Effect of Fluoroethylene Carbonate Electrolyte Additives on the Electrochemical Performance of Nickel-Rich NCM Ternary Cathodes

It has been well established recently that fluorinatedelectrolyteadditives such as fluoroethylene carbonate (FEC) could promote theformation of LiF-based solid electrolyte interphases that can stabilizelithium metal anodes. Meanwhile, the impact of FEC additives on thecathode side, particularly for the high energy density nickel-richLiNi(1-x-y )Co( x )Mn( y )O(2) (NCM) ternary cathodes, remains unclear. In this study, weinvestigated the structural and chemical composition of a cathodeelectrolyte interphase (CEI) and its electrochemical performance toelucidate the effect of FEC additives on the LiNi0.9Co0.05Mn0.05O2 (NCM90) cathode for highenergy lithium-ion batteries. It is discovered that the FEC additivein carbonate electrolyte (BE-FEC) can produce a LiF-based CEI, whichcould stabilize the NCM90 surface and improve the cycle performanceat low cut-off voltage. The formation of a thick LiF layer under highcut-off voltage and high rate has been observed to result in increasedpolarization and slower Li+ transport kinetics, ultimatelyleading to a deterioration in battery performance. On the other hand,in a carbonate electrolyte (BE) and under low voltage, the unstableLi(2)CO(3)-based CEI components on the NCM90 surfacewith an intermediate rock salt phase in between contribute to poorlong-term performance and reduced reliability. While under high voltage,the BE sample shows superior electrochemical performance due to theformation of a thin LiF layer from the decomposition of LiPF6. Our work provides a comprehensive understanding of the role ofFEC in the CEI of nickel-rich cathodes, offering practical guidancefor the design of electrolytes for high-energy high-voltage nickel-richcathodes.