Separator-SEI interactions: Unlocking new pathways for lithium metal battery stability

The solid-electrolyte interphase (SEI), which is critical for the stability of lithium metal batteries (LMBs), is simply assumed to exist only on the lithium metal surface. Corresponding research and modifications have been focused on the lithium metal surface, but the intrinsic high activity of lithium limits the workability and simplicity of modification methods. Herein, another long-neglected location for SEI, within the separator, has been cross-validated with a subsequent proposal of an integrated "separator-SEI-Li" system. Positive affection of limited separator pore size on SEI stability and lithium dendrite inhibition is confirmed. Inspired by this physical size modulation effect, a polyvinylidene fluoride is employed to facilely reduce the pore size of the commercial polypropylene separator to strengthen the SEI for stable LMBs. As expected, assembled with this optimized separator, a cycle life of over 1000 h in symmetric cells and an impressive energy density of 468.9 Wh kg- 1 in LMBs can be achieved. Thinking SEI through in another separator side not only simplify the modification strategy, but also provides an unlimited prospect for commercialization.