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Study finds flooded lead-acid battery performance & cycle life increased by adding dCNT to PAM and NAM; benefit for start-stop

Researchers with Molecular Rebar Design report that the addition of discrete carbon nanotubes (dCNT), which they call Molecular Rebar, to both the positive and negative electrodes (Positive Active Material, PAM and Negative Active Material, NAM) in conventional flooded lead-acid batteries results in: little change to reserve capacity; improved cold cranking, increased charge acceptance, and enhanced overall system efficiency. The company had earlier reported on the impact of dCNT addition primarly to the negative electrode. (Earlier post.)

Life cycle tests show >60% increases when dCNT are incorporated into the negative electrode and up to 500% when incorporated into both electrodes, with water loss per cycle reduced >20% (High-Rate Partial State of Charge, HRPSoC and SBA S010 idling start-stop testing). A paper describing the study and the results is published in an open access paper in the Journal of Power Sources.

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Effect of dCNT on Basic Battery Performance Parameters. (A) Reserve capacity tests (25 A discharge until voltage < 10.5 V) show batteries containing dCNT perform similarly to Control batteries. (B) Cold-cranking, durational tests (270 A discharge until voltage < 6 V at -18 ˚C) show improvement when dCNT is incorporated at the negative electrode and a greater improvement when incorporated in both electrodes. (C) Cold-cranking, voltage tests (270 A discharge at -18 ˚C, voltage read at 30 s) show little change between batteries containing dCNT and controls. (D) The cumulative charge factor shows batteries containing dCNT in the negative electrode or the negative and positive electrode absorb >15% more energy and pass >4% more charge than dCNT-free controls. Sugumaran et al. Click to enlarge.

In order to meet the demands of modern lead acid battery applications, the technology must provide higher levels of charge acceptance to boost system efficiency and delay common failure mechanisms such as sulfation or dendritic growth. For example, in the modern automobile, advanced systems such as navigation, heating, and air conditioning can increase electrical energy consumption beyond that which the alternator can replenish during normal vehicle operation. The battery system therefor operates at a detrimental energy deficit. In order to maintain batteries at higher states of charge and avoid irreversible sulfation, modern applications demand increased charge acceptance. As a second example, batteries operating in hybrid-electric automobiles as well as some grid storage applications must be able to effectively accept charge in quick, high-current bursts or risk negative electrode passivation. If these challenges can be surmounted, lead acid batteries will remain competitive with other chemistries in the automobile, storage, and telecom markets, amongst others.

—Sugumaran et al.

As one approach to address these issues, carbon has been added to the NAM during paste preparation in a variety of forms including carbon black, activated carbon, graphite and carbon nanotubes. Carbon additives have been found to increase the charge acceptance of a battery by more than 200%—but at the cost of paste rheology and paste density. Reductions in paste density directly lead to decreased active material adhesion to the grids, decreased battery capacity which requires higher active material masses to reach specification, and insufficient cold-cranking performance, the authors note.

Further drawbacks include the need for new paste processing machinery, and the potential introduction of gas-evolving impurities into the electrode. If the carbon additive is particularly high in iron residuals remaining from its production, for example, gas evolution and water loss will increase, leading to premature battery failure.

Molecular Rebar’s dCNT are cleaned, functionalized, individualized, multi-walled, carbon nanotubes which are easily incorporated into battery pastes as a concentrated, pourable fluid. The fluid replaces a portion of the water used during the paste mixing process, requiring no alteration to existing industrial production lines.

In this latest study, the researchers incorporated dCNT into the negative electrode or both the negative and positive electrodes and compared the resulting batteries to dCNT-free control batteries across various performance metrics including pasting properties; basic performance (formation, reserve capacity, and cold temperature performance); advanced performance (polarization and triple electrode studies); gassing; cycle life (HRPSoC and SBA models); and battery failure mechanisms.

Of particular note for start-stop/micro-hybrid applications, the team found in HRPSoC testing that the baseline batteries did not complete 4000 cycles before reaching the End of Discharge (EOD) voltage limit (10.38 V). Batteries incorporating dCNT in the negative electrode reached 4000 cycles well before 10.38 V. Moving beyond the parameters of the test, the researchers removed the 4000 cycle limit for the second round of cycles and found that the battery containing dCNT achieved a further 6648 cycles before reaching the EOD limit.

