Crystalline vs. Amorphous Silicon Anode Overhang: Investigating the Anode Overhang in Silicon-Dominant (70 wt. %) Lithium-Ion Batteries

Graphite is the most commonly used anode material in lithium-ion batteries (LIBs), while silicon has emerged as a promising alternative to meet increasing energy density demands. In practical cell designs, electrode misalignment is mitigated by implementing a geometrical anode overhang (AOH). While AOH effects in graphite based systems are well known, their influence in silicon- dominant anodes remains insufficiently understood. Here, the influence of AOH in silicon- dominant LIBs is investigated using crystalline silicon, amorphous silicon, and no AOH configurations. X-ray diffraction showed that storage does not alter the crystal structure of the crystalline silicon in the AOH, indicating the absence of lithium uptake from the electrochemically active area (AA) into the crystalline silicon particles within the AOH. Local anode potential measurements using gold wire reference electrodes further showed that the 103 mV potential gradient between the AA and the AOH is insufficient to drive lithium transport into the AOH. In contrast, when the AOH contains amorphous silicon, lithium redistribution between the AA and the AOH occurs, lowering the lithiation degree and increasing the anode potential in the silicon AA, thereby reducing parasitic reactions during storage. These findings highlight the dependence of AOH effects on silicon crystallinity.