Interfacial Engineering Using a Thiophene-based Electrolyte Additive for High-Voltage Lithium-Ion Batteries

Ni-rich layered oxides, such as LiNi0.8Co0.1Mn0.1O2 (NCM811), are increasingly favored for high-energy-density lithium-ion batteries (LIBs) with long lifespans. However, the electrochemical performance of NCM811 cathodes significantly deteriorates at elevated temperatures and high voltages exceeding 4.3 V vs. Li/Li+. In this study, we present 2,5-dimethyl-3-(phenylsulfonyl)thiophene (DMPST) as an electrolyte additive, creating thermally and electrochemically stable interfaces on electrodes. The electron-rich sulfonyl motif of DMPST attracts Li+ ions, generating free PO2F2– anions and promoting the creation of a cathode electrolyte interphase (CEI) upon the addition of LiPO2F2. DMPST also forms a dual-layered solid electrolyte interphase with a P–O-rich outer layer and a sulfur-rich inner layer, mitigating the graphite anode degradation in full cells. The thiophene moiety in DMPST constructs a polymer-like CEI in conjunction with LiPO2F2, which adeptly accommodates volumetric stresses associated with high delithiation processes at 4.5 V. This mitigates transition metal leaching and reduces crosstalk in NCM811/graphite cells. The synergistic application of LiPO2F2 and DMPST enables exceptional capacity retention, demonstrating 73.5% (135.2 mAh g–1) after 500 cycles at 4.5 V and 25 °C, and 78.4% (142.7 mAh g–1) after 500 cycles at 4.2 V and 45 °C. This study provides valuable insights into the design of electrolyte additives for operation under high temperatures and high voltages, grounded in a fundamental understanding of LIB degradation mechanisms.