As a researcher deeply involved in the safety of energy storage technologies, I have observed that the global push for energy transition and climate change mitigation has significantly accelerated the deployment of renewable energy sources such as solar and wind power. The lithium-ion battery energy storage system (BESS), with its high energy density, fast response, and long cycle life, has emerged as a critical technology for addressing renewable energy intermittency and enhancing grid stability. It is now widely applied in generation, transmission, and end-user sectors. Despite these advantages, the increasing frequency of fire and explosion incidents in recent years has caused severe casualties and property losses, raising urgent concerns about the safety of BESS. In this comprehensive study, I systematically analyze the risk factors, evolution mechanisms, and prevention technologies for fire and explosion in BESS, aiming to improve the safety and reliability of these systems for sustainable energy applications.
1. Risk Factor Analysis of Fire and Explosion in Lithium-ion Battery Energy Storage Systems
1.1 Battery Thermal Runaway
Thermal runaway is the primary root cause of fire and explosion in BESS. When heat generated inside a battery cannot be dissipated in time, the temperature rises sharply, triggering a series of irreversible chemical reactions that ultimately lead to thermal runaway. The inducing factors are complex and diverse, encompassing both internal and external causes.
From an internal perspective, impurities introduced during cell manufacturing, microstructural defects in electrode materials, and instability of the electrolyte can cause internal short circuits during operation, leading to thermal runaway. When an internal short circuit occurs, the current surges, generating substantial Joule heat, which rapidly elevates the battery temperature, as described by the following equation:
$$ Q = I^2 R T $$
where \( Q \) is the heat generated (J), \( I \) is the current (A), \( R \) is the resistance (Ω), and \( T \) is the time (s). As the temperature rises, the chemical reaction activity between the electrode materials and the electrolyte increases, further releasing heat and creating a vicious cycle that culminates in thermal runaway. The main chemical reactions include:
(1) Reaction between the negative electrode and electrolyte:
$$ \text{LiC}_6 + x\text{PF}_5 \rightarrow \text{LiF} + \text{LiPF}_y + \text{C}_6 + (x-y)\text{PF}_3 + (x-1)\text{F}_2 $$
(2) Reaction between the positive electrode material (e.g., LiCoO₂) and electrolyte:
$$ \text{LiCoO}_2 + \text{C}_2\text{H}_4\text{O}_3 \rightarrow \text{Li}_2\text{CO}_3 + \text{Co}_3\text{O}_4 + \text{CO}_2 + \text{C} $$
External factors such as overcharging, over-discharging, overheating, and mechanical abuse are also major triggers. Overcharging can cause lithium dendrites to pierce the separator, leading to short circuits; over-discharging induces irreversible structural changes in electrode materials, increasing failure risk; high temperatures exacerbate heat generation and insufficient dissipation; mechanical abuse such as collision or crushing damages internal structures and can trigger electrode short circuits, ultimately leading to thermal runaway.
1.2 Electrical Faults
Electrical faults are a significant source of fire and explosion risk. Short circuit faults have complex origins. The battery management system (BMS) may have deviations in voltage and current monitoring, causing overcharge or over-discharge that leads to internal short circuits. Long-term operation degrades insulation, especially under high temperature and humidity, which damages insulating layers and causes line short circuits. Loose connections or poor contact can generate localized overheating under high currents, also triggering short circuits. The following table summarizes the statistical causes of short circuit faults:
| Fault Type | Percentage (%) | Typical Example |
|---|---|---|
| BMS monitoring deviation | 35 | Overcharge of a single cell leading to internal short circuit |
| Line insulation aging | 40 | Insulation breakdown under relative humidity ≥ 60% |
| Loose connection | 20 | Contact point melting due to high current |
| Other (e.g., lightning) | 5 | Surge voltage breaking through battery insulation |
1.3 Design and Installation Defects
Ineffective system design introduces safety hazards. Mismatched battery selection for the application—for instance, using low-rate batteries in high-power-demand scenarios—forces the batteries into sustained high-load operation, accelerating aging and increasing thermal runaway risk. Improper series/parallel configuration can cause voltage and current imbalance among battery modules, leading to overcharge or over-discharge of some cells, compromising lifespan and safety.
