A new doping element to improve the electrochemical performance of Li_1.2Mn_0.54Ni_0.13Co_0.13O₂ materials for Li-ion batteries

In this study, vanadium (V) was firstly used to dope alone or with molybdenum (Mo) in Li[Li _0.2Mn_0.54Co_0.13Ni_0.13]O₂ to enhance its electrochemical performance. A series of V-doped lithium-rich materials Li_1.2Mn_0.54-xNi_0.13Co_0.13V_xO₂ (0 ≤ x ≤ 0.04) and V/Mo co-doped lithium-rich materials Li_1.2Mn_0.54-x-yNi_0.13Co_0.13V_xMo_yO₂ (0.02 ≤ x ≤ 0.03, 0 ≤ y ≤ 0.03) with varied doping ratios have been successfully synthesized through a sol-gel method. The XRD results indicate that both Li_1.2Mn_0.54-xNi_0.13Co_0.13V_xO₂ (0 ≤ x ≤ 0.04) and Li_1.2Mn_0.54-x-yNi_0.13Co_0.13V_xMo_yO₂ (0.02 ≤ x ≤ 0.03, 0 ≤ y ≤ 0.03) materials have a typical hexagonal α-NaFeO₂ structure. The electrochemical performance of the original and doped Li[Li _0.2Mn_0.54Co_0.13Ni_0.13]O₂ samples was evaluated. The results present that cycling performance of Li_1.2Mn_0.54-xNi_0.13Co_0.13V_xO₂ materials is significantly enhanced in comparison to the original material. When the doping amount of V is 0.02, the discharge capacity of the Li_1.2Mn_0.54-xNi_0.13Co_0.13V_xO₂ materials after 300 cycles at 1 C (142.0 mA h/g) is slightly higher than the initial value (140.3 mA h/g) and that of undoped materials (112.0 mA h g⁻¹ after 150 cycles at 1 C). The rate performance of V and Mo co-doped materials is significantly improved. When x = 0.03 and y = 0.03, the discharge capacity of the Li_1.2Mn_0.54-x-yNi_0.13Co_0.13V_xMo_yO₂ materials at 5 C is 52.7% of that at 0.1 C while the discharge capacity ratio of the single-doped V materials is only 39.8%. The doping of V and Mo can effectively inhibit the transformation of Li[Li _0.2Mn_0.54Co_0.13Ni_0.13]O₂ materials from layered structure to spinel structure in the charging-discharging process, and increase the ionic conductivity of the Li[Li_0.2Mn_0.54Co_0.13Ni_0.13]O₂ materials, thus the electrochemical properties of the materials are obviously improved.