Sacrificial Additive C60-Assisted Catholyte Buffer Layer for Li1+xAlxTi2–x(PO4)3-Based All-Solid-State High-Voltage Batteries

All-solid-state batteries with oxide electrolytes and high-nickel layered oxide cathodes (LiNixCoyMnzO2 and LiNixCoyAlzO2, x + y + z = 1, x ≥ 60%) have received widespread attention owing to their high energy density and high safety. However, they generally suffer from interfacial structural instability when coupled with solid-state electrolytes, which strongly diminishes the longevity of the battery. In this work, we propose adding a sacrificial additive C60 to the catholyte buffer layer between Li1.4Al0.4Ti1.6(PO4)3 (LATP) and LiNi0.8Co0.1Mn0.1O2 (NCM811) to enhance the electrochemical stability under high-voltage operating conditions. A uniform and robust cathode–electrolyte interphase (CEI) film enriched with LixPOyFz, LiPxFy, and C60Fn is spontaneously formed on the surface of the cathode particles. In addition, the NCM811/Li solid-state battery delivers a discharge capacity of 150.3 mAh g–1 with a retention of 85% after 200 charge–discharge cycles at 0.5 C. This study offers a practical approach toward realizing LATP-based all-solid-state high-voltage batteries characterized by exceptional cycling stability.