Guest post written by Noam Kedem
Noam Kedem?is VP of marketing for?Leyden Energy, a Fremont, California-based company that makes batteries for consumer electronics, electric vehicles and storage applications.
Noam Kedem
Speculation about the design of Apple?s much-anticipated iPhone 5 got a big boost from the launch of the new iPad. It was apparent that Apple had faced some rather stringent design tradeoffs between feature set, form factor and battery life. The company carried it off with its usual engineering panache, but even so, the new iPad is a bit thicker and heavier than its predecessor, and with less battery life.
What does this portend for the iPhone 5?
Others can speculate more ably on the display and processor choices Apple faces. What I?d like to focus on is the battery. From my perspective, a fundamental problem is that while Apple can count on ever-increasing performance in the silicon involved, the lithium-ion (Li-ion) batteries that power virtually all mobile devices are practically standing still: they use the same chemistry platform as they did 20 years ago. Absent a change in battery chemistry, Li-ion is going to impose some limitations on where Apple can go with the iPhone 5?s design and spec sheet.
The new or upgraded features expected in the iPhone 5 that will require the most from the battery are the display, 4G LTE wireless connectivity and a more powerful processor. Leaked images show the Retina display growing from three and a half to four inches; not surprising, since the average Android phone display is now over four inches. 4G LTE connectivity seems like a no-brainer, too, given the demands of mobile video, iCloud features and the Android competition. We can also expect a faster version of the A5 processor with even more powerful 3D graphics.
Each of these new features can end up drawing more power and generating more heat. Both of those are challenges for Li-ion technology. That?s why the new iPad?s battery ended up being some 70 percent bigger and heavier than its predecessor yet still offers somewhat shorter battery life, and why Apple faces some difficult choices for the iPhone 5. The iPhone 5 battery is going to have to be notably bigger than its predecessor. Even with the increase in battery?s X and Y dimensions made possible by a larger screen, the result could still be shorter battery life?in terms of run-time per charge, cycle life and calendar life.
This is because Li-on battery technology is falling short in two areas: energy density and thermal sensitivity. Energy density determines the amount of run-time you can pack into a give size (volumetric) or weight (gravimetric) of a battery. Unfortunately, Moore?s Law doesn?t apply to batteries. Since the first Li-ion batteries hit the market in 1991, the transistor count in the devices they power has increased a thousandfold in response to consumer demand for more features and higher performance. Li-ion batteries have eked out a mere 3X increase in their volumetric energy density in that same period, and battery manufacturers are having a harder and harder time squeezing more energy into them.
Increased packaging efficiency is one way of getting higher energy density. For instance, the non-removable Li-ion pouch cells now used in the majority of smartphone models eliminate the protective casing needed for user-replaceable batteries. They?re just a sealed bag containing carefully stacked or wound anode and cathode sheets, separators between them, and?permeating all of these layers?a liquid electrolyte. By relying on the smartphone case for protection, there?s more room for the active materials that actually store energy.
Packaging efficiency is where Apple may have a slight advantage when it comes to the iPhone 5. There are two ways to place a battery in a smartphone. One way is two layers of electronics (screen and circuitry) with a space ?carved out? for the battery. This is the approach taken in the iPhone 4S. The alternative is to use three layers: screen, circuitry, and battery, as in the Motorola RAZR line (both RAZR and RAZR MAXX).
At first glance, it would seem that the three layer approach, by permitting a larger battery, would deliver longer run-time, but the narrower battery in the carve-out approach actually offers higher energy density. Li-ion pouch batteries have a built-in printed circuit board that is connected to the positive and negative terminals of each cell and provides active protection against short circuits, overcharge and forced discharge. A narrower, rectangular battery can put this PCB on the short edge, leaving more room for the active materials and thus delivering a somewhat higher energy density than a square battery.
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