Electrochemical characterization of LiFePO4 prepared by hydrothermal synthesis

RITA M. HUMANA.; OMAR AYYAD; ZAHILIA CABAN-HUERTAS; ARNALDO VISINTIN; PEDRO GOMEZ-ROMERO

San Salvador de Jujuy

Workshop; IWLiME 2016: 3rd International Workshop on Lithium, Industrial Minerals and Energy; 2016

Universidad Nacional de Jujuy

The lithium-ion batteriesare energy storage systems of high performance and low cost for use in multipleportable devices. These require the use of increasingly smaller and lighterbatteries with high energy and power density, fast charging and long servicelife. Moreover, these systems are promising for use in electric or hybridvehicles [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 environmentalcompatibility. Lithium iron phosphate (LiFePO4)is a promising candidate for the use as cathodematerial in lithium-ion batteries, especially the batteries for hybrid electricvehicles or pure electric vehicles because of its high theoreticalcapacity, low cost, good thermal stability, abundant raw materials,safety, low toxicity, structural stability, excellent electrochemicalproperties and low environmental impact.  The active material can be reversibly chargedand discharged with a stable voltage profile at 3.45 V vs. Li+/Li witha very small change in unit cell parameters during the LiFePO4/FePO4phase transition. Despite its high theoretical specific capacity (170mAh/g) and long cycling lifetime, the high-rate performance of the raw LiFePO4is 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 surfacecoating have been tried to improve the capacity and rate performance of LiFePO4as cathode for batteries. Increasing the conductivity by coating the LiFePO4surface with carbon [7, 8] or conducting polymers, [9, 10] has been two of themost popular. In addition to coating, the control of surface microstructureconstitutes another general approach towards faster electrode reaction forbatteries. These structures could be easilyand effectively coated with a thin and uniform carbon layer for increasedconductivity, as it is well established for simpler microstructures. Thecarbon coating can produce composite materials for cathodes with improvedperformance; it has been widely used to improve the conductivity of electrodematerials.In this work,the preparation and characterization, using physic and electrochemicaltechniques, of LiFePO4 and LiFePO4/C as cathodes, for lithium-ion batteries,are presented. The structure and chemical composition of the materials werecharacterized 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-dischargecurves at different current densities, cyclic voltammetry, and electrochemical impedancespectroscopy (EIS) techniques.XRDmeasurements confirmed production of highly crystalline LiFePO4 cathode material.The morphological characterization of the materials revealed that the carbon isdistributed uniformly in the LiFePO4 particles. Electrochemicalmeasurements confirmed increasing the intra-particle conductivity by carbon. Theelectrochemical tests exhibited that the electrodes with LiFePO4/C show bettercapacity than the LiFePO4 composite electrodes, being this fact probably due tothe high conductivity carbon.