Samsung held a press conference today detailing the results of its investigation into the battery fires that plagued its Galaxy Note7. Reports of phones catching fire appeared soon after it went on sale August 19, 2016. After an initial investigation identified faulty batteries from one of its suppliers as the root cause, later identified by the US Consumer Product Safety Commission as Samsung SDI, Samsung announced a global exchange program on September 2, where phones containing the faulty battery would be replaced by ones using a battery from a second supplier; however, after this new batch of phones continued to catch fire, it became clear that the Note7’s battery problem was more complicated. Without a solution in hand, the company was forced to cease production and suspend sales of the Note7 on October 11. To date, Samsung said 96% of the roughly 3 million phones sold to customers around the world have been recovered.

Over the past several months, Samsung has been working to uncover the root cause of the Note7’s battery fires. The company’s own internal investigation involved over 700 engineers and data gathered from testing 200,000 phones and 30,000 Note7 batteries. To facilitate the testing, Samsung built a large-scale test facility that automated various charging and discharging scenarios that ultimately replicated the failures that occurred in the field.

To ensure it found the true cause or causes of the failures, it examined everything from the battery to hardware to software to manufacturing and logistics. Samsung tested both wired and wireless charging over a range of voltages and currents, with the Note7’s rapid charging feature both enabled and disabled. To see if the phone’s IP68 rated environmental protection caused heat buildup inside the sealed chassis, it tested phones with and without the back cover in place. It even checked to see if the Note7’s iris scanning feature or running certain preloaded and third-party apps resulted in excessive battery current.

In addition to its own internal testing, Samsung also enlisted the aid of two independent testing labs—Exponent Engineering and Scientific Consulting and UL—for battery and electronics testing and hired TÜV Rheinland to investigate possible causes due to logistics and assembly.

Ultimately, these investigations revealed that the Note7 fires were caused by different design and manufacturing defects in the batteries from both suppliers. The lithium-ion batteries used in the Note7 were constructed from long strips of an insulating separator sandwiched between positive and negative electrode foils spirally wound to create an electrode assembly inside a heat-sealed polymer pouch. Electrode tabs were welded to the positive and negative foil electrodes for external connection points.

For the batteries from Samsung SDI (referred to as “Company A”), the polymer pouch did not provide enough room for the negative electrodes in the upper-right corner closest to the negative tab. Either through normal expansion and contraction of the battery while charging/discharging, or through damage caused during manufacturing or assembly (as discovered by UL), the negative electrodes were bent after contacting the pouch corner, stretching the separator. If the separator failed, the cell would short circuit, which could lead to a runaway thermal failure. UL also discovered that the separator was too thin in some samples, which would increase the likelihood of this type of failure.

The pouch design of the batteries supplied by “Company B” (Amperex Technology), which were used in the Note7 replacements, had sufficient clearance around the electrodes. The failure of these batteries was instead due to poor control of the ultrasonic welding process used to attach the positive tab to the positive electrode. This spot welding process created sharp protrusions that could bridge the gap between the positive tab and the neighboring negative electrode during normal expansion and contraction of the battery due to thermal cycling, causing an electrical short. Some samples were also found to be missing a layer of protective insulation tape under the positive tab (the separator material was still in place), increasing the likelihood of a short circuit.

For batteries from both companies, the use of high-energy density cells increased the risk for thermal runaway during a short circuit, especially when the battery was in a high state of charge.

UL and Exponent also tested the Note7’s internal charging circuitry along with external charging accessories, including Samsung’s charger and popular third-party chargers. UL found that the Note7’s battery temperature and maximum current drain did not exceed rated limits and that battery current, voltage, and temperature did not exceed the battery’s specifications when charging with Samsung’s included charger. Exponent also found the Note7’s internal battery protection circuitry capable of defending it against chargers operating outside specifications. Based on their investigation, the companies concluded that the Note7’s electronics did not contribute to failures of either manufacturer's batteries.

To reduce the likelihood of future battery failures, Samsung is implementing an 8-point Battery Safety Check that involves additional inspection and testing, and improving training for everyone involved in handling batteries, both during assembly and shipping. It’s also adding more space and brackets around the battery to protect it from crush related failures, improving the safety standards for the materials inside the battery, and improving its software algorithms that control the battery charging temperature, current, and duration. Samsung confirmed that the upcoming Galaxy S8 will benefit from these new procedures and features, noting that they will not significantly impact the S8’s release date, which will occur sometime after Mobile World Congress this year.

