Molecular sieve based Janus separators for Li-ions redistribution to enable stable lithium deposition

During operation of a lithium metal battery, uneven lithium deposition often results in the growth of lithium dendrites and causes a rapid decay in battery performance and even leads to safety issues. This is still the main hurdle hindering the practical application of lithium metal anodes. We report a new type of Janus separator fabricated by introducing a molecular sieve coating on the surface of the polypropylene separator that serves as a redistribution layer for lithium ions. Our results show that using this layer, the growth of lithium dendrites can be largely inhibited and the battery performance greatly improved. In a typical Li||Cu half-cell with the Janus separator, the Coulombic efficiency of the lithium metal anode can be maintained at > 98.5% for over 500 cycles. The cycling life span is also extended by a factor of 8 in the Li||Li symmetric cell. Furthermore, the high-strength coating improves the mechanical properties of the separator, thus enhancing safety. The effectiveness of our strategy is demonstrated by both the inhibited growth of lithium dendrites and the improved battery performance. Our methodology could eventually be generalized for electrode protection in other battery systems.