A chemical element that is abundant in nature, sodium (Na) is found in seawater and salt deposits on all continents. Experts estimate that the substance can be an important alternative to the energy storage process, with the potential to replace up to 25% of the space currently occupied by lithium batteries, which equip electric cars, drones, smartphones, notebooks, tablets and other electronic devices.
A team from the School of Electrical and Computer Engineering at the State University of Campinas (Feec-Unicamp) is working to develop the first prototype of a Brazilian sodium battery. Today only Chinese manufacturers offer commercial batteries with the technology, and the first electric vehicles with these units are expected to hit the market later this year.
The Brazilian project is being developed within the Center for Innovation in New Energies (Cine), an Engineering Research Center (CPE) supported by FAPESP and the Anglo-Dutch oil company Shell. “We already have the ability to develop the technology and produce the first prototypes,” says physicist Hudson Zanin, professor at Feec-Unicamp and head of the research program.
Together with colleagues from the Santa Catarina company WEG, which specializes in the manufacture of electric motors, Unicamp researchers recently submitted a project proposal to the federal program Rota 2030, to encourage innovation in the automotive production chain. The purpose of the proposal is the development and production of 1 ampere-hour (Ah) sodium batteries, with 1.2 kilowatt-hour (kWh) energy storage units, suitable for equipping hybrid electric cars. These vehicles run on liquid fuels such as gasoline and ethanol and have an additional electric motor powered by the internal combustion engine itself.
Sodium and lithium battery technologies, Zanin explains, are very similar. In both, ions (a set of atoms endowed with an electrical charge) perform the task of transporting and storing electrons during the process of charging and discharging energy. For this, the ions penetrate the electrode structure, which consists of a positive pole, the cathode, and a negative pole, the anode.
The difference is that the sodium ion is larger than the lithium ion and therefore has more difficulty penetrating the electrode structure. This requires the development of electrodes that facilitate this function. “In lithium batteries, the anode is made of graphite. in sodium batteries, from another carbon structure. One uses lithium-based cathodes and the other sodium,” reports Zanin.
In August 2022, the Unicamp team published an article on Journal of Energy Storage demonstrating the possibility of using a new material, formed from carbon nanotubes with niobium pentoxide nanoparticles, in the manufacture of electrodes, increasing the capacity and speed of sodium ion electrical charge transport and storage. The study evaluated sodium electrodes used in batteries and in supercapacitors, which are electronic devices used to store energy.
The research was conducted during computer engineer Carla Martins Real’s PhD in electrical engineering, under Zanin’s guidance, and involved researchers from the State University of Kansas, in the United States, and from the federal universities of Mato Grosso. (UFMT) and the Jequitinhonha and Mucuri Valleys (UFVJM), in Minas Gerais.
Financial viability
Lithium batteries are currently considered the most efficient technology for energy compression (see Pesquisa FAPESP issue no. 285). In the same physical volume, they can carry 30% more energy than a sodium battery. In addition, they are more durable because they have better cyclicity, i.e. they perform a greater number of energy charge and discharge cycles. While a lithium battery performs 12,000 cycles during its useful life, sodium batteries currently do not reach 4,000 cycles.
Zanin believes, however, that sodium plants have relative competitive advantages that could boost their use in the coming years. “Sodium is an affordable input available in any country. Refining it on a large scale will make the sodium battery more economically viable compared to the lithium battery, which will face strong market demands,” he says.
Lithium is a mineral with limited known reserves and is confined to a few countries such as Bolivia, Chile, Argentina, Portugal and Australia. In Brazil, the only known commercially viable reserve is in the Jequitinhonha Valley, Minas Gerais. According to a 2021 estimate by the International Energy Agency (IEA), lithium consumption is expected to increase 75-fold by 2050.
Global consultancy Benchmark Mineral Intelligence estimates that 59 new lithium mines will need to be opened just to meet the demands expected until 2035. “As there will not be enough lithium for everyone, sodium may be an alternative,” it says. Zanin.
