Fast charging

02Apr 2016

For a seemingly simple device with only two electrical connections to it, a battery is deceivingly misunderstood by the broad population, especially as batteries are now a common fixture in our technology-laden daily lives. I will highlight in this post five common misconceptions about the lithium-ion battery:

1. STAND ON ONE LEG, EXTEND YOUR ARM, THEN PLUG YOUR CHARGER INTO YOUR DEVICE:

Well, not literally, but the acrobatic move captures the perceived hypersensitivity of the average consumer about past or secret special recipes that can help your battery. One of the silliest one I ever heard was to store the battery in the freezer to extend its life. PLEASE, DO NOT EVER DO THIS! Another silly is to charge the battery once it drops below 50%, or 40% or 30%….Let me be clear, you can use your phone down to zero and recharge it, and it will be just fine.

It is also now common to find apps that will “optimize” your battery. The reality is they do nada! Don’t bother.  Don’t also bother with task managers; no they don’t extend your battery life. Both Android and iOS are fairly sophisticated about managing apps in the background.

Turning off WiFi, GPS and Bluetooth will not extend your battery life, at least not meaningfully. These radios use such little power that turning them off will not give you any noticeable advantage. The fact is that your cellular radio signal (e.g., LTE) and your display (specifically when the screen is on) are the two primary consumers of battery life — and turning these off render your mobile device somewhat useless.

Lastly is the question of “should I charge the battery to 100%?” Well, yes! but you don’t have to if you don’t want to or can’t. In other words, stop thinking about it. The battery is fine whether you charge it to 100% or to 80% or anything else. Sure, for those of you who are battery geeks, yes, you will get more cycle life if the battery is not charged to 100%. But to the average population, you can do whatever you like — your usage is not wrong. These are design specifications that the device manufacturer is thinking about on your behalf.

2. LITHIUM BATTERIES HAVE LONG MEMORIES:

Yes, as long as the memory of a 95-year old suffering from Alzheimers!! Sarcasm aside, lithium ion batteries have zero memory effects. Now, if you are a techie intent on confusing your smartphone or mobile device, here’s a little trick. Keep your device’s battery between 30% and 70% always….this will confuse the “fuel gauge,” that little battery monitor that tells you how much juice you have left. The battery will be just fine but the fuel gauge will not report accurately. Every so often, the fuel gauge needs to hit close to zero and 100% to know what these levels truly are, otherwise the fuel gauge will not accurately report the amount of battery percentage. This is like your gas gauge in your car going kaput…it does not mean that the battery has memory or other deficiencies. Should you suspect that your fuel gauge is confused, charge your phone to 100% and discharge it down to 10% a few times. That is sufficient to recalibrate the gauge.

3. WE NEED NEW BATTERY CHEMISTRIES — THE PRESENT ONES ARE NO GOOD:

This one garners a lot of media interest. Every time a research lab makes a new discovery, it is headline news and makes prime time TV. The reality is that the path from discovery in the lab to commercial deployment is extremely rocky. There have been dozens such discoveries in the past 5 – 10 years, yet virtually none have made it into wide commercial deployment. History tells us it takes over $1 billion and about 10 years for a new material to begin its slow commercial adoption cycle….and for now, the pipeline is rather thin. Additionally, present lithium ion batteries continue to improve. Granted, it is not very fast progress, but there is progress that is sufficient to make great products….just think that current battery technology is powering some great electric vehicles.

Let me be more specific. Present-day lithium ion batteries are achieving over 600 Wh/l in energy density — that is nearly 10x what lead acid batteries can deliver. This is enough to put 3,000 mAh in your smartphone (sufficient for a full day of use), and 60  kWh in your electrical car (enough for 200 – 250 miles of driving range). With the proper control systems and intelligence, a mobile device battery can last 2 years or more, and an electric vehicle battery can last 10 years. Does it mean we stop here? of course not, but this sense of urgency to develop new materials or chemistries is rather misplaced. Instead, we need to keep optimizing the present batteries materials and chemistries. Just reflect on how silicon as a semiconductor material was challenged by other candidate materials in the 1980s and 1990s (do you remember Gallium Arsenide), only for it to continue its steady progress and become an amazing material platform for modern computation and communication.

