The Basics

31Mar 2020

While the current situation has put us all in unfamiliar territory, one bright spot has been the willingness of so many people and organizations to offer advice and assistance. With hundreds of millions of us isolated in our homes, making especially intensive and important use of our phones and computers, it seems like an opportune moment to share four battery-specific recommendations that can help ensure your personal safety and extend the lifespans of all our devices as we adjust to this period of uncertainty, and WFH normalcy.

First, and most imperatively in the near term, never ignore a battery that is swelling. This can happen over the course of just a few days, especially in aging devices, and is a sign of internal failure that can put you and your family at risk of fire or injury. If your phone starts bulging or separating, even slightly, or your laptop or tablet won’t sit flat, its battery is likely swelling. In this case, stop using the device immediately and contact its manufacturer for help. Second, watch out for heat. If the backside of your phone gets uncomfortably hot while it’s charging, that’s a warning sign, and once again time to contact the device manufacturer. More broadly, avoid placing devices in high-heat situations, especially when charging. The classic case is of a ride-share driver, with their windshield-mounted phone continuously charging while baking in direct sun, but it can also occur at home if your phone is charging on a sunny windowsill, above a radiator, or nestled into a blanket. The combination of an elevated charge situation and high ambient heat may increase the risk of a fire and is certain to degrade a battery’s health prematurely. More detail about heat and batteries can be found here.

Third, be especially careful with aftermarket batteries and chargers, even ones that carry a familiar brand name, because counterfeiting has become more and more common, and incentives to do so will only increase during a global emergency. This is a good reason to extend the life of your original batteries for as long as possible. While it can be annoying when smartphone manufacturers restrict users and unauthorized repair shops from doing battery replacements, it’s done in part because there’s ample evidence that fake replica batteries have a much higher risk of fire than authentic ones, and because the replacement process is often not straightforward. Likewise, cheap chargers can create overheating by delivering too much current, which can create a similar fire risk for your batteries.

Finally, extending the lifespan of our phones, laptops, tablets, and other daily-use devices will take on extra importance, especially with phone prices creeping into four digits. In my experience, preserving battery health is the single best way of doing this. I wrote some time ago about basic strategies; here are some updated recommendations to consider:

  • Avoid “fast-charge” approaches and use the lowest amount of charging current possible. Although it takes longer, charging your phone from a computer using a USB cable is much gentler on the internals of the battery. (Note that this principle also applies to electric vehicles – super-fast charging stations are hard on your vehicle battery.)
  • Avoid charging your phone overnight, because it’s better to not keep the battery at 100 percent charge for extended periods. I aim to keep my charge levels between 25 and 85 percent unless I’m traveling, and my year-old smartphone battery health has not degraded at all.
  • Per the previous point, Apple’s iOS operating system offers battery health monitoring, and in the newest version(13.0)  the option of “Optimized Battery Charging,” which learns your daily charging routine. This is worthwhile, and we’re starting to see other manufacturers and even mobile operators become more attuned to this type of functionality, particularly in Asia.

We all have plenty to worry about in these unusual times; hopefully these bits of advice will help prevent battery-related problems from adding to your load.

30Dec 2019

Whether related to the stock market, presidential elections or climate, December is the month to make predictions for the coming year and decade. So what battery trends should we expect for the upcoming 2020-2030 decade?

1.Lithium-ion batteries will power more applications — electrification of everything:  The 2019 Nobel Prize in Chemistry highlights the progress lithium-ion batteries achieved in the past four decades. From a laboratory experiment in the 1970s, they are now ubiquitous in consumer devices. Increasingly, they are making inroads in transportation and grid storage applications. 

There is no question that the 2020s are the decade of electrification of transportation, from electric vehicles to buses and trucks. The number of available electric-vehicle (EV) models jumped from about ten in 2015 to over 75 in 2020, including categories of sports cars, sedans, SUVs and light trucks. Automotive companies and their supply chain are inexorably transforming. This will not be an easy transformation — there will be winners and losers. Car manufacturers and Tier-1 suppliers that will not adapt in the next couple of years risk becoming irrelevant. The nature of skilled labor in transportation is also transforming. Labor unions are taking notice but much training is needed for this new labor force.

