Li-ion batteries (LIBs) have been widely used in portable electronic devices and electric vehicles due to their high specific energy, cyclic stability, and low environmental pollution [1] [2] . Especially, Nickel-cobalt-manganese ternary cathode material has become the largest incremental LIBs cathode material in the global market due to its advantages of high specific capacity. In recent years, the demand for energy density has gradually increased, so the focus of cathode material is on the nickel-rich ternary material, high voltage ternary material and high compacted density ternary material [3] . In applications, such as in the new energy vehicle market, high-nickel multi-element cathode materials and high voltage ternary materials are gradually improving their price/performance ratio by increasing their nickel content while reducing their cobalt content. However, they still face challenges, such as poor structural stability, surface microcracks and particle fragmentation, rapid decay in cycle life, poor thermal stability, and poor safety performance [4] - [12] . In addition, since the structure of spherical particles, namely the secondary particles, is inevitably fractured during the electrode rolling and the repetitive lithiation/delithiation process as a result of transient diffusion. Compared with the single crystal large particles of lithium cobalt oxide material, the ternary cathode material belongs to the small agglomerates (≤0.5 µm), the compacted density (≤3.5 g/cm³) is lower, and the energy density cannot be effectively improved. Thus, it is of significance to understand the inner structures of agglomerates.

In this study, the inner structure of agglomerates is investigated, which refers to the arrangement of plate-like primary particles in the secondary particles. The Nickel-cobalt-manganese ternary cathode material with a larger size of the inner structure of agglomerates (~2 µm) is prepared, which can not only enhance the density of the secondary spherical particles, but also improve the compaction density (~3.70 g/cm³). Therefore, the larger size of the inner structure of agglomerate has a more complete crystal structure, showing a better electrochemical performance.

Synthesis of Materials. The spherical precursor Ni_0.5Co_0.2Mn_0.3(OH)₂ was synthesized by a modified co-precipitation method. Briefly, proper amounts of NiSO₄, CoSO₄ and MnSO₄ (cationic ratio of Ni:Co:Mn = 5:2:3) were added to a strongly stirred tank reactor under nitrogen atmosphere, forming 2.0 mol∙L⁻¹ solution. 4.0 mol∙L⁻¹ NaOH solution and 2.0 mol∙L⁻¹ ammonia were added at the same time. The obtained precursor was then dried at 100˚C for 12 h in the air. After drying, the precursor and Li₂CO₃, MgO were ball milled for 6 h. The Li/TM molar ratio was fixed at 1.05. Meanwhile, Mg element at 0%, 0.10%, 0.15%, 0.20%, 0.25% stoichiometric ratio was added. The cathode material was heated to 500˚C at a rate of 3˚C/min, then to 900˚C at a rate of 2˚C/min and finally calcined for 12 h. For comparison, the different samples were heated to 910˚C, 920˚C at a heating rate of 2˚C/min, respectively. Three cathode materials were denoted as NCM-1, NCM-2 and NCM-3.

The post-treated LiNi_0.5−xCo_0.2Mn_0.3Mg_xO₂ was pulped, filtered, washed, dried, broken and sieved under the solid-liquid ratio (1:5); After sifting, LiNi_0.5−xCo_0.2 Mn_0.3Mg_xO₂ was heated to 910˚C at a rate of 2˚C/min and finally calcined for 8 h. By comparison, the different samples were heated to 930˚C, 950˚C at a heating rate of 2˚C/min and finally calcined for 8h, respectively. Three cathode materials were denoted as NCM-4, NCM-5 and NCM-6. The powder with high pressure solid density was obtained by air flow crushing.

Materials Characterization. The particle size distribution was measured on a laser diffraction instrument (Malvern Mastersizer 3000, Malvern, UK) with dynamic light scattering methods. The sample structures were identified by using powder X-ray diffraction (XRD, Cu Ka radiation, Bruker D8 Advance). The morphology and element distribution were analyzed using a scanning electron microscope (SEM, JSM-6700F) equipped with an energy dispersive spectrometer (EDS, Horiba, EX-250). The metal ion content was determined by the inductively coupled plasma atomic emission spectrometry (ICP-AES).

Electrochemical Tests. The working electrode was prepared by mixing active materials (LiNi_0.5−xCo_0.2Mn_0.3Mg_xO₂, 85 wt%), carbon black conductive additive (Super P, 8 wt%), and polyvinylidene fluoride binder (PVDF, 7 wt%) dissolved in N-methylpyrrolidone (NMP). The slurry was then casted on aluminum foil and followed by drying at 120˚C for 24 h in vacuum oven. Electrolyte was a mixture of ethylene carbonate (EC) and dimethyl carbonate (DMC) containing lithium hexafluorophosphate (LiPF₆) and Celgard 2400 film was used as separator. The cells were assembled in an argon-filled glove box with H₂O and O₂ concentrations below 0.1 ppm. All the electrochemical performances were performed on a LAND CT2001A (Wuhan, China) battery program-control test system between 3.0 and 4.3 V at different charge/discharge rate 0.2C/0.2C and 1C/1C (1C = 150 mAh∙g⁻¹) at 23 ± 2˚C.

In this paper, the high compacted density LiNi_0.4985Co_0.2Mn_0.3Mg_0.0015O₂ cathode material for lithium-ion batteries has been prepared. XRD results reflect that the cathode material shows good crystallinity and layered structure. SEM reveals that the cathode material delivers good sphericity and concentrated particle size distribution. The compacted density of the electrode plate is above 3.68 g/cm³. Electrochemical tests show that it exhibits a better cycle performance of more than 97.5% capacity retention after 100 cycles at 1C.

The authors acknowledge funding support from the Key Research and Development Program of Lanzhou Resources and Environment Voc-Tech University (No. X2022ZD-07), and Natural Science and technology development guidance plan Fund Project of Lanzhou (No. 2022-ZD-149).

The authors declare no conflicts of interest regarding the publication of this paper.

Zhi, F.P., Wang, J.H., Zhang, X.M. and Zhang, J. (2024) Research on Preparation and Electrochemical Performance of the High Compacted Density Ni-Co-Mn Ternary Cathode Materials. Advances in Materials Physics and Chemistry, 14, 47-53. https://doi.org/10.4236/ampc.2024.143004