4. LITHIUM-ION BATTERIES ARE EXPENSIVE:

What made silicon the king of semiconductor materials is its amazing cost curve, i.e., decreasing cost per performance, aka Moore’s law. Now, lithium ion batteries don’t have an equivalent to Moore’s law, but, the cost of making lithium ion batteries is dropping fast to the point they are rapidly becoming commoditized. A battery for a smartphone costs the device OEM somewhere between $1.50 and $3.00, hardly a limiting factor for making great mobile devices. GM and Tesla Motors have widely advertised that their battery manufacturing costs are approaching $100 /kWh. In other words, a battery with sufficient capacity to drive 200 miles (i.e., 50 to 60 kWh) has a manufacturing cost of $5,000 to $6,000 (excluding the electronics)…with continued room for further cost reduction. It’s not yet ready to compete with inexpensive cars with gas engines, but it sure is very competitive with mid-range luxury vehicles. If you are in the market for a BMW 3-series or equivalent, I bet you are keeping an eye on the new Tesla Model 3. Tesla Motors pre-sold nearly 200,000 Model 3 electric vehicles in the 24 hours after its announcement.  This performance at a competitive price is what makes the present lithium ion batteries (with their present materials) attractive and dominant especially vis-a-vis potentially promising or threatening new chemistries or new materials.

5. LITHIUM-ION BATTERIES ARE UNSAFE:

Why do we not worry about the immense flammability of gasoline in our vehicles? Isn’t combustion the most essential mechanism of gas-driven cars? Yet, we feel very safe in these cars. Car fires are seldom headline news. That’s because the safety of traditional combustion engine cars has evolved immensely in the past decades. For example, gas tanks are insulated and protected in the event of a car crash.

Yes, lithium is flammable under certain but well known conditions. But the safety of lithium ion batteries can be observed as religiously as car makers observe the safety of combustion engines. It is quite likely that some isolated accidents or battery recalls may occur in the future as lithium ion batteries are deployed even wider than they are today. In mobile devices, the track record on safety has been very good, certainly since the battery industry had to manage the safety recalls at the turn of the century. Is there room for progress and can we achieve an exceptional safety record with lithium ion batteries? Absolutely yes. There are no inherent reasons why it cannot be achieved, albeit it will take time, just like the automotive and airline industries have continuously improved the safety of their products.

18Mar 2016

The new Galaxy S7 and its sister smartphone the S7 Edge are receiving rave reviews. So let’s take a look at their batteries. A brief comparison table shows the new S7 and S7 Edge side-by-side with the older S6 and the Note 4.

comp-table

Let’s make a few key observations starting with the charge rate and charging time. The S7 and S7 Edge use a maximum measured charging current of 3A, which works out to charging rate of 0.8 C (3/3.6) for the S7 Edge and 1.0 C for the S7. The charge times to 80% are 58 and 50 minutes respectively. That’s faster than any iPhone, present or past, that typically charge at a rate of about 0.7 C. This earlier post explains the meaning of charge rate. We didn’t measure the battery capacity of the S7 but that of the S7 Edge came in at 3,521 mAh, fairly close to the advertised capacity of 3,600 mAh — that’s a nice hefty capacity that should last at least one full day.

S7-edge-profile

Charge profile for the Galaxy S7 Edge (blue line is capacity and green line is charge voltage)

The S7 and S7 Edge are using batteries with a higher nominal maximum charge voltage of 4.4V compared to the older 4.35V standard. See the photo below. Surprisingly, teardowns of the S7 and S7 Edge (US models) show that these batteries come from ATL, not from Samsung’s battery division, Samsung SDI.

Battery vendors are now increasing the maximum charge voltage to 4.4V to raise the energy density of the battery by an additional 5%. However, both S7 and S7 Edge do not charge to this maximum voltage — instead, they charge the battery to only 4.35V. The green curve in the charging chart above shows the maximum voltage of 4.35V (not 4.4V) at the end of the charge cycle. This means that the battery true capacity is actually 5% higher…in other words, the S7 Edge has an intrinsic battery capacity that is near 3,700 mAh, but Samsung is instead choosing to operate it at 3,521 mAh.

Is it confusing enough? So why would Samsung sacrifice this additional capacity and not mention it in the capacity label on the battery? There are several reasons. First, it is quite likely that the swelling of this battery is severe at 4.4V that it limits Samsung’s quest to build thin smartphones. By reducing the voltage to 4.35V, the effects of swelling are somewhat mitigated. Second, the S7 and S7 Edge are both running at a fast charge rate. We observed in a previous post that the older Galaxy Note 4 suffered from a poor cycle life problem due to fast charging — the battery died within less than a year of operation. Reducing the voltage to 4.35V mitigates some of these cycle life problems, of course at the expense of a loss in capacity.

An astute reader might say: “Well, 3,600 mAh is plenty capacity for me!” That might be true, but you are paying for a bigger battery and using a physically larger battery than you need. It’s a compromise! The point here is to illustrate these increasingly difficult compromises that Samsung had to go through when it came to the battery.

I think for now, I might want to stick with Sony Xperia X’s battery — that’s a battery I know I can rely on.

