Current Collector Engineering for New Efficient Bioresorbable Sodium‐Ion Batteries

ABSTRACT Developing bioresorbable energy sources that eliminate the need for secondary surgery for device removal remains a major challenge in resorbtronics. In this work, we present an alternative fabrication strategy for new bioresorbable quasi‐solid Na‐ion batteries using Mo or Mg thin films as current collectors. The assembled batteries were characterized using scanning electron microscopy, spectroscopic techniques including X‐ray photoelectron spectroscopy, physicochemical, and electrochemical characterization techniques. Results demonstrate that the choice of current collector strongly influences electrochemical performance. Mo‐based batteries delivered a discharge capacity of 6.8 mAh cm − 2 at a C/2 rate, approximately twice that of Mg‐based counterparts whose performance is limited by oxidation reactions. Moreover, Mo‐based batteries exhibited stable cycling with 86% capacity retention after 100 cycles at 2C. In vitro cytotoxicity assays showed cell viability above the 70% threshold indicating that the tested materials are non‐cytotoxic according to ISO 10993 guidelines. Implantation studies confirmed safe degradation of Mo‐based batteries supported by in vivo monitoring of animal health behavior and ex vivo organ analyses, including organ weight, ALT measurements, and histological evaluation of skin at the implantation site after three months. Additionally, the operational lifetime of implanted batteries can be tuned from days to months by controlling encapsulation layer thickness.