Inadequate thermal management system design is another critical issue. If the system cannot effectively control operating temperature, excessive heat generation cannot be dissipated promptly, leading to overheating and thermal runaway. Conversely, in low-temperature environments, insufficient heating reduces performance and raises safety risks.
2. Evolution Mechanism of Fire and Explosion in Lithium-ion Battery Energy Storage Systems
2.1 Chain Reactions Triggered by Thermal Runaway
When thermal runaway occurs in a lithium-ion cell, a complex chain reaction unfolds. First, the rising temperature causes the decomposition of the solid electrolyte interface (SEI) film on the negative electrode. Beyond a certain threshold, the SEI film breaks down, releasing heat and combustible gases such as carbon monoxide and hydrogen. These gases mix with air to form a combustible mixture, which ignites in the presence of an ignition source.
After SEI decomposition, the negative electrode material comes into direct contact with the electrolyte, triggering vigorous oxidation-reduction reactions that release substantial heat. As the reaction progresses, the temperature and internal pressure continue to rise. When the pressure exceeds the mechanical strength of the cell casing, the casing ruptures, ejecting high-temperature, combustible materials. This ejected mass forms a jet flame, which can initiate thermal runaway in adjacent cells, leading to a cascade of fires. The process is depicted in the diagram below (inserted conceptual representation).
2.2 Fire Propagation and Spread Mechanisms
In BESS, fire propagates and spreads primarily through three modes: thermal radiation, thermal conduction, and thermal convection, in addition to flame propagation.
For flame propagation, the laminar flame propagation speed is given by:
$$ S_L = \frac{m”}{\rho_u} $$
where \( S_L \) is the laminar flame speed (cm/s), \( m” \) is the mass burning rate (kg/(m²·s)), and \( \rho_u \) is the density of the unburnt mixture (kg/m³). The turbulent flame propagation speed is:
$$ S_T = S_L (1 + \alpha Re^n) $$
where \( S_T \) is the turbulent flame speed (cm/s), \( \alpha \) is the turbulence influence coefficient, \( Re \) is the Reynolds number, and \( n \) is the Reynolds exponent (taken as 0.25 in this analysis).
Thermal radiation follows the Stefan-Boltzmann law:
$$ Q_{\text{rad}} = \varepsilon \sigma A (T_1^4 – T_2^4) $$
where \( Q_{\text{rad}} \) is the radiative heat transfer rate (W), \( \varepsilon \) is the emissivity, \( \sigma \) is the Stefan-Boltzmann constant (5.67×10⁻⁸ W/(m²·K⁴)), \( A \) is the surface area (m²), \( T_1 \) and \( T_2 \) are the absolute temperatures of the hot and cold bodies (K). For long-distance radiation, the heat flux can be estimated by:
$$ q = \frac{\dot{Q}}{4\pi r^2} $$
where \( q \) is the heat flux (W/m²), \( \dot{Q} \) is the total radiative heat flow (W), and \( r \) is the distance between the source and the receiving surface (m).
Thermal conduction follows Fourier’s law:
$$ Q_{\text{cond}} = -k A_2 \frac{dT}{dx} $$
where \( Q_{\text{cond}} \) is the conductive heat transfer rate (W), \( k \) is the thermal conductivity (W/(m·K)), \( A_2 \) is the cross-sectional area (m²), and \( dT/dx \) is the temperature gradient (K/m).
