Synthesis of Single-Crystalline Ni-Rich Cathodes for Lithium-Ion Batteries With Superior High-Voltage Stability by Mo/Nb Dual Doping

Single-crystalline Ni-rich cathodes are promising candidates for high-energy density lithium-ion batteries due to their grain-boundary-free structures, which effectively reduce structural degradation associated with intergranular microcracks often seen in polycrystalline materials. However, these single-crystalline cathodes face challenges such as slow Li⁺ diffusion kinetics, significant parasitic interface reactions, and irreversible phase transitions at elevated cut-off voltages, which can lead to the formation of intragranular cracks and impede their practical usage. In this study, the single-crystalline LiNi_0.8Co_0.15Al_0.05O₂ (NCA) was synthesized by stripping grain boundaries from polycrystalline NCA through Mo/Nb dual doping. The Mo doping near the grain surface significantly reduces parasitic interface reactions, while Nb doping within the bulk of grains helps to improve harmful irreversible phase transitions. The synergistic effect of Mo/Nb dual doping in single-crystalline NCA effectively suppresses intragranular crack formation during prolonged cycling at high cut-off voltages. Therefore, the Mo/Nb co-doped cathode demonstrates enhanced structural stability and electrochemical activity, achieving an impressive capacity retention of 82.4% after 500 cycles at 1 C between 2.8 and 4.7 V, surpassing both polycrystalline and single-crystalline NCA doped only with Mo or Nb. This work provides a new strategy to synthesize single-crystalline NCA combined with effective dual doping, advancing the development of high-energy density lithium-ion batteries.