S7edge-battery

22Feb 2016

We are very proud to announce today at Mobile World Congress in Barcelona that the new Sony Xperia devices will incorporate Qnovo’s adaptive charging solutions. Sony Mobile announced today new smartphones offering twice the battery cycle life in addition to long battery life — both key attributes to a satisfactory consumer battery experience.

Xperia-X-Series-Transparent-5f944d1d7c7eafea0259fbd81edbc406-1080x635

I have written openly about the battery compromises that mobile device makers routinely put in place without telling consumers about them. This previous post shows how the Samsung Note 4 suffers from poor cycle life (its battery died after only months of use), yet Samsung was too busy promoting the fast charging feature of the Note 4 and omitted to share what happens to cycle life. I am not picking on Samsung only….battery compromises are routine in an industry that is struggling to come up with a solution to the vexing battery problems that plague consumers.

The reason why consumers keep complaining about the battery is that device manufacturers have to address simultaneously three important battery attributes: i) battery capacity, ii) long cycle life and longevity, and iii) reasonably fast charging, all of those while still offering an attractive device look and feel (read, thin). Let’s quantify each from the perspective of the consumer.

Capacity: Android smartphones need somewhere in the range of 2,500 to 3,200 mAh to offer a solid one to two days of battery life. Some manufacturers are better than others when it comes to power management. Those that have good power management can live on the low end of this spectrum. Those that have less efficient electronics, radios and displays will require a battery on the high end of this range. Capacity is not typically an attribute that device OEMs can hide, so most premium smartphones already satisfy this requirement.

Cycle life, or longevity: This is a measure of how long the battery will retain its capacity with constant use. Assuming one cycle of charging-and-discharging per day, cycle life is an approximate measure of how many days of use you will get with your smartphone before feeling that it is no longer lasting you a whole day. This is often a hidden specification from the consumer and one where many, if not most, smartphone OEMs compromise — simply because by the time the consumer discovers it, several months have passed. The Samsung Note 4 is a prime example of inadequate cycle life.  Given that many consumers keep the expensive smartphones for two years or even longer, cycle life needs to be at least 800 cycles or more. Sadly, many smartphones ship with batteries capable of meeting 300 to 500 cycles…this is just not enough, and this is one of the reasons of dissatisfaction of consumers and one of the underlying reasons that consumers complain about their experience.

Charging rate: Most Android smartphones are now introducing charge rates between 0.7C and 1.0C. This earlier post explains in more detail the what “C” means. At 0.7C, the device charges to 50% in about 40 minutes — that’s about what iPhones can do. If your phone battery can last an average of 1 to 2 days, then at 0.7C, you will get about 3 to 6 hours of use if you plug it in for a quick 5-minute charge. In other words, every 5 minutes plugged to the wall gets you 3 to 6 hours of use.  At 1.0C, it goes a little faster. The device now charges to 50% in 30 minutes. At this rate, every 5 minutes plugged to the wall gives you 4 to 8 hours of use. At 1.5C, which is really fast, 5 minutes of charging earn you 6 to 12 hours of use.

We are proud to be associated with Sony Mobile and proud that they have adopted Qnovo’s adaptive charging solutions in their Xperia line. The battery continues to be an area in need of improvement, and Qnovo is in the lead to complement battery materials with innovative intelligent charging solutions that can take the battery performance to a whole new level. In an environment where claims from various vendors promise exceptional battery performance yet fail to deliver, Qnovo stands out above the crowd with solutions that have been rigorously vetted and solutions that deliver real improvement that consumers want. And this is just the beginning.

01Feb 2016

Ask smartphone users about their battery experience and you often get the typical answer: “it sucks!” But why? and what is the problem?

iPhones suffer from a small battery capacity, so it is understandable that Apple users get upset with their short battery life. But the Android phones? Most boast of larger batteries, in fact much larger batteries, that tend to do exceptionally well when they are new. Browse the web and you will find that many Android smartphones, when tested new, do give the consumer a full-day of use. So, again, what is the problem? and what leads the consumer to wake up after a few months of use  bewildered about the battery life that evaporated? This post is for you if you experienced this battery problem.

I posted last year, on 27 March 2015, a blog on testing a brand new Samsung Note 4 and its battery. Samsung was proud about introducing fast charging in this device…”50% in about 30 minutes,” Samsung claimed. The fresh battery was tested at the time to have a charge capacity of 3,185 mAh. One of my colleagues used this phone as his primary device since then. He recently complained about not getting a full day of use from his device, so we tested the battery this past weekend. What did we find?

After 310 days of use, the measured battery capacity is 2,591 mAh, or 81% of the original capacity less than a year ago. Ouch! Samsung, that really hurts! Samsung did not tell the consumers that fast charging was killing their batteries.

