The deployment of renewable energies is advancing at a historic pace. However, as they become more prevalent in the energy system, large-scale storage systems are required to prevent electricity generated during solar and wind production peaks from being lost. Global investment in these technologies continues to grow., and in the most dynamic markets, about 80% of new large-scale developments already combine solar energy with battery systems. Nevertheless, the international supply chain faces major challenges due to dependence on metals such as lithium and cobalt.
To diversify these solutions, the scientific community has turned its attention to a highly abundant resource: saltwater from the seas. This search for new formulas complements stationary storage methods investigating everyday, low-impact materials, such as sand batteries for thermal storage. This opens up a range of solutions that allow renewable energy generation to be decoupled from the time of consumption.
Although the development of lithium-ion batteries marked a historic turning point in the electrification of transportation and electronics, for which the Nobel Prize in Chemistry was awarded in 2019, grid storage requires innovation in other areas. One of the most promising technologies in this field is seawater batteries (SWBs), which are currently in the research phase and have great potential in terms of storage. They represent a technological shift because they use the salts present in the aquatic environment—specifically sodium ions (Na⁺)—as the active material for storing energy. Rather than being sealed cells from start to finish, they have an open part that interacts with the seawater and oxygen in the environment. When charged with renewable electricity, the battery traps sodium from the saltwater and accumulates it at its negative pole. When discharging, the process naturally reverses, returning the sodium to the sea and releasing the stored electricity to the grid.
To keep this reaction stable and prevent water from degrading the internal components, these cells use a NASICON-type solid separator (sodium super-ionic conductor), a high-strength ceramic material. Unlike conventional plastic membranes, this ceramic component acts as a selective filter, allowing only sodium ions to pass through. This prevents two common problems associated with equipment submerged in seawater: the build-up of encrusted salts (scaling) and the adhesion of algae or microorganisms (fouling).
A three-in-one solution: renewable energy, water reuse, and carbon capture
Seawater batteries’ greatest potential lies in their ability to integrate various sustainability-contributing applications within a single operating cycle:
- Integrated water desalination: By combining the NASICON ceramic separator with a complementary membrane to capture chloride, the battery separates the salt from seawater while simultaneously storing electricity. This advantage is strategic for coastal regions subjected to periods of water stress. According to the Spanish Desalination and Reuse Association (AEDyR), Spain is leading the way in water reuse in Europe with rates between 10% and 13% of the flow treated through advanced systems, highlighting the energy efficiency of water treatment.
- Passive CO₂ capture: During discharge, the system naturally generates sodium hydroxide. This alkaline substance spontaneously reacts with the carbon dioxide (CO₂) dissolved in seawater and with minerals such as calcium or magnesium, causing the gas to transform into stable solid carbonates. This carbon sequestration mechanism operates without the need for heat or additional energy consumption.
The road towards industrial scale
Testing in laboratories and research centers has progressed from tiny button batteries to larger prototypes assembled in independent modules. This modular structure allows cells to be stacked like blocks, enabling adaptation to industrial facilities, docks, and generation parks at sea. The European Union is seeking to increase its capacity in this environment.
Although technical challenges remain to advance its commercial implementation, seawater battery research demonstrates how innovation can expand energy storage alternatives. Exploring new materials, resources, and applications creates opportunities for developing more efficient and sustainable solutions that can complement the advancement of renewable energies and utilize available resources more effectively.
