Lead Battery Capacitor Hybrid could enable widespread microhybrid cars for 4-10% efficiency boost

CNET – Axion Power International has a developed an advanced lead-acid battery it hopes will attract automakers and grid storage providers. The basic chemistry and components are the same, but the company has an activated carbon negative electrode, a change that leads to better performance over time.

The company is targeting start-stop hybrids in particular. Also called microhybrids, start-stop systems feature a small battery to run a car’s electronics when idle and to aid in accelerating.

Unlike an all-electric car, the fuel efficiency savings from start-stop technology are incremental. Ford, for example, estimates an efficiency gain between 4 and 10 percent for its system.

One of the advantages of Axion Power’s approach is that its technology can be fitted into existing manufacturing lines.

Axion Power – The PbC® battery is a hybrid device that uses the standard lead acid battery positive electrode and a supercapacitor negative electrode that is made of activated carbon. The specific type of activated carbon we use has an extremely high surface area (1500 m2/g) and has been specifically formulated by Axion for use in electrochemical applications.

The full technical description of Axion’s proprietary PbC® technology is a “multi-celled asymmetrically supercapacitive lead-acid-carbon hybrid battery.” Like a lead-acid battery, our battery consists of a series of cells. Within the individual cells, however, our construction is more complex. Where the negative electrodes in lead-acid batteries are simple sponge lead plates, our negative electrodes are five-layer assemblies that consist of a carbon electrode, a corrosion barrier, a current collector, a second corrosion barrier and a second carbon electrode. These electrode assemblies are then sandwiched together with conventional separators and positive electrodes to make our battery, which is filled with an acid electrolyte, sealed and connected in series to the other cells.

We have been testing laboratory prototypes of Axion’s PbC® batteries since April 2004. Our test protocol requires a complete charge-discharge cycle every 7 hours to a 100% depth of discharge. During testing, our laboratory prototypes have withstood more than 2,000 cycles before failure. In comparison, most lead-acid batteries designed for deep discharge applications can only survive 300 to 500 cycles under these operating conditions. Based on the work completed during the laboratory development stage, we believe our application specific prototypes will offer several key performance advantages over conventional lead-acid batteries, including:

* significantly faster recharge rates;
* significantly greater charge acceptance
* significantly longer cycle lives in deep discharge applications; and
* minimal required maintenance.

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