Capacitive effects in Li1−xNi0.3Co0.3Mn0.3O2-LixCy Li-ion cells

There are few publications about quantitative measurement of capacitance in Li-ion cells which in addition distinguish between pure electrostatic double-layer capacitance and capacitance caused by Faradaic effects. The measurement techniques electrochemical impedance spectroscopy, pulse current measurement and cyclic voltammetry are used to analyze a conventional high-energy Li-ion cell consisting of Li-nickel-manganese-cobalt-oxide Li1−xNi0.3Co0.3Mn0.3O2 as positive and graphite LixCy as negative electrode material. The results show the highest capacitance of the full cell at a frequency of 10 mHz at approximately 40% state-of-charge (SOC), which is equal to the cell voltage around 3.64 V, attributed to intercalation capacitance. Toward higher frequencies around 1 Hz, the capacitance increases with SOC. The measurements reveal that the positive electrode mainly causes this sensitivity of capacitance on SOC or electrode potential at around 1 Hz.