Sunday, January 20, 2013


iPhone ... battery is solid, gray shape
It has been a while since I wrote about Science and Technology, or even Art and Design. This is the STEAMD blog, after all. OK, a little science (plus, as usual, a little autobiography). I’ve been preparing for a visit with Linda’s dad and his friend. We planned to go up to Loveland for lunch. Ardys had asked about e-readers and if they could duplicate “big print books.” Of course, they can. All e-readers, including the Kindle, my favorite, have adjustable font size and can display big print.

I planned to demonstrate that to her. In preparation, I check out my Kindle and found the battery nearly discharged. Now Kindle e-readers use “e-paper.” There are a number of features of e-paper that make it ideal for an e-reader. One is the fact that it is very readable in direct sun light. As you all know, the iPad or iPhone or MacBook or any similar technology from any other manufacturer, is washed out and hard to read in the direct sun.

Another useful feature of e-paper is that power is not required to maintain a page. If there is no backlight, then the only time e-paper uses power is to change the page. So a Kindle device can last for weeks with a single battery charge.

Not so with most other portable devices. Battery life has been an issue, a selling point, and a driven goal to extend since the first unplugged power tools appeared on the market place. 

I was provided with several IBM ThinkPads through the years. I would always order them with the extra large battery. In the IBM designs, the extra cells forced the battery case to extend out the back. HP chose to add more battery mass downward, providing a built-in tilt to the keyboard. My Ford Flex, which is filled with electrical gadgets, has a battery bigger than a breadbox … and if it ever fails, I suspect I’ll learn it is one of the most expensive made.

World War II submarines had a room filled with lead-acid batteries before the nuclear power submarine provided much longer lasting power. Many a WWII submarine epic involved the need to surface and charge the batteries using the diesel engines.

I recall the early yard tools using Nichol-Cadmium or Ni-Cad batteries. They had an unfortunate “memory” effect that if they weren’t run all the way down in discharge, then they would get lazy and not provide as much power before giving up. If you left your lawn clipper always plugged in, and only used it sparingly, the Ni-Cads would not provide deep power on a day when a lot of clipping was desired.

This problem with Ni-Cads has been substantially improved, but still many insist that batteries should be fully discharged before recharging.

The smartphone market revolves around one question: how do you fit all-day access to all of a consumer's favorite apps and services comfortably into one hand? (The tablet market? Two hands.) As mobile devices have increased in power, the demand for longer lasting batteries has only increased.

No smartphone manufacturer has managed to provide the solution fully, because they all face a fundamental dilemma. The electronics that enable faster performance, higher-speed data, better video and gaming, a more vivid and detailed screen, etc., are moving at the speed of Moore's Law.

The scientists and engineers have been working on the problem. The best solution so far is a battery type called Lithium ion. Yet even the lithium ion (Li-ion) pouch cell batteries that power today’s devices can't keep up. Little wonder that battery life is the biggest complaint of smartphone users!

The feature vs. run-time battle this imposes on smartphone designers is why the new iPad came in thicker and heavier than its predecessor. The battery needed to power the Retina Display, 4G LTE, and general and graphic processing improvements is 70 percent bigger and heavier. Even so, the new iPad's battery life (run-time) is slightly less than that of the iPad 2. The new iPhone 5 provided a slightly larger battery size, mainly through the bigger case dimensions and the elimination of the bulky 30-pin connector, than the iPhone 4s. The result was that it demonstrates marginally longer battery life than its predecessor, even though the new iPhone is faster and more powerful with a bigger display and LTE network.

Li-ion battery constraints go a long way toward explaining why smartphone vendors spend millions on incremental design advantages in a market that's moving with blinding speed. If you're trying to figure out what your iPhone 6 -- or your next Android device or Windows Phone -- is going to look like, here are six rules you need to know about batteries. Just as Christians follow the Ten Commandments and Libertarians rave about the Bill of Rights, battery designers and engineers must follow these six rubrics as they balance the design of a battery and the size and shape of the device it will be installed in.

1. Battery in a bag

A Li-ion pouch cell is a sealed bag containing carefully layered anode and cathode sheets, separators between them, and -- permeating all of these layers -- a liquid electrolyte. Although tablet batteries comprise several cells (three in the new iPad), smartphones are generally powered by single cells. Either way, at one end of the battery, a printed circuit board (PCB) is connected to the positive and negative terminals of each cell and provides active protection against short circuits, overcharge, and forced discharge. Li-ion pouch cells tend to be fragile and rely on the smartphone case for protection, and so officially are not user-replaceable.

