Fig. 1: The concept of optical fiber in situ detection at the lithium electrode interface.

a Schematic diagram of a TFBG sensor positioned in close proximity to the electrolyte–electrode interface of a lithium metal battery. This configuration enables in situ detection of interfacial species concentration and mass transport. b Schematic plots for species concentration distribution (blue curves), and corresponding lithium dendrites morphologies. c Spatial-temporal evolution characteristics of species concentration near the surface of the lithium anode as verified by an optical fiber sensor. The distance between optical fiber sensor and lithium surface is 0, 25, and 125 μm, respectively. d Spatial distribution of species concentration (red fitting line) near a lithium anode during lithium plating