Lithium flow between active area and overhang of graphite anodes as a function of temperature and overhang geometry

Abstract Recent studies have shown that aging measurements of lithium-ion-cells can be affected by the charge conditions during storage prior to the measurement due to the anode's geometric excess with respect to the cathode. In this contribution, the lithium flow between this anode overhang and the active anode is investigated as a function of time as well as temperature. For the measurements, four different cell types with graphite anodes and different cathode materials have been used. For wound cells, the charge flow out of the overhang displays a distinct kink after 2.4–13 h. This kink is shown to be caused by the end of the discharge of the short overhang along the cell's length. Using simulations with a transmission line model, the graphite potential plateaus have been identified as the reason for this rather abrupt behavior. Subsequently, the charge flow is solely determined by the lithium flow out of the long overhangs at the jelly roll ends, which can continue for several hundred hours. For stacked cells, this transition is more gradual due to the superposition of different overhang geometries. The measured temperature dependence of the speed of lithium flow has a factor of 1.4 per 10 K temperature difference. This corresponds to the conductivity variation of the electrolyte with temperature.