Another problem with lithium, the researcher explains, is that the process of refining the ore to get it to the right grade for use in batteries consumes a lot of energy. When the energy sources used are not renewable, he points out, the production process has a large environmental impact. “Extracting and processing sodium, on the other hand, has a very low carbon footprint,” he compares.
Even with these advantages, chemist specialized in electroactive materials Roberto Manuel Torresi, from the Institute of Chemistry of the University of São Paulo (IQ-USP), believes that sodium batteries should not replace lithium storage units, but occupy places in different markets.
According to him, lithium batteries, because of their density, tend to dominate lightweight electronics. The technology using sodium should be applied to stationary batteries, those used in energy security systems in data centers and ATMs, or in the storage of wind and solar photovoltaic energy, reducing interruptions in the supply of electricity caused by the lack of wind and sun . . “In other words, sodium batteries are interesting, but they are for specific applications,” says Torresi.
electric mobility
Zanin, however, also sees potential in electric mobility. Initially, his expectation is that the technology will be used in large vehicles such as buses, trucks, trains and ships.
In China, automakers have announced that they are preparing to launch electric cars with sodium-ion batteries later this year. BYD, which also produces batteries, will use its own technology and Chery will use units designed by Chinese battery maker CATL. Since February, an electric model from Jac Motors has been testing with a system created by HiNa Battery.
French car manufacturer Renault, which maintains a partnership with China’s Jiangling Motors Electric Vehicle (JMEV), announced for the second half of the year the launch of its first sodium battery vehicle, with technology provided by China’s Farasis Energy. “Abundant sodium supplies in almost all countries,” Zanin predicts, “will allow the emergence of various energy storage technologies and different production processes around the world.”
For Flávia Consoni, founder and coordinator of the Laboratory for the Study of the Electric Vehicle (Light), based at the Institute of Geosciences (IG) at Unicamp, the battery is still the most important obstacle to the expansion of electric mobility due to increasing demand for natural resources and the environmental and social impacts resulting from mining. Therefore, initiatives exploring the use of minerals other than lithium are always welcome and necessary. “The sodium battery is already a reality for stationary applications. Sure, it has potential for other purposes, but it’s still a prospect for the future. Despite recent developments, there are still technological issues associated with the technology, such as increasing its energy density. These are aspects that need to be taken into account, especially considering applications that require high energy density.”
not to catch fire
An undesirable characteristic of batteries is that they are flammable. Shocks, punctures and overheating pose safety risks for smartphone, laptop and electric vehicle users. An additive capable of preventing this equipment from catching fire was developed by researchers at Cine, a center supported by FAPESP and Shell.
“The additive is a polymer that, added to the battery electrolyte, prevents fire,” describes physicist Hudson Zanin, from Feec-Unicamp. The recipe for the polymer used is kept secret, as the technology is under patent analysis at the National Institute of Industrial Property (INPI).
An electrolyte is a generally liquid substance responsible for conducting electrical ions between the two poles (cathode and anode) of a battery. It is usually produced from fossil hydrocarbons, obtained during the oil refining process. That’s why it’s flammable.
“The innovation created by our group uses conventional electrolytes to which an additive is added that plasticizes and joins its molecules, preventing a possible fire in the equipment,” explains Zanin. In tests conducted at Unicamp, batteries with the additive were cut, punctured and exposed to fire and did not burn or explode.
The additive, according to the researcher, will have very little involvement in the composition of the electrolyte. As the polymer used in its construction is cheap and accessible, the final implementation of this technology should not have a significant impact on the final cost of the battery or supercapacitors, electronic devices also used for energy storage.
The newly founded company Brenergies Solutions of São Paulo, a Feec-Unicamp spin-off made up of professors and students from the institution, should be responsible for bringing the additive to market. There is no set deadline yet.
The global search for technologies to prevent battery combustion produced its first product in 2021, with the international release of a less flammable lithium-iron-phosphate (LFP) battery developed by Chinese electric vehicle maker BYD. According to the company, the new battery was subjected to extreme test conditions, punctured, crushed and heated in an oven at 300 degrees Celsius without any fires or explosions. The unit already equips some BYD vehicles.
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