Improved Charge Storage Performance of Fe-Doped Li-Rich Ni–Mn–Co Oxide Li_1.2Ni_0.13Mn_0.54Co_0.13O₂ in Half- and Full Lithium-Ion Cells

Layered Li- and Mn-rich (LMR) oxides are considered as major/foremost charge storage materials for Li-ion cells due to their remarkable charge storage capacities of ≥250 mAh g^–1. Despite this, they face the challenges of capacity and discharge potential fading after extensive cycling, which may arise due to the conversion of layered material to spinel and the movement of transition metals to the alkali metal layer. Herewith, Fe-substituted LMR oxide materials Li_1.2Ni_0.13Mn_0.54Co_0.13–xO₂ (x = 0.03, 0.05) and Li_1.2Ni_0.13Mn_0.54–xCo_0.13O₂ (x = 0.05) are prepared by using the sol–gel synthesis and annealing at a temperature of 900 °C for 12 h. The charge storage performance of pristine Li_1.2Ni_0.13Mn_0.54Co_0.13O₂ (LNMCO) and Fe-doped materials such as Li_1.2Ni_0.13Mn_0.54Co_0.10Fe_0.03O₂ (LNMCF_0.03O), Li_1.2Ni_0.13Mn_0.54Co_0.08Fe_0.05O₂ (LNMCF_0.05O)_, and Li_1.2Ni_0.13Mn_0.49Fe_0.05Co_0.13O₂ (LNMF_0.05CO) has been investigated by galvanostatic charge–discharge cycling, where they possess charge storage capacities of around 264, 266, 235, and 255 mAh g^–1, respectively, when cycled at 20 mA g^–1 (C/10) with capacity retention values of 69.8, 68.3, 90.7, and 81.5% after completing 140 cycles at C/5 rate. Thus, the substitution of Co or Mn with Fe improves the electrochemical cycling stability. Among all these four samples, Fe-substituted material LNMF_0.05CO demonstrates a superior rate capability compared to others. Interestingly, the fading of discharge voltage is found to be less in the case of Fe-substituted materials. These results demonstrate that LNMCF_0.05O and LNMF_0.05CO have better cycling stability, low voltage fade, and better rate capability than pristine LNMCO and LNMCF_0.03O materials. In the full cell, the pristine LNMCO and LNMCF_0.05O materials exhibit storage capacities of 266.2 and 230.0 mAh g^–1, respectively, in the initial cycle at C/10 rate (1.8–4.7 V), and the capacity retention values are found to be around 76.2 and 90.9% after 200 cycles upon cycling at a C/2 rate, thus demonstrating the significant improvement in the electrochemical performance upon substitution of Co with Fe.