Novel Urea-Based Molecule Functioning as a Solid Electrolyte Interphase Enabler and LiPF6 Decomposition Inhibitor for Fast-Charging Lithium Metal Batteries

The practical application of lithium metal batteries is impeded by the growth of dendrites and decomposition of electrolytes especially at high temperature in normal carbonate-based electrolytes. Herein, a novel urea-based molecule, 1,3-dimethyl-2-imidazolidinone (DMI), with a high donor number is proposed, which exhibits an extraordinary solubility of LiNO₃ of over 5 M. As a result, a sufficient amount of LiNO₃ is readily introduced into the carbonate electrolytes with DMI as an additive, and an average coulombic efficiency of 99.1% for lithium plating/stripping is achieved due to a stable solid electrolyte interphase (SEI) rich in inorganic-rich lithium salts. The Li||Li symmetric cell achieves a stable operation for over 2500 h at 0.5 mA cm^-2 and 1 mAh cm^-2, and a granular shape of deposited Li metal is still preserved even at a high current density of 10 mA cm^-2. Besides, the decomposition of LiPF₆ is inhibited benefiting from its enhanced dissociation after the addition of DMI/LiNO₃ and DMI's function as a PF₅ scavenger. Consequently, the Li||LiFePO₄ cell succeeds to achieve an excellent capacity retention of 95.6% after 2200 cycles at a high rate of 5C, and a stable operation is realized at a high temperature of 60 °C even under harsh conditions (45 μm ultrathin Li and ∼1.5 mAh cm^-2 LiFePO₄). This work enriches the solvents and additives pool for stable and high-performance lithium metal batteries and will shed light on future developments of advanced battery electrolytes.