Power Surge

In today’s ergonomically conscious dental practices, the increasing availability of cordless technology is welcome news. We explore innovations in rechargeable batteries that are leading the charge toward unplugged dentistry.

When Marty McFly and Doc Brown couldn’t locate a source for plutonium to supply the flux capacitor with the 1.21 gigawatts of electrical power needed at precisely 88 mph to slingshot Marty through time, in Robert Zumeckis’ Back to the Future, they had to rely on lightning. So last century. In today’s race to the future, with all of its forward-looking developments in alternative energy, all that might be needed to fire up the time-traveling DeLorean is a houseplant, a few mushrooms, or a little sweat equity … in the literal sense.

Thanks to the growing interest in renewable resources — and a little imagination — planet-saving innovative research in rechargeable batteries is gaining altitude. Even auto industry giants appear to be acquiescing to the growing reality of electric cars. In fact, General Motors recently announced plans to become an all-electric automaker by 2023 through a combination of fuel-cell electric and battery-powered electric vehicles.1

But rechargeable battery innovation is not limited to the auto industry. Those who research such things are seemingly leaving no stone unturned, as they explore everything from batteries that run on easy-to-come-by commodities (inculding spit, urine and sweat) to those that can be recharged through photosynthesis, bacteria and fungi. And, as noted by the United States Department of Energy’s Joint Center for Energy Storage Research, whose research is led by Argonne National Laboratory, batteries that have the ability to store power generated by wind and solar farms, and that are capable of supplying it when needed, will be game changers in building a clean-energy future.2

CURRENT STATE OF AFFAIRS

These days, lithium-ion batteries are the ones most of us typically encounter. “Almost all rechargeable batteries powering handheld devices today are based on lithium-ion technology,” says Alexander Teran, PhD, co-founder and chief battery engineer at Berkeley, California-based Blue Current — an early stage battery materials company that utilizes technology from Lawrence Berkeley National Laboratory and the University of North Carolina at Chapel Hill.

In fact, according to George Kerchner, executive director of the nonprofit Rechargeable Battery Association (PRBA), “Lithium-ion batteries are the preferred choice for thousands of portable consumer, military and medical applications, including innovative dental products.”

First marketed by Sony in the early 1990s, lithium-ion batteries have undergone a continual evolution, becoming not only lighter and thinner, but offering greater capacities in terms of energy density — the amount of energy that can be stored.

Lithium is a soft, silvery alkali metal — reportedly the lightest metal on Earth. Found in minerals and in saltwater, lithium is said to hold a charge much more effectively than other metals such as lead, zinc and nickel-cadmium, and doesn’t suffer from memory effect. This means that, unlike other batteries, lithium-ion batteries do not have to be fully drained before recharging, as they do not “remember” the shortened cycle. Unfortunately, this battery technology is relatively expensive. And there is a safety issue.

Says Teran, “Lithium-ion batteries contain a liquid electrolyte, which is composed of lithium salts dissolved in an organic solvent, to facilitate ion transport between the negative and positive electrode. These organic solvents tend to be very flammable, so in the unlikely, but all too familiar event of a battery failure, they can energetically fail. These failures can result from latent manufacturing defects or thermal, physical, or electrical abuse of the battery.”

Take, for example, the Samsung Galaxy Note 7 exploding phones, which led to a massive recall. Samsung, in fact, recently determined that the cause of the unfortunate incidents was that the batteries had manufacturing irregularities that led to overheating.3

Indeed, safety can be compromised by a problem with the thin plastic separator that separates the positive and negative electrodes inside lithium-ion batteries. If that separator is breached or distorted in any way so that the electrodes touch each other — which reportedly is what happened in Samsung’s case — a short circuit can occur. This can ignite the electrolyte. In addition to manufacturing defects, growth of moss-like dendrites inside batteries may lead to a breach. Overcharging can also reportedly lead to such problems.


LITHIUM-ION BATTERY BASICS

Batteries, in general, are like miniature silos. But instead of storing grain, they store energy. Batteries create electricity from internally stored energy by converting chemical energy to electrical energy. Nonrechargeable batteries and rechargeable batteries produce electrical current the same way. But in the case of rechargeable batteries, such as lithium-ion batteries, the electrochemical reaction is reversible.

The internal architecture of a lithium-ion battery is made up of four components: an anode (negative) electrode, a cathode (positive) electrode, and a separator membrane and electrolyte, which separate the two. Typically, in lithium batteries, although there are variations, lithium serves as the electrolyte, graphite makes up the negative electrode, and lithium cobalt oxide the positive electrode.

When charging, the anode gathers an excess of lithium ions, which flow from the cathode through the electrolyte and microperforations in the separator. This leaves the cathode drained of ions. During discharge, the ions flow back through the electrolyte and separator to the cathode.

In the course of either process, electrons, which cannot travel directly between electrodes, through the electrolyte and separator, must instead take an alternate route via a closed circuit, which occurs when the two ends of the battery are connected while charging or discharging. During discharge, electrons travel through this connection (the path of least resistance), back to the cathode, powering whatever device is connected along the way. During the charging phase, the electrons travel in the opposite direction, through a charger, back to the anode.

