Metal Organic Frameworks (MOF)- Effective Sulfur Encapsulant in Lithium Sulfur Batteries

The demand for electric vehicles continues to grow as society is shifting away from fossil fuels. Due to this, the need for improved energy storage is required to meet the needs of these vehicles, such as being able to travel similar distances to fossil fuel based vehicles without stopping to charge the system. Currently, Lithium Ion batteries are the most advanced batteries available, but can, on average, only reach up to 300 miles per charge in an electric vehicle. A promising battery configuration is Lithium Sulfur batteries, which utilizes sulfur as the positive electrode (cathode) and lithium as the negative electrode (anode). These batteries can reach capacities of nearly 1672 mAh/g, which is over five times the magnitude of the state of the art lithium batteries. Unfortunately, these batteries have a short lifespan, not reaching even 100 cycles, whereas the lithium ion batteries can perform consistently for up to 1000 cycles. This is due to the dissolution of the sulfur ions into the electrolyte, causing the sulfur electrode to lose material over time. Through the use of metal organic frameworks (MOFs), this dissolution of the sulfur ion into the electrolyte was prohibited. By injecting the sulfur into the MOF and using this as the structure for the positive electrode, the sulfur would be trapped in the porous, cubic formation. The lithium ions would be able to infiltrate and attach to the sulfur to form the lithium polysulfide compounds, before breaking apart during the charging stage. Through testing of both zinc and magnesium MOF structures, it was found that after 40 cycles of discharging, the capacity leveled at approximately 600 mAh/g, compared to the stable capacity at approximately 30 mAh/g for a pure sulfur electrode. After reaching stability, a decrease of 9.4% for Zinc and 2.7% for Magnesium was observed, whereas commercial sulfur decreased at 47%.