As thermal abuse is one of the most common cause for the thermal runaway (TR) of lithium ion battery (LIB), a three-dimensional model was firstly developed within frame of open source computational fluid dynamics (CFD) code OpenFOAM to study the effects of various battery materials, external heating conditions and heat dissipation conditions on battery thermal runaway behavior. The developed model was validated by the measurements for LiCoO2 (LCO), LiNi0.8Co0.15Al0.05O2 (NCA) and LiFePO4 (LFP) cells, which shows good agreement with experimental results. The validated model was then applied to investigate and rank the thermal safety and thermal stability of different battery materials (i.e. cathode, anode, electrolyte and separator) from the perspective of heat generation. The results indicate that batteries with Li4Ti5O12 anode and LiFePO4 cathode show better thermal safety and stability than other materials.
In addition to the thermal abuse, the electrical abuse condition is also a common cause to induce the thermal runaway of LIBs. Slight overcharge of LIBs could occur due to inadequate design of battery management system or unexpected malfunction of charger. As slight overcharging is difficult to detect, the generated heat could easily accumulate as the cycle process prevails, result in unwanted cell temperature increases with propensity for TR. A three-dimensional (3-D) predictive tool for the transition of the cylindrical 21700 LIB from slight overcharging cycle to TR was developed by implementing the published models for heat generation from various thermal decomposition reactions and ISC into in-house version of the opensource CFD code OpenFOAM. The code is validated with newly conducted experiments involving both normal cycle and a slight overcharging. The predicted cell temperature and voltage evolution during normal cycle and adiabatic condition have achieved reasonably good agreement with the measurements.
The above studies received attentions from the international peers. For example, the well-known expert in the field of thermal safety of lithium ion batteries, Academician of the Chinese Academy of Sciences, Prof. Minggao Ouyang from Tsinghua University has cited the ER’s studies in his several published papers (Appl. Therm. Eng. 2021, 199:117521; J. Power Sources 2021, 504:230065; Energy, 2023, 268:126646), and positively affirmed that “Kong et al. [32] developed a 3D electro-thermal model using the OpenFOAM platform with good experimental validation. The results revealed that the battery composed of a Li4Ti5O12 anode and LiFePO4 cathode is safer than others”.
In addition, a multi-scale and multiphase modelling framework was firstly proposed to predict the multiphase venting process of the LIB single cell due to TR. The proposed model covered the entire chain of chemical reactions and physical transformation during TR. A lumped model in battery cell scale unveiled the interplay of thermal abuse progression and pressure accumulation. The CFD model coupled with the discrete phase model (DPM) was adopted to simulate both generated gases and ejected particles.
After developing the TR, venting and jet fire model for a single cell, we developed a model framework based on the conjugate heat transfer to predict the TR propagation behaviour considering the interaction between jet fire and TR propagation in module. Simulation results demonstrate that increasing the space confinement degrees shortens the propagation time interval by enhancing the convection from ejected gases and the radiation from flame. The reduction of ceiling height extends the flame extension length and significantly accelerates the cell-to- cell failure, highlighting the impacts of jet fire on TR propagation.
