Effect of Carbon Interlayer Preconditioning on In-Situ Plated Lithium Metal Stability in Anode-Free Solid-State Batteries

Carbon-based mixed ionic–electronic conducting interlayers regulate lithium plating in anode-free sulfide solid-state batteries, yet their preconditioning-dependent evolution remains insufficiently understood. Here, the effect of electrochemical preconditioning on carbon interlayers and the stability of subsequent in situ plated Li is systematically investigated using a decoupled protocol that distinguishes carbon lithiation from Li plating by electrochemical criteria. Without preconditioning, higher lithiation current densities lead to reduced Li stability. Mild low-current preconditioning reduces the dependence of Li reversibility on the carbon lithiation current density and increases the Li stripping efficiency from ∼67% to ∼80% under high-current lithiation condition. In contrast, preconditioning with high-current lithiation leaves residual electrochemical features during the following lithiation step before Li plating and does not provide the same improvement. Raman spectroscopy and time-resolved electrochemical analyses show that preconditioning modifies carbon structural disorder, polarization, and relaxation behavior. The results indicate that preconditioning history and the lithiation current density before plating affect the electrochemical state of the carbon interlayer and subsequently influences plated Li stability.