As a researcher deeply involved in the safety analysis of energy storage systems, I have conducted extensive experimental studies to unravel the fire propagation characteristics and energy transfer mechanisms in double-layer energy storage battery. This work focuses on lithium iron phosphate (LiFePO₄) batteries, widely adopted in energy storage power stations due to their high energy density and long cycle life. However, their susceptibility to thermal runaway and subsequent fire propagation poses significant safety risks. My investigation aims to quantify the energy transfer pathways during fire initiation and propagation, providing critical insights for designing safer energy storage battery systems.
Experimental Design and Methodology
The experiments utilized 100Ah LiFePO₄ batteries arranged in double-layer configurations. Three distinct setups were tested:
- Group 1: 1 battery per layer (non-propagating group).
- Group 2: 2 batteries per layer (non-propagating group).
- Group 3: 3 batteries per layer (fire-propagating group).
Key parameters of the energy storage battery is summarized in Table 1.
Table 1: Specifications of the 100Ah LiFePO₄ Energy Storage Battery
| Parameter | Value |
|---|---|
| Nominal Capacity | 100 Ah |
| Mass | 2245 ± 5 g |
| Dimensions (L×W×H) | 130 mm × 36 mm × 211.8 mm |
| Specific Heat Capacity | 985.3 J·kg⁻¹·°C⁻¹ |
| Thermal Conductivity | 21.24 W·m⁻¹·°C⁻¹ |
Each battery was charged to 100% state-of-charge (SOC) and subjected to controlled heating at the bottom layer to trigger thermal runaway. Temperature profiles, voltage changes, and flame dynamics were recorded using K-type thermocouples and high-speed cameras.
Key Observations and Results
1. Temperature Evolution and Thermal Runaway
Thermal runaway in energy storage battery exhibited distinct temperature rise patterns. For the fire-propagating group (Group 3), the peak temperature of top-layer batteries reached 640.2°C, 22.1% higher than the bottom-layer batteries (524.3°C). The maximum temperature rise rate for the top layer was 14.0°C·s⁻¹, 86.7% higher than the bottom layer (7.5°C·s⁻¹). This disparity underscores the amplified hazards associated with vertical fire propagation in energy storage systems.
Table 2: Temperature Characteristics During Fire Propagation
| Parameter | Bottom Layer | Top Layer | Difference |
|---|---|---|---|
| Peak Temperature (°C) | 524.3 | 640.2 | +115.9 |
| Max. Temp. Rise Rate (°C·s⁻¹) | 7.5 | 14.0 | +6.5 |
2. Energy Transfer Pathways
The cumulative energy transferred from the bottom to the top layer was quantified for each configuration. In Group 3, the total energy triggering fire propagation was 379.7 kJ, distributed as follows:
- 47.5% through the bottom surface (conductive heat transfer).
- 52.5% through the side surfaces (radiative and convective heat transfer).
The energy accumulation process followed a stepwise pattern, as described by:Qtrig=Qbo+Qside+Qself+QdissQtrig=Qbo+Qside+Qself+Qdiss
where QselfQself (self-heating) and QdissQdiss (dissipation) were negligible.
Table 3: Cumulative Energy Transfer in Fire Propagation
| Bottom Layer Configuration | Energy Transferred (kJ) |
|---|---|
| 1 Battery | 249.1 |
| 2 Batteries | 334.3 |
| 3 Batteries | 379.7 |
3. Stages of Fire Propagation
The fire propagation process in energy storage battery involved three distinct phases:
- Flame Baking Stage: Gentle heating from ignited gases, with an average temperature rise rate of 6.4–7.6°C/min.
- Flame Jet Stage: Intense heating during thermal runaway, with rates doubling to 13.9–17.6°C/min.
- Synchronized Thermal Runaway: Simultaneous failure of multiple batteries, driven by cumulative energy transfer.
Mechanistic Insights and Safety Implications
1. Critical Energy Thresholds
The minimum energy required to trigger thermal runaway in a single energy storage battery was determined as 341.8 kJ, aligning closely with experimental observations (379.7 kJ). This threshold serves as a benchmark for designing fire suppression systems.
2. Mitigation Strategies
To enhance the safety of energy storage battery systems, the following measures are proposed:
- Thermal Barriers: Install insulation materials between battery layers to block conductive and radiative heat transfer.
- Early Detection Systems: Monitor temperature gradients and gas emissions during the flame baking stage to enable timely intervention.
- Structural Modifications: Avoid direct exposure of battery surfaces to flames by integrating protective casings.
Conclusion
This study elucidates the fire propagation dynamics and energy transfer mechanisms in double-layer energy storage battery. Key findings include:
- Vertical fire propagation in energy storage systems is driven by cumulative heat transfer, with 52.5% of energy transmitted through side surfaces.
- Top-layer batteries exhibit 22.1% higher peak temperatures and 86.7% faster thermal runaway rates compared to bottom layers.
- A critical energy threshold of ~380 kJ triggers synchronized thermal runaway in multi-layer configurations.
These insights pave the way for safer energy storage battery designs, emphasizing the need for multi-path heat mitigation and real-time monitoring systems. Future work will explore scalable solutions for large-scale energy storage installations, ensuring reliability without compromising safety.
Formula Appendix
- Energy Accumulation:
Q=c⋅m⋅ΔTQ=c⋅m⋅ΔT
where cc = specific heat capacity, mm = mass, ΔTΔT = temperature rise.
- Heat Transfer Through Battery Surfaces:
Qbo=λ⋅Aboσ∫0t(Tbo−Tave) dtQbo=σλ⋅Abo∫0t(Tbo−Tave)dt
where λλ = thermal conductivity, AboAbo = bottom surface area, σσ = conduction distance.