Si Swarf Wrapped by Graphite Sheets for Li-Ion Battery Electrodes with Improved Overvoltage and Cyclability

Abstract

Composites of flake-shaped Si nanopowder from swarf treated as an industrial waste and ultrathin graphite sheets (GSs) (Si:C = 5:1 wt) are used in Li-ion battery electrodes. Si nanopowder is dispersed and wrapped between GSs fabricated from expanded graphite. The delithiation capacity of the Si/GS composite electrode during 300 cycles is 1.69 ∼ 0.83 mAh cm−2 (0.5 C), while that of the electrode with C-coated Si nanopowder (Si:C = 10:1 wt) fabricated in C2H4 is 1.55 ∼ 0.72 mAh cm−2. The series resistances (Rs) for the Si/GS electrode are a half and two-thirds of those for the C-coated Si electrode at the 6th and 300th cycles, respectively. The charge transfer resistance (Rct) for the Si/GS electrode is two-thirds of that for the C-coated Si electrode at the 300th cycle. GS bridges are formed across cracks, and suppress cracking and peeling-off of Si. Agglomerated GSs wrap Si/GS composites, and work as stable frameworks that secure electrolyte paths and buffer spaces for Si volume change. In the C-coated Si electrodes, Si frameworks fuse after the 300th cycle, leading to low delithiation capacities. The delithiation capacity of 4 mAh cm−2 for more than 75 cycles is achieved by the Si/GS electrode at the current density of 5 mA cm−2 with delithiation limitation at 1200 mAh g−1.

Enhanced Lithium Storage Performance in Si/MXene Porous Composites

“…At present, the specific capacity of commercial graphite negative electrode materials is close to the theoretical value (372 mAh g −1 ), and silicon (Si) has attracted the attention of researchers because of its high theoretical specific capacity [1]. However, during the lithiation/delithiation process, the large expansion of the silicon may cause severe mechanical stress, leading to the pulverization of the silicon and further the continuous worsening of the cycling capacity [2,3]. In addition, due to the crack of silicon, an unstable solid electrolyte interface (SEI) is prone to form consistently and therefore the extra and irreversible consumption of Li-ion in electrolytes [4,5].…”

Decreasing Deformation and Heat as Well as Intensifying Ionic Transport of Si Using a Negative Thermal Expansion Ceramic with High Ionic Conductivity

“…One is to design various morphologies, including nanospheres, nanowires, nanofilms, nanotubes, , and porous silicon, to mitigate bulk effects and reduce structural collapse . Another is to form silicon composites with other materials such as amorphous carbon, various graphites (natural graphite, expanded graphite, and graphene), − conductive polymers, Metal-organic frameworks (MOFs), Mxene, metals (Ag, Al, Cu, and Sn), and oxides (TiO 2 , SiO x , and Al 2 O 3 ) to buffer volume change or improve electrical conductivity. However, most of these methods only consider the volumetric effects and electrical conductivity of silicon and ignore the heat damage and deformation, which will bring disadvantages such as structural degradation, internal stress, deteriorating interface, and undesirable side reactions.…”