Operando Raman and ToF-SIMS Insights into a CEI-Regulated Zn2+ Storage Mechanism in V2O5 Nanosheet Cathodes

Abstract Vanadium pentoxide (V2O5) is considered a promising cathode material for aqueous zinc-ion batteries (AZIBs) due to its multivalent redox capability and layered crystal structure. However, its practical application is hindered by poor cycling stability, primarily resulting from the sluggish diffusion kinetics of Zn2+ ions. In this work, a nanosheet V2O5 morphology was demonstrated via a surfactant-free sol–gel method to address this limitation, which delivers a high initial specific capacity of 432.9 mA h g–1 at 0.1 A g–1, along with excellent cycling stability over 1000 cycles at 2 A g–1. The estimated diffusion coefficient for Zn2+ transport is seen to improve from 10–14 to 10–10 cm2 s–1 after cathode-electrolyte interphase (CEI) formation. Kinetic analysis reveals a significant enhancement in pseudocapacitive contribution (38 to 83%) as the scan rate is increased from 0.1 to 6 mV s–1. In-situ Raman spectroscopy was enabled through the design, construction, and use of a custom spectrocell, demonstrating notable variations in the bending and stretching vibrations of V-O bonds, indicating structural deformation of the VO5 lattice during cycling. Furthermore, the formation of the CEI was systematically investigated using time-of-flight secondary ion mass spectrometry (ToF-SIMS) depth profiling. The analysis reveals a multilayered interphase structure consisting of fluorocarbon species in the outer layer, ZnF2 and ZnS as intermediate products, and sulfate-derived compounds in the inner layer. These findings are further corroborated by in-situ electrochemical impedance spectroscopy (EIS) and post-cycling high-resolution transmission electron microscopy (HRTEM) observations. Overall, this study provides insights into the interfacial chemistry and structural evolution of V2O5 cathodes for advanced AZIB systems.