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

Abstract

In the current study, we found that the substitution of Mn in Li and Mn-rich oxides with Co results in the improved electrochemical performance in Li-ion batteries. The Co-containing Li and Mn-rich oxide, Li 1.2 Ni 0.2 Mn 0.48 Co 0.12 O 2 exhibit a specific capacity of about 205 mAh g -1 at C/5 rate with 83% capacity retention after 140 cycles along with a higher rate capability and also maintained a higher average discharge voltage upon cycling than that of Li 1.2 Ni 0.2 Mn 0.6 O 2 . • Influence of Co on the performance of Li and Mn-rich oxides has been tested. • Li 1.2 Ni 0.20 Mn 0.48 Co 0.12 O 2 exhibits a high specific capacity of 224 mAh g -1. • Interestingly, Li 1.2 Ni 0.2 Mn 0.48 Co 0.12 O 2 exhibits a specific capacity of 113 mAh g -1 at 4C rate, which is higher than Li 1.2 Ni 0.2 Mn 0.6 O 2 (70 mAh g -1 ) • EIS study indicates the low charge transfer resistance at high voltages for Li 1.2 Ni 0.2 Mn 0.48 Co 0.12 O 2. Layered Lithium and Mn-rich oxides, xLi 2 MnO 3 ·(1–x) LiMO 2 (M=Ni, Mn, Co) such as Li 1.2 Ni 0.2 Mn 0.6 O 2 (without Co) and Li 1.2 Ni 0.13 Mn 0.54 Co 0.13 O 2 (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 1.2 Ni 0.2 Mn 0.6 O 2 (LNMO) and Li 1.2 Ni 0.20 Mn 0.48 Co 0.12 O 2 (LNMCO) are synthesized by a sol-gel method followed by sintering at 900 o 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 -1 , 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 1.2 Ni 0.2 Mn 0.6 O 2 has a specific capacity around 70 mAh g -1 at 4C current rate, whereas Li 1.2 Ni 0.20 Mn 0.48 Co 0.12 O 2 exhibits 113mAh g -1 at the same current rate. This result clearly demonstrates that Li 1.2 Ni 0.20 Mn 0.48 Co 0.12 O 2 has a better rate capability than Li 1.2 Ni 0.2 Mn 0.6 O 2 material. During cycling, an excessive average discharge voltage is also maintained for Li 1.2 Ni 0.20 Mn 0.48 Co 0.12 O 2 .