Fluorine Doping for Improved Lithium and Manganese-Rich Layered Cathode Performance

Lithium- and manganese-rich (LMR) cathodes represent a promising cathode active material for the next-generation lithium-ion batteries (LIBs) due to their high energy density, low material cost, and structural stability across wide operating voltage window. However, the LMR-type cathode faces challenges involving high irreversible capacity due to oxygen release during the first formation cycle. In order to mitigate this drawback, we present a novel approach to surface modification by fluorine (F) doping on Li1.15Ni0.28Mn0.57O2–xFx cathodes. The cathode powder was treated with various amounts of NH4F, aiming for F concentrations of x = 0.01, 0.03, 0.05, and 0.1, followed by heat-treatment at 450 °C to achieve surface fluorination. Various characterization techniques were applied to investigate the impact of the F-doping on the electrochemical performance and thermal safety. The results showed that the F-doping led to the reductions of overall oxidation state of the transition metals (Ni and Mn) at the cathode surface region. The F-doping in Li1.15Ni0.28Mn0.57O2–xFx promoted the formation of spinel phases, as evidenced by distinct peaks at 2.75 VvsLi in the dQ/dV profiles, which is accompanied by reducing the Li2MnO3 phase. Such phase transitions in the cathode surface region contribute to the decrease in the irreversible capacity and enhanced thermal abuse tolerance of the Li1.15Ni0.28Mn0.57O2–xFx cathodes. Our results suggest that the presence of pre-existing spinel phase on the surface of LMR cathode can be beneficial for LIB performances.