In recent years, the rapid development of the electrochemical energy storage industry has been driven by global carbon neutrality goals. Lithium-ion batteries, known for their high energy density, long cycle life, and low self-discharge rate, are ideal for energy storage applications. However, these energy storage cells exhibit poor adaptability to high-temperature environments. When the ambient temperature exceeds 45°C, their cycle life degrades rapidly, and significant heat generated during charging and discharging can raise battery temperatures, potentially leading to thermal runaway and safety hazards. Additionally, temperature uniformity is critical for the performance and longevity of energy storage cells. A uniform temperature distribution minimizes temperature differences within the battery system, enhancing overall efficiency. For instance, electric vehicle batteries require operation within an optimal temperature range of 25–40°C, with temperature variations between cells kept below 5°C. Thus, developing efficient and reliable cooling systems is essential for maintaining the performance of energy storage cells.
This study focuses on liquid-cooled battery packs commonly used in energy storage systems. Three distinct liquid cooling plate designs are proposed and evaluated for thermal performance and load-bearing capacity under 0.5 C charge-discharge cycles. The objective is to identify the optimal design that ensures effective heat dissipation, temperature uniformity, and structural integrity for energy storage cells. The following sections detail the battery pack model, design schemes, experimental methodologies, results, and comprehensive analysis.
Liquid-Cooled Battery Pack Model and Cooling Plate Designs
The liquid-cooled battery pack comprises two cell modules, a liquid cooling plate, and a battery management unit (BMU). The cooling strategy involves bottom cooling of the energy storage cells, where a 1–1.5 mm thick thermally conductive structural adhesive enhances heat transfer and electrical insulation between the cells and the cooling plate. Insulating pads between cells prevent thermal propagation in case of a single cell failure. During 0.5 C charge-discharge cycles, heat is transferred from the energy storage cells to the coolant via the liquid cooling plate, maintaining safe operating temperatures. The cooling plate also supports the entire battery pack mass (300–400 kg), necessitating robust structural design. Key performance metrics include散热能力 (heat dissipation capability), temperature uniformity, pressure drop, and load-bearing capacity. The cooling plate must exhibit minimal deformation (≤2 mm) under a 300 kg load. Three design schemes are proposed, as summarized in Table 1.
| Scheme | Flow Channel Type | Load-Bearing Structure | Manufacturing Process |
|---|---|---|---|
| Scheme 1 | Three-Parallel One-Series (U-Type) | Bottom Reinforcing Beams | Stamping and Conventional Brazing |
| Scheme 2 | W-Type | Self-Supporting with Internal Fins | Stamping with Fins and Conventional Brazing |
| Scheme 3 | Counterflow Labyrinth | Self-Supporting with Complex Fins | Vacuum Brazing |
The flow channel models for each scheme are illustrated in the figures above. Scheme 1 features a U-type channel with simplified geometry, Scheme 2 incorporates W-type channels with integrated fins for enhanced heat transfer, and Scheme 3 employs a counterflow labyrinth design with multi-directional fins to improve temperature uniformity.
Experimental Methodology
Thermal Performance Testing
The thermal performance test platform consists of a chiller, charge-discharge equipment, an environmental chamber, flow meters, temperature sensors, and the battery pack. The chiller provides coolant at a controlled temperature and flow rate, while the charge-discharge equipment enables 0.5 C cycling. The environmental chamber maintains a stable ambient temperature. Flow meters and temperature sensors monitor coolant conditions. The test procedure is as follows:
- Set the environmental chamber and chiller outlet temperature to 25°C to initialize the battery pack temperature.
- Stabilize the battery management system (BMS) temperature at (25±2)°C, set the chiller to 18°C, and initiate 0.5 C charge-discharge cycles.
- After each charge or discharge cycle, shut down the equipment and allow the chiller to run for 30 minutes before proceeding to the next cycle.
- Repeat the process for multiple cycles to collect data.
Key parameters for thermal performance testing are listed in Table 2.
| Parameter | Value |
|---|---|
| Charge-Discharge Rate | 0.5 C |
| Coolant | 50% Deionized Water + 50% Ethylene Glycol |
| Flow Rate (L/min) | 5 |
| Inlet Temperature (°C) | 18 |
| Ambient Temperature (°C) | 25 |
Temperature uniformity is calculated as the difference between the maximum and minimum temperatures of the energy storage cells at any given time:
$$\Delta T = T_{\text{max}} – T_{\text{min}}$$
where \(\Delta T\) is the temperature difference, \(T_{\text{max}}\) is the maximum temperature, and \(T_{\text{min}}\) is the minimum temperature.
Pressure drop across the cooling plate is defined as:
$$\Delta P = P_{\text{in}} – P_{\text{out}}$$
where \(\Delta P\) is the pressure drop, \(P_{\text{in}}\) is the inlet pressure, and \(P_{\text{out}}\) is the outlet pressure.
Load-Bearing Testing
The load-bearing test platform includes weight blocks, the cooling plate, and a support frame simulating the battery pack cluster. Deformation is measured at marked points on the cooling plate surface before and after applying a 312 kg load. The test procedure involves:
- Inspecting the cooling plate for defects and marking measurement points.
- Placing the plate on the support frame and measuring initial deformation using a straight edge and feeler gauge.
- Applying weight blocks between the battery installation beams and measuring deformation after 12 hours.
- Calculating the deformation as the absolute difference between initial and final measurements.
