Structural, Electrical, and Electrochemical Properties of a Na2O-V2O5 Ceramic Nanocomposite as an Active Cathode Material for a Na-Ion Battery

Abstract

In this paper, a relationship between the structure and the electrical properties of a nanocrystalline composite ceramics xNa2O·(100 − x)V2O5 with ‘x’ of 5, 15, 25, 35, and 45 mol%, abbreviated as xNV, was investigated by X-ray diffractometry (XRD), X-ray absorption spectroscopy (XAS), Cyclic Voltammetry (CV), Electrochemical impedance spectroscopy (EIS), and cathode active performance in Na-ion battery (SIB). For the expected sodium vanadium bronzes (NaxV2O5) precipitation, the preparation of xNV was performed by keeping the system in the molten state at 1200 °C for one hour, followed by a temperature decrease in the electric furnace to room temperature at a cooling rate of 10 °C min−1. XRD patterns of the 15NV ceramic exhibited the formation of Na0.33V2O5 and NaV3O8 crystalline phases. Moreover, the V K-edge XANES showed that the absorption edge energy of ceramics 15NV recorded at 5479 eV is smaller than that of V2O5 at 5481 eV, evidently indicating a partial reduction from V5+ to V4+ due to the precipitation of Na0.33V2O5. In the cyclic voltammetry, reduction peaks of 15NV were observed at 1.12, 1.78 V, and 2.69 V, while the oxidation peak showed up only at 2.36 V. The values of the reduction peaks were related to the NaV3O8 crystalline phase. Moreover, the diffusion coefficient of Na+ (DNa+) gradually decreased from 8.28 × 10−11 cm2 s−1 to 1.23 × 10−12 cm2 s−1 with increasing Na2O content (x) from 5 to 45 mol%. In the evaluation of the active cathode performance of xNV in SIB, ceramics 15NV showed the highest discharge capacity 203 mAh g−1 at a current rate of 50 mA g−1. In the wider voltage range from 0.8 to 3.6 V, the capacity retention was maintained at 50% after 30 cycles, while it was significantly improved to 90% in the narrower voltage range from 1.8 to 4.0 V, although the initial capacity decreased to 56 mAh g−1. It is concluded that the precipitation of the Na0.33V2O5 phase improved the structural and electrical properties of 15NV, which provides a high capacity for the Na-ion battery when incorporated as a cathode active material.

Debye Temperature Evaluation for Secondary Battery Cathode of α-SnxFe1−xOOH Nanoparticles Derived from the 57Fe- and 119Sn-Mössbauer Spectra

“…Figure 6 a–c show the charge–discharge capacities of Sn0, Sn10, and Sn15, respectively, as cathode materials in LIBs. A small plateau at 1.61 V was observed in the first discharge in Sn0, Sn10, and Sn15, corresponding to Li intercalation before the reduction reaction, given the layered structure of α-FeOOH [ 13 , 49 , 52 , 53 , 54 , 55 , 56 ]. In the first charge cycle of Sn0, the voltage gradually increases to 3.6 V without a significant plateau, while Sn10 and Sn15 exhibited plateaus at 3.56 and 3.45 V and the voltage increased to 4 V. In addition, the large irreversible capacity shown in Sn0 can be attributed to the formation of LiOH and/or decomposition of a polytetrafluoroethylene (PTFE) binder that occurred during the discharge.…”

“…Figure 8 a shows the XANSES spectra in the energy range from 7080 eV to 7200 eV to obtain the changes in pre-edge peak and absorption energy of the S10 and Sn15 compared with the standard materials (Fe 2 O 3 ). The absorption energy is defined as the normalized absorbance at 0.5 of each spectrum [ 54 , 55 ]. In addition, when the absorption energy shifts to high, it indicates that the oxidation state of Fe has increased [ 16 , 17 ].…”

“…Figure8ashows the XANSES spectra in the energy range from 7080 eV to 7200 eV to obtain the changes in pre-edge peak and absorption energy of the S10 and Sn15 compared with the standard materials (Fe2O3). The absorption energy is defined as the normalized absorbance at 0.5 of each spectrum[54,55]. In addition, when the absorption energy shifts to high, it indicates that the oxidation state of Fe has increased[16,17].As we can see, the absorption energy of both samples before and after testing the battery and Fe2O3 are close to each other at approximately 7122.45 eV, therefore, we figured out the part of the spectra and inserted it to the right and at the bottom of Figure8a.…”

Ramifications of chromium-to-bismuth ions substitution on the structural and optical characteristics of bismuth borate glasses for optoelectronic applications

“…Lately, glasses incorporating transition metal oxide have exhibited intriguing spectroscopic and electrical characteristics attributed to the presence of ions in multiple valence states [10,11]. Among various transition metal oxides, chromium oxide (Cr 2 O 3 ) serves as a nucleating agent.…”