In recent years, the global demand for efficient energy storage solutions has surged, driven by the integration of renewable energy sources and the need for grid stability. Among various energy storage technologies, the battery energy storage system (BESS) has emerged as a critical component due to its versatility and rapid response capabilities. As a researcher focused on thermal management in energy storage, I have dedicated efforts to addressing the challenges associated with heat dissipation in high-capacity lithium-ion batteries, which are prone to thermal runaway under extreme conditions. This article details the development of an immersion oil-based coolant specifically designed for BESS applications, emphasizing its formulation, performance evaluation, and safety enhancements. The increasing energy density and scaling of battery modules in BESS necessitate advanced cooling techniques to prevent overheating, which can lead to reduced efficiency, lifespan degradation, or catastrophic failures. Immersion cooling, where batteries are directly submerged in a dielectric fluid, offers a promising solution by enabling uniform heat transfer and mitigating thermal propagation. However, the success of this approach hinges on the coolant’s properties, such as thermal conductivity, electrical insulation, and material compatibility. Through systematic research, I have formulated a novel coolant that meets these requirements, leveraging molecular refining techniques and additive optimization to achieve superior performance in real-world BESS scenarios.
The formulation of the immersion coolant began with the selection of an appropriate base oil, as it constitutes the primary component influencing thermal and electrical properties. For this study, I sourced high-quality crude oil fractions and applied molecular refining to isolate hydrocarbon components with optimal carbon chain lengths and boiling ranges. This process ensured a balance between low viscosity for efficient heat transfer and high flash point for safety. The base oil’s key characteristics, including kinematic viscosity, flash point, and pour point, were evaluated to identify suitable candidates. Table 1 summarizes the performance data of various base oil components considered during the initial screening phase.
| Property | Component 1 | Component 2 | Component 3 | Component 4 | Test Method |
|---|---|---|---|---|---|
| Kinematic Viscosity at 40 °C (mm²/s) | 10.75 | 9.25 | 7.18 | 9.08 | GB/T 265 |
| Flash Point (°C) | 172 | 168 | 150 | 158 | GB/T 3536 |
| Density at 20 °C (kg/m³) | 830.8 | 850.5 | 881.9 | 864.8 | SH/T 0604 |
| Pour Point (°C) | -64 | -63 | -56 | -62 | GB/T 3535 |
| Acid Value (mg KOH/g) | 0.01 | 0.01 | 0.01 | 0.01 | GB/T 7304 |
Based on this analysis, I blended multiple components to achieve a base oil with tailored properties for the BESS coolant. The target was to maintain a kinematic viscosity between 9–11 mm²/s at 40 °C, ensuring adequate fluidity for heat exchange while minimizing pumping losses. The flash point was set above 160 °C to reduce fire risks, and the pour point was kept below -50 °C to guarantee performance in low-temperature environments. The blended base oil exhibited a viscosity of 9.36 mm²/s at 40 °C, a flash point of 166 °C, and a pour point of -69 °C, aligning with the desired specifications for a BESS application. This formulation provides a foundation for enhancing the thermal management of battery energy storage systems, where efficient heat removal is crucial for preventing thermal runaway and extending cycle life.
Next, I focused on improving the oxidative stability of the coolant, as prolonged exposure to elevated temperatures in a BESS can lead to degradation, formation of acidic compounds, and reduced insulation properties. Antioxidants play a vital role in scavenging free radicals and inhibiting oxidation chains. I selected 2,6-di-tert-butyl-p-cresol (T501) as the primary antioxidant due to its effectiveness in hydrocarbon-based fluids. To determine the optimal concentration, I conducted rotating oxygen bomb tests at 140 °C, measuring the induction time as an indicator of oxidative resistance. The relationship between antioxidant concentration and oxidation stability can be modeled using the following empirical formula for induction time (t):
$$ t = k \cdot [A]^n $$
where [A] is the antioxidant concentration, k is a rate constant, and n is an exponent derived from experimental data. The test results, presented in Table 2, show that increasing T501 content initially enhances oxidation resistance, but beyond a certain point, the benefits plateau due to saturation effects.
| Sample ID | Antioxidant Content (%) | Rotating Oxygen Bomb Time (min) | Test Method |
|---|---|---|---|
| 0# | 0 | 61 | SH/T 0193 |
| 1# | 0.1 | 304 | SH/T 0193 |
| 2# | 0.2 | 441 | SH/T 0193 |
| 3# | 0.3 | 504 | SH/T 0193 |
| 4# | 0.4 | 508 | SH/T 0193 |
| 5# | 0.5 | 515 | SH/T 0193 |
From the data, a T501 concentration of 0.4% was chosen as the optimum, providing a rotating oxygen bomb time of 508 minutes while avoiding unnecessary costs. This formulation ensures long-term stability in a BESS, where the coolant must withstand cyclic heating and cooling without significant degradation. The antioxidant mechanism involves the donation of hydrogen atoms to peroxy radicals, effectively terminating oxidation chains and preserving the coolant’s insulating properties. The generalized reaction can be expressed as:
$$ ROO• + AH → ROOH + A• $$
where ROO• is a peroxy radical and AH is the antioxidant. This approach enhances the reliability of the battery energy storage system by maintaining coolant integrity under operational stresses.
