Janus‐Architectured Lithium Replenishment Separators Boosting Longevity of Anode‐Free Lithium Metal Batteries

Abstract Addressing the issue of inactive dead lithium deposition on the anode side remains a significant challenge for anode‐free lithium metal batteries. While lithium compensation techniques can mitigate lithium depletion, directly introducing lithium compounds into the cathode material may degrade the electrode structure. Here the design and fabrication of a novel lithium replenishment separator (LRS) using a lithium compensation agent of Li 2 C 4 O 4 is reported. The electrospun LRS demonstrates excellent ionic conductivity of 1.82 mS cm −1 and a high Li + transference number of 0.51. Such a functionalized LRS not only provides additional active lithium for anode‐free lithium metal batteries but also promotes uniform deposition of lithium metal. Compared with conventional polyolefin‐based separators, the LRS effectively boosts LiFePO 4 ||Cu anode‐free batteries with enhanced cyclability. These results suggest this LRS strategy can find promising applications in next‐generation anode‐free batteries with high energy densities.