Welcome back to the ABACUS Blog for the monthly update. In the month of July the topic of Safety for Lithium-ion batteries will be discussed.
In the forward and reverse logistics chain of a Lithium-ion battery, storing and handling the battery safely is of vital importance. Some of the pre-failure processes that needs to be managed and minimised through proper storage and handling in the supply chain are:
- Cells being operated or stored in extreme temperatures (high temperature leading to modification of surface films on the electrodes, low temperature leading to the breakdown of adhesives causing anode to pull away from current collector)
- Cell damage and defects that can cause internal short circuits leading to localised heating spots
- High charge/discharge current during state-of-charge adjustment (Wheat=I2 * Zint)
- Improper connections causing high resistance
- Mechanical damage (Crash, Vibration, Mishandling)
In terms of safety for the people involved in the reverse logistics supply chain there are two scenarios to consider namely safety to prevent an event and safety to handle an event that occurred.
For safety to prevent an event there are three things that I want to highlight:
1. In the UK the Heatlh and Safety Executive (HSE) under the Health and Safety in the workplace act of 1974 created a guide for handling batteries safely. Also, for High Voltage (HV) batteries with DC voltages greater than 50V it is important to be certified to work with HV equipment and HV training is essential for making a traction Lithium-ion battery safe.
2. Safe packaging requirements for transportation is covered under the ADR regulations in the EU but no proper international standards or guides exist for proper storage for Lithium-ion batteries that I am aware of.
3. Appropriate State-of-Charge (SoC) of the cell when put into storage needs to be considered. Some of the factors to consider when adjusting a cell's state-of-charge for storage are the following:
- How long can the cells be stored for? (shelf life) - the cell's self-discharge rate and storage temperature needs to be considered carefully to ensure cell do not reach a SoC level that is two low and can damage the cell. Higher temperatures will cause the self-discharge rate to increase.
- Transport requirements: For example from 1 April 2016 all Lithium-ion battery packs shipped by air under IATA package instruction 965 must be at no more than 30% state of charge due to the possibility of cells or batteries in a higher state of charge could reach more violently if damaged or abused.
For safety to handle an event the following is worth noting:
- There are first responder guides available for various vehicle brands at http://www.evsafetytraining.+org/resources.aspx. The issues with the guides are that the responders are guided to cut the 12V line and from a testing point of view and ADR transport regulation point of view this makes verifying the status of the battery more difficult.
- Procedures to make batteries safe after venting or fire such as to put it in a salt water bath to discharge the battery because damaged packs need to be rendered safe before transportation. This destructive approach has major limitations as it does not guarantee the pack is safe and produces toxic gas and corrosive lithium chloride with undesirable environmental consequences.
Thus it is important to carefully consider all the safety aspects when working with lithium batteries and to have a clearly defined mitigation plan to prevent incidents.
Until next time!