With the base oil and antioxidant optimized, I proceeded to formulate the final immersion coolant, designated as EBC160. The product was subjected to comprehensive quality control tests to verify compliance with the target specifications. Key parameters included kinematic viscosity, flash point, pour point, acid value, water content, breakdown voltage, and evaporation loss. Additionally, safety assessments such as acute skin irritation and lethal dose (LD50) were performed to ensure non-toxicity and environmental compatibility. The test results, summarized in Table 3, confirm that EBC160 meets all critical requirements for use in a BESS.
| Property | Target Specification | EBC160 Result | Test Method |
|---|---|---|---|
| Kinematic Viscosity at 40 °C (mm²/s) | 9–11 | 9.36 | GB/T 265 |
| Kinematic Viscosity at 100 °C (mm²/s) | Report | 2.31 | GB/T 265 |
| Flash Point (°C) | ≥160 | 166 | GB/T 3536 |
| Pour Point (°C) | ≤-50 | -69 | GB/T 3535 |
| Acid Value (mg KOH/g) | ≤0.02 | 0.01 | NB/SH/T 0836 |
| Water Content (μg/g) | ≤30 | 21 | SH/T 0207 |
| Breakdown Voltage (kV) | ≥50 | 62 | GB/T 507 |
| Rotating Oxygen Bomb at 140 °C (min) | ≥400 | 540 | SH/T 0193 |
| Evaporation Loss at 50 °C, 168 h (%) | ≤0.5 | 0.08 | In-house Method |
| Acute Skin Irritation/Corrosion | Non-irritating | Non-irritating | GB/T 21604 |
| LD50 (μg/g) | >2000 | >2000 | OECD 423 |
The EBC160 coolant demonstrates excellent insulation properties, with a breakdown voltage of 62 kV, far exceeding the minimum requirement of 50 kV. This is crucial for a BESS, where electrical isolation between battery cells prevents short circuits and ensures operational safety. The low evaporation loss of 0.08% indicates minimal fluid loss over time, reducing maintenance needs in sealed systems. Moreover, the non-irritating nature and high LD50 value make it environmentally benign, aligning with sustainability goals for battery energy storage systems. The formulation process involved blending the base oil with 0.4% T501 antioxidant, followed by filtration and degassing to remove impurities and moisture. This results in a coolant that not only dissipates heat effectively but also protects the BESS from internal corrosion and degradation.
Material compatibility is a critical aspect of coolant development, as the fluid must not react adversely with components within the BESS. I conducted accelerated aging tests by immersing various metals and polymers in EBC160 at 85 °C for 336 hours, simulating long-term exposure in a battery energy storage system. The materials included conductive parts like terminals and busbars, as well as insulating materials such as PET films and gaskets. After aging, I measured mass changes and inspected for visual alterations like swelling or discoloration. The compatibility was further assessed by analyzing the coolant’s properties post-test, including water content, acid value, dielectric dissipation factor, permittivity, and breakdown voltage. The mass change data, shown in Table 4, reveal minimal variations, indicating no significant interaction between the coolant and materials.
| Material | Initial Mass (g) | Final Mass (g) | Mass Change Rate (%) |
|---|---|---|---|
| Fishbone Support | 20.5265 | 20.5347 | 0.04 |
| Sampling Wire | 4.3545 | 4.3615 | 0.16 |
| Green Connector | 1.3286 | 1.3288 | 0.00 |
| White Connector | 1.1258 | 1.1262 | 0.04 |
| PET Film | 2.0694 | 2.0587 | -0.52 |
| Temperature Sampling Wire | 1.8850 | 1.8058 | -4.20 |
| Blue Adhesive | 0.3622 | 0.3618 | -0.02 |
| Blue Film | 0.5966 | 0.5988 | 0.11 |
| Separator Membrane | 0.2240 | 0.2245 | 0.22 |
| Pressure Relief Valve | 0.0256 | 0.0257 | 0.39 |
| Top Adhesive Sheet | 1.5787 | 1.5802 | 0.09 |
| Top Cover Plastic | 4.2115 | 4.2213 | 0.23 |
| Positive Terminal | 1.6842 | 1.6840 | -0.01 |
| Positive Tab | 3.4385 | 3.4387 | 0.06 |
| Negative Tab | 7.3506 | 7.3500 | -0.01 |
Post-test analysis of the coolant, detailed in Table 5, shows negligible changes in key properties, confirming that EBC160 remains stable and non-reactive. The dielectric dissipation factor stayed below 0.00009, and the breakdown voltage exceeded 60 kV, underscoring its suitability for a BESS. This compatibility ensures that the coolant will not compromise the integrity of battery components over its service life, reducing the risk of failures in critical energy storage applications.