Three cells of an iPad Li-ion battery

2. Squeezing in run-time

The energy density of a Li-ion pouch cell determines how much run-time you can pack into a given size (volumetric) or weight (gravimetric). Li-ion technology hit the market in 1991. Since then, processor transistor count has increased more than a thousand-fold, Li-ion energy density only threefold. Denser electronics are what make dazzling features possible, but they draw ever more power. Unfortunately, battery manufacturers are having a harder and harder time increasing energy density. This is why non-replaceable Li-ion pouch batteries are popular with smartphone and tablet designers. Without the protective case needed to make a battery safe for consumers to handle -- which does nothing for energy capacity -- they are thinner and pack more run-time into a smaller space.

In this regard, the non-user-replaceable batteries that Apple has used since the original iPhone were more an engineering design point than the artistic bent that many complained drove Steve Jobs and his products. Yes, a non-removable battery helped make all the iPhones smooth and svelte, but it was a real positive impact on the battery life to use the phone itself as the battery’s container.

3. The length, width, and thickness of cells

Energy density is affected by the thickness and the ratio between width (X) and length (Y) of a Li-ion pouch cell. Volumetric energy density falls off as the pouch gets thinner because the packaging takes up a higher percentage of battery volume. The optimal X-Y ratio arises because when the PCB is installed on the short edge of a narrow battery, there's more room for the active materials (anode and cathode) that actually store energy. All other things being equal, a narrow, thicker battery will deliver better volumetric energy density than a more square one. The longer length of the new iPhone helped provide a longer battery. See how it all fits together? And you thought the bigger iPhone screen was just for HD video!
(An interesting Apple patent reveals ways to mold batteries in more complex shapes to fit into places like the bezel that are presently impossible to use.)

4. The necessity of keeping cool

Li-ion pouch cells don't like it hot -- a common condition for smartphones, as anyone who's ever had to wait out the "cool down" error message knows. The standard Li-ion chemistry depends on an electrolyte that reacts with residual moisture to create hydrofluoric acid (HF), the most corrosive of all chemical compounds. HF can actually eat through most metals and even glass.

Like all chemical reactions, this process doubles in speed with every increase in temperature of 10 degrees Celsius. The result is reduced calendar and cycle life: not only does run-time degrade with simple age, but each charge and discharge further reduces it, until the battery just doesn't last long enough between charges. Worse, Li-ion cells generate heat themselves during charge and discharge: the more power your smartphone calls for or the faster you charge it, the hotter the battery gets.

5. Building a smartphone

Three-layer or "carve-out"? The Motorola Droid Razr line (both Razr and Razr Maxx) is an example of the three-layer approach to smartphone design: screen, circuitry, and battery. The iPhone 4 comprises two layers -- screen and electronics -- with a space carved out of the Printed Circuit Board (PCB) for the battery. In either case, a bigger screen means room for a bigger battery. Regardless of the other advantages of each approach, the narrower, thicker battery possible with Apple’s carve-out approach will offer higher energy density. In a three-layer design, it's also more difficult to shield the battery from components that generate heat and thus shorten battery life. (The three layer design, on the other hand, may be cheaper to build and easier to repair. All engineering is a trade-off.)

6. Chemistry: Wild card of the deck

Improvements in Li-ion chemistry may offer dramatic increases in energy density, giving smartphone designers more choices in the feature vs. battery life battle. There's a lot of promising research into new active materials and some new solutions already on the market. One of these uses a new Li-imide electrolyte that doesn't generate hydrofluoric acid and thus delivers a dramatic improvement in thermal stability and battery life. It also permits effectively thinner batteries by eliminating most of the swelling in thickness characteristic of current Li-ion pouch cells over their useful life, which forces designers to sacrifice cavity space to accommodate the swelling.

Don't expect dramatic departures in design from Apple or any other smartphone vendor until Li-ion pouch cells take the next step. This could come as soon as 12 to 18 months from now. New active materials (for example, silicon anode and high voltage/high capacity cathodes) combined with the new electrolyte mentioned above could deliver a 20 percent boost in run-time per charge in the same size battery. For the eventual iPhone 6, such a battery would give Apple more flexibility to consider faster processors, power hungrier displays, and more apps without sacrificing run time, and make it easier to maintain the iPhone's famously sleek appearance.

In the meantime, keep your eye on Li-ion battery news with the six things above in mind, and you'll have a better idea of what to expect from the next generation of iPhone or Android smartphones. I look forward to the time that I don’t have to charge my iPhone any more often than I charge by Kindle reader. In the meantime, I’m on the lookout for one of those solar cell phone chargers so I can take my iPhone deep into the mountains and not have to look around for a current bush. That will be the ticket. There I’ll be; deep in the wilderness, enjoying the wildlife and natural scenery, without any modern technology to distract me. Suddenly, my phone rings. “Can you pick up a loaf of bread on the way home?” “Honey, I’m deep in the wilderness with no access to modern technology. Where am I going to find bread?”

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