Foreign media report (SodiumBatteryHub, a UK-based sodium-ion battery media outlet, August 13, 2026): Research groups led by Professor Tuan Guo and Professor Wenjie Mai of Jinan University, together with Professor Yongjin Fang of Wuhan University, published a paper titled "Operando tracking of ion kinetics and state-of-charge via multiresonant fiber-optic grating sensors in sodium-ion batteries" in the optics journal Light: Science & Applications (DOI: 10.1038/s41377-026-02388-1). They proposed an implantable multiresonant fiber-optic grating (MFG) sensor that exploits the sensitivity of the fiber evanescent optical field to interfacial refractive-index changes, enabling in-situ (operando) monitoring of sodium-ion concentration changes at the electrode-electrolyte interface during normal charge/discharge operation, achieving a refractive-index resolution of 10⁻⁶ RIU and sub-micron spatial resolution without disassembling the cell.
From a technical standpoint, the MFG sensor decodes ion-transport kinetics by monitoring the amplitude of a cut-off mode in the multiresonant grating and its time derivative. The study identified an "intermediate stage" between ion adsorption at the electrode surface and diffusion into the electrode bulk; electrodes with a shorter intermediate stage exhibit better fast-charging performance, suggesting that fast-charging bottlenecks depend not only on bulk diffusion but also on early interfacial dynamics. The study also built an ion-flux-based SoC estimation model: the time integral of the optical signal amplitude shows a highly linear relationship with battery state of charge, offering a physically grounded route for SoC monitoring in battery management systems, avoiding the deviations of conventional voltage/current-integration methods under temperature, aging and hysteresis effects.
It should be clarified that this is laboratory-stage fundamental research (coin-cell/experimental-level validation); "academic results are not yet commercialized." The sensor still requires engineering validation and scale integration and cannot be equated with a commercial product; the reported SoC linear relationship is based on measurements under experimental conditions, and its applicability in real battery management systems needs further verification.