Uracil-Based Additives for Enabling Robust Interphases of High-Voltage Li-Ion Batteries at Elevated Temperature by Substituent Effects

Rational chemical structures of solid electrolyte interphase (SEI) films play a key role in high-energy-density batteries, especially working at high-voltage and high-temperature conditions. Herein, uracil (UC) and 2-thiouracil (TUC) as bifunctional electrolyte additives, collectively called UC-based additives, have been employed in the LiNi0.5Co0.2Mn0.3O2 ǁgraphite pouch cell operated with an elevated upper cutoff voltage of 4.5 V vs. Li+/Li for precisely tailoring the SEI films. The presence of these additives in the baseline electrolytes are preferentially decomposed and induce to form interphases on both electrodes. Moreover, the SEI layers can be further optimized via tuning rational substituent of the UC-based additives. As a result, the UC-induced SEI films exhibit the most suitable and robust microstructures on both electrodes, leading to inhibit the gas generation, protecting the structural stability of both cathode and anode materials, and mitigating transition metal ion dissolution at the cathode and deposition on the anode surface. In this contribution, the pouch full cell containing 0.3 wt% UC has high capacity retention of 93.1% after 180 cycles at 45 oC. The related SEI-forming mechanisms are also proposed and studied in this work, which can facilitate the investigation of efficient multifunctional electrolyte additives for high-voltage Li-ion batteries.