|100x magnification sketch of the network of foam pores. Pore size may vary by application.|
Firefly Energy (earlier post) has received a US patent for a new carbon-foam lead-acid battery technology that it believes has the potential to revolutionize the existing global lead-acid battery market as well as serve applications such as hybrid electric vehicles and plug-in hybrids.
Firefly contends it can deliver lead-acid battery performance comparable to NiMH, but at about one-fifth the cost, and with greatly reduced weight compared to traditional lead-acid batteries.
As a result, the company believes it can play an important role in accelerating the adoption of hybrid and plug-in hybrid vehicles through cost reduction and availability.
The Firefly battery replaces the conventional lead plates in a lead-acid battery with a lightweight carbon or graphite foam to which the chemically active material—in the form of a paste or slurry—has been applied.
The use of the foam structure increases the interface between the electrodes and the active chemistry; the carbon material resists corrosion and sulfation build-up, reducing weight and delivering a formidable jump in specific power, energy and cycle life. The technology is not limited to use in lead-acid batteries.
Firefly is a spinoff from Caterpillar, which had assigned the problem of pursuing increased performance for lead-acid batteries used by Caterpillar’s product groups to Kurt Kelley, who is now Firefly Energy’s Chief Scientist.
Since Kurt, an accomplished material scientist, had never designed a battery before, his problem-solving approach was unconstrained by the conventional battery wisdom held by lead acid battery technologists.—Edward Williams, CEO and Firefly Energy co-founder
Kelley came up with the idea of using a foam carbon composite to address the corrosion and sulfation issues, and to remove the bottlenecks to achieving the theoretical power of the lead-acid chemistry.
A major restriction to lead-acid battery efficiency is the lack of interface area between the active chemistry and the electrodes. Although the chemistry is theoretically capable of delivering approximately 170 Watt Hours per Kilogram (Whr/kg), lead-acid batteries only average around 30 Whr/kg.
Up to now, achieving a higher surface area within a given lead-acid battery box required the addition of more and thinner lead electrodes. However, lead electrodes corrode, so increasing surface area by putting thinner lead electrodes in the battery increases corrosion and decreases battery life.
Removing the corrosive heavy lead grids and replacing them with a graphite foam addresses both issues (increased surface area and decreased corrosion). Furthermore, the design of the Firefly battery removes one-half to two-thirds of the lead out of the battery.
Firefly Energy is now beginning to promote the use of its foam lead-acid batteries in plug-in hybrid applications. Senior Vice President Mil Ovan most recently made that pitch at the Energy Independence 2020 Summit organized by US Senator Dick Durbin (D-IL) in Chicago.