Porous MXene Synthesis and Applications for Batteries

Efficient electrochemical energy storage devices are of particular importance for accelerating the widespread adaption of renewable energy, and electrode materials are critical to achieve optimal system performance. MXene (transition metal carbides and/or nitrides) are recently discovered two-dimensional materials with desirable properties such as metallic conductivity and high hydrophilicity. They have shown promises in applications such as lithium ion, zinc ion and dual ion batteries, but limitations such as hazardous precursor, uncontrollable edge terminations and low surface area have restricted fulfillment of their potentials. Moreover, insights into the precise mechanism of MXene in composite formation and electrochemical reactions are still limited. To address the above issues, this thesis mainly focuses on developing novel strategy to synthesize high surface area porous MXene with uniform terminations, while probing their capability as high-performance electrodes for different types of battery systems. Particular focus is placed on investigating the influence of uniform Cl-termination and in-plane porosity on MXene when used as dual-ion battery anode. Afterwards, functions of the porous MXene as Prussian blue analogue (PBA) crystal growth inducing host for composite material and zinc ion redistribution protective layer for dendrite-free Zn anode are systematically investigated. Firstly, a novel one-step eutectic mixture etching method is developed to synthesize Cl-terminated MXene (Ti3C2Cl2) with abundant in-plane porosity through carefully controlling the phase transition of the etchants. Specifically, precise selection of etching parameters and salt mixture composition activates a mechanism that enables both pore generation and preservation through timely formation of solid salt particles within the material structure. The resulting in-plane porous MXene sheets exhibit homogeneously distributed mesoporosity and four-folds expansion in surface area to 85 m2 g−1. X-ray spectroscopy characterizations reveal predominately edge Cl-terminations with minimal oxidation on the as-synthesized samples, which ensure orderly crystal arrangement. Meanwhile, density functional theory calculations confirm lower diffusion barrier that are beneficial for ion diffusion. When evaluated as anode for dual ion batteries, the optimized porous Ti3C2Cl2 achieves a high specific capacity and excellent capacity retention. This work opens a green chemistry approach of incorp