Electric utilities will implement more energy storage projects on their grids — partly driven by regulations as well as the proliferation of clean-energy grids with distributed wind and solar generation. 

Industrial applications with historically smaller unit volumes will benefit from the increased proliferation of lithium-ion batteries. As communities seek cleaner air, we will see local regulations banning just about anything powered by fossil fuel, from forklifts to lawnmowers.

2. Batteries will deliver better performance but with optimized compromises:

Bill Gates’ famous quote in 1981 “640KB ought to be enough [memory] for everybody” stands as a stark reminder that there is not enough of a good thing. Just like computers flourished with more computational power and memory, mobility will continue to thrive with more available battery capacity. Next-generation 5G wireless smartphones require more battery capacity. Electric vehicle drivers require longer driving ranges (300+ miles). More battery capacity means a continued drive to look for newer materials with higher energy density. 

The public will become more discerning and expecting better battery warranties. Longer cycle life (lifespan) while fast charging will become a standard of performance especially in transportation.

But at what cost? Manufacturers will learn to optimize the battery’s capacity, size, cycle life and charging time to the target application or user case. Electric vehicles in fleets will have  vastly different battery designs than those for, say, residential commuters. Backup batteries used in conjunction with solar power will be even more different. Buyers of electric vehicles will learn how to make informed choices based on the battery. Much like buyers historically learned to understand the difference between 4- and 8-cylinder engines, they will become more literate in understanding the differences between kWh-ratings.

3. Battery prices will continue to decline, but at a slower pace:

The cost of lithium-ion batteries declined in the past decade from over $1,100 per kWh to $150 per kWh in 2019. Forecasters expect this figure to drop below $100 in 2023. At such levels, electric vehicles will reach cost parity with traditional vehicles using internal combustion engines (ICE) — without government buyer incentives. Driven by scale, increased volumes, and a dominant battery manufacturing based in China, standard batteries are increasingly become commoditized. Supply chains are becoming more specialized in addressing the commoditization of batteries. In an effort to improve the profitability of EV models, auto manufacturers will increasingly apply traditional cost disciplines to their battery supply chain, spanning improved manufacturing efficiencies to hedging. A few select applications in need of higher performance will benefit from new developments in advanced materials, e.g., providing higher energy density, albeit at a higher cost, but probably with limited penetration.

The risk of trade tensions with China will continue to loom over the battery supply chain. Even as lithium-ion battery manufacturing facilities come online in other parts of Asia and Europe, China will continue to dominate the lithium-ion battery supply chain, from sourcing raw materials to final assembly. The United States federal and state governments will need to formulate clear policies to address the rapid transition to a battery-centric transportation system — or risk escalating trade tensions with China around battery technologies and manufacturing.

4. Batteries will become safer in the field:

Smartphones routinely catch fire in many parts of Asia — and it’s not even headline news. That will change. That must change. The expected standard of battery safety must improve substantially, especially as larger battery capacities become available (in electric vehicles or electric grids). Efficient inspection methods at the manufacturing site and intelligent battery management systems in the field can improve battery safety by orders of magnitude. 

Yet, it is sadly inevitable that battery fires will become headline news in the future before the industry invests heavily in improving battery safety, possibly even with intervention of some governments.

5. Governments will step in to regulate the recycling of lithium-ion batteries:

The industry will recognize that the recycling of lithium-ion batteries is existential to its future growth. The impact of lithium-ion batteries on the environment, from mining raw materials to disposal of depleted batteries, will be devastating if economic recycling methods are not put in place. For example, lead acid batteries are the no. 1 recycled consumer item in the United States with a recycling rate in excess of 99%. Unfortunately, history shows that governments will need to step in and regulate certain recycling targets for lithium-ion batteries. 

08Apr 2019

Let’s say you love to ride your bicycle and that you want to measure speed without using fancy computers and GPS. What would you do?

