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

Abstract

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 LiNi_0.52Co_0.2Mn_0.28O₂ (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/Li_xBO_yF_z-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 LiNi_0.52Co_0.2Mn_0.28O₂ 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).