Why Do Square Shell Lithium Batteries Need Blue Film?

The main reasons for wrapping a blue film (blue membrane) around the outside of square shell lithium batteries involve multiple functional requirements and process considerations. The following is a detailed explanation:

• Insulation protection and short - circuit prevention design

The outer shell of prismatic batteries is usually made of metal materials (such as aluminum alloy). Direct contact may cause short - circuits between batteries or with external components. As an insulating layer, the blue membrane effectively isolates the metal surface and prevents accidental conduction. Enhanced safety: In scenarios where battery packs are densely arranged, the blue membrane reduces the risk of short - circuits caused by shell contact, improving overall safety.

• Corrosion prevention and sealed environment protection

The blue membrane can isolate corrosive environmental factors such as moisture, salt spray, and acid - alkaline substances, delaying the oxidation and rusting of the metal shell and extending the battery life. Sealing assistance: Some blue membrane materials have waterproof and dust - proof properties. When combined with the battery packaging process, they further enhance the sealing performance. - Figure: Appearance of the battery before membrane wrapping

• Mechanical protection against physical damage

During transportation, assembly, or use, the blue membrane can reduce scratches and collisions on the battery shell, preventing the internal structure from being exposed or the electrolyte from leaking due to shell damage. Cushioning effect: Some blue membranes are elastic and can absorb minor impacts, protecting the structural stability of the internal electrodes and separators of the battery.

• Thermal management and optimized heat dissipation

Some blue membrane materials are added with thermally conductive particles (such as ceramics and graphite), which can help evenly distribute the battery surface temperature and avoid local overheating. At the same time, dark colors (such as blue) may be more conducive to heat radiation. Insulation function: In extremely high - temperature environments, the blue membrane may act as an insulating layer to reduce the impact of external heat on the battery.

• Identification and management for model differentiation

Blue is often used to identify specific battery models, capacities, or voltage levels, facilitating quick identification during production line sorting and maintenance. Brand recognition: Manufacturers strengthen their brand image through a unified color (such as CATL's iconic blue membrane) and prevent counterfeiting at the same time. Traceability information: Some blue membranes are printed with QR codes or batch numbers. Combined with the color, production data can be quickly traced.

• Process and cost optimization for automated adaptation

The blue film has high contrast in the visual inspection system, facilitating machine - vision positioning and detecting the integrity of the wrapping, thus improving production efficiency. Material cost: Insulating film materials such as blue PET (polyester) are mature and have low costs, balancing performance and economic benefits.

• Special functional requirements - flame - retardant performance

Some blue membranes are added with flame retardants, which can delay the spread of fire when exposed to high temperatures, meeting battery safety standards. UV resistance: Blue pigments may have better UV - resistant properties, delaying the aging of the membrane material and being suitable for outdoor energy storage scenarios.

Summary The blue membrane of prismatic batteries is not just a simple packaging but a key component integrating functions such as insulation, protection, thermal management, and identification. The choice of color (blue) may be due to technical considerations (such as heat dissipation and detection adaptation) or part of the manufacturer's brand strategy. In practical applications, the specific characteristics of the blue membrane will vary according to the battery's use (such as power batteries and energy storage batteries) and the manufacturer's design.