High-school physics to the rescue! All we need is the circumference of the wheel then count the number of rotations the wheel makes in a certain amount of time that we can measure with our stopwatch. The speed, v, is calculated as the number of rotations, N, multiplied by the circumference, L — that’s the total distance traveled by the wheel — divided by the measured time, T. Put in one simple equation:

We replace the circumference with the radius, R, because it is easier to measure the radius of the wheel:

The speed equation becomes:

Therefore, measure the wheel radius, then count the number of rotations, and clock them with a watch…et voila, you can measure speed.

You quickly realize that you have an approximation of speed because it fails to take into account other factors that can introduce errors, for example temperature. On a hot day, the wheel expands a little making the radius longer.  Then you realize that the thickness of the rubber tire is not exact — it varies across manufacturers. With aging, the rubber gets worn out. It becomes thinner and consequently the radius is a little smaller. You may think these are small effects but if you are racing, they can make the difference between winning and losing.

So what is the relevance of a bicycle wheel to a battery?

Scientists understand the electrochemistry inside a battery.  They represent this science with many complex equations — like Fick’s law, Tafel’s equation, and several other mathematical forms. Yet, these equations remain insufficient to describe batteries in real life. 

Much like the wheel, there are significant variations in manufacturing across batteries from the same manufacturer or from different manufacturers. Temperature dependence, aging, presence of defects…etc. are significant additional considerations that impact the performance and safety of the battery.

Capturing these “real-life” considerations is what makes a model of the battery useful.  By “model” I mean a sufficiently accurate representation of the battery that one can use to make meaningful conclusions. For example, a good model can be used to predict the end of life of the battery. It can be used to identify counterfeit batteries or find defective batteries before they become a fire hazard.

Developing the model entails collecting data — millions of measurements — to capture manufacturing variations, temperature dependence, defects…etc. It takes a long time to collect statistically meaningful data across different types of batteries, from different manufacturers and across a board range of operating conditions.

The battery model is not static — it must improve over time or it becomes obsolete. One must keep updating it so it learns and adapts to newer battery materials, newer battery designs and manufacturing processes. This learning process can be in the test lab, or it can be in the field — in other words, intelligent algorithms can learn from batteries deployed in smartphones or other devices already in the hands of users.

Possessing intelligent algorithms and useful battery models is a powerful combination to make key predictions about the battery’s health and safety…that can make the difference between a safe battery and a fire.

14Nov 2018

Geoffrey Fowler at the Washington Post recently published an article observing that phone battery life is getting worse. I enjoyed my conversations with Geoffrey as he researched the topic. But why is the phone battery life getting worse? Why are batteries not keeping up with the new crop of smartphones? 

Like so many things in life, it is all about energy balance. Our doctors tell us that we need to balance our calories: Calories we eat versus the calories we expand on exercise. And so the smartphone needs to balance its energy stored in the battery versus the energy it spends on use. So I distill this to two simple questions on energy demand and supply:

  1. Why is the energy demand growing with increased use of our smartphones?
  2. Why can’t we have a bigger battery to supply our growing energy needs in a smartphone?

So let’s tackle the first question by examining the sources that drive energy consumption in a smartphone. There are three parts in your smartphone that are energy hogs:

  • Your screen….ok, I am sure you all know that ;
  • Your processor….some of you probably know that too ;
  • Your radios. Not your FM radio! Radios means the cellular connection, WiFi connection, bluetooth, GPS….anything that communicates with the outside world using radio waves.

Energy consumption for each of these parts depends on the nature of the hardware and you, the user — that’s the length of time you spend on the device. 

The energy used by a screen is quite large, even with the new OLED screens. Screens are getting a bigger numbers of pixels. Each pixel consumes energy. More pixels means more energy.  Every time you turn the screen on, it’s more energy that the battery has to supply.  And that adds up rapidly. 

If you follow various chatrooms, you probably know that “screen time”, meaning the total amount of available battery time with your screen on, is probably about 6 hours, give or take – regardless of what the smartphone maker advertises about all day use or more.

