Synthesis of $LiCo_{1-x}Mn_xO_2$ from a low-temperature route and characterization as cathode materials in Li-ion cells

Manganese-substituted lithium–cobalt oxides, $LiCo_{1-x}Mn_xO_2 \hspace {3mm}(0 \leq x \leq 0.5)$, have been rapidly synthesized at $350 ^o C$ 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 $R \bar{3} m$ space group having a layered structure and the samples with $x \geq 0.3$ 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 $138 mA \hspace {2mm} h \hspace {2mm}g^{-1}$. With an increase in x, the capacity decreases and reaches about $80 mA \hspace {2mm} h \hspace {2mm} g^{-1}$ 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