Abstract
Lithium-ion batteries, while pivotal for renewable energy storage and electric vehicles, face critical safety challenges due to thermal runaway (TR) under abusive conditions. This study investigates the efficacy of various thermal insulation materials—phase change materials (PCMs), glass fiber aerogel, and basalt fiber aerogel—in mitigating thermal runaway propagation (TRP) within high-energy-density 147 Ah ternary lithium-ion battery modules. Experimental results demonstrate that basalt fiber aerogel with a thickness of 3.0 mm effectively blocks TRP, maintaining downstream battery temperatures below 102.5°C and enabling normal discharge cycles post-TR. Commercial thermal runaway warning sensors achieved early detection 22 seconds prior to TR when basalt aerogel was employed. These findings provide actionable insights for designing safer lithium-ion battery systems through optimized thermal management strategies.
1. Introduction
The global transition toward carbon neutrality has accelerated the adoption of lithium-ion batteries in electric vehicles (EVs) and grid-scale energy storage. However, safety incidents involving thermal runaway—triggered by mechanical, thermal, or electrical abuse—remain a persistent concern. During TR, exothermic reactions within the battery escalate temperatures to >800°C, releasing flammable gases and ejecting molten materials. If unmitigated, TR propagates to adjacent cells, leading to catastrophic failure.
Thermal insulation materials are critical for interrupting heat transfer between cells. While prior studies have explored phase change materials (PCMs) and aerogels for TR suppression, their effectiveness in high-capacity ternary lithium-ion batteries (NCM/NCA chemistries) remains underexplored. This work addresses this gap by evaluating insulation materials based on:
- Thermal conductivity (λ, W·m⁻¹·K⁻¹)
- Thickness (δ, mm)
- Early warning compatibility with gas sensors
2. Experimental Design
2.1 Battery and Insulation Material Specifications
The test subject was a 147 Ah prismatic ternary lithium-ion battery (NCM chemistry) with parameters detailed in Table 1.
Table 1: Key parameters of the 147 Ah lithium-ion battery
| Parameter | Value |
|---|---|
| Nominal capacity | 147 Ah |
| Voltage range | 2.8–4.35 V |
| Energy density | 564 Wh |
| Mass | 2380 g |
| Dimensions | 45 × 220.8 × 105.2 mm |
Three insulation materials were tested:
- PCM: λ = 0.5 W·m⁻¹·K⁻¹, δ = 2.5 mm, latent heat = 1250 J·g⁻¹
- Glass fiber aerogel: λ = 0.035 W·m⁻¹·K⁻¹, δ = 2.5 mm
- Basalt fiber aerogel: λ = 0.03 W·m⁻¹·K⁻¹, δ = 2.0, 2.5, 3.0 mm
2.2 Thermal Runaway Triggering and Monitoring
TR was induced using a mica heating plate (500 W power input) attached to the cell surface. Temperature profiles were recorded via K-type thermocouples at four critical locations:
- T1: Heating plate surface
- T2: Safety valve of TR-initiated cell
- T3: Rear surface of TR-initiated cell
- T4: Adjacent cell surface
A commercial gas sensor monitored volatile organic compounds (VOCs) like ethyl methyl carbonate (EMC) and diethyl carbonate (DEC), triggering alarms at concentrations ≥1 ppm.
3. Theoretical Framework
3.1 Heat Transfer Dynamics During TR
The energy balance during TR propagation is governed by:ρCp∂t∂T=∇⋅(k∇T)+q˙gen−q˙loss
where:
- ρ: Density (kg·m⁻³)
- Cp: Specific heat (J·kg⁻¹·K⁻¹)
- k: Thermal conductivity (W·m⁻¹·K⁻¹)
- q˙gen: Heat generation rate from exothermic reactions
- q˙loss: Heat dissipation to surroundings
Insulation materials reduce q˙gen transmission by increasing thermal resistance:Rth=kδ
3.2 TR Propagation Criteria
A downstream cell undergoes TR if:\int_{0}^{t_{\text{TR}}}} \left( \dot{q}_{\text{in}} – \dot{q}_{\text{loss}} \right) dt \geq Q_{\text{crit}}
where Qcrit (~300 kJ for 147 Ah cell) is the critical energy to trigger self-sustaining reactions.
4. Results and Analysis
4.1 Performance of 2.5 mm Insulation Materials
Phase Change Material (PCM):
- TR initiated at t=251s, T3 peaked at 612°C.
- Downstream cell (T4) reached 487°C, entering TR after 562 s.
- Conclusion: PCM failed to block TRP due to limited latent heat absorption.
Glass Fiber Aerogel:
- TR occurred at t=267s, with T4 stabilizing at 240°C for 260 s before TR at 785 s.
- Conclusion: Delayed but inevitable TRP due to gradual heat accumulation.
Basalt Fiber Aerogel (2.5 mm):
- TR initiated at t=270s, but T4 plateaued at 185.9°C without TR.
- Conclusion: Basalt aerogel’s lower λ (0.03 vs. 0.035 W·m⁻¹·K⁻¹) enhanced heat blockage.
4.2 Thickness Optimization of Basalt Aerogel
2.0 mm Basalt Aerogel:
- T4 peaked at 134.0°C.
- Sensor triggered at t=184s, 5 s post-TR initiation.
3.0 mm Basalt Aerogel:
- T4 max = 102.5°C.
- Sensor alarmed at t=485s, 22 s before TR (t=507s).
- Post-TR downstream cell retained 4.17 V voltage and 98% capacity.
Table 2: Comparison of insulation performance
| Material (Thickness) | Tmax, downstream (°C) | TR Propagation | Early Warning |
|---|---|---|---|
| PCM (2.5 mm) | 487 | Yes | No |
| Glass aerogel (2.5 mm) | 240 → 487 | Yes | No |
| Basalt aerogel (2.0 mm) | 134 | No | Late (5 s) |
| Basalt aerogel (3.0 mm) | 102.5 | No | Yes (22 s) |
5. Mechanism of TR Suppression
5.1 Thermal Resistance vs. Material Thickness
The basalt aerogel’s effectiveness correlates with its thermal resistance:Rth=kδ∝δ
For δ = 3.0 mm:Rth=0.030.003=0.1m²\cdotpK\cdotpW⁻¹
This resistance reduced heat flux to downstream cells by 89% compared to PCM.
5.2 Gas Sensor Response Dynamics
The 3.0 mm basalt aerogel allowed slower, more detectable gas diffusion. Sensor response time (tsensor) relates to VOC diffusion velocity (v):tsensor=vδ
With v=0.14mm\cdotps⁻¹ for DEC/EMC mixtures:tsensor=0.143.0≈21.4s
This aligns with the observed 22 s early warning.
6. Conclusion
This study demonstrates that basalt fiber aerogel with δ ≥ 3.0 mm effectively suppresses TRP in high-energy lithium-ion batteries by:
- Increasing thermal resistance (Rth) to limit heat flux.
- Slowing gas diffusion to enable early detection.
- Preserving downstream cell functionality post-TR.
Future work will optimize aerogel compositions for minimized weight and enhanced fire resistance. These insights advance the design of inherently safer lithium-ion battery systems for EVs and renewable energy storage.