A soft non-porous separator and its effectiveness in stabilizing Li metal anodes cycling at 10 mA cm⁻² observed in situ in a capillary cell

While lithium metal anodes have the highest theoretical capacity for rechargeable batteries, they are plagued by the growth of lithium dendrites, side reactions, and a moving contact interface with the electrolyte during cycling. Here, we synthesize a non-porous, elastomeric solid-electrolyte separator, which not only blocks dendritic growth more effectively than traditional polyolefin separators at large current densities, but also accommodates the large volume change of lithium metal by elastic deformation and conformal interfacial motion. Specially designed transparent capillary cells were assembled to observe the dynamics of the lithium/rubber interface in situ. Further experiments in coin cells at a current density of 10 mA cm⁻² and an areal capacity of 10 mA h cm⁻² show improved cycling stability with this new rubber separator.