A look inside the world of batteries

23Jun 2017

Fast charging is a common feature of most modern smartphones. In a few more years, it may become a standard feature for electric vehicles too. Yet, asking a consumer how long it would take to charge their device will most likely result in a confused answer. Even tech-savvy engineers will find it more challenging to provide a consistent figure for charge times. Why is it so?

There are several parameters that impact total charge time. Some of them may be obvious. For example, charging the smartphone with a small AC adapter will make less current available to charging, so it will take longer to charge. Similarly, browsing the web while charging will divert precious electrons away from the charging process. Again, it becomes slower.

But the less obvious parameters relate to definitions. That’s right, definitions of what it means to say the battery is “full.” This post will shed some light on two such definitions.

For the purpose of this explanation, I will use the standard charging methodology called CC-CV (constant current, constant voltage). The charging current is constant until the battery reaches its maximum specified voltage (in this example, it is 4.35 V) at which point the charging circuitry reverses the order and fixes the voltage while letting the current decay to near zero. When the charging current becomes “sufficiently small,” the battery is then considered fully charged.

Therefore, our first definition relates to the meaning of “sufficiently small” and therefore, the meaning of 100% full. There is a misconception that the battery is “full” when its terminal voltage reaches a maximum specified voltage (e.g., 4.35 V). That is not correct. The battery is considered full when its charging current decays to a value below a pre-defined threshold. This threshold is called the termination current and is calculated relative to the charge capacity of the battery.

Let’s say, as an example, a battery can hold a charge capacity of 1,000 mAh. Some companies consider this battery full when its charging current decays to a value of 1,000/20 = 50 mA. This is called C/20 termination. Other companies establish a different threshold of C/10, which means the charge is considered complete when the charging current decays to a value of 1,000/5 = 200 mAh.

The figure below shows the charging current (in green) for an actual lithium-ion battery with a capacity of 3,300 mAh. The charging current displayed on the right axis remains constant for the first 49 minutes (that’s the constant current portion), and then it begins to decay (that’s the constant voltage portion). Note that the axis for the charging current is on a logarithmic scale, so the decay is exponential (not linear). The current reaches a value of C/5 (660 mA) after 68 minutes, and a value of C/20 (150 mA) 28 minutes later, or 96 minutes after the start of charge.

 

 

Hence the first observation: Set a lower threshold for the termination current and make your total charge time significantly faster. Now note that this only makes the “total” charge time faster because the device manufacturer defines a different value for “full.” It does not impact the charge time to 50% or 80% of full.

Of course, this now begs the question: Wouldn’t the device manufacturer who chooses to use a lower termination current end up adding more charge to the battery, and hence lasting a little longer for the day. Yes, that is true, and that leads us to the second definition.

Our second definition relates to the time when the smartphone lights up green and says “charge full.” In other words, this relates to what the smartphone “displays”, not what it really measures, but rather what it chooses to tell you as a consumer. And here, all device OEMs are complicit. They all, virtually without exception, choose to display 100% full at an earlier time before the termination current is reached. You must be scratching your head now and saying, “isn’t that a form of lying?” Well, it is a matter of perspective. The reality remains that virtually all smartphones will say 100% in the upper right hand corner of the displays before the charging current reaches its termination value.

To see this effect, let’s examine the figure again but now point our eyes to the blue and red curves corresponding to the axis on the left hand side. The blue curve is the true and actual charge value of the battery during the charging process. You will notice that the blue curve hits 100% when the termination current of C/20 is reached. In contrast, the red curve is what the smartphone actually displays on the front screen. The red curve says “100% full” much earlier, at about 65 minutes. At that moment in time, the battery is only about 95% full, but the smartphone takes a little liberty in rounding the value up to 100%. One can argue that the delta is really small, and for most consumers, they are happy to be at 80% or 90%. There is some truth to that. But now, as a consumer, you know that the value the smartphone displays is not really what it measures. If you really, really want to reach the true 100% full level, then keep your device connected to the charger for another 30-ish minutes.

04May 2017

A long time ago in a galaxy far, far away

smartphones used primitive energy sources called batteries 

that users could easily replace.

Then came the Apple iPhone and made it difficult to swap out the battery.

Batteries failed too often and even caught fire. Users got upset.

But the labels on the batteries stayed the same.


