Printable two-dimensional materials for energy storage devices

2D materials have been attracting more and more attention for energy storage devices including supercapacitors and batteries because of their unique physical and chemical properties induced by dimensional reduction. The aim of research presented in this thesis was to develop a deep understanding of devices’ electrochemical performance with 2D materials and address some of the challenges currently faced by the printed 2D electronics field. 2D δ-MnO2 nanosheets which shows high theoretical specific capacitance were firstly studied as electroactive materials for micro-supercapacitors in this thesis. A printable water-based δ-MnO2 nanosheet ink was developed to demonstrate the possibility of inkjet printing 2D nanosheets. However, the poor electronic conductivity of δ-MnO2 nanosheets limits the devices electrochemical performance like power density. To improve the electronic conductivity of δ-MnO2 nanosheets, defect engineering of MnO2 nanosheets by atomic-level substitutional doping of 3d metal ions (Fe, Co and Ni) was investigated. Heterostructures constructed from different 2D nanosheet building blocks show promise for energy storage applications, since materials with different properties can be combined. Such 2D heterostructures were fabricated by inkjet printing MXene and graphene oxide (GO) nanosheets into a stacking structure. Enhancing power density and cycling life are crucial for a good battery. Due to the distinct electronic properties, shortened ion diffusion paths and more active site capability, an inkjet printed 2D materials heterostructure as cathode for a lithium-ion battery was studied in detail.