Nanopurification of silicon from 84% to 99.999% purity with a simple and scalable process

Abstract

Silicon, with its great abundance and mature infrastructure, is a foundational material for a range of applications, such as electronics, sensors, solar cells, batteries, and thermoelectrics. These applications rely on the purification of Si to different levels. Recently, it has been shown that nanosized silicon can offer additional advantages, such as enhanced mechanical properties, significant absorption enhancement, and reduced thermal conductivity. However, current processes to produce and purify Si are complex, expensive, and energy-intensive. Here, we show a nanopurification process, which involves only simple and scalable ball milling and acid etching, to increase Si purity drastically [up to 99.999% (wt %)] directly from low-grade and low-cost ferrosilicon [84% (wt %) Si; ∼$1/kg]. It is found that the impurity-rich regions are mechanically weak as breaking points during ball milling and thus, exposed on the surface, and they can be conveniently and effectively removed by chemical etching. We discovered that the purity goes up with the size of Si particles going down, resulting in high purity at the sub-100-nm scale. The produced Si nanoparticles with high purity and small size exhibit high performance as Li ion battery anodes, with high reversible capacity (1,755 mAh g −1 ) and long cycle life (73% capacity retention over 500 cycles). This nanopurification process provides a complimentary route to produce Si, with finely controlled size and purity, in a diverse set of applications.Si | purification | nanoparticles | low grade | Li ion battery E lemental Si has a large impact on the development of modern society, with different purities and sizes widely used for different applications (1-6). Achieving precise purity control is a crucial step in the development of semiconductor devices, because impurities alter the basic properties (mechanical, optical, electrical, and thermal) of semiconductors substantially. For example, it is well-known that silicon wafers need to be refined to a purity of 99.9999999% (wt %) (nine nines) for integrated circuits. In the case of photovoltaics, it is regarded that the purity of Si needs to be above 99.9999% (wt %) (six nines) to enable long carrier diffusion length (2, 7). Also, it has also been shown that Si nanowires and nanoparticles can provide several advantages, such as absorption enhancement, efficient carrier extraction, and reduced requirements for material quality (8-12). Si is also one of the most important materials for thermoelectrics, where both nanosize and heavy doping are necessary to effectively scatter phonons and tune the electronic properties, respectively (13-16). With rapid development in the past decade, Si has become one of the most promising candidates for lithium ion battery anode (17-26), where Si nanoparticles with purity above 99% (wt %) and sizes below 150 nm have shown very high capacity without mechanical fracture during electrochemical cycling (27)(28)(29).Although Si, widely distributed in dusts, sands, and planets as various forms of sil...

Challenges and Recent Progress in the Development of Si Anodes for Lithium‐Ion Battery

“…Traditionally, silicon nanostructures are fabricated either from top-down (chemical etching) or bottom-up (CVD) method, which typically involve either toxic silane precursors or expensive high purity silicon sources. Recently, it is found that various low grade silicon [7,48,88,89,90] and natural sources [91][92][93][94][95][96] can serve as cost-effective sources to produce nanostructured silicon for lithium-ion battery.…”

“…The purity of these obtained nanoparticles can also be improved by acid etching processes up to 99.999% (wt%). [7] During high energy ball-milling processes, the impurity-rich regions containing Fe, Al, and Ca are mechanically weak, can be easily exposed on the surface, and be effectively removed through acid etching. Therefore, it can be easily understood that the purity goes up with the smaller size of Si particles in this nanopurification process (Figure 11b).…”

“…b) Reproduced with permission. [7] Copyright 2015, National Academy of Sciences. c) Reproduced with permission.…”

Production of High Purity Metals: A Review on Zone Refining Process

“…In addition, there are also some other analytical methodologies, such as Atomic absorption spectrometry with graphite furnace (AASGF) with the limit of detection limit range between 10 -400 ppb [20], Spark source mass spectrometry (SSMS) with detection limit of sub ppm [60], X-ray fluorescence (XRF) with detection limit of 0.001% [61], and van der Pauw Hall effect measurement [18] [62]. The detailed comparison of these high purity analysis methods has been presented in Table 4.…”

CMOS Position-Based Charge Qubits: Theoretical Analysis of Control and Entanglement

“…In support of the scientific and technological feasibility of the proposed charge qubit, the purity of silicon in modern high-volume commercial nanometer-scale CMOS has dramatically increased since the previous wave of realizations of the charge qubit [39]. This has been driven by increasingly sophisticated CMOS lithographic processes with ultrahigh switching speed of devices as well as improved defect tolerances, required to achieve ever increasing densities of functioning transistors (tens of millions per mm 2 ) on microprocessor chips.…”