Recycling of kerf loss silicon: An optimized method to realize effective elimination of various impurities.

Photovoltaic solid waste, particularly diamond-wire sawing silicon powder (DWSSP), has emerged as a significant concern in the industry. Consequently, the recycling and reuse of such waste have become a prominent research focus. In this study, focusing on achieving direct recycling and reuse of DWSSP, the key driving factors for effective purification were identified. It was found that simply increasing the melting temperature and time was insufficient to completely remove volatile impurities, and the migration process in the melt had to be taken into consideration. Additionally, this study focused on analyzing the instability model of inter-granular grain growth and its impact on the stable migration of impurities, with particular attention to the microstructure of inter-granular micro-regions. The thermal control directional solidification technique focused on controlling the temperature gradient during the melt solidification process. This approach helped stabilize the microstructure, enhance impurity migration, and ultimately led to a more effective purification of DWSSP.

Recycling of diamond-wire sawing silicon powder by direct current assisted directional solidification.

As the unavoidable by-products in the production of solar cells, the recycling and reuse of diamond-wire sawing silicon powder (DWSSP) have always been a key issue in the solar energy industry. However, until now, there is no effective method to achieve effective recovery of high-purity silicon. In this work, a new method was proposed to achieve the recycling of DWSSP. Direct current, as an external means, was introduced into the recycling process of DWSSP, and its influence mechanism on impurity removal process was also discussed. By optimizing the local temperature gradient at the front of the Solid-Liquid interface, and the impurity diffusion behavior at the front of the interface was improved. After purification, the impurity content in the silicon ingot is reduced significantly. Among them, Al, as the main metal impurity element was reduced to less than 5ppmw (from 13580ppmw), and Ni (80.78ppmw), Fe (57.60ppmw), Ti (5.79ppmw), etc. decreased to less than 1ppmw. This work improved the purification efficiency of DWSSP, and put forward an optimized recycling method, which is expected to realize the direct reuse of DWSSP in the photovoltaic industry.

Economic synthesis of sub-micron brick-like Al-MOF with designed pore distribution for lithium-ion battery anodes with high initial Coulombic efficiency and cycle stability.

Metal-organic frameworks (MOFs) have exhibited great potential for lithium-ion batteries (LIBs). However, to date, it is difficult to fabricate MOF electrode materials with regular shape and rational pore distribution by an economic approach, and the currently achieved MOF electrode materials usually have a relatively low initial Coulombic efficiency and poor cycle stability, which is not satisfactory for practical application. In this study, by using the recycled AlCl3 solution after dealloying treatment of Al-Si alloy, an evenly distributed brick-like Al-MOF with sub-micron size and rational pore distribution was synthesized for the first time. Because of the larger size and more macropores, the as-prepared Al-MOF electrode exhibits superior initial Coulombic efficiency as high as 96.6% for LIB anodes. Moreover, on account of the irregular crystal defects at the edge of the designed macropores, which result from unstable connection between the inorganic nodes (AlO6 octahedral cluster) and the organic linkers (PTA) and result in the formation of spherical nano-sized particles with better structural stability, the electrode materials show excellent cycle stability with discharge attenuation rate of 0.051%. The electrochemical performance considerably outperforms that of reported Al-MOF anodes and some representative MOF anodes in other studies. The robust realization of high initial Coulombic efficiency and cycle stability defines a critical step to capturing the full potential of MOF electrode materials in practical LIBs.

Recycling Si waste cut from diamond wire into high performance porous Si@SiO2@C anodes for Li-ion battery.

The Si particle waste cut from diamond wire in photovoltaic industry is chose as an environmental friendly and low-cost resource for Li-ion battery. In this study, the pollutions of SiO2 layer, adhered trace metal and organic impurities on the Si particle waste can be removed by the facile processes of corrosion and pyrolysis. The removal ratios of organic and metal impurities were 70.42% and 66.76%, respectively. The different kinetic models for the removal of metal impurities demonstrate that the leaching is more suitable for controlling by second-order reaction of homogeneous models (R2 =0.992, m=2). The preparation analysis of porous Si@SiO2 with a 3D cluster nanoporous structure using a special bubble corrosion method was firstly proposed and discussed intensively. The first discharge and charge capacities of porous Si@SiO2 @C composites reached 2579.8 and 2184.1 mAh/g, the initial CE reached 84.66%, and the corresponding capacities after 100 cycles reached 1051.4 and 1038.2 mAh/g, which showed the better electrical performance. This study establishes a theoretical basis for recycling Si particle waste cut from diamond wire, and provides technical support for the energy sustainable development.

Facile Synthesis of Double-Layer-Constrained Micron-Sized Porous Si/SiO2/C Composites for Lithium-Ion Battery Anodes.

Advanced Si-based anode materials with nano-sized porous structures and constrained coating layers present attractive prospects for lithium-ion batteries. A brand-new design of double-layer-constrained micron-sized (>20 µm) porous Si/SiO2/C is proposed through facile synthesis processes using cheap Al-Si alloy as feedstock. The three-dimensional spherical coral-like porous Si structure is composed of primary Si (as a supporting framework), eutectic Si rods, and uniformly distributed conductive element Al, which is beneficial for providing void space and uniformly conductive sites. A 4 nm SiO2 thin layer is introduced on the surface of porous Si structure using preoxidation treatment, which has the effect to constrain the volume expansion of Si. The outer C layer can further improve the electrical conductivity and structural stability. The discharge and charge capacities of the porous Si1/SiO2/C composite are 933.3 and 929.2 mAh/g at 0.1 A/g after 100 cycles, respectively. The charge attenuation rate of porous Si1/SiO2/C in each loop is only 0.08%, and the lithium-ion diffusion coefficient of this composite is 4.20 × 10-12 cm2·s-1/2.

Kinetics of volatile impurity removal from silicon by electron beam melting for photovoltaic applications.

A full domain control model is established for impurity transportation in the liquid phase, gas-liquid interface and gas phase of silicon to analyze the dynamic mechanics of impurity removal. The results show that the overall mass transfer coefficient mainly depends on the temperature and the chamber pressure. Its value increases with the increase of temperature or the decrease of chamber pressure. Under the same melting condition, the order of the overall mass transfer coefficients for P, Al and Ca is kP > kAl > kCa, indicating that P is easier to remove by evaporation. Mass transfer in the gas phase is the rate-controlling step for volatile impurity removal at the temperature above the melting point of silicon. The rate-controlling step transits to evaporation on the gas-liquid interface then to mass transfer in the liquid boundary layer as the temperature increases. During electron beam melting, the removal of P is controlled by both evaporation on the gas-liquid interface and mass transfer in the liquid boundary layer, and the removal of Al and Ca is controlled by evaporation on the gas-liquid interface.