Abstract

Nowadays, 2D MXene materials have attracted significant attention due to their unique structural, physical, and chemical properties. As a rising star within the 2D material family, MXenes exhibit a unique combination of multi-functional groups and possess a high surface area. Numerous investigations in recent years have shed light on the creation of MXene-polymer composites tailored for applications in the realm of energy storage. The particular significance is rechargeable batteries and supercapacitors, as they bear substantial promise for making substantial strides in the pursuit of sustainable energy solutions. However, the production of thoroughly exfoliated /delaminated 2D MXene nano-sheets is still a major challenge, limiting their potential for practical applications. Thus far, MXene flakes display colloidal stability only in a few polar solvents. Conversely, they are unstable in nonpolar or low polarity solvents, while critically important to significantly expand the spectrum of applications for MXenes. Furthermore, MXenes tend to get oxidized in the presence of oxygen and water during storage, handling, processing, delamination, and applications under ambient conditions.
In the present study, a self-assembly method to prepare ionomer-modified MXenes has been developed for the first time. Hyperbranched polyethylene ionomers containing quaternary ammonium ions are designed to prepare stable and highly concentrated modified Ti3C2Tx MXene dispersions in various nonpolar and low-polarity organic solvents. As a result, the interlayer spacing of Ti3C2Tx MXene is expanded to more than 5 nm (9.33 nm based on TEM results) with at least a 400% increase compared to the original spacing of 1 nm and can be delaminated to a few-layer or single-layer nano-flakes. The modification also markedly improves the oxidation stability of MXene sheets due to the presence of the tightly surface-bound hydrophobic hyperbranched polyethylene protecting layer.
Herein, an ionomer self-assembly strategy has been demonstrated to achieve high magnesium ion storage capability with pillar-structured Ti3C2Tx MXene. With the expansion of interlayer spacing of Ti3C2Tx MXene upon the ionomer intercalation and the affinity of the hyperbranched polyethylene-skeleton of the ionomers to THF-based electrolyte, the delaminated ionomer-modified MXene shows significantly improved electrochemical performance as a cathode material for Mg batteries. Subsequently, a symmetrical two-electrode supercapacitor exhibits a high capacitance in an ionic liquid electrolyte.
This thesis offers insights into the engineering of MXene electrode materials for applications in electrochemical energy storage.