A breakthrough technology that provides carbon nanotubes as they were intended: clean, individualized and free from clumping is finally delivering on the promises of these innovative structures. Immediate benefits are seen in improving the design and performance of lead-acid batteries.
More than 25 years ago, carbon nanotubes were hailed for their theorized potential of boosting the performance of engineered materials in a broad range of commercial applications. The excitement cooled down when it was found that the common fluid bed reaction processes of producing the tubes resulted in highly entangled nanotube clusters that seemed impossible to disentangle and also showed a tendency to retain high residual impurities. Importantly, the fuzzy clusters prevented the effective dispersion of the tubes in their intended material, thus greatly compromising their use and significance.
Game-Changing New Technology
A new technology, globally patented over the past few years and commercialized as MOLECULAR REBAR® (MR), has emerged as a game changer in the field of nanotechnology. The MR process enables the continuous production of disentangled, clean and discrete carbon nanotubes (see Fig. 1) which can then be custom-tailored formulations for ease of use in various materials.
The proprietary technology is believed to offer an enormous potential for enhancing the performance of energy storage applications and is currently being investigated by various battery manufacturers, world-wide.
More than just an additive, these nanotubes provide significant benefits in terms of battery manufacture, performance, and life. The “Rebar” in Molecular Rebar stands for Reinforcement, creating a conductive and strengthening network on a nanoscale level deep inside the active mass of the battery plates. It nano-connects the lead and carbon particles, resulting in tighter and deeper pore structures for enhanced durability. It also provides a consistently greater granular sulfation. All this can significantly reduce the effective lead input required to meet battery specifications while requiring only a very small MR content of typically less than one gram per battery. Since about 75 percent of the cost of a lead-acid battery is associated with lead, this means that battery manufacturers will be able to capitalize on the new technology immediately.
Unique Properties Backed by Comprehensive Testing
In essence, the nanoscale MR reinforcement brings the active material together and enhances the robustness of the battery plate structure. By nano-wiring all the lead particles, it improves the nerve level of the system and makes it stronger. In addition, the nanotubes alter the crystal packing to enhance the surface area and modify the pore structure for better charge acceptance. Notably, they also restrict the growth of sulfate crystals, making it easier to dissolve them again for more consistent battery recovery.
Immediate applications under evaluation are next-generation lead-acid batteries for use in automotive and other mobility segments, including both starter and deep-cycle batteries. Tests have shown that Molecular Rebar carbon nanotubes may help at least double the cycle life of a typical lead-acid battery, while helping manufacturers downsize new battery designs, reduce battery production costs, increase output and achieve higher economies of scale. Similar benefits are expected from the use of MR in lithium-ion batteries and markets beyond energy storage.
As with any new technology, thorough testing is key to acceptance. The BDS Battery Lab (Fig. 2) in Austin, Texas, is fully equipped to provide a comprehensive evaluation of MR activity in a battery for prospective customers as well as internal researchers. It is capable of evaluating and confirming battery performance as specified by any of the world’s leading specification-setting agencies as well as proprietary or in-house protocols, including failure mode analysis, on-site customer support and joint field trials build further confidence in the unique MR nanotube properties. Currently, BDS regional teams are actively collaborating with more than 160 customers world-wide at various stages along the value chain.
Significant Benefits in All Types of Lead-Acid Batteries
Available in 10 liter jugs, 200 liter drums and 1,000 liter totes, the discrete carbon nanotubes are supplied in pourable liquid form to facilitate their uniform incorporation into the battery paste. As functionalized and open-ended carbon nanotubes, they offer optimum aspect ratios, enabling exceptional improvements in mechanical strength and electrical performance. Data shows enhanced charge acceptance, cold-cranking performance, and increased cycle life under normal duty and high rate partial state of charge.