Next is the processor. Fortunately, that piece of hardware used to be a major energy hog but with the new generation of processors from Qualcomm or Apple or Samsung, they have become quite efficient. How much efficient? About twice more efficient than the previous generations from a few years back. All good news, right? well, not quite.

You see, processors have become efficient indeed, but now they are running a lot more frequently than they ever did. Think about an SUV parked in the garage versus a Honda Civic used for Ubering. Which one uses more energy?

A few years ago, we used our smartphones for texting and emailing….now, we stream videos. So while these processors are efficient, they are being taxed by video and social media. Net net, they are consuming more energy from the battery. How can you tell? watch how hot your smartphone becomes when you stream videos or take 4k movies on your device. That’s your processor getting hot.

Let’s talk now about radios. That’s a growing problem for the battery, so much that carriers like AT&T and Verizon in the US, or DoCoMo in Japan are really worried about it.

On one hand, carriers love that you use more and more data…that’s how they make money. But data use means your cellular connection is on, a lot more than before. 

But you say wait, isn’t 5G cellular connection better than LTE? Think of 5G as adding more lanes on the internet superhighway as compared to LTE. It means more cars, a lot more cars, will use the highway. It means more energy will be consumed. And the battery needs to supply this energy.

The FCC is just auctioning a new range of frequencies between 24 GHz and 47 GHz for the future 5G spectrum. By comparison, LTE runs at frequencies between 0.5 GHz and 2 GHz. Why is this important? Energy use goes up with frequency. So by going to the new 5G frequency, energy consumption will grow with it, worsening the burden on the battery. In other words, the future will tax the battery even more!

Bottom line: our smartphones and our user behavior mean our appetite for more energy will continue to grow.

Now we can tackle the second question: Why can’t the device manufacturer put a bigger battery in the smartphone? 

It is simple: Bigger battery capacity means a physically bigger battery. Batteries are improving so slowly such that the only way to give users more battery capacity is by making the device larger or thicker. The recent iPhone XS, XR and XS Max show a clear trend to making larger devices that can hold larger batteries.

Will that be enough for the future? not really. Smartphone sizes can’t get any bigger. At 6 in or greater screen sizes, they are already too large to hold in one hand. They may get a little thicker but not by much. Our human hands determine the optimal physical form for a smartphone.

So what gives? I don’t know yet, but most likely, our behavior and expectations. It is quite likely that users may charge their smartphones more frequently in one day…perhaps charge twice instead of once. Some users might be happy with fewer pixels in their devices. Others may turn off their Facebook and social media apps. 

Regardless of how we adapt to the future of smartphones, the battery will continue to be the weakest link, and the one in most need for innovation.

07Nov 2016

For the average reader, electrochemical impedance spectroscopy, often abbreviated as EIS, is more than a mouthful. Understanding its utility can be relegated to the category of unresolved mysteries. Today’s post will shed some light and a little intuitive thinking on this powerful method.

The reader’s first question might be “why are you talking about EIS in a battery blog?” The answer is simple. EIS is the foremost standard  tool in laboratories around the world to measure electrochemical processes and reactions. Electrochemistry, one of the most extensive branches in chemistry, is the study of chemical reactions that have an inherent relationship to electricity, i.e. they can either generate electricity or can be influenced by electricity. Yes, you guessed right, batteries are a prime example of electrochemistry. Another practical example of electrochemistry put to good use: the gold plating on your necklace or bracelet.

What does the name EIS imply? Electrochemical impedance is scientific jargon that refers to the electrical resistance of the device under study, in this case, the lithium-ion battery. In its most elemental form, impedance is voltage divided by current. For electrical engineers, it represents components such as resistors or capacitors. For other scientists, it represents the resistance the device exhibits against the flow of electricity.

Spectroscopy is the branch of science that deals with how a property changes with frequency. Hence, EIS is the methodology and science that seek to understand how impedance measurements change with frequency, and more particularly, how these changes are intimately tied to the underlying chemical reactions.

