Sodium batteries with a longer useful life and immune to temperature thanks to a new electrolyte

A research team from Pacific Northwest National Laboratory (PNNL) belonging to the Department of Energy of the United States, has developed a sodium ion battery with a high life cycle, overcoming what is the biggest handicap of this technology to replace lithium batteries. The works focused on change the type of salt flowing through the electrolyte in such a way that it was possible to avoid the slowing down of the electrochemical reactions that maintain the flow of energy.

The perfect battery is impossible to achieve. That is why a combination of criteria is necessary to balance to try to achieve a product that meets all of them without being the best in any: safety, energy density, power, life cycle and high percentages of reuse and recycling, all of this , at the lowest possible cost.

In the case of this last criterion, low cost, sodium ion batteries are ideal candidates. This material is obtained from the oceans or the earth’s crust and is therefore cheap, abundant and sustainable. They also offer advantages to now operating at high temperatures, since they are not flammable and work well in cold climates. Although they don’t have as much capacity as lithium batteries, when cycled at high voltage (4.5 volts), they can greatly increase the amount of energy that can be stored in a given weight or volume. However, they give degradation problems when loading and unloadingwhich, until now, has hampered its commercialization.

The PNNL research team has worked around this drawback by modifying the ingredients that make up the liquid core of the battery. That change avoids the performance issues that sodium-based batteries have seen. The research and its results have been published in the journal Nature Energy. The director of the research, Jiguang (Jason) Zhang, a pioneer in battery technologies with more than 23 patented inventions, claims to have shown “that sodium ion batteries have the potential to be a durable and environmentally friendly technology.”

As Zhang explains, in batteries, the electrolyte is the “blood” that circulates and maintains the flow of energy. It is formed by dissolving salts in solvents, resulting in charged ions that flow between the positive and negative electrodes. Over time, the electrochemical reactions that keep energy flowing slow down and the battery stops being able to recharge. In current sodium-ion battery technologies, this process occurs much faster than in lithium-ion batteries.

electrolyte salt batteries sodium ions pnnl-interior
In laboratory tests, scientists greatly expanded the number of charge and discharge cycles to more than 300 with minimal capacity loss (less than 10%) for a coin-sized battery.

The current recipe for sodium ion battery electrolyte results in the protective film on the negative end (the anode) dissolving over time. This film is critical because it allows sodium ions to pass through, conserving battery life. The technology designed by PNNL works by stabilizing this protective film.

The PNNL team attacked the problem by changing the liquid solution and the type of salt that flows through it to create a new chemical recipe for the electrolyte. The new electrolyte also generates an ultra-thin protective layer on the positive pole (the cathode) which contributes to the additional stability of the entire unit.

In laboratory tests, for the first time, scientists greatly expanded the number of charge and discharge cycles (over 300) with a minimal capacity loss (less than 10%) for the case of a coin-sized battery.

Technology recently developed by PNNL researchers uses a solution that works well as a natural fire suppression system that it is impervious to temperature changes and that it can operate at high voltages. The key to this feature is precisely the ultra-thin protective layer that is created on the anode that remains stable once formed, providing the extended life cycle.

Sodium ion battery technology still late with respect to achieving a high rate of energy density. However, its advantages, such as resistance to temperature change, stability and long cycle life, make it competitive with lithium because they are valuable for implementation in light electric vehicles and even for grid energy storage.

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