Samsung is eager to move past the Galaxy Note7 and begin the process of regaining consumer trust, which is one reason why it’s sharing the results of its investigation. In a further bid to improve battery safety throughout the industry and repair its reputation, Samsung said it will share its new 8-point inspection plan with global standards organizations.

Comments Locked


View All Comments

  • Samus - Tuesday, January 24, 2017 - link

    App,e did the same thing going to high voltage lipo cells years ago. They either got lucky or went with a reliable manufacturer. It was a mild boost to 3.8-3.9v from 3.7, without increasing the amps. Samsung went the other route and increased amps, which turned out to be a little riskier since that causes a larger battery case.
  • JoeyJoJo123 - Monday, January 23, 2017 - link

    Why is everyone still parroting this meme that "da battery be 2 big 4 da phone"?

    The analysis here presents two things:

    1) Nothing is wrong with the phone's electronics by itself and the phone's electronics performed well to control incoming voltage/amperage during charge/discharge cycles.

    2) Problems inherent with the battery fires are due to short-circuits of the battery itself, leading to thermal runaway, for two different reasons from two different suppliers.

    a) For Samsung SDI, it was persistent damage to the top-right corner of the battery pouch where electrodes in close proximity may short-circuit during thermal expansion/contraction experienced during charge/discharge cycles.

    b) For Amperex Tech, it was persistent damage to the positive terminal of the battery pouch, due to spotty welding.

  • linster - Monday, January 23, 2017 - link

    Because battery size and capacity may have a role here, more so for Samsung SDI's battery than for Manufacturer B. If Samsungs requests a certain capacity in a specific volume, battery manufacturers may have to perhaps push design limitations that may results in what we see here in this analysis.
  • vladx - Monday, January 23, 2017 - link

    Exactly, that's what I meant also.
  • JoeyJoJo123 - Monday, January 23, 2017 - link

    Except, again, battery size wasn't the issue here.

    It was electrodes near negative terminal aren't spaced enough to prevent short-circuiting during thermal expansion/contraction, and spotty welding on the positive terminal for the battery.

    It should be blatantly obvious from manufacturer B, whose only issue was spotty welding for the positive terminal, that the battery size dimensions and capacity weren't an issue; The batteries by design were flawed and the quality wasn't thoroughly tested by two independent manufacturers.
  • JoeyJoJo123 - Monday, January 23, 2017 - link

    Meaning, they can get even larger capacity batteries in the phone and it would work out _just_fine_, if they did their due diligence QA on the battery manufacturing process to ensure what was being delivered wasn't faulty.

    Again >"muh battery size" has nothing to do with it.
  • Meteor2 - Monday, January 23, 2017 - link

    So what are you saying? That the batteries could have been manufactured safely? That's not clear to me from the article. The 'how' is outlined but not really the 'why' -- was the battery design impossible to manufacture safely at scale?
  • FunBunny2 - Monday, January 23, 2017 - link

    -- Except, again, battery size wasn't the issue here.

    read up the NYT piece: . "Pushing to make the battery thinner and more powerful, Samsung opted for an exceptionally thin separator in its battery." clearly, Samsung specified the power from the battery and specified the dimensions of the insulating film
  • lilmoe - Monday, January 23, 2017 - link

    Stop parroting BS articles just because they support your hate towards Samsung.

    Three independent entities were hired to perform thorough analysis of the situation. When each of their representative took the podium, first thing they stated their names, their educational and expertise levels, and the amount of experience they have in that specific, explicitly related field.

    And what do we get from the NYT? A fellow in social studies? lol

    You guys are hilarious. It's amazing how far people go in believing and citing clowns just to prove an invalid, prejudice arguments.
  • FunBunny2 - Monday, January 23, 2017 - link

    "And what do we get from the NYT? "

    reporting information from folks who are too scared to be on the record??? could be that Samsung is in the "alternative facts" universe with The Donald.

Log in

Don't have an account? Sign up now