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29th September 2023 (10 Topics)

Lithium-ion battery fires

Context

The onset and intensification of lithium-ion battery fires can be traced to multiple causes, including user behavior, such as improper charging or physical damage.

What are Lithium-ion batteries?

  • A lithium-ion battery is a type of rechargeable battery that uses lithium ions as the primary component in its electrochemical system.
  • It is widely used in portable electronic devices, electric vehicles, and various energy storage applications.
  • Basic structure:
    • A battery is made up of an anode (a negative electrode), cathode (a positive electrode), separator, electrolyte, and two current collectors (positive and negative).
    • The electrodes are typically made of materials that can intercalate lithium ions during charging and discharging cycles.
    • Common cathode materials include lithium cobalt oxide (LiCoO2), lithium manganese oxide (LiMn2O4), and lithium iron phosphate (LiFePO4).
    • Graphite is commonly used as the anode material.
  • Functioning:
    • During a discharge cycle, lithium atoms in the anode are ionized and separated from their electrons.
    • The lithium ions move from the anode and pass through the electrolyte until they reach the cathode, where they recombine with their electrons and electrically neutralize.
    • The lithium ions are small enough to be able to move through a micro-permeable separator between the anode and cathode.
    • In part because of lithium’s small size (third only to hydrogen and helium), Li-ion batteries are capable of having a very high voltage and charge storage per unit mass and unit volume.

Advantages of Li-ion batteries

Disadvantages

  • They have one of the highest energy densities of any battery technology today.
  • This means they can store a significant amount of energy for their size and weight.
  • They also exhibit a relatively low self-discharge rate when compared to other rechargeable batteries, allowing them to hold their charge for extended periods.
  • In addition, Li-ion battery cells can deliver up to 3.6 Volts, 3 times higher than other technologies.
  • This means that they can deliver large amounts of current for high-power applications.
  • Li-ion batteries have no memory effect, a detrimental process where repeated partial discharge/charge cycles can cause a battery to ‘remember’ a lower capacity.
  • These batteries do not contain toxic cadmium, which makes them easier to dispose of than Ni-Cd batteries.
  • Li-ion batteries have a tendency to overheat, and can be damaged at high voltages.
  • In some cases, this can lead to thermal runaway and combustion.
  • This has caused significant problems, notably the grounding of the Boeing 787 fleet after onboard battery fires were reported.
  • Li-ion batteries require safety mechanisms to limit voltage and internal pressures, which can increase weight and limit performance in some cases.
  • Li-ion batteries are also subject to aging, meaning that they can lose capacity and frequently fail after a number of years.
  • Another factor limiting their widespread adoption is their cost, which is around 40% higher than Ni-Cd.

 

 

What causes these fires?

  • As these batteries are the powerhouses that fuel our smartphones and laptops –and has the ability to store heaps of energy in a small space.
  • When EV batteries do overheat, they’re susceptible to something called “thermal runaway”.
  • This chemical reaction can be triggered from faults in the battery – whether that’s an internal failure (such as an internal short circuit), or some kind of external damage. In extreme cases, it causes the battery to catch fire or explode.

 

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