Assessing the critical current density of all-solid-state Li metal symmetric and full cells

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All-solid-state Li metal batteries (Li-ASSBs) have drawn much attention in recent years owing to their potential in achieving high energy densities. However, the low critical current density (CCD) of Li-ASSBs at room temperature remains a major bottleneck which limits the prospects for commercialization. Most studies reported so far have demonstrated CCDs significantly lower than conventional lithium-ion batteries, along with a lack of consistency across such reports. While these CCD inconsistencies can be attributed to variations in pressure, temperature, and solid electrolyte chemistry, crucial parameters often omitted in the literature, such as the fabrication pressure used and duration for which it is applied, both of which are required to achieve good contact between Li metal and the solid electrolyte. Here, the relationship between the fabrication pressure contact hold time of Li metal versus CCD is reported, thus elucidating the effect of controlled Li deformation on the CCD. The CCDs for symmetric and full cell architectures are also evaluated, where the effect of volumetric expansion and associated changes in cell stack pressure are examined. Finally, a constant pressure cell design is introduced to mitigate the negative effects of volume change during cycling, allowing the Li-ASSB to achieve higher CCDs at room temperature.