How will the recall shape the future of the lithium-ion battery?

by Isidor Buchmann

Cadex Electronics Inc.
isidor.buchmann@cadex.com
www.buchmann.ca - www.BatteryUniversity.com
Novbember 2006

Longer battery runtimes have been the wish of many consumers. Battery manufacturers have responded by packing more active material into a cell and making the electrodes and separator thinner. This enabled a doubling of energy density since lithium-ion was introduced in 1991.
High energy density comes at a price. Manufacturing methods become more critical the denser the cells become. With a separator thickness of only 20-25µm, any small intrusion of metallic dust particles can have devastating consequences. Sony, the maker of the lithium-ion cells, which are being recalled, says that on rare occasions microscopic metal particles may come into contact with other parts of the battery cell, leading to a short circuit within the cell.

Lithium-ion batteries are nearing their theoretical energy density limit and battery manufacturers are beginning to focus on improving manufacturing methods and increasing safety. David Perlmutter, Senior VP and General Manager of Intel's Mobility Group says, "Right now, the industry is working primarily on improving the manufacturing and reliability of traditional lithium-ion batteries."

The recall is unfortunate. It's a huge task that will have a long-term ripple effect. Economists predict a setback in form of shipping delays and higher battery prices. Recycling 10 million lithium-ion packs is no easy task. The roughly 70 million cells in these faulty packs will need to be replaced. Sanyo is the largest manufacturer of lithium-ion and produces 42 million cells per month. Sony follows second with monthly production of 27 million cells and Samsung is at 26 million.

Battery users will ask, "Are there alternatives to lithium-ion that are safer?" Yes, there are newcomers but experts and industry analysts remind consumers that the traditional cobalt-based lithium-ion powering our laptops and cell phones isn't likely to be replaced soon.

The newcomers are the manganese and phosphate lithium-ion. In terms of thermal stability, these two candidates are superior to cobalt. The cobalt-based cell becomes thermally unstable at 150°C (302°F), a condition that can lead to a thermal runaway in which flaming gases are vented. In comparison, manganese and phosphate can sustain temperatures of up to 250°C (482°F) before becoming unstable.

The manganese system, also know as spinel, has been around since 1996. Low internal resistance and high current loading make these batteries ideal for power tools. The phosphate-based chemistries by Valence Technologies and A123Systems go head-to-head with spinel. They differ from lithium-ion in having a nominal voltage of 3.3V instead of the customary 3.6V.
Although superior in safety and capable of delivering higher load current, manganese and phosphate systems have one major drawback against cobalt: lower energy density. Figure 1 shows the Wh/kg of lead acid, nickel-cadmium, nickel-metal-hydride next to the three lithium-ion chemistries. One can see the soaring energy density of cobalt over other chemistry.

Figure 1: Energy densities of common battery chemistries. Lithium-cobalt enjoys the highest energy density. Manganese and phosphate systems are terminally more stable and deliver high load currents.

Will the fuel cell be a likely replacement?
During the last years, fuel cell technology has gained much hype and many see this power source as the gateway to the future. The fuel cell is not new; Sir William Grove built the first model in 1839. Although ahead of the internal combustion engine then, the fuel cell remained a scientific oddity until the 1950s when this power source was used for US space and military programs for the first time. In the 1980s, the fuel cell had another rebirth when scientists and stock promoters envisioned a world powered by this clean power source, fed by an inexhaustible fuel, hydrogen. They forecasted that cars would be run by fuel cells and households be powered by electricity generated from back-yard fuel cell units. High manufacturing costs and short service life have been in the way of making this a reality.

The fuel cell uses hydrogen and oxygen as fuel. Combining the two gases generates electricity and water. There is not combustion; no pollution. The byproduct is pure water. The system runs so clean that Ballard, a developer of fuel cell stacks, offered the guests tea from the hot water produced by the fuel cell. The theoretical energy output of the fuel cell is high, however, over half is lost in heat.

During the past years, portable versions of the fuel cells have emerged. The most promising miniature fuel cell is the direct methanol fuel cell (DMCF). DMCF is inexpensive, convenient, does not require pressurized hydrogen gas and provides a reasonably good electrochemical performance. Current systems produce 900 Wh of power and offer an energy density of 102 Wh/l. This is still large in size compared to an electrochemical battery and further reductions will be needed. Charging consists of replacing the cartridge on the fly. This provides a continued source of energy, similar to fueling a car.

Toshiba unveiled a prototype fuel cell for a laptop but described the technology as being in its 'infancy.' The company gave no indication as to when the product would be commercially available. A direct battery replacement that offers high power, small size and competitive price is still several years away. Figure 2 shows a DMFC by Toshiba. The micro fuel cell on the left is capable of providing 300mW of continuous power. The fuel is 99.5% pure methanol stored in a 10 mL tank. The refueling process is shown on the right.

Figure 3: Fuel cell powered bicycle lamp. The 21cc cartridge provides the equivalent energy of about 10 AA disposable alkaline batteries. The only by-product is water vapor. The runtime between refueling is 20 hours. Courtesy of Angstrom Power

According to Angstrom Power, the micro hydrogen™ bike lights have delivered good performance in winter and spring conditions and the user feedback is positive. The hydrogen fuel is stored in a 21cc cartridge, providing the equivalent energy of about 10 AA disposable alkaline batteries. The only by-product is water vapor. Refueling takes a few minutes and provides a continuous runtime of about 20 hours.

As good as the fuel cell may look from the outside, 15-years of experiments has not solved a number of persistent problems. One is the slow start-up; another is the low electrochemical activity at the anode. This is especially apparent with the DMCF. Each cell produces about one volt and when loaded, the relatively high internal resistance causes the voltage drops quickly. Figure 4 illustrates the voltage drop as a function of load current. As can be seen, the power band is quite narrow.

Figure 4: Power band of a portable fuel cell. High resistance causes the cell voltage to drop rapidly with load. The power band is limited to about 300-800mA.

Loading is not critical with a small bicycle light, especially when low-drain LED technology is used. A laptop, on the other hand, requires about 40 watts of power and a small fuel cell cannot provide enough output to sustain the demand. The system needs a battery as back up. In essence, the fuel cell becomes a slave to the battery and serves more like a charger. The same applies to a fuel cell-powered cell phones and cameras.

The fuel cell has not seen the same earth-shattering breakthroughs that microelectronics has enjoyed. The Moore's laws don't apply here. The continued struggle is low power, large size, premature aging and high cost. There are also transportation issues that inhibit passengers from bringing fuel on an aircraft. These rules will likely change in the next two years. The ICAO dangerous goods panel (DGP) has already established an exclusion to allow the transport and operation of methanol fuel cells on commercial flights. This same standard will not yet apply to storage of hydrogen gas, however.

Conclusion
When examining alternative power sources, the traditional battery starts to look awfully good. It is small, clean, quiet and provides an instant source of power when needed. Similar to the combustion engine in a car, the battery will be hard to replace with something that offers equivalent energy density and is affordable. An inexhaustible fuel cell would be nice, but for now we are beholden to the old-fashioned electrochemical concept, called a battery. There are no major developments on the horizon that will change the way we use portable equipment and atomic fusion as a potential portable power source hasn't entered the race yet.

About the Author
Isidor Buchmann, founder and CEO of Cadex Electronics Inc., has studied the behavior of rechargeable batteries in practical, everyday applications for two decades. As an award-winning author of many articles and books on the subject, Mr. Buchmann has delivered battery-related technical papers around the world. Cadex is a Canadian company specializing in the design and manufacturing of advanced battery testing instruments. For product information please visit www.cadex.com