New Nitrate Additive Enabling Highly Stable and Conductive SEI for Fast‐Charging Lithium Metal Batteries

Polyester‐based electrolytes formed via in situ polymerization, have been regarded as one of the most promising solid electrolyte systems. Nevertheless, it is still a great challenge to address the issue of their high reactivity with metallic lithium anode by optimizing the components and properties of solid electrolyte interphase (SEI). Herein, a new class of N‐containing additive, isopropyl nitrate (ISPN) that can be miscible with ester solvents is demonstrated, and a chemically stable and ion‐conductive LiF‐Li 3 N composite SEI is constructed. In addition, ISPN can induce the formation of anion‐enriched solvation structures and reduces the desolvation barrier of Li + , resulting in fast transport of Li + . With the addition of ISPN, ionic conductivity of the electrolyte has nearly doubled, reaching as high as 5.3 × 10 −4 S cm −1 . What's more, the LiFePO 4 (LFP)|ISPN‐PTA|Li cell exhibits exceptional cycle stability and fast charging capabilities, maintaining stable cycling for 850 cycles at 10 C rate. Even when paired with the high‐voltage cathode, the LiNi 0.6 Co 0.2 Mn 0.2 O 2 (NCM622)|ISPN‐PTA|Li cell achieves an impressive capacity retention of 97.59% after 165 cycles at 5 C. This study offers a novel approach for ester‐based polymer electrolytes, paving the way toward the development of stable and high‐energy Li metal battery technologies.