Fast charging

31Aug 2017

We proudly announced today that the new LG flagship smartphone, the LG V30, includes Qnovo’s adaptive charging technology. The V30 uses Qnovo’s QNI solution, our most sophisticated algorithms to manage its lithium-ion battery. In this post, we open our doors to give our readers insight to our technology and QNI in particular.

As complex and exotic as the battery may seem, you, the consumer, care only about a handful of things.

First, will the battery last you a whole day of use, no marketing gimmicks?

Second, will it charge fast enough? You don’t need blink-of-an-eye-charging but you don’t want to wait long too.

Third, will it last you at least two years or more, given that you are paying a premium price?

And lastly, can you rely that it will not risk your safety and the safety of those around you?

These attributes collectively define your overall battery experience; not one of them, but all of them together.

To last you a full day, the battery must have plenty of charge capacity, i.e., a lot of mAh. This is equal to a range between 3,000 to 3,500 mAh for today’s crop of smartphones. Anything more than that will make the smartphone unwieldy or too thick. To fit a 3,000 mAh battery in the small physical space inside a smartphone means high energy density. Today’s state of the art is near 650 Wh/l operating at a maximum voltage of 4.4 V. That’s the first headache already. At this high voltage and high energy density, the battery is really not happy and needs a lot of caring. I mean a lot of caring!

Fast charging the battery amplifies all the concerns of high voltage and high energy density, and makes them a lot worse. And if you have to charge more than once a day, well, this battery will need even more caring.

High energy density, high voltage and fast charging together are the factors that make the battery fail before two years, and risk making your battery unsafe.

Therein lies the challenge. How do we care for the battery ? and why has this required level of care become so much more sophisticated than ever before ?


As the old adage goes, “You can’t fix what you can’t measure.”

This leads to an important and critical new concept for batteries: Measuring what is happening within the battery, all the time, in real time, and then deciding what to do. By “within” I mean the “chemistry” that is taking place inside the battery…the stuff that you don’t see. This is called, in engineering terms, closed-loop feedback. Engineers know it, study it, and use it in countless situations.

Qnovo’s software adapts to your smartphone a measurement technique widely used in battery laboratories. It is called electrochemical impedance spectroscopy (abbreviated as EIS). It helps our scientists understand what happens inside the battery without destroying it. Qnovo’s innovation is in implementing EIS in your smartphone so that it is always monitoring your battery’s internal chemical processes.

We announced earlier this year that the Qualcomm® Snapdragon 835 that powers the LG V30 includes hardware that accelerates Qnovo’s algorithms. Indeed, the additional hardware in the Qualcomm Snapdragon 835 chipset extends the utility of EIS inside the smartphone. The hardware in this new chipset enables measurements and frequencies that were not available in older chipsets. Qnovo’s QNI software takes advantage of this new hardware to gain deeper insight into the battery, again all in real time.

Now we get to the second portion of closed loop: What to do after making a measurement. As it turns out, and we thank science for that, charging the battery is a powerful knob to alter and affect what happens inside the battery. Qnovo’s adaptive charging takes the information from the EIS measurement, and then adjusts the charging current to reduce and mitigate possible harmful reactions detected during previous measurements.

With QNI, this “closed loop” happens a lot faster than its sister software product, QNS. As a result, it is able to detect more potential problems and react appropriately. Throughout a single charge, QNS makes approximately 200 measurements on the battery, whereas QNI makes close to 20,000 measurements.

Over the past years, we have collected a gigantic database of measurements on batteries from the vast majority of battery manufacturers. We have tested large quantities of batteries under diverse and extreme conditions. This knowledge allows Qnovo to train our algorithms to make them more efficient and more accurate especially as battery materials continue to evolve.


The skeptic might ask, “Great, but how does it help me, the end user?”

The most important benefit that the user derives is the health of the battery. You get a healthy battery AND more capacity AND fast charging…in other words, the consumer gets a great battery experience encompassing the attributes mentioned at the beginning of this post.

You, the consumer, do not have to worry whether your usage might hurt the battery. You don’t have to worry about fast charging because it might damage the battery. You don’t have to worry about charging to less than full because it helps the battery’s longevity. None of these should be your concerns and none should keep you thinking about the battery. Qnovo’s adaptive charging takes care of these battery issues in the background, and gives you a healthy battery with the best user experience.

So, if you are in the market for a new smartphone, do consider an LG V30 and do enjoy its battery experience.

