Molecular engineering of a nitrate ester additive for ultrastable Ni-rich NCM811 cathodes via anion-rich solvation-structure

Despite their promise for high-energy-density lithium-ion batteries, Ni-rich layered oxide cathodes (e.g., NCM811) face limited application due to interfacial instability from irreversible phase transitions and an unstable CEI at high voltages. Here, we innovatively design a novel organic nitrate additive, 2-ethylhexyl nitrate (2EHN) to address above-mentioned issues. The key innovation lies in molecularly integrating a terminal nitrate group into an organic solvent. It overcomes the poor solubility limitations of conventional LiNO₃ while effectively mimicking its beneficial interface-stabilizing effects. 2EHN features a low HOMO energy level, enhancing oxidation stability, and promotes an anion-aggregated solvation structure, leading to the formation of a thin, uniform, and inorganic-rich cathode-electrolyte interphase (CEI). This optimized CEI, enriched with nitrogen-containing species (e.g., LiN x O y ), effectively suppresses irreversible phase transitions, electrolyte decomposition, and transition metal dissolution. Consequently, cells with the 2EHN-modified electrolyte exhibit significantly improved cycling stability (a capacity retention of 92.2% after 600 cycles at room temperature (3.0–4.3 V, 1/3 C) and 89.9% after 200 cycles at 55°C), rate capability, and thermal safety. At pouch cell level, by using the proposed electrolyte, 1 Ah NCM811||Graphite pouch cell delivers a high-capacity retention of 96.8% after 200 cycles. This work provides a practical electrolyte engineering strategy for next-generation high-energy-density lithium-ion batteries.