High-rate performance and suppressed voltage decay of Li and Mn-rich oxide cathode materials upon substitution of Mn with Co for Li-ion batteries

Layered Lithium and Mn-rich oxides, xLi₂MnO₃·(1–x) LiMO₂ (M = Ni, Mn, Co) such as Li_1.2Ni_0.2Mn_0.6O₂ (without Co) and Li_1.2Ni_0.13Mn_0.54Co_0.13O₂ (upon substitution of both Mn and Ni with Co) are reported with high specific capacity. However, there is no report yet on the performance of Lithium and Mn-rich oxides when only Mn in these oxide cathodes is partially substituted with Co. In the current study, Lithium and Mn-rich cathodes such as Li_1.2Ni_0.2Mn_0.6O₂(LNMO) and Li_1.2Ni_0.20Mn_0.48Co_0.12O₂(LNMCO) are synthesized by a sol–gel method followed by sintering at 900 °C for 12 h and their electrochemical performance has been evaluated at C/10 rate for 2 cycles (2.0–4.7 V) followed by 2.0–4.6 V at C/5 rate for 140 cycles. LNMO and LNMCO exhibit initial discharge capacities of around 210 and 224 mAh/g, respectively at the C/10 rate, with capacities retentions of 80.9 and 82.4 % after 140 cycles upon cycling at the C/5 rate. However, with an increase in the rate, Li_1.2Ni_0.2Mn_0.6O₂ has a specific capacity around 70 mAh/g at 4C current rate, whereas Li_1.2Ni_0.20Mn_0.48Co_0.12O₂ exhibits 113 mAh/g at the same current rate. This result clearly demonstrates that Li_1.2Ni_0.20Mn_0.48Co_0.12O₂ has a better rate capability than Li_1.2Ni_0.2Mn_0.6O₂ material. During cycling, an excessive average discharge voltage is also maintained for Li_1.2Ni_0.20Mn_0.48Co_0.12O₂.