The first thing Samsung talked about during a pre-launch briefing on its Galaxy Note 7 back in July was the phone’s battery and its new "fast charging" technology. The subtext was pretty clear: "Our phone has a bigger battery and charges up faster than the (then-forthcoming) Apple iPhone 7."
This new feature has become one of the main theories on why the battery in the Note 7 had a tendency to blow up—a malfunction that necessitated one of the biggest and costliest product recalls in consumer tech history.
Ultimately, the reason Samsung took the dramatic step to discontinue the Galaxy Note 7 was that it was unable to pinpoint with certainty the reason the batteries in the phones were blowing up. As Samsung engineers struggled to recreate the problem, the pressure grew from regulators and the media to make a decisive move.
After the first wave of Note 7 explosions were reported, Samsung thought it knew what the problem was. On September 2, when I asked Samsung for a technical explanation of the Note 7 battery problem, the company replied:
"An overheating of the battery cell occurred when the anode-to-cathode came into contact which is a very rare manufacturing process error."
Samsung thought at the time the problem was occurring only in batteries made by its SDI subsidiary. So it set about replacing all the suspect phones with ones containing batteries made by another supplier, ATL (Amperex Technology Ltd., a subsidiary of TDK). That SDI would have botched the production of the batteries sounded odd because, as IDC analyst Will Stofega pointed out, the subsidiary has a long history of making batteries that work and don't blow up.
On September 23, reports that those phones were also blowing up began coming in. Today, Samsung has a far less definite-sounding answer to the question of "why."
"A thorough investigation takes time, and it would be premature to speculate on outcomes of the investigation," a Samsung spokesperson said in an email statement Wednesday. "In the U.S., we have received a small number of reported cases of issues with replacement Note 7 devices. We are working around the clock to analyze the causes of the reported cases."
The New York Times reported that many Samsung engineers have been trying to replicate the fault that made the SDI and ATL batteries explode, but have failed. So on the day the Galaxy Note 7 became a discontinued product, the cause of its demise remained a big fat question mark.
Several theories have emerged over the past few weeks about why both the SDI and ATL batteries overheated. One theory goes that it was the design of the battery, not the "manufacturing process" (as Samsung originally said), that caused the problem. The battery design could have been completed by Samsung engineers then fed to SDI and ATL to manufacture according to spec.
A Korean government regulator concluded that the positive and negative charged plates inside the batteries were too close to one another at the rounded edges of the phone. When positive and negative poles in a lithium ion battery physically touch, a very rapid and violent chemical reaction takes place. The regulator also pointed to defective coating material on the negative electrode.
The reason these findings are interesting is because they suggest that the phone’s overall design may be affecting the safety of the battery. The plates being too close together may have resulted from the intense competitive pressure to produce ever thinner phones. And not just thinner phones, but phones that also contain more components. The Note 7, for instance, had a new iris scanner on board, and also retained the analog headphone jack, which takes up a lot of space. The regulator also pointed to the battery design within the phone’s rounded edges—another new design trait in the Note 7.
There’s also an intense market demand for phones that charge faster, and it’s Samsung’s attempt to meet this demand that may be the most compelling explanation for the explosions. Samsung said its new fast-charging technology lets the battery in the Note 7 charge to 50% capacity in 30 minutes, a claim born out in my tests.
Here’s how fast charging works: USB chargers with fast-charging circuitry built in can send a higher power output into the smartphone. Any charger with an output of greater than 10 watts is considered "fast charging." The Note 7 uses a USB-C charger with fast-charging tech inside. Specialized power management chips inside the phone moderate the power level it can handle without overheating the phone or overcharging the battery.
Qualcomm supplies its 820 Snapdragon processor and various power management chips for one of the two versions of the Note 7. The company points out, however, that those chips aren’t involved in the regulation of the power flowing into the battery during charging. "Qualcomm does not provide any of the battery charging electronics commonly used in both versions of the Note 7," a Qualcomm spokesperson said in an email to Fast Company.
Qualcomm also points out that the power management chips it supplies for the Note 7 are also used in other mass market phones (Samsung's Galaxy S7 and S7 Edge, Xiaomi's Mi Max, and ZTE's Nubia Z9 Max) that don’t blow up. Qualcomm's own QuickCharge technology was indeed used in one version of the Note 7, but only for its protocols used in communication between the various power management chips in the device.
Lithium-ion batteries in phones contain three major physical structures: a positive electrode made of Lithium cobalt oxide, a negative electrode made of carbon, and a separator layer made of micro-perforated plastic. The layers are submerged in an organic solvent substance. During charging, lithium ions move through the plastic barrier layer from the positive lithium electrode and attach to the negative carbon electrode. As the battery is used (discharged) the opposite happens: Lithium ions move back over to the positive electrode.
Lithium-ion batteries can become unstable if charged at a higher-than-specified voltage rate. The cathode material can become an oxidizing agent, losing its stability and producing carbon dioxide. If pressure within the cell continues to rise, a safety interrupt is supposed to kick in. If such an interrupt doesn’t happen (for whatever reason), pressure within the cell can continue to rise and the safety membrane around the cell can burst, causing the cell to "vent with flame." When battery manufacturers say "vent with flame," they mean "explode."
"It casts a pall over the whole fast-charging technology; you have to be concerned," says Steve Rizzone, CEO of the long-range wireless charging tech supplier Energous. "The whole idea of rapid charging is going to have a negative connotation to it." Rizzone says that problem points to the need for a new way of charging devices. While the technology has yet to be productized, Rizzone believes the constant over-the-air charging Energous is building will let users constantly be "topping off" the charge in their phone’s battery, which would lighten the load on the battery.
So the Note 7 debacle, whatever the exact cause, may have been the result of a smartphone maker trying to respond to the marketplace and simply asking too much of the battery technology we have today. "What you’re seeing is proving more and more that powering larger batteries, and charging those batteries quicker, the battery chemistry can’t keep up with those requirements," Rizzone says.
Lithium-ion batteries are far more reliable and safer than earlier battery technologies, but there are limits to the amount of miniaturization, power capacity, and rate of charging phone makers can impose on them.
Maybe it was inevitable. Maybe Samsung was just unfortunate enough to be the first phone maker to (loudly and violently) run smack into the wall, the outer limits of what lithium-ion technology can safely be asked to do.