The Role of Ion Transport in the Failure of High Areal Capacity Li Metal Batteries

Recent advancements in electrolyte research have substantially improved the cycle life of Li metal batteries (LMBs) but often under moderate areal capacity. The design principles overwhelmingly emphasize the reduction of electrolyte reactivity toward Li. In this work, we find that high areal capacity (>6 mAh cm–2) Li||sulfurized polyacrylonitrile (SPAN) batteries fail primarily due to shorting events when paired with four types of localized high-concentration electrolytes (LHCEs), which is correlated with electrolyte transport properties, including ionic conductivity and Sand’s capacity. These LHCE systems, despite their high Coulombic efficiencies for Li metal cycling, produce macroscopically non-uniform Li deposits when operating under transport limitation. This deficiency leads to short circuit over repeated cycling, as evidenced by a quantitative, statistical analysis of SEM images. Based on these insights, we fabricated a 2 Ah pouch cell, which demonstrates a cell energy density of >260 Wh kg–1 for more than 70 cycles. Our findings emphasize the significance of the bulk transport properties of electrolytes and the statistical morphological information on cycled Li for long-life LMBs.