In the search for new, sustainable, environmentally friendly and, above all, safe energy storage solutions, one technology is currently attracting a great deal of attention: sodium-ion batteries.
This is hardly surprising, as they offer a number of advantages that make them particularly attractive for today's energy-conscious and environmentally friendly markets.
But what types of sodium-ion batteries are there, and why should you consider them as a viable option for the future?
The different types of sodium-ion technology
All sodium-ion batteries (often also called salt batteries or salt accumulators) share a basic principle: they use sodium ions that move back and forth between the electrodes to store or release electrical energy.
And yet, not all sodium-ion batteries are the same. Let's take a look at the different types, their specific properties and possible applications:
1. Thermal batteries with sodium metal
The best-known examples of this category include sodium-sulphur batteries (NAS) and sodium-nickel chloride batteries, also known as ZEBRA batteries.
These batteries use a solid electrolyte (sodium β-aluminate) that allows sodium ions to move between the anode and the cathode. However, this is only possible at high operating temperatures between 270 and 350°C, because the anode must be in the form of liquid sodium. At 100–120 Wh/kg, the energy density is very good compared to lead systems.
Cutaway model of a ZEBRA battery. Source: RudolfSimon, CC BY-SA 3.0,
One of the outstanding advantages of NAS and ZEBRA batteries is their extraordinary robustness. They can be used in a wide temperature range (-20°C to +60°C) and are therefore suitable for stationary applications.
They are mainly used for the backup power of critical infrastructure, as well as for load levelling and frequency regulation in power grids. Their ability to function in extreme temperature environments also makes them ideal for industrial applications – such as heavy industry, where they can help to increase energy efficiency and ensure process stability.
But NAS and ZEBRA batteries can also be used in urban transport systems, such as underground railways. Their robustness enables them to operate even under the harsh conditions of urban transport systems, providing a reliable and long-lasting source of energy.
Despite their many advantages, however, NAS and ZEBRA batteries do have disadvantages:
The production of these cells is more complex and therefore cannot be produced in the quantities and at the prices of classic wound cells. As a result, so-called economies of scale in production to reduce prices are not achieved.
The necessity to maintain high operating temperatures leads to increased energy consumption and higher operating costs. Furthermore, their energy density is only at a mediocre level compared to lithium battery technology, which limits the possible uses and economic viability of these batteries in certain applications.
In summary, however, it can be said that NAS and ZEBRA batteries offer a possible solution for stationary applications, while they are not suitable for mobile applications due to their weight and size.
Nevertheless, their suitability for integration into renewable energy systems and critical infrastructure, together with their ability to provide reliable emergency power, makes them a valuable element of modern energy infrastructure. Especially in times when sustainable and robust energy storage solutions are becoming increasingly important.
2. Sodium-ion batteries with aqueous electrolytes
Sodium-ion batteries with aqueous electrolytes, often also referred to as saltwater batteries, represent a particularly innovative category in the world of energy storage systems and can be assigned to the category of redox-flow batteries. They are particularly safe due to their water-based electrolytes and therefore represent an attractive alternative to traditional battery technologies.
These batteries use a solid electrolyte (sodium βaluminate) that allows sodium ions to move between the anode and the cathode. However, this is only possible at high operating temperatures between 270 and 350°C, because the anode must be in the form of liquid sodium. At 100-120 Wh/kg, the energy density is very good compared to lead systems.
Source: Greenrock
Their greatest strength is their exceptional safety, achieved by using non-flammable materials. They also have remarkable tolerance of deep discharge and can be safely discharged down to 0V without damage.
Advantages of saltwater batteries:
The robustness of these batteries against deep discharges makes them extremely reliable and low maintenance, making them ideal for applications where regular maintenance is difficult or costly.
Their environmental friendliness – due to the absence of heavy metals and hazardous chemicals – also minimises the risk of environmental damage and makes their disposal or recycling easier and safer.
