Chemical element abundant in nature, sodium (Na) is found in marine waters and saline reserves on all continents. Experts estimate that the substance could be an important alternative in the energy accumulation process, with the possibility of replacing up to 25% of the space occupied today by lithium batteries, which equip electric cars, drones, smartphones, notebooks, tablets and other electronic devices. .
A team from the Faculty of Electrical and Computer Engineering of the State University of Campinas (Feec-Unicamp) is working on the development of the first prototype of a Brazilian sodium battery. Today, only Chinese manufacturers offer commercial batteries with the technology, and the first EVs with these modules 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 capacity to develop the technology and produce the first prototypes,” says physicist Hudson Zanin, a professor at Feec-Unicamp and leader of the research project.
Together with colleagues from the Santa Catarina company WEG, specialized in the production of electric motors, Unicamp researchers recently presented a project proposal within the federal Rota 2030 programme, to encourage innovation in the automotive production chain. The scope of the proposal is the development and production of 1 ampere-hour (Ah) sodium batteries, with 1.2 kilowatt-hour (kWh) energy storage modules, suitable for equipping hybrid electric cars. These vehicles are powered by liquid fuels, such as petrol and ethanol, and have an additional electric motor powered by the same combustion engine.
The technologies of sodium and lithium batteries, explains Zanin, are very similar. In both, ions (a set of atoms with an electric charge) carry out the task of transporting and storing electrons during the processes of energetic charge and discharge. This is why the ions penetrate the structure of the electrodes, which are made up 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 a harder time penetrating the electrode structure. This calls for the development of electrodes that facilitate this operation. “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-based,” Zanin points out.
In August 2022, the Unicamp team published an article about Energy Storage Journal demonstrating the potential of using a new material, formed by carbon nanotubes with niobium pentoxide nanoparticles, in the construction of electrodes, increasing the capacity and speed of transport and storage of the electric charges of sodium ions. The study evaluated sodium electrodes used in batteries and supercapacitors, which are electronic devices used for energy storage.
The research was carried out during the electrical engineering doctorate of computer engineer Carla Martins Real, under the guidance of Zanin, and involved researchers from the State University of Kansas, in the United States, and the federal universities of Mato Grosso ( UFMT) and the Jequitinhonha and Mucuri Valleys (UFVJM), in Minas Gerais.
Economic viability
Lithium batteries are currently considered the most efficient technology for energy compression (see Pesquisa FAPESP n. 285). With the same physical volume, they are able to carry 30% more energy than a sodium battery. They are also more durable because they have better cycling properties, i.e. they carry out a greater number of energy charge and discharge cycles. While a lithium battery performs 12,000 cycles during its useful life, sodium batteries, as yet, do not reach 4,000 cycles.
Zanin believes, however, that sodium modules have significant competitive advantages that could increase their use in the coming years. “Sodium is an affordable input available in any country. Its large-scale refining will provide higher economic viability to the sodium battery than the lithium battery, which will face strong market demands,” he says.
Lithium is a mineral with limited known reserves and presence limited to a few countries, such as Bolivia, Chile, Argentina, Portugal and Australia. In Brazil, the only commercially viable commercial reserve is located 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 calculates that 59 new lithium mines will need to open just to meet projected demand through 2035. “Since there won’t be enough lithium for everyone, sodium may be an alternative,” says Zanin.
Another problem with lithium, the researcher explains, is that the process of refining the mineral to reach the appropriate grade for use in batteries consumes a lot of energy. When the energy sources used are not renewable, he underlines, the production process has a great environmental impact. “Sodium mining and processing, on the other hand, has a very low carbon footprint,” he compares.
Even with these advantages, the chemist specialized in electroactive materials Roberto Manuel Torresi, of the Institute of Chemistry of the University of São Paulo (IQ-USP), estimates that sodium batteries should not replace lithium storage modules, but occupy niches in different markets.
According to him, lithium batteries, due to their density, tend to predominate in light electronics. The technology using sodium should be applied in stationary batteries, those used in energy security systems in data centers and ATMs or in wind and solar photovoltaic energy storage, reducing interruptions in the electricity supply caused by lack of wind and sun. “In other words, sodium batteries are interesting, but intended for specific applications,” Torresi says.
electric mobility
Zanin, however, also sees potential in electric mobility. At first, he expects the technology to be used in large vehicles, such as buses, trucks, trains and ships.
In China, automakers have announced they are preparing to launch electric cars with sodium-ion batteries later this year. BYD, which also makes batteries, will use its own technology, and Chery will use modules designed by Chinese battery maker CATL. Since February, an electric model from Jac Motors has been being tested with a system created by HiNa Battery.
French automaker Renault, which maintains a partnership with China’s Jiangling Motors Electric Vehicle (JMEV), has announced the launch of its first sodium battery vehicle in the second half of the year, with technology supplied by China’s Farasis Energy. “The abundance of sodium supplies in virtually all countries,” Zanin predicts, “will allow for the emergence of various energy storage technologies and different manufacturing processes around the world.”
For Flávia Consoni, founder and coordinator of the Laboratory for the Study of the Electric Vehicle (Lightweight), based at the Institute of Geosciences (IG) of Unicamp, the battery continues to be the main bottleneck for the expansion of electric mobility due to the growing demand for natural resources and the environmental and social impacts resulting from mining. Therefore, initiatives investigating the use of other minerals 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 the recent advances, there are still technological problems associated with the technology, such as the increase in its energy density. These are aspects that need to be considered, especially considering applications that require high energy density.”
not to catch fire
An undesirable feature of batteries is that they are flammable. Knocks, punctures and overheating endanger the safety of smartphone, notebook and electric vehicle users. An additive capable of preventing these appliances from catching fire has been developed by researchers at Cine, a center supported by FAPESP and Shell.
“The additive is a polymer which, when added to the battery electrolyte, prevents fire,” describes physicist Hudson Zanin, of Feec-Unicamp. The recipe of the polymer used is kept secret, as the technology is in the patent analysis phase at the National Institute of Industrial Property (INPI).
The electrolyte is a generally liquid substance responsible for the conduction of electric ions between the two poles (cathode and anode) of a battery. It is usually produced from fossil hydrocarbons, obtained in the process of refining petroleum. That’s why it’s flammable.
“The innovation created by our group uses conventional electrolytes to which an additive is added which plasticizes and joins the molecules, preventing a possible fire in the equipment”, explains Zanin. In tests carried out 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 a very small share in the formulation of the electrolyte. Since the polymer used for its manufacture is cheap and accessible, the possible application 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 São Paulo startup Brenergies Solutions, a spin-off of Feec-Unicamp made up of professors and students of the institute, should be responsible for making the additive available to the market. There is no deadline set yet.
The global search for technologies to prevent battery combustion spawned its first product in 2021, with the international launch of a less flammable lithium iron phosphate (LFP) battery developed by Chinese electric vehicle maker BYD. According to the company, the new battery has been subjected to extreme test conditions, punctured, crushed and heated in an oven at 300 degrees Celsius without registering a fire or explosion. The module already equips some BYD vehicles.