Surface/Interface Study on Full xLi₂MnO₃·(1 − x)LiMO₂(M = Ni, Mn, Co)/Graphite Cells

We report the behavior of full Li-ion cells with a xLi 2 MnO 3 ·(1 − x)LiMO 2 (M = Ni, Mn, Co) (hereafter called HE-NCM) cathode and a graphite anode. The cells' cycling behavior, especially with regard to the degradation processes (mainly of the electrolyte) occurring in the 5 V region, does not strongly depend on the cycling rate but rather on the calendar time of cycling. At the fast 1 C rate, we demonstrate 250 cycles with more than 80% capacity retention in a standard carbonate electrolyte. A surface analysis combining post-mortem scanning electron microscopy (SEM) and X-ray photoemission spectroscopy (XPS) revealed differences in the electrodes' surface composition and morphology, and the suggested explanation for these differences was found in the thickness of the polymer layer developed at the surface of the particles.