Synthesis of LiCo_1-xMn_xO₂ from a low-temperature route and its characterization as cathode material in Li-ion cells

Abstract

Manganese-substituted lithium-cobalt oxides, LiCo_1-xMn_xO₂ (0≤ x≤ 0.5), have been rapidly synthesized at 350 °C by a solution combustion method using diformyl hydrazine (DFH) as a fuel. Physical properties of these compounds are discussed in the light of structural [X-ray diffraction (XRD) and scanning electron miscroscope (SEM)] and spectroscopic (FTIR and Raman) studies. The samples with x<0.3 are indexed in R3^¯m space group having a layered structure and the samples with x≥ 0.3 in Fd3m space group with a modified spinel structure. Electrochemical characterization of these samples has been studied using cyclic voltammetry, galvanostatic charge-discharge cycling in the potential range 3-4.5 V and impedance spectroscopy. Specific capacity of the compound with x=0.2 has been found to be about 138 mA h g^-1. With an increase in x, the capacity decreases and reaches about 80 mA h g^-1 at x=0.5. From impedance spectroscopy, it has been found that the charge-transfer resistance is minimum for the sample with x=0.2, which supports the charge-discharge cycling data.