Structural, Transport and Electrochemical Properties of LiFePO₄ Substituted in Lithium and Iron Sublattices (Al, Zr, W, Mn, Co and Ni)

Janina Molenda; Andrzej Kulka; Anna Milewska; Wojciech Zając; Konrad Świerczek

doi:10.3390/ma6051656

Structural, Transport and Electrochemical Properties of LiFePO₄ Substituted in Lithium and Iron Sublattices (Al, Zr, W, Mn, Co and Ni)

Materials (Basel). 2013 Apr 29;6(5):1656-1687. doi: 10.3390/ma6051656.

Authors

Janina Molenda¹, Andrzej Kulka², Anna Milewska³, Wojciech Zając⁴, Konrad Świerczek⁵

Affiliations

¹ Department of Hydrogen Energy, Faculty of Energy and Fuels, AGH University of Science and Technology, al. A. Mickiewicza 30, 30-059 Krakow, Poland. molenda@agh.edu.pl.
² Department of Hydrogen Energy, Faculty of Energy and Fuels, AGH University of Science and Technology, al. A. Mickiewicza 30, 30-059 Krakow, Poland. akulka1986@o2.pl.
³ Department of Hydrogen Energy, Faculty of Energy and Fuels, AGH University of Science and Technology, al. A. Mickiewicza 30, 30-059 Krakow, Poland. anna.milewska@agh.edu.pl.
⁴ Department of Hydrogen Energy, Faculty of Energy and Fuels, AGH University of Science and Technology, al. A. Mickiewicza 30, 30-059 Krakow, Poland. wojciech.zajac@agh.edu.pl.
⁵ Department of Hydrogen Energy, Faculty of Energy and Fuels, AGH University of Science and Technology, al. A. Mickiewicza 30, 30-059 Krakow, Poland.

Abstract

LiFePO₄ is considered to be one of the most promising cathode materials for lithium ion batteries for electric vehicle (EV) application. However, there are still a number of unsolved issues regarding the influence of Li and Fe-site substitution on the physicochemical properties of LiFePO₄. This is a review-type article, presenting results of our group, related to the possibility of the chemical modification of phosphoolivine by introduction of cation dopants in Li and Fe sublattices. Along with a synthetic review of previous papers, a large number of new results are included. The possibility of substitution of Li⁺ by Al³⁺, Zr⁴⁺, W⁶⁺ and its influence on the physicochemical properties of LiFePO₄ was investigated by means of XRD, SEM/EDS, electrical conductivity and Seebeck coefficient measurements. The range of solid solution formation in Li_1-3xAl_xFePO₄, Li_1-4xZr_xFePO₄ and Li_1-6xW_xFePO₄ materials was found to be very narrow. Transport properties of the synthesized materials were found to be rather weakly dependent on the chemical composition. The battery performance of selected olivines was tested by cyclic voltammetry (CV). In the case of LiFe_1-yM_yPO₄ (M = Mn, Co and Ni), solid solution formation was observed over a large range of y (0 < y ≤ 1). An increase of electrical conductivity for the substitution level y = 0.25 was observed. Electrons of 3d metals other than iron do not contribute to the electrical properties of LiFe_1-yM_yPO₄, and substitution level y > 0.25 leads to considerably lower values of σ. The activated character of electrical conductivity with a rather weak temperature dependence of the Seebeck coefficient suggests a small polaron-type conduction mechanism. The electrochemical properties of LiFe_1-yM_yPO₄ strongly depend on the Fe substitution level.

Keywords: Fe-site substitution; Li-ion batteries; Li-site substitution; LiFePO4; cathode material; electrochemical properties; transport properties.