Electrochemical studies of spinel LiNi0.5Mn1.5O4 cathodes with different particle morphologies

Six spinel LiNi0.5Mn1.5O4 (LNMS) samples with different morphologies were synthesized via a PVP (polyvinylpyrrolidone)-assisted gel combustion method by varying the calcination temperature from 800 degrees C to 1050 degrees C. XRD tests were used to characterize the crystal structure and phase purity. SEM images clearly revealed the evolution of the particle size (from sub-micrometer to micrometer), shape and degree of agglomeration with increasing calcination temperature. Charge/discharge tests indicated that the LNMS samples composed of larger primary particles had better cyclic performance than those composed of smaller primary particles. Among the six samples. LNMS1050-6 (calcined at 1050 degrees C) and LNMS1000-6 (calcined at 1000 degrees C) demonstrated excellent capacity retentions of 97.6% and 97.3%, respectively, after 200 cycles with a 1 C rate at room temperature. The cyclic performance of LNMS1050-6 and LNMS1000-6 at 55 degrees C was also remarkable, showing capacity retentions of 97.1% and 96.0%, respectively, after 50 cycles at a 1 C rate. Rate capability tests indicated that among the six LNMS samples, the single-crystal-like LNMS1000-6 with a moderate particle size (1-3 mu m) showed the best rate capability. It delivered 132.9 mAh g(-1), 130.2 mAh g(-1), 128.1 mAh g(-1) and 124.5 mAh g(-1) at rates of 1 C, 5 C, 10 C and 15 C, respectively. Electrochemical impedance spectroscopy (EIS) measurements showed that larger primary particles exhibited slower interface impedance increases upon cycling than smaller particles. (C) 2012 Elsevier Ltd. All rights reserved.