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Lithium-Ion Battery Safety

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Lithium-Ion Battery Safety
Tennen-Gas/Wikimedia Commons/cc-by-sa-3.0

Lithium ion batteries power the portable electronic product market giving us great battery life in a light weight package. Unfortunately, lithium ion batteries have safety issues that can result in the battery catching on fire or exploding, destroying the device and possibly hurting anyone near the battery. There have been several hgh profile lithium ion battery failures in products made by major electronic manufacturers like Apple, Dell and Sony. Proper design, safety measures, testing, and standards can reduce the chance of failure in lithium ion batteries.

Dangers and Causes of Failures

Lithium-ion batteries use a fair amount of lithium in their construction and, unfortunately, lithium is a very reactive and flammable metal and most alloys used in lithium ion batteries are also reactive. If a lithium-ion battery becomes overheated or overcharged, the battery may enter a state of thermal runaway and can rupture, catch on fire or explode. Lithium-ion batteries contain a lot of chemical energy and, in extreme cases, when a lithium-ion battery explodes; the explosion is very powerful, powerful enough to embed metal parts of the battery in a steel I-beam. Safer lithium-ion chemistries are available, but they cannot store as much energy as standard lithium batteries. Safety critical applications, such as electric vehicles and power tools, are the main application for the safer lithium-ion chemistries.

All lithium-ion batteries have safety features integrated in to the battery itself and support circuitry to protect the battery during operation and charging. Battery packs will include circuitry that can provide over voltage, thermal shutoff, and over current protection which help prevent overcurrent and overcharging conditions which can result in rupture, ignition, or explosion. Additionally, individual cells in the battery are required to have the following safety features:

  • Shut-down separator (for over temperature)
  • Tear-away tab (for internal pressure)
  • Vent (pressure relief)
  • Thermal interrupt (overcurrent/overcharging)

Recalls and Restrictions

No matter how many safety features are included, defects will happen. Over the last decade there have been several high profile recalls of lithium-ion batteries. Nokia recalled 46 million cell phone batteries at risk of exploding, Lenovo recalled 205,000 batteries, Dell recalled 22,000 laptop batteries after one caught on fire, and Sony recalled 10 million batteries used in a variety of laptops. In most instances, the recall was due to design defects that allowed contaminates to prevent the safety features from working or were due to problems in the manufacturing of the batteries. One such failure of a lithium-ion laptop battery occurred in mid-air during a commercial flight.

Lithium-ion batteries installed in devices have been allowed on most flights since they became the primary means of powering portable electronics. However, overly large batteries, containing more than 25 grams of lithium are forbidden from commercial air travel and only a limited number of lithium-ion batteries may be transported in carry-on luggage. Rules about lithium-ion batteries and aircraft vary by country and service, with some countries restricting shipping of lithium-ion batteries and products that contain lithium-ion batteries. Recently the USPS banned the shipment of anything that contained a lithium-ion battery to an overseas address due to several fires that were caused by lithium-ion batteries during transit.

Standards

Due in part to the dangers of lithium-ion batteries, several product safety standards have been developed to address lithium-ion batteries. The standards include several UL, IEC, UN, NEMA, IEEE, and SAE standards. Typically, batteries will need to meet several standards, often UL, IEC and UN transportation standards. The tests that are performed as part of meeting certification for the standards include:

  • Forcing a short circuit
  • Applying an abnormal charge
  • Forced rapid discharge
  • Crush testing
  • Impact testing
  • Shock and vibration
  • Heating
  • Thermal cycling
  • Low pressure (high altitude simulation)
  • Projectile or pierce testing
  • Reverse charging
  • Internal short testing
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