The Basics

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:

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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.

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16Jan 2016

Our new website presents our suite of products called Adaptive Charging Software. It is fair to say that everyone understands and recognizes the meaning of “Charging” and “Software”…but “Adaptive”? What does it really mean? The purpose of this post is to give the reader an intuitive feeling of the meaning of (and consequently the need for) “adaptive” as it relates to technology.

Let’s first start with the classical definition of adaptive:

a•dapt•ive (ə-dăpˈtĭv)  adj. Relating to or exhibiting adaptation.

Ok, it relates to adaptation, but adapting to what? and why? For that, let’s illustrate with an example at how adaptive algorithms and software became instrumental to modern photography.

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22Sep 2015

Pause for a second and wonder why electric vehicles have frustratingly limited driving ranges? or why your smartphone lasts only for a few limited hours instead of an entire month? Yet, a good ol’ combustion-engine car can go for hundreds of miles without a problem. This is the manifestation of energy density. Let’s talk about it in more detail and hopefully give the reader a bit of more intuitive sense on the importance of this metric.

Energy density, as the title implies, is a measure of how much energy is stored in a certain volume. A battery or a gas tank has a certain limited volume, therefore it is important to have a metric that relates to how much energy can be stored in that volume. Obviously, energy is what powers our smartphones or vehicles, therefore energy density is a metric that describes how far one can drive  or use a device given the limited amount of energy stored in the “tank.”

The following table compares a select number of energy-storing materials or mechanisms, all the way from the traditional lead-acid battery (the type that you will find under your hood) to much more sophisticated energy sources such as nuclear fission. So what is this table telling us?

EnergyDensity3

The first nine rows are all batteries, or devices that can store electrical energy. Batteries are either primary (i.e., non-rechargeable) or secondary (fancy term for rechargeable). The last three rows are widely used energy sources in our society today and are used here for comparison purposes: Ethanol and gasoline are examples of carbon-based fuels, and the last row, well, we all know what nuclear power can do, both the good and the evil.

The first observation: Even the best battery, the absolute best, has 10X lower energy density that carbon-based fuels. That means the same tank (or equivalently sized battery) will let you drive 10X more miles using carbon-based fuels. I cheated a little here — electric systems are more efficient than carbon-fuel systems, so the difference is more like 3X rather than 10X, but that will be left to another discussion.

The second observation: The difference between the best battery and worst battery (in terms of energy density) is substantial, also about a factor of 10X. Lead-acid batteries, discovered over a 150 years ago, don’t provide a lot of energy density. NiCd batteries also leave a lot to desire. Do you remember the bulky batteries in the early cell phones back in the 1990s? Or just google the GM EV1, the first electric vehicle from GM that used lead acid batteries.

But…there is always a but: While NiCd have for the most part disappeared, lead acids are incredibly inexpensive, and they survive. Until the day comes when the price point of alternative batteries drops radically, lead acids will continue to be the king of batteries in applications where energy density is not critical — i.e., where it is ok to occupy a larger volume, for example backup systems for cell phone towers.

The third observation: Energy density increased by a factor of 10X over 150 years! That’s not terribly promising unless the future brings forth some serious breakthroughs in materials. Is there anything on the horizon? There is a lot of promising good material research, but when one takes into account cost, cycle life, and other constraints such as manufacturing and capital, it is very hard to point to one particular technology that is likely to be commercialized in the next 5 years. So the wait and the hope continue.

The fourth observation: Lithium-ion technologies, first commercialized by Sony in 1991, encompass a wide range of energy densities depending on the particular choice of material for the electrodes. Lithium-ion batteries using nickel-cobalt-aluminum oxide (NCA) electrodes — the type used in the Tesla Model S — have over 3X the energy density of lithium-ion batteries with lithium iron-phosphate  (LFP) electrodes. So why is anyone considering LFP lithium-ion batteries: Cycle life! Welcome to the world of compromises.

