Influence of Ru substitution on Li-rich 0.55Li2MnO3·0.45LiNi1/3Co1/3Mn1/3O2 cathode for Li-ion batteries

Li-rich cathode 0.55Li2MnO3·0.45LiNi1/3Co1/3Mn1/3O2 or written in a solid solution form Li(Li0.20Mn0.54Ni0.13Co0.13)O2 doped with trace Ru is synthesized using a traditional co-precipitation method. The structural and morphological characterizations are carried out by employing inductively coupled plasma emission spectrometry (ICP), X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM). Ru doping causes variation of lattice constants in both Li2MnO3 and LiNi1/3Co1/3Mn1/3O2 components according to the results of Rietveld refinement. Electrochemical measurement shows that Li(Li0.19Mn0.54Ni0.13Co0.12Ru0.01)O2 possesses the best performance, especially at high rate. A discharge capacity as high as 182 mAh g−1 at a current density of 500 mA g−1 (2 C) is achieved with a capacity fade of as low as 0.06% per cycle in the following 700 cycles. Such improvement is associated with the prominent appearance of spinel-like regions transferred from the original Li2MnO3 component in which Ru facilitates the phase transformation via enhancing the ability of Li diffusion in both Li2MnO3 and LiNi1/3Co1/3Mn1/3O2 components. The improvement in Li diffusion is also confirmed from the electrochemical impedance spectroscopy (EIS) analysis.

► We synthesized Ru-doped Li-rich Li(Li0.2−xMn0.54Ni0.13Co0.13−xRux)O2.
► Modified Li(Li0.19Mn0.54Ni0.13Co0.12Ru0.01)O2 exhibits significantly-improved rate and cycle performance.
► Increase in electrochemical performance is caused by increase of interslab distance and reduction of Li2MnO3-like regions.
► Spinel-like phase transformation is also facilitated by Ru doping.