Preparation and Characterization of Electrochemical Devices for Energy Storage and Debonding

University dissertation from Stockholm : KTH Royal Institute of Technology

Abstract: Within the framework of this thesis, three innovative electrochemical devices have been studied. A part of the work is devoted to an already existing device, laminates which are debonded by the application of a voltage. This type of material can potentially be used in a wide range of applications, including adhesive joints in vehicles to both reduce the total weight and to simplify the disassembly after end-of-life, enabling an inexpensive recycling process. Although already a functioning device, the development and tailoring of this process was slowed by a lack of knowledge concerning the actual electrochemical processes responsible for the debonding. The laminate studied consisted of an epoxy adhesive, mixed with an ionic liquid, bonding two aluminium foils. The results showed that the electrochemical reaction taking place at the releasing anode interface caused a very large increase in potential during galvanostatic polarization. Scanning electron microscopy images showed reaction products growing out from the electrode surface into the adhesive. These reaction products were believed to cause the debonding through swelling of the anodic interface so rupturing the adhesive bond.The other part of the work in this thesis was aimed at innovative lithium ion (Li?ion) battery concepts. Commercial Li-ion batteries are two-dimensional thin film constructions utilized in most often mechanically rigid products. Two routes were followed in this thesis. In the first, the aim was flexible batteries that could be used in applications such as bendable reading devices. For this purpose, nano-fibrillated cellulose was used as binder material to make flexible battery components. This was achieved through a water-based filtration process, creating flexible and strong papers. These paper-based battery components showed good mechanical properties as well as good rate capabilities during cycling. The drawback using this method was relatively low coulombic efficiencies believed to originate from side-reactions caused by water remnants in the cellulose structure. The second Li-ion battery route comprised an electrochemical process to coat carbon fibers, shown to perform well as negative electrode in Li-ion batteries, from a monomer solution. The resulting polymer coatings were ~500 nm thick and contained lithium ions. This process could be controlled by mainly salt content in the monomer solution and polarization time, yielding thin and apparently pin-hole free coatings. By utilizing the carbon fiber/polymer composite as integrated electrode and electrolyte, a variety of battery designs could possibly be created, such as three-dimensional batteries and structural batteries.