<< Previous page INDEX Next page >>
Introduction
During the last few decades, rechargeable batteries have made only moderate improvements in terms of higher capacity and smaller size. Compared with the vast advancements in areas such as microelectronics, the lack of progress in battery technology is apparent. Consider a computer memory core of the sixties and compare it with a modern microchip of the same byte count. What once measured a cubic foot now sits in a tiny chip. A comparable size reduction would literally shrink a heavy-duty car battery to the size of a coin. Since batteries are still based on an electrochemical process, a car battery the size of a coin may not be possible using our current techniques.
Research has brought about a variety of battery chemistries, each offering distinct advantages but none providing a fully satisfactory solution. With today’s increased selection, however, better choices can be applied to suit a specific user application.
The consumer market, for example, demands high energy densities and small sizes. This is done to maintain adequate runtime on portable devices that are becoming increasingly more powerful and power hungry. Relentless downsizing of portable equipment has pressured manufacturers to invent smaller batteries. This, however, must be done without sacrificing runtimes. By packing more energy into a pack, other qualities are often compromised. One of these is longevity.
Long service life and predictable low internal resistance are found in the NiCd family. However, this chemistry is being replaced, where applicable, with systems that provide longer runtimes. In addition, negative publicity about the memory phenomenon and concerns of toxicity in disposal are causing equipment manufacturers to seek alternatives.
Once hailed as a superior battery system, the NiMH has also failed to provide the universal battery solution for the twenty-first century. Shorter than expected service life remains a major complaint.
The lithium-based battery may be the best choice, especially for the fast-moving commercial market. Maintenance-free and dependable, Li-ion is the preferred choice for many because it offers small size and long runtime. But this battery system is not without problems. A relatively rapid aging process, even if the battery is not in use, limits the life to between two and three years. In addition, a current-limiting safety circuit limits the discharge current, rendering the Li-ion unsuitable for applications requiring a heavy load. The Li-ion polymer exhibits similar characteristics to the Li-ion. No major breakthrough has been achieved with this system. It does offer a very slim form factor but this quality is attained in exchange for slightly less energy density.
With rapid developments in technology occurring today, battery systems that use neither nickel, lead nor lithium may soon become viable. Fuel cells, which enable uninterrupted operation by drawing on a continuous supply of fuel, may solve the portable energy needs in the future. Instead of a charger, the user carries a bottle of liquid energy. Such a battery would truly change the way we live and work.
This book addresses the most commonly used consumer and industrial batteries, which are NiCd, NiMH, Lead Acid, and Li-ion/polymer. It also includes the reusable alkaline for comparison. The absence of other rechargeable battery systems is done for reasons of clarity. Some weird and wonderful new battery inventions may only live in experimental labs. Others may be used for specialty applications, such as military and aerospace. Since this book addresses the non-engineer, it is the author’s wish to keep the matter as simple as possible.