Why New Energy Battery Packs Require Waterproof and Explosion-Proof Valves
With the rapid development of new energy vehicles and energy storage systems, lithium-ion battery packs have become the core energy storage components, undertaking the critical task of power supply and energy storage. However, the closed operating environment, complex working conditions, and inherent chemical properties of battery packs pose potential safety hazards such as pressure imbalance, water intrusion, and thermal runaway. As a key safety component integrating multiple protection functions, waterproof and explosion-proof valves (also known as breathable explosion-proof valves) play an irreplaceable role in ensuring the stable, safe, and long-term operation of battery packs. This article will elaborate on the necessity of waterproof and explosion-proof valves for new energy battery packs from multiple dimensions, including working principle, functional requirements, and application scenarios.
First and foremost, waterproof and explosion-proof valves are essential to maintain pressure balance inside and outside the battery pack, thereby preventing seal failure. New energy battery packs are required to meet strict IP67 or even IP68 protection standards to resist the intrusion of external moisture, dust, and other contaminants. This high level of sealing creates a relatively closed internal environment. During the operation of the battery pack, factors such as charging and discharging heat generation, ambient temperature changes, and altitude fluctuations will cause thermal expansion and contraction of the internal gas, resulting in pressure imbalance between the inside and outside of the battery pack. According to the ideal gas law, when the battery pack undergoes temperature shock tests between -40℃ and 60℃ as specified in the national standard GB38031-2025, the internal gas volume will expand significantly, generating a certain pressure difference. If this pressure difference cannot be adjusted in a timely manner, it will exceed the bearing capacity of the sealing interface, leading to seal failure, damage to the battery case, and even the loss of IP protection level, laying hidden dangers for subsequent safety accidents.
The core material of waterproof and explosion-proof valves is expanded polytetrafluoroethylene (micro) film, which has a dense microporous structure with pore diameters ranging from 0.1 to 10 μm. The average diameter of air molecules is only 0.0004 μm, which can freely pass through the film, while the diameter of water droplets is about 400 μm, far larger than the pore diameter of the film. Coupled with the excellent hydrophobicity of the micro film, water droplets cannot wet and spread on its surface but form spherical droplets and slide off, achieving the dual functions of waterproofing and breathability. In normal working conditions, the valve allows bidirectional gas circulation through the micro film, dynamically balancing the internal and external pressure of the battery pack, avoiding deformation or seal damage caused by pressure imbalance, and ensuring the structural integrity of the battery pack.
Secondly, waterproof and explosion-proof valves can effectively prevent condensation and internal corrosion, protecting the electrical performance of the battery pack. When the external air humidity is high, the sudden temperature drop of the battery pack (such as from high-temperature operation to low-temperature environment) will cause the relative humidity inside the pack to reach or exceed 100%, and the excess water vapor will condense into liquid water. Condensation water not only may cause short circuits in high-voltage electrical circuits, leading to battery failure or even fire but also accelerates the corrosion of internal metal parts, reducing the service life of the battery pack. The breathable function of the waterproof and explosion-proof valve can promote the exchange of dry air inside and outside the battery pack, adjust the internal humidity, and fundamentally inhibit the formation of condensation water. At the same time, the micro film also has excellent chemical resistance and oil repellency, which can effectively block dust, oil stains, and corrosive gases from entering the battery pack, further protecting the internal components.
The most critical function of waterproof and explosion-proof valves is to provide emergency pressure relief in extreme cases of thermal runaway, preventing battery pack explosion. Lithium-ion batteries may experience thermal runaway due to factors such as overcharging, over-discharging, short circuits, or physical damage. During thermal runaway, the battery core will undergo violent chemical reactions, generating a large amount of flammable and explosive gases in a short time, resulting in a rapid surge in internal pressure of the battery pack. For example, when a cylindrical 18650 battery core fails, the heat generated can cause six adjacent cores to fail simultaneously, and the gas generation rate can reach 25 L/s. If the high-pressure gas cannot be discharged in a timely manner, the internal pressure of the battery pack will exceed the bearing limit of the case, leading to case rupture, gas leakage, and even violent explosion, causing serious safety accidents.
Waterproof and explosion-proof valves are designed with a pressure threshold trigger mechanism to respond quickly to extreme pressure changes. When the internal pressure exceeds the preset threshold (usually 20-40 kPa), the mechanical trigger device activates immediately. Piston-type explosion-proof valves compress the spring to open the pressure relief channel, while thimble-type explosion-proof valves use high-pressure gas to break the breathable film, achieving instant pressure relief. The thimble-type explosion-proof valve has an extremely fast pressure relief speed of less than 1 second and a large air permeability of more than 5 L/s, which can quickly discharge a large amount of gas generated by thermal runaway, significantly reducing the internal pressure of the battery pack and preventing explosion escalation. In addition, the directional pressure relief design of some explosion-proof valves can guide the discharged gas to a safe area, avoiding secondary hazards such as ignition of surrounding components.
The selection and configuration of waterproof and explosion-proof valves are closely related to the type of battery core and application scenarios, further reflecting their necessity. For high-energy-density ternary lithium batteries with high thermal runaway risks, explosion-proof valves with directional rapid pressure relief functions are usually selected; for lithium iron phosphate batteries with higher thermal stability, ordinary waterproof and breathable valves with lower costs can be used. The setting of the opening pressure threshold needs to comprehensively consider the battery system characteristics and application environment, generally taking 60%-80% of the maximum pressure-bearing failure value of the case and adding a safety factor of 1.2-1.5 to prevent false triggering or failure risks. For example, if the maximum pressure-bearing failure pressure of the battery case is 30 kPa, the opening pressure of the explosion-proof valve is usually set to 24 kPa after considering the safety factor, ensuring that pressure relief is triggered in advance before the case is damaged.
In practical applications, waterproof and explosion-proof valves have become a mandatory safety component in various new energy battery scenarios. In new energy vehicles, they protect the power battery pack from the impact of rainwater, road dust, and temperature changes during driving, ensuring the safety and reliability of the vehicle; in energy storage systems, they adapt to harsh outdoor environments such as high humidity, high dust, and extreme temperatures, preventing battery pack failures caused by environmental factors and thermal runaway. Even in portable power supplies, waterproof and explosion-proof valves can effectively discharge slight gas generated by batteries, control charging temperature rise, and improve product safety and service life.
In conclusion, waterproof and explosion-proof valves are indispensable core components for new energy battery packs, integrating pressure balance, waterproof and dustproof, anti-condensation, and emergency explosion-proof functions. They not only solve the problems of pressure imbalance and environmental corrosion in the normal operation of battery packs but also provide the last line of defense against explosion hazards caused by thermal runaway. With the continuous improvement of battery energy density and the expansion of application scenarios, the performance requirements for waterproof and explosion-proof valves will become higher and higher. The continuous innovation and optimization of their materials, structures, and functions will further promote the safe and sustainable development of the new energy industry.