Solution-Grown Phosphorus-Hyperdoped Silicon Nanowires/Carbon Nanotube Bilayer Fabric as a High-Performance Lithium-Ion Battery Anode

The solution synthetic method can produce large quantities of silicon nanowires (SiNWs) for various applications, such as energy storage, texturing and composites materials, etc. However, solution-grown SiNWs exhibit very low conductivity compared to chemical vapor deposition (CVD)-grown SiNWs due to their poor crystallinity or reaction byproducts such as insulating polysiliane or polyphenylsilane. Here, we report the large-scale synthesis of phosphorus-hyperdoped Si nanowires (PH-SiNWs) with atomic ratios of the P content ranging from 1 to 2 atom % via the tin­(Sn)-seeded supercritical fluid–liquid–solid (SFLS) through the use of red P nanoparticles as dopant precursors. The resistivity of PH-SiNWs is 4.3 × 10^–3 Ω·m, which is about 6 orders of magnitude lower than bulk silicon (Si) (1.86 × 10³ Ω·m) and about 3 orders of magnitude lower than intrinsic SiNWs (1.19 Ω·m). PH-SiNWs can be assembled on fabrics used as active materials for lithium-ion batteries, and combined with carbon nanotube fabric as current collectors, the bilayer fabrics can be used as freestanding independent lithium-ion battery anodes without the need for binders and additive. The PH-SiNWs/carbon nanotube (CNT) bilayer fabric anode reaches 820 mAh g^–1 after 1000 cycles at a charge/discharge rate of 2 A g^–1, whereas the intrinsic SiNWs/CNT bilayer fabric only sustains its performance at the first 20 cycles. The PH-SiNWs/CNT bilayer fabric anode shows the first example of a solution-grown Si nanowire anode with a 1000-cycle life. The ex situ transmission electron microscopy (TEM) image shows that an evolved PH-SiNWs nanopore structure was formed after the cycle, whereas the intrinsic SiNWs anodes did not develop holes. This result can be attributed to the uniform doping of P in the Si nanowire, which enables the formation of nanopores for rapid lithium-ion transport tunnels.