Why frequency? Frequency adds a lot more information about the nature of the chemical process that is taking place. In science, frequency plays a very important role. Take for example the difference between blue and red light. They are both made of photons, but differ in frequency. Medical MRI imaging depends on the frequency of the oscillation of the hydrogen atoms in our bodies. Distinguishing between different broadcast stations on the radio dial operates on similar principles. In other words, we use frequency to uniquely identify chemical or physical processes.

With this long introduction, let’s dive a little deeper into EIS as related to a lithium-ion battery. If you were to measure the impedance of a standard electrical resistor component — the kind of components you may find inside your smartphone — you will find that you will measure exactly the same impedance value whether you apply a low voltage or a high voltage, or whether you measure at low frequency or high frequency. In other words, for this resistor component, the value is independent of voltage (also known as bias) and frequency. Resistors are consequently easy components to understand.

That is NOT the case for a battery.  Change the voltage or frequency and you will get a different value. In other words, the battery can look like a resistor in some circumstances, or like a capacitor in others, or some complex combinations of both. When we change the voltage of the battery, it now operates at a different “state of charge,” in other words, it will have a different amount of electrical charge stored in it. As I described in this earlier post on fuel-gauges, the terminal voltage of the battery is a direct proxy of the amount of electrical charge stored in the battery, which is the state of charge (or the percentage of battery remaining).

In contrast, changing the frequency relates to different electrochemical processes that occur inside the battery. Such electrochemical processes could relate to the diffusion of the electrical charge (in this case, the lithium ions) from one electrode to the other. One can imagine that the ions have to travel a certain distance and insert themselves in the “Swiss-cheese” matrix of the material. So intuitively, this feels like a slow process, and it is. It takes several seconds to even minutes for the lithium ion to go through this diffusion process — meaning that diffusion of ions is characterized by a low-frequency signature. A distinctly different electrochemical process is how lithium ions and electrons interact right at the surface of the electrode. This interaction involves electrons and ions over very short distances. Intuitively, one can see that this can be a very fast reaction, usually on the order of microseconds. Hence its signature contains high frequency signals.

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All of this goes to say that the impedance value at a particular frequency is a “unique signature” for the underlying electrochemical process of interest to our study. And that is what makes EIS such a powerful tool. To the trained scientist, he or she can read the EIS measurement as a map of the various electrochemical processes and reactions that are taking place inside the battery without cutting it open or damaging it. It also provides tremendous insight into what can also go wrong inside the battery. Not all electrochemical processes are desirable. For example, the underlying process that causes lithium metal plating is highly undesirable and can be readily measured using its unique EIS signature.

So how is the measurement made? In the laboratory, the oft-expensive and bulky instrument applies a small electrical current at a well defined frequency to the battery, then measures the voltage. Divide the voltage by the current and you now have the impedance at this frequency. For example, apply 1 mA of current at a frequency of 100 Hz, you might measure 0.5 mV. Hence the impedance is 0.5mV/1mA = 0.5 ohms at 100 Hz. This, of course, does not take into account the complex value of the impedance but it is a simple illustration of the concept. “Complex” numbers are mathematical tools to show values that have both real and imaginary components. Don’t worry if you don’t understand them fully —the key thing is that an impedance measurement has two values to represent it.

eis

A full EIS chart shows by convention the imaginary component of the impedance (vertical axis) vs. its real value (horizontal axis). The far left of the chart shows the measurements made at high frequencies, in particular highlighting what happens in the metal conductors inside the battery as well as what occurs at the surfaces of the electrodes. As we follow the purple dots and move towards the right, the frequency of the signature gradually decreases highlighting now a different set of electrochemical processes, in particular what happens at the insulating interface between the electrode and the electrolyte (also known as SEI layer). Ultimately, to the far right of the chart, the frequency is low and is unique to the diffusion effects of the lithium ions.

An EIS tool is present in every electrochemistry laboratory around the world. Young graduates in this discipline spend countless hours operating this tool. It is not a small instrument…it fits on a desk, may weigh several pounds, and costs several thousands of dollars. Now imagine how the world would look like if an EIS tool can somehow fit inside each and every smartphone!