Uracil-based additives for enabling robust interphases of high-voltage Li-ion batteries at elevated temperature by substituent effects

Abstract

Rational chemical structures of solid electrolyte interphase (SEI) films play a key role in high energy density batteries, especially those 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 LiNi_0.5Co_0.2Mn_0.3O₂‖graphite pouch cell operated with an elevated upper cutoff voltage of 4.5 V vs. Li⁺/Li for precisely tailoring the SEI films. The additives present in the baseline electrolytes is preferentially decomposed and induces the formation of interphases on both electrodes. Moreover, the SEI layers can be further optimized by tuning the 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 inhibition of the gas generation, thus, protecting the structural stability of both cathode and anode materials, and mitigating the transition metal ion dissolution at the cathode, and deposition on the anode surface. In this research, the pouch full cell containing 0.3 wt% UC has a high capacity retention of 93.1% after 180 cycles at 45 °C. The related SEI-forming mechanisms are also proposed and studied in this work, and this facilitates the investigation of efficient multifunctional electrolyte additives for high-voltage Li-ion batteries.