Samsung recently made a recall for the Galaxy Note 7 after multiple users reported battery fires and explosions. What made this action necessary and why do lithium-ion batteries have such a bad reputation for causing fires?

The Great Recall

Samsung announced that all Galaxy 7 Note devices should be recalled as users have reported overheating batteries, fires, and even explosions. The Galaxy 7 Note was released on September 2nd (pre-orders from August 16th) and has only been on the shelves for a month. However, this does not imply that all Samsung devices are dangerous as there have been 92 reports out of a total of 1 million devices in the US.

Even so, these incidents have gotten a lot of media attention given that the damage caused by the devices has been enough to burn people and cause fires (as one individual found out when he left his Note 7 in his Jeep charging).

But why are these batteries catching fire? What is it about lithium-ion batteries that make the susceptible to such an explosive end? To answer these questions, we need to understand how a lithium-ion battery works.

 

Li-Ion Batteries

Like most batteries, Li-ion batteries consist of three main parts: the anode (+ terminal), an electrolyte, and a cathode (-).

In Li-ion batteries, the anode is usually made from Lithium-Cobalt Oxide (new batteries may use Lithium Iron Phosphate) and the cathode is made of carbon. The electrolyte in such batteries must be able to transfer positive ions between electrodes but be an insulator to an electrical current (electron flow). Electrolytes vary between batteries but are commonly lithium salts in an organic solvent.

 

Simple cutaway of the Li-ion battery. Image courtesy of Tkarcher (own work) [CC BY-SA 3.0]

 

Charge Cycle

When a Li-ion battery is charged, lithium ions are removed from the anode and embed themselves into the porous carbon cathode. At the same time, electrons from the anode are removed and electrons flow to the cathode where they bond with the lithium ions to deposit lithium metal into the carbon.

 

Discharge Cycle

During a discharge cycle (when a load is connected across the battery terminals), electrons from the cathode are attracted to the anode which results in the embedded lithium ions in the carbon cathode to travel through the electrolyte and back to the anode where again they combine with electrons to form metallic lithium.

The electron flow and ion flow in the electrolyte complement each other and the charge process can only occur if both processes are active. If one stops (for example, the electron flow), then so will the other process (in this case, the ion flow).

 

Overheating

So why do Li-ion batteries have a bad habit of overheating and catching fire?

The issue comes down to two factors:

  • Speed of lithium ion deposition on the carbon cathode
  • Temperature of the battery

When a lithium battery is being charged, the Li ions need to be embedded into the cathode which is known as intercalation. This process is very important because, instead of depositing metallic lithium on the surface of the cathode, the lithium ions penetrate the porous regions of the cathode.

If a Li-ion battery is charged too quickly, the Li ions are deposited on the surface of the cathode as plated lithium instead of being trapped the porous regions. This is serious as the distance between two plates in a typical Li-ion battery is very small (measuring in mm’s). As the lithium-plated layer becomes thicker, it can eventually make contact with the anode which creates a short circuit.

 

Electroplating showing how the cathode increases in physical dimension.

 

This short circuit can then lead to a massive amount of current discharge which heats up the battery. As the battery heats up, it runs the risk of entering thermal runaway where the increase in temperature makes the reaction occur faster which loops back to increasing the temperature. This can lead to the cell smoking, igniting, and even exploding.

So how is such an issue overcome?

The answer involves electronics that constantly monitor the batteries' temperature, voltage, and current output. During charging, the battery is carefully monitored and the charge current is kept low. This intentionally increases the time taken to charge the battery but results in the lack of lithium plating on the cathode. When batteries are in use, the controller can keep measuring the temperature of the battery and shut down cells if needed to prevent further damage.

 

Li-Ion Explosives

The situation with Samsung and their potentially dangerous batteries is not new. In fact, it is very common to hear about Li-ion batteries causing damage and fires including hoverboards, Apple iPhones, and even laptops.​

 


So why are these batteries still in use if they can present a very real danger?

In short, we keep using Li-ion batteries because they have a number advantages over other rechargeable batteries and regular batteries.

Firstly, Li-ion batteries are rechargeable, unlike normal batteries that you may find in some cameras, remotes, and toys.

Secondly, Li-ion batteries do not suffer from a phenomenon called “memory effect” as much as other rechargeable batteries (such as NiMH and NiCd). Simply stated, memory effect is when a battery loses its ability to store charge if it isn't completely discharged before being charged again.

Li-ion batteries are also lightweight and have a higher energy density as compared to other rechargeable technologies. This makes Li-ion the choice for portable devices, power tools, and even electric vehicles.

 

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Summary

Li-ion batteries are heavily used for their properties in weight and energy density, but this comes at a cost that some of these batteries may fail and cause damage.

If incidences continue to rise with faulty Li-ion batteries, then it may not be long before government intervention may change the rules with such power sources.