In the more aggressive Japanese SBA S0101 testing, dCNT boosted the performance of simple, flooded automotive battery to performance levels usually only reached by those advanced batteries. Incorporation of dCNT into the negative or negative and positive electrodes allowed a battery to reach 9999 or 35300 cycles, respectively. When compared to the control battery reaching 5883 cycles, this represented a 60% or 500% increase in lifetime.

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Effect of dCNT on Cycle Life, SBA S0101. (A) Discharge voltage curves retrieved from single batteries containing dCNT in various electrodes is shown with the 6.0 V limit indicated. Addition of dCNT to the negative electrode results in increased cycle life, but a larger effect is observed in batteries with dCNT in both electrodes. (B) Charging voltages of each battery are shown. (C) Data showing average cycle life of 3 batteries as horizontal bars with vertical bars drawn to encompass all data. Sugumaran et al. Click to enlarge.

To explain the observed performance, the authors introduce a new hypothesis: the dCNT/Had Overcharge Reaction Mechanism.

At its core, our hypothesis posits that the surface of dCNT could act as a transient storage medium for adsorbed hydrogen (Had). A quickly-mobilizable supply of high-powered reducing agents, such as these Had, could explain many of our observations regarding the performance of dCNT in the negative electrode of lead acid batteries. In the positive electrode, where hydrogen production is thermodynamically disfavored, dCNT may be fulfilling a different function, potentially one involving mechanical or material strength improvements as opposed to electrochemical enhancements.

… In these ways, transient hydrogen adsorption could explain all of our reported results. Although other CNT may be capable of performing some of these roles, only dCNT are capable of performing them uniformly, and completely, across the entire electrode so that the entire lead matrix feels their effect, even at low dCNT loading concentrations (0.16%). The quality of the dCNT dispersion through the matrix is fundamental to our interpretation of our dCNT/Had Overcharge Reaction Mechanism. The dCNT/Had hypothesis is far from proven, requiring significant research and fine tuning before more general acceptance. A full investigation of the hypothesis, supported with appropriate experimentation and analysis, will be the subject of our next report.

—Sugumaran et al.

Resources

  • Nanjan Sugumaran, Paul Everill, Steven W. Swogger, D.P. Dubey (2014) “Lead Acid Battery Performance and Cycle Life Increased Through Addition of Discrete Carbon Nanotubes to Both Electrodes,” Journal of Power Sources, doi: 10.1016/j.jpowsour.2014.12.117

Comments

Kellydorsey8

"Life cycle tests show >60% increases when dCNT are incorporated into the negative electrode and up to 500% when incorporated into both electrodes, with water loss per cycle reduced >20% (High-Rate Partial State of Charge, HRPSoC and SBA S010 idling start-stop testing)."

This is massive if economic and true.

Engineer-Poet

This harks back to the Firefly Energy carbon-foam battery, where the lead was only used as active material rather than the main structure and electrical connection too.  It's a different form of carbon, but the principle appears to be the same.  If the amount of lead per battery can be cut, so much the better.

It would be interesting to see an analysis of how this would affect the battery performance in electric bicycles and scooters.

CheeseEater88

Basically, if true, would make all automotive starter batteries maintenance free, this could help bury the cost of going to a 48v micro hybrid setup / stop start

mahonj

Could also be great for off grid systems if the 500% increase in life cycle is realised in normal operation.
Then it comes down to cost of production and recycling etc.
Lead acid batteries are a bit heavy for EVs (!) but could be fine for micro hybrids and stop/start, and domestic storage.

Imagine what the Germans could do with their solar if they could store even half of it till later on in the evening.

Ditto for small off grid systems in the developing world.
Solar has got really cheap, but it really needs storage to get the best out of it, and this might be it.

kalendjay

All for the same additional cost as nanomaterials in cosmetics, I think. But sez here that hydrogen adsorbtion could be the key. If that's the case, lead-fiberglass electrodes might be an avenue for research, since they might cut the lead and the weight out of batteries.

HarveyD

Amazing to see how old technologies like ICEVs and Lead batteries can be improved to better compete against newer technologies and extend effective life duration.

Fortunately, it will only delay the massive arrival of new technologies by a few year.

