Revealing the Intrinsic Ion Species, Diffusion Paths, Governing Factors for Charge Carriers of Cement‐Based Structural Capacitors (CSCs)

ABSTRACT Integrated structural/functional rechargeable CSCs combine the load‐bearing properties of construction with electrochemical energy storage, thereby expanding the functional capabilities of modern buildings by providing distributed and adaptive energy storage. However, many fundamental scientific issues‐including the dominant ionic species, ion diffusion pathways, and the key factors governing charge‐carrier transport—remain unclear, hindering the rational design of CSCs. In this work, we first employ a unidirectional charging method to identify Na + and K + as the dominant charge carriers in CSCs. Subsequently, a novel Zn‐based cement structural capacitor (Zn‐CSC) is designed, in which Zn‐containing species serve as a tracer to qualitatively reveal the direction and spatial pathways of field‐assisted ion transport through the interconnected porous network of the cement matrix. Furthermore, the fundamental factors governing charge‐carrier behavior are investigated: (1) the concentration of charge carriers in the cement pore solution is positively correlated with the energy‐storage performance of CSCs; (2) a reduction in the water content of the cement electrolyte hinders the transport of Na + and K + ions, leading to diminished energy‐storage capability; and (3) the solidified, percolating 3D micro‐/nanoporous network formed within the cement electrolyte serves as the critical pathway for efficient charge‐carrier transport.