16Aug 2017

School started this week for most of us so it is time to resume the posts. Today’s post continues with insight into the subtleties of the lithium-ion battery. It is surprising how a simple device, with only two contacts, can be so intriguing and complex.

As summer nears to an end, several smartphone makers ready their newest and greatest devices for launch. Samsung announces their Note 8 on 23 August. LG is announcing their flagship V30 a week later. And we are not forgetting Apple as they ready their newest iPhones in September.

All of these new devices will come with amazingly beautiful and large displays, top-of-the-line processors and of course, batteries to power them. At an expected price point in excess of $700, consumers are keeping their smartphones for two or even three years. So will their batteries last that long?

We will examine here one of the parameters that impact the longevity of the battery…and give you some tidbits on what you can do to keep your battery fresh for longer than average. Today’s post is on voltage. Voltage is the alt-nature to state-of-charge (SOC). This is very much the principle of operation of the fuel gauge — how you get to read at the top of your screen the percentage of remaining battery life.

When I say voltage, I mean the maximum voltage that the battery will see. It also determines the maximum available capacity in mAh. Look at the label of a battery and you will observe a maximum voltage during charge and maximum capacity for that battery. Most state-of-the-art batteries operate at a maximum voltage around 4.35 V or 4.4 V. This is also the voltage that corresponds to a 100% battery reading.

If you choose to charge your smartphone to a lesser percentage, say to only 90%, then the battery voltage stops at a lower value. For a battery that is rated 4.35 V, 100% corresponds to 4.35 V. At 95%, the voltage is 4.30 V. And at 90%, the voltage is 4.25 V. These are small differences in voltage values, but significant differences in capacity.

Let’s take a particular example with a battery having a maximum capacity of 3,100 mAh at 4.35 V. Therefore, at 4.25 V, the maximum available capacity becomes a little over 2,800 mAh.

You are now wondering: why would anyone want to do that?

The answer is: Battery longevity. If you don’t have the best battery, or your smartphone manufacturer is not putting the best battery management intelligence on your device, then you ought to be very concerned whether your battery will last you more than one year. Battery issues after 6 months or one year are a significant cause for warranty returns.

Let’s back it up with some measured data.

The following chart shows the maximum available capacity for a battery rated at 3,100 mAh at 4.35 V. At this voltage, this battery will only last about 400 cycles, or about a year. You will complain about the loss of use much before that.  The brown line shows that your battery has lost 250 mAh of capacity after 6 months….that’s about 2 hours of use time. Ouch!

 

Now, let’s look at the case where the smartphone is charged to only 95%. That is a maximum available capacity of 3,000 mAh instead of 3,100 mAh. Now follow the dark green curve in the chart. It fades at a much slower rate than the brown line. In fact, it crosses over the brown line at about 300 cycles, or about 10 months. In other words, after 10 months, it offers more capacity. This illustrates the tradeoff between voltage and longevity.

A smartphone maker who has implemented advanced intelligence on their battery (like Qnovo’s) will not suffer from this ailment. But if you suspect that your device does not have such intelligence, then you will do yourself a big favor by charging your battery to a maximum of 95% or even lower if you can.

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 higher threshold for the termination current to make your total charge time significantly faster. Now note that this only makes the “total” charge time faster. It does not impact the charge time to 50% or 80% of full.

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”, i.e., what it chooses to tell you as a consumer vs. the real measured figure. 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. To many consumers, the difference between 95% and 100% is sufficiently small to effectively consider the device full at either value. There some truth to that. But 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 (as a percentage of total charge capacity). You will notice that the blue curve hits 100% when the termination current of C/20 is reached, i.e., about 96 minutes after start of charge. 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%.  The difference between these two values is about 30 minutes.

Same device.  Same battery. Same charging current. Yet change the definition and feel that the charging is a lot faster. As a consumer, you now 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. And don’t worry, you cannot “overcharge” your battery. Your device contains all the proper circuitry and intelligence for that.

22Nov 2016

Qualcomm announced this week their 4th generation Quick Charge™ technology to be available in their upcoming Snapdragon 835 chipset. Quick Charge™ 4 continues to build on making fast charging an integral part of modern smartphones and consumer devices. In this latest generation, Qualcomm adds a number of key features, in particular, higher efficiency in delivering the power from the wall socket to the device, more power available for charging faster, and better thermal management. I applaud the continued evolution of Qualcomm’s QC technology.

