Phosphorus Doped Silicon Nanowires as High-Performance Li-Ion Battery Anodes and Supercapacitor Electrodes

In order to address the challenges of poor cyclic stability and modest rate capability of Si-based anodes for Li-ion batteries, n-type Si nanowires (SiNWs) with varying phosphorus dopant content are developed via hot-wire-assisted vapor-liquid-solid growth directly on Cu current collectors. The process leads to uniform doping of the crystalline Si (c-Si) core and amorphous Si (a-Si) shell, with the increase in dopant content changing the SiNW morphology from “grass-like” to “solid tube-like.” Optimal phosphorus concentrations enhance the cyclic stability and rate-capability, leading to ≈94% capacity retention after 100 cycles at 1C and exhibit 53% of the C/5 capacity at 5C. As a supercapacitor electrode, an areal capacitance of ≈847 mF cm⁻² at 5 mV s⁻¹ is obtained, which is ≈6.5 times higher than their undoped counterpart. An areal energy density of 0.26 mWh cm⁻² at a power density of 3.17 mW cm⁻² is obtained with a symmetric supercapacitor, which is superior to most Si-based supercapacitors reported in the literature. Thus, the study helps to develop a correlative understanding of the effect of phosphorus doping and the resultant changes on SiNW morphology and on their electrochemical performances, while also demonstrating the feasibility of their usage in high-energy-density Li-ion batteries and supercapacitors.