The Effects of Ru4+ Doping on LiNi0.5Mn1.5O4 with Two Crystal Structures

Doping of Ru has been used to enhance the performance of LiNi0.5Mn1.5O4 cathode materials. However, the effects of Ru doping on the two types of LiNi0.5Mn1.5O4 are rarely studied. In this study, Ru4+ with a stoichiometric ratio of 0.05 is introduced into LiNi0.5Mn1.5O4 with different space groups (Fd3¯m, P4332). The influence of Ru doping on the properties of LiNi0.5Mn1.5O4 (Fd3¯m, P4332) is comprehensively studied using multiple techniques such as XRD, Raman, and SEM methods. Electrochemical tests show that Ru4+-doped LiNi0.5Mn1.5O4 (P4332) delivers the optimal electrochemical performance. Its initial specific capacity reaches 132.8 mAh g-1, and 97.7% of this is retained after 300 cycles at a 1 C rate at room temperature. Even at a rate of 10 C, the capacity of Ru4+-LiNi0.5Mn1.5O4 (P4332) is still 100.7 mAh g-1. Raman spectroscopy shows that the Ni/Mn arrangement of Ru4+-LiNi0.5Mn1.5O4 (Fd3¯m) is not significantly affected by Ru4+ doping. However, LiNi0.5Mn1.5O4 (P4332) is transformed to semi-ordered LiNi0.5Mn1.5O4 after the incorporation of Ru4+. Ru4+ doping hinders the ordering process of Ni/Mn during the heat treatment process, to an extent.