Test parameters for load-bearing evaluation are provided in Table 3.
| Parameter | Value |
|---|---|
| Weight Block Mass (kg) | 312 |
| Straight Edge Length (mm) | 900 |
| Ambient Temperature (°C) | 25 |
Deformation is computed as:
$$\Delta D = |D_1 – D_2|$$
where \(\Delta D\) is the deformation, \(D_1\) is the initial measurement, and \(D_2\) is the measurement after loading.
Experimental Results and Analysis
Thermal Performance Results
Thermal performance data for the three schemes during one charge-discharge cycle are summarized in Table 4. All schemes maintain maximum temperatures below 35°C, indicating effective散热能力 for energy storage cells. Scheme 3 exhibits superior temperature uniformity with a difference of approximately 1°C, compared to 5°C for Scheme 1 and 3°C for Scheme 2. Pressure drop is highest in Scheme 3 (18.3 kPa), followed by Scheme 2 (15.6 kPa) and Scheme 1 (10.3 kPa), showing a positive correlation with temperature uniformity. Discharge cycles generally result in higher temperatures than charge cycles, suggesting greater internal heat generation during discharge.
| Scheme | Maximum Temperature (°C) | Minimum Temperature (°C) | Temperature Difference (K) | Pressure Drop (kPa) | Cycle Type |
|---|---|---|---|---|---|
| Scheme 1 | 33 | 28 | 5 | 10.3 | Charge |
| 35 | 31 | 4 | Discharge | ||
| Scheme 2 | 32 | 29 | 3 | 15.6 | Discharge |
| 31 | 28 | 3 | Charge | ||
| Scheme 3 | 32 | 31 | 1 | 18.3 | Charge |
| 33 | 32 | 1 | Discharge |
The temperature profiles during charge-discharge cycles reveal that cell temperatures stabilize approximately 30 minutes before the end of charging, indicating steady-state cooling. Discharge cycles show more complex temperature dynamics, with an initial rise, a mid-cycle plateau, and a final increase, highlighting the need for further investigation into the heat generation mechanisms of energy storage cells during discharge.
Load-Bearing Results
Deformation measurements for the three schemes under a 312 kg load are presented in Table 5. The B-column test points experience the largest deformation due to the support structure and torque effects. Scheme 1 shows the highest deformation (up to 1.55 mm) because of its thin stamped design, which requires additional reinforcing beams. Scheme 2, with integrated fins, reduces deformation but still exhibits significant values (up to 1.15 mm). Scheme 3 demonstrates the smallest deformation (≤0.85 mm), attributed to its thicker construction and multi-directional fins that enhance structural rigidity.
| Scheme | Test Point | A-Column Deformation | B-Column Deformation | C-Column Deformation |
|---|---|---|---|---|
| Scheme 1 | 1 | 0.15 | 1.00 | 0.15 |
| 2 | 0.60 | 1.15 | 0.60 | |
| 3 | 0.35 | 1.55 | 0.80 | |
| 4 | 0.70 | 1.45 | 0.70 | |
| 5 | 0.10 | 1.55 | 0.65 | |
| Scheme 2 | 1 | 0.20 | 0.85 | 0.15 |
| 2 | 0.40 | 0.80 | 0.20 | |
| 3 | 0.60 | 1.15 | 0.20 | |
| 4 | 0.40 | 1.10 | 0.20 | |
| 5 | 0.10 | 0.80 | 0.30 | |
| Scheme 3 | 1 | 0.45 | 0.85 | 0.35 |
| 2 | 0.10 | 0.45 | 0.05 | |
| 3 | 0.03 | 0.25 | 0.15 | |
| 4 | 0.10 | 0.05 | 0.05 | |
| 5 | 0.05 | 0.05 | 0.03 |
Discussion
The experimental results highlight the trade-offs between thermal performance, pressure drop, and structural integrity in liquid cooling plates for energy storage cells. Scheme 1, while meeting basic散热要求, suffers from poor temperature uniformity and high deformation due to its simple flow channel and thin construction. Its stamping process incurs high模具 costs but is suitable for mass production. Scheme 2 improves temperature uniformity and load-bearing capacity through integrated fins, yet deformation remains suboptimal. Scheme 3 excels in both temperature uniformity and structural performance, owing to its complex labyrinth flow channel and vacuum brazing process. However, the higher pressure drop in Scheme 3 demands more powerful pumping systems, and vacuum brazing may limit mass production scalability.
The positive correlation between pressure drop and temperature uniformity can be explained by enhanced fluid mixing and heat transfer in complex flow channels. For energy storage cells, maintaining minimal temperature variations is crucial to prevent performance degradation and ensure longevity. The load-bearing capacity directly impacts the thermal interface thickness, as excessive deformation can alter the adhesive layer, affecting heat transfer efficiency.
Conclusion
This study evaluates three liquid cooling plate designs for energy storage cells through thermal and load-bearing tests. Scheme 1 is suitable for applications with low temperature uniformity requirements and no load-bearing needs, but it requires additional structural support. Scheme 2 offers a balance of thermal performance and cost-effectiveness, with improved temperature uniformity and self-supporting capabilities. Scheme 3 provides the best overall performance, with exceptional temperature uniformity and load-bearing capacity, making it ideal for high-demand energy storage systems. However, its higher pressure drop and manufacturing complexity must be considered. Future work should focus on optimizing flow channel designs to reduce pressure drop while maintaining performance, and exploring advanced manufacturing techniques for scalable production. These findings provide valuable insights for the design and optimization of liquid cooling plates in energy storage applications.