Effect of doping LiMn2O4 spinel with a tetravalent species such as Si(IV) versus with a trivalent species such as Ga(III). Electrochemical, magnetic and ESR study

Three cathode compounds for lithium ion batteries, LiMn2O4, LiMn1.95Si0.05O4 and LiMn1.9Ga0.1O4 have been synthesized by the freeze-drying method. All samples present partially sintered particles of 80 nm average size, corresponding to single crystalline phases with cubic spinel structure. The substitution of a little portion of Mn(IV) by Si(IV) in the crystal framework leads to more expanded and regular MnO6 octahedra, whereas the replacement of some Mn(III) by Ga(III) induces the opposing effect. The ESR measurements support the effectiveness of doping as an evolution of the width of the resonance signal with the composition is observed. A complete magnetic study has been carried out, including ac and dc magnetic susceptibility measurements at different fields, FC and ZFC, and magnetization versus field. Due to the in-built magnetic frustration in spinel structure and the competition between different exchange pathways, the insertion of small quantities of dopants causes significant differences in the magnetic behaviour. The electrochemical study has revealed very good values of specific capacity for LiMn1.95Si0.05O4 reaching 146 mA h g(-1) and 139 mA h g(-1) at C/10 and 1C rates, respectively. A capacity retention up to 75% has been observed for the three samples after 300th cycles. (C) 2012 Elsevier B.V. All rights reserved.