Mitigating battery thermal runaway through mild combustion

Abstract

With the fast expansion of electric vehicle market, thermal runaway of Li-ion battery has become a major concern for ground transportation and public safety. Fundamentally, thermal runaway initiation of a Li-ion battery bears intrinsic similarity to a gas-phase thermal explosion process, where the system response is controlled by the competition between the heat generation and heat loss, each with distinct temperature dependence. In this work, the fundamentals of mild combustion described by the stretched S-curve is revisited from one-step overall reaction with and without reactant depletion. The key dimensionless parameter that can lead to mild combustion are identified. Furthermore, the critical state of Li-ion battery thermal runaway in the small Biot number limit has been theoretically and computationally analyzed using detailed thermochemistry of battery thermal runaway. With insight from the stretched S-curve concept, the conditions corresponding to the loss of criticality are investigated, where in principle only mild heat release can occur. It is found that reducing the reaction heat associated with negative-electrode and electrolyte has the strongest effect to mitigate thermal runaway, where the reaction heat of electrolyte decomposition plays a minor role. Li-ion battery thermal runaway can be mostly prevented if the reaction heat of the cathode and anode with electrolyte are both reduced by an order of magnitude. The results stimulate future experiments seeking novel battery materials, and can provide useful guidance on the screening of safer battery materials to reduce the possibility of thermal runaway.