Mechanical vs. Porous Membrane Pressure Release Vents: A Lithium Battery Perspective

Suitably designed and tested pressure release vents (PRV) play a crucial role in the safe operation of a lithium battery pack. Battery packs undergo a wide range of harsh environmental and operational conditions. PRVs offer safety by ensuring that the pack remains depressurized and can quickly evacuate gases in the event of cell failure.

There are predominantly two types of Pressure Release Vent (PRV) technologies:

(1) Mechanical PRVs are designed to open at pre-determined pressure and discharge gases until pressure drops to an acceptable level within the system. Performance of such vents depend on the characteristics of the spring/counterweight used.

(2) Membrane PRVs are a venting technology that use porous membrane that breathes continuously, always keeping the system at close to zero differential pressure. These membranes allow only air to pass, while dust, water and other contaminants are kept out. Performance depends on the type of porous membrane used – ideally PTFE, which is naturally hydrophobic and stable at high temperatures. Oleophobic treatment and a variety of porosity is available that can address specific engineering challenges.

This article presents the difference between these technologies and showcases how membrane based PRVs may have certain advantages worth keeping in mind.

1. Continuous pressure relief improves life of the battery

A porous membrane provides continuous breathing, which starts at very low pressure differentials (close to zero) ensuring the system always remains pressure free. A mechanical PRV allows the battery to operate under a pressurized condition until the valve actuation pressure is reached. Operating the battery in a pressurized condition reduces the life of both components and the pack as a whole. This pressurized condition reduces the life of lithium cells, seals and electronics.

2.?Absence of moving parts

Membrane based PRVs do not have any moving parts such as a spring or counterweights. The absence of moving parts avoid many issues:

(a)???Failure of moving part

(b)??Fatigue and wear of moving part

(c)???Water/contamination ingress during functioning

(d)??Reliability of opening and closing function over time

(e)???Risk of debris jamming the component

3. Continuous pressure relief prevents faults due to moisture buildup

Battery packs encounter temperature led pressure buildups inside the battery pack. Unless this pressure is efficiently equalized, the heating and cooling of free air will lead to moisture buildup. Membrane based PRVs offer such pressure equalization and avoid internal condensation issues. Hence, electrical failures and possible thermal runaway events can be avoided.

4. Membrane burst function

During any unfavorable situation such as high-pressure and high-temperature conditions during thermal runaway, the vent allows gases to escape quickly to avoid damage to enclosure. In a membrane PRV, the porous membrane will rupture at a specific pressure and efficiently allow a large quantity of air to move out quickly.

5.?Customized solutions – Rapid development

Membrane based PRV solutions can be easily customized for a wide range of applications in diverse engineering domains. Different porosities, treatments for repelling aggressive chemicals, flow rates, burst pressures and water ingress needs can all be modified quickly. Validating custom parts using mechanical technology may end up being a costly and time-consuming affair.