High-Speed voltammetry of Mn-doped LiCoO₂ using a microelectrode technique

The microelectrode technique was applied to investigate the electrochemical properties of LiC_1-xMn_xO₂ (x = 0, 0.01, 0.05, 0.2, or 0.5) synthesized using the citrate process. From the X-ray diffraction measurements, an expansion of the c-axis and a decrease in the crystal size of the materials were observed on substitution of Mn into LiCoO₂. In the electrochemical measurements, the high-speed cyclic voltammogram for the Mn-substituted materials gave one set of peaks at 3.9 V vs. Li/Li⁺. The apparent chemical diffusion constant (D_app) of LiCo_0.8Mn_0.2O₂ obtained from the potential step experiment was 6.4 × 10^-8 cm²/s, which is larger than that of LiCoO₂. The increase in D_app is attributable to the expansion of the c-axis and/or the decrease in the crystal size. In addition, the increase in Mn substitution up to 20% lead to an improvement in the kinetic reversibility and the cycle stability of LiCoO₂.