 


Whether you browse the web searching for a teardown of your favorite smartphone, or are sufficiently skilled to take a smartphone apart, you will always find a battery, a lithium-ion battery, with a whole bunch of markings on it.  Some of them are obvious to decipher, such as the name of the manufacturer. Other label marks may be puzzling such as a dog safety mark — yes, dogs seem to occasionally savor batteries. Then there are cryptic numbers that can mean very little to the average reader. The purpose of today’s post is to shed some light on what one can glean from the label of a lithium-ion battery.

The left photograph above is for the battery used in the iPhone 7 while the right photograph is for the Samsung S8 battery. The iPhone 7 battery has fewer markings than its Samsung S8 counterpart. That is typical of Apple’s batteries. It clearly shows the Apple logo but it does not say who manufactured the cell. Rumors abound on who manufactures Apple’s batteries in Asia, but Apple does not disclose this information on their battery labels. By contrast, the Samsung label clearly states that Samsung SDI manufactured this particular cell in Korea, and assembled it with its electronics in its factory in Vietnam.

Battery labels also state some required product certification marks depending on where the smartphone is sold. Both of these cells carry the PSE mark required by the Japanese Electrical Appliance and Material Safety Law. The Samsung S8 cell also carries the European CE mark as well as the Korean KC certification mark indicating compliance with the European and Korean product safety requirements. The iPhone battery carries the UL recognized component mark for the US market (which looks like a cRUus logo). These marks usually indicate that the product conforms with certain guidelines established by a regulatory body or government, but they do not guarantee the safety of the battery. Safety remains the responsibility of the smartphone manufacturer.

Both iPhone 7 and Samsung S8 battery labels also state some important electrical characteristics, in particular the battery’s capacity and its voltage. Battery capacity is stated in two units: maximum charge capacity measured in milli-amp-hours (mAh), and maximum energy stored in the battery measured in Watt-hours (Wh). The first is a measure of electrical charge (how many ions the battery can hold). The latter measures the total amount of energy. If you recall your high-school physics, energy is electrical charge multiplied by voltage. That is the third figure that one can read on the battery label.

For the iPhone 7, the maximum charge capacity is 1,960 mAh. For the Samsung S8, it is a nominal 3,000 mAh. In terms of maximum energy stored, the iPhone 7’s figure is 7.45 Wh which pales in front of the S8’s value of 11.55 Wh. So when we say that the Samsung S8 has a bigger battery than the iPhone 7, we mean that its  capacity is larger, not that it is physically bigger.

Now we get to the tricky conversation regarding voltage. First, we notice that the iPhone 7 battery reads only one value, 3.8 V. The Samsung S8 batteries reads two values: (i) a nominal voltage of 3.85 V and (ii) a charge voltage of 4.4 V. What do they mean?

Let’s start with the easy one. The charge voltage is the maximum voltage that the battery can be used in charging the cell. The Samsung S8 cell is rated to a maximum of 4.4 V. It does not mean that the charging is at 4.4 V. It only means that it can go as high as 4.4 V. We know that Samsung derates the cell to 4.35 V instead of 4.4 V to mitigate concerns about safety.

The nominal voltage needs a lot more explaining.  For that, we will need to examine the next graph showing the battery’s voltage and its dependence on state of charge (the measure of how full it is).

When a typical lithium-ion battery is empty (at zero percent), the voltage across its two terminals is low, about 2.9 V. As the battery is charged, its voltage will rise to its maximum charge voltage.  The “average” voltage throughout this charging process is called “nominal voltage.” It turns out that if the maximum voltage is 4.4 V, the corresponding nominal voltage is 3.85 V. But if the maximum voltage is only 4.35 V, then the nominal voltage is 3.80 V. So it becomes easy to figure out that the iPhone 7 has a maximum voltage of 4.35 V even though it is not stated on its battery label.

You have now become an expert in reading battery labels. But whatever you do, always remember to stay safe and keep your battery away from metal objects.

21Apr 2017

T’is the season of new smartphone releases. The Samsung S8 is here and the drums are beating loud ahead of the much anticipated Apple iPhone 8 (or Edition, or whatever they will call it).

These devices and their makers clearly tout their performance features: faster processors, better camera, pretty displays, more memory….etc. But for this year and possibly for many years to come, the #1 feature is look and feel, otherwise known as industrial design, or just plain ID.

