Phenyl 4-Fluorobenzene Sulfonate as a Versatile Film-Forming Electrolyte Additive for Wide-Temperature-Range NCM811//Graphite Batteries

摘要

LiNi0.8Co0.1Mn0.1O2 (NCM811) cathodes paired with a graphite anode have emerged as a promising alternative for current power batteries. Unfortunately, the structural degradation of Ni-rich cathodes at high working voltages brings about serious capacity fading, sequentially hampering their practical use in lithium-ion batteries (LIBs). In this work, phenyl 4-fluorobenzene sulfonate (PFBS) is investigated as a multifunctional film-forming additive to suppress the structural degradation of NCM811 and alleviate the chemical decomposition of electrolyte solvents. Computational and experimental results prove that the PFBS molecule preferentially undergoes electrochemical reactions rather than the electrolyte solvents on both the cathode and anode to form a stabilized and uniform solid electrolyte interphase (SEI). The presence of 1.0 wt % PFBS is conducive to maintaining a stable SEI at the NCM811 cathode, thus mitigating the irreversible structural transformation and holding the stability of the SEI on the graphite surface. Due to the multifunctional feature of PFBS, the electrochemical performances of the NCM811//graphite pouch cell significantly improved at -20, 25, and 45 degrees C. Notably, the pouch cell with a PFBS additive achieved a capacity retention of 89.9% over 400 cycles at 1C at 25 degrees C, which is much superior to that of 29.3% for the PFBS-free one. Furthermore, the pouch cell with 1 wt % PFBS in electrolyte also achieved superior capacity retention at 45 degrees C (89.01%) and -20 degrees C (49.18%) at 1C. Theoretical calculation and X-ray photoelectron spectroscopy analysis reveal that the -OSO2- and -F functional groups of PFBS not only joined in the formation of a stable SEI but also facilitated the diffusion of Li ions. The excellent cycling performance achieved in a wide-temperature region with PFBS demonstrates that this functional molecule has prospects for application in power LIBs.

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