Publication: Enabling high-rate capability by combining sol-gel synthesis and solid-state reaction with PTFE of 4.2 V cathode material LiVPO<inf>4</inf>F/C
Date
01-06-2021
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Abstract
LiVPO4F (LVPF) is a promising high voltage (4.2 V vs. Li/Li+) and high energy density (655 Wh kg−1) cathode material for lithium ion batteries. The challenge is to prepare phase pure and conducting material suitable for battery application. In this work carbon coated LiVPO4F (LVPF/C) is synthesized by sol-gel method, and the effect of carbon coating and control on F content on the structure, morphology, electrochemical properties of LVPF/C are studied comprehensively. Li3V2(PO4)3 and Li9V3(P2O7)3(PO4)2 form as minor secondary phases when LVPF is prepared without carbon source. In contrast Li3V2(PO4)3 and V2O3 are found when lauric acid is used as carbon source. Using optimal concentration of polytetrafluoroethylene (35 wt. % PTFE) and lauric acid (27 wt. % LA) in the synthesis yields carbon coated LVPF (LVPF/C-35) with best electrochemical performance. Lattice parameters of LiVPO4F are consistent with the reported values. Electrochemical properties of the LVPF/C-X cathodes (X = 25, 35 and 45 wt. % PTFE) show the discharge capacities of ∼ 85.4 (∼ 7), ∼ 114.7 (∼ 84.1), ∼ 102.7 (∼ 14.2) mA h g−1 at 0.1C (10C) rates, when scanned in the voltage range of 3.0–4.5 V vs. Li/Li+. A flat potential profile at ∼ 4.2 V vs. Li/Li+ is seen during charging-discharging profiles of the LVPF/C-X samples. From CV studies, the diffusion coefficient is found to be of the order of 10−16 cm2s−1 during oxidation and reduction. BET surface area is more (∼ 75.95 m2 g−1) for LVPF/C-35 compared to other two samples. From Electrochemical impedance spectroscopy, the influence of charge-transfer resistance resulting from the cathode electrolyte interface layer on electrochemical properties is studied.
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Electrochemical properties, Lithium ion battery, LiVPO F cathode 4, PTFE