Poly(vinylidene fluoride)-based Janus separators with an ultrathin conductive layer for suppressing lithium dendrite growth

Lithium dendrites, growing during the charging and discharging processes, can pierce the separators and lead to internal short circuits, which is one of the main factors resulting in thermal runaway of lithium metal batteries (LMBs). In this work, we developed a poly(vinylidene fluoride) (PVDF)-based Janus separator with an ultrathin polypyrrole (PPy) layer towards efficiently suppressing lithium dendrite growth. The PPy layer with thickness of approximately 200 nm has Pyrrole-N with lone pairs of electrons, which can act as nucleation sites for lithium ions. As a result, lateral lithium deposition can be achieved on the anode, thus preventing the lithium dendrites from piercing the separators. Stable stripping/plating performance over extended cycling and a capacity retention rate of 76.8% after 1000 cycles have been achieved in the Janus PVDF/PPy separator-based Li//Li symmetric cells and Li//LiFePO 4 half cells, respectively. The development of Janus separators with conductive polymer layers presents a promising solution for improving the safety and electrochemical performance of LMBs.