Image source: Purdue University
Nowadays, people rely heavily on lithium-ion batteries. Under the driving of electric vehicles and battery energy storage systems, the demand for lithium batteries and lithium mines is increasing day by day. However, when lithium materials are finally used up, will there be energy catastrophe?
Therefore, Purdue University in the United States turned to sodium ion batteries, which are more abundant in raw materials and cheaper in materials. Recently, they have successfully solved the problem of “disability” of charge and discharge ions in sodium-ion batteries, and further improved the stability and capacity of battery charge and discharge.
Sodium is slightly better than the lithium mine in the content and cost of the earth's crust. The content of sodium crust is as high as 2.6%, and the content of sodium is more than 6th. In comparison, lithium is only 27, if it is cost, lithium and sodium are more It is 100 times different, lithium is about 15,000 US dollars per metric ton, and sodium is 150 US dollars. Obviously sodium is more successful in battery, but why is sodium ion battery still not commercialized?
At present, scientists have been able to control the sodium-water combustion reaction, but on the road to commercialization, sodium-ion batteries still have a major obstacle to be solved - sodium ions are easily lost during battery charging and discharging.
The sodium ion battery operates in the same way as a lithium ion battery. It mainly relies on sodium ions moving between the cathode and the anode to operate, but the sodium ions tend to adhere to the anode during charge and discharge without moving to the cathode.
This situation is also known as solid-electrolyte interphase (SEI), which forms a film of a thousandths of a millimeter thick on the graphite electrode, which protects the carbon particles from harmful reactions with the acidic electrolyte while allowing ions to be at the electrode. With the electrolyte, Vilas Pol, an associate professor of chemical engineering at Purdue University, said that the SEI phenomenon is not a bad thing, but the SEI film is too thick to consume the sodium ions needed for charging.
Therefore, Purdue University proposed a solution. If sodium is made into a powder, it can provide the required sodium for SEI to protect the carbon particles, and does not consume the sodium ions required for charging and discharging.
In order to reduce the contact between sodium and water vapor, the team conducted experiments in a glove box filled with inert gas argon, and used ultrasonic waves to melt the bulk sodium to form a milk-like liquid. Finally, the liquid was cooled and suspended. In the hexane solution, the sodium particles can be evenly distributed in the solution.
The experimental results are also quite in line with the scientists' expectations. After a few drops of sodium suspension are added to the anode or cathode, the sodium ion battery charge and discharge stability and battery capacity are effectively improved. Pol said that as long as the electrode processing process is slightly modified Can improve battery performance, which is another way to help sodium ion batteries go commercial.
Although the volume of sodium ions is about twice that of lithium ions, the weight or energy density may not be comparable to that of lithium-ion batteries, but the cost of this technology is relatively low, which is expected to significantly reduce the cost of grid-level battery energy storage systems. Leading the development of sodium ion batteries, the new technology of Purdue University has submitted a temporary application.
