Effect of transition metal composition on electrochemical performance of nickel-manganese-based lithium-rich layer-structured cathode materials in lithium-ion batteries

To evaluate the effect of transition metal composition on the electrochemical properties of Li-rich layer-structured cathode materials, Li1.2NixMn0.8−xO2 (x=0.2, 0.25, 0.3, and 0.4) were synthesized, and their electrochemical properties were investigated. As nickel content x increased in Li1.2NixMn0.8−xO2 (x=0.2, 0.25, 0.3, and 0.4), charge-discharge capacities at a low C-rate (0.05C) decreased. The results obtained by dQ/dV curves indicate that, as the nickel content increased, the discharge capacity below 3.6V greatly decreased, but that above 3.6V increased. As the C-rate of the discharge process increased, the discharge reaction of Li1.2NixMn0.8−xO2 (x=0.2) below 3.6V greatly decreased. In contrast, that above 3.6V slightly decreased. This indicates that the discharge reaction above 3.6V exhibits higher rate performance than that below 3.6V. For the high-nickel-content cathodes, the ratio of the discharge capacity above 3.6V to the total discharge capacity was high. Therefore, they exhibited high rate performance. Figure shows the discharge curves of Li1.2NixMn0.8−xO2 (x=0.2 and 0.3) within potential range of 2.5−4.6V (vs. Li/Li+) at 0.05 and 3C. At low C-rate (0.05C), the discharge capacity of high-nickel-content cathode (Li1.2Ni0.3Mn0.5O2) was less than that of low-nickel-content cathode (Li1.2Ni0.2Mn0.6O2); however, the discharge potential and capacity of Li1.2Ni0.3Mn0.5O2 was higher than those of Li1.2Ni0.2Mn0.6O2 at high C-rate (3C). This means that the increase in Ni/Mn ratio was effective in improving rate-performance. [Display omitted]