As fast charging becomes an entrenched technology in the mobile landscape, the emphasis on battery safety itself during fast charging begins to take priority. As I highlighted in this earlier post, fast charging done improperly causes irreparable damage to the battery causing a loss of capacity (mAh) or worse yet, battery safety problems. Combining fast charging with high-energy density cells, especially the new generation that is operating at 4.4V, is a recipe for potential disasters. This post is about what can go wrong when we mix fast charging with high-energy density batteries, but neglect to implement the necessary charging intelligence and the necessary controls around the battery.

First, let me clarify a few things.

  • Fast charging includes the realm of charging the battery at rates near or above 1C . At 1C, the battery charges to half-full from empty (0 to 50%) in 30 minutes. QC 4.0 is capable to going at twice that rate, or 2C. That is very fast.
  • High-energy density batteries are those with energy densities in excess of 600 Wh/l, with the most recent ones at or near 700 Wh/l. The newest generation of these batteries are almost universally operating at 4.4V. This earlier post explains the risks and perils of operating at this voltage.
  • The last point I want to clarify is that the common charging approaches, namely CCCV and step charging do NOT provide any intelligence or controls around charging. They are open-loop methods with no mechanism to gauge the state or health of the battery in order to make the proper adjustments and avoid the risks that I will highlight below.

The mix of fast charging and high-energy batteries makes a very volatile situation. This reminds me of fancy car commercials with the fine print warning at the bottom of the screen: “Professional drivers on a closed course. Do not attempt.” Fast charging high-energy batteries is rapidly approaching this realm of cautionary warnings. The consequences of neglecting such advice can be dire especially as smartphone fires are fresh in our collective memories.

So what can go wrong?

To begin with, lithium metal plating is a huge risk when one attempts to fast charge a 4.4V cell. We see lithium plating on most if not all cells from reputable battery suppliers when charged using CCCV or step charging. This is a serious problem if not mitigated with the proper battery intelligence. Left unchecked, lithium metal plating can lead to safety hazards and potential fires. What makes lithium metal plating even more hazardous is that it is not easy to detect its presence inside your smartphone. By the time it develops into a potential electrical short inside the battery, it is often too late. Therefore it is imperative that the intelligence in the battery management seeks to avoid its forming from the very beginning of the battery’s life in your smartphone.

A second serious hazard is excess swelling of the battery. Yes, the battery will physically grow thicker as it is repeatedly charged. It is nearly impossible to measure the thickness of the battery once it is embedded inside your smartphone. Clever estimates of the thickness without physically touching the battery belong to the category of advanced intelligent algorithms that are becoming increasingly necessary. You might say: so what, let the battery swell! Excessive swelling will most certainly break your display screen.

A third hazard relates to the battery’s behavior at high temperature. The electronics inside your device consume power and cause the smartphone to get hot.  Those of you who have fast charging on your devices will attest to this fact. One misconception is that the battery itself heats up because of fast charging. That is not correct. The battery gets hot because of the heat generated by the electronics inside the smartphone. These temperatures can rise inside the smartphone to 40 °C, and in some many cases approaching 45 °C. These elevated temperatures accelerate the degradation of materials inside the battery especially at the elevated voltages. This leads to a rapid loss of charge capacity (your mAh drop very quickly) accompanied with excessive swelling of the battery. If you are an Uber driver with your smartphone fast charging on your dashboard on a hot summer day, this does not bode well for you.

These are only three examples of potential battery safety hazards associated with fast charging high-energy density cells using traditional charging methods…each one of them can lead to serious battery safety problems. That’s a good time to heed the warning in the car commercials. If you are not a professional, please do not attempt.

19Jul 2016

This post includes contributions from Robert Nalesnik. I discussed in the past how fast charging requires two components: i) power delivery – that means getting extra electrical power from the wall socket to the battery and ii) battery management – that means making sure you don’t destroy the battery’s lifespan with all the extra power.

How much more power do you need? Quite a bit more if you want to charge considerably faster. It’s like your car engine: if you want to go faster then you will consume more gas. For a typical smartphone, power levels go up from the conventional 5 Watts to 15 or even close to 20 Watts in some cases.

Delivering higher levels of power is a very active area. Qualcomm has Quick Charge, Mediatek has Pump Express, and there is the USB Power Delivery standard with support from Intel, and the Chinese manufacturer Oppo has VOOC. Not surprisingly, with so many parties trying to influence or even define the standards of power delivery, there is plenty of confusion to go around.

