Dual modification of single-crystal Ni-rich cathodes for enhanced thermal safety in pouch cells

The trade-off between high energy density and thermal safety in nickel-rich cathodes remains a critical challenge for lithium-ion batteries. This study presents a dual-modification strategy combining fluorine (F⁻) doping with LiCoO₂ (LCO) coating to improve the thermal stability of single-crystalline LiNi_0.83Co_0.12Mn_0.05O₂ (SCNCM). We show that F⁻ doping enhances bulk stability by substituting oxygen and forming strong TM–F and Li–F bonds, while the LCO coating suppresses interfacial side reactions. In-situ XRD and DSC-TG-MS analyses indicate that the modified material exhibits delayed phase transitions and reduced oxygen release, due to suppressed cation migration and improved oxygen lattice stability. Accelerating rate calorimetry tests confirm that pouch cells using the modified cathode achieve a 45 °C higher onset thermal runaway temperature (T₂) and a 70 °C lower peak temperature (T₃), along with reduced oxygen gas emission. Furthermore, the dual-modified cathode retains 91.5 % capacity after 450 cycles at 0.33C, matching the performance of pristine SCNCM without compromising rate capability. This work demonstrates the synergistic role of bulk doping and surface coating in balancing energy density and thermal safety, providing a viable approach to developing advanced Ni-rich cathodes for high-performance LIBs.