III Encuentro sobre Nanociencia y Nanotecnología de Investigadores y Tecnólogos Andaluce

Cruz-Yusta, M.

Franger, S.

Morales Palomino, Julián

Santos-Peña, J.

Trócoli Jiménez, Rafael

Repositorio Institucional de la Universidad de Córdoba

- 85 -  P-33 EFFECT OF BORON ADDITION ON THE ELECTROCHEMICAL PROPERTIES OF LiFePO4   R. Trócolia, M. Cruz a, J. Moralesa, J. Santos Peñaa, S. Franger b aDepartamento de Química Inorgánica e Ingeniería Química,  Edificio Marie Curie, Campus de Rabanales, 14071 Córdoba bLaboratoire de Physico−Chimie de l’Etat Solide, Université Paris XI, Orsay (Francia)  LiFePO4 , a phosphate with structure related to olivine, is currently the most promising positive electrode for lithium ion batteries [1]. The competitiveness of this compound comes from both, the maximal capacity (170 mAh/g) and the flat potential (3.5V) that LiFePO4 can supply. However, rate capability of this electrode is somewhat small due to the slow lithium insertion/deinsertion kinetics.   In order to save this drawback, several groups adopted the successful strategy of reducing the particle size of the material to a nanometric level. In this communication, we adopted a different approach: the modification of pristine LiFePO4 by introducing B into the system. Samples were prepared by heating a mixture consisting of LiFePO4 and BPO4 in different doping levels (3, 6 and 9 % in weight ratio) at 700°C. On the one hand, X−rays diffraction patterns revealed a crystalline biphasic system when BPO4 was added in 9% level. On the other hand, the phospholivine cell parameters remained unchanged for all the systems. Taking into account the ionic radii criterion, these results are likely to indicate that, up to a 9% B level, the materials are composites containing an amorphous boron−based phase and LiFePO4. Transmission electron microscopy images (Fig.1) revealed the nanosized structure of the composites and suggested the amorphous phase to be surrounding the LiFePO4 particles as a thin film.   Electrochemical measurements (galvanostatic, potentiostatic and electrochemical impedance spectroscopy) were carried out on cells based on the systems. An improved rate capability for the 3%B “doped” phosphate was observed and will be discussed on the basis of the electronic and ionic conductivities of this material.                Figure 1. TEM image of 3%B−LiFePO4 prepared in this work. Scale bar =500 nm.10                                                  10 Nanjundaswamy K.S.; Goodenough J.B. J. Electrochem. Soc. 1997, 144, 1188. 

Effect of boron addition on the electrochemical properties of LiFePO4

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Repositorio Institucional de la Universidad de Córdoba