Molten Salt Batteries - Salt in Batteries?

Introduction

Salt isn’t usually what comes to mind when you think of batteries or energy storage. That’s usually lithium-ion batteries. They are in our phones and laptops, and they are even starting to get integrated into our energy grids. While they have their advantages, they have numerous disadvantages that are hard to ignore. For example, do you remember when phones were igniting on planes and a certain make had to be banned from carrying onto them? Lithium is highly reactive, overly so. Another component of the lithium-ion batteries, cobalt, is mined mostly in the Democratic Republic of Congo. Sadly, the conditions of miners are appalling. Lastly, as the European Parliament’s document states “Nonetheless, European battery energy storage deployments are expected to plateau over the 2024 - 2027 period due to Li-ion scarcity." All of the above mean that we must transition to a different technology, rather fast. One alternative is attracting lots of attention. In applications such as Energy Management Systems (EMS), we are already seeing some successes of molten salt battery EMSs. But why salt?

Quick Chemistry Lesson

Salt is in abundance on Earth. It can be found in our oceans, underground, and in our soil. It’s highly valuable to us because of sodium. Sodium shares many of the same characteristics with Lithium.

How is that possible?

Let’s take a step back. To simplify, all atoms have the same two parts. The nucleus (the core) and the electron cloud (the electron orbits). Now, sodium and lithium have a single electron in their outermost valence shell (you can call it the outer orbit). This configuration makes them highly reactive. When these electrons are involved in chemical reactions, such as those in batteries, they can move easily, which is crucial for the conduction of electricity.

In molten salt batteries, salts are melted to create a liquid electrolyte that facilitates the movement of ions, particularly sodium ions, between the battery's electrodes. This process enables the storage and release of energy. The use of sodium, instead of the more expensive and less abundant lithium offers a cost-effective alternative for large-scale energy storage solutions. Additionally, sodium-based systems can potentially offer better safety and thermal stability compared to their lithium counterparts.

Current Adoption of Molten Salt Batteries

Currently, organizations and companies are using Molten Salt Batteries (MSBs) for large-scale energy storage (as well as heat storage) solutions, helping to balance supply and demand in electrical grids & storing large amounts of energy in solar power plants. Some research is being conducted to use them in electric vehicles, although the high temperature required poses some challenges; therefore, I wouldn’t count on seeing them there.

Advantages Driving the Adoption

There are several advantages that drive the adoption of MSBs:

• Safety: They are non-flammable and have a low risk of thermal runaway, making them safer compared to other battery technologies.
• Long Cycle Life: MSBs can endure thousands of charge and discharge cycles, making them suitable for applications requiring durability and longevity. According to research, they can withstand 4500 charge/discharge cycles with 80% capacity.
• High Efficiency: They achieve high energy conversion efficiencies with low internal resistance, leading to less energy loss during operation.
• Scalability: Their modular design allows for easy adaptation to different energy storage needs, from small-scale systems to large grid-level installations.

Comparing Molten Salt Batteries with Other Technologies

How do MSBs compare with rivaling technologies?

1. Lithium-Ion Batteries

• Energy Density: Lithium-ion batteries have a higher energy density compared to molten salt batteries, making them more suitable for applications where space is limited, such as in electric vehicles and portable electronics.
• Operating Temperature: Lithium-ion batteries operate at ambient temperatures and do not require the high temperatures (250-300°C) that molten salt batteries do. This makes lithium-ion batteries more practical for everyday applications.
• Cycle Life: While lithium-ion batteries typically have a cycle life of 500-2,000 cycles, molten salt batteries can potentially exceed 4,500 cycles, offering longer life spans for stationary applications.
• Safety: Molten salt batteries have a significant safety advantage, as they are non-flammable and have a lower risk of thermal runaway compared to lithium-ion batteries, which can be prone to fires if damaged or improperly managed.

2. Sodium-Ion Batteries

• Material Availability: Sodium-ion batteries use sodium, which is abundant and inexpensive, similar to the raw materials used in molten salt batteries. This can make both technologies more sustainable and cost-effective in the long run.
• Performance: Sodium-ion batteries are still in the development phase and generally do not yet match the performance metrics of lithium-ion batteries. However, they can operate at lower temperatures than molten salt batteries, making them more versatile for various applications.
• Cycle Life: Sodium-ion batteries typically offer a shorter cycle life compared to molten salt batteries, which may make MSBs more appealing for applications requiring frequent cycling.

3. Flow Batteries

• Scalability: Flow batteries, such as vanadium redox flow batteries, are highly scalable and can be easily adjusted for larger storage capacities. This scalability is also a feature of molten salt batteries, which can be modularly designed for different applications.
• Energy Density: Flow batteries generally have lower energy densities compared to lithium-ion and molten salt batteries, making them less suitable for applications where space is at a premium.
• Cycle Life and Efficiency: Flow batteries can offer long cycle lives and are capable of deep discharges without significant degradation, similar to molten salt batteries. However, they tend to have lower round-trip efficiencies compared to lithium-ion batteries.

In short, if you need extremely high durability combined with impressively high safety, then molten salt batteries are your choice.

Examples of Projects Where Organizations Are Using Molten Salt Batteries with Success

Crescent Dunes Solar Energy Project

The Crescent Dunes Solar Energy Project is a 110 MW concentrated solar power (CSP) plant with 10 hours of molten salt energy storage located near Tonopah, Nevada. It was the first commercial-scale CSP plant in the U.S. to use a central receiver tower and advanced molten salt storage technology.

Kyoto

Molten salt solutions may also be used for thermal storage. That’s Kyoto’s approach with their Heatcube. Heatcube enables energy load shifting by storing energy from renewable sources when it is abundant, allowing for its use at a later time. This approach ensures that energy consumption occurs at its greenest and lowest cost. The stored heat ensures a reliable energy supply, mitigating the impact of market fluctuations and political influences on pricing. Crucially, Kyoto offers their solution in a Heat as a Product (HaaP) model as well as in a Heat as a Service (HaaS) model. For more information, visit their website.

Conclusion

Molten salt batteries offer exciting benefits for our net-zero future. Their safety combined with their extremely long life & the ability to use them as both energy & heat storage makes them optimal for a multitude of applications. In the face of limited supply of lithium and possible shortages of that element on the European market, molten salt batteries are posed to become important parts of the energy storage jigsaw puzzle.