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FULLY DIGITAL - NO PUBLIC : PhD Defence Yang Wang | Printable two-dimensional materials for energy storage devices

Printable two-dimensional materials for energy storage devices

Due to the COVID-19 crisis measures the PhD defence of Yang Wang will take place online in the presence of an invited audience.

The PhD defence can be followed by a live stream.

Yang Wang is a PhD student in the research group Inorganic Materials Science (IMS). His supervisor is J.E. ten Elshof from the Faculty of Science and Technology (TNW).

The functionalities of 2D materials offers tremendous opportunities for energy storage applications. By utilizing versatile inkjet printing technology, low-cost and large-scale energy storage devices can be fabricated on different substrates to meet various demands. The research in this thesis is focused on printing different 2D nanosheets as active materials for supercapacitors and Li-ion batteries applications.

In Chapter 2, a printable ink of two-dimensional δ-MnO2 nanosheets with an average lateral size of 89 nm and around 1 nm thickness was prepared in water solution. A small amount of Triton X-100 was added as surfactant to reduce the surface tension of water and propylene glycol was used to increase viscosity of water to meet the requirements of inkjet printer. By optimizing the ink formulation and printing parameters, uniform printed films were achieved without undesired “coffee-ring” effect. Thickness dependent specific capacitance of inkjet printed δ-MnO2 electrodes were studied. As a proof of concept, all-solid-state symmetrical micro-supercapacitors were fabricated by inkjet printing δ-MnO2 nanosheets as active materials.

In Chapter 3, defect engineering of MnO2 nanosheets by substitutional doping of 3d metal ions (Co, Fe and Ni) was performed to improve the specific capacitance of MnO2 electrodes. Printable inks of doped MnO2 nanosheets were prepared based on the same ink formulation consisting of Triton X-100 and propylene glycol. The electrochemical performances of doped and pristine printed MnO2 nanosheet electrodes were investigated. First principles calculations were carried out to gain further insight into the effect of aliovalent doping on the electronic properties of MnO2 nanosheets. All-solid-state symmetrical micro-supercapacitors were fabricated by printing Fe-doped MnO2 nanosheets as active materials.

In Chapter 4, all-inkjet-printed nanosheets heterostructures were fabricated by printing MXene nanosheets as electrodes and graphene oxide (GO) nanosheets as solid-state electrolyte in sandwiched and interdigitated configurations. Printing parameters were optimized to achieve a clear interface between MXene and GO layers. The printed 2D heterostructures with sandwiched configurations showed high capacitance without any liquid electrolyte present. In contrast, the printed 2D heterostructure with interdigitated configurations only showed comparable capacitance by adding water on top of the devices. The capacitances of both devices could be tuned by adding different liquid electrolytes on top.

In Chapter 5, a 2D heterostructure cathode was fabricated by printing water-based V2O5 nanosheets and MXene nanosheets composite inks on a current collector to serve as a cathode for Li-ion batteries. MXene nanosheets show excellent electronic conductivity and are highly hydrophilic, which results in good adhesion between printed electrodes and current collectors. Inkjet printing was employed to fabricate electrodes with well controlled surface roughness and precisely controlled thickness. We demonstrate inkjet printed V2O5/Ti3C2Tx thin film cathodes in lithium-ion batteries with high capacity and long cycling life.

In Chapter 6, the crucial challenges and opportunities of printable 2D materials for energy storage devices are discussed.