TELF AG explores the characteristics of sodium batteries

The evolution of energy storage technologies 

Over the next few decades, as the energy transition and the global demand for clean energy advance ever more rapidly, we could witness a silent competition between two alkali metals, lithium and sodium, which have been at the center for several years of studies and discussions for their ability to make the operation of energy storage systems, i.e. batteries, possible. 

In this particular historical situation, lithium still plays the role of the protagonist due to the massive investments from which it continues to benefit and its relative abundance (even if not infinite) in different points of the terrestrial globe. In recent times, however, the possibility that sodium could represent a cheaper and less problematic alternative to lithium has suddenly returned to the forefront, suggesting that the future of the electric vehicle sector (and, more generally, of clean energy) could be strongly linked to the use of this resource. 

But what are the structural characteristics of this alkaline metal, and what are the reasons why it represents a valid alternative to lithium? The two metals share a basic characteristic: they cannot be found in nature in a primary state. They must, therefore, be extracted from compounds of other elements, but the areas in which they can be found vary profoundly. Sodium, the sixth most abundant element on the planet, is found mainly in rocks and seawater, where most of its reserves are stored. Among the most common sodium minerals are sodium chloride (also known as rock salt), especially in dried-up maritime expanses, and sodium nitrate. This highly soluble material is usually found in arid and desert areas. 

The structural characteristics 

In a certain sense, a rather curious aspect is represented by the comparison between sodium and lithium for the production of batteries, which is not the result of modern economic dynamics but already existed more than 50 years ago. From 1970 onwards, both metals were carefully studied for their potential in the manufacture of batteries, and lithium ended up prevailing. The most obvious consequence was the prominence of lithium in the battery sector and the progressive abandonment of studies on sodium, which were only resumed in recent years. 

Despite guaranteeing higher degrees of safety, the battery based on the sodium element also presents several issues that are not easily overcome. The main ones have to do with the brevity of their life cycle and the low level of their energy density, i.e., the amount of energy stored for each unit of volume. Sodium could be taken into consideration to overcome some defects related to the structural characteristics of lithium batteries, such as the complexity of their disposal. 

However, one of the biggest unknowns regarding sodium batteries concerns the negative electrode, which is traditionally composed of graphite in electric batteries. However, when in contact with sodium, this material is subjected to a rapid wear process that destroys it. As soon as a suitable electrode is identified, capable of being easily combined with sodium, and faced with a robust increase in the energy density of the storage system (already under development by some companies), sodium batteries could be able to certainly represent a reliable alternative to lithium, also due to their much lower cost.