Deep Breathing for EV Batteries

Optimum venting is a key to maximizing EV battery pack performance and safety. An expert offers five important design considerations.

Optimized battery venting is vital to ensure system integrity in edge cases such as when the EV fords cool water deep enough to put the warm battery pack into thermal shock and cause a rapid vacuum event. Shown is a Volkswagen pack undergoing water immersion testing at the OEM’s Chattanooga, Tenn., battery test facility. (Lindsay Brooke)

As batteries become more sophisticated, the need to protect them from the elements has never been greater. Battery pack engineers understand vehicle applications and by marrying them with proper venting technology, they are helping to advance electric vehicle performance and safety.

Optimized battery venting is vital to ensure system integrity in edge cases such as when the EV fords cool water deep enough to put the warm battery pack into thermal shock and cause a rapid vacuum event. Shown is a Volkswagen pack undergoing water immersion testing at the OEM’s Chattanooga, Tenn., battery test facility. (Lindsay Brooke)

Below are five important design considerations to help maximize EV battery pack performance:

1. Provide pressure equalization

Temperature and elevation changes can cause pressure variations inside a pack enclosure. Vents allow air to flow in and out of the enclosure, which helps equalize the pressure. Higher airflow allows faster equalization and lower maximum pressure differentials. As pressure builds in an operating system, the weakest point will be found, so a properly designed vent takes the pressure off sensitive components within a vehicle and helps maintain proper airflow.

The rate of pressure change also needs to be considered. Pressure changes are often driven by temperature changes inside the battery pack due to environmental conditions, charging, and discharging. As the rate of pressure change increases, higher airflow is required.

Added dual-stage battery vents reduces battery pack pressure buildup during temperature changes. Calculations shown assume a free air volume of 20 liters and a temperature change of 45C over 12 minutes. (Donaldson Corp.)

To handle fluctuating pressure changes, the size and number of vents, type of membrane, airflow properties, and outside conditions need to be considered at the onset of development. Implementing the appropriate type and number of battery pack vents can help manage the internal pack pressure at differential operating conditions.

2. Engineer for ingress protection

While airflow requirements are critical to managing pressure levels in battery packs, ingress protection to keep out contaminants is also an important consideration. A key parameter to use during the design and testing phases is the ingress protection (IP) rating, which indicates the effectiveness of sealing enclosures against foreign bodies and moisture.

Typical contaminants a battery vent must protect against include water (spray and submersion), oil, dust, and sand particles. Donaldson’s dual-stage battery vents, for example, utilize a unique body design and Tetratex ePTFE membrane – a proprietary filtration media – to provide exceptional battery pack protection.

As ingress protection is increased, emergency degassing airflow may be decreased, so proper venting solutions need to find the optimal balance between ingress protection and degassing airflow.

3. Account for edge cases

A closeup of Donaldson’s Tetratex media. This expanded ePTFE membrane has a unique microstructure that is naturally hydrophobic and offers protection from temperature and thermal fluctuations, moisture and other harmful contaminants. (Donaldson Corp.)

EV battery packs and enclosures are created to handle unexpected edge cases, which are events that occur at extreme operating parameters. While edge cases occur infrequently, it’s important that a venting solution is optimized to help reduce the risk of damage to the battery pack and mitigate component failure or costly repair.

Examples of edge-case scenarios include:

  • DC fast charging: This charging process is significantly faster than regular charging stations and generates extra heat and pressure on an EV battery.
  • Hill climbs: The competitive sport of uphill racing (i.e., Pike’s Peak) causes a sudden change in altitude and increases the pressure and temperature in a vehicle battery.
  • Water fording: Driving off-road through a creek can put a warm battery pack in thermal shock and cause a rapid vacuum event from the cool water.
  • Air transportation: A vehicle being transported within a cargo aircraft will be impacted by pressure changes from the altitude variation.
  • Rock impact: Rocks or other hard debris hitting the undercarriage of a vehicle can cause a pressure spike inside the battery pack.

Our testing process includes a comprehensive design failure mode and effect analysis. This analysis looks at the severity and frequency of possible edge cases and tracks them in a validation plan. We work with customers to understand what extreme conditions their vehicles may experience and what requirements are needed to retain driving performance during a sudden edge case scenario.

4. Mitigate emergency degassing events

As with edge cases, optimum battery pack vent design helps manage emergency degassing events, such as a thermal runaway. Such events happen when pressure rises to a concerning level and gas needs to be immediately released from the pack.

Dual-stage venting solutions are designed to help manage escalated situations. Stage one equalizes pressure while preventing the ingress of water and contaminants. Stage two venting fully opens in response to rapid pressure and heat buildup to allow expanding gases to escape and reduce further damage to remaining cells. In most situations, a single vent assembly can accomplish both functions. This mechanism helps prevent further damage to battery cells or a pack enclosure.

5. Perform a full temperature-range validation

Our engineering and product teams design battery pack vents to operate in a variety of operating temperatures. We frequently perform tests in a full range of extreme temperatures to see how our vents handle burst pressure, emergency degassing, pressure cycle, thermal cycle, thermal soak, thermal shock, and vibration.

Venting is a critical component of EV battery thermal management. As temperatures rise or fall, a breathable vent provides pressure equalization to protect battery housing seals. We work directly with OEMs to ensure our vents are tested across the full range of temperatures experienced in an EV battery pack.

The demand for innovative EV batteries that provide more power and longer range will continue, with advanced battery pack vent designs playing a major role. They must protect against any element that arises while on the road.

Shane Campbell, a graduate chemical engineer and product-development veteran, is a product manager in Donaldson’s Integrated Venting Solutions business unit.