Your smartphone has a problem. It will last only as long as the rechargeable battery housed inside it. After about three years, what is inside that battery may have degraded so much that it can’t hold a charge anymore. And since it’s too expensive to replace, people end up buying a new phone when the old one’s battery dies. But new research might help extend the life of such batteries, perhaps almost forever.
Smartphones and other devices — from tablets and computers to the Apple Watch and electric cars — rely on lithium-ion batteries. Like all batteries, lithium-ion ones contain two electrodes. Its anode (AN-ode), marked with a minus sign, releases electrons. Its cathode (KATH-ode), marked with a plus sign, collects electrons. After several hundred charges, though, these batteries can no longer hold a charge. Part of the reason is that some of the lithium in the cathode has leaked out.
For years, scientists have experimented with replacing a cathode’s lithium with nanowires made of different types of metals. Nanowires are filaments that are much thinner than a human hair.
It takes a lot of nanowires to make a cathode. But using them may allow engineers to create batteries that are smaller and more powerful. Unfortunately, nanowires alone won’t change how long a cathode lasts.
Here’s why: To store energy, nanowires are given a coating of manganese oxide. When repeatedly recharged, that coating will eventually turn brittle and fall off. So nanowires, like the lithium they’re meant to replace, can only be recharged so many times. After that, you still end up with a dead battery. But a young chemist thinks she’s found a way to make nanowire structures less brittle.
A possible solution
Mya Le Thai is a graduate student at the University of California, Irvine (UC-Irvine). She’s been conducting her own experiments with cathodes. And instead of using metals that can corrode — that is, undergo a damaging reaction — she builds the wires out of gold. She coats these gold wires in manganese oxide, then adds a new step. She dips the coated nanowires in a special gel.
This gel works as an electrolyte. That gel is seeded with nonmetallic ions (charged molecules) that can carry an electric charge. Other researchers have used an electrolyte gel to replace highly combustible electrolyte liquids. But this may be the first time anyone has used it as a coating for nanowires, says George Crabtree. He heads the Joint Center for Energy Storage Research in Chicago, Ill. This center explores new ways to store energy.
Le Thai made two cathodes, each with 375 double-dipped nanowires. To test them, she charged, discharged and then recharged them again. She did this up to 200,000 times over three months. No matter how many times she did this, the nanowires stayed mostly intact. This is an improvement over the 5,000 or 6,000 times that nanowires typically can be recharged before falling apart.
“We looked at them under an electron microscope and the manganese oxide was not falling off at all. That blew us away,” says Reginald Penner. He heads the UC-Irvine chemistry department. He also coauthored the new study. “The gel seems to be softening the oxide material," he says. And that appears to keep the wires from breaking.
Other studies have explored the idea of using nanowires. Those earlier wires “never worked as well as you’d hope,” notes Crabtree. At the Chicago-based center, he pays close attention to nanowire developments that might lead to better batteries. And the new work by the UC-Irvine team seems different, he says. “This looks like it may be a step forward.” Still, the real test will be seeing if the nanowire cathodes will scale up, he says. By that, he means whether they will work in a real battery — or many real batteries.
“The way you make things in a factory is very different from the way you make them in a lab,” he notes. “The factory has to be cheap, fast and reliable. Will this become [part of] the next battery? We’ll see.”
Back to work
Penner says his team is not even close to manufacturing batteries. Their next step will be to build cathodes out of a whole “shag carpet” of nanowires. The team also needs to figure out how to make these shaggy-carpet cathodes more powerful. At the moment, he thinks they might be able to power a small LED light for a few minutes. But that’s not enough power to prove useful for smartphones or anything else, he notes.
Still, Le Thai, Penner and their lab collaborators hope their research may one day lead to batteries that will let all kinds of gadgets last, and last. And last!
(for more about Power Words, click here)
anode The negative terminal of a battery, and the positively charged electrode in an electrolytic cell. It attracts negatively charged particles.
battery A device that can convert chemical energy into electrical energy.
cathode The positive terminal of a battery, and the negatively charged electrode in an electrolytic cell. It attracts positively charged particles.
chemistry The field of science that deals with the composition, structure and properties of substances and how they interact with one another. Chemists use this knowledge to study unfamiliar substances, to reproduce large quantities of useful substances or to design and create new and useful substances. (about compounds) The term is used to refer to the recipe of a compound, the way it’s produced or some of its properties.
corrosion (v. to corrode) A chemical reaction in which metals react with gases or other materials in their environment and undergo a type of degradation. The rusting of iron, for instance, is one example of corrosion that is driven by exposure to moisture.
combustion (adj. combustible) The process of burning.
degrade To break down into smaller, simpler materials — as when wood rots or as a flag that’s left outdoors in the weather will fray, fade and fall apart.
electrode Materials that serve as an anode or cathode, attracting negatively or positively charged particles. Or things that serve as electric conductors through which current leaves or enters something else.
electrolytes Non-metallic minerals that that work as ions (electrically charged molecules) to carry electrical charges. Certain minerals in blood or other bodily fluids can can serve as the ions that move to carry a charge. Electrolytes also can serve as the ions that move a charge within a battery.
electron A negatively charged particle, usually found orbiting the outer regions of an atom; also, the carrier of electricity within solids.
electron microscope A microscope with high resolution and magnification that uses electrons rather than light to image an object.
engineer A person who uses science to solve problems. (v.) To design a device, material or process that will solve a problem or unmet need.
fracture (noun) A break. (verb) To break something and induce cracks or a splitting apart of something.
graduate student Someone working toward an advanced degree by taking classes and performing research. This work is done after the student has already graduated from college (usually with a four-year degree).
LED (light-emitting diode) A type of semiconductor device that produces light.
lithium A soft, silvery metallic element. It’s the lightest of all metals and very reactive. It is used in batteries and ceramics.
manganese The chemical element of atomic number 25, a hard gray metal of the transition series. Manganese is an important component of special steels.
molecule An electrically neutral group of atoms that represents the smallest possible amount of a chemical compound. Molecules can be made of single types of atoms or of different types. For example, the oxygen in the air is made of two oxygen atoms (O2), but water is made of two hydrogen atoms and one oxygen atom (H2O).
nano A prefix indicating a billionth. In the metric system of measurements, it’s often used as an abbreviation to refer to objects that are a billionth of a meter long or in diameter.
nanowire A wire or rod on the order of a billionth of a meter in cross-section or in circumference. It is usually made from some type of semiconducting material.
smartphone A cell (or mobile) phone that can perform a host of functions, including search for information on the Internet.
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Original Journal Source: M. Le Thai et al. 100k cycles and beyond: Extraordinary cycle stability for MnO2 nanowires imparted by a gel electrolyte. ACS Energy Letters. Vol. 1, April 20, 2016, p. 57. doi: 10.1021/acsenergylett.6b00029.