Synthesis of LiCr0.2Ni0.4Mn1.4O4 with superior electrochemical performance via a two-step thermo polymerization technique

We synthesize LiCr0.2Ni0.4Mn1.4O4 cathode materials by two-step and one-step polymerization methods, and investigate the differences in structures and electrochemical performances of the materials according to these two ways. The physical properties and electrochemical performances of products are analyzed by many characterization methods including thermal gravimetric analysis (TG), X-ray diffraction (XRD), scanning electron microscopy (SEM), particle size analysis, galvanostatic charge–discharge test, cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The results show that LiCr0.2Ni0.4Mn1.4O4 particles prepared via two-step process possess pure spinel phase with Fd3m space group, and uniform size distribution with no obvious agglomeration. It exhibits an initial discharge capacity of 145.5 mAh g−1 at 1 C (1 C = 140 mA g−1), and a stable cycling performance demonstrated by exceeding 140 mAh g−1 after 100 cycles. Besides, a discharge capacity of 128.7 and 111.6 mAh g−1, with high capacity retention of 88.5% and 76.7% relative to 1 C, is gained at 10 C and 20 C at room temperature (25 °C), respectively. Such good performances can be attributed to the higher Li+ diffusion coefficient of 4.37 × 10−11 cm2 s−1 by calculation from EIS. The cyclic voltammetry and electrochemical impedance spectroscopy test results confirm that lithium-ion cells assembled by the two-step sample as positive electrode exhibit lower polarization and impedance than those of one-step sample.