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) poses significant safety risks under abusive conditions, such as mechanical, thermal, or electrical stress. Once TR occurs in a single cell, it can propagate to adjacent cells, leading to catastrophic failure. This study investigates the effectiveness of various thermal insulation materials in suppressing TR propagation within a 147 Ah ternary lithium-ion battery module. Experimental results demonstrate that material selection and thickness critically influence heat transfer mitigation, enabling safer battery pack designs.
Thermal Runaway Mechanism and Heat Transfer Model
TR in LIBs is triggered by exothermic reactions, including SEI decomposition, electrolyte decomposition, and cathode material breakdown. The heat generation rate ($q$) during TR can be expressed as:
$$
q = \sum_{i} \Delta H_i \cdot r_i
$$
where $\Delta H_i$ is the enthalpy change of reaction $i$, and $r_i$ is the reaction rate. The temperature evolution follows the heat diffusion equation:
$$
\rho c_p \frac{\partial T}{\partial t} = \nabla \cdot (k \nabla T) + q
$$
where $\rho$, $c_p$, and $k$ represent density, specific heat capacity, and thermal conductivity, respectively.
Experimental Setup and Material Properties
Three insulation materials were tested between adjacent 147 Ah ternary LIBs:
| Material | Thickness (mm) | Thermal Conductivity (W/m·K) |
|---|---|---|
| Phase Change Material (PCM) | 2.5 | 0.25 |
| Glass Fiber Aerogel | 2.5 | 0.035 |
| Basalt Fiber Aerogel | 2.0–3.0 | 0.030 |
Thermal runaway was induced using a mica heater (500 W) attached to the first cell. Temperature profiles were monitored at critical locations:
| Sensor | Location |
|---|---|
| T1 | Heater surface |
| T2 | Above safety vent |
| T3 | Downstream cell interface |
Results and Analysis
The TR propagation time ($t_{prop}$) and maximum downstream temperature ($T_{max}$) varied significantly with insulation materials:
| Material | $t_{prop}$ (s) | $T_{max}$ (°C) |
|---|---|---|
| PCM | 562 | 800+ |
| Glass Fiber | 518 | 240 |
| Basalt Fiber (3.0 mm) | N/A | 102.5 |
For basalt fiber aerogel, the critical thickness preventing TR propagation was determined by solving the thermal resistance equation:
$$
R_{th} = \frac{L}{kA}
$$
where $L$ is material thickness, $k$ is conductivity, and $A$ is contact area. A 3.0 mm basalt fiber layer achieved $R_{th} > 0.15$ K/W, effectively blocking heat flux above 1.5 kW.
Early Warning System Integration
A commercial gas sensor detected electrolyte vapors (e.g., ethyl methyl carbonate) during TR initiation. The alarm threshold corresponded to:
$$
C_{alert} = \int_{0}^{t} \frac{dn}{dt} e^{-\lambda t} dt \geq 1
$$
where $dn/dt$ is gas emission rate and $\lambda$ is decay constant. For 3.0 mm basalt fiber insulation, the sensor triggered 22 s before TR, enabling preventive measures.
Post-Test Battery Analysis
Downstream cells protected by basalt fiber retained functionality with minimal capacity loss ($\Delta Q < 2\%$), validated through discharge tests:
$$
Q = \int_{0}^{t_{end}} I(t) dt
$$
where $I(t)$ is discharge current. Voltage recovery to 4.17 V confirmed structural integrity despite thermal exposure.
Conclusion
Basalt fiber aerogel demonstrates superior TR propagation suppression in lithium-ion battery modules compared to PCM and glass fiber. A 3.0 mm thickness provides optimal thermal resistance while enabling early gas detection. This work establishes design guidelines for safer lithium-ion battery systems in high-energy applications.