Electrochemical Performance and Thermal Stability of Iron Oxyfluoride (FeOF) for Sodium-Ion Batteries

Abstract

Self-synthesized rutile iron oxyfluoride (FeOF) was studied as a cathode material for Na-ion batteries. The highly crystalline FeOF provided an initial discharge capacity of 246 mAh g´1 in a voltage range of 1.0-4.0 V, followed by 88% of capacity retention after 20 cycles. This discharge-charge reaction of FeOF between 0.8 and 4.0 V are advanced by the Fe 2+ /Fe 3+ redox reaction. That is, no conversion reaction was involved in the application of FeOF as a cathode material for Na-ion batteries because of the low potential of Na-insertion. In addition, the structure change of FeOF from rutile to cubic during Na ion insertion, which was similar to that in Li-ion batteries. No remarkable HF release was detected even up to 700˝C, indicating a low toxic risk of the FeOF cathode. The thermal properties of sodiated and desodiated FeOF electrodes in the associated electrolyte were investigated by DSC (Differential scanning calorimetry) up to 500˝C. Sodiated FeOF electrodes showed larger exothermic heat generation than desodiated ones, especially at a temperature higher than 380˝C. Finally, the thermal stability of FeOF cathodes in the associated Li-and Na-ion battery electrolytes was quantitatively compared with variations of the electrode/electrolyte ratio.

Fluorinated Materials as Positive Electrodes for Li- and Na-Ion Batteries

“…In 2013, Kitajou et al tested FeOF previously prepared by roll quenching . This highly crystallized FeOF shows an excellent reversible capacity of 246 mAh g –1 (4.0–1.0 V, 10 mA g –1 ) after 20 cycles corresponding to a retention capacity of 80% (0.8Na + ) . Similarly with the electrochemical reactivity of lithium, a too low cutoff potential, less than ∼1 V, considerably reduces reversibility.…”

“…125 This highly crystallized FeOF shows an excellent reversible capacity of 246 mAh g −1 (4.0−1.0 V, 10 mA g −1 ) after 20 cycles corresponding to a retention capacity of 80% (0.8Na + ). 141 Similarly with the electrochemical reactivity of lithium, a too low cutoff potential, less than ∼1 V, considerably reduces reversibility. A study published in 2019 proposes a synthesis of FeOF nanoparticles that involves a calcined Metal Organic Framework precursor (Fe-MIL-88B), fluorinated by the addition of H 2 SiF 6 before solvothermal reaction at 200 °C for 10 h. in 1-propanol.…”

Comparison study of electrochemical and thermal stability of Na 3 V 2 ( PO 4 ) 3 in different electrolytes under room and elevated temperature

“…A comparison of the two results revealed that the overall exothermic behavior of NVP in NaClO 4 ‐based electrolyte was mainly affected by NVP. Meanwhile, the most obvious finding to emerge from the analysis was that reactions between NVP and EC:DEC or PC solvent were responsible for the heat generation when NVP combines with NaClO 4 ‐based electrolyte, because NaClO 4 salt was fairly stable and did not decompose in the entire experimental range 71 . Looking at Figure 10C, it was apparent that the heat release of NVP in NaPF 6 EC:DEC electrolyte began about 130°C and continued to the end of the experiment.…”

Critical overview of polyanionic frameworks as positive electrodes for Na-ion batteries

“…Notably, the rutile-FeOF (P 4 2 /mnm) structure was tested as a NIB cathode and showed a reversible transition to cubic-Na x FeOF. [35] However, this FeOF↔Na x FeOF transition was accompanied by significant hysteresis in the corresponding voltage-capacity profiles, with possible contributions from electrolyte decomposition and/or other side reactions. [35] Importantly, the chemical class TMOFs has not been systematically explored, either computationally or experimentally, as NIB cathodes, so far.…”

“…Also, most of the oxyfluoride structures that have been reported have undergone either amorphization or an irreversible structural transition during electrochemical cycling. [32][33][34][35] Although Li-ion mobility is not hindered in both disordered rocksalt, [36] and amorphized, [37] oxyfluorides, studies have not analysed Na-ion mobility in similar frameworks. Notably, the rutile-FeOF (P 4 2 /mnm) structure was tested as a NIB cathode and showed a reversible transition to cubic-Na x FeOF.…”