New fragmented carbon nanotube adhesive conductor could eliminate need for binders in Li-ion electrodes
A team of researchers at the University of Delaware has discovered a “sticky” conductive material that may eliminate the need for binders in Li-ion battery electrodes. Bingqing Wei, professor of mechanical engineering and doctoral student Zeyuan Cao recently discovered that fragmented carbon nanotube macrofilms (FCNT) can serve as adhesive conductors, combining two functions in one material. Their work is reported in ACS Nano, and they have filed a patent application on the discovery.
The problem with the current technology is that the binders impair the electrochemical performance of the battery because of their insulating properties. Furthermore, the organic solvents used to mix the binders and conductive materials together not only add to the expense of the final product, but also are toxic to humans.—Bingqing Wei
FCNTs are web-like meshes with “tentacles” that are coupled with active lithium-based cathode and anode materials. They are then assembled using simple ultrasound processing. The process employs no organic solvents.
The adhesive FCNT conductors provide not only a high electrical conductivity but also a strong adhesive force, functioning simultaneously as both the conductive additives and the binder materials for lithium-ion batteries. Such composite electrodes exhibit superior high-rate and retention capabilities compared to the electrodes using a conventional binder (PVDF) and a conductive additive (CB).
An in situ tribology method combining wear track imaging and force measurement is employed to evaluate the adhesion strength of the adhesive FCNT conductors. The adhesive FCNT conductors exhibit higher adhesion strength than PVDF. It has further been confirmed that the adhesive FCNT conductor can be used in both cathodes and anodes and is proved to be a competent substitute for polymer binders to maintain mechanical integrity and at the same time to provide electrical connectivity of active materials in the composite electrodes. The organic-solvent-free electrode manufacturing offers a promising strategy for the battery industry.—Cao and Wei (2014)
The approach could also be employed for electrode preparation for other energy storage devices such as electrochemical capacitors.
Zeyuan Cao and Bingqing Wei (2014) “Fragmented Carbon Nanotube Macrofilms as Adhesive Conductors for Lithium-Ion Batteries,” ACS Nano doi: 10.1021/nn500585g