Synthesis, Characterization and Evaluation of GO-LFP as Cathode Material for Li-ion Battery

M.G, ORTIZ; M.P. QUIROGA ARGAÑARAZ; K. JORI; A. RODRIGUEZ; J.M. RAMALLO LOPÉZ; F. REQUEJO; VISINTIN A.

Mar del Plata

Congreso; 34 th Topical Meeting ISE; 2023

International Society of Electrochemistry - ISE

The aim of the present work was to study the improvements that can be introduced in active materials of LiFePO4 (LFP) to be used as cathodes in Li-ion batteries. Intensive attention has been focused on the LiFePO4 because of its low cost, excellent abuse tolerance, a reversible specific capacity of 170 mAh g-1, a flat charge/discharge profile at intermediate voltage (3.45 V vs. Li+/Li), and long cycle life[. However, one of the limitations of LFP is associated with its low conductivity. To overcome this problem, modifications to the synthesis were proposed, such as time and temperature reaction, additives (ascorbic acid), and the incorporation of carbon-based materials. The purpose of these modifications was to reduce the grain size of the particles, as well as to provide them with greater conductivity through a conductive carbon coating that facilitates the migration of Li ions in the cathode charge-discharge process. To increase the conductivity and stability of Fe2+, various graphene-oxide reduction treatments were tested. LFP was synthesized by the solvothermal route of LiOH.H2O, FeSO4.7H2O, and H3PO4 using ethylene glycol as solvent; graphene oxide (GO) was added in different synthesis steps. These new materials were electrochemically evaluated. Structural and chemical characterization was performed by X-ray absorption techniques at Fe K-edge (XANES) and X-ray diffraction (XRD). The formationmechanism and the influence of GO on the morphology of LiFePO4 micro- and nanocrystals were investigated. The results of electrochemical performance measurements revealed that the charge/discharge cycling characteristics of the samples varied by tailoring their carbon coating. Particularly, the rhomboid-like LiFePO4 without GO particles presented an initial discharge capacity of 141 mAh/ g at C/2 rate similar values for LFP materials with GO, but the cycling stability of this sample was better than that of LFP materials without GO. Also, the position of Fe K-absorption edge indicates a +2 oxidation state for Fe atoms that are found mostly forming LFP (82%) with a small fraction of FeO (18%). These results coincide with XRD data that indicate there is 86% concordance with LFP.