Lithium-ion batteries (LIBs) are widely utilized in electric vehicles and energy storage systems due to their high energy density and long cycle life. However, thermal runaway (TR) triggered by localized overheating remains a critical safety challenge. This study investigates the heat propagation dynamics and TR characteristics of a 50 Ah LiFePO4 battery under terminal overheating caused by loose connecting plates. A three-dimensional lumped TR model coupled with chemical reaction kinetics is developed to analyze temperature evolution and heat generation mechanisms. Furthermore, an oblique-channel liquid cooling plate is proposed to mitigate thermal accumulation and improve temperature uniformity.
1. Electrochemical-Thermal Coupling Model
The thermal runaway process is governed by four exothermic reactions: SEI decomposition, anode-electrolyte reaction, cathode-electrolyte reaction, and electrolyte decomposition. The total heat generation rate $Q_{\text{tot}}$ is expressed as:
$$ Q_{\text{tot}} = \sum H_i W_i R_i \quad (i = \text{sei, ne, pe, e}) $$
where $H_i$, $W_i$, and $R_i$ represent the reaction enthalpy, material mass fraction, and reaction rate, respectively. The reaction rates follow Arrhenius-type equations:
$$ R_{\text{sei}} = A_{\text{sei}} \exp\left(-\frac{E_{a,\text{sei}}}{RT}\right) c_{\text{sei}}^{n_{\text{sei}}} $$
$$ R_{\text{ne}} = A_{\text{ne}} \exp\left(-\frac{t_{\text{sei}}}{t_{\text{sei},0}}\right) \exp\left(-\frac{E_{a,\text{ne}}}{RT}\right) c_{\text{ne}}^{n_{\text{ne}}} $$
The energy conservation equation for the battery system is:
$$ \rho C_p \frac{\partial T}{\partial t} = \nabla \cdot (k \nabla T) + Q_{\text{tot}} $$
| Reaction | $A$ (s⁻¹) | $E_a$ (kJ/mol) | $H$ (J/kg) |
|---|---|---|---|
| SEI decomposition | 1.667×10¹⁵ | 135.1 | 2.57×10⁵ |
| Anode reaction | 2.5×10¹³ | 135.1 | 1.714×10⁶ |
| Cathode reaction | 2×10⁸ | 103.0 | 1.947×10⁵ |
| Electrolyte decomposition | 5.14×10²⁵ | 274.0 | 6.2×10⁵ |
2. Terminal Overheating Characteristics
Localized heating at battery terminals (3 cm² area) induces severe heat accumulation near the tabs. Figure 1 demonstrates the temperature distribution during different TR phases:
Key findings under terminal overheating conditions:
- TR trigger time decreases exponentially with heating power:
$$ t_{\text{TR}} = 5120.5 \exp(-0.0023P) \quad (R² = 0.98) $$
where $P$ is the heating power (100–225 W). - Peak temperature increases by 27.9°C when heating power rises from 100 W to 225 W.
- Temperature standard deviation during pre-TR phase exceeds 18.4°C, indicating significant thermal gradients.
| Parameter | 100 W | 156 W | 225 W |
|---|---|---|---|
| TR trigger time (s) | 5120.5 | 2111.0 | 1299.0 |
| Peak temperature (°C) | 696.9 | 721.5 | 724.8 |
| Max heating rate (°C/s) | 12.7 | 24.3 | 38.6 |
3. Comparative Analysis of Heating Locations
Three overheating scenarios are compared:
- Terminal heating (3 cm²)
- Bottom heating (18.2 cm²)
- Front heating (224 cm²)
The temperature rise during TR phase follows:
$$ \Delta T_{\text{TR}} = \frac{T_{\text{peak}} – T_{\text{trigger}}}{t_{\text{peak}} – t_{\text{trigger}}} $$
| Location | ΔTTR (°C/s) | tTR (s) | Tpeak (°C) |
|---|---|---|---|
| Terminal | 14.3 | 1299 | 705.5 |
| Bottom | 11.9 | 1233 | 695.1 |
| Front | 12.8 | 1264 | 698.3 |
4. Oblique-Channel Liquid Cooling Design
To address localized heating near tabs, an oblique-channel cooling plate (27.5° inclination angle) demonstrates superior performance:
$$ \text{Cooling efficiency} = \frac{T_{\text{baseline}} – T_{\text{cooled}}}{T_{\text{baseline}} – T_{\text{inlet}}} \times 100\% $$
Key advantages compared to straight-channel designs:
- 18.9% reduction in temperature standard deviation
- 9.0% lower average temperature at 900 s operation
- 31% higher heat transfer coefficient
| Design | ΔTmax (°C) | σT (°C) | Pressure drop (Pa) |
|---|---|---|---|
| Oblique-channel | 8.2 | 2.1 | 142 |
| Straight-channel | 11.7 | 2.6 | 118 |
5. Conclusion
This study reveals critical insights into lithium-ion battery thermal management:
- Terminal overheating causes 17.2% faster TR propagation than bottom heating due to concentrated thermal accumulation near tabs.
- The oblique-channel cooling plate reduces peak temperatures by 206°C compared to uncontrolled TR scenarios.
- Heating power density (W/cm²) inversely correlates with TR trigger time:
$$ t_{\text{TR}} = 1853 P^{-0.67} \quad (R² = 0.94) $$
These findings provide essential guidelines for designing safer lithium-ion battery systems with enhanced thermal management capabilities.