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 °C to 1050 °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 °C) and LNMS1000-6 (calcined at 1000 °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 °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 μm) 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.

► LiNi0.5Mn1.5O4 with different morphologies was obtained by firing at 800–1050 °C.
► Single-crystal-like micrometric particles were got at 1000 °C and 1050 °C.
► Best capacity retention of 97.1% after 50 cycles at 55 °C.
► Best rate capability of discharging 124.5 mAh g−1 at 15 C rate.
► Larger primary particles showed slower interfacial impedance evolution.