7 3/8 x 9 1/4 T echnical / Build Your Own Electric Vehicle / Leitman / 373-2 / Chapter 8
Chapter 8: Batteries While lead and sulfuric acid would not be my initial choice for any construction project—one of the heaviest elements mated with one of the nastiest compounds— reliability, performance, and cost all weigh heavily in the lead-acid battery’s favor. In fact, lead-acid’s suitability for so many applications has greatly diminished even the need to search for alternatives. But the recent save-the-environment, reduce-oil-dependency, and let’s-try-electricvehicles changed consciousness altered the pattern. Government, industry, and university laboratories all over the planet reflect this change. Pouring money on a problem never guarantees a solution, but it does guarantee that a lot more will be happening, and that some of what happens will be usable and good. Let’s look at future battery trends starting with the consortium that’s pushing the outside of the battery envelope—the USABC. In 1991, Ford, General Motor, and Chrysler (joined by the Department of Energy and the Electric Power Research Institute) had a better idea—the United States Advanced Battery Consortium (USABC). In short, the Electric and Hybrid Vehicle Research, Development and Demonstration Act of 1976 recognized the need for battery development; the Department of Energy defined and funded it; and the USABC focused the efforts. The near-term result was that a plethora of projects was honed down to just three high-energy battery research areas that could deliver significant vehicle range and power advantages: lithium polymer, lithium metal sulfide, and nickel metal hydride. Some of these batteries are considered the best of the best battery technologies on the market.
Future Batteries: The Big Picture Table 8-5, adapted from an SAE paper, shows the entire story at a glance. Notice that 11 different battery technologies are on the list, and they are not equal. In very general terms, higher energy density and power density are desirable and look easy to do—on paper. Getting both at the same time, along with high cycle-life and low cost in a battery that operates efficiently over a range of temperatures, can be manufactured and supported by infrastructure, and causes no harm to people or the environment, has proven to be a bit more elusive. Notice that none of the batteries developed thus far— even the tried and proved lead-acid battery—even approaches its theoretical specific energy value. We still have a long way to go.
Lead-Acid
The big money involved in the lead acid battery business made some major improvements to the lead-acid batteries of the early 2000s superior to their 1990s counterparts. Along the way to higher specific energy and specific power, lead-acid batteries evolved to add sealed as a regular option. While it is higher in cost, it is less efficient (versus convenience of not watering). The flow-through (the conventional type you’re accustomed to) has improved by greater plate thickness, improved separators, and higher specific gravity electrolyte solution). The other options available are tubular (electrode improvement) and gelled (electrolyte improvement, which I have used in some of the electric vehicles I have worked with).
Nickel-Cadmium
Close on the heels of lead-acid today, this battery type promises to be even better in the future. Its advantages over lead-acid today (less pronounced decrease in capacity under
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