Visualizing surface-enriched Li storage with a nanopore-array model battery

The coupling of model batteries and surface-sensitive techniques provides an indispensable platform for interrogating the vital surface/interface processes in battery systems. Here, we report a sandwich-format nanopore-array model battery using an ultrathin graphite electrode and an anodized aluminum oxide (AAO) film. The porous framework of AAO regulates the contact pattern of the electrolyte with the graphite electrode from the inner side, while minimizing contamination on the outer surface. This model battery facilitates repetitive charge–discharge processes, where the graphite electrode is reversibly intercalated and deintercalated, and also allows for the in-situ characterizations of ion intercalation in the graphite electrode. The ion distribution profiles indicate that the intercalating Li ions accumulate in both the inner and outer surface regions of graphite, generating a high capacity of ~ 455 mAh·g⁻¹ (theory: 372 mAh·g⁻¹). The surface enrichment presented herein provides new insights towards the mechanistic understanding of batteries and the rational design strategies.