Generally speaking, a battery is an enclosed store of chemicals that react under controlled conditions to produce an electrical charge. In some batteries, like the common alkaline versions used in toys and flashlights, the chemical process goes one way, and once it 's done, the battery is exhausted. With other kinds of batteries, the chemical reactions are reversible, and a current flowing through them converts the chemicals back to a state where they can again release a charge.
Today's batteries come in several forms and use a lot of exotic components with odd acronyms. Beginning at the common end of the spectrum, the lead acid batteries now used to start the typical car are made up of plates (or electrodes) of lead and lead oxide, with an electrolyte solution of water and sulfuric acid in between. Putting those chemicals in contact with those metals produces an electric potential that can be drawn down as needed. And it's reversible: As the engine sends a current back to the battery, it regains its ability to start the car. Lead acid batteries are cheap, well understood, and generally safe. But they' re too crude to save us: They hold too little energy per unit of weight, take too long to charge, and need to be maintained and replaced regularly. It ' s just about over, in other words, for traditional lead acid batteries.
Alkaline batteries sandwich an alkaline electrolyte between electrodes of zinc and manganese oxide. They' re cheap but not especially powerful and can't be recharged. But they're adequate for toys and flashlights, which until recently accounted for the bulk of the mobile device market. With no reason to pack more power into a smaller space, little research was directed at small, powerful batteries. Then along came the laptop and cell phone, and suddenly the consumer products industry developed a burning, multibillion-dollar need for light, powerful, long-lasting batteries that can be recharged hundreds of times. The result: a wave of progress that might just culminate in the something powerful enough to allow green tech to really take off.
The first new battery model was nickel-cadmium,, or NiCd, with potassium hydroxide as the electrolyte and electrodes of nickel hydroxide and cadmium. NiCds are rechargeable, which makes them acceptable for digital cameras. But they lack the energy density to run a hybrid vehicle. Next came nickel-metal hydride, or NiMH, which is similar to NiCd but replaces cadmium with a hydrogen-absorbing alloy. A NiMH battery has two or three times the capacity of a comparable NiCd, which makes it adequate for the secondary role played by a traditional hybrid vehicle 's battery. But it still lacks the energy density necessary to run a plug-in hybrid or an all-electric car.
This brings us to a battery technology called lithium-ion (Li-ion), with electrodes of lightweight lithium and carbon. Currently the battery of choice for laptops and cell phones, its power-to-weight ratio is better than NiCd and five times that of a conventional lead acid battery. It holds a charge longer and can be recharged more often. As you ' ll recall from the previous chapter, next-generation plug-in hybrids and electric vehicle makers hope to use such batteries in various configurations. But the lithium-ion batteries on the market in early 2007 were far from perfect. For one thing, they tended to burst into flames, which is a problem for laptops but more than a problem at 70 miles per hour on the highway with the kids strapped into the back seat. They also took a lot longer to recharge than a gas tank takes to refill. And they still lacked the power to give an electric car a range comparable to today's internal combustion models. The safety issues in particular caused most major automakers to push their heavily hyped plug-in hybrid introductions back from 2008 to 2010 or later.
But the next generation of Li-ion batteries might do the trick. In late 2007, Nevada start-up Altairnano announced "nanostruc-tured electrodes" that lengthen battery life, increase stability, and— this is very big—allow its batteries to recharge within a few minutes. Indiana-based EnerDel claimed to have a fully functional Li-ion battery pack all ready to go for the hybrid market. And Toshiba announced a "super charge ion battery" that recharges up to 90 percent of its energy in just five minutes and lasts a decade or more. Meanwhile, labs around the world are reporting dramatic progress on both safety and power. Chapter 24 mentions a few of the more promising breakthroughs.
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