Electro Energy Bipolar Wafer Cell Battery Technology for PHEV Applications

Electro Energy, Inc. (EEI) has developed a bipolar battery utilizing a patented wafer cell design, applicable to both NiMH and Li-Ion chemistries. This battery is particularly suitable for meeting the high-voltage, high- energy demands of modern and emerging plug-in hybrid vehicles (PHEVs). EEI´s battery technology has the potential to provide a rebuttal to the most common argument for not developing and mass-producing PHEVs, which is that presently available battery technologies do not provide sufficient energy density at a low enough cost and in a small enough package to make such vehicles practical. The EEI battery design is such that conventional current tabs, collectors, and inter- cell connections are eliminated, yielding a battery that is smaller and lighter than a comparable non-wafer battery having an equivalent energy density. In addition, the stacked wafer design has lower internal impedance than conventional batteries, allowing for higher discharge rates and less internal heat build-up. The NiMH version of this battery design has already been successfully demonstrated by EEI in the conversion of a Toyota Prius hybrid electric vehicle (HEV) to a PHEV. A next generation PHEV conversion using a Li-Ion wafer cell battery is presently being implemented. This paper will discuss the advantages of the wafer cell design, past experiences and results obtained with the NiMH PHEV conversion, and future expectations for the Li-Ion PHEV conversion.