|The PowerGenix 120-cell 1.2 kWh HEV pack sitting atop the larger NiMH pack in a Prius.|
PowerGenix, a San Diego-based developer of high-performance, sealed rechargeable nickel-zinc (NiZn) batteries for power tools and other applications, introduced its rechargeable D cells for hybrid electric vehicles (HEVs) this week at the Advanced Automotive Battery and Ultracapacitor Conference in Tampa, Florida. (Earlier post.)
The 6.5 Ah, 1.6V NiZn D cells offer energy and power densities of 100 Wh/kg and 2,500 W/kg in their first generation, according to PowerGenix CEO Dan Squiller, with more room for improvement in subsequent iterations. NiZn packs can deliver 30% more power and increased energy density, as well as reduced size, weight and cost relative to existing Nickel Metal-Hydride (NiMH) technologies.
The company brought a Toyota Prius retrofitted with a 120-cell, ~1.2 kWh NiZn battery pack to highlight the size and weight savings of PowerGenix’s technology to the AABC event.
Early NiZn batteries (first developed in the 1920s) suffered from short cycle life due to dendrite growth leading to short circuiting, caused by the high solubility of zinc oxide—a discharge product of the zinc anode in the alkaline electrolyte. In addition to dendrite formation, zinc oxide solubility can result in shape change and densification of the anode on repeated charge/discharge cycles.
The basis of PowerGenix’s approach to making its NiZn battery commercially viable is a patented electrolyte formulation that reduces zinc solubility and prevents the dendrite shorting and shape changing problems. Further enhancement of cell capability is due to cathode and anode materials that are free of any heavy metal elements.
In addition to addressing the cycle life problems, PowerGenix’s approach allows the NiZn cells to be manufactured on existing NiMH and NiCd lines—a considerable advantage considering the on-going investment in NiMH production being made.
The NiZn battery pack is easily integrated into existing hybrid control systems—the battery’s operational state of charge range is approximately the same as that of NiMH.
With a power density that can compete with some Li-ion chemistries, the NiZn cells have none of the Li-ion thermal safety issues; with the inorganic KOH electrolyte, there is no thermal runaway. NiZn is also about half the cost of Li-on technology, according to Squiller.
Despite the ongoing advancement in Li-ion technologies, vehicle applications are just beginning (with the exception of the Li-ion stop-start system in the low-volume Toyota Vitz in Japan) in 2009. As a result, NiMH is still anticipated to have a significant automotive presence in hybrid applications for a number of years.
Squiller suggests that the automotive battery market will segment over the next few years, with the rapidly scaling Li-ion systems supplying energy storage solutions for very high energy applications (PHEVs and EVs and some upper-end full hybrids) at high consumer cost. NiMH—or, in PowerGenix’ scenario, NiZn—will continue to serve the more economical, lower-end hybrid vehicles with lower energy requirements but still demanding power requirements.
PowerGenix plans call for licensing its technology to one of the major NiMH battery manufacturers, such as Sanyo. “Better chemistry and better cell design basically is just an ante to get to the table,” said Squiller, noting that selling into the automotive market requires the participation of a major manufacturer with quality processes, global logistics and a worldwide supply chain.