Battery Progress Inches Forward

By Ed Sperling

Chip companies that have been betting the future on better battery technology and holding off on the often painful process of reducing voltage should probably start rethinking their plans.

Battery technology is not expected to improve by more than 3% per year, and even that may slow. Compared with the chip side, there are no breakthrough materials such as halfnium or technologies like high-k/metal gate or air gap to enable design engineers to hit the reset button. In batteries, those minimal gains already are coming from advanced materials applied to the anode (-) and cathode (+) of the batteries, as well as significantly higher density for holding more charge in the same space.

The basic variables in a battery haven’t changed, though. It’s still a balance between capacity, cycle life and safety. Add too much capacity and weight becomes a factor. Use cheap materials and the batteries hold less charge over time. Increase the density too much and the batteries pose a fire risk.

New Materials

At the center of most batteries—at least the ones in common use—are the anode and cathode and an electrolyte solution. Typically the electrons move from a negatively charged anode to the positively charged cathode, and the electrolyte is used to store the electrons and prevent them from flowing freely. When the battery is recharged, the flow is reversed. (There are exceptions, such as electrolytic cells where the cathode is actually negative, but use of that technology is far more limited.)

By adding a ceramic layer on the anode, Samsung has been able to lower the resistance with a smoother surface while also improving safety. It also has doped the cathode with aluminum and other materials to prevent leakage. All of this comes at a price, though, and battery makers are keenly aware of how much the market will bear.

“We found that 33% of consumers are willing to pay $45 for an extra hour of battery life,” said Sean Lee, head of Samsung marketing and business development in the United States. “A 2.8 amps/hour battery produces 10.5 watt hours. A 3.0 amps/hour battery produces 11.2 watt hours. The higher capacity has allowed up to 11 hours of battery life for a netbook and 10 hours for a notebook, but actual time varies significantly depending upon applications being used.”

Samsung also is working on a high-density graphite anode and a higher-voltage electrolyte to reduce the amount of gas inside a battery. Lee said the company expects to shift to a silicon anode system in Q3 of next year, which will increase energy efficiency by up to 30%. It expects to reach 3.4 amps/hour by 2012 using that approach. But all of that won’t show up in longer battery life. By lowering the voltage slightly, cycle life—the overall number of times a battery can be charged—can be increased to 1,000 charges.

Panasonic is making similar tradeoffs with weight, according to Atsuo Yoneda, one of the company’s lithium-ion development engineers. Rather than increasing battery life, the focus in many applications is to reduce the weight by decreasing the number of batteries and making sure they hold their charge longer. The company is looking at a 3.6 amp/hour battery using a cathode made of lithium-cobalt-aluminum oxide, or NNP.

Shapes and materials

No matter what shape the batteries are in—either cylindrical or flat—the determining factor on battery life and the amount of power being stored is density and size. This is a basic area equation, and the shape of the battery doesn’t affect much.

Cost is another matter, entirely. Andy Keates, power sources enabling manager at Intel, said that prismatic cells are about 40% more expensive for the same capacity. One reason is the majority of those flat cells are custom sizes. They can enable the manufacturing of thinner notebook computers, for example, but they don’t change the battery life.

What’s more important, by far, is the material used in batteries, and there are a bunch. But the battery material expected to continue dominating the market is be lithium ion, which is the successor to lithium cobalt oxide, or LCO. As the chart below shows, there are a slew of technologies available. Lithium ion wins, however, on the basis of consistent power delivered over the longest period of time, versus a burst of power in the lithium iron phosphate.

Figure 1: While some exotic combinations have been developed and tested, none beats lithium ion for most portable electronics. (Source: Intel)

Other considerations for the future

One of the more interesting ramifications for battery technology is what happens when voltages drop inside of SoCs.

“Right now we’re seeing voltages as low as 2.5 volts,” said Keates. “It may go as low as 2 volts on the discharge curve, which leads to a tradeoff because voltage regulators may lose efficiency at less than two volts.”

That means that instead of just designing more power-efficient chips, now they have to include more power efficient regulators—and all of this because everyone was counting on batteries to improve enough so that battery life of devices could be extended. At this point in time, at least, it looks as if the faith in battery technology improvement was over-optimistic.