Ultra-Soluble 1-Azaphenothiazine Additive Stabilizes High-Voltage LiCoO₂ for 500 Wh Kg^-1 Lithium Metal Pouch Cells

High-voltage LiCoO₂ is a promising cathode candidate for achieving high-energy lithium metal pouch cells. However, further application is still hindered by irreversible structural degradation and severe interfacial side reactions that accelerate capacity decay. Herein, 1-Azaphenothiazine (1-APT) is incorporated as a cathode slurry additive (1 g mL^-1 in N-methyl-2-pyrrolidone) to promote the optimization of the LiCoO₂ interface during the electrode coating process. The ultra-soluble 1-APT promotes the formation of inorganic-rich components within the cathode-electrolyte interphase (CEI), mitigates the reaction of Co⁴⁺ with the electrolyte, and enhances the interfacial stability of LiCoO₂, thereby enabling 4.7 V LiCoO₂ with an initial capacity of 229.8 mAh g^-1 and 73.2% capacity retention after 200 cycles. More importantly, Li||LiCoO₂-1-APT pouch cells exhibit remarkable electrochemical performance, achieving specific energies of 515.7 , 497.4 , and 484.9 Wh kg^-1 at discharge rates of 0.5C, 1C, and 2C, respectively. Notably, the 5 Ah pouch cell exhibited the capability to maintain an energy density of 411.4 Wh kg^-1 after 100 cycles at 0.5C. This work presents a practical and effective strategy for optimizing cathode interfaces, thereby enabling the stabilization of high-voltage cathodes.