טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentYehezkel Shani
SubjectDevelopment of Carbon Fabric as a Lightweight Highly
Conductive Current Collector for Li-ion Battery
DepartmentDepartment of Energy
Supervisor Professor Yair Ein-Eli
Full Thesis textFull thesis text - English Version


Abstract

Nowadays, Lithium-Ion is the most commonly used battery type. However, energy demands by portable electronic devices and mostly electric vehicles are getting higher with the advancements of those technologies, making the current Li-Ion technology insufficient, and therefore requiring the development of an improved Li-ion battery with higher specific energy. Carbon nanotubes (CNT) fabrics were studied and evaluated as anode current collectors, replacing the traditional copper foil current collector in Li-ion batteries. CNT fabrics are highly conductive, ultra-light weighted, thin, flexible and cost effective and therefore considered a superior candidate in the replacement of the copper foil. In this research, two approaches towards the implementation of the CNT fabric as the current collector were studied.

The first approach suggests the use of a bare CNT fabric current collector aiming for high energyhigh-energy applications. Galvanostatic measurements reveal high values of irreversible capacities (as high as 28%), resulted mainly from the formation of the solid electrolyte interphase (SEI) layer at the CNT fabric surface. Various pre-treatments to the CNT fabric prior to active anode material loading have shown that the lowest irreversible capacity is achieved by immersing and washing the CNT fabric with iso-propanol (IPA) or tert-butanol (T-butanol), which dramatically modified the fabric surface.  Additionally, the use of very thin CNT fabrics (5 µm) results in a substantial irreversible capacity minimization. A combination of IPA rinse action and utilization of the thinnest CNT fabric provides the lowest irreversible capacity of 13%.

The second approach suggests the use of a copper coatedcopper-coated CNT fabric current collector aiming for high power applications. Electrodeposition of copper on the surface of carbon nanotubes (CNT) fabrics is demonstrated upon immersion in two copper electrolytes:  acid copper sulfate (pH 0.5) and alkaline copper pyrophosphate (pH 8.6). The cathodic electrochemical behavior of the CNT fabric in the two electrolytes was evaluated and potentiodynamic characteristics were presented. Potentiostatic copper deposition on the outer surface of the CNT fabrics revealed different surface morphologies obtained from the two electroplating baths. Other factors affecting the copper surface morphology were presented such as CNT cleaning procedure, CNT thickness and various electrolyte additives. It was established that the deposited copper films are characterized by high uniformity, homogeneity and planarity and excellent adhesion of the copper films to CNT fabric was obtained. Finally, the performance of the coated CNT fabric as the anode current collector in a Li-ion battery is demonstrated.

The novelty of this research lies in improving both gravimetric and volumetric energy densities of the Li-ion battery without changing the chemistry of the cell. Furthermore, this research reports on two simple procedures to overcome the high irreversible capacity value while using graphite active material, and therefore preserve the high voltage when a CNT fabric current collector is used.