PbC batteries. PbC batteries are multi-celled asymmetrically supercapacitive lead-acid-carbon hybrid batteries. Like a lead-acid battery, it comprises a series of cells. However, where the negative electrodes in lead-acid cells are simple sponge lead plates, Axion negative electrodes are five-layer assemblies comprising 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 the battery, which is filled with an acid electrolyte, sealed and connected in series to the other cells.

PbC battery. Click to enlarge.

Compared to advanced lead-acid batteries, the PbC batteries:

• Support higher [10-20x] charge acceptance and faster recharge [5-10x] in partial state-of-charge (PSOC) applications;

• Offer an 4x increase in cycle life in 100% depth-of-discharge applications; and

• Sustain 80-85% round trip efficiency in PSOC applications; 90-95% in deep cycle applications.

Compared to Li-ion batteries:

• PbC batteries are more affordable [3x] than lithium-ion or supercapacitors;

• PbC batteries have recycling value at end-of-life [$35/lbs], while Lithium-ion batteries have recycling cost at end-of-life [~$75/lbs].

The high-performance PbC batteries are ideally suited for hybrid locomotive applications due to their high charge acceptance, fast charge and discharge capabilities (important in regenerative braking), and their inherent ability to equalize voltage when utilized in large-string configurations, Granville noted.

That last feature—the ability to self-regulate in large-string configurations—is especially valuable in the NS-999 application, Granville told Green Car Congress.

NS-999. NS originally built NS-999 in early 2009 with lead–acid batteries; however, the lead–acid system consistently failed field testing. NS began working with Axion in October 2009.

They determined that the problem was that the lead-acid batteries were getting out of synch, in terms of charge level. The only way to get them back into synch, said Granville, was overcharging. But overcharging resulted in gassing and dry out and early battery failure.

It was the wrong battery management system and the wrong battery. Our PbC tends to regulate itself. The low batteries in the string will accept more current and bring themselves up to an equalization level without drying out. It is an inherent property within the activated carbon—a U-shaped resistance curve—the less charge in the battery, the smaller the amount of resistance, so it accepts voltage more readily and more quickly that the battery charged with more voltage, which has a higher resistance to it.

We’re not throwing stones or rocks at lead acid battery industry. There are some things it can’t do. One of those is perform uniformly in large strings. Larger strings bring out the problems with lead acid batteries.

—Tom Granville

While Axion has a proprietary battery management system that it uses, for the railroad application and for large-string applications in general, the self-regulation of the batteries works very well, Granville said.

The battery-electric switchers will be charged at wayside charging stations in the yard.

Line-haul. NS’ main emphasis will be the line-haul, over-the-road locomotives, Granville said, which is where the real fuel savings and emissions reduction will accrue. Axion is working with the railroad on its $8B Crescent Corridor project.

The Crescent Corridor is a 2,500-mile (4,023-km) rail network supporting the supply chain from Memphis and New Orleans to New Jersey. NS is making improvements that will enable it to handle more rail freight traffic. These include straightening curves, adding signals, building passing lanes and double tracks, constructing and expanding terminals, and running more efficient trains.

This will include 80 new locomotives, Granville said, although not all will be hybrids.

The basic approach, as described by Granville, is to use a “boost locomotive”—a hybrid locomotive utilized in conjunction with a standard locomotive that would come into play when needed for an uphill climb, and that would recharge via regenerative braking. The topography of a particular line thus becomes critical.

The PbC batteries, with their enhanced capacity for charge acceptance can take on the charge and not have it want over a period of time.

What happens with lead acid is that they develop large lead sulfate crystals. The sulfate starts to grow and develops a rock-like lead crystal structure that doesn’t easily take charge acceptance. This limits the ability of battery to take on recharge. In the case of NS, it would limit the opportunities to take on regen braking. It would also pin the charge level—the amperage level that the batteries could put out—to certain levels that are less than ours.

—Tom Granville

Micro-hybrids. In May, the US Department of Energy (DOE) awarded a $150,000 Small Business Innovation Research (SBIR) Phase I grant to Axion Power to fund a commercialization plan for the use of its PbC batteries in a low-cost, high-efficiency dual battery architecture for micro-hybrid (i.e., start-stop) vehicles. (Earlier post.)

The proposed system uses a very small starter battery, the sole function of which is to start the engine. The PbC battery would run all the electronics in the car. Axion is looking at both a 12V and a 16V application, Granville said. The 16V application fits in the same form factor as the 12V and offers an opportunity to increase the voltage into the vehicle, he noted.

We are also working on the two battery system because the OEMs are also adding more electronics all the time to the vehicles. All of these things that are new put more and more strain on the battery and create the need for the battery to have excess energy.

—Tom Granville

Micro-hybrid testing against VRLA. OEM target is 100 A of dynamic charge acceptance. Source: Axion. Click to enlarge.

Axion has been working with BMW since 2009, and is currently in vehicle testing.

Stationary. Most recently, Axion signed a project-specific Letter of Intent with privately-held Rosewater Energy Group, based in Fort Lauderdale, Florida concerning a strategy to create and market a variety of energy storage and conversion products for the high-end residential market.

The project calls for the incorporation of Axion’s PbC technology into a product package that offers distortion-free secure home power; an ability to store energy from renewable sources and from the electric grid; an ability to sell energy back to the electric grid; an opportunity to protect some, or all, of the residential circuitry and to prioritize these circuits.

The companies, which are also working together to market PowerCubes for other applications, will preview the new array of products for the residential market at the CEDIA EXPO in Indianapolis during the first week of September.

In November of 2011, Axion commissioned a .5 MW/.25 MWh PowerCube. (Earlier post.) The same building block technology is used in the manufacture of smaller cubes, 100 kW all the way down to 10kW. The residential cube is an example of the smaller units, the first of which was completed in June of 2011.

That prototype cube serves as the design cornerstone for the new residential units, and has been housed at Clover Lane since Axion’s test phase began last summer. This 10 kW/12 kWh residential cube will be providing home owners with power quality, uninterruptible power back up, and the ability to store energy from renewable sources such as solar and wind. In addition, the unit has the ability to be grid connected, so that on either a regular, or an occasional basis, a home owner can participate in demand response and/or power curtailment.

The Residential Energy Cube contains all electronics and strings of PbC batteries. These strings are equalized by the PbC’s inherent battery properties and by the proprietary battery management system, Granville said.

This seems like a lot of products for a small company, but it’s the same battery, just in different applications.

—Tom Granville

Resources

• Gerhard A. Thelen (2011) Energy Savings, a Key to Successful Railroading (Presentation at William W. Hay Railroad Engineering Seminar, UIUC)