Si-based three-dimensional assembly for lithium-ion batteries

Silicon is considered the fulcrum of the next generation lithium-ion systems due to its exceptional capacity and low working voltage. Many instabilities are associated with the huge volume expansion during lithium alloying, generating material degradation and inducing rapid capacity devolution. Thus, a suitable Si-based anode relies on engineered nanostructures that can avoid the lithiation-induced cracking and architectures that can accommodate the volumes changes, while sustaining scalability and simplicity required for commercial adoption. We detail on the fabrication of an intertwined material based on flexuous Si nanowires (f-SiNWs). The large-scale synthesis of f-SiNWs relies on metal assisted chemical etching. A chemical peeling procedure has been developed to facilitate the separation of f-SiNWs from their substrate by adjusting the concentration of oxidizing agent to favor the formation of a porous segment. By scanning probe microscopy techniques, we study the morphological, electrical and mechanical properties of the f-SiNWs. The three-dimensionally-entangled f-SiNWs-based materials are assembled via a vacuum filtration technique with MWCNTs as percolative conductive pathways. In the absence of binders, the cohesion between layers of active materials and the structural integrity of the assembly are offered by f-SiNWs. These materials exhibit improved electrochemical performance with ionic liquids compared to conventional electrolytes. A thin Ni coating on the f-SiNWs has been found to further enhance the cycling life of these materials. The mechanical and electrochemical robustness of the Si-based electrode are mainly assigned to the flexuous nano-architecture of the SiNWs [G. Sandu et al. submitted]