BatteryBits
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BatteryBits

How to Prevent Electric Dreams from Going Up in Flames: The Challenge of Battery Safety

  • While instances of fires are lower in EVs compared to ICE vehicles, incidents involving EVs tend to garner outsized public attention.
  • The industry is still working to understand the challenge of battery safety; OEMs and cell manufacturers cannot afford multiple safety-related recalls during this period of industry-wide transition.
  • OEMs need to take a robust, testing-driven approach to ensure that EV battery packs exceed the levels of safety outlined in regulations and standards.
  • Safety must be considered from the early stages of battery design ideation–it is easier to design safe batteries than it is to impart safety to an already-designed system.
  • Standards and regulatory frameworks need to be expanded for the EVTOL space, and unified across different markets for EVs.

Total Recall

A comparison of recalls prompted by battery safety concerns. Source: Eli Leland, Voltaiq.

Safety considerations for batteries on the move

How to police battery safety?

  1. Understand the trade-offs of the use case well to choose the right cell for the application.
  2. Adhere to the voltage and temperature limits established by the cell manufacturer.
  3. Implement module/pack level safety measures based on cell-level protections (CID/PTC).
  4. Characterize cell failure using calorimetry to size mitigation systems and develop predictive tools.
  5. Develop robust test methodologies for cells, modules and packs by combining existing standards.
  6. Perform independent safety testing of cells either internally or at qualified laboratories.
  7. Perform exhaustive safety testing early in the design process to inform design decisions.
  8. Cover low-probability cases and worst-case scenarios to ensure the module/pack is resistant to single-cell failures and side-wall ruptures.
  9. Choose the appropriate passive propagation mitigation method based on cell format.
  10. Consider thermal management systems that can also mitigate thermal runaway propagation (e.g., immersion cooling).
  11. Ensure that vent gases from one cell in the pack do not impinge on other cells, and that there are no sources of ignition in the vent flow path.
  12. Perform pack-level testing with live packs to simulate field failures.
  13. Implement a sufficient number of sensors (temperature, voltage, humidity, isolation, vent gas concentration) to capture changes that may indicate the onset of thermal runaway.
  14. Implement early anomaly detection and monitor as many cells/groups as possible to detect thermal runaway well before it occurs. Examples of anomalies:
    a. Excessive self discharge or drop in block voltage during rest periods
    b. Long taper current charging times
    c. Noisy voltage profiles during charge and discharge
    d. Excessive cell heating near the end of charging
    e. Charge capacity being higher than discharge capacity, beyond typical losses
    f. Change in efficiency of charge/discharge over a short period of time
  15. Identify and prevent any sources of high-voltage arcs, and use fast-acting fuses.
  16. Publish standardized and detailed emergency response guides for first responders.
  1. Ensure that cells are designed specifically for the given application to avoid abuse (e.g., separator thickness and coatings are different for consumer electronics and EVs).
  2. In addition to component level calorimetry, characterize heat flow in a full cell to determine contributions of each component during thermal failure.
  3. Even if minor changes are made to cell chemistry, assess cell safety comprehensively.
  4. Firmly establish with customers the cell’s operational limits and failure boundaries.
  5. Develop robust systems to identify manufacturing issues that can affect safety behavior.
  6. Continually inspect manufacturing quality and subject production cells to periodic testing to remain vigilant of drifts.
  7. Apprise customers of chemistry/construction modifications with implications on safety.

Can batteries fly safely?

New Chemistries, Stationary Storage and Second Life

Prevention is better than cure

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