Enhancement of performance and kinetics of layered Li2MnO3 by Fe doping

Layered Li2MnO3 exhibits great potential as a high-capacity cathode used in lithium-ion batteries, but materials synthesized by traditional solid-phase methods exhibit poor activity and poor cycling stability. In this work, Li2MnO3 nanoparticles were synthesized by solid state method combined with high-energy ball milling, in which Fe was doped at transition metal sites to obtain a Li-rich cathode material (Li1.32Fe0.034Mn0.64O2). We systematically studied the effects of Fe doping and calcination temperature on the crystal structure and electrochemical properties and conducted kinetic studies using the galvanostatic intermittent titration technique (GITT), electrical impedance spectroscopy (EIS) and density functional theory (DFT) calculations. Our results demonstrate that the performance was significantly improved, its discharge capacity is about 235 mAh g−1 after 10 cycles compared 138 mAh g−1 of the pristine sample. The GITT and EIS results show that the Fe-doped sample had smaller charge transfer impedance, larger lithium-ion diffusion coefficient and lower internal polarization than the pristine. The activation energy results show the Fe-doped sample has larger activation energy at the late discharging period due to the anion redox reaction activation, indicting its O activation is more active than Li2MnO3. Moreover, the DOS results showed that the Fe-doped sample had a narrow band-gap, indicating good electrical conductivity. The CI-NEB results showed that the Fe-doped sample had a high transition metal ion migration energy barrier, indicating that its structure was stable. In conclusion, Fe doping is helpful to active the anion redox reaction in Li2MnO3 and improve its electrochemical performance as a low cost and high-capacity cathode materials.