Comparison of life cycle assessment between hydrogen production from silicon waste and alkaline water electrolysis.

With global warming becoming increasingly severe, environmental issues are receiving international attention. Crystalline silicon is an indispensable and important raw material for photovoltaic and semiconductor fields, but the cutting of crystalline silicon materials generates a large amount of silicon wastes. This article evaluates the environmental impact of a hydrogen production process using diamond-wire sawing silicon waste (DSSW) using the life cycle assessment (LCA) methodology. For comparison, it was also analyzed the environmental impact of the alkaline water electrolysis (AEL) hydrogen production route. In the DSSW alkaline catalyzed hydrolysis (DACH) hydrogen production route, the hydrogen production stage accounts for the main contribution of nine environmental impact indexes, including GWP, PED, ADP, AP, EP, ODP, ET, HT-cancer, and HT-non cancer, exceeding 56 %. Whereas for the AEL route, the environmental impacts of the electrolytic cell manufacturing stage can be neglected, and the operating stage contributes almost all the environmental impacts, contributing more than 92 % to the twelve environmental impact indexes. Compared to the AEL route, the DACH route has higher environmental impacts, with GWP index reaching 87.78 kg CO2 -eq/kg H2, PED index reaching 1772.90 MJ/kg H2, and IWU index reaching 622.37 kg/kg H2 which are 2.85, 4.07 and 7.56 times higher than the former, respectively. Although the environmental impact of the DACH route is significant, most of its indirect impacts were caused by the use of raw materials, and the energy consumption and direct environmental impact are both low. The environmental impact of the AEL route is mainly indirect effects generated due to the use of electricity. If clean renewable energy sources (e.g., solar PV, hydropower, geothermal or biofuels), were used for the AEL route, all twelve environmental impact indexes would be significantly reduced.

Recycling of photovoltaic silicon waste for high-performance porous silicon/silver/carbon/graphite anode.

The rapid development photovoltaic industry has generated a huge amount of waste ultra-fine silicon cutting powder. The management and value-added recovery of silicon cutting waste is highly important for both environmental remediation and economic efficiency. In this work, silicon waste was used as a cost-effective raw material for the preparation of silicon/graphite anode for lithium-ion batteries. First, porous Si embedded with Ag particles (pSi/Ag) was produced by silver-assisted chemical etching (Ag-ACE). Then, pSi/Ag was loaded on a micron-sized graphite matrix (pSi/Ag/G), and organic carbon (C) produced by the pyrolysis of polyvinylpyrrolidone (PVP) acted as a link to closely connect pSi/Ag and graphite to form the pSi/Ag/C/G composite. The incorporated Ag particles and the porous structure improve electron transfer and mitigate the volume expansion effect of silicon. The novel design and structure of the anode can maintain the integrity of the electrode during cycling, and thus strongly improve cycling stability. The prepared pSi/Ag/C/G composite exhibited a large initial discharge capacity of 2353 mAh/g at 0.5 A/g and good initial coulombic efficiency of 83%, delivering a high capacity of 972 mAh/g at 1 A/g after 200 cycles. This work confirmed the possibility of the preparation of lithium battery silicon-carbon anode from silicon waste and provides a promising new avenue for value-added utilization of silicon cutting waste materials.

PSi@SiOx/Nano-Ag composite derived from silicon cutting waste as high-performance anode material for Li-ion batteries.

Integration of photovoltaic (PV) power generation and energy storage has been widely believed to be the ultimate solution for future energy demands. Herein, an ingenious method was reported to make full use of photovoltaic silicon cutting waste (SiCW) natural characters fabricating PSi@SiOx/Nano-Ag composite as anode material for high-performance lithium-ion batteries. The sheet-like structure with nano/micropores and native SiOx layer addressed the volume expansion issues of Si material. Ag nanoparticles greatly enhanced electrical conductivity of composite and promoted Li+/e- transport. Synergistic effect of the designed PSi@SiOx/Nano-Ag composite contributed outstanding cyclic performance with reversible capacity of 1409mAhg-1 after 500 cycles. Notably, full LIBs with PSi@SiOx/Nano-Ag anode and commercial Li[Ni0.6Co0.2Mn0.2]O2 (NCM622) cathode delivered stable capacity of 137.5mAhg-1 at current density of 200 mA g-1, accompanying with a high energy density of 438 Wh kg-1. Furthermore, electrochemical Li+ storage behavior of this PSi@SiOx/Nano-Ag electrode was studied, and reaction mechanism and crystal structure evolution during cycles were also revealed by in-situ XRD analysis. The synthesis method is facile and cost-effective, which paves a novel way towards high-performance Si-based anodes and promising markets for both solar photovoltaic and lithium-ion battery industries.

High-Performance Porous Silicon/Nanosilver Anodes from Industrial Low-Grade Silicon for Lithium-Ion Batteries.

Silicon (Si) has been considered as one of the most promising candidates for the next-generation lithium-ion battery (LIB) anode materials owing to its huge theoretical specific capacity of 4200 mA h g-1. However, the practical application of Si anodes in commercial LIBs is facing challenges because of the lack of scalable and cost-effective methods to prepare Si-based anode materials with proper microstructure and competitive electrochemical performances. Herein, we report a facile and scalable method to produce multidimensional porous silicon embedded with a nanosilver particle (pSi/Ag) composite from commercially available low-cost metallurgical-grade silicon (MG-Si) powder. The unique hybrid structure contributes to fast electronic transport and relieves volume change of silicon during the charge-discharge process. The pSi/Ag composite exhibits a large initial discharge capacity (3095 mA h g-1 at a high current of 1 A g-1), an excellent cycling performance (1930 mA h g-1 at 1 A g-1 after 50 cycles), and outstanding rate capacities (up to 1778 mA h g-1 at a higher current of 2 A g-1). After the samples are modified by reduced graphene oxide, the capacities of the pSi/Ag@RGO composite electrode can still be maintained over 1000 mA h g-1 after 200 cycles. This study provides a simple and effective strategy for production of high-performance anode materials.

Novel