So by now, you are probably disappointed about the future of batteries! It is true that the progress of batteries over the last 150 years has been slow, and it is true that batteries can’t yet compete with carbon-based fuels…but that does not mean that the incremental progress in batteries is insufficient to meet many needs of our society. Yes, they can be better, but present batteries boasting 700 Wh/l can and are sufficient to provide an electric vehicle with a range of 300 miles. In other words, don’t expect miracles in batteries, but do expect that incremental technologies from materials to algorithms and electronics will be sufficient to address a wide range of energy storage needs, including smartphones that can last an honest day to electric vehicles with a range of 200 – 300 miles.

There is plenty to look forward to here, just be careful about wild claims of amazing discoveries. If there are too good to be true, then there is a probably a good reason to be skeptical.

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14Aug 2015

Not yours, of course….the smartphone’s waist. We see a race among the smartphone makers to go thin. The iPhone 6 Plus is 6.9 mm thick and it is already been outflanked by some new devices coming from China. In particular, the Oppo R5 boasts a thickness of only 4.85 mm, and the Vivo X5 Max is an even thinner 4.75 mm. So what determines how thin one can go?

Naturally, the mechanics of the device are clearly one limiting factor…nobody wants their smartphone to “bend.” For the most part, manufacturers are now using hardened aluminum cases for added resistance to bending. With the exception of some early complaints about the iPhone 6 Plus, there have been no credible reports of additional bending failures. Another limiting factor is the touch screen. There have been some great innovation here, most of it related to fusing the touch glass with the display, thereby reducing the touchscreen thickness. For example, the AMOLED screen on the Vivo X5 Max is only 1.35 mm thick.

So that leaves the battery as the last frontier…why am I not surprised? The battery seems to consistently win the title of bottleneck, and this is the topic of today’s discussion. Why can’t we make batteries ultra thin?

The answer is actually “yes, we can.” Batteries can be made really thin, I mean thinner than you might imagine, sub 1 mm. But naturally, there are tradeoffs. The first tradeoff is that thinner batteries cannot boast the same energy density than their thicker counterparts — there is just too much “electrical overhead” (e.g., connectors, plates) that they become dominant when the battery is too thin. See this earlier post that shows the impact of thickness on energy density. For a smartphone device, somewhere around 3 mm is the lower limit of battery thickness. Some smartphone makers instead choose to go thick just to provide more battery capacity — the most recent example is the Moto X whose thickness is a whopping 11 mm, more than double Oppo’s thickness !!!! So the first tradeoff is battery capacity vs. stylishness. Judging from the market trends, stylishness seems to be winning for now.

There is also a second and very important tradeoff, and that relates to swelling. I described in a very early post what happens to the battery as it ages…it bloats, and consequently becomes unsafe. This “swelling” phenomenon, through which the battery physically grows, has two components. They are shown in the next chart.

This chart shows the actual and measured thickness of a 3-Ah cell used in the LG G2 smartphone. It is a polymer cell and is embedded (i.e., non-removable) inside the mobile device. The thickness is measured over 60 cycles of charging and discharging. One readily observes two separate trends, almost like a yoyo on an escalator:

  • One trend is a fast variation in thickness with a known periodicity of one cycle (this is the yoyo effect). The thickness varies by about 0.15 mm, or approximately 3% of the cell’s thickness but is a fully reversible effect. This is due to the physical expansion of the graphite anode. During charging, lithium ions intercalate (fancy language for “insert themselves”) inside the carbon-graphite material (also known as matrix) thereby pushing the carbon atoms aside and causing physical growth. During discharge, the opposite happens and the anode returns to a thinner state.
  • The second trend is a slow, semi-linear growth in thickness (this is the escalator effect). This is related to irreversible damage to the graphite anode — as the lithium ions go in and out of the anode, they leave just a tiny bit of damage that accumulates over time into this irreversible thickening of the anode (and consequently of the cell). As one can immediately observe, this second trend is significantly larger in magnitude than the first trend. For this cell made by LG Chem, the increase in thickness over 60 cycles is 0.15 mm, or 3% of the original thickness. Typically, over 500 cycles, this may reach 8 or even 10%.

As a result, manufacturers of smartphones need to make an allowance inside the device for the battery cell to grow in time — this allowance is somewhere between 10 and 15% of the cell’s thickness, or up to 0.7 mm; quite a significant number. Failing to provide this allowance risks placing large pressures on the touchscreen and cracking it.

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