Dual-electrode interphase engineering via a fluorinated sulfonate additive for high-performance lithium-ion batteries

High-voltage LiCoO 2 /graphite batteries suffer from severe interfacial degradation-unstable solid electrolyte interphase (SEI) on graphite and structural degradation with cobalt dissolution on LiCoO 2 -limiting long-term cycling stability. In this work, a highly fluorinated electrolyte additive, 2,2,2-trifluoroethyl trifluoromethanesulfonate (TTMS), is incorporated into a commercial carbonate electrolyte (1M LiPF 6 in DEC/EC/EMC, 2:3:5 by mass) to regulate electrode-electrolyte interfacial chemistry and enhance cell durability. Theoretical calculations and electrochemical characterization show that TTMS possesses a high reduction potential, enabling its preferential decomposition on graphite to form a stable, Li + -conductive and low-impedance SEI. Concurrently, TTMS undergoes oxidative decomposition on LiCoO 2 , constructing a robust cathode-electrolyte interphase (CEI) enriched in fluorinated and sulfonate-derived species that suppress cobalt dissolution and alleviate electrode polarization. Benefiting from coordinated SEI/CEI stabilization, Li/graphite half-cells with TTMS retain 320.8 mAh·g −1 after 400 cycles (99.8%), while Li/LiCoO 2 cells achieve 84.8% capacity retention after 250 cycles at 1C, markedly outperforming the baseline electrolyte (52.1%). Furthermore, LiCoO 2 /graphite pouch cells with 3% TTMS exhibit an approximately 20% improvement in capacity retention after 200 cycles at 1C. Overall, TTMS functions as a versatile, dual-electrode interphase-forming additive that simultaneously stabilizes anode and cathode interfaces, thus greatly boosting the cycle life and practical applicability of carbonate-based Li-ion batteries.