Summary Sodium vanadyl orthophosphate NaVOPO4 is an attractive High‐Potential cathode material for Na‐ions batteries with three polymorphs (α, β, and α1). In this work, pure phase of monoclinic α‐NaVOPO4 was synthesized by sol‐gel method and the origin of its poor electrochemical activity was investigated. Sample characterization using X‐ray diffraction, Raman spectroscopy, magnetic measurement and Fourier transform infrared (FT‐IR) spectroscopy confirm the formation of a single phase of monoclinic NaVOPO4 without any impurities. Electrochemical properties were also characterized using cyclic voltammetry, galvanostatic charge‐discharge and electrochemical impedance spectroscopy. The results indicate that α‐NaVOPO4 exhibit a good ionic conductivity but the charge transfer resistance is large. Optical analysis and DFT calculations both showed that the α‐NaVOPO4 is a semi‐conductor with a band‐gap energy of 2.24 eV which explain the origin of the high charge transfer resistance measured using EIS technique. From all these experimental and theoretical results, the poor electrochemical activity of α‐NaVOPO4 can be associated to its low intrinsic electronic conductivity. Electronic and ionic properties of the NaVOPO4 polymorphs are not yet fully characterized. Here, the monoclinic NaVOPO4 was investigated and the material exhibits a high voltage, a good ionic conductivity and good stability, but it exhibits a poor performance. The EIS, optical, and DFT result explain the origin of such behavior. A detailed magnetic study was also reported in this paper.

The molten salt synthesis method became an excellent synthesis technique to elaborate nanomaterials because of its meritorious advantages including low cost, easy to scale up, simple to operate, and environmental friendliness. For this reason, the compound LiMn 1.2 Ni 0.3 Cr 0.1 Co 0.15 Al 0.23 La 0.02 O 4 was synthesized for the first time by molten salt method using NaCl as the salt and a nonstandard manganese source with metallurgical grade. The obtained cathode material was analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier-transformer infra-red (FT-IR), and electrochemical characterization. XRD and FT-IR results confirm the stability and formation of pure spinel phase without any impurities. TEM images showed that the spinel synthesized phase consists of 77 to 135 nm-sized polyhedral nanoparticles. The cyclic voltammogram results showed that the synthesized spinel cathode material exhibits two-main redox peaks at 4.06/3.9 V and 3.1/2.8 V vs Li + /Li, which indicate the possibility of insertion of extra lithium in the spinel structure. Galvanostatic charge-discharge studies were also carried out showed that the prepared spinel material has two discharge plateaus in the potential window of 1.5 to 5 V and a discharge capacity of 179 mAh g À1 at 0.1 C, which is higher than the theoretical value which confirms the insertion of extra lithium in the spinel structure and enhance the capacity of the cathode material. The electrochemical impedance spectroscopy was performed, and the Li-ion diffusion coefficient was also calculated.