In the context of global efforts toward carbon neutrality, electrochemical energy storage technologies, particularly those utilizing energy storage lithium batteries, have emerged as pivotal enablers for renewable energy integration. Lithium-ion batteries, characterized by high energy density and extended cycle life, are extensively deployed in electric vehicles, grid-scale energy storage systems, and maritime applications. However, the escalating adoption of energy storage lithium battery systems has been accompanied by an increasing frequency of fire and explosion incidents stemming from thermal runaway events within battery compartments. These episodes, often triggered by overcharging, overheating, or mechanical abuse, can lead to the rapid release of toxic and flammable gases, posing severe threats to infrastructure, personnel, and the environment. This study employs an experimental approach to systematically examine the combustion and explosion characteristics of multi-component flammable gases generated during thermal runaway in energy storage lithium battery compartments, aiming to furnish critical data for enhancing safety protocols in such systems.
The experimental apparatus comprised a gas compounding system, high-pressure storage vessels and piping networks, an array of pressure transducers interfaced with a data acquisition system, and a 20 kV electric spark igniter. To simulate the diverse gas compositions resulting from thermal runaway in energy storage lithium battery systems under varying operational conditions, gas mixtures were formulated based on documented compositions from prior research. The primary constituents included hydrogen (H₂), carbon monoxide (CO), methane (CH₄) as a representative hydrocarbon, and carbon dioxide (CO₂). The volumetric fractions of these components were varied to encompass scenarios observed during different states of charge and abuse conditions, with hydrogen volume fraction specifically ranging from 25% to 70%. The release pressures of the gas mixtures were set at 500 kPa, 1000 kPa, and 2000 kPa to replicate the internal pressures that can develop within constrained energy storage lithium battery packs during failure.
The experimental procedure initiated with evacuating the system to ensure integrity, followed by the sequential introduction of gases into the storage vessel via the compounding system. Upon activation of the spark igniter and data acquisition, the downstream ball valve was opened, permitting the pressurized gas mixture to discharge through a 10 cm diameter, 100 cm long venting pipe. Ignition occurred at the pipe orifice, resulting in jet flames and combustion-induced overpressure waves. Post-test purging with nitrogen ensured operational safety. The reliability of the methodology was corroborated through repeat trials, which demonstrated consistent overpressure peaks with minimal deviation, affirming the robustness of the experimental setup for assessing hazards in energy storage lithium battery environments.
| Case | H₂ (%) | CO (%) | CH₄ (%) | CO₂ (%) |
|---|---|---|---|---|
| 1 | 25 | 6 | 19 | 50 |
| 2 | 40 | 12 | 23 | 25 |
| 3 | 55 | 5 | 16 | 24 |
| 4 | 70 | 7 | 9.5 | 13.5 |
The combustion and explosion dynamics of the gas mixtures were quantified through overpressure measurements at strategic locations: P1 (0.5 cm from ignition source), P2 (50 cm downstream), and P3 (100 cm downstream). The overpressure development for a release pressure of 500 kPa is illustrated in Figure 4, where the peak overpressure at P1 increased from 18.99 Pa at 25% H₂ to 252.66 Pa at 70% H₂. This substantial rise underscores the dominant role of hydrogen in amplifying combustion intensity due to its broad flammability limits and high burning velocity. The attenuation of overpressure with distance was evident, with P2 and P3 recordings showing reductions of up to 50% relative to P1, highlighting the localized nature of the blast wave. The relationship between hydrogen fraction and overpressure can be modeled using the expression for combustion energy release:
$$ E_c = \sum_{i} x_i \cdot \Delta H_{c,i} $$
where \( E_c \) is the total combustion energy, \( x_i \) is the mole fraction of component \( i \), and \( \Delta H_{c,i} \) is its heat of combustion. For hydrogen, \( \Delta H_{c,H_2} = -241.8 \, \text{kJ/mol} \), significantly higher than that of methane (\( -890.8 \, \text{kJ/mol} \) per mole but lower per unit mass), explaining the heightened reactivity with increasing H₂ fraction.
