Currently, Lithium-ion batteries rule the roost. However, there are several disadvantages to this technology. The first is that Lithium is not an abundant material. Compared to this, Sodium is one of the most abundantly available materials on the earth, therefore it is cheap. That makes it the most prime promising candidate for new battery technology. So far, however, the limited performance of Sodium-ion batteries has not allowed them a large-scale integration into the industry.
PNNL, or the Pacific Northwest National Laboratory, of the Department of Energy, is about to turn the tides in favor of Sodium-ion technology. They are in the process of developing a Sodium-ion battery that has excelled in laboratory tests for extended longevity. By ingeniously changing the ingredients of the liquid core of the battery, they have been able to overcome the performance issues that have plagued this technology so far. They have described their findings in the journal Nature Energy, and it is a promising recipe for a battery type that may one day replace Lithium-ion.
According to the lead author of the team at PNNL, they have shown in principle that Sodium-ion battery technology can be long-lasting and environmentally friendly. And all this is due to the use of the right salt for the electrolyte.
Batteries require an electrolyte that helps in keeping the energy flowing. By dissolving salts in a solvent, the electrolyte forms charged ions that flow between the two electrodes. As time passes, the charged ions and electrochemical reactions helping to keep the energy flowing get slower, and the battery is unable to recharge anymore. In the present Sodium-ion battery technologies, this process was happening much faster than in Lithium-ion batteries of similar construction.
A battery loses its ability to charge itself through repeated cycles of charging and discharging. The new battery technology developed by PNNL can hold its ability to be charged far longer than the present Sodium-ion batteries can.
The team at PNNL approached the problem by first removing the liquid solution and the salt solution in it and replacing it with a new electrolyte recipe. Laboratory tests proved the design to be durable, being able to hold up to 90 percent of its cell capacity even after 300 cycles of charges and discharges. This is significantly higher than the present chemistry of Sodium-ion batteries available today.
The present chemistry of the Sodium-ion batteries causes the dissolution of the protective film on the anode or the negative electrode over time. The film allows Sodium ions to pass through while preserving the life of the battery, and therefore, quite significantly critical. The PNNL technology protects this film by stabilizing it. Additionally, the new electrolyte places an ultra-thin protective layer on the cathode or positive electrode, thereby helping to further contribute to the stability of the entire unit.
The new electrolyte that PNNL has developed for the Sodium-ion batteries is a natural fire-extinguishing solution. It also remains non-changing with temperature excursions, making the battery operable at high temperatures. The key to this feature is the ultra-thin protection layer the electrolyte forms on the anode. Once formed, the thin layer remains a durable cover, allowing the long cycle life of the battery.