Sacrificial Additive C₆₀-Assisted Catholyte Buffer Layer for Li_1+<i>x</i>Al_<i>x</i>Ti_2–<i>x</i>(PO₄)₃-Based All-Solid-State High-Voltage Batteries

All-solid-state batteries with oxide electrolytes and high-nickel layered oxide cathodes (LiNi_<i>x</i>Co_<i>y</i>Mn_<i>z</i>O₂ and LiNi_<i>x</i>Co_<i>y</i>Al_<i>z</i>O₂, <i>x</i> + <i>y</i> + <i>z</i> = 1, <i>x</i> ≥ 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 Li_1.4Al_0.4Ti_1.6(PO₄)₃ (LATP) and LiNi_0.8Co_0.1Mn_0.1O₂ (NCM811) to enhance the electrochemical stability under high-voltage operating conditions. A uniform and robust cathode-electrolyte interphase (CEI) film enriched with Li_<i>x</i>PO_<i>y</i>F_<i>z</i>, LiP_<i>x</i>F_<i>y</i>, and C₆₀F_<i>n</i> 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.