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 Li1.2Ni0.13Mn0.54Co0.13–xO2 (x = 0.03, 0.05) and Li1.2Ni0.13Mn0.54–xCo0.13O2 (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 Li1.2Ni0.13Mn0.54Co0.13O2 (LNMCO) and Fe-doped materials such as Li1.2Ni0.13Mn0.54Co0.10Fe0.03O2 (LNMCF0.03O), Li1.2Ni0.13Mn0.54Co0.08Fe0.05O2 (LNMCF0.05O), and Li1.2Ni0.13Mn0.49Fe0.05Co0.13O2 (LNMF0.05CO) 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 LNMF0.05CO
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 LNMCF0.05O and LNMF0.05CO have better cycling stability,
low voltage fade, and better rate capability than pristine LNMCO and
LNMCF0.03O materials. In the full cell, the pristine LNMCO
and LNMCF0.05O 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.