The market of lead-acid batteries can be differentiated into four major segments, each characterized by a number of particular challenges to meet apart from enhanced performance levels:
- Flooded automotive starter batteries, requiring longer lifetimes, lower warranty costs and reduced lead content for net cost reductions
- Sealed auto/motorcycle batteries with improved consistency in capacity and cold cranking amps throughout life as well as extended cycle life and reduced warranty failures
- E-mobility batteries providing shorter recharge times, higher reach and lower water consumption
- Stationary solar energy accumulators with longer life, shorter recharge times and lower water consumption
Molecular Rebar can make a significant contribution to meeting all these requirements in higher-performing lead-acid batteries. Compared to advanced carbon additives, Molecular Rebar-based products show superior mixing properties with the water, acid and lead of battery pastes mixes.
Moreover, they can be used alongside carbon, expanders or other solutions to provide further functional or even corrective benefits. By creating a network of nanotubes, they add lasting strength and durability to the plates.
These potential advantages apply to all types of lead-acid batteries, from starting, lighting and ignition to deep cycle batteries, from valve regulated designs, including sealed, absorbed glass mat and gel cell technologies, to lead-calcium and lead-antimony modified alternatives. One particular application segment where the use of MR can greatly help solve performance challenges is modern start-stop engines which drain a lot of battery energy.
Battery Downsizing without Compromising Performance
Pilot projects and case studies with selected customers have confirmed the effective and efficient feasibility of the MR technology in lead-acid batteries. The discrete carbon nanotubes can easily be incorporated in existing battery manufacturing processes without requiring additional capital costs of modifications. Overall, the technology has shown to enable batteries that charge much faster and last much longer than non-dCNT solutions.
One particular issue that was addressed in a field test with more than 20.000 batteries over a period of 12 months was the failure rate of flooded batteries for heavy-duty trucks. Market research had shown a troublesome 10 percent battery warranty rate with trucks operating in “super hot” climate areas. After implementation of Molecular Rebar technology, the failure rate due to over-charge or water loss decreased 80 percent, and total warranty returns were cut in half to < 5%.(Fig. 5).
Likewise, in a customer case study investigating the life of motorcycle batteries it was found that the maximum number of charge cycles before failure can be raised from typical 5,000 to over 10,000 when using dCNT technology, while at the same time reducing battery formation time by 25 percent. Another Molecular Rebar project with a leading European battery manufacturer resulted in a significant performance increase, especially with regard to charge acceptance, of batteries designed for automotive start/stop systems.
Furthermore, a heavy truck battery downsizing study also revealed that the battery design itself can be improved by leveraging the benefits of Molecular Rebar to remove active mass with only minimal design changes required. Apart from saving weight and volume, customers managed to reduce their net manufacturing cost by up to 10 percent without compromising battery life performance in accordance with SAE J2185. Design validation of after-market 110 Ah product lines with only 8 instead of 9 plates on the negative and positive sides is in progress.
Next to automotive starter batteries, which are designed to provide a very large amount of current for a short period of time without being discharged below 50 percent, dCNT technology has an equally attractive fit in deep cycle lead-acid batteries for e-drive applications. Examples span from forklift trucks and golf buggies to small watercraft, which need steady amounts of currents and normally consume up to 100 percent of battery power before recharging. Carbon nanotubes may also help reduce the size and weight of these deep cycle batteries, which normally have considerably thicker plate grids than starter batteries.
Similar performance and design benefits are expected to materialize in the field of lithium-ion batteries for e-mobility. Beyond energy storage, Molecular Rebar offers further potential in innovative material science, for instance by enhancing the properties of specialty resins and functional compounds.
Breakthrough nanotechnology commercialized by SABIC Specialties’ Black Diamond Structures is opening a wide window for higher-performance and cost saving next-generation lead-acid batteries in automotive engineering and other mobility markets. The company’s proprietary manufacturing process produces discrete carbon nanotubes that eliminate the clumping issues associated with conventional carbon nanotube production, helping manufacturers unlock significant improvements in battery life, performance, design and manufacturing efficiency.
Molecular Rebar® discrete carbon nanotubes are manufactured by Black Diamond Structures (BDS), an Austin TX based joint venture formed in 2014 between SABIC Ventures US LLC and Molecular Rebar Design. BDS, which is managed as part of SABIC’s Specialties business and holds the exclusive rights to the MR technology, operates a full-scale manufacturing plant with a capacity for up to 5 million liters per years as well as world-class battery testing capacities.
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