Strategic Approach to Diversify Design Options for Li-Ion Batteries by Utilizing Low-Ni Layered Cathode Materials

Over the past few years, considerable attention has been paid to high-Ni layered cathode materials for high-energy Li-ion batteries (LIBs); however, these materials intrinsically have low thermal stability. Alternatively, the high-voltage operation of low-Ni materials may be one of the attractive ways to provide various options for designing advanced LIBs. Here, the structural, electrochemical, and thermal properties of LiNi_0.5Co_0.2Mn_0.3O₂ (NCM523) and LiNi_0.80Co_0.15Al_0.05O₂ (NCA) are investigated by setting up the same initial discharge capacity. In the high-voltage region, NCM523 exhibits less anisotropic lattice distortion and maintains wider Li-ion channels than NCA. After long-term cycling, reduced Ni ions are observed near the cracks, grain boundaries, or between the primary particles in both materials, however, the chemical states of the Ni ions in NCA are more heterogeneously distributed, and the particle pulverization and microcrack propagation are more prominent; the structural integrity and electrochemical properties of the material are degraded. Moreover, the cyclability and thermal stability of NCM523 are superior to those of NCA, despite the higher charge cut-off voltage of the former. Therefore, the utilization of low-Ni layered cathode materials operated at high voltage is a strategic approach to expand the design factors of advanced LIBs.