Dual‑salt electrolyte design enabled by synergistic solvation and interfacial regulation for fast charging of lithium‑ion batteries

To address the performance limitations of conventional LiPF6-carbonate electrolytes under extreme temperatures and high-rate charging, lithium difluoro(oxalato)borate (LiDFOB) is introduced into the LiPF6-carbonate electrolyte to form a dual-salt system. The optimization mechanism enhancing the fast-charging capability of LiNi0.52Co0.2Mn0.28O2 (NCM523) cathode is systematically explored. Molecular dynamics simulations and electrochemical characterization demonstrate the reconstruction of Li+ solvation structures, expanding the voltage window and reducting Li+ desolvation barriers. In addition, the incorporation of LiDFOB induces the generation of a LiF/LixBOyFz-enriched cathode-electrolyte interphase, which effectively suppresses the dissolution of transition metals. In situ impedance measurements reveal the accelerated interfacial charge transfer kinetics. As expected, the NCM523 cathode achieves an 82 % state-of-charge (SOC) in 12 min at 5 C (25 °C) with 87 % capacity retention after 100 cycles, and exhibits a 65 % higher discharge capacity at 1 C than the baseline at −20 °C. The 1 Ah pouch cells based on LiNi0.52Co0.2Mn0.28O2 cathodes, graphite anodes, and 0.5 wt% LiDFOB-modified electrolyte demonstrate fast-charging capabilities: charging 97 % of the pouch cell capacity within 30 min (2 C) and 80 % within 15 min (4 C) at 25 °C. This study offers a practical electrolyte design strategy that enhances the fast-charging performance of lithium-ion batteries (LIBs) over a wide temperature range (from −20 to 25 °C).