| Material Tested | Water Content (μg/g) | Acid Value (mg KOH/g) | Dielectric Dissipation Factor (25 °C) | Permittivity (25 °C) | Breakdown Voltage (kV) |
|---|---|---|---|---|---|
| Blank | 22.7 | 0.006 | 0.00006 | 2.13 | 64.8 |
| Fishbone Support | 23.9 | 0.005 | 0.00005 | 2.11 | 63.5 |
| Sampling Wire | 22.2 | 0.006 | 0.00006 | 2.12 | 61.8 |
| Green Connector | 21.8 | 0.006 | 0.00006 | 2.11 | 63.5 |
| PET Film | 22.4 | 0.006 | 0.00003 | 2.12 | 65.2 |
| White Connector | 23.1 | 0.007 | 0.00006 | 2.13 | 67.3 |
| Temperature Sampling Wire | 20.3 | 0.006 | 0.00005 | 2.12 | 64.6 |
| Blue Adhesive | 22.2 | 0.006 | 0.00008 | 2.12 | 61.7 |
| Blue Film | 21.8 | 0.006 | 0.00008 | 2.12 | 60.3 |
| Separator Membrane | 22.9 | 0.006 | 0.00009 | 2.13 | 63.1 |
| Pressure Relief Valve | 23.9 | 0.006 | 0.00007 | 2.12 | 68.1 |
| Top Adhesive Sheet | 23.5 | 0.006 | 0.00006 | 2.11 | 64.3 |
| Top Cover Plastic | 23.1 | 0.005 | 0.00005 | 2.11 | 65.3 |
| Positive Terminal | 24.3 | 0.006 | 0.00006 | 2.11 | 64.9 |
| Positive Tab | 24.0 | 0.006 | 0.00006 | 2.13 | 66.8 |
| Negative Tab | 24.8 | 0.006 | 0.00005 | 2.12 | 64.7 |
Safety performance is paramount in a BESS, as thermal runaway can lead to fires or explosions. To evaluate the efficacy of EBC160 in preventing such events, I conducted nail penetration tests comparing batteries exposed to air versus those immersed in the coolant. In air, a short circuit caused rapid temperature rise above 400 °C, igniting the electrolyte and producing flames. In contrast, batteries submerged in EBC160 experienced controlled heat dissipation, with surface temperatures peaking at 280 °C and the coolant remaining at 48 °C. The heat absorption capacity of the coolant can be described by the heat transfer equation:
$$ Q = m \cdot c_p \cdot \Delta T $$
where Q is the heat absorbed, m is the mass of coolant, c_p is the specific heat capacity, and ΔT is the temperature change. The immersion approach effectively quenches thermal propagation, as the coolant acts as a heat sink and oxygen barrier. The following image illustrates the dramatic difference in safety outcomes, highlighting the protective role of immersion cooling in a BESS.
This test confirms that EBC160 can mitigate thermal runaway risks in a battery energy storage system, addressing a fundamental safety concern. The coolant’s high specific heat and thermal conductivity facilitate efficient energy dissipation, while its insulating properties prevent electrical arcs. In a full-scale BESS, this translates to enhanced reliability and reduced maintenance costs, as the system can operate safely under high load conditions. The development of such coolants is essential for the widespread adoption of immersion cooling in battery energy storage systems, particularly as energy densities continue to increase.
In conclusion, the EBC160 immersion coolant represents a significant advancement in thermal management for battery energy storage systems. Through careful selection of base oils and antioxidants, I have created a product that excels in oxidation stability, electrical insulation, and material compatibility. The safety tests demonstrate its ability to prevent thermal runaway, making it a viable solution for next-generation BESS designs. Future work will focus on scaling up production and conducting long-term field trials to validate performance in diverse operating environments. As the demand for efficient energy storage grows, innovations like EBC160 will play a crucial role in ensuring the safety and sustainability of battery energy storage systems worldwide.