Advanced Anode and Cathode Materials for Li-ion Batteries: Application to Printing Methodology

Abstract

Batteries play an important role in energy storage applications spanning from electric vehicles, portable electronic devices to stationary storage grids. Basic structure of a lithium-ion battery (LIB) consists of two electrodes; the anode and the cathode separated by an ion-conductive electrolyte. With the advent of portable electronic products (such as internet of things, IoT), there is a growing need for rechargeable batteries with smaller size, smaller weight and higher energy densities. In recent years, inkjet printing has intrigued with the introduction of solution processed printed electronics (PE). PE and printed batteries have gained interest because they are inexpensive, easy to fabricate, up-scalable for large production and printing is possible on various kinds of substrates. Most research efforts strive for “better” batteries with high reversible capacities or the enhancement of the capacities of the state-of-the-art battery systems. Printing is a fast and inexpensive process and printed batteries with lower thickness values could be developed with the printing technique. The battery ink formulation can be tuned during printing procedure to achieve capacity and potential required for fully printed circuit. The demand for batteries that are thinner, and lighter with higher energy density has motivated the research into the next generation LIB electrodes, some of which will be explored in this work. The first focus of this dissertation is on the development of an alloying type anode material for the LIB, namely silicon (Si) and the assessment of its electrochemical and structural characteristics. The printability of Si/C anode inks and the effect of carbon coating on the improvement of the cycling process are analyzed. Later a full cell comprising of printed Si/C anode and NCM is fabricated. This full cell was used to deliver power to a printed electrolyte gated graphene transistor. In the next part of this work, a new material class was developed, namely the high entropy fluorides (HEFs). To realize the printed full cell battery a printed cathode was needed, so a conversion cathode material composed of fluoride-based materials was formulated. Collectively, high entropy materials (HEMs) consist of the solid solution of various elements, homogenously distributed. HEF based materials were synthesized via a facile direct mechanochemistry route that can be used to incorporate multiple cations in a single-phase rutile structure. Due to high electronegativity of fluorine, transition metal fluorides are interesting candidates for cathode materials because of their high theoretical capacity (>571 mAh/g) in contrast to the conventional intercalation cathodes. The multi-cation substitution may provide a new path for tailorable electrochemical properties of the conversion electrodes via entropy effects. However, the underlying conversion reaction mechanisms in the HEFs are yet to be explored and this forms the second part of this study. The comprehensive examination shows that HEF cathodes follow a conversion reaction mechanism and the capacity loss occurs due to kinetically limiting factors affecting the cathode side. For investigating the performance of the batteries, various electrochemical methods such as galvanostatic cycling, cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) are applied. A variety of structural characterization techniques were also employed to confirm the phase purities of electrode materials. Fabrication of batteries via printing was followed in this dissertation. Thickness of printed batteries are in millimeters range due to their reduced size and it can act as a power source for printed electronics. Finally, a full cell with carbon coated Si/C anode and HEF cathode is assembled and the viability of a completely printed full cell is demonstrated.