Multifunctional and multidimensional Na-ion structural coaxial energy storage cell

The seamless integration of energy storage into load-bearing structures represents a major step toward lightweight, multifunctional, and sustainable systems for next-generation electrification and digitalization. Here, we report a coaxial structural energy-storage cell capable of simultaneously withstanding mechanical loads and delivering stable electrochemical performance. The architecture consists of a carbon-fiber-reinforced polymer (CFRP) outer shell, a Cu electrode, a Na + solid-state ferroelectric electrolyte, and an Al inner electrode, enabling direct coupling between electrochemical and mechanical responses. Scanning Kelvin Probe (SKP) mapping reveals a continuous electrochemical potential across the Na + -electrolyte/Al interface, indicative of efficient charge redistribution driven by Fermi-level differences. SKP and first-principles simulations confirm the formation of electric double-layer capacitors at both the Cu/electrolyte and CFRP/electrolyte interfaces. Three-point bending tests demonstrate retention of electrochemical function under deformation, with a flexural modulus of 59.8 ± 1.2 GPa and a maximum flexural stress of 397.1 MPa, while synchrotron X-ray micro-computed tomography verifies interfacial integrity. Systematic variation of the Al-rod radius reveals a strong geometric dependence of long-term voltage stability, with the 3-mm configuration achieving optimal ionic conductivity (54.0 μS.cm -1 ) and a dielectric constant exceeding 10 7 . Ab initio simulations reproduce the observed chemical potentials and confirm spontaneous ferroelectric polarization. These results establish a new class of ferroelectric-driven structural batteries that combine mechanical robustness, electrochemical stability, and scalable composite manufacturing.