Replacing batteries with supercapacitors
Most batteries we use on a daily basis are rather inefficient. Rechargeable lithium batteries – like the one on your phone – take long to recharge and have short cycling lifetimes. This is detrimental to the environment and ultimately expensive.
Supercapacitors have the ability to store static electricity between two oppositely charged plates, and they have the benefit of being faster and more durable. However, the energy density (or amount of energy that can be stored per unit volume) of most supercapacitors is still considerably lower than most batteries. This is related to the capacitance of the supercapacitor, which depends on the material of the electrodes.
Researchers have experimented with negative electrodes made of molybdenum dioxide (MoO2) nanostructures, which could provide a high specific capacitance, but these are limited by slow kinetics and volume change upon cycling. This impedes electrochemical stability and leads to rapid degradation upon cycling.
To solve this problem, a group of researchers led by Prof. Seong Chan Jun, have designed a tubular nanostructure of MoO2 combined with nitrogen-doped carbon hybrids (MoO2@NC) as the negative electrode. The hollow nature of the structure provides a higher surface-to-volume ratio for the charge to distribute, enhancing its electrochemical performance. At the same time, the N-doped carbon enhances the electrolyte transportation of the material. This was synthesized along with a copper cobalt sulfide (CuCo2S4) structure as the positive electrode to complete the supercapacitor.
This resulted in a supercapacitor that performed significantly better than those previously reported in the literature. The flexible, hollow carbon substrate provided a large surface area that was also better able to alleviate volume change during cycling, improving electrical conductivity. The structure achieved what the author Prof. Jun described as an “ultrahigh”energy density of 65.1 W h kg -1 at a power density of 800 W kg -1. Approximately 90.6% of the initial specific capacitance was retained after 5000 cycles, and after 2000 bending cycles, the device exhibited 92.2% retention.
“Developing more efficient ways to store energy could significantly change the way we interact with electronics”, says Prof Jun. Flexible supercapacitors could make wearables more user-friendly. They are better for the environment, and lighter in weight. Because they can deliver and accept significantly faster than batteries, affordable and smaller supercapacitors have the potential to change the electric car industry.
Updated in August 2019
Professor Ki Jun Yu
Professor Donghyun Kim