Lead-Carbon batteries are a possible game changing energy storage technology. The Economist published an article about Axion Power International (AXPW.OB) titled “Lead-acid Batteries Recharged” and Sandia National Laboratories released a report detailing side-by-side testing of lead-acid, lead-carbon and Li-ion batteries.
A conventional lead-acid battery is a simple affair, made up of a series of cells each containing a positive electrode made of lead dioxide and a negative electrode of metallic lead. These are immersed in an electrolyte of dilute sulphuric acid.
In Axion’s battery the negative electrode is replaced with one made from activated carbon, a material used in supercapacitors. Normal capacitors—those that power the flashguns in cameras for instance—can be charged and discharged rapidly, but cannot store much energy. Supercapacitors are meatier versions that are able to hold a reasonable amount of energy as well as taking it in and releasing it quickly. Some, indeed, are already used in tandem with the lithium-ion batteries in electric cars to boost acceleration and recapture energy during so-called “regenerative” braking. Axion’s plan, therefore, is to have the best of both worlds by building a lead-acid/carbon hybrid, or PbC.
The primary goals of lead-carbon research have been to extend the cycle lives of lead-acid batteries and increase their power. Basically, developers start with conventional lead-acid chemistry and add carbon components to the negative electrodes. While the carbon components increase specific power and reduce a chemical reaction called “sulfation” that occurs during charging cycles and is the principal reason ordinary lead-acid batteries fail. Lead-carbon batteries are different from other types of batteries because they combine the high energy density of a battery and the high specific power of a supercapacitor in a single low-cost device.
Over the last several years, lead-carbon researchers have followed three different development paths:
the following graph highlights the magnitude of the cycle-life improvements that lead-carbon technologies offer today.
This Sandia graph is the first time I’ve seen independent comparative test data for advanced lead-acid technology, advanced Li-ion technology and emerging lead-carbon technology on the same page. Since it’s coming from Sandia I have no reason to suspect a technology bias.
In addition to the cycle-life data represented by the colored lines, the Sandia graph provides parenthetical power data expressed in terms of “C rates;” a measure of the time required for a battery to deliver its stored energy. For example, if a 10-volt battery has a nominal 100 Amp-hour rating, it can theoretically deliver 500 watts for two hours at a 0.5 C rate; 1,000 watts for one hour at a 1 C rate; 2,000 watts for a half hour at a 2 C rate; or 4,000 watts for 15 minutes at a 4 C rate. Historically, lead-acid batteries have had C rates of less than one while higher C rates have been the exclusive province of supercapacitors and premium-priced battery chemistries.
As the Sandia graph shows, they began testing the lead-carbon Ultrabattery at a 1 C rate, doubled the power and tested at a 2 C rate and then doubled the power again and tested at a 4 C rate. By the time the testing was completed, the Ultrabattery had survived more than 17,000 cycles at increasing C rates. This is just one series of tests, but it provides irrefutable proof that lead-carbon is re-writing the rules when it comes to both cycle-life and battery power.
A 10-fold improvement in the performance of any technology is by definition highly disruptive. The fact that lead-carbon achieved these disruptive performance gains using cheap and plentiful raw materials that are readily available from domestic sources and easily recyclable for use in new batteries using existing infrastructure is an absolute game changer; particularly when the closest comparable technology is based on expensive imported raw materials that are not easily recyclable for use in new batteries using existing infrastructure.
Li-ion technology can be a problem because it requires expensive imported raw materials, the bulk of the global manufacturing base is in Asia, the batteries are far too expensive for large-scale energy storage systems and there are many alternative uses for Li-ion batteries that are largely insensitive to battery prices
The best lead-acid batteries are more than adequate for many emerging energy storage applications and a new generation of advanced lead-carbon batteries will change the landscape dramatically. The Sandia graph is the first independent confirmation, but more information will become available as the lead-carbon battery developers complete their testing and introduce commercial products to the market.
Normal lead-acid starter batteries do not compete well against Li-ion in terms of cycle-life or power. However the picture changes dramatically when you realise that lead-carbon batteries are expected to offer comparable cycle-lives and power for about 40% of the cost of Li-ion. Li-ion is the only rational choice for portable electronics, power tools, electric bicycles and hybrid scooters.
There is also little doubt that Li-ion will be the battery of choice for sleek packaging, size and weight. However, when it comes to large-scale energy storage applications like HEVs and utility support installations, size and weight are simply design issues. They are not mission critical constraints that justify paying a 150% premium for similar performance.
In another project, called Power Cube, Axion is putting banks of its PbCs into a shipping container, which can then be used as a mobile energy-storage system that can supply up to 1MW of power for 30 minutes or 100KW for ten hours. Power Cubes could help deliver power to local electricity grids that might otherwise suffer “brownouts” as a consequence of demand temporarily exceeding supply. They might also provide an answer to the problem of matching the supply of solar and wind energy to the demand for electricity, by storing electricity during the day, or during particularly windy periods, so that it is available at night, or during periods of calm.
In the early days of an industrial revolution, function is more important than form and fundamental economics drove the mass market to the cheapest solution. There is no reason to believe the renewable energy revolution will be any different. Lead-carbon batteries are game changers for alternative energy storage.