In-situ quantitative monitoring of dendrite growth in aqueous zinc batteries utilizing an extrinsic fiber Fabry-Pérot cavity.

The non-uniform growth of zinc dendrites in aqueous zinc batteries severely limits their cycling performance and safety. Moreover, continuous quantitative characterization of this growth process remains a critical challenge for understanding dendrite growth kinetics and guiding the optimization of control strategies. In this work, we fabricate an extrinsic fiber Fabry-Pérot (F-P) cavity formed by the zinc electrode/dendrite interface and the fiber end-face, enabling in-situ optical tracking of the Zn deposition/dissolution process. Based on the relationship between the cavity length evolution induced by dendrite growth and the interference spectrum response, we establish an optical characterization model for interfacial dynamics. By introducing the effective dendrite height (heff) as an equivalent parameter, we transform the complex and non-uniform interfacial topography into a continuously analyzable quantity, thereby facilitating real-time quantification of dendrite growth. In-situ monitoring results reveal notable asymmetry in the Zn deposition and dissolution processes and further demonstrate that this method can sensitively track interfacial evolution. Building on this, we extend the method as a screening tool for electrolyte optimization. We compare dendrite growth behavior between ZnSO4 electrolytes containing glucose and the reference system, quantitatively assessing the inhibitory effect of the additive. This work introduces a novel in-situ optical method for quantitative characterization of interfacial evolution in aqueous zinc batteries and offers a practical route for rapid evaluation of electrolyte regulation strategies.