First, let’s refresh some basic high-school science:     Electrical power = current x voltage.

So if we want to deliver more power, we can either increase the current, the voltage or both. Increasing current is relatively easy but more current means a lot more heat…that is until something begins to melt. Not good! That usually puts an upper limit somewhere between 3 and 5 A on the charging current.

The other approach is to increase voltage, from the conventional 5 V up to 9 V, or even 12 V, and in some limited cases even more.

High current charging

High-current charging leverages the fact that modern single-cell lithium ion batteries can be charged using an inexpensive 5 V AC adapter that can be manufactured for about one dollar.

Increasing the charging current is limited by i) the maximum current rating of the USB cable between the AC adapter and the mobile device, as well as of the tiny connector in your device where the USB cable plugs in; ii) cost and iii) heat and safety.

Let’s do some math. A typical USB cable assembly can support a maximum current of 1.8 A. So 5 x 1.8 = 9 Watts max. That’s fine for standard charging but not sufficient for fast charging a smartphone. The new USB type-C cables (with symmetrical connectors that can be used in any orientation you like) can support up to 3 A, in other words, a maximum of 15 Watts. Much better! Under some very limited cases and using special cables, one can push USB type-C to 5 A, or 25 Watts. But at 5 A cost begins to skyrocket, so instead, we see designs gravitating towards 3 A, or equivalently 15 Watts.

To put this in perspective, 15 Watts can charge your typical 3,000 mAh battery at a rate of 1 C, meaning you will get 50% of your battery charge in 30 minutes, and a full charge in  over an hour.

A quick word on heat: if you remember Ohm’s law from your high-school physics, heat increases as the square of the current. That means as the charging current increases from 1.8 A to 3 A, or 1.66X, heat inside your device will increase as 1.66 x 1.66 = 2.8X. Ouch! That’s a lot of heat to remove from the device….and a great topic for a future post.

Power1

High voltage charging

Let’s pause for a moment and think about the high-voltage transmission lines that we frequently see from highways outside of urban areas. Electric utility companies transport electrical power from power-generating stations (e.g., dams) that can be hundreds of miles from a city. If they use the 120 V that you get at your outlet, then the overhead transmission lines will have to carry millions of amperes…this is not only physically impossible, but also economically just prohibitive. So the transmission lines run at a much higher voltage, anywhere up to 800,000 volts. These transmission lines naturally don’t come straight to your house. Instead, they terminate into smaller substations (hidden off main roads near your neighborhood) where the voltage is then gradually “stepped down.”

That’s the same concept used in mobile devices. The voltage from the AC adapter is now raised above 5 V. But what voltage should it be? 9 V, 12 V? more? This is decided by a “handshake” protocol between a specialized chip (usually the power management IC, also known as PMIC) inside your smartphone and the AC adapter when the USB cable is plugged in. This is the approach taken with Qualcomm’s Quick Charge and the USB Power Delivery standard, each using a different signaling mechanism. There is a saying among power supply engineers that “voltage is cheaper than current”, and indeed lower cost components and cables are a primary benefit of high voltage charging.

The USB Power Delivery (USB PD) standard allows voltages of 5, 9, 15 and 20 V and currents up to 3 A. This gives power levels of 15, 27, 45 and 60 W, respectively. Additionally, currents up to 5 A are allowed at 20V, enabling up to 100W. Qualcomm has similar predefined power levels at 5, 9, 12, and 20 V. High-voltage charging has a clear advantage of attaining power levels above 25 W, which makes it the preferred choice for laptops, ultrabooks and 2 in 1s tablets.

power2

How will this abundance of approaches settle out in the market? From a historical perspective, Qualcomm was early to see an opportunity to define high voltage charging in a simpler and cheaper way than the USB committee. They launched Quick Charge 2.0 in 2013 and followed up with the latest 3.0 version in 2015. Qualcomm has been quite successful establishing Quick Charge as a defacto charging standard for smartphones. More recently, Intel and others are successfully driving USB PD and the Type-C connector into PC markets and Type-C is well on its way to become the standard connector across all classes of mobile devices.

In smartphones, the next few years will likely still see multiple power delivery approaches, with chipset and adapter vendors evolving to multi-standard support to bridge compatibility gaps – meaning a smartphone can support multiple protocols such Qualcomm, USB PD, Pump Express…etc. From a Qnovo perspective, we are agnostic and complementary to whatever power delivery approach our customers choose. The higher power makes greater the need for the second component of fast charging: battery management.