Thermal convection is calculated using Newton’s cooling law:
$$ Q_{\text{conv}} = h A_3 (T_w – T_f) $$
where \( Q_{\text{conv}} \) is the convective heat transfer rate (W), \( h \) is the convective heat transfer coefficient (W/(m²·K)), \( A_3 \) is the surface area (m²), \( T_w \) is the wall temperature (K), and \( T_f \) is the fluid temperature (K). For natural convection, the Nusselt number is commonly expressed as:
$$ Nu = C (Gr \cdot Pr)^n $$
where \( Nu \) is the Nusselt number, \( C \) is an empirical constant, \( Gr \) is the Grashof number, \( Pr \) is the Prandtl number, and \( n \) is an empirical exponent. As an example, if the laminar flame speed \( S_L = 10 \) cm/s, \( \alpha = 0.5 \), \( Re = 100 \), and \( n = 0.25 \), then the turbulent flame speed becomes:
$$ S_T = 10 \times (1 + 0.5 \times 100^{0.25}) = 10 \times (1 + 0.5 \times 3.162) \approx 25.81 \text{ cm/s} $$
Thus, the turbulent flame speed is significantly higher than the laminar value, accelerating fire spread. When a battery fire occurs, flames and hot cells radiate heat to surrounding objects, thermal conduction through metal connectors triggers adjacent cell thermal runaway, and thermal convection through hot gases and ventilation ducts transfers heat and disperses flammable gases, collectively accelerating fire propagation.
2.3 Explosion Formation Conditions and Process
An explosion in BESS requires that combustible gases mix with air within the flammable range and encounter an ignition source of sufficient energy. During thermal runaway, large volumes of flammable gases are released, including hydrogen, carbon monoxide, and light hydrocarbons. These gases accumulate inside the battery enclosure and mix with air to form a combustible mixture. When the concentration falls within the explosive limits, any ignition source—such as an electrical spark or open flame—can trigger an explosion.
To assess whether a mixture is within the explosive risk range, the Le Chatelier principle can be applied. The lower explosive limit (LEL) and upper explosive limit (UEL) of the mixture are given by:
$$ \text{LEL}_{\text{mix}} = \frac{100}{\frac{y_1}{\text{LEL}_1} + \frac{y_2}{\text{LEL}_2} + \cdots + \frac{y_n}{\text{LEL}_n}} $$
where \( \text{LEL}_{\text{mix}} \) is the mixture LEL (vol%), \( y_i \) are the volume fractions of each combustible component, and \( \text{LEL}_i \) are the individual LEL values. Similarly,
$$ \text{UEL}_{\text{mix}} = \frac{100}{\frac{y_1}{\text{UEL}_1} + \frac{y_2}{\text{UEL}_2} + \cdots + \frac{y_n}{\text{UEL}_n}} $$
Different combustible gases have distinct minimum ignition energies (MIE), as shown in the following table:
| Combustible Gas | MIE (mJ) |
|---|---|
| Hydrogen | 0.02 |
| Methane | 0.28 |
| Carbon monoxide | 0.021 |
3. Fire and Explosion Prevention and Control Technologies for Lithium-ion Battery Energy Storage Systems
3.1 Battery Material and Design Improvements
To enhance safety at the source, developing intrinsically safer battery materials is crucial. For positive electrode materials, lithium iron phosphate (LFP) offers excellent thermal stability and safety, making it widely used in BESS. Compared to traditional materials such as cobalt oxide, LFP maintains structural stability at high temperatures, significantly reducing thermal runaway risk. For negative electrodes, silicon-based materials are promising due to their high theoretical specific capacity, but they suffer from large volume changes during cycling, which can damage the electrode structure. Researchers are addressing this through nanostructuring and material composites to improve stability and cycle life. The typical lithium-ion battery structure is schematically represented by a layered configuration including positive and negative terminals, separator, electrolyte, and casing.