Other rechargeable batteries include nickel cadmium batteries, nickel metal hydride batteries, and lead acid batteries — which is considered the oldest rechargeable battery.


PROBLEM SOLVING

But researchers are working on countless variations of lithium-ion batteries to address these and other issues. “Lithium ion is still a relatively young battery technology,” says Kerchner. “The most exciting and promising developments today are increases in energy densities, allowing for smaller batteries and significant improvements on safety designs.”

David L. Wood, III, PhD, is a batteries research expert at Oak Ridge National Laboratory, located near Knoxville, Tennessee. He says that the reason for so many iterations in lithium-ion technology is because researchers hope to simultaneously achieve low cost, high energy and power densities, long life cycles, and extremely fast recharging. Says Wood, “There are many parallel paths with respect to active materials, electrode architectures, and cell designs aiming to achieve various combinations of these goals. Some of the most exciting technologies are the areas of high-voltage cathodes, silicon (Si)-based anodes, lithium-sulfur (Li-S) batteries, and particularly all-solid-state lithium-ion batteries — cells that do not have a liquid electrolyte.”

In fact, Teran notes that research efforts at Blue Current are focused on developing solid electrolytes for solid-state lithium batteries. “In solid-state batteries, the flammable organic solvent is replaced with an ionically conductive solid material,” he explains. “Such batteries are not only safer, but also enable the use of new active material that results in devices with higher energy density than current lithium-ion battery technology. There is a tremendous amount of interest in solid-state batteries,” Teran adds. “However, the technology is still under development.”

Other researchers take a different tack when it comes to exploring the possibilities of batteries based on the lithium-ion chemistry. Says Daniel Abraham, PhD, a senior scientist at Illinois-based Argonne National Laboratory, “Our goal is to increase the storage capacity of battery cells, while also improving performance, safety and life. Our research enables the batteries in cell phones and laptops to get smaller and lighter, and the batteries in electric vehicles to be safer and longer lasting.” Among the developments described by Abraham is the ability to charge batteries rapidly so that the time required to charge a car battery is comparable to the time required to fill up the gas tank.

For Mihri Ozkan, PhD, a professor of electrical and computer engineering in the Department of Electrical and Computer Engineering at the University of California, Riverside (UCR), the cost of batteries is a major concern. She notes that this is especially true in terms of creating affordable zero-emission vehicles. “To address this,” she says, “we have been working on alternative natural resources and waste resources to make battery-grade electrode materials. The ultimate goal is to achieve better performance at low cost. In the near term, battery technologies based on silicon-based anode materials may lead the way. After silicon, future battery technologies based on sulfur cathodes could be very promising.” She notes that the Ozkan Energy Lab at UCR is currently working on both technologies to power the zero-emission electric cars of the future.

COVERING THE BASES

There is little doubt that the challenges for researchers in this field are many. Says Ozkan, “One of the most important design challenges is safety. While packing more capacity, attention must be paid to the temperature factor and any harmful gas evolution that may occur during use. There are several materials with potentially better battery performance, which have yet to be validated in terms of safety.”

Abraham believes it’s easier to develop smaller batteries for the marketplace, but he notes, “The challenges that need to be overcome include performance reproducibility, in that identical cells should deliver identical performance, and safety. Cells should not overheat or explode, even under abusive conditions.”

Kerchner agrees, saying that for PRBA members, who manufacture small, rechargeable lithium ion (and lithium metal) batteries that are safe and dependable over a long period of time, continuity is key. “The greatest challenge,” he says, “is the fact that these small batteries can be manufactured in very large numbers (hundreds of millions on an annual basis). This requires a sophisticated understanding of how the batteries must be consistently manufactured to very precise specifications.”

Teran adds, “One of the challenges with small batteries is that the ratio of packaging materials to active material tends to be higher, resulting in devices with lower energy density than if you used the same technology in a larger battery.”

But Abraham notes that many of these challenges can be overcome by selecting the appropriate combination of materials that comprise the cell, or interior of the battery. For example, Wood explains that among the greatest challenges in raising energy density are the integration of the next-generation nickel-rich, high-voltage cathodes and the ability to operate them at cell voltages above 4.4 volts. Says Wood, “These materials suffer from structural degradation (crystal structure changes) when repeatedly charged to high cell voltages approaching 4.8 volts. The use of silicon at the anode offers promise for significantly increasing energy density, but high silicon contents result in excessive long-term capacity fade due to a different type of structural degradation (particle cracking) of the material.”

Wood adds that thick coatings with advanced electrode architectures are also extremely important for reducing the weight and volume of advanced lithium-ion batteries. In addition, lithium metal holds the promise of higher storage capacity if it were used as an anode. But there are complications. Says Wood, “Using lithium metal at the anode is the holy grail for lithium-based batteries but many challenges remain related to the prevention of lithium dendrites during long-term operation.”