New technologies, smarter devices, and better materials may reduce the risk of such devices failing—but these changes may need to come sooner rather than later because it won’t be long before someone becomes seriously hurt from one of these power sources.

 

Comments

20 Comments


  • Andrej Rehak 2016-10-24

    Isn’t there something wrong in this article? In Li-ion batteries when they are discharged i was always taught that the electrons travel from anote to cathode… So the section describing the Charging and Discharging process shoould have their headers exchanged.

  • oldew 2016-10-30

    http://chemistry.about.com/od/electrochemistry/a/How-To-Define-Anode-And-Cathode.htm
    No, Andrej Rehak, you have missed it somehow. The cathode discharges electrons in use. But in the charging scenario, electron flow is reversed. It should also be noted that batteries are conventionally reasoned according to its positive charge allocations. (hole flow as it is in my mind) That is why the positive terminal of conventional batteries is red. For safety sake, at this time a note to the novice: For large stationary battery the negative battery terminal usually gets a Red conductor and the positive terminal the Black conductor.

    • rod-e 2016-11-03

      What nonsense - Red is positive and black is negative in this universe.  Large stationary batteries are common with telecommunications, and the standard has /always/ been red for positive, even when positive is referenced to earth/ ground.  False info such as that above is potentially very dangerous, especially for newcomers.

  • redrooster01 2016-11-03

    Lithium Batterys wont be around for much longer if Hemp Batterys take hold.along with common sense. Recent discoverys have found that Pyrolized Hemp fiber gives much more better performance than Lithium Batterys,theyre non toxic,cheap,safe,dont heat up or explode,all this before any attempt has been made to optimise them! You can DIY your own batterys by watching the instructable videos on Robert Murray Smiths YouTube channel.

  • AdeV 2016-11-04

    When it comes to explosive batteries, there’s none more so than the Lithium Polymer (LiPo) batteries commonly used in radio controlled aircraft/cars/etc. these days. These batteries seem to have very high charge/discharge capabilities, yet if you overcharge them, undercharge them, or even just drop one on the floor, it goes up in smoke (often spectacularly). Does anyone know why this is? And, if it could be made shockproof would LiPo become the new “Battery du jour” of the laptop/mobile phone industry?

    • Doktor Jones 2016-11-04

      As mentioned in the article, the internal separation between anode and cathode is very small. If any plating has occurred, even if it’s not enough to short the anode and cathode by itself, the mechanical shock of being dropped can short them. In most cases it’s only momentary and causes no noticeable effects, but if the polymer dielectric gets damaged in the process and the short remains… *POOF* goes the magic smoke.

      • Doktor Jones 2016-11-04

        I think the solution would be to make a) a “self-healing” dielectric that can recover from such damage, and/or b) integrated electronics on the battery that can somehow detect plating and initiate some sort of reversal process.

  • jjustin 2016-11-04

    Note that NiMH batteries do not have a memory effect - only NiCd have a memory effect. The advantage of Li-ion is the higher energy density - more energy can be stored in an equivalent form factor.

  • chrisindallas 2016-11-04

    Wasn’t this Samsung’s first theory? While the science behind the article seems correct, I believe Samsung found out that the charge rate wasn’t the problem and rather it was being caused by changes to the battery when it is bent. The structure of the battery+phone wasn’t strong enough to withstand physical damage, leading the battery to malfunction. Unfortunately for Samsung, they cut the charge rate by 60% and the phones still failed. This is what one of their competitors reported when they analyzed the Note 7.

  • chrisindallas 2016-11-04

    Wasn’t this Samsung’s first theory? While the science behind the article seems correct, I believe Samsung found out that the charge rate wasn’t the problem and rather it was being caused by changes to the battery when it is bent. The structure of the battery+phone wasn’t strong enough to withstand physical damage, leading the battery to malfunction. Unfortunately for Samsung, they cut the charge rate by 60% and the phones still failed. This is what one of their competitors reported when they analyzed the Note 7.

  • Vabeachmike 2016-11-04

    I was kinda disappointed in this article.  A better title would have been “Why Lithium Batteries Explode”.  There was no discussion about the specifics of the Note 7 flaws.

  • vaggabond 2016-11-04

    Very generic article.
    There is little battery monitoring could have done to prevent this. It was marginal battery design.

