چكيده به لاتين
Nowadays, batteries are one of the advancements of societies for energy storage. Among them, lithium-ion batteries have unique and remarkable properties. The electrochemical properties of lithium-ion batteries mostly depend on the cathodic materials, among which novel, multi-anion structures are attractive. LiVPO4F falls into this category, which has a Tavorite structure. This high voltage cathode (4.1 V vs. Li/Li+) holds long cycle life, excellent thermal stability, and stable crystal structure. This cathode produces theoretical capacity of 156 mAh/g, and also it has a high redox couple (V4+/V3+) among polyanionic compounds. In this study, LiVPO4F was synthesized by the solution combustion method using CTAB, as a fuel, and then calcinated at 800 °C. To improve electrochemical performance, various carbon sources, including carbon super p (20 %wt), sucrose (20 %wt), multi-walled carbon nanotubes (MWCNTs) (10 %wt), and reduced graphene oxide (rGO) (5 %wt) were composited with this compound. For structural and chemical studies, thermogravimetric analysis, X-ray diffraction, X-ray photoelectron spectroscopy, Raman spectroscopy, BET, along with scanning and transmission electron microscopy were performed. After battery fabrications from the synthesized powders, electrochemical tests of initial charge-discharge, cyclic voltammetry, and impedance were recorded for all five samples. The results showed that the primary LVPF/C cathode has an initial discharge capacity of 79 mAh/g at the 1C rate, besides cycling stability of 80.2% after 50 cycles. The composite with the highest cathodic performance was LVPF/rGO with an initial discharge capacity of 121 mAh/g at 1C and excellent cycling stability of 97.52% after 70 cycles. To do so, rate capability analysis for LVPF/rGO with different C rates in 50 cycles was conducted. Also, by examining the electrochemical impedance, a reduction of 67.74% resistance was observed from the primary cathode LVPF/C to the LVPF/rGO cathode.
