Fast charging

30Sep 2014

I covered in the prior post about the ill consequences of charging a lithium-ion battery using constant current, constant voltage (or simply CCCV). The damage incurred within the battery during charging with CCCV is attributed to a series of undesirable side reactions that effectively reduce the effectiveness of the primary energy storage reaction. In other words, during charging, one desires that all the energy goes into the ideal reaction that stores energy inside the battery. In reality, CCCV charging promotes a number of bad reactions that effectively damage the internal structure of the battery, and reduces the battery’s ability to store electrical energy.

I will not go into the details of these side reactions; they are fairly involved and can be quite complex for the average person. But they are reasonably understood by our scientists. For example, one of them is the formation of lithium metal deposits when lithium ions combine together. Others relate to the physical damage to the electrodes and the decomposition of the electrolyte solution.

A few of these undesirable side reactions, but certainly not all of them, have been shown to exhibit a dependence on voltage. Specifically, some of the damage accelerates when the voltage of the battery approaches 4.35 Volts….or in other words, when the battery is approaching 100% full charge. This is why a common tip is to charge the battery up to about 80% instead of the full 100%. 

So step charging, probably introduced several decades ago, was an early attempt to charge the battery very gently at the higher range of voltages, or when the battery is approaching full. It is simple: it means reducing, or stepping down the current, when the battery voltage reaches say 4.1 Volts, or say around 60% or 70% of its maximum charge. However, extensive tests and results over the past many years have shown that the damage reduction was at best minimal. There were indeed a few cases where step charging seemed to have helped, but these were few and far in between, and worse yet, there was not much consistency. In other words, step charging did not deliver a solution.

I will leave the discussion of better, more sophisticated, charging methodologies to another post, but let me address here why step charging fundamentally is flawed or at best, incomplete.

First, step charging is only attempting at alleviating the amount of charging when the battery is nearing its highest voltages. But the damage to the battery is not only due to high voltage. It is due to more complex reactions of which voltage is but only one parameter. Failing to recognize the relationships between all the damage elements makes step charging quite ineffective. This is particularly acute in more modern lithium-ion batteries with high energy densities (or higher capacities). 

Second, step charging, much like CCCV, is an open loop solution. In other words, it has no knowledge of the battery’s inner reactions, inner health, inner status, and consequently  has no means to measure or assess the rate at which these undesirable damaging reactions at taking place. So let’s say for the sake of example, we have two batteries from the same type and vendor, but with  manufacturing variations between them (which is very common). Let’s further say that one battery is better, and that its damage seems to occur at an onset voltage of 4.1 Volts. Let’s also say that the difference in manufacturing causes the damage in the second battery to occur at a lower voltage of say 4.0 Volts. So if step charging reduces the charging current at 4.1 Volts, then one battery will see an improvement but the other will not. And if one were to say let’s drop the charging current at 4.0 Volts to be safe and cover both batteries, then there is a serious penalty to charging times — charge times will balloon significantly.

So in a nutshell, if someone is promoting to you step charging as a solution, my advice is simple: RUN!

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29Sep 2014

CCC…what? Yes, it is a mouthful and it stands for “constant current constant voltage.” It is presently the charging approach used for lithium ion batteries. As I indicated earlier, it was invented in the 19th century for charging lead-acid batteries, and somehow it became the default charging methodology for present-day lithium-ion batteries. This is what your smartphone, tablet and your electric vehicle do to charge your lithium-ion battery.

As the name implies, the electronics in the battery management system (see the earlier post on BMS) charge the battery initially with a constant amount of charging current. The higher the charging current, the faster the charging time; and consequently, the higher the power; and therefore, the bigger the AC adapter (or wall charger) to accommodate the higher power rating. That’s why a tablet adapter, typically rated around 12 Watts, is bigger than a typical smartphone adapter which is rated at or near 5 Watts. And that’s why an electric vehicle requires a far bigger charger, rated above 6,000 Watts.

As the battery is charged, its terminal voltage rises. A single lithium-ion battery starts near 3 Volts, and as it charges, its terminal voltage will rise above 4 Volts. When the voltage reaches a predefined limit, often 4.35 Volts, the charging electronics will switch from a constant current to a constant voltage — this is to ensure that the voltage across the terminals of the battery never exceed 4.35 Volts. Higher terminal voltages risk the trigger of unsafe failures. Incidentally, never charge a lithium-ion battery with a charger that was not designed specifically for lithium-ion batteries.

Now a lithium-ion battery’s internal chemistry is quite complex. When the battery is being charged, lots are happening inside the battery. As I explained in prior posts, lithium ions are traveling from one electrode to the other and inserting themselves within the electrode. This is all happening within the battery and is transparent to you, the end user. Alongside this charging process, as you might imagine, there are other bad and undesirable things that are happening too. For example, it is easy to imagine that all the lithium ions will travel together and happily make the journey from one electrode to another. In reality, these lithium ions will “collide” and they will bond together to form dangerous  deposits of lithium metal. These lithium ions are now out of the picture and can no longer participate in storing electrical energy. It is analogous to traffic jams on highways because cars do get into accidents; the notion that cars on a highway will travel merrily at 65 mph and stay in their own lanes is somewhat naive and left only to a utopian universe.

Now, it turns out that CCCV charging is greatly responsible in how lithium ions travel inside the battery. There is sufficient proof now that CCCV is one of the key factors that accelerate the damage inside the battery exhibited by the loss of lithium ions. Think of it as the ill-timed traffic lights or poorly marked signs on the road that can cause unnecessary accidents.

