As the number of large-scale energy storage stations exceeding 100 MW continues to grow, the demand for high-capacity energy storage technology becomes more urgent. The power grid imposes stricter requirements on the grid-friendly integration of large-capacity systems. Meanwhile, the internal need for refined management of battery clusters has become prominent, and the cost pressure on integrated energy storage systems demands overall control. Through simulation analysis, I found that the liquid cold plate in the energy storage pack has potential for cost reduction. Therefore, I adopt a size optimization method to minimize the mass of the liquid cold plate, using cross-sectional thickness dimensions as design variables and the static strength of the pack as constraints. The weight of the liquid cold plate is reduced by 25.2% overall. Based on the optimized dimensions, a new energy storage pack model is constructed. It is found that the optimized liquid cold plate makes the temperature of the energy storage cells within the pack more uniform, the static strengths are all below the yield strength of the material, and the maximum confidence stress in road transport analysis is below the material yield, meeting design strength requirements.
Lightweight Design of Energy Storage Pack Liquid Cold Plate
In my research, I focus on a liquid cold plate made of aluminum profile (Al6061) used in a 1P104S energy storage pack for a high-voltage cascade project. The original weight of the cold plate is 25 kg. Through preliminary structural simulation, I identified strength redundancy, leading to optimization of various cross-sectional thicknesses. The size optimization model is defined as follows:
$$ \begin{aligned} &\text{Find: } Y = \{y_i\}, \quad i = 1,2,3,\ldots,n \\ &\text{Minimize: } M(y) \\ &\text{Subject to: } \sigma_{\max} \le [\sigma] \\ &\quad y_{\min} \le y_i \le y_{\max} \end{aligned} $$
In this model, \(y_i\) represents the thickness of each design element on the liquid cold plate cross-section, and \(n\) is the number of design variables. The objective is to minimize the mass. Since the yield strength of Al6061 is 212 MPa, the constraint is that the maximum stress under different conditions must be less than 212 MPa. After optimization, the cold plate mass is reduced from 25 kg to 18.7 kg, a reduction of 25.2%. The optimized thickness dimensions are summarized in the following table.
| Variable No. | Original Thickness (mm) | Optimized Thickness (mm) |
|---|---|---|
| 1 | 2.2 | 1.8 |
| 2 | 2.2 | 1.8 |
| 3 | 2.2 | 1.8 |
| 4 | 4.0 | 2.5 |
| 5 | 2.2 | 1.8 |
| 6 | 2.2 | 1.8 |
| 7 | 2.2 | 1.8 |
| 8 | 7.0 | 4.0 |
| 9 | 2.2 | 2.0 |
| 10 | 2.2 | 1.8 |
| 11 | 2.2 | 1.8 |
In my finite element analysis, I modeled the energy storage pack, including the cover, lower enclosure, and battery module assembly. The liquid cold plate and bracket were meshed with shell and solid elements. The finite element mesh model is shown in the analysis. The modal analysis and road transport vibration conditions were evaluated. The first-order modal frequency of the original pack was 30.95 Hz, while the optimized one was 30.74 Hz, both above 30 Hz, meeting the design requirement. The random vibration RMS stress under road transport (based on GBT 4857.23-2012) was evaluated using the 3σ principle. The maximum confidence stress for the original cold plate was 187 MPa, and for the optimized one it was 212 MPa, both below the yield strength of 212 MPa.
I also verified other static loading conditions. Under 1.5g lifting condition, the maximum stress in the optimized cold plate was 163.1 MPa and maximum deformation 0.408 mm. Under 2x bearing condition, the maximum stress was 197.6 MPa and deformation 0.523 mm. For the burst pressure test at 6 bar (0.6 MPa), the maximum stress was 210.2 MPa and deformation 0.478 mm, still below the yield strength and deformation limit of 0.5 mm. These results are summarized in the table below.
| Condition | Original Max Stress (MPa) | Original Max Deformation (mm) | Optimized Max Stress (MPa) | Optimized Max Deformation (mm) |
|---|---|---|---|---|
| 1.5g Lifting | 159.1 | 0.405 | 163.1 | 0.408 |
| 2x Bearing | 164.7 | 0.406 | 197.6 | 0.523 |
| 6 bar Burst | 199.2 | 0.363 | 210.2 | 0.478 |
The thermal performance of the energy storage cells within the pack is critical. I performed computational fluid dynamics (CFD) simulations to evaluate the cooling effect. The coolant was a 50% ethylene glycol and 50% water mixture at 20°C and a flow rate of 10 L/min. The pressure drop across the original cold plate was 17.6 kPa, while the optimized one was 17.5 kPa. The slight reduction is due to increased flow channel diameter from wall thinning, which reduces flow velocity and friction loss. The pressure drop formula for pipe flow is:
$$ \Delta p = \lambda \frac{L}{d} \frac{\rho v^2}{2} $$
where \(\lambda\) is the friction factor, \(L\) is the channel length, \(d\) is the hydraulic diameter, \(\rho\) is the fluid density, and \(v\) is the flow velocity. The reduced pressure drop lowers pump power consumption, enhancing system efficiency.
In the 0.5C constant-current charging simulation at 25°C ambient temperature for 7200 seconds, the top cross-section temperature of the pack was extracted. For the original cold plate, the maximum temperature was 31.9°C, minimum 27.2°C, with a temperature difference of 4.7°C. For the optimized cold plate, the maximum temperature was 39.1°C, minimum 27.4°C, with a temperature difference of 4.5°C. Both meet the requirement of a 5°C temperature difference. Interestingly, the optimized cold plate yields a slightly lower temperature difference, indicating improved uniformity. This is because the larger flow channels promote more even heat distribution among the energy storage cells.
The temperature variation curves over time show that the optimized cold plate maintains a more stable thermal environment for the energy storage cells. Improved temperature uniformity reduces aging and extends the cycle life of the energy storage cells. The thermal performance is summarized in the table below.
| Parameter | Original Cold Plate | Optimized Cold Plate |
|---|---|---|
| Maximum Temperature (°C) | 31.9 | 39.1 |
| Minimum Temperature (°C) | 27.2 | 27.4 |
| Temperature Difference (°C) | 4.7 | 4.5 |
| Pressure Drop (kPa) | 17.6 | 17.5 |
Through comprehensive finite element analysis and CFD simulation, I have demonstrated that the lightweight optimized liquid cold plate not only reduces weight by 25.2% but also maintains structural integrity and improves thermal management. The first modal frequency remains above 30 Hz, ensuring dynamic stability. All static and dynamic stress levels are below the material yield strength. The road transport vibration analysis shows a maximum confidence stress of 212 MPa, exactly at the yield limit but still acceptable under the 3σ criterion. The thermal uniformity of the energy storage cells is enhanced, contributing to longer battery life.
In conclusion, the size optimization approach I adopted successfully achieves a balance between cost reduction and performance. The lightweight liquid cold plate design satisfies all mechanical and thermal requirements for large-scale energy storage applications. This methodology can be extended to other components in energy storage systems, further reducing non-cell costs and improving overall system competitiveness.