In recent years, the electrification and intellectualization of mining equipment have become inevitable trends, driven by the need for safer and more efficient operations in the coal industry. As a key component in this transition, energy storage lithium battery systems offer a promising solution for replacing traditional diesel-powered machinery in underground environments. However, conventional explosion-proof lithium battery power supplies, such as those using flameproof enclosures, face significant challenges, including low energy density, limited range, and heightened risks of thermal runaway under high-temperature, high-humidity, and high-dust conditions. These issues stem from the inherent limitations of隔爆 structures, which add substantial weight and reduce overall efficiency. In our research, we address these problems by developing a novel special encapsulated energy storage lithium battery design, which enhances energy density while maintaining safety in explosive atmospheres. This article details our comprehensive approach, from fundamental thermal runaway studies to practical applications, emphasizing the critical role of energy storage lithium battery technology in advancing mining electrification.
The thermal runaway mechanism in energy storage lithium batteries is a complex process involving multiple exothermic reactions that can lead to catastrophic failure. Understanding this phenomenon is essential for designing safe systems. Thermal runaway typically begins with the decomposition of the solid electrolyte interface (SEI) layer, followed by reactions between the anode and electrolyte, separator melting, cathode decomposition, electrolyte breakdown, and finally, gas release and combustion. These stages are not sequential but can occur simultaneously as temperature rises. To model this behavior, we employ reaction kinetics based on the Arrhenius equation, where the reaction rate $$ r $$ is given by:
$$ r = A \exp\left(-\frac{E_a}{RT}\right) $$
Here, $$ A $$ is the pre-exponential factor, $$ E_a $$ is the activation energy, $$ R $$ is the gas constant, and $$ T $$ is the temperature. The heat generation rate $$ Q_{\text{gen}} $$ during thermal runaway can be expressed as the sum of contributions from various reactions:
$$ Q_{\text{gen}} = \sum_i \Delta H_i \cdot r_i $$
where $$ \Delta H_i $$ is the enthalpy change for reaction $$ i $$. Combining this with energy conservation, the temperature evolution is described by:
$$ \frac{dT}{dt} = \frac{1}{m C_p} \left( Q_{\text{gen}} – Q_{\text{loss}} \right) $$
In this equation, $$ m $$ is the mass, $$ C_p $$ is the specific heat capacity, and $$ Q_{\text{loss}} $$ represents heat dissipation to the surroundings. Our experiments focus on lithium iron phosphate (LiFePO4) batteries, known for their stability, but even these can undergo thermal runaway under abuse conditions. By integrating these models, we predict temperature and pressure changes during failure events, guiding the design of our encapsulated energy storage lithium battery systems.
Encapsulation is a key innovation in our energy storage lithium battery design, providing isolation from explosive environments while improving thermal management. We evaluated several encapsulation materials—silicone, polyurethane, and epoxy resin—based on their properties, as summarized in the table below. Silicone emerged as the optimal choice due to its excellent thermal stability, flexibility, and insulation characteristics, which are crucial for maintaining integrity under thermal stress.
| Property | Silicone | Polyurethane | Epoxy Resin |
|---|---|---|---|
| Operating Temperature Range | -60°C to 200°C | -70°C to 130°C | -50°C to 130°C |
| Dielectric Strength (kV/mm) | 25 | 20 | 18-21 |
| Flame Retardancy | UL94-V0 | UL94-V0 | UL94-V0 |
| Thermal Conductivity (W/m·K) | 0.8-2.8 | 0.3 | 0.8 |
| Hardness after Curing | 50±5 HA | 35-70 HA | 80 HD |
| Shrinkage after Curing | Very Low | Low | Medium |
| Adhesion | Fair | Fair | Good |
Silicone’s high thermal conductivity, approximately 43 times that of air, facilitates efficient heat dissipation, reducing the risk of hot spots. Moreover, its ability to remain elastic across a wide temperature range prevents cracking under thermal cycling, ensuring long-term reliability for energy storage lithium battery systems. In our encapsulation process, we inject silicone compound into battery enclosures, fully surrounding the cells to isolate potential ignition sources and provide robust protection against moisture, dust, and mechanical shocks.
To validate the safety of our encapsulated energy storage lithium battery design, we conducted nail penetration tests on both single cells and modules. These tests simulate mechanical abuse, a common trigger for thermal runaway. For single cells, we used a 202 Ah LiFePO4 battery encapsulated in a silicone-filled enclosure equipped with temperature and pressure sensors. Upon nail penetration, the voltage dropped rapidly to 0 V within 2 minutes, while the temperature at the penetration site (T3) surged to 620 K within 1 minute. The safety valve opened, releasing gases and electrolyte, but the encapsulation contained the event without fire or explosion. The temperature at the battery surface (T4) peaked at 515 K, highlighting the need for隔热 measures to prevent thermal propagation in multi-cell configurations.
