A Liquid Electrolyte-Based Lithium-Ion Battery Cell Design for Operando Neutron Depth Profiling

In this study, we present a novel cell design for liquid electrolyte-based lithium-ion batteries (LIBs) to detect the lithium distribution across an electrode by neutron depth profiling (NDP). This newly developed cell design allows to obtain electrochemical data comparable to a standard laboratory cell making use of 500 μm diameter holes to assure a homogeneous compression over the entire electrode area. We present operando NDP data recorded during the formation of a porous graphite electrode where we can both distinguish between irreversibly bound lithium within the solid electrolyte interphase (SEI) and reversibly intercalated lithium into graphite, and quantify the lithium concentration profile across the electrode. The amount of lithium reversibly intercalated into the graphite electrode (≈LiC6), based on one lithium per electron of charge (1 Li/e-), was found to corroborate well with the lithium amount quantified using operando NDP. However, comparing the irreversible capacity with the amount of lithium detected as SEI within the graphite anode, a significantly smaller Li/e- ratio was observed. Furthermore, we confirm that small amounts of lithium alloy into the copper current collector, using NDP and complementary ex situ X-ray photoelectron spectroscopy (XPS).