A Comprehensive Guide to the Sealing Design of Aluminum Battery Casings for Electric Vehicles

With the rapid development of the new energy vehicle industry, power batteries have become one of the core systems for vehicle safety and performance. Power batteries not only perform energy storage functions, but their structural reliability, environmental adaptability, and safety protection capabilities directly affect the lifespan and operational safety of the entire vehicle. In this system, the power battery casing plays a crucial role in load-bearing, protection, and isolation, and sealing design is a key technical aspect of power battery casing engineering.

 

In practical applications, if the power battery casing fails to seal, it can lead to problems such as water ingress, coolant leakage, and internal gas spillage, which in severe cases can cause cell performance degradation or even thermal runaway risks. Therefore, conducting systematic and engineered sealing design for aluminum power battery casings is an important topic in current electric vehicle structural design.

 

 

Power battery casings typically adopt a box-type structure, consisting of an upper cover, a lower tray, and a bottom protective structure. With the continuous improvement of battery energy density and integration, integrated water-cooled plate solutions have become the mainstream configuration. The lower tray is typically composed of an aluminum profile frame and a water-cooling plate, while the upper cover is used to achieve the final sealing of the entire pack.

 

Driven by the demands for lightweighting and structural integration, aluminum alloy materials are increasingly widely used in power battery casings. Aluminum casings not only offer weight advantages but also demonstrate significant process adaptability in extrusion, welding, and modular design, making them widely used in structural solutions such as the Aluminum Case for automotive batteries and the Aluminum Case for EV Lithium Battery Packs.

 

From a sealing design perspective, aluminum power battery casings involve multiple potential leakage interfaces, including the annular sealing interface between the upper cover and the lower tray, the aluminum profile splicing seams, the connection interface between the water-cooling plate and the frame, and the protective interfaces related to the bottom protective structure. The design complexity and reliability requirements of these interfaces vary, necessitating a systematic balance between structure, materials, and manufacturing processes.

 

 

1. Sealing Design Concept of the Upper Cover Structure

The power battery upper cover is the core component for achieving overall pack sealing. Engineering practice shows that a one-piece structural design is more suitable for the top cover to reduce the leakage risk caused by component splicing. Regardless of whether the top cover uses steel or aluminum, the design focus is on ensuring a continuous and uniform sealing interface with the lower tray.

 

During the design process, positioning holes and fastening features should be placed outside the main sealing interface to avoid interfering with the sealing path. Simultaneously, the sealing surface of the top cover must have good flatness and continuity. If necessary, the sealing area can be precision-machined to improve sealing reliability.

 

2. Sealing Strategy for the Lower Tray and Aluminum Profile Frame

The lower tray is the main load-bearing structure of the power battery, typically using an aluminum profile frame or a cast aluminum integral structure. For frame-type tray designs, the joints formed by the aluminum profile splicing become a significant weak point in the seal.

 

In engineering design, closed-section aluminum profiles combined with self-sealing linear connection technology can effectively improve structural strength and sealing stability. At the same time, designing a continuous sealant path in the profile splicing area is an important means of ensuring long-term airtightness. This design approach is widely used in power battery structures, such as the Aluminum Case for Car LiFePO4 Battery Pack and the Aluminum Case for Electric Motor Car LiFePO4 Battery Pack.

 

 

The water-cooled plate not only performs thermal management functions but also often participates in the overall sealing of the power battery casing in integrated schemes. Due to the high-pressure cooling medium inside the water-cooled plate, its self-sealing capability is particularly critical.

 

In engineering, a one-piece or brazed water-cooled plate structure is preferred to reduce potential leakage points such as welding and screw connections. Under the premise of achieving self-sealing of the water-cooled plate, a ring-shaped sealing interface similar to a top cover can be formed between it and the aluminum profile frame. The sealing level of this interface is usually consistent with the overall pack sealing requirements. This design approach has high engineering applicability in the system development of the Aluminum Case for Powerwall Lithium Battery Pack and LFP Battery Aluminum Case.

 

 

The main function of the bottom guard plate is to prevent the battery pack from being impacted by stones, foreign objects, and road conditions during driving. Compared to the top cover and lower tray, the bottom protector is typically not designed as a primary airtight interface.

 

In designs that do not participate in the overall pack sealing, the design focus of the bottom protector is on structural strength and foreign object protection. When the lower insulation material has water-absorbing properties, a basic waterproofing design can be added according to the overall vehicle protection standards. Its sealing rating is usually referenced from the protection requirements of the underbody structural components.

 

 

Besides the main structural components, fasteners and mechanical connection points can also become potential leakage channels. In engineering practice, the following principles are recommended for control: minimize the number of fasteners involved in sealing; for unavoidable connection points, use structural components with built-in sealing rings to achieve local self-sealing; prioritize fastener placement near the outer edge of the casing to avoid entering the main sealing area. This principle also applies to small and medium-sized battery systems, such as Aluminum Case for Electric Bike Battery Pack and the Aluminum Case for Li-ion Electric Bike Battery Pack.

 

 

From a systems engineering perspective, the sealing design of aluminum power battery casings should not be conducted in isolation, but rather optimized in conjunction with structural design, manufacturing processes, and assembly procedures. By designing the sealing path as a continuous, closed, integrated system and rationally selecting sealing materials with controllable compression ratios, assembly efficiency and after-sales maintainability can be considered while meeting sealing performance requirements.

 

In actual projects, through repeated verification of the sealing material compression ratio, fastener spacing, and assembly processes, a balance between cost and reliability can be achieved while ensuring airtightness. This systematic sealing concept has gradually become the mainstream direction in the development of aluminum power battery casings.

 

 

The sealing design of aluminum power battery casings is a highly systematic engineering problem, involving multiple dimensions such as structural form, material selection, manufacturing processes, and assembly logic. By rationally dividing key sealing interfaces and combining integrated structural design with the application of self-sealing technology, the safety and long-term reliability of power battery systems can be significantly improved.

 

With the continuous development of electric vehicles, electric buses, and energy storage systems, aluminum power battery casings will be promoted in more application scenarios, and their sealing design methods will continue to evolve and be continuously optimized and applied in structural systems such as aluminum shells for lithium iron phosphate battery cells and lithium prismatic cells aluminum shells.