At elevated release pressures of 1000 kPa, the overpressure peaks exhibited more pronounced gradients. For instance, at 40% H₂, P1 and P2 peaks were 220.86 Pa and 148.40 Pa, respectively, indicating a 32.81% decay over 0.5 m. This attenuation is characteristic of blast waves propagating in unconfined spaces, governed by the Friedlander equation:
$$ P(t) = P_0 \cdot e^{-t/\theta} \cdot (1 – t/t_d) $$
where \( P(t) \) is the overpressure at time \( t \), \( P_0 \) is the peak incident overpressure, \( \theta \) is the decay constant, and \( t_d \) is the duration. The surge in P1 peak to 484.16 Pa at 70% H₂ and 1000 kPa underscores the synergistic effect of hydrogen content and storage pressure on explosion severity. In scenarios mimicking high-pressure scenarios in energy storage lithium battery systems, such as 2000 kPa release pressure, the overpressure profiles displayed complex behaviors, including multiple peaks due to ignition instabilities. For 55% and 70% H₂ mixtures, P1 peaks reached 655.46 Pa and 677.22 Pa, respectively, suggesting that beyond a threshold, pressure effects may overshadow compositional variations in dictating blast strength.
| H₂ Fraction (%) | Release Pressure (kPa) | P1 (Pa) | P2 (Pa) | P3 (Pa) |
|---|---|---|---|---|
| 25 | 500 | 18.99 | 16.62 | 11.91 |
| 40 | 500 | 75.34 | 52.18 | 35.67 |
| 55 | 500 | 148.92 | 112.45 | 78.33 |
| 70 | 500 | 252.66 | 185.28 | 126.38 |
| 25 | 1000 | 64.10 | 58.22 | 42.15 |
| 40 | 1000 | 220.86 | 148.40 | 95.63 |
| 55 | 1000 | 248.03 | 207.38 | 132.19 |
| 70 | 1000 | 484.16 | 352.27 | 228.44 |
| 25 | 2000 | 425.48 | 307.01 | 222.95 |
| 40 | 2000 | 352.27 | 290.40 | 190.97 |
| 55 | 2000 | 655.46 | 548.91 | 385.62 |
| 70 | 2000 | 677.22 | 593.45 | 412.78 |
The differential pressure analysis between sensor pairs further elucidates the blast wave propagation dynamics. The pressure difference \( \Delta P_{12} = P1 – P2 \) and \( \Delta P_{23} = P2 – P3 \) were computed to quantify attenuation. For most cases, \( \Delta P_{12} \) exceeded \( \Delta P_{23} \), consistent with the inverse-square law decay of shock waves in air. However, at 70% H₂ and 2000 kPa, \( \Delta P_{23} \) diminished, indicating that high hydrogen fractions and pressures promote more uniform energy distribution, potentially due to accelerated flame speeds and reduced spatial gradients. The jet flame development, captured through high-speed imaging, revealed a transition from initial blue hemispherical flames to elongated red-tipped jets, with lengths approaching 200 cm at higher H₂ fractions. The flame length \( L_f \) can be correlated with the gas release rate using the dimensionless Froude number:
$$ Fr = \frac{u^2}{g \cdot d} $$
where \( u \) is the jet velocity, \( g \) is gravity, and \( d \) is the orifice diameter. For Fr > 1, momentum-dominated jets exhibit extended lengths, as observed in energy storage lithium battery failure scenarios where rapid gas discharge occurs. The combustion efficiency \( \eta_c \) of the mixtures, defined as the ratio of actual heat release to theoretical maximum, was estimated to exceed 0.85 for H₂-rich blends, underscoring the completeness of reactions and the associated risk of secondary explosions in confined spaces.
The findings underscore the criticality of hydrogen concentration and system pressure in modulating the hazards associated with thermal runaway in energy storage lithium battery compartments. Specifically, hydrogen volume fractions exceeding 40% markedly elevate the risk of destructive overpressures, particularly when coupled with release pressures above 1000 kPa. The jet flames, capable of extending up to 2 m, pose additional thermal radiation threats to adjacent equipment and structures. These insights advocate for the implementation of robust gas detection systems, pressure relief mechanisms, and flame arrestors in energy storage lithium battery designs to mitigate catastrophic outcomes. Future work should focus on real-time monitoring of gas compositions and the development of predictive models for explosion thresholds in varied enclosure geometries.
In conclusion, this experimental investigation delineates the combustion and explosion parameters of flammable gases released during thermal runaway in energy storage lithium battery systems. The data presented herein provide a foundation for advancing safety standards and operational guidelines, ensuring the secure deployment of energy storage lithium battery technologies in the pursuit of sustainable energy solutions. The integration of compositional and pressure controls is paramount to minimizing the inherent risks and fostering the resilient growth of the energy storage sector.