Assessment of Surface Heterogeneity: a Route to Correlate and Quantify the 1st Cycle Irreversible Capacity Caused by SEI Formation to the Various Surfaces of Graphite Anodes for Lithium Ion Cells

Abstract

Abstract The formation of the solid electrolyte interphase (SEI) and the corresponding irreversible capacity (C irr) of graphite negative electrodes in lithium-ion batteries strongly depend on the surface morphology and surface chemistry of the respective graphite material. In particular, not only the BET specific surface area but also the absolute and relative extent of the basal plane and the “non-basal plane” surface area play a crucial role in SEI formation, as the transport of lithium ions into/from the anode during the charge/discharge operation mainly takes place via the prismatic surfaces. In this work, we report on the assessment of the graphite surface heterogeneity and the correlation between the amount of the different graphitic surfaces and the irreversible capacity. Based on the analysis of gas sorption data, we will show the influence of graphite surface groups on the adsorptive potential distribution of graphitic materials, in particular on the high energy surface sites (above 60 K), i.e. the so-called “defect” surfaces. These are related to polar carbon surface groups, such as carboxylic groups, alcohol groups or lactone groups. In contrast, less polar surface groups like quinone groups seem not to be related to the “defect” surface area, but belong to the prismatic surface area (below 50 K). Furthermore, we will demonstrate that the irreversible capacity of the first charge/discharge cycle is nearly proportional to the “non-basal plane” surface area, independent from the type of graphitic material.