Abstract
Silicon (Si) has been perceived as a promising anode material for lithium-ion batteries for decades due to its superior theoretical capacity, environmental benignity, and earth abundance. To accommodate the drastic volume expansion during lithiation, which is the primary drawback leading to poor cycling life, a novel structural design via fabricating the Marimo-like carbon nanotubes frameworks with silicon nanoparticle (SiNP) filling in internal space has been developed. This facile fabrication procedure involves an in-spaced polymerization process through ex situ polymerization, using pyrrole monomers with a soft organic template in which well-dispersed SiNPs are present. Carbonization post-treatment is then performed to construct rigid conductive networks. The thus-fabricated 3D Marimo-like hybrid structure exhibits a remarkably improved electrochemical performance as compared with that of the simple ball-milling method, which mainly originates from their structural advantages, including the built-in buffer spaces and the robust line-to-line contact mode between the components. The state-of-the-art structure exhibits an optimal high-rate capability (422 mAh g−1 at a current rate of 2 A g−1) and long cycling stability (916 mAh g−1 for 200th cycles at a current rate of 0.2 A g−1), achieving the requirements for industrial production with the facile and cost-effective synthetic approach. In addition, a prominent anodic material of silicon ultranano particles (SiUPs, size < 10 nm) using recycled Si wafer fractures as raw materials and further improvement called top-down dispersion for high-capacitive Li-ion batteries has been addressed originally in this work. Economic benefits and outstanding electrochemical properties, including shorter Li-ion diffusive paths and low-strained effects as a result of the unique ultra-nanometric structure, make such SiUPs possess superior advantages for scalable manufacturing procedures as compared to other nanometric Si powders and become the priority as starting materials for Si-based anodes potentially. Meanwhile, an advanced top-down dispersive process has been optimized systematically to prevent severe particles aggregations to ameliorate the electrochemical performance of SiUPs electrodes. In addition to avoiding pre-aggregations, this top-down dispersion brings in adequate buffer spaces, constructed by dispersive media (graphite flakes) and well-dispersive ultrasmall SiUPs nanoclusters (size < 100 nm), alleviating drastic volume variation and local stress during cycling. This improved SiUPs electrodes maintained 1200 mAh g-1 capacity over 300 cycles under a high current density of 0.8 A g-1, coupled with ca. 98.5% reversibility. On their basis of these advantages, including low cost, facile manufacture and high performance, this original approach provides a pathway to achieve commercial high-capacitive Si-C composite anodes for Li-ion batteries. Furthermore, breakthrough ultranano Si-inserted nitrogen-doped graphene nanosheets (SiUPs@N-GNS) were designed as anode materials in Lithium ion batteries. A continuous manufacturing process, including top-down dispersion and bottom-up synthesis, was addressed incorporated with facile and cost-effective strategies to the industrialization. With this architecture, the volume variation induced by high capacitive SiUPs during lithiation/delithiation processes was suppressed effectively by means of several strain-released functions to extend the cycling lifetime. The intrinsic properties, such as particle size and configuration, and the well spatial distribution demonstrated by SiUPs would alleviate the volume change and local expansion within nanoarchitecture. Furthermore, in addition to establishing conductive networks, extended 2D-folded N-GNS enclosed by SiUPs provided the mechanical supports to buffer structural variations to stabilize active electrodes. As a leading high capacity graphene-based anode material, this state-of-the-art design exhibited long cycling performance up to 600 cycles at the current density of 0.5 A g-1 with the specific capacity of more than 1200 mAh g-1 and low capacity fading of less than ca. 0.09 % per cycle.