Welding Formability And Functional Applications In Lithium Metalanode Of Silver Nanowires Based On Plasmonic Welding

Nanowelding technology provides a bottom-up approach to build architectures and devices of unprecedented richness.In the past two decades,studies on nanowelding,including its methods,mechanisms,and applications,have gradually become the sally-ports for modern welding science and technology.Welding at nanoscale is not a simple extension of traditional macro-welding but truly helps to integrate the scientific and technical natures into the theoretical system of welding.In this thesis,the weldability of one-dimensional silver nanowires based on plasmonic welding,and the functionality of the welded silver nanowire networks were investigated.As an example,we explored one application of the welded structures in lithium metal anode.Firstly,the surface plasmon resonance in single silver nanowires and crossed nanowire junctions were calculated using the finite-difference time-domain method,as well as the evolution of the electric fields near a spot weld during its morphological changes.The silver nanowires for welding were synthesized by the polyol process.After illumination,the junctions were welded together locally,while regions away from the junctions were unaffected and no further morphological changes were observed.Secondly,the microstructures of spot welds were finely characterized,we found that the atoms first migrated along the surface of silver nanowires from the contact to the transition zone,then the free atoms were deposited on one nanowire surface of the a crossed nanowire junction,allowing epitaxial recrystallization onto that surface to form the final morphology of a spot weld.Our theoretical analysis reveals that the locality and self-limitation of the surface diffusion are the results of a combination of surface curvature change and strain relaxation,hence the formation of a spot weld is mainly determined by size and strain of nanowires,as well as their internal temperature increases.Furthermore,we proposed a strategy for adjusting the internal temperature of the nanowires separately based on the polarization dependence of plasmon coupling.The proposed strategy makes it possible to control the morphologies of spot welds,which is of a great significance to promote nanowelding technology.Lastly,the free-standing silver nanowire networks with high conductivity and high mechanical stability were fabricated via sunlight-induced plasmonic welding.We also explored the application of the welded nanowire networks in lithium metal anode as 3D current collectors.By studying the electrochemical behavior of lithium deposited on the networks,it is proved that the lithiophilicity of silver is the main inducement for the uniform lithium coverage at the nanowires,and the formation of surface alloy can serve as a buffer layer for lithium deposition.In our case,lithium metal anode can run formore than 150 cycles with a stable average columbic efficiency of 93.2% at the current density of 1m A cm-2,which is due to that the mechanical stability of the free-standing silver nanowire network current collector was effectively improved by our nanowelding process.