Electricity powers our modern world, and storing energy is essential when consumption isn’t immediate. Everyday devices run on batteries, and vehicles are moving away from fossil fuels toward electricity. In this context, developing new sustainable and economical batteries is a real necessity.
Several CSIC research groups focus on improving energy storage and supply systems. Their work aims to use more abundant and sustainable materials or to develop complementary systems that can meet future energy needs. Thermoelectric concepts can power devices without continuous energy storage in some cases.
“Batteries are chemical devices that store energy,” explains M. Rosa Palacín, a researcher at the Barcelona Institute for Materials Science (ICMAB). “A battery consists of one or more electrochemical cells with two electrodes separated by an electrolyte, a liquid that conducts ions but not electricity. Electrons move between electrodes through an external circuit, creating the electric current. Meanwhile, ions travel through the electrolyte, balancing the electric current inside the battery.”
During discharge, the negative electrode material is oxidized and the positive electrode material is reduced. When these reactions are reversible, the battery can be recharged by applying an external current that drives the reverse reactions. Lithium-ion technology remains the most widely used rechargeable battery type for electronic devices and electric vehicles.
“If metallic lithium could be used, batteries could store even more energy,” Palacín notes. “One alternative under investigation is solid electrolytes, but these systems require operation at higher temperatures to ensure rapid ion conduction, which is not ideal for broad use.”
In every scenario, lithium tends to be scarce and costly. Researchers are exploring alternatives for the negative electrode, including calcium and magnesium, which are more abundant and cheaper, with the aim of increasing energy density while maintaining sustainability criteria.
Calcium and magnesium batteries
The main advantage of calcium and magnesium batteries is their potential for very high energy density, potentially double that of lithium. They also promise lower costs. Realizing voltages comparable to lithium remains a challenge, and researchers are considering hybrid approaches that combine high energy density calcium and magnesium batteries with high power supercapacitors.
Researchers M. Rosa Palacín and Alexandre Ponrouch at ICMAB are developing the components of these batteries, including the two electrodes and the electrolyte. A complete battery has not yet been built, but electrolytes have been developed that improve calcium and magnesium electrode performance.
“Research in this area is in an early stage where each component must be optimized,” Ponrouch explains. “Since lithium technology exists, it is advantageous to study the key challenges with new materials such as ion mobility in electrodes and electrolytes, contamination or moisture susceptibility, and the complex processes at electrode–electrolyte interfaces.”
Redox flow batteries to store renewable energy
New electrical energy storage systems include vanadium redox flow batteries. To explore their development, CSIC supports the Interdisciplinary Thematic Platform (PTI), a research structure connecting scientists, companies, and administrations to solve high-impact social problems. The Flowbat platform, established in 2019 and coordinated by Ricardo Santamaría of INCAR, has achieved a promising prototype.
“Higher performance redox flow batteries could significantly improve the energy storage framework. Large-scale electricity generation, often driven by hydroelectric pumping and compressed air technologies, raises environmental concerns and depends on geographic location,” notes Zoraida Gonzalez from the same center. These batteries offer lower costs and reduced environmental impact compared with some alternatives, such as lithium-ion systems. The initial aim was to create a small-scale demonstrator, a 1 kilowatt vanadium redox flow cell, which became available in mid-2021 with encouraging results.
The platform’s next objective is to design, manufacture, commission, and test a 50 kilowatt battery in real environmental conditions by late 2022. Like other batteries, it uses two electrodes where redox reactions occur during charging and discharging, separated by membranes. Its distinctive feature is two external tanks for storing electrolytes. The modular design also allows scaling to smaller applications.
Real-world commissioning of the 50 kW battery would demonstrate the platform’s potential to the scientific community and end users, aligning with European Green Deal and sustainable development goals.
Thermoelectric generators for the internet of things
Luis Fonseca of the Barcelona Microelectronics Institute (IMB) and his team are developing silicon microstructures that harvest energy from ambient temperatures to power low-energy sensors. Using silicon technology, thermoelectric microgenerators can power devices in the Internet of Things and sensors that operate autonomously on hot surfaces, especially when paired with a rechargeable secondary battery to maintain a continuous charge.
Fonseca emphasizes the enduring strength of silicon technology that underpins the information society and supports mature, scalable production using abundant materials. He notes the challenge of creating architectures that convert ambient temperature differences into usable electrical energy while integrating thermoelectric materials compatible with silicon. To date, integrating silicon nanowires into silicon structures has opened a pathway for fully silicon-based device manufacturing at scale.
“Bringing silicon technologies together with functional materials has been a dialogue between two distinct technological worlds: microfabrication and advanced materials. This approach enables the production of a large number of Internet of Things devices at a reasonable cost and with manageable environmental impact,” Fonseca remarks. The research also extends into microenergy collaborations like Epistore, which develops micro fuel cells using hydrogen to reduce reliance on fossil fuels.
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