Abstract
A tri-dimensional interweaving kinked silicon nanowires (k-SiNWs) assembly, with a Ni current collector co-integrated, is evaluated as electrode configuration for lithium ion batteries. The large-scale fabrication of k-SiNWs is based on a procedure for continuous metal assisted chemical etching of Si, supported by a chemical peeling step that enables the reuse of the Si substrate. The kinks are triggered by a simple, repetitive etch-quench sequence in a HF and H2O2-based etchant. We find that the inter-locking frameworks of k-SiNWs and multi-walled carbon nanotubes exhibit beneficial mechanical properties with a foam-like behavior amplified by the kinks and a suitable porosity for a minimal electrode deformation upon Li insertion. In addition, ionic liquid electrolyte systems associated with the integrated Ni current collector repress the detrimental effects related to the Si-Li alloying reaction, enabling high cycling stability with 80% capacity retention (1695 mAh/gSi) after 100 cycles. Areal capacities of 2.42 mAh/cm2 (1276 mAh/gelectrode) can be achieved at the maximum evaluated thickness (corresponding to 1.3 mgSi/cm2). This work emphasizes the versatility of the metal assisted chemical etching for the synthesis of advanced Si nanostructures for high performance lithium ion battery electrodes.
Highlights
A tri-dimensional interweaving kinked silicon nanowires (k-SiNWs) assembly, with a Ni current collector co-integrated, is evaluated as electrode configuration for lithium ion batteries
We report a continuous synthesis of kinked SiNWs (k-SiNWs) by metal assisted chemical etching sustained by chemical peeling that facilitates the extraction of the k-SiNWs and allows for the reuse of the Si substrate
We find that k-SiNWs, when used as active material in a lithium ion battery, show major benefits considering the simplicity of the proposed synthesis, the particular k-SiNWs morphology as well as the favorable association of mechanical and electrochemical properties
Summary
We selected Ni to investigate the effect of surface passivation on the electrochemical performance of the k-SiNWs-based assembly[18]. While we explored the feasibility of k-SiNWs as active material for lithium ion battery electrodes and used Ni as a model system to further emphasize passivation as a requirement for stable cycling of Si-based anodes, the 33 nm-thick conformal coating of k-SiNWs is expected to increase by 20% the weight of the integrated current collector compared to the conventional Cu foil. In this sense, lighter functional materials such as conducting polymers can successfully replace the metallic current collector and enable full exploitation of Si anodes[49,50]. The enhanced electrochemical performance of the electrodes results from the synergy between the k-SiNWs three-dimensional interlocking features and the critical contributions of the Ni coating associated with the robust SEI film activated by the ionic liquid electrolytes
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