An Ultralight Composite Current Collector Enabling High‐Energy‐Density and High‐Rate Anode‐Free Lithium Metal Battery

Anode-free lithium (Li) metal batteries are promising alternatives to current Li-ion batteries due to their advantages such as high energy density, low cost, and convenient production. However, the copper (Cu) current collector accounts for more than 25 wt% of the total weight of the anode-free battery without capacity contribution, which severely reduces the energy and power densities. Here, a new family of ultralight composite current collectors with a low areal density of 0.78 mg cm^-2, representing significant weight reduction of 49%-91% compared with the Cu-based current collectors for high-energy Li batteries, is presented. Rational molecular engineering of the polyacylsemicarbazide substrate enables enhanced interfacial interaction with the sputtered Cu layer, which results in excellent interfacial stability, flexibility, and safety for the obtained anode-free batteries. The battery-level energy density has been significantly improved by 36%-61%, and a maximum rate capability reaches 5 C (10 mA cm^-2) attributed to the homogeneous Li⁺ flux and smooth Li deposition on the nanostructured Cu layer. The results not only open a new avenue to improve the energy and power densities of anode-free batteries via composite current collector innovation but, in a broader context, provide a new paradigm to pursue high-performance, high-safety, and flexible batteries.