Imaging the 4D Chemical Heterogeneity of Single V₂O₅ Particles During Charging/Discharging Processes

Microparticle cathode materials are widely used in secondary batteries. However, obtaining dynamic chemical heterogeneities of these microparticles is challenging, hindering in-depth mechanistic investigation of the underlying processes. For example, although vanadium pentoxide shows promise as an electrode material for zinc ion batteries, its poor performance's root cause is elusive. Herein, a fluorescence/scattering dual-mode spinning disk confocal microscopy-based approach is developed to visualize the 4D chemical heterogeneity of single V₂O₅ particles during cycling. Dual-mode in situ imaging identifies valence state changes of vanadium ions with high spatiotemporal resolution. A unique difference is observed between the scattering intensities of a particle's bottom electric contact points and the rest parts during the discharging process. In contrast, fluorescence intensity variation suggests high consistency across the particles. Correlative Raman, UV-Vis spectroscopy, and electrochemical impedance spectroscopy analyses suggest the precipitation of V³⁺ species at the bottom interface of the V₂O₅ electrode, leading to increased electron transfer resistance and compromised overall performance. A coordination strategy between ethylene diamine tetraacetic acid and V³⁺ is proposed for inhibiting V³⁺ precipitation, and its effectiveness is further verified by imaging and electrochemical impedance spectroscopy analyses. Insights from the imaging approach presented herein will enable the rational design of high-performance batteries.