So you might ask, how come this issue was not observed in the past? Well, lithium-ion batteries of yesteryear are akin to a rural highway with very few cars on it. So even if the highway signage was defective, there were relatively few cars on the road. Batteries from past years have low energy densities, and consequently have fewer lithium ions to go around, so they were more forgiving. But modern batteries are now packing higher energy densities, in other words, they contain a lot more lithium ions than their older sisters ever did, and thus are extremely sensitive to how they are charged. This combination of high energy density batteries with CCCV charging is a recipe for excessive damage, less capacity, short cycle life, and consequently, a very poor consumer experience. 

Think about it next time you wonder why your battery seems to be losing its freshness.

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23Sep 2014

I love my electric vehicle, or EV, as we affectionately call our electric cars here in California. I love that it is quiet. I love its fast pickup from a stop. I love that it requires practically zero service: no oil change; no transmission service; no timing belts. Of course, I love too that it is eco-friendly and driving in the carpool lane. I am bullish on the future of electric vehicles, but first, the technology has to evolve a little more to give the consumer less anxiety, the topic of today’s writing.

No, it is not a Tesla. It is not a Leaf. I am one of the early adopters of a Ford Focus Electric. It looks like a regular Ford Focus so it does not stand out in traffic. I nominally get about 80 miles of range which includes a lot of freeway driving…my normal daily commute. Slower driving in stop-and-go traffic increases my range to about 100 miles. Shave 10 or 15 miles during our mild California winters.

My vehicle is powered by a 24 kWh lithium-ion battery pack that is manufactured by LG Chemical, but in reality, only about 19 or 20 kWh are available to me. That’s because to provide a 100,000-mile warranty, the battery has to reach 100,000 divided by 80 miles = 1,250 cycles minimum. So battery manufacturers and car makers choose to reduce the capacity of the battery to gain cycle life. Remember the whack-a-mole strategy from earlier posts. Using the water analogy, if you don’t fill up the water bucket to the top, you can fill it more times over its life. Tesla Motors, Leaf and virtually every car maker employs this strategy. For the time being, it’s ok, but that has to be addressed over time in order to make electric cars more affordable for the broad population.

When I first bought my car, my range anxiety was high. The car dashboard displayed how many miles of driving I had available in the tank, ehem, battery. I charged my car overnight, and I started my morning with about 80 miles. By the time I got to work, the dashboard showed less than 60 miles.  I was nervous every time my dashboard dropped below 50 miles, so I charged as frequently as I could. That’s range anxiety. 

Now, nearly a year and half later, my behavior has changed drastically. I drive my car down to 10 or even 5 miles left in the battery. I plan my route. I know my destination and I know my return route. Keeping 50 or more miles for insurance does not make any more sense. I became comfortable with the given range of 80 miles and I use it effectively. I consistently get about 80 miles, and in the time since I bought it, my comfort level increased and my trust in my dashboard’s range estimate has increased. Of course, my maximum driving range was still limited to the greater Bay Area. I cannot drive my car to, say, Los Angeles, but I do use nearly every mile available to me in battery.

However, my range anxiety got replaced with something else: Charging anxiety. You see, if I am comfortable taking my battery down to nearly zero, I need to know that I am close to a charging outlet when I stop. Good news here! The San Francisco Bay Area has lots of charging outlets. But the problem is the speed of charging. If my battery is near zero, it takes a whopping 20 hours to charge it at 120-Volt, and a mere 4 to 5 hours using the 240-Volt chargers. Ouch! That is not acceptable. That is at the core of anxiety in battery-powered cars, phones, or anything else. We need to charge them fast, and I mean really fast….As fast as filling up your gas tank at the gas station. 

If you look at what Tesla Motors is doing and what Elon Musk keeps advertising, none of it is about extending the range of their cars. Their publicized priorities are about building cars for the masses (in other words, lower price point) and secondly about charging their cars fast, in half an hour or so.  

Fast charging…we need it. Remember that!

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16Sep 2014


If you are a consumer who has wondered why your lithium-ion battery in your mobile device fails your expectations, this blog is for you. If you are technically savvy but you are not a chemist, and often wondered how this lithium-ion battery works the way it does, then this blog is for you. If you are just curious about how to get more out of your lithium-ion battery, then again, this blog is for you.

You have searched the internet for information on the battery inside your gizmo, how it works, how you should take care of it, what the fancy technical terms really mean, and what the manufacturer is promising you and what you are really obtaining….and I am sure you often felt frustrated because, well, little of it made sense to you. You are not alone.

The fact is batteries have for a long time been a forgotten corner of technology. Before mobile devices became anchored in our daily lives, the battery meant that blackbox under the hood of our cars. Batteries did not evoke “clean” or “high-tech.” We wanted a low-cost battery that cranked our engines even in the coldest days of winter.

Then came mobile devices, and now electrified vehicles… and things got more complicated. Everyone had an opinion, or a theory. “No, don’t discharge to empty!” or “Beware, it has a memory effect.” The fact is most of this advice is not based on real science and has little merits. True battery experts are hard to find…universities don’t graduate enough of them, and they are in high demand.

This blog is intended to be read either as individually independent posts, or collectively as one continuous reading. The titles are summarized in the Table of Contents on the right hand side. Start with whichever topic you would like depending on your fluency level.

In the next post, we will start with the basics: What the terms really mean when one describes a battery.

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