Industrial design includes how the device feels in the hand and eliminating or at least reducing the bezel to make the display reach out to the edges. It also includes thickness and profile, often some type of a rounded design that is comfortable in the palm. Invisible to the consumer are the havoc that these aesthetic features wreak on the battery. For example, thin smartphones mean thinner batteries; I mean really thin (less than 3 mm). Round profiles can mean non-planar batteries to maximize space utilization inside the smartphone. Are these batteries difficult and expensive to make? Absolutely. Given that the battery consumes between ½ to ⅔ of the overall space inside the smartphone, pushing the industrial design means serious business as far as the battery is concerned. Today’s post shows how your choice of a smartphone as a consumer impacts the battery and its underlying design.

First, and above all, every consumer wants his or her smartphone to last at least a full day. Now the definition of a “full day” is subjective, but there is broad consensus that it translates to a battery capacity of at least 3,000 mAh, preferably near 3,500 mAh for the top of the line smartphones. Indeed, if we examine the average capacity in smartphones over the past 5 years, we see that it has grown at about 8% annually. A battery in a 2017 smartphone contains about 40 – 50% more capacity (mAh) than it did in 2012.

Capacity

The smartphones are also getting thinner, so lesser volume available for the battery. The chart below shows the thickness of iPhones (in orange) and Samsung Galaxy line (in blue) over the past few years. The trend is clear!

Capacity is increasing. Volume is decreasing. That’s more energy in a smaller volume. In other words, the energy density is rising rapidly thus creating serious headaches because of various implications to safety and quality as well as cost.

If you are a battery vendor and need to increase energy density, what can you do? First, you can pack more material inside the battery to store more of the lithium ions. Second, you can increase the voltage. If you recall from your high-school physics, electrical energy is the product of electrical charge × voltage. More voltage translates to more energy. If we look at the maximum voltage of batteries that have been shipping commercially in the past few years, we immediately notice that the voltage has risen from 4.20 V to 4.40 V for one individual cell. We even see prototypes today at 4.45 V and above. The chart below shows that going from 4.20 V to 4.40 V provides an additional 20% in energy, or the equivalent of four battery generations.

volts

The challenge is that at these elevated cell voltages there is a heightened risk of lithium plating. Operating at 4.40 V is far from obvious or trivial. The margin of error is extremely small at these voltage levels. Manufacturing defects or design fluctuations are sufficient to cause the formation of lithium metal plating thus risking a potential battery fire.

So when you choose your next smartphone, be it a Samsung, Apple or any other brand, keep in mind how your choice as a consumer drives the OEM and in turn it drives the battery technology. The smartphone and its battery are ultimately the responsibility of the OEM, but an informed consumer will make the right and safe choice.

31Mar 2017

We, that’s all of us on this planet, buy every year 1.6 billion smartphones. It works out to one new smartphone every year for every four living human beings on this planet. Cumulatively, we own and use 4 billion smartphones around the world. Every region of the world, rich or poor, is buying smartphones. Many developing nations in the Middle East, Africa, and Asia are growing their smartphone subscriptions at a fast rate. Ericsson reports that by 2021, there will be 6.3 billion smartphone subscriptions, that’s nearly every man, woman and child around the world. Impressive!

Of course, each and every one of these smartphones has a battery in it. Your first reaction is: “that’s a lot of batteries.” Yes, that is true. Sadly, many of these batteries go to landfills after they are exhausted. The easiest way to gauge the size of the market for batteries is to calculate the entire energy supplied by all of them. Of course, that is a large number. It is measured in billions of watt-hours, abbreviated as GWh. As a reference mark, the battery in a top of the line Tesla S is 100 kWh. One GWh = 1 million kWh = 10,000 Tesla S.

 

Screen Shot 2017-03-31 at 9.48.15 AM

 

In 2016, the battery factories around the world manufactured about 50 GWh worth of batteries for consumer devices. That drives an industry and a market worth in excess of $10 billions annually. Forecasts indicate that the consumer market will use about 65 to 70 GWh worth of batteries in 2020. Our appetite for more batteries is insatiable and the numbers show it.

Now let’s look at batteries in electrified vehicles, including both hybrid plug-in cars and pure electric cars (xEVs). This is a relatively new market. The Tesla S first came in 2012. The Nissan Leaf came a little earlier in 2011. Many states in the US or countries around the world haven’t yet experienced or experimented with such vehicles. In 2016, all of these vehicles accounted for a mere 0.9% of all car sales. In total, they amounted to less than 1 m vehicles in 2016.

