Size effects of micro-pattern on lithium metal surface on the electrochemical performance of lithium metal secondary batteries

Two micro-patterns of different sizes (50 and 80 μm) are designed to have equivalent capacities of 1.06 and 2.44 mAh cm⁻² by building a computational battery model. After preparing two stamps each possessing a micro-pattern design, the corresponding pattern is properly imprinted on the surface of 100 μm lithium metal, which is confirmed by scanning electron microscopy. When both micro-patterned lithium metals are electrochemically reduced and oxidized up to 1 mAh cm⁻² in Li/Li symmetric cells at 1 or 2 mA cm⁻², the 80 μm-patterned lithium shows a more stabilized lower overpotential during long-term cycling than the 50 μm-patterned and bare lithium, probably due to the lithium anchoring effect and a larger empty volume in the patterns. Additionally, an overflow of lithium deposits is easily observed in the 50 μm-patterned lithium metal, while the 80 μm-patterned lithium metal holds most of the lithium deposits within the patterns. When both micro-patterned lithium metals are assembled to full cells with a LiNi_0·6Co_0·2Mn_0·2O₂ cathode of 2 mAh cm⁻², the 80 μm-patterned lithium metal shows much better electrochemical performances with stable plating/stripping behavior within the patterns.