Li metal has become a strong candidate for anode due to its high theoretical specific capacity and lowest electrochemical potential. However, the poor reversibility caused by continuous chemical and electrochemical degradation hinders the practical application of Li metal. Solid-solution-based metal alloy phases have been proposed as hosts for regulating the non-dendrite electrodeposition, but the fundamental understanding remains unclear due to the drastically different deposition behaviors of Li on them. Here we found the difference in the diffusion coefficient of Li atoms on solid-solution-based metal alloy phases (Li-Mg and Li-Ag alloys) was a major contributor to the different deposition behaviors. The low Li atom diffusion coefficient of Li-Mg alloy showed a preferential Li accumulation on the upper surface rather than the inward-growth plating of Li atoms into alloy foil in Li-Ag alloy. By the process of secondary recrystallization, we improved the diffusion coefficient of Li atoms in Li-Mg alloy that facilitates the inward transfer rather than surface plating of Li atoms. In this case, the recrystallized Li-Mg alloy underwent a solid-solution phase change in the delithiation–lithiation cycles which yielded a high Coulombic efficiency of 99.3% with a reversible gravimetric capacity of 2,874 mAh·g⁻¹ and superior cycling stability over 5,000 h without dendrite growth.

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.