 

GWh

 

However, in battery lingo, these cars accounted for an increasingly large number of GWh. The year 2016 was the first year that the battery capacity used in xEVs equalled that of all consumer devices, about 50 GWh. By 2020, xEVs will account for ⅔ of all battery production in the world. No wonder Elon Musk and the major car makers pay a lot of attention to their supply chain, including building these Gigafactories.

 

17Mar 2017

History recalls how great the fall can be

While everybody’s sleeping, the boats put out to sea

Borne on the wings of time

It seemed the answers were so easy to find

Roger Hodgson, Supertramp, from Fool’s Overture, 1977

MWC 2017 is over. The crowds came and saw ideas and innovations. The media covered and reviewed. Awards were made. Yet a sense of public amnesia seemed to hover over the battery safety problems that the Samsung Note 7 brought to surface in 2016. Yes, Samsung shows the deep scars of these fateful days. Yes, there is a real fear among the device manufacturers. And yet, the fear and concerns are also accompanied with a sense of paralysis, a sense of a rudderless ship when it comes to safety, and a sense of wishful thinking that the Note 7 fires were an aberration in time that the industry will put behind it.

I will spend today’s post to discuss how Samsung’s SDI, the primary battery supplier of the Samsung Note 7, is trying to lead its way through the choppy waters of the battery industry. Jun Young-Hyun, an executive who ran Samsung’s memory business, became in late February of this year SDI’s newest CEO, the company’s third in only five years. The information here is specific to Samsung SDI but the intent is to provide an insight into how the incumbents are redefining themselves in the presence of aggressive competition from Chinese battery suppliers.

SDI_OPM

A Goldman Sachs’ report charts the decline in operating margin for SDI’s lithium-ion battery product lines. Driven primarily by rising competition and decreasing productivity in their cylindrical and polymer batteries, the operating margin dropped by nearly half over the last ten years with little hope of recovery. Samsung SDI’s revenues, like many of the incumbents, came primarily from consumer devices including laptops, tablets and smartphones, totaling nearly $2.5 billion in 2016. But these revenues have been flat and are forecasted to stagnate despite rising unit volumes, reflecting the aggressive pricing competition from China.

Panasonic, through its successful relationship with Tesla, was the first to demonstrate that it can shift its revenue base from consumer batteries to automotive batteries. SDI and LG Chem seek to replicate the story.

SDI’s growing revenues in the past years in both xEV (encompassing both electrical vehicles and plug-in hybrids) as well as energy storage systems (ESS) reflect that strategy. Samsung SDI forecasts revenues from xEV to exceed $1.5 billion in 2018. The company reports that their ESS line is near breakeven, but that their xEV product line will lose nearly $200 million in 2017.

SDI_Revenues

As LG Chem and SDI increasingly focus their attention on growing their share in xEV and ESS batteries, their Chinese competitors are busy winning market share in consumer devices, and more specifically, in smartphones. Samsung SDI, LG Chem, Panasonic and Sony Energy constituted the vast majority of battery units shipped into consumer devices. In 2016, China-based ATL garnered nearly a third of that market and has become a major supplier to several device OEMs including Samsung Electronics, the maker of the Samsung Galaxy smartphones. Such a scenario was unthinkable only a few years back. Samsung SDI was in effect a sole supplier to Samsung Electronics.

These shifting tectonics in the supply chain carry severe implications to the device OEMs. On the positive scale, more competition means savings to them. But in the process, these device OEMs are losing what once was a comfortable relationship with their battery sister companies. Samsung Electronics’ relationship with Samsung SDI allowed it to influence its technology and product roadmap. Samsung SDI provided its sister company with exceptional support. The same can be said of LG and its relationship with LG Chem, and Sony’s relationship with Sony Energy. Many pillars of this comfort zone will at least change if not vanish, and that will only cause the device OEMs a lot more anxiety about their battery supply chain. The poor quality and safety record of Chinese battery suppliers is very real. The safety problems of the Note 7 will only amplify these anxieties, even if not publicly displayed.

History recalls how great the fall can beIt seemed the answers were so easy to find.”   Timeless words.