Dendrite growth of alkali metal anodes limited their lifetime for charge/discharge cycling. Here, we report near-perfect anodes of lithium, sodium, and potassium metals achieved by electrochemical polishing, which removes microscopic defects and creates ultra-smooth ultra-thin solid-electrolyte interphase layers at metal surfaces for providing a homogeneous environment. Precise characterizations by AFM force probing with corroborative in-depth XPS profile analysis reveal that the ultra-smooth ultra-thin solid-electrolyte interphase can be designed to have alternating inorganic-rich and organic-rich/mixed multi-layered structure, which offers mechanical property of coupled rigidity and elasticity. The polished metal anodes exhibit significantly enhanced cycling stability, specifically the lithium anodes can cycle for over 200 times at a real current density of 2 mA cm–2 with 100% depth of discharge. Our work illustrates that an ultra-smooth ultra-thin solid-electrolyte interphase may be robust enough to suppress dendrite growth and thus serve as an initial layer for further improved protection of alkali metal anodes.

Conventional lithium‐ion batteries have approached their capacity and energy density limits. Use of lithium metal anode can enable high‐energy batteries. However, the safety hazards and lithium dendrite formation associated with lithium metal require safe electrolytes to replace flammable liquid ones. In recent years, solid‐state electrolytes have attracted tremendous attention. Among them, composite polymer electrolytes (CPEs) with different constitutions have the unique advantages of low interfacial resistance, high ionic conductivity, and flexible characteristics. Here, the basic properties and analysis methods related to CPEs are discussed. Following that, the components added into the polymer matrix, such as organic solvents, nanostructured ceramics, and fast‐ion‐conductive inorganics are classified. CPEs used in low‐cost Na and K batteries are briefly discussed. It is hoped that the review can supply both advances and fundamentals to the researchers in this field and provide guidance for the development of CPEs for lithium battery systems, and beyond.

Lithium metal anodes suffer from poor cycling stability and potential safety hazards. To alleviate these problems, Li thin‐film anodes prepared on current collectors (CCs) and Li‐free types of anodes that involve direct Li plating on CCs have received increasing attention. In this study, the atomic‐scale design of Cu‐CC surface lithiophilicity based on surface lattice matching of the bcc Li(110) and fcc Cu(100) faces as well as electrochemical achievement of Cu(100)‐preferred surfaces for smooth Li deposition with a low nucleation barrier is reported. Additionally, a purposely designed solid–electrolyte interphase is created for Li anodes prepared on CCs. Not only is a smooth planar Li thin film prepared, but a uniform Li plating/stripping on the skeleton of 3D CCs is achieved as well by high utilization of the surface and cavities of the 3D CCs. This work demonstrates surface electrochemistry approaches to construct stable Li metal–electrolyte interphases towards practical applications of Li anodes prepared on CCs.