The olivine crystal structure of LiFePO4 results in an improved discharge process compared with those of other lithium structures. Source: STL Life Power

"Batteries not included." Remember when those words, printed on the side of a box, could quickly deflate your enthusiasm for a shiny new toy? As we got older, our high-tech "toys" got more complex and impressive. But the batteries that powered them stuck to the same basic formulations, with their insufficient power densities, limited life span, relatively high replacement costs and environment-fouling disposal issues.

Or did they?

Smart grids, hybrid cars and renewable energy sources are the high-profile darlings of the green movement, but behind the scenes, chemists and engineers are working hard to reduce the lowly battery's ecological footprint. Recent spins on nickel- and lithium-based battery chemistries, such as nickel oxyhydroxide, olivine-type lithium iron phosphate and nanowires, are gunning to displace the venerable but problematic alkaline-manganese dioxide formulation in the AA sockets of tomorrow's gadgets.

Nickel oxyhydroxide (NiOOH or NiOx) batteries have been on the market for a number of years. They are similar to alkalines but use a nickel-based cathode to produce a higher voltage (1.7 V, vs. 1.5 V for alkaline equivalents).

NiOx batteries typically excel in high-drain applications (for example, digital cameras or portable gaming units), where they are claimed to offer twice the life of equivalent alkaline batteries. In low-drain applications such as remote controls, however, the life span of a NiOx battery is similar to that of an alkaline equivalent.

Sony recently became the first company to commercialize a lithium-ion variant, developed by American researchers, that uses olivine-type lithium iron phosphate (LiFePO₄) as the cathode. Sony uses the new cathode material in combination with a proprietary particle-design technology that's said to minimize electrical resistance, to achieve a rechargeable battery design with a 3.3-V output, 1,800-W/kg power density and long life span, retaining more than 80 percent of its capacity after 2,000 charge/discharge cycles. The battery offers fast charges (achieving 99% of full charge in 30 minutes) and maintains stable voltage discharge when in use.

The Sony battery is being used in some of the company's power tools and has gotten positive reviews from those who have tested it in action.

The first LiFePO₄ technology patent was awarded in 1996 to John Goodenough and his team at the Uni- versity of Texas. LiFePO₄ was developed as a solution to the low discharge rate and short cycle life of other lithium-ion cell structures, such as lithium cobalt oxide and lithium manganese oxide.

LiFePO₄ is a highly stable material that scientists believe can serve numerous consumer applications, from rechargeable batteries for products like mobile phones and gaming units to larger-scale applications such as electric vehicles (Chevrolet's upcoming Volt uses a 220-cell Li-ion battery).

The olivine crystal structure of LiFePO4 results in a smaller crystal lattice deformation than occurs with other battery structures, enabling an improved discharge process. As a result, the cycle life of the material is extremely long, and LiFePO4 demonstrates an excellent shelf life when not in use. It can withstand oxidation and acidic environments.

From a battery safety standpoint, the cell structure of LiFePO₄ remains stable under extremely high temperatures, from 300°C to 500°C, and it can withstand a maximum of 700°C. At such temperature extremes, other lithium batteries begin to disintegrate and can potentially explode.

Proponents of LiFePO₄ point to the potential environmental benefits of faster-charging, longer-lived battery technologies. And the possibilities for LiFePO₄-based electric car batteries that would cover more miles between charges might garner interest from car makers looking to compete with the Volt.