LEXICON

Anode: Negative electrode.
Battery: Creates electricity from internally stored energy subsequent to charging from electrical outlet.
Cathode: Positive electrode.
Electrode: Electrical conductor.
Electrolyte: The medium inside a battery cell that transports ions between anodes and cathodes.
Electrons: Negatively charged subatomic particles.
Fuel cells: Make electricity only through chemical reaction, with energy derived from fuel stored in a connecting tank.
Ions: Electrically charged particles, such as atoms or molecules.


BACK TO THE FUTURE

Looking ahead, there is general agreement that research will continue to be centered around lithium-ion battery improvement. “Lithium-ion batteries will remain the battery of choice for many years to come, not just for consumer products and medical devices but also electric and hybrid vehicles and increasingly for battery storage of electricity from solar and wind energy,” forecasts Kerchner. “We expect to see higher energy densities, solid electrolytes, and possibly more rechargeable lithium metal battery technologies making their way into the marketplace.”

Teran agrees that lithium-based chemistries are here to stay, particularly for portable devices. “The specific flavors and combinations of active materials inside the batteries will continue to improve slowly,” he explains, “resulting in a gradual increase in energy density.”

But Teran also reports that the biggest change in the last few years, especially for large-format applications such as electric vehicles, has been the unexpectedly fast drop in battery prices. “This trend is expected to continue for a few more years, as global production ramps up to meet the needs of the electric vehicle market,” he says. “Long-term, keep an eye out for safer, higher-energy, solid-state batteries.”

Likewise, Wood foresees the development of all-solid-state configurations with advanced solid electrolytes made of glasses, polymers, or ceramics. He also predicts high-energy Li-S batteries, thick solid-state cathodes with advanced architectures for fast charging, and high power density. “Sodium-ion batteries may become more popular in the market as well, due to inherent cost advantages of the materials,” he notes.

Abraham observes that when it comes to storage capacity, the lithium-ion cell is almost near its limit. Therefore, he says, “Researchers are working on new chemistries that can further increase the storage capacity of the cell. These technologies include the use of lithium metal along with materials such as sulfur and oxygen. Also, there are many groups around the world working on “beyond lithium-ion chemistries,” which include the use of magnesium, calcium and aluminum ions in battery cells. These newer chemistries still face significant challenges, such as battery life. Because of these challenges, my guess is that these newer designs are likely to gain significant commercial traction only after the year 2025.”

Ozkan predicts that safety will remain a high priority as research moves forward. To this end, she says, “High-performance batteries may first have silicon added, with gradually increasing concentration, to the design of new classes of anode materials. This could be followed by the introduction of sulfur cathode materials into the next generation.” Ozkan adds that other alternative materials, such as sodium and magnesium, are also being studied to potentially replace lithium. But she concludes that the goals in battery development are multifold. “Overall,” she says, “the number of factors considered when coming up with a new battery technology include safety, cost, performance, green materials/processing, and safe disposal.”

REAL-WORLD APPLICATIONS

So, benefits inherent in saving the planet not withstanding, what do all of these developments mean for you and your dental customers? Cordless technology, available in everything from curing lights and obturation systems to intraoral cameras and ultrasonics, is a popular choice for busy practitioners who value chairside portability. It is also good for ergonomics, which is enhanced by cordless devices, thanks to the elimination of cord drag, as well as the availability of handpieces that are increasingly streamlined and lighter in weight due to the use of smaller sized batteries.

In addition, batteries that offer quick charging and quick discharge ensure that power is readily available. Increased power density, extended life between charges, and lower cost are further benefits offered by many of the battery iterations being developed. Perhaps most important is enhanced safety built into new lithium-ion batteries through elimination or reduction of heat buildup and the risk of shorts. This can be a big advantage for dental practitioners who would rather not set their patients’ hair on fire, and so reassuring for those who prefer to wear loupes that are less likely to burst into flames.

These and other continued improvements in batteries for cordless options that have become practice necessities can translate to improved practice efficiency, quality of care, and a nigh-on bulletproof bottom line. And that’s a power surge of the best kind. So the next time your flux capacitor — or your customer’s piezoelectric ultrasonic handpiece — needs a charge, you may need look no further than the nearest potted plant.

BONUS WEB CONTENT

References

  1. DeBord M. GM promises 20 all-electric cars by 2023. Business Insider: Finance. Available at: businessinsider.com/gm-to-launch-20-all-electric-cars-by-2023-2017-10. Accessed October 20, 2017.
  2. Crabtree G. Better batteries hold promise for a sustainable future. Joint Center for Engery Storage Research. Available at: jcesr.org/better-batteries-hold-promise-for-a-sustainable-future/. Accessed October 20, 2017.
  3. Martin TW, McKinnon JD. Samsung investigation blames battery size for Galaxy Note 7 fires. The Wall Street Journal. Available at: wsj.com/articles/samsung-investigation-blames-battery-size-for-galaxy-note-7-fires-1484906193. Accessed October 20, 2017.

Featured Image by OHAN63/ISTOCK/GETTY IMAGES PLUS

From MENTOR. December 2017;8(12): 14-18.

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