Bad Assumptions & Why Lithium-Ion Batteries Still Catch Fire

The lithium-ion battery is a fact of modern life. Cellphones, laptops, cameras, tablets, and many other items take advantage of this convenience. Even so, we still read news articles about batteries of this type exploding, catching fire, or otherwise causing concern. There have even been aircraft lost due to lithium-ion battery fires. The news continues to have stories about the 787's batteries, such as this aircraft accident report and this article on battery-fire aircraft crashes.

Each cell in a pack consists of a pair of electrodes, one of which is lithium, separated by a polymer or other separator, and an ether electrolyte (similar to what is used to start a car). Under certain conditions, this potentially volatile combination can overheat, vent, or combust. There is a wide variety of conditions that can cause combustion, including over-charge, over-temperature, decompression, impact or crushing, short circuit, or over-discharge. There are other items of concern, such as cell balance. This wide range of potential faults means a variety of methods for preventing issues needs to be employed.

There are a variety of standards for lithium-ion batteries. There are UL standards, IEEE standards, IEC standards, and a number of others. When it comes to sending batteries by air, only batteries that have passed the IEEE standard, for example, are protected from de-compression. Some laptops and cellphones have batteries that pass this standard. Many others have batteries in which that capability does not exist or has not been tested, so their status is unknown.

Semiconductor vendors have created a variety of special integrated circuits to manage and charge lithium-ion batteries. Some have good temperature accuracy, but no cell-balancing capability. Others offer good cell-balancing (bleeding off charge to match the cells in a stack), but poor temperature accuracy. Lack of cell-balancing can cause some cells in a multi-cell pack to over-charge and others to under-charge. One example of the reason that temperature accuracy is important is that, although a large number of today's laptops use low-end, relatively cool-running CPUs, a number of laptops feature warm-running (70°C) high-end processors and graphics accelerators.

If you take one of these latter units, discharge the battery at 70°C by using just battery power during the day, and then let it sit turned off in a hotel room at 25°C while charging the battery overnight, then a sizable error between the apparent charge energy and discharge energy can occur. This can potentially result in over-charge or over-discharge, either of which can cause the pack to swell or even leak ether.

My older Toshiba has these issues, with a hot GPU and hot CPU, coupled with no cell-balancing. This means that in a way it's a ticking bomb, I suppose. What are your experiences with this issue?

This article was originally published on EBN's sister publication EE Times .

3 comments on “Bad Assumptions & Why Lithium-Ion Batteries Still Catch Fire

  1. William Murray
    April 24, 2014

    Still kind of a mess, but better than 7 years ago when recalls were rampant — The IEEE standard does not specify cell ballancing, nor do any of the other standards — when dealing with a multi-cell pack — and none of them have a test / standard such that short circuit energy is limited to less than that required to ignite ether(may be really hard to make reliable)

  2. Houngbo_Hospice
    April 25, 2014

    Why is it that difficult to come up with a common cell-balancing standard?

  3. Himanshugupta
    April 26, 2014

    I have not experience any exploding battery but i have had problems with leaking, swollen batteries that reduce their lifetime tremendously. I think the lack of general knowledge or guidelines make the usage very difficult for average user. Most of the time there are labels that warn about the potential hazards of the battery but do not specify how to protect the batteries for longer life and safe use.

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