The issue of uncontrollable Li dendrite growth, caused by irregular lithium deposition, restricts the wide applications of Li metal based high energy batteries. In this paper, a polypropylene separator with a sputtered platinum nanolayer has been developed to improve the stability of the Li metal anodes. It was found that cells using the modified separators resulted in a smooth Li surface and a stable electrode-electrolyte interface. On the one hand, platinum nanolayers can enhance the mechanical properties and micro-structures of commercial polypropylene separators. On the other hand, platinum nanolayers provide stable Li deposition during repeated charging/discharging by a bidirectional growth mechanism. After long-time cycling, the dendrites from opposite directions and dead Li are integrated into a flat and dense new-formed Li anode, decreasing the risk of low Coulombic efficiency and cycling instability that may end in cell failure. This design may provide new ideas in next-generation energy storage systems for advanced stable metallic battery technologies.