The use of elements such as lithium, cobalt and nickel for the manufacture of batteries implies a dependence on scarce (and, therefore, expensive), toxic materials whose extraction and processing causes numerous environmental problems; Two million liters of water are needed to extract 1,000 kilos of lithium. Researchers are urgently searching for substitutes that are abundant, renewable, biodegradable, safe, and low in cost and environmental impact. The solution may be close: sodium and calcium, two abundant elements that are being investigated to prevent Demand for lithium will multiply by 60 in two decades, according to EU forecasts.
Added to the unstoppable proliferation of home and portable devices are the two biggest challenges: the electrification of mobility and the storage of renewable energy to provide continuous power. “There are not enough lithium, cobalt and nickel ions to meet everyone’s needs,” says John Abou-Rjeily, a researcher at the company Tiamat Energy, which emerged from the National Scientific Research Center of France (CNRS).
This doctor in Physics and Chemistry of Materials researches, according to what he publishes horizon, as an alternative sodium, one of the most abundant chemical elements in the Earth’s crust and whose processing and use is, unlike lithium, safer and cheaper. On the contrary, it requires more volume, which is why current developments are not yet suitable for small devices.
They also cannot compete with the range that current storage systems bring to electric cars. But they could serve as alternatives on shorter routes, the majority. “While I would never challenge the 500 kilometer range of lithium-ion batteries, this type of sodium-ion could be more competitive for smaller stretches. They could be cheaper for short and medium distances by car, explains Abou-Rjeily.
Researchers from the Chalmers Universities of Technology (Sweden) and Delaware (United States) are along the same lines, according to a study published in Energy. “There is a tendency to demand a really large battery. But according to research, generally, a slightly smaller one, with less range than that of a gasoline tank, is sufficient, since the only time in which you would need a greater autonomy is for a trip of six hours or more, in which case , the driver could charge on the go. There is too much emphasis on the need for a really long range and this leads to an increase in the price of the vehicle and a greater use of resources for electric cars,” says Frances Sprei, Professor at Chalmers.
For this doctor in Energy and Environment, this change in mentality is necessary to adapt charging facilities where people spend the most time: at home and at work. Sprei regrets that, on the contrary, many European countries focus on the charging network on roads and tracks.
This simple modification of the perception of needs would further promote sodium as an alternative, since it would allow it to be deployed in homes and workplaces as energy storage systems from renewable sources. Magdalena Graczyk-Zajac, professor at the Technical University of Darmstadt in Germany, and member of the European project, works in this sense. SIMBAwhich concludes its first phase next June.
You could drive the car for free for eight or nine months a year
Magdalena Graczyk-Zajac, professor at the Technical University of Darmstadt
The researcher is committed to storing the energy captured by home photovoltaic panels in a rechargeable sodium ion domestic battery. This would power the homes and charge the electric vehicles of its residents with a significant cost reduction. “You could drive the car for free for eight or nine months a year,” she says. The prototype is already in laboratory tests.
One part, the anode, is made of hard carbon, which can be obtained from wood or other biological waste. For the cathode, Prussian white is tested, a chemical compound from a blue pigment of the same name, but with more sodium and rich in iron, one of the most abundant metals.
The Basque research center CIC energiGUNE, has its own development in this area: a sodium metal anode with a thickness of only seven microns (70 times thinner than current ones) achieved through a physical evaporation process. “This advance,” according to this center, “opens the door to the manufacture of flexible solid-state batteries with the thin sodium anode, a safer, cheaper and smaller alternative to the current batteries with liquid electrolyte in which uses graphite.”
“Sodium cannot be easily laminated due to its sticky texture, similar to plasticine,” explains Montse Galcerán, principal investigator of this project to CIC energiGUNE. “To date, the most common method used to roll a block of sodium was as basic as processing it with a hammer, but this meant that a thin and homogeneous sheet could not be obtained, and, therefore, there was a large excess of unused sodium in the batteries. Thanks to evaporation, we have managed to overcome that obstacle,” she assures.
This thinning of the anode allows us to reduce the amount of sodium needed, and the costs, weight and dimensions of the batteries, while increasing energy density (greater storage capacity) and safety.
If the raw material is cheap, so can the batteries
Rosa Palacín, Institute of Materials Science of Barcelona (ICMAB-CSIC)
Another element that is used as a substitute for lithium is calcium. “It is one of the most abundant elements in the Earth’s crust and is not concentrated in specific geographic areas, as is the case with lithium. If the raw material is cheap, the batteries can also be cheap,” says Rosa Palacín, from the Institute of Materials Science of Barcelona (ICMAB-CSIC) and member of the project. CARBAT to horizon.
Using calcium as a negative electrode offers advantages over graphite in lithium-ion batteries, since it has a greater accumulation capacity per kilogram (energy density) than conventional lithium batteries, which also form tiny rigid structures called dendrites and They can cause short circuits or explode after many uses, according to the entity.
“When calcium passes through the electrolyte, two electrons flow out, instead of one, as in the case of lithium. It can be assumed that a battery of the same size would offer greater autonomy if used in an electric vehicle, as long as a suitable positive electrode is found,” explains Palacín.
The key is choosing the most appropriate components. “It appears that ultimately all working electrolyte salts contain boron. We use calcium tetrafluoroborate dissolved in a mixture of ethylene and propylene carbonate,” says the researcher.
Other researchers from the Technical University of Denmark are seeking, in the project SALBAGE, a battery made from an aluminum anode and a sulfur cathode. Aluminum is even more abundant than calcium, but incorporating it into a battery poses similar difficulties.
“All the materials used are cheap. Aluminum, sulfur, the electrolyte itself and urea are very, very cheap. Even the polymer is,” says Danish university researcher Juan Lastra, who defends this option to store energy from a wind or solar park.
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