By Lucas Bettle 

 

Energy storage systems are critical to supporting the scaling of renewable energy infrastructure, along with a variety of off-grid applications. While lithium-ion batteries currently dominate areas such as electric vehicles (EVs) and consumer electronics, resource scarcity and environmental impact pose significant challenges.

Saltwater battery technology is a potential alternative that offers the prospect of safe and sustainable solutions in key applications such as stationary, off-grid, and marine energy storage. This article compares saltwater batteries and lithium-ion systems to highlight areas where this technology can serve as a viable alternative for a more sustainable future.

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Saltwater Battery Technology

Saltwater batteries operate using sodium-based redox reactions in a variety of different designs. Sodium ions migrate toward and are deposited on an anode, which is often made of carbon materials, to avoid issues such as dendrite formation (Park, 2016). On the cathode side, the saltwater solution supports reactions such as oxygen evolution (OER) to balance the redox process. Designs can be as simple as a zinc-copper electrode pair immersed directly in saltwater, driven by zinc oxidation (Bhawal, 2024).

The performance of saltwater batteries is heavily dependent on cell design. Modern innovations, such as the use of a sodium (Na) superionic conductor (NASICON) membrane, facilitate sodium ion conduction while also avoiding direct contact between saltwater and reactive anode materials to improve durability (Hwang, 2018). The electrolyte’s salt concentration is critical, with higher concentrations theoretically improving energy density to as high as 423 Wh/kg (Jumare, 2020).

There are many performance factors to consider when evaluating saltwater batteries, including energy density, power density, cycle life, and safety. While theoretical energy densities can be competitive, current implementations lag behind lithium-ion systems at 100 to 200 Wh/kg compared to 200 to 300 Wh/kg (Park, 2016). However, saltwater batteries show exceptional cycle life, with some designs achieving 5,000 to 10,000 cycles. The water-based electrolyte also improves thermal stability by allowing passive cooling and avoids risks associated with flammable organic solvents (Hwang, 2018).

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Benefits of Adopting Saltwater Battery Systems

Saltwater batteries have a variety of properties that make them preferable to lithium-ion batteries in certain applications. Saltwater batteries are inherently safe, avoiding the serious thermal runaway risks associated with lithium-ion systems (Park, 2016).

The raw materials required to produce saltwater batteries are abundant and inexpensive. Sodium chloride is a ubiquitous resource that avoids the geopolitical supply risks and high production costs associated with critical minerals such as lithium and cobalt (Jumare, 2020). The environmental impact is much lower, along with having an end-of-life recycling process that is simpler and less hazardous, allowing for a sustainable circular economy for energy storage systems (Costa, 2021).

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Laboratory tests have shown that saltwater battery systems can achieve exceptional performance even after hundreds of cycles, with some designs showing potential for 5,000 to 10,000 cycles under optimal conditions (Park, 2016). With a long cycle life, low material costs, and favorable lifecycle costs, preliminary economic models suggest a current cost of around $189 per kWh (Park, 2016). While this value is roughly double the current bulk cost of lithium-ion batteries, further refinement and scaling could see costs become competitive.

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Current Challenges to Saltwater Battery Adoption

There are still some challenges facing saltwater batteries as the development of the technology moves forward. Lower energy density than lithium-ion batteries means a larger physical footprint to store the same amount of energy, posing a challenge in applications where space is limited (Park, 2016).

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Scaling current saltwater battery systems to multi-kWh or MWh deployments requires addressing a variety of engineering challenges. Maintaining consistent ion flow and minimizing internal resistance across physically larger modules both require advanced electrode design and uniform cell assembly (Bhawal, 2024).

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High current conditions can cause unwanted side reactions in certain saltwater battery designs. For example, changes in pH and other factors may lead to chlorine evolution (CER) competing with oxygen evolution (OER) at the cathode, reducing efficiency and damaging electrodes (Hwang, 2018). Addressing these reactions requires the development of improved catalyst and electrode design to maintain stable performance.

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Saltwater batteries also face a significant challenge entering a market dominated by the mature lithium-ion industry. The infancy of the technology and limited manufacturing scale of saltwater batteries make competing with lithium-ion batteries a significant hurdle. Several commercial ventures have failed to take off, among the most notable being the 2017 bankruptcy of Aquion Energy (Moore, 2017).

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Key Saltwater Battery System Applications

While limitations may prevent saltwater batteries from being a potential option in every application, there are certain areas where the technology’s unique benefits make it an ideal choice.

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Stationary energy storage and microgrids are applications where the footprint is less important, and both safety and lifecycle are top factors to consider. There are many remote islands, villages, or industrial sites that can benefit from stable, environmentally friendly storage (Yukselen, 2020).

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The use of saltwater-based cells is also suited to coastal or marine infrastructure, including navigational buoys, ocean sensors, or small-scale wave farms. The chemistry of saltwater batteries avoids complications related to corrosion that other options, such as lithium-ion batteries, would face in these challenging applications (Kim, 2022).

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Residential and commercial backup are also key applications where saltwater systems can replace lithium-ion batteries. The increased need for safety, along with less focus on footprint, makes saltwater batteries an excellent choice for storage from rooftop solar and other small-scale renewable energy systems (Bhawal, 2024). The same is also true for industrial uninterruptible power supplies in manufacturing plants, data centers, and other facilities that would significantly benefit from the non-flammable alternative to lithium-ion solutions (Yukselen, 2020).

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Balancing Safety, Sustainability, and Performance With Saltwater Batteries

Saltwater batteries represent an emerging, environmentally sound approach to large-scale energy storage. While current technology doesn’t reach the energy density of lithium-ion batteries, improvements in environmental impact, supply chain ethics, and safety make saltwater batteries a potential option for any application in which they are feasible.

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Even with current constraints, saltwater batteries provide a viable option for energy storage in various municipal, residential, commercial, and industrial applications where the footprint isn’t a deciding factor. As development continues, expected improvements in energy density and lower costs could see widespread adoption of saltwater batteries. Today, saltwater batteries are an environmentally sound, sustainable, and safe choice for stationary energy storage applications.

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References

1. Bhawal, S. (2024). Common Salt Water Battery for Sustainable Energy Solutions in Remote Areas. 2024 3rd Odisha International Conference on Electrical Power Engineering, Communication and Computing Technology (ODICON).

2. Costa, C. (2021). Recycling and environmental issues of lithium-ion batteries: Advances, challenges and opportunities. Energy Storage Materials.

3. Hwang, S. M. (2018). Rechargeable Seawater Batteries—From Concept to Applications . Advanced Materials.

4. Jumare, I. (2020). Energy storage with salt water battery: A preliminary design and economic assessment. Journal of Energy Storage.

5. Kim, D. (2022). Development of Rechargeable Seawater Battery Module. Journal of The Electrochemical Society.

6. Moore, D. (2017). Hyped battery maker Aquion Energy files for Chapter 11 bankruptcy . Pittsburgh Post-Gazette.

7. Park, S. (2016). Saltwater as the energy source for low-cost, safe rechargeable batteries. Journal of Materials Chemistry.

8. Yukselen, C. (2020). A Business Model Using Salt Water Battery and PV Panels for Continuity of Supply. 2020 International Conference on Smart Grids and Energy Systems (SGES).