Li3V2(PO4)3/Li3PO4 Cathode Materials for Li-Ion Batteries: Synthesis and Characterization

Abstract

Li3V2(PO4)3/Li3PO4 (LVPO/LPO) composites as cathodes for Li-ion batteries were synthesized by the hydrothermal method and subsequently annealed in an Ar atmosphere. The effect of Li3PO4 content on the crystal structure, morphology and the related magnetic and electrochemical properties of Li3V2(PO4)3/Li3PO4 composites, containing 7.5 wt% and 14 wt% of Li3PO4 (LVPO/LPO-7.5 and LVPO/LPO-14) was investigated. The microstructure and morphology of the obtained composites were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM); magnetic and electrochemical properties investigations were performed using the electron spin resonance and galvanostatic methods, respectively. It was shown that Li3V2(PO4)3/Li3PO4 composites exhibit a high discharge capacity, good cycle performance (105 and 120 mAh g−1 for the 200th cycle at 1C for LVPO/LPO-7.5 and LVPO/LPO-14, respectively), and insignificant changes in the surface morphology after 200 lithiation/delithiation cycles. Our results demonstrate that the increase in Li3PO4 content led to a decrease in the Li stoichiometry and magnetic inhomogeneity in Li3V2(PO4)3 phase; thus, the improvement in the electrochemical performance of LVPO/LPO composites due to incorporation of Li3PO4 can be attributed to their chemical and magnetic inhomogeneity.

Li3V2(PO4)3 Cathode Material: Synthesis Method, High Lithium Diffusion Coefficient and Magnetic Inhomogeneity

“…The unit cell contains Z = 4 formula units. The obtained lattice parameters are very close to those that were previously reported and can slightly differ depending on the synthesis process and monoclinic axis selection [ 13 , 32 , 33 , 37 , 38 , 39 , 40 , 41 , 42 ]. The structure of LVPO consists of a three-dimensional framework of slightly distorted VO 6 octahedra and PO 4 tetrahedra.…”

“…The second condition for ESR detection from the exited (S = 1) state in the conventional perpendicular state is that the energy of the microwave field should be sufficient for the transition between these sublevels. Based on a set of experimental data given in the literature [ 31 , 45 , 46 ] and our previous works [ 13 , 32 , 33 ], no signal is expected from trivalent vanadium in perpendicular mode for the above reasons, which may exist separately or together. The direct probe of V 3+ via the ESR test was presented in [ 31 ].…”

“…The comparison of Curie–Weiss temperature and Curie constant values with the same values for Li 3 V 2 (PO 4 ) 3 (86 wt.%)/Li 3 PO 4 (14 wt.%) composite seems difficult due to the small linear range in the temperature dependence of the inverse magnetic susceptibility to approximate by the Curie–Weiss law ( Figure S5 ). The deviation from the Curie–Weiss law in the Li 3 V 2 (PO 4 ) 3 (86 wt.%)/Li 3 PO 4 (14 wt.%) composite is due to the presence of a significant number of magnetically correlated regions [ 13 ].…”

“…Among various candidates, lithium vanadium phosphate Li 3 V 2 (PO 4 ) 3 (LVPO) emerged as a material of interest due to its impressive electrochemical properties. The study and creation of efficient LVPO cathode materials are driven by the need to address some of the critical challenges faced by current LIBs technologies, including limited energy density, reduced cycle life and issues related to safety and environmental impact [ 13 , 14 , 15 ]. LVPO, with its unique crystal structure and electrochemical stability, presents an opportunity to overcome these obstacles, offering a pathway to higher energy densities and enhanced safety features.…”

“…Electron spin resonance (ESR) detects the qualitative and quantitative information of unpaired electrons contained in local atoms or molecules of matter and the structural characteristics of its surrounding environment. NMR is commonly used in the study of light elements such as Li, Na, O and F, while ESR is suitable for the evaluation of transition metals (Fe, Co, Mn, V) and oxygen vacancies and for the characterization of redox processes [ 13 , 31 , 32 , 33 ]. Owing to the ultrahigh sensitivity to magnetization, magnetometry can accurately monitor the magnetic changes caused by electron transfer during electrochemical processes, and it is a powerful tool for investigating conversion or alloy-type alkali metal ion batteries (AMIBs), spin-based devices [ 34 , 35 ] or solid electrolyte interphase characterization by operando magnetometry [ 36 ].…”