Improving cyclic stability of LiCoO2 charged to 4.5 V by using succinic anhydride as co-solvent

Abstract

Enhancing the cutoff charge voltage of LiCoO2 can obviously increase energy density but deteriorate its cyclic stability. To address this issue, succinic anhydride (SA) is chosen as an efficient co-solvent to improve the cyclic stability of LiCoO2 electrode charged to 4.5 V (vs. Li/Li+). LiCoO2/Li half-cell with 10 wt% SA achieves 39% increased discharge capacity after 200 cycles at 0.5 C (1 C = 185 mA h g−1), compared to the one in base electrolyte between 3 and 4.5 V. Additionally, the mechanism of how SA improves the cyclic stability of LiCoO2 under high charge voltage is elucidated by electrochemical impedance spectroscopy, linear sweep voltammetry, scanning electron microscopy, X-ray diffraction, transmission electron microscopy, and X-ray photoelectron spectroscopy. All the results consistently show that SA yields a more compact and stable passivation layer on the surface of LiCoO2 than that without SA, leading to the much higher cyclic stability for LiCoO2 electrode at high cutoff voltage.