Improved electrochemical performance of LiNi0.8Co0.1Mn0.1O2 cathode materials via incorporation of rubidium cations into the original Li sites

Abstract

Layered Rb_xLi_(1−x)Ni_0.8Co_0.1Mn_0.1O₂ (x = 0, 0.005, 0.01, 0.02) materials were synthesized with different Rb concentrations using a solid state reaction method. All the materials were calcined at 800 °C for 12 h in a flowing oxygen atmosphere using NiO, CoO, MnO₂, Rb₂CO₃ and LiOH·H₂O as the raw materials. The influences of the amount of Rb⁺ ions in the cathodes on the electrochemical performance were investigated in detail. It was found from the results that the electrochemical performances of Rb doped materials were greatly improved. Among them the Rb0.5% sample presented the best performance; it delivered an initial discharging capacity of 188.9 mA h g⁻¹ at 0.5C, improved by 13.52% when compared with that of a sample without Rb. A capacity retention of 88.9% after 100 cycles and an excellent high-rate performance of 152.3 mA h g⁻¹ at 5C rate were also recorded for the same sample. The Li⁺ ion diffusion coefficient calculated from EIS turned out a value of 1.14 × 10⁻¹⁰ cm² s⁻¹, which is 3.42 times that of the non-doped sample. Both the enhanced performance and the accelerated Li⁺ ion diffusion could be explained by the changes in crystal structures. XRD whole pattern refinement revealed that the Rb⁺ ions were incorporated into the lattice by replacing the original Li⁺ ions, which resulted in reduced ionic mixing and the expansion in the c axis that led to the enhanced electrochemical performance. As a whole, incorporation of Rb in LiNi_0.8Co_0.1Mn_0.1O₂ by this approach showed great potential to serve as a promising cathode material for future applications.