Thermodynamic measurements pertaining to the hysteretic intercalation of lithium in polymer-derived silicon oxycarbide

Silicon oxycarbide (SiCO), made from the polymer route from siloxane-based precursors, has impressive capacity for serving as anodes in Li+ batteries. However, the voltage–charge cycle exhibits significant hysteresis: the magnitude of the insertion voltages is low, while the extraction voltages are high. Here, we present coulometric titration results on both traverses of the cycle that lead to a measurement of an intrinsic polarization within the half-cell. This polarization-potential, which is measured to be 250–500 mV, is attributed to a differential between the potential of Li ions across the anode–electrolyte interface. In the second set of experiments the polarization was measured after coating the powders of the active anode material with a few monolayers of alumina by atomic-layer deposition (ALD). These results showed a shift of the hysteresis curve by ∼50 mV, which is attributed to a space–charge double layer, most likely at the alumina–electrolyte interface. In the third result, the distribution of the “density of states” at different voltage levels where Li is inserted, and extracted, from SiCO is measured. The distribution is broad reflecting the amorphous nature of SiCO, and consistent with the strongly sloping behavior of the voltage–charge capacity profile of the charge–discharge cycle.