Influence of Li content on the structure and electrochemical performance of Li1+xNi0.25Mn0.75O2.25+x/2 cathode for Li-ion battery

The cathode materials of Li1+xNi0.25Mn0.75O2.25+x/2 (x = 0, 0.1, 0.2, 0.3, 0.4 and 0.5) with different content of lithium have been synthesized in this paper. The materials with different lithium content show distinct differences in structure and charge/discharge characteristics. The layered-spinel composite structure has been detected in the Li1+xNi0.25Mn0.75O2.25+x/2 electrodes, when the lithium content is lower than 1.5. The coulomb efficiency of Li1+xNi0.25Mn0.75O2.25+x/2 electrode is increased with the content of lithium decreasing. The cyclic and rate performances of layered-spinel composite electrodes Li1+xNi0.25Mn0.75O2.25+x/2 (0 ≤ x ≤ 0.4) are better than that of layered Li1.5Ni0.25Mn0.75O2.5. Among the layered-spinel composite electrodes, Li1.3Ni0.25Mn0.75O2.4 electrode shows the best capacity retention (98.2% for 40 cycles) and rate capacity (102 mAh g−1 at 10 C), while that of Li1.5Ni0.25Mn0.75O2.5 are 94.5% for 40 cycles and 11 mAh g−1 at 10 C. Electrochemical impedance spectroscopy (EIS) results show that the charge transfer resistance (Rct) of Li1.3Ni0.25Mn0.75O2.4 electrode is lower than that of Li1.5Ni0.25Mn0.75O2.5. The enhanced cyclic and rate performances of Li1.3Ni0.25Mn0.75O2.4 cathode are attributed to the lower Rct, three-dimensional interstitial space of LiNi0.5Mn1.5O4 phase and the lower content of Li2MnO3 in Li1.3Ni0.25Mn0.75O2.4 cathode material.