Dimensionless thermal safety framework for nickel-enriched lithium-ion batteries: From runaway onset to extinction thresholds

Nickel-enriched lithium-ion batteries (LIBs) offer high energy density but exhibit heightened susceptibility to thermal runaway (TR), posing critical safety risks for electric vehicles and energy storage systems. This study establishes a unified, dimensionless framework to assess TR risk and determine extinction thresholds—cooling conditions under which TR cannot self-sustain. Calorimetry at heating rates of 10–20 °C min⁻¹ quantifies enthalpy release, onset, and peak exothermic reactions, providing temperature-dependent heat generation inputs. These data are embedded into a heat balance model to determine the critical Nusselt number (Nu_cr) that marks the boundary between self-heating and quenching. The safety zone is defined at the inflection point of the heat-flow curve, capturing the earliest stage of instability. Results show that faster heating delays initial decomposition in nickel-rich cathodes but intensifies autocatalytic reactions, lowering onset temperatures in structurally stabilized variants. Non-dimensionalization across cell geometries and coolant properties yields a universal energy parameter for TR suppression, enabling direct comparison of designs. The theory links fundamental TR mechanisms to practical extinction thresholds, offering actionable criteria for safer, cost-effective thermal management in next-generation LIB systems.

Novelty and Significance Statement

This work is the first to formulate a unified, dimensionless safety assessment theory that quantitatively links thermal runaway (TR) onset mechanisms in nickel-enriched lithium-ion batteries to extinction thresholds for TR suppression. Unlike prior studies that treat TR behavior and cooling requirements separately, our approach integrates experimentally measured, temperature-dependent heat generation into a heat balance model to derive critical Nusselt numbers and a universal energy parameter applicable across cell geometries and coolant properties. This framework enables direct, design-ready identification of the cooling conditions required to quench early-stage instability—providing both a mechanistic understanding of TR kinetics and a practical criterion for safe, cost-effective thermal management in high-energy LIB systems.