Synthesis and characterization of 3D nanowire networks for high-areal capacity Li-ion battery anodes

Details

Supervisors

Piraux, Luc ; Vlad, Alexandru

Faculty

Ecole polytechnique de Louvain

Degree label

Master [120] : ingénieur civil en chimie et science des matériaux

Abstract

The following master thesis studies the synthesis of three-dimensional (3D) interconnected transition metal core-shell nanocomposites (M-MOx), fabricated via polymer template-assisted electrodeposition and followed by controlled oxidation conditions. The attractive property of the 3D nanowires (NWs) is the combination of a very efficient metallic current collector M and a redox-active material MOx with superior performance as anode material for secondary lithium-ion batteries. Transition metal oxides react electrochemically with lithium in a so-called conversion reaction: while charging Li-ion batteries, the transition metal oxide shell should form Li2O and metallic particles M and while discharging, Li2O is decomposed and the metallic particles are oxidized. MOx is able to store more than two lithium ions per molecule which makes it a suitable candidate compared to other classical insertion anode materials. Furthermore, the electronic and ionic transport are enhanced at the nanoscale. Indeed, the metallic core improves the electrical connection between the active material and the current collector and the diffusion length for the lithium ion is smaller as well. Another advantage is the porous structure of the 3D NW network itself which accommodates well the volumetric changes during the lithiation and delithiation process. Moreover, the high surface-to-volume ratio between the electrolyte and the electrodes makes these structures favorable as the electrochemical reaction takes mainly place on the surface, which leads to higher Li+ storage. Nickel, iron, copper and cobalt-based NWs with diameters of 40 nm or 230 nm have been prepared successfully. Thermal annealing was carried out at temperatures ranging from 250 °C to 400 °C and for copper a chemical oxidation in alkaline conditions as well as direct cathodic electrodeposition of copper oxides in alkaline solution were investigated. Structural characterization was performed via Scanning Electron Microscopy. The mass of active materials MOx was estimated via Alternating Gradient Magnetometer measurements or Energy-Dispersive X-ray Spectroscopy. Finally, the electrodes were assembled in half-cells with lithium metal as counter electrode and Galvanostatic Charge–Discharge cycles were recorded on a Battery Testing System. From this study, it came out that Co-Co3O4 showed the highest coulombic efficiencies after the first cycle, close to 100%, and delivered very high capacities with even an increase in capacity from 1200 to 1370 mA·h/g after the first cycle. As expected, Cu-CuO delivered higher capacity than Cu-Cu2O. The lowest delithiation potential was reached by the Fe-Fe2O3 and the lowest lithiation potential was recorded for Ni-NiO. Motivation to carry on with the appealing research of 3D nanostructured conversion reaction-based anodes for Li-ion microbatteries is maintained but commercial applications for electric cars still remain a challenge due to the poor cycle life.