As demands for driving range and charging efficiency in new energy vehicles continue to rise, battery thermal management systems have become a critical factor determining the performance and safety of battery packs. Due to structural differences inherent in their packaging formats, thermal management strategies vary for each cell type.
I. Core Objectives and General Logic of Thermal Management
Battery thermal management essentially involves the precise regulation of thermal processes within the battery pack. Its core objectives include: maintaining the battery within an optimal operating temperature range, preventing localized overheating, mitigating the risk of thermal runaway, balancing the needs for high-temperature cooling and low-temperature heating, and minimizing temperature differentials between cells to enhance consistency.
ACEY BMS testing equipment verifies the proper functioning of battery temperature sensing, over-temperature protection, and cell balancing features.
Thermal processes within the pack consist of four main components: first, electrochemical heat generated by the battery's internal chemical reactions, which is directly linked to battery design; second, ohmic heat generated by current flowing through conductors, determined by the electrical circuit design; third, heat conduction between the cells and pack components, governed by structural design and the thermal management strategy; and fourth, convective heat transfer involving fluids (liquid or air cooling), which serves as the primary heat dissipation pathway for the system.
Current mainstream thermal management solutions fall into four categories: direct cooling systems (e.g., BMW i3/X5), liquid cooling systems (e.g., Tesla, Audi), air cooling systems (e.g., Nissan Leaf, Prius), and phase-change material (PCM) cooling systems.
II. Comparison of Characteristics and Thermal Management Strategies for the Three Cell Types
Due to differences in packaging structures, the three cell types differ in their fundamental parameters and thermal management logic:
| Comparison Item | Cylindrical Cell | Prismatic Cell | Pouch Cell |
| Representative Models | 18650, 21700, 26650 | L135, L148, L173 | 118, 161 |
| Core Advantages & Disadvantages | Mature process, high yield, good consistency, but heavy weight, low specific energy | Simple structure, relatively high energy density, strong impact resistance, but complex model variety, difficult to unify processes | Lightweight, high energy density, low internal resistance, good cycle performance, but poor consistency, high cost, prone to leakage |
| Single-Cell Heat Dissipation Area | 3674 mm² (18650 spec) | 38296 mm² (148 spec) | 73094 mm² (161 spec) |
1. Thermal Management for Cylindrical Cells
Modules using cylindrical cells typically employ a bidirectional liquid cooling flow design. In this configuration, both ends of the cooling channels serve as inlets and outlets, preventing insufficient cooling at the channel's end-a problem that could otherwise arise from the coolant's temperature rise as it flows through the system. Materials such as Stycast 2850/CT-which are electrically insulating yet highly thermally conductive-are used to fill the gap between the battery cells and the cooling pipes. This achieves three core benefits: first, it transforms the contact between the cells and the pipes from line contact to surface contact, significantly boosting heat transfer efficiency; second, it facilitates heat exchange between cells, passively improving temperature uniformity across individual units; and third, it increases the overall thermal mass of the battery pack, thereby reducing the magnitude of the average temperature rise.
2. Thermal Management for Prismatic Cells
Prismatic cell modules typically house 32 VDA-standard cells; every four cells share a single friction-stir-welded cold plate. These cold plates are connected in parallel via piping to ensure system-wide temperature uniformity. The heat transfer path is: cell → thermal interface material (TIM) → base/side plate → cold plate. This configuration offers structural stability and meets the application requirements of various scenarios, including commercial vehicles.
3. Thermal Management for Pouch Cells
Pouch cells are typically bonded to a composite housing made of plastic and 0.35mm sheet aluminum; the aluminum transfers heat to the module edges, while the plastic component provides electrical insulation and structural interlocking. Key module components include end plates, cover plates, busbars, heat dissipation plates, buffer pads, and NTC sensors. Regarding thermal management, 1mm-thick liquid cooling plates-featuring machined flow channels-are placed between individual cells. This ensures direct contact between every cell and the cooling plate; heat is conducted through the TIM to the heat dissipation plate and then into the cooling plate for dissipation. This solution offers the highest ratio of effective heat dissipation area.
Core Similarities and Differences Among the Three Solutions
Similarities: All three enhance heat dissipation efficiency by adding cooling channels, accelerate heat transfer rates using highly thermally conductive media, and employ active cooling methods for temperature control.
Differences:
| Comparison Item | Cylindrical | Prismatic | Pouch |
| Thermal Conduction Medium | Cell itself + thermally conductive filler | Cell itself + thermally conductive adhesive + base plate/side plate | Cell itself + thermally conductive adhesive + heat spreader |
| Thermal Conduction Path | Cell → thermally conductive adhesive → bracket/liquid cold plate | Cell → thermally conductive adhesive → base plate/side plate → cold plate | Cell → thermally conductive adhesive → heat spreader → cold plate |
| Effective Heat Dissipation Area | 918 mm² (18650) | 3996 mm² (148) | 36547 mm² (161) |
| Effective Heat Dissipation Area Ratio | 25% | 10.40% | 50% |
Additionally, there are significant differences regarding the choice of cooling medium, the layout of the cooling plates, and the ultimate heat dissipation performance.