Unlocking photo-assisted rechargeable iron-ion batteries via dual-functional nanostructured VO₂ photo-cathodes

The use of photo-assisted rechargeable batteries integrating solar harvesting and electrochemical storage represents a sustainable approach for next-generation energy devices. Herein, we demonstrate for the first time a non-aqueous photo-rechargeable iron-ion battery using flower-type VO₂ nanorods, synthesized via a hydrothermal route, as an efficient photocathode material. The structural and morphological characterization by XRD, TEM, BET, XPS, FESEM, Raman, and UV-vis spectroscopy confirms the formation of monoclinic VO₂(B) with a nanorod morphology and strong optical absorption. First, a detailed photo-response analysis was conducted using I-V, chronoamperometry, and chronopotentiometry characteristics of the synthesized photocathode VO₂ with band alignment under dark and illuminated conditions. Further detailed electrochemical investigations were conducted after the photo-rechargeable device fabrication, including cyclic voltammetry and galvanostatic charge-discharge, revealing stable Fe-ion insertion/extraction with good reversibility and high capacity. Under illumination by CV analysis, VO₂ exhibits a strong photoresponse, enabling enhanced charge separation and interfacial kinetics with ∼25% enhancement of the CV area at 1 mV s^-1. The GCD results suggest a high capacity of 207 mAh g^-1 under illumination, ∼45% higher than that in the dark. The device delivers reliable photo-rechargeability at multiple current rates, achieving 65% capacity retention under light-driven charging, and maintains excellent stability over 400 cycles. The GITT and EIS analyses show a higher diffusion coefficient under illumination. Demonstrations were also performed, including the single-device and 4-device series connected to LEDs. The post-XRD and SEM analyses were also performed to show the electrode stability during GCD cycling. These results establish VO₂ as a dual-function material that effectively combines light absorption and electrochemical activity, positioning non-aqueous photo-rechargeable Fe-ion batteries as a promising platform for sustainable and scalable energy storage beyond conventional rechargeable batteries.