Design News, May 2013

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Electronics & Test Upgrading Batteries Lead-Acid to Lithium-Ion: Big Challenges But Worthwhile Power and energy density of rechargeable lithium cells is far higher than alternatives. By Robin Tichy, Electrochem Solutions Inc. Source: Electrochem Solutions Inc. B atteries based on lithium-ion chemistry have been in the news quite a lot recently, mostly due to the problems of the Boeing 787 Dreamliner's advanced power system. While the root causes of those problems are still unclear, the reality is that rechargeable lithium-based power has been used very successfully in countless millions of installations, and its use is increasing at a rapid rate. Nearly all of today's smartphones, laptop PCs, and many other consumer products are designed from the start with Liion batteries. Market forecasts differ, as they always do, but they give an idea of the installed base and growth. Frost & Sullivan says the total worldwide market for lithium-based batteries was $11.7 billion in 2012 and will double by 2016; Fredonia Group predicts that the market for lithium-based power for portable devices (nongrid, non-EV/HEV) will group at a compounded annual rate of 9.7 percent between 2011 and 2025. The reason for this growth is simple:The power and energy density of rechargeable lithium cells is far higher than alternatives, such as the long-established sealed lead-acid (SLA) technology. Figure 1 shows the dramatic contrast in energy density by weight and size for the Li-ion family, compared to SLA; it also shows that nickel-cadmium and nickel metal hydride fall between those two types. At the same time, the demands being placed on batteries — in terms of both power consumption and desired run time — are increasing. In addition to their higher capacity, they have lower maintenance requirements compared to SLAs, another significant benefit, and can also tolerate thousands of charge/discharge cycles without degradation. Further, their nominal voltage remains relatively constant (flat) until they are near the end of their rated capacity, which simplifies the design of the powerregulator subsystem. Figure 1: Both gravimetric and volumetric energy densities of Li-ion chemistries are far superior to SLA, NiCd, and NiMH cells; note that the "cloud" of the Li-ion is due to the many available "recipes." The use of Li-ion goes beyond just new designs alone. Due to multiple benefits of the chemistry, they are also being retrofitted into upgrades for both primary and backup power of existing products, including applications in industrial (data loggers, control), military (radios, navigation), and medical (infusion pumps, wheelchairs, ventilators) markets. There are environmental considerations when using leadbased cells. Lithium does not exist as a free element, and thus does not have the waste impact of lead-based cells. Under federal law in the US, used nickel-cadmium (NiCd) and lead-acid batteries must be managed as universal waste, and many states Design News | MAY 2013 | w w w. d e s i g n n e w s . c o m –38– magenta cyan yellow black ES244620_DN1305_038.pgs 05.02.2013 07:02 UBM

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