Influence of Li content on the structure and electrochemical performance of Li_(1-x)Ni_(0.25)Mn_(0.75)O_(2.25+x/2) cathode for Li-ion battery

摘要

The cathode materials of Li_(1-x)Ni_(0.25)Mn_(0.75)O_(2.25+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 Li_(1-x)Ni_(0.25)Mn_(0.75)O_(2.25+x/2) electrodes, when the lithium content is lower than 1.5. The coulomb efficiency of Li_(1-x)Ni_(0.25)Mn_(0.75)O_(2.25+x/2) electrode is increased with the content of lithium decreasing. The cyclic and rate performances of layered-spinel composite electrodes Li_(1-x)Ni_(0.25)Mn_(0.75)O_(2.25+x/2) (0 ≤ x ≤ 0.4) are better than that of layered Li_(1.5)Ni_(0.25)Mn_(0.75)O_(2.5). Among the layered-spinel composite electrodes, Li_(1.3)Ni_(0.25)Mn_(0.75)O_(2.4) electrode shows the best capacity retention (98.2% for 40 cycles) and rate capacity (102 mAh g~(-1) at 10 C), while that of Li_(1.5)Ni_(0.25)Mn_(0.75)O_(2.5) 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 (R_(ct)) of Li_(1.3)Ni_(0.25)Mn_(0.75)O_(2.4) electrode is lower than that of Li_(1.5)Ni_(0.25)Mn_(0.75)O_(2.5) The enhanced cyclic and rate performances of Li_(1.3)Ni_(0.25)Mn_(0.75)O_(2.4) cathode are attributed to the lower R_(ct), three-dimensional interstitial space of LiNi_(0.5)Mn_(1.5)O_4 phase and the lower content of Li_2MnO_3 in Li_(1.3)Ni_(0.25)Mn_(0.75)O_(2.4) cathode material.