This is all explained in the next chart showing the capacity of the same Samsung Note 4 battery fresh as measured in March 2015, and after use in January 2016. The vertical axis shows the measured battery capacity in mAh as the battery is charged using the Samsung AC adapter. The horizontal axis is charging time. For the techies among you, both were charged to a cutoff current of C/20 at room temperature.

Samsung Note 4 battery

After 310 days of regular office and personal use (this device was not abused and was not exposed to extreme conditions), the battery’s capacity dropped to 2,591 mAh, or 81% of its initial capacity. In other words, 594 mAh of capacity were lost! That’s somewhere near 3 to 4 hours of use in one day that evaporated! In technical terms, a battery at 80% of initial capacity is deemed dead and in need of replacement.

That’s the pain that consumers feel after using their devices for a few months, but can’t really articulate the nature of their problem. It is simple: Some smartphone OEMs do not want to publish that their batteries lose capacity with time, or worse yet, that their claims of fast charging are damaging the batteries. As a consumer, start paying attention to the battery specifications. Ask for the capacity figure; ask for how fast it charges; and equally important, ask about the cycle life of the battery. That’s a measure of the battery’s longevity and a measure that you will not be disappointed with your purchase only a few months down the line.

22Jan 2016

I described in the earlier post how adaptive systems turned smartphones into great cameras. Let’s now talk about how adaptivity and adaptive charging can make a battery perform far better.

Let’s start briefly with the basic operation of a lithium ion battery. The early posts of this blog describe the operation of the lithium-ion battery in more detail.  I will briefly recap here the basic operation and explain where its performance is limited. For the reader who wants to learn more, select “The Basics” category tag and feel free to review these earlier posts.

The figure below illustrates the basic structure of a lithium-ion battery. On the left hand side, one sees an electron microscope image of a battery showing the anode, the cathode and the separator, essentially the three basic materials that constitute the battery. On the right hand side, one sees a sketch illustrating the function of these materials during the charging process: The lithium ions, “stored” inside the individual grains of the cathode, move through the separator and insert themselves inside the grain of the graphite anode. If you are an engineer or physicist, you are asking, “where are the electrons?”  A neutral lithium atom becomes an ion in the solution, travels through the separator to the anode. The electron travels in the opposite direction through the external circuitry from the Aluminum collector to the Copper collector, where then it is captured by a lithium ion to form a molecular lithium-carbon bond.

Structure of the lithium ion battery

This seems simple enough, so what can go wrong? lots! I will focus here on a handful of mechanisms that become critical as the battery’s storage capacity and energy density increase. Looking at the diagram above, it is hopefully obvious that increasing energy density means to the reader packing more and more ions into this little sketched volume. It means reducing the dimensions of the anode, the cathode, the separator, and trying to saturate the capabilities of the anode grains to absorb ions. It’s like when you try to put as much water as possible inside a sponge. Now, in this process, small variations in manufacturing become really detrimental to performance. Look at the left photograph and observe the coarseness of the grain size for both electrodes. That means the uniformity of the ionic current is poor. As the energy density rises, a large number of ions are all rushing from the cathode to the anode. But this lack of uniformity creates stress points, both electrical and mechanical, that ultimately lead to failure:  gradual loss of material, gradual loss of lithium ions, and gradual mechanical cracking, all leading in time to a gradual loss of capacity and ultimate failure.

I will jump to two key observations. First, it should be apparent that when energy density is low, these effects are benign, but when energy density is high, there are so many ions involved in the process that small manufacturing variations become detrimental. Second, it should be apparent too that faster charging results in the same effect, i.e., more ions are trying to participate in the process.

Clearly, battery manufacturers are trying to improve their manufacturing processes and improve their materials — but let’s face it, this is becoming an incredibly expensive process. Smartphone and PC manufacturers are not willing to pay for more expensive batteries. This is very similar to the earlier post about camera lenses. Make great lenses but they become very expensive, or shift the burden to computation and correct the errors dynamically and adaptively.

That’s precisely what adaptive charging does: Be able to measure the impact of the manufacturing variations, embedded defects, non-uniformity of material properties and what have you in real time, assess what these errors are and how they may be progressing in time, then adjust the voltage and current of the charging current in such a way to mitigate these “errors”….then keep doing it as long as the battery is in operation. This makes each battery unique in its manufacturing history, material properties, and performance, and lets the charging process get tailored in an intelligent but automated fashion to the uniqueness of the battery.

It’s a marriage of chemistry, control systems and software, that shifts the burden from expensive manufacturing to less expensive computation. But what is clear is that it does not make battery manufacturing any less important, and it does not replace battery manufacturing — it is complementary. It is no different that how adaptive algorithms in the camera are complementary to the lens, not replacing it. This is cool innovation!