Nanosized LiMyMn2-yO4 (M = Cr, Co and Ni) spinels synthesized by a sucrose-aided combustion method -: Structural characterization and electrochemical properties

Spinels of composition LiMyMn2-yO4, M = Cr3+, Co3+, or Ni2+, Y = 0.1 and 1 for the Cr and Co dopants, Y=0.05 and 0.5 for the Ni sample, have been synthesized by a sucrose-aided combustion method. The samples as prepared require of an additional thermal treatment at 700 degrees C, I h to get stoichiometric single-phase spinels. The samples consist of aggregated particles of small size (45-50 nm) as deduced from transmission electron microscopy and X-ray powder diffraction. The electrochemical behaviour of the six spinels as cathodes in lithium cells has been analysed at 5 and 4V under high current, 1 C rate. At 5 V the discharge capacity of LiNi0.5Mn1.5O4 is higher than the one shown by LiCrMnO4 and LiCoMnO4, and it shows an elevated cyclability, i.e. capacity retention of 85.3% after 100 cycles. At 4 V the discharge capacity is similar for LiNi0.05Mn1.95O4, LiCr0.1Mn1.9O4 and LiCo0.1Mn1.9O4, and all the three spinels show similar and very high cyclability, i.e. capacity retention >90% after 100 cycles. The spinels preserve their starting capacity up to currents as high as 2 C rate. The nanometric size of the samples explains the high rate capability of the synthesized spinels. (C) 2007 Elsevier B.V. All rights reserved.