Engineering Alloying and Conversion Interlayers for Anode‐Less Solid‐State Batteries

Anode‐less solid‐state batteries offer a pathway to maximize energy density while simplifying device manufacturing. However, the absence of an initial lithium (Li) reservoir demands precise control over Li deposition, a process usually hindered by interfacial instability and the lithiophobic nature of commonly employed current collectors (CCs). Therefore, effective interfacial design is crucial. In this regard, metallic and oxide interlayers offer a promising strategy to improve Li deposition, but detailed insights into their electrochemical behavior in combination with solid electrolytes (SEs) remain poorly understood. Accordingly, we engineer 50 nm thick zinc (Zn) and copper oxide (Cu 2 O) interlayers sputtered directly onto the LLZO SE, covered by a 600 nm thick Cu CC. The interlayer composition and Li deposition behavior were investigated by using a range of techniques. The results demonstrate that Zn interlayers facilitate Li deposition via in situ formation of Li–Zn alloys. Differently, the Cu 2 O interlayers drive Li 2 O formation, which contributes to more homogeneous Li deposition. The stability of alloying and conversion processes are studied to assess the impact on cycling performance. Overall, this work provides insights into the implementation of alloying and conversion‐based interlayers in solid‐state anode‐less systems and highlights key performance‐limiting factors, offering interfacial design strategies for further improvement.