    Better article here:
    http://www.powerelectronicsnews.com/technology/pushing-to-the-very-edge-of-safe-li-ion-charging

  • Alex Welti 2016-11-04

    The main thing I get from this article is that charging too fast is the main problem… Can someone tell me if discharging too fast is a potential problem?  Also, if you limit the current by some means so neither happens too fast, are there any dangers with over-charging, over-discharging, applying voltages that are too high, or draining the battery until the voltages are too low?  Because, I would like to use Li-Ion batteries for projects, and if it is as simple as limiting current, that seems too good to be true… I was thinking it was a lot more complicated and would need an MPU to keep track of counting each electron as it traveled in or out of the battery… (that’s supposed to be funny)... Thanks for any knowledge you can share with me…

  • hp1729 2016-11-04

    Interesting, but doesn’t answer the question of why these specific batteries behave so differently? is it the size and power density of this specific model of the battery? Are they charged too fast?
    In hover boards is it the discharge rate that is the problem, since the fires happen while in use, not while charging. If the fire starts inside the battery itself no electronics safety features are going to help. right?

    • jgruszynski 2016-11-04

      That’s because it’s probably not merely the battery that is different.  Indeed the #1 thing about LiPO batteries is how the charge and discharge cycles are handled. 

      I’m guessing this same battery is probably used in dozens if not hundreds of other products with zero problems.  If so, then it can’t be the battery. 

      The more likely variable is how the charge and discharge cycles are handled which is typically handled by a switched converter circuit which can dynamically adjust to the changing Thevenin/Load impedance of the battery over the cycle plus adjust to changing charger voltage and to changing application load conditions of the phone itself to try to match source and load.

      When you screw this balance up and the battery starts to charge or discharge too quickly, you get fire problems.  This is clearly what is happening here somehow.

      You are exactly right about HoverBoard fires.  If you look at the implementation of most of these, there is literally NO converter at all - most hook the battery switched directly between charger DC and H-bridge driver.  This asking for a battery fire with LiPO!!  Epic Fail design.

      Ok but Samsung et al. actually understand this so they DO use converters.  But designing a proper converter is not actually easy.  The inductor design alone can be 50-100 steps that must be exactly followed and correctly. 

      And sometimes companies and their managers may foolishly assign green interns the job of designing power supplies and power converters (because power is “simple”, “unglamorous”, “unsexy” and obviously intern work).

      This is why I think blaming the battery is quite like BS if there are any other users of the same battery model - someone should check that!  If so then it’s far more likely a design flaw in the charge/discharge circuitry combined with issues relating to power consumption variance exceeding the range of this same circuitry combined with the limits defined by the battery. 

      For example, maybe they specified power of the CPU/GPU based on the data sheet (which is Epic Fail) BUT the one thing that is highly variant and dependent on vagaries of the particular software running at the moment is: CPU/GPU power consumption. 

      Then, hypothetically, imagine that their get a run of CPUs from Samsung Semi which have slightly above spec power consumption and left unsaid is that because of process issues the process variance on parameters like Vt, Iddq, etc. is a bit wider than the original design assumed (e.g. assumed ±5% but this batch are ±20%).  Suddenly the power budget has tail that exceeds the converter design assumption or perhaps the design had too small a margin itself.  We really don’t know but this is often how such problems arise.

      So if you have a converter design on the edge and you happen to have the wrong mix of OS and SW running that pushes nominal power consumption over the edge into that process tail, then the converter allows discharge of the battery faster than it’s supposed to, then that leads directly to overheating and fire risk.

      This is strictly what we don’t know and haven’t heard anything cogent from Samsung so far.  Given their SOP I’m guessing they’ll never volunteer the information if it suggests or creates conflict or failure (it’s an Asian thing).  It’s probably something that either some in “journalist” should be asking them directly or someone will need to get some Note 7s, reverse engineer and failure analyze a few.

      I used to do failure analysis on far more complex systems (satellites and launch systems) and mundane yet cascaded failures like this are surprisingly common when things fail unexpectedly and catastrophically.  The obvious things get covered but it’s the interdependencies you can’t always see clearly or assumed away as impossible or irrelevant that bite you in the ass.  And it’s usually the part that someone decided was “so simple we don’t need to worry about it” - until you do.  You simply can never assume things - always “trust but verify”.

  • cuyler1 2016-11-05

    99.9% of the time the answer of these batteries problems are “The human factor”! The guy found out whenever he left the phone in his Jeep. Leave a child or pet in same jeep is doing the same thing. Read the OWNERS MANUEL and temperatures are explained yet idiots always say “I don’t know why ? !” as it is their own fault. Kids on y/t chopping ,burning , overcharging and not having the proper equipment to maintain the batteries shows dramatic results.
      The R/C aircraft which exploded was the operators’ error! I can always find that the idiot which had problems is the problem!
      I and millions of others use these batteries everyday without ever encountering failure,fires or explosions.

    • Teufelwolf 2016-11-06

      The greater the energy density of any item, the more dangerous it gets. That is why the “atomic car” of the 1950’s never caught on. Or the reason why a lot of those “150 mpg” engines of the 1950’s never saw the light of day… not because of any conspiracy - just that in order to get that much energy out of gasoline often required a engine that WOULD explode in an accident.