Crown Ether Functionalized Conductive Carbon for High-Voltage Spinel LiMn_1.5Ni_0.5O₄/Graphite Cell

The effect of functionalization of the carbon additive (acetylene black) of a composite LiMn1.5Ni0.5O4 cathode, with benzo-15-crown-5 ether, on the electrode/electrolyte interfaces and electrochemical behavior of a LiMn1.5Ni0.5O4/Li half-cell and LiMn1.5Ni0.5O4/graphite cell is investigated. Functionalization was achieved by spontaneous reduction of 4′-aminobenzo-15-crown-5 ether by acetylene black (AB). The resulting materials were characterized by infrared spectroscopy and thermogravimetric analysis. Complexation of manganese by benzo-15-crown-5 was investigated using ultraviolet–visible spectroscopy. The electrochemical behavior of cells was studied by galvanostatic cycling and electrochemical impedance spectroscopy. The LiMn1.5Ni0.5O4/Li half-cells with modified acetylene black showed improved capacity retention and Coulombic efficiency compared to LiMn1.5Ni0.5O4/Li half-cells with unmodified acetylene black. A similar behavior was observed for LiMn1.5Ni0.5O4–AB/graphite cells with modified AB. Postmortem energy dispersive X-ray spectroscopy analysis of the graphite anode following constant current cycling showed smaller amounts of fluorine, oxygen, phosphorus (resulting from decomposition products of electrolyte), manganese, and nickel for the full-cell made with crown ether modified AB. The increased cycling performance of the LiMn1.5Ni0.5O4–AB/graphite cell with modified AB can be associated with the presence of grafted groups on the carbon additive of the composite cathode surface, which can trap a fraction of metallic ions dissolving from cathode, thus decreasing the amount of transition metal deposited on the graphite anode. Furthermore, benzo-15-crown-5 crown ether groups on the carbon additive can mitigate parasitic reactions such as electrolyte decomposition and carbon degradation.