Crystallization of the Na2FexNi1−xP2O7 Glass and Ability of Cathode for Sodium-Ion Batteries

Abstract

Although the sodium phosphate cathode active materials based on the Ni 3+ /Ni 2+ redox reaction are expected to develop a high discharge potential, none of the studies aimed at practical application have been reported due to its poor kinetics showed in the sodium phosphate. Herein, we substituted active Fe for a part of Ni, expecting to activate the potential deriving from the Ni 3+/2+ in Na 2 Fe x Ni 1−x P 2 O 7 glass-ceramics. Precursor glasses were prepared by the melt-quenching method and exhibited surface crystallization tendency due to heterogeneous nucleation. In the charge-discharge testing, all the flat potential showed in the discharge process derived from the reduction of Fe 3+/2+ . However, from the dQ/dV plot, there were two weak reduction peaks at 4.3 and 4.4 V in the discharge process of Na 2 Fe 0.25 Ni 0.75 P 2 O 7 . Combining with the oxidation peak at 4.6 V in the second charge process of Na 2 NiP 2 O 7 , we believe the reduction peaks at 4.3 and 4.4 V were derived from the Ni 3+/2+ .

Synergistic Effects of Redox Couples and Oxygen Vacancies Improve the Tetracycline Degradation Property of La2NiMnO6

“…The synergistic effects of OVs and the cycle transformation of Mn 4+ /Mn 3+ and Mn 4+ /Mn 2+ not only effectively separated the e – and h + but also facilitated the production of • O 2 – . E­(Mn 3+ /Mn 2+ ) = 1.51 V and E­(Ni 3+ /Ni 2+ ) = 1.69 V were higher than the E VB of all catalysts, resulting in nonoccurrence of the cycle conversion of Mn 3+ /Mn 2+ and Ni 3+ /Ni 2+ . …”

Sodium-Storage Performance of K+-Intercalated NaxCu0.2Mn0.8O2

“…During the charging and discharging process of KCM-Na, the (002) diffraction peak of the P2 phase was retained at all potentials, indicating that the sample maintained the crystalline P2 phase structure. When the potential was increased from 1.4 to 3.8 V, the (002) distance of KCM-Na slightly increased from 5.590 to5.647 Å and then decreased to 5.570 Å when the potential drops from 3.8 to 1.4 V, proving that the charge–discharge reaction of KCM-Na is highly reversible . The ex situ XRD of KCM shows a different pattern.…”

“…Multiple broad redox peaks appear in the dQ/dV curves of all samples, which may correspond to the local phase transitions caused by Na + intercalation/deintercalation. 31,32 Specifically, NaCM and KCM have sharp oxidation peaks at 2.3 V, while those of KCM-Na and NaCM-K appear at 2.4 and 2.5 V, corresponding to the oxidation potential of Mn 3+ /Mn 4+ . This result proves an evident redox reaction at around 2.3−2.5 V. Figure 4c is the capacity-rate curves of the four samples, showing the specific capacity of each sample at 1−10 C. KCM-Na has the highest capacity among all the samples at different rates, which reached 128.5, 114.7, 99.4, 87.2, and 71.2 mAh g −1 at 2/3/5/7/10 C. The second-highest capacity is in NaCM-K, which reached 120.1, 104.9, 92.1, 79.8, and 60.2 mAh g −1 at 2/3/5/7/10 C. In comparison, KCM and NaCM showed lower capacity and lower rating performance.…”

Laser‐induced modification and external pressureless joining Na2FeP2O7 on solid electrolyte

“…Under this study's experimental conditions the irradiated part is turned into a glassy state by laser irradiation. In previous studies, 40,41 compared the electrical conductivity of vitreous NFP and crystallized NFP, crystal shows higher electrical conductivity than that of glass—the electrical conductivity of the sample crystallized by re‐heating after laser irradiation is further improved. Therefore, in the future, laser irradiation that avoids melting and directly form crystal is preferable.…”