Delineating the relationship between separator parameters and practical lithium metal batteries characteristics

Lithium metal batteries (LMBs), composed of lithium anodes and high-nickel-content LiNixMnyCozO2 (x + y + z = 1), are considered the pinnacle of next-generation batteries. Despite the importance of evaluating LMB in practical conditions, there is a lack of clear standards for LMB separators, which critically affects battery performance and energy density. Here, we investigated the effects of separator thickness on the cell performance and energy density of a practical LMB by using various-thickness polyethylene (PE) separators. As the separator thickness decreases the volumetric energy density increases and LMB performance improves. We also showed that pore closure in separators is a major roadblock hindering the long-term operation of LMBs. Therefore, we establish the ideal LMB separator design, which is a thin and robust separator having pore closure suppression functionality for ensuring long-term stable high-energy-density LMBs.