Sucrose-aided combustion synthesis of nanosized LiMn 1.99− yLi yM 0.01O 4 (M = Al 3+, Ni 2+, Cr 3+, Co 3+, y = 0.01 and 0.06) spinels : Characterization and electrochemical behavior at 25 and at 55 °C in rechargeable lithium cells

Abstract

Doubly doped LiMn 1.99− y Li y M 0.01O 4 (M = Al 3+, Ni 2+, Cr 3+, Co 3+; y = 0.01 and 0.06) spinels have been synthesized by the sucrose-aided combustion method. Combined TG/DTA and XRD studies have shown that stoichiometric single-phase spinels are formed after annealing of the samples at 700 °C for 1 h. The samples obtained are nanocrystalline materials having a narrow size-distribution and a coherent domain size between 40 and 60 nm, depending on the amount of fuel (sucrose) used in the synthesis. The influence of the Li-excess, the type of M n+ -dopant cation and the amount of fuel used in the synthesis on the electrochemical behavior of the spinels in a Li-cell at room and at elevated temperature (55 °C) has been studied. At 25 °C all the spinels synthesized have a good capacity retention after 100 cycles, QRt-100 > 92%. At 55 °C the increase of the Li-excess improves the cycling performances. Rate capability studies show that the spinels retain >90% of their capacity even at 5 C rate. The synergic effect of the Li-excess and the particle size on the electrochemical properties of the spinels as cathode material has been settled. The LiMn 1.93Li 0.06M 0.01O 4, (M = Al 3+, Ni 2+) spinels, with cyclabilities >99.9% by cycle at both 25 and 55 °C, and high rate capabilities, are the ones that show the best electrochemical properties.