Structure and Electrochemical Properties of LiCo1 – yFey PO4 Solid Solutions – High-Voltage Cathode Materials for Lithium-Ion Rechargeable Batteries
O. A. PODGORNOVA and N. V. KOSOVA
Institute of Solid State Chemistry and Mechanochemistry, Siberian Branch of the Russian Academy of Sciences, Ul. Kutateladze 18, Novosibirsk 630128 (Russia)
E-mail: kosova@solid.nsc.ru
Keywords: lithium-ion rechargeable cells, cathode materials LiCo1 - yFeyPO4, mechanical activation, crystal structure, cycling
Pages: 53–59
Abstract
Single-phase superfine LiCo1–yFeyPO4 solid solutions were synthesized with the use of a mechanochemically stimulated carbothermal reduction of iron and cobalt oxides throughout the entire range of 0 ≤ y ≤ 1. The mechanical activation was carried out using an AGO-2 planetary mill. According to the scanning electron microscopy, the average primary particle size of the samples synthesized ranges within 200–250 nm. According to the XRD phase analysis, all the samples crystallize in the orthorhombic system, with space group Pnma. The volume of the unit cell increases with increasing the content of iron in samples. According to Mцssbauer (NGR) spectroscopy, all iron ions are in the oxidation state 2+ in an octahedral environment typical for olivine. Electrochemical properties of Li1 – yFeyPO4 were investigated by means of galvanostatic cycling. It has been demonstrated that with the increase of Fe content a marked shift in the potential of the Co2+/Co3+ pair toward lower voltage values occurs, whereas the potential of the Fe2+/Fe3+ pair remains almost unchanged.
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