Microchemical and electro-thermal operando analytical characterization of reaction kinetics, heat generation and interfacial degradation in lithium-ion batteries under extreme fast-charge/discharge conditions

In lithium-ion batteries, extremely fast-charge/discharge conditions cause considerable electrochemical and thermal stress that leads to accelerated degradation and a lack of operational safety. In this study, we established an integrated, operando approach for analyzing reaction kinetic data along with heat production and interfacial degradation data under high C-rate cycling. This dual-use method collects spatially resolved microchemical diagnostics in conjunction with synchronized thermal/electrical measurement to provide insight on transient physicochemical phenomena during dynamic battery operation. Quantitative analysis demonstrates significant amounts of non-equilibrium reaction kinetics at current densities ranging from 8 to 10C. In addition, it is possible to observe large regions of heterogeneous heat generation and localized temperature increases of 25–30 °C+. Operando microchemical characterization shows that as fast-charge conditions are implemented, solid-electrolyte interaction develops, the onset of lithium plating occurs and compositional heterogeneity is exhibited at the interfaces between electrodes and electrolytes. Further, we demonstrate that electro-thermal maps indicate localized thermal feedback that encourages parasitic reactions and increases internal resistance growth. An analytical framework was developed that establishes quantitative correlations between reaction rate, heat generated and interfacial degradation during extreme fast-charging conditions. This information leads to a better understanding of the processes leading to failure, while providing a diagnostic tool to evaluate high-power battery materials, enhance fast-charge protocols and improve reliability and safety of advanced electrochemical energy storage systems. • Developed a coupled microchemical and electro-thermal operando framework for lithium-ion batteries under extreme fast cycling. • Identified pronounced reaction kinetics distortion and non-equilibrium electrochemical behavior at high C-rates. • Quantified irreversible heat generation and resolved localized hotspot formation during aggressive charge/discharge. • Revealed strong electro-thermal feedback mechanisms accelerating interfacial degradation processes. • Detected operando microchemical signatures of SEI instability, lithium plating, and chemical heterogeneity. • Established multi-physics links between reaction dynamics, heat generation, and degradation pathways.