycles.…”