SJC

"discrete carbon nanotubes"
No mention of the cost to make those in quantity.

Harvey,

I don't think the intent is to delay anything.
Cellulose ethanol is not an attempt to delay EV adoption.
There is no grand conspiracy to delay EV sales,
they don't sell a lot for several reasons.

HarveyD

Why 120 plus years were required to significantly improve lead batteries and ICEVs?

Did the arrival of better LION batteries, HEVs, PHEVs, BEVs and FCEVs have something to do with it?

The arrival of new improved technologies normally put pressure on old existing technologies to improve to try to maintain market share.

That is going to happen with Lead batteries, HEVs, PHEVs and ICEVs in their fight to survive?

Henry Gibson

There are several old patents about incorporating carbon forms in lead batteries. Firefly batteries with negative carbon foam can now be purchased in the US and India and reduce greatly the sulphation of negative plates. EFFPOWER and ATRAVERDA, both disappeared, reduced lead and increased current flow by the use of bipolar plates with no need for cell connectors. EFFPOWER was designed to replace Toyota type hybrid batteries with high power low capacity. Atraverda eliminated much lead structure with ceramic titanium conductor.

Most of the active volume of a lead battery is the electrolyte; it represents about seven times the lead active material volume. Foam electrodes with the lead active materials attached to the internal foam surfaces in a very thin layer and the electrolyte fully contained in the foam is a very good way to build a high capacity lead battery with long life. A long available but little known form of carbon, glassy carbon, greatly resists electrolytic destruction and might be available for use. Replacing much of the present lead plate structure with high conductivity graphite or other fibers for strength and conductivity would reduce the weight and increase life and power of lead batteries. The ZEBRA battery also now available as the GE DURATHON could be a permanent part of a modern automobile for increased capacity along with a low capacity high power lead battery or even L-ION. A new flywheel from Ricardo for starting and braking could also eliminate the lead battery use with the Durathon. The present high cost of automobiles allows durathon units to be installed as a low percentage of the price and can be charged from grid. They are not suited for use where not connected to the grid every few days or used every day. They were used in european TH!NK vehicles. They have a life of as much as twenty years; capacity similar to L-Ion and use cheap common materials for construction. Cells still working from failed automotive units can be reused as stationary solar energy storage units after 20 years or less. New nickle iron batteries are now available but require more cost and maintenance but have infinite life. ..HG..

Henry Gibson

Even though Artemis got involved a few years back in tilting at windmills, They have continued to work with their very efficient digitally activated hydraulic motors and pumps which can reduce fuel consumption in city automobile driving to one half without reducing engine size and even more with reduced engines or the NOAX digital free piston engine. Highway driving uses only 70 percent of the fuel. This is without expensive batteries or motors and motor electronics. Artemis with Bombardier and Ricardo are about to test partial hydraulic drive and flywheel energy recovery braking on Diesel passenger trains. Artemis has demonstrated a partial hydraulic bus. Hydraulic Artemis transmissions in windmills eliminates gear wear, power electronic frequency converters and expensive heavy generators. Perhaps the Netherlands will now use Artemis technology to build drainage pumps that use wind energy directly again without conversion to electricity.

No new batteries, fuel cells, electronic drives or biofuels are needed to reduce transportation fuel consumption by at least 30 percent and perhaps as much as 60 percent with digital engines too. Air chambers and flywheels can now give all the acceleration most humans can withstand in an automobile with only a very small engine or even turbine for long range and cheap paraffin or diesel fuel and low maintenance cost. Turbines eliminate all objections to diesel fuel.

Riccardo and Artemis technology allows the use of Bladon or Capstone air bearing turbines in automobiles without the use of large electric motors and generators and electronic power convertors. Turbines have automatic cleaner emissions and eliminate engine oil and cooling systems which can combine with 50 percent fuel reduction and lower cost vehicles and maintenance. ..HG..

Brotherkenny4

These are not deep cycles. This is starter battery cycle tests. When they can make lead acid do 6000 deep cycles I'll be impressed. Start-stop is a low tech attempt at partially solving our enslavement by the oil industry, but it not a real solution. Over a hundred years and now some minute improvements. I guess when you have a huge market for a product that breaks down regularly and customers who willingly pay whatever you ask, you don't really want technical improvement.

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