Fig 1. The crystal structure of the lithium-ion component of LiFePO2 material can form tunnels or channels that make it somewhat unstable.
Fig 2. Dating from 2008, this hexapod, a.k.a., walking vehicle, employs a LiFePO2 battery for its power source.
Hydro-Quebec, a corporation owned by the Canadian government that generates, transmits, and distributes electricity in Quebec, has entered an agreement with the University of Texas at Austin to employ lithium-ion (Li-ion) technologies researched, developed, and patented by John Goodenough, a professor at the university’s Cockrell School of Engineering. In addition to an undisclosed initial payment, the agreement brings future royalties into the university’s coffers.
The reason for Hydro-Quebec’s commitment is Goodenough’s discovery of a lithium-iron-phosphate (LiFePO2) cathode material that yields much lighter and significantly longer-lasting Li-ion batteries. His developments also provide more layers of safety for end users and are environmentally friendly.
The use of LiFePO2 as a cathode material for rechargeable batteries began as the brainchild of Goodenough and his research group at the University of Texas in 1996. Initially, the material exhibited a longer life cycle plus better thermal and chemical stability than available Li-ion batteries of the day.
On the downside, LiFePO2 batteries tend to have a lower energy density than Li-ion components. For example, the energy density of a new LiFePO2 battery can be approximately 12% to 16% lower than a comparable Li-ion battery. However, this lower voltage and energy density phenomena is offset over time by an intrinsically slower rate of energy loss in comparison to Li-ion components using cobalt or manganese cathodes.
One approach to correct this low electrical conductivity entails reducing the particle size and coating LiFePO2 particles with conductive materials like carbon. Another method involves doping techniques with materials such as aluminum, niobium, and zirconium. These doping techniques are used today in numerous commercially available LiFePO2 batteries.
Another disadvantage of LiFePO2 is its lower electrical conductivity at ambient room temperature. The obvious solution is to operate the battery in higher temperatures. But the optimal operating temperature may not be the best for the circuits the battery is powers.
Other solutions to conductivity versus temperature issues include reducing the size of the LiFePO2 particles or using highly conductive coatings on the interface between the battery and circuit. Conductive coatings enable a boost in conductivity by three to four times. Overall, researchers have found that these doping techniques yield better results, reportedly up to eight orders of magnitude.
One last concern for LiFePO2 is its crystal structure (Fig. 1). Under pressure, the material forms channels or tunnels in the Li-ion portion, which means the structure is unstable.
Thanks to Goodenough and his team, LiFePO2 batteries have been available for some time now. “We knew it was a promising technology, but the market was not ready for it in 1996 when we started on this endeavor,” Goodenough said.
Specifying approximately 2000 charge/discharge cycles, LiFePO2 batteries find employment in cell phones, laptops, MP3 players, power tools, hybrid autos, electric cars, and energy storage in Smart Grid applications.
Back in 2007, Lithium Technology Corp. unveiled a LiFePO2 battery with cells large enough for use in hybrid cars. Another example, from the robotics/vehicle sector, is a hexapod vehicle featured in a 2008 episode of Discovery Channel’s Prototype This (Fig. 2).
Companies holding sublicense agreements to produce/sell LiFePO2 components include Sumitomo Osaka Cement Co. Ltd., Mitsui Engineering & Shipbuilding Co. Ltd., Tatung Fine Chemicals Co., and Advanced Lithium Electrochemistry (Cayman) Co. Ltd..
And the future is looking even brighter. For one, iron and phosphate are less expensive than cobalt. Second, since it appears that LiFePO2 is non-toxic and therefore less expensive to handle than lithium cobalt dioxide, it is obvious to see why Hydro-Quebec is anxious to get its hands on this technology—and the University of Texas can’t wait to get its hands on the royalties.
The University of Texas