Visualizing Transition Metal Ion Dissolution: Understanding Degradation in Ni-rich Layered Oxide Cathodes

Ni-rich layered oxides LiNixMnyCozO2 (NMC, x ≥ 0.8) are among the most promising cathode materials for high-energy-density lithium-ion batteries due to their high theoretical capacity and reduced cost. However, interfacial electro-chemo-mechanical instabilities, particularly the dissolution of transition metals (TM) at the electrode–electrolyte interface, continue to compromise their long-term stability. TM dissolution interlinks phase transitions, parasitic interfacial reactions, and irreversible capacity loss, yet its underlying mechanisms remain elusive owing to the limited spatial and temporal resolution of conventional characterization techniques. This project proposes the development of a multimodal operando optical imaging platform capable of directly visualizing the spatial origin and dynamics of TM²⁺ dissolution at single-ion resolution. The platform integrates ion-localization optical nanoscopy (ION), developed by the applicant, with interferometric scattering (iSCAT) microscopy, a complementary technique introduced to battery research by the host group. This combination enables real-time, correlative mapping of TM ion release alongside lattice Li⁺ distribution within individual NMC particles. By synchronously visualizing Li⁺ heterogeneity and systematically evaluating the influence of electrolyte components (salts, solvents, and additives), this approach allows for mechanistic decoupling of lattice-driven and electrolyte-induced degradation pathways. The platform will enable quantitative assessment of electrolyte effects and guide the rational design of optimized cathode materials to improve the cycling stability of Ni-rich NMC cathodes. Beyond advancing fundamental insights into Ni-rich NMC cathode degradation, the proposed methodology establishes a versatile operando imaging framework applicable to other energy-dense TM-based cathode systems, such as lithium-rich layered oxides, where similar TM dissolution challenges persist.