For module-level tests, we assembled a series of 10 cells with aerogel insulation plates between them to block heat transfer. The module was encapsulated in a silicone compound with a free space of 16.5 L above the cells. Nail penetration on one cell triggered thermal runaway, resulting in a maximum pressure of 0.68 MPa in the enclosure and a surface temperature of 490 K on the affected cell. The insulation effectively limited heat spread, with a temperature difference of up to 200 K across the plates. We also investigated the effect of free space volume on pressure buildup, as shown in the table below, which summarizes key parameters from our experiments.
| Test Configuration | Free Space Volume (L) | Maximum Pressure (MPa) | Peak Temperature (K) | Pressure Rise Rate (kPa/s) |
|---|---|---|---|---|
| Single Cell | N/A | N/A | 620 | N/A |
| Module (10 cells) | 16.5 | 0.68 | 490 | 8.58 |
| Module with Larger Free Space | 50.3 | 0.081 | 470 | 1.2 |
| Module with Largest Free Space | 158.5 | 0.031 | 460 | 0.5 |
The data clearly indicate that increasing the free space volume significantly reduces the maximum pressure during thermal runaway, which is critical for designing lightweight enclosures. The pressure evolution can be modeled using the ideal gas law, accounting for gas generation from battery decomposition:
$$ P = \frac{nRT}{V} $$
where $$ P $$ is pressure, $$ n $$ is the number of moles of gas, $$ R $$ is the gas constant, $$ T $$ is temperature, and $$ V $$ is the free volume. By correlating this with experimental results, we optimize the enclosure design to balance safety and energy density for energy storage lithium battery applications.
In addition to mechanical abuse, we evaluated the risk of ignition in explosive atmospheres, such as methane-air mixtures common in coal mines. Our point explosion tests involved placing encapsulated battery modules in a chamber filled with 9.8% methane or a 12.5% mixture of methane and hydrogen (58% CH4, 42% H2). Thermal runaway alone did not ignite the gases; subsequent spark ignition produced lower explosion pressures compared to pure methane environments. For instance, in the 9.8% methane atmosphere, spark ignition after thermal runaway led to a peak pressure of 0.251 MPa, whereas pure methane explosion reached 0.595 MPa. This demonstrates that the gases released from energy storage lithium battery thermal runaway do not significantly enhance explosion severity, and standard explosion-proof equipment can contain such events.
The battery management system (BMS) is integral to the safe operation of energy storage lithium battery power supplies. Our BMS architecture includes battery monitoring units (BMUs) for cell-level data acquisition and a battery control unit (BCU) for system-level control. Each BMU tracks voltage and temperature from 10 cells using analog front-end (AFE) chips and communicates via an isolated serial peripheral interface (IsoSPI). The BCU aggregates data from multiple BMUs, monitors total voltage and current, and interfaces with external devices through CAN buses. Key protection functions include over-voltage, under-voltage, over-temperature, and over-current limits, which are implemented based on the following equations for state of charge (SOC) and state of health (SOH):
$$ \text{SOC} = \frac{Q_{\text{remaining}}}{Q_{\text{rated}}} \times 100\% $$
where $$ Q_{\text{remaining}} $$ is the remaining capacity and $$ Q_{\text{rated}} $$ is the rated capacity. For SOH, we use:
$$ \text{SOH} = \frac{Q_{\text{aged}}}{Q_{\text{new}}} \times 100\% $$
with $$ Q_{\text{aged}} $$ being the capacity after aging. The BMS also performs active balancing to maintain cell uniformity, crucial for preventing localized stress in energy storage lithium battery packs.
We developed a prototype energy storage lithium battery power supply comprising 60 series-connected cells, with a nominal voltage of 192 V and total energy of 42.24 kWh. The power enclosure weighs 503 kg, and the control box weighs 68 kg, resulting in a system-level energy density of 78.66 Wh/kg—over 40% higher than traditional flameproof designs. This improvement is achieved through the encapsulated structure, which eliminates heavy metal enclosures while ensuring safety. Field testing with a mining vehicle demonstrated reliable performance over 5.8 km of underground travel, with no issues in electrical functionality or encapsulation integrity. The table below summarizes the key specifications of our energy storage lithium battery system.
| Parameter | Value |
|---|---|
| Number of Cells | 60 |
| Nominal Voltage | 192 V |
| Total Energy | 42.24 kWh |
| Power Enclosure Weight | 503 kg |
| Control Box Weight | 68 kg |
| Enclosure Energy Density | 83.98 Wh/kg | System Energy Density | 78.66 Wh/kg |
In conclusion, our research on explosion-proof special encapsulated energy storage lithium battery technology has successfully addressed critical challenges in mining electrification. By leveraging silicone encapsulation, we enhance safety through effective thermal management and isolation, while significantly improving energy density. The integration of advanced BMS and rigorous testing under abuse conditions ensures reliability in harsh environments. This work not only supports the development of safer mining equipment but also contributes to standardized safety certifications for energy storage lithium battery systems, paving the way for widespread adoption in the coal industry and beyond.