Effect of particle size on rate capability and cyclic stability of LiNi_0.5Mn_1.5O₄ cathode for high-voltage lithium ion battery

Abstract

LiNi_0.5Mn_1.5O₄ samples with their particle sizes from micro to nano are synthesized via polyvinylpyrrolidone (PVP)-assisted coprecipitation of nickel and manganese hydroxide. Their morphology, structure, and performance as cathode of high-voltage lithium ion battery are investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and charge/discharge test. The characterizations from SEM and XRD show that the particle size of the resulting LiNi_0.5Mn_1.5O₄ is tunable from micro to nano by controlling the concentrations of PVP for the formation of nickel and manganese hydroxide precursor. The results from CV, EIS, and charge/discharge test reveal that reducing the particle size of LiNi_0.5Mn_1.5O₄ results in its less interfacial resistance for lithium insertion/desertion process, leading to its improved rate capability. Meanwhile, the cyclic stability of LiNi_0.5Mn_1.5O₄ is also improved when its particle size is changed from micro to nano, but too smaller particle size is not beneficial to its cyclic stability, especially at elevated temperature. When evaluated in LiNi_0.5Mn_1.5O₄/Li half cell, the resulting LiNi_0.5Mn_1.5O₄ samples of 800, 250, and 125 nm, in average, deliver a 20 C rate capacity of 40, 58, and 71 mAh g⁻¹, while they exhibit a capacity retention of 79, 89, and 82 % after 250 cycles with 0.5 C rate at room temperature and 33, 77, and 64 % after 200 cycles with 1 C rate at 55 °C, respectively. This difference in capacity retention becomes more significant in LiNi_0.5Mn_1.5O₄/graphite full cells due to the effect of graphite anode.