3.2 Monitoring and Early Warning Technologies
Real-time monitoring and early warning are critical for risk prevention. Voltage and current monitoring evaluates the state of charge and health, alerting for overcharge, over-discharge, or overcurrent. Temperature sensors continuously monitor battery module and enclosure temperatures; when thresholds are exceeded, cooling systems activate and alarms sound. Pressure sensors detect abnormal internal pressure, triggering ventilation and pressure relief. Gas composition monitoring uses catalytic combustion or semiconductor sensors to detect hydrogen and carbon monoxide concentrations, issuing warnings before reaching explosive limits. The following table lists typical monitoring parameter thresholds:
| Parameter | Normal Operating Range | Abnormal Warning Range |
|---|---|---|
| Voltage (single cell) | 2.5 – 4.2 V | < 2.5 V (over-discharge) or > 4.2 V (overcharge) |
| Current | 0 – 120% of rated | > 120% (overcurrent) |
| Temperature (battery module) | 25 – 45 °C | > 45 °C (heating warning) |
| Temperature (enclosure) | 20 – 35 °C | > 35 °C (overheat) |
| Pressure (inside cell) | 0 – 0.1 MPa | > 0.1 MPa (abnormal pressure) |
| Hydrogen concentration | 0 – 0.04 vol% | > 0.04 vol% |
| Carbon monoxide concentration | 0 – 0.005 vol% | > 0.005 vol% |
3.3 Optimized Thermal Management System
I optimize the thermal management system based on battery operating characteristics. A hybrid liquid-cooling and air-cooling solution is employed, using proportional-integral-derivative (PID) algorithms to adjust coolant flow and fan speed, keeping the temperature difference across the battery stack within ±2 °C. Phase change materials (PCMs) are embedded between cells to absorb transient heat via latent heat of fusion, combined with metal heat sinks to enhance conduction. Temperature monitoring points are arranged in a grid pattern, feeding real-time data to the BMS for predictive control. The ideal operating temperature range for the battery is 25–45 °C. When the temperature exceeds 40 °C, the cooling system’s activation power is linearly related to temperature rise, as shown by:
$$ P = K \times (T – T_0) $$
where \( P \) is the cooling system power (W), \( K = 15 \) W/°C is the thermal coefficient, \( T \) is the real-time temperature (°C), and \( T_0 = 40 \) °C is the reference temperature. This relationship is derived from experimental data, allowing the system to increase cooling power as temperature rises to avoid heat accumulation.
3.4 Fire Suppression and Explosion Protection Measures
When a fire or explosion occurs, effective suppression and mitigation measures are essential. Among extinguishing agents, fine water mist offers excellent cooling and minimal water damage; perfluorohexanone and heptafluoropropane are highly effective but costlier, and both are widely used for lithium-ion battery fires. For explosion protection, the battery enclosure is designed with explosion-proof structures. The area of pressure relief vents is calculated precisely using:
$$ A = 10 C’ V^{2/3} $$
where \( A \) is the vent area (m²), \( C’ \) is the enclosure volume (m³), and \( V \) is the pressure relief coefficient (or related correction factor). For example, if the enclosure volume \( C’ = 80 \) m³ and assuming \( V = 1 \) (for preliminary calculation), the vent area would be:
$$ A = 10 \times 80 \times 1^{2/3} = 10 \times 80 \times 1 = 800 \text{ m}^2 $$
In practical applications, the specific \( V \) value must be determined according to battery type, flammable gas characteristics, and relevant safety codes to ensure effective pressure venting.
4. Conclusion
Lithium-ion battery energy storage systems (BESS) serve as a cornerstone technology for the energy transition and the construction of new power systems. Their safety performance directly impacts energy security and public safety, forming a critical foundation for stable energy system operation. My study has identified four core factors—battery thermal runaway, electrical faults, design and installation defects, and abnormal environmental conditions—as the primary triggers for fire and explosion in BESS. I have systematically elucidated the internal mechanisms of chain reactions during thermal runaway, inter-cell fire propagation, and the formation of explosive shock waves. To address these risks, the industry has developed a multi-dimensional prevention and control technology system covering battery material innovation, structural design optimization, thermal management upgrades, multi-parameter monitoring and early warning, and efficient fire suppression and explosion protection devices. Nevertheless, existing technologies still have gaps that require targeted research to drive continuous iteration and improvement in prevention and control measures. This will strengthen the barrier for the large-scale, safe deployment of BESS.