Electrochemical Characterization Of LiFePO4 Prepared By Hydrothermal Synthesis,

R. M. HUMANA; O. AYYAD, ; Z. CABAN-HUERTAS; VISINTIN A.; P. GOMEZ-ROMERO

JUJUY

Workshop; IWLIME International Work shop; 2016

International Work shop

The lithium-ion batteries are energy storage systems of high performance and low cost for use in multiple portable devices. These require the use of increasingly smaller and lighter batteries with high energy and power density, fast charging and long service life. Moreover, these systems are promising for use in electric or hybrid vehicles [1, 2]. However, the successful use of the lithium in the field, requires improvements in relation to the properties of electrode materials, such as cost, energy density, cycle life, safety, and environmental compatibility. Lithium iron phosphate (LiFePO4) is a promising candidate for the use as cathode material in lithium-ion batteries, especially the batteries for hybrid electric vehicles or pure electric vehicles because of its high theoretical capacity, low cost, good thermal stability, abundant raw materials, safety, low toxicity, structural stability, excellent electrochemical properties and low environmental impact. The active material can be reversibly charged and discharged with a stable voltage profile at 3.45 V vs. Li+/Li with a very small change in unit cell parameters during the LiFePO4/FePO4 phase transition. Despite its high theoretical specific capacity (170 mAh/g) and long cycling lifetime, the high-rate performance of the raw LiFePO4 is restricted by its poor electronic conductivity (10−9 S/cm) [3] as well as low lithium ion diffusion rate [4-6]. Many different approaches involving surface coating have been tried to improve the capacity and rate performance of LiFePO4 as cathode for batteries. Increasing the conductivity by coating the LiFePO4 surface with carbon [7, 8] or conducting polymers, [9, 10] has been two of the most popular. In addition to coating, the control of surface microstructure constitutes another general approach towards faster electrode reaction for batteries. These structures could be easily and effectively coated with a thin and uniform carbon layer for increased conductivity, as it is well established for simpler microstructures. The carbon coating can produce composite materials for cathodes with improved performance; it has been widely used to improve the conductivity of electrode materials.In this work, the preparation and characterization, using physic and electrochemical techniques, of LiFePO4 and LiFePO4/C as cathodes, for lithium-ion batteries, are presented. The structure and chemical composition of the materials were characterized by X-Ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and thermogravimetric analysis (TGA). The electrochemical characterization was carried out using charge-discharge curves at different current densities, cyclic voltammetry, and electrochemical impedance spectroscopy (EIS) techniques.XRD measurements confirmed production of highly crystalline LiFePO4 cathode material. The morphological characterization of the materials revealed that the carbon is distributed uniformly in the LiFePO4 particles. Electrochemical measurements confirmed increasing the intra-particle conductivity by carbon. The electrochemical tests exhibited that the electrodes with LiFePO4/C show better capacity than the LiFePO4 composite electrodes, being this fact probably due to the high conductivity carbon.