Template-free Synthesis Of Arrayed Nanostructured Anodes For Application In Lithium-Ion Batteries

Along with the fast development of human society and science and technology, the demand for lithium-ion batteries (LIBs) with better electrochemical performance is urgent. However, the commercial LIBs are behind people’s expectations.Nanostructured electrodes with arrayed construction become an advanced research hotspot nowadays. Compared with traditional planar electrodes, nanostructured array electrodes can provide buffer space for the large volume changes of active materials during the Li+insertion/extration, faster electron and ion transfer speed, and they can also greatly improve the adhesion ability of the active material to the substrate. What’s more, they can be directly used as the anode electrode, with no conductive addictive or binder needed. Owing to the unique advantages, especially the excellent rate capability, the nanostructured electrodes with arrayed construction have been considered as one of the ideal choices for next-generation LIBs.In this dissertation, a serious of nanostructured electrodes with arrayed construction has been synthesized via new and facile non-template synthesis methods. Different from the traditional template-engaged methods, non-template methods are simple, time-saving, economical and efficient. By using the immersing, hydrothermal, voltage-controlled, and heat reduction methods, Ag nanowall arrays, Ag nanoparticle arrays, CoO nanowire arrays, NiO nanowall arrays, Co nanowire arrays have been in situ generated on the current collector substrate. On the basis of these array nanostructures, Ag-Si, Ag-Ge, Ag-Co3O4, Ag-NiO core-shell nanowall arrays, Ag-Si, Ag-NiO core-shell nanoparticle arrays, CoO-Si core-shell nanowire arrays, NiO-Si core-shell nanowall arrays, Co-Ge core-shell nanowire arrays have been prepared via the RF-sputtering method. These nanostructured electrodes all show excellent electrochemical performance. The main innovative results are displayed as follows:(1) Ag nanowall arrays and Ag nanoparticle arrays have been successfully synthesized by using a facile immersing method, with the substrate acting as the reducing agent, and applied to LIBs as a kind of versatile structural support, which can efficiently improve the electrochemical performance of anode materials.(2) On the basis of the Ag nanowall and Ag nanoparticle arrays, Ag-Si, Ag-Ge, Ag-Co3O4, Ag-NiO core-shell nanowall arrays, Ag-Si, Ag-NiO core-shell nanoparticle arrays have been successfully synthesized by using RF-sputtering method. Owing to their unique structural advantages, the core-shell nanostructured array electrodes exhibit stable cycling performance. At a current density of 0.2 C, the Ag-Si core-shell nanowall arrays exhibit a discharge capacity of 1679 mAh g-1 after 400 cycles; the Ag-Ge hybrid electrode show a capacity of 839 mAh g-1 after 30 cycles; Ag-Co3O4 nanostructured electrode show a capacity of 720 mAh g-1 after 30 cycles; Ag-NiO nanoflower electrode show about 800 mAh g-1 after 100 cycles; Ag-Si nanoparticle arrays show a capacity of over 1600 mAh g-1 after 50 cycles; Ag-NiO nanoparticle array electrode show a capacity of about 500 mAh g-1 after 100 cycles.(3) CoO-Si, NiO-Si oxide-silicon hybrid nanostructured electrodes have been synthesized by using hydrothermal method and RF-sputtering technique. When tested as anodes for LIBs, the oxide component can only act as the structural support and react with lithium only in the first discharge process taking advantage of the difference of the delithiation potential of the oxide and silicon. The as-synthesized nanostructured CoO-Si electrodes show a capacity of 1811 mAh g-1 after 200 cycles, and the NiO-Si nanostructured electrodes is found to offer a capacity of 1940 mAh g-1 after 100 cycles, better than the plain Si film electrode, which drops below 430 mAh g-1 after 20 cycles.(4) CoO nanowire arrays have been synthesized as precursor via hydrothermal method. Then, Co nanowire arrays have been obtained by heat reduction of CoO nanowires in H2/Ar atmosphere. Finally, Co-Ge core-shell nanowire arrays are fabricated by RF-sputtering method. The as-synthesized arrayed electrodes exhibit a capacity of 1535 mAh g-1 at 0.2 C after 100 cycles, and when the current rises to 5 C, they can still offer a capacity of 1239 mA h g-1.