An intrepid team of researchers at MIT have made a remarkable find in lithium battery technology – by using carbon nanotubes as one of a battery’s electrodes, they can increase the amount of power it can deliver by up to 10 times (compared to a conventional lithium-ion battery). Batteries are the driving force behind many great innovations in green tech but they are typically limited by the amount of power they can store, so this new finding stands to shape the future of sustainable technology.
To come to their conclusion, the team, led by Yang Shao-Horn and Paula Hammond, dipped a base material in solutions laced with carbon nanotubes that were treated with simple organic compounds that gave them either a positive or negative net charge. The dipping creates layers which, when alternated on a surface, bond tightly together because of the complementary charges, creating a stable and durable film.
So how is the new electrode material different from a conventional battery? Well, regular batteries like the ones typically used in portable electronics are made up of three parts: two electrodes (the anode, or negative electrode, and the cathode, or positive electrode) separated by an electrolyte. When the battery is in use, positively charged lithium ions travel across the electrolyte to the cathode, producing an electric current, and when it is recharged, an external current causes these ions to move the opposite way, embedding them in the spaces in the porous material of the anode.
In the MIT team’s battery, carbon nanotubes (lilliputian tubes of rolled-up carbon atom sheets) “self-assemble” into a tightly bound structure that is porous at the nanometer scale (billionths of a meter). The nanotubes also have many oxygen groups on their surfaces that have the ability to store many lithium ions, enabling the nanotubes to actually act as the positive electrode in lithium batteries. Hammond explains that the “electrostatic self-assembly” process is vital because carbon nanotubes have the tendency to clump together in bundles when on a surface, leaving fewer exposed surfaces to undergo reactions. However, by incorporating organic molecules on the nanotubes, they assemble in a way that “has a high degree of porosity while having a great number of nanotubes present.”
The new electrode’s energy output for a given weight was shown to be five times the amount of traditional capacitors, and the total power delivery rate was 10 times that of typical lithium-ion batteries, which the team attributes to good conduction of ions and electrons in the electrode, and efficient lithium storage on the surface of the nanotubes.