Disadvantages and areas of application:
Despite their many advantages, saltwater batteries have a very low energy density (10 - 25 Wh/kg) and are therefore not suitable for many applications. Their size and weight limit their use in areas where space and weight efficiency are crucial.
They are technically suitable for stationary applications from a certain system size, but are not economically viable for small-scale systems, such as those in the home.
In larger energy infrastructures, they can also be used as part of a comprehensive energy distribution and load management system to ensure a reliable, safe and environmentally friendly energy supply.
In summary, sodium-ion batteries with aqueous electrolytes offer a safe, cost-effective and environmentally friendly solution for stationary energy storage applications.
Their ability to be deeply discharged without damage, their simple and safe chemistry, and their low maintenance costs make them particularly valuable for applications that require long-term, stable energy storage.
3. Sodium-ion batteries with organic electrolytes
At Salzstrom, we have chosen this type of sodium-ion battery because it is the most advanced choice for energy storage. Especially for stationary storage applications such as in combination with photovoltaic systems.
Source: Freepik
These batteries use organic electrolytes that make it possible to achieve higher cell voltages and thus significantly increase the energy density. This means that they can store a higher amount of energy in a smaller space, making them particularly efficient.
Advantages of sodium-ion batteries with organic electrolytes
Although the energy density of these batteries, at 120-160 Wh/kg, is still slightly lower than that of lithium iron phosphate (LFP) cells, which achieve between 150-190 Wh/kg, the progress in development is very promising and an approximation to the energy densities of LFP is already within reach. In the laboratory, energy densities of 200 Wh/kg have already been achieved with sodium-ion cell chemistries).
In addition, sodium-ion batteries with organic electrolytes offer twice the power density of lithium batteries. This means that a sodium-ion battery can be charged twice as fast as its lithium counterpart.
Another advantage is the wide temperature range. Sodium-ion batteries with organic electrolytes can be operated effectively in a range from -40°C to +60°C and therefore require a much less complex temperature management system than lithium systems. This reduces the system costs of outdoor installations.
Cost-effectiveness and sustainability
Sodium-ion batteries with organic electrolytes are already competitive with LFP batteries in the first product generation and have the potential to be 10% - 30% cheaper than LFP once comparable quantities are produced.
The carbon footprint of sodium-ion batteries with organic electrolytes is also smaller than for lithium or lead batteries, making them a more environmentally friendly alternative for energy storage.
Conclusion
In summary, these three types of sodium-ion batteries each offer individual advantages for different applications and challenges in modern energy storage.
The thermal batteries with sodium metal, in particular the NAS and ZEBRA batteries, are ideal for stationary applications that require long-term and reliable energy supply due to their high temperature resistance and robustness.
Their ability to operate in extreme conditions makes them a valuable resource for renewable energy storage and emergency power supply, as well as for industrial applications that require high energy densities.
Sodium-ion batteries with aqueous electrolytes offer an excellent option for stationary energy systems due to their environmental friendliness and high safety, especially where safety and easy maintenance are a priority and energy density is not an issue.
Sodium-ion batteries with organic electrolytes, on the other hand, set new standards in terms of energy density and robustness, which surpass many of the properties of lithium-ion batteries.
These batteries are particularly suitable for use in photovoltaic systems, where they not only drastically increase safety but also improve profitability and the efficiency of energy use. Their resilience to temperature fluctuations and their longevity make them an ideal choice for sustainable energy storage solutions.
So, as you can see, each type has its own specific strengths and applications that make it suitable for different requirements and operating environments. As these technologies continue to develop and become more integrated into various energy infrastructures, we can expect a more efficient, economical and environmentally friendly energy supply.
A look into the future
Sodium-ion technology is only at the beginning of its potential. At Salzstrom, we are committed to further developing and making this technology accessible in order to make a significant contribution to the energy transition.
With our sodium-ion batteries with organic electrolytes, we are very well positioned to meet the ever-growing challenges of the energy market and to play a key role in the development of sustainable energy storage solutions.
And we invite you to join us as we redefine the world of energy storage – for a clean, safe and sustainable future.
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