Comparison of monocrystalline and secondary LiNi_0.5Co_0.2Mn_0.3O₂ cathode material for high-performance lithium-ion batteries

Secondary(S-NCM) and monocrystalline (M-NCM) LiNi_0.5Co_0.2Mn_0.3O₂ cathode materials were prepared via synthesizing Ni-Co-Mn hydroxide precursors following by heat treatment operations. The materials of S-NCM and M-NCM are characterized by various means in order to describe the microstructure in detail, such as X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and transmission electron microscope (TEM). The results of the physical characterization and electrochemistry measurement identify that the 3-4 μm thick monocrystalline cathode materials exhibit lower cation mixture and avoid the cracks of the particles. Electrochemical performance tests were taken at the various voltage of 3.0–4.3/4.4 V under different temperatures (25 °C and 45 °C) respectively. The electrodes of S-NCM always show higher discharge capacity than that of M-NCM at 0.1–2 C, while the electrochemical performances of M-NCM electrode become better at a high rate (5 C), especially at a high temperature (45 °C). The M-NCM electrode reaches 101.4 mAh g⁻¹ (61.9%, 3.0–4.3 V, 258 cycles), 112.7 mAh g⁻¹ (63.4%, 3.0–4.4 V, 258 cycles), which exhibits better electrochemistry performance than that of S-NCM sample, demonstrating the expected properties of the micron-sized single crystal cathode. In addition, the single crystal cathode materials can alleviate side reactions and keep up the layered structures stability during the charging/discharging process. It is testified that the M-NCM cathode materials are propitious for LIBs with long-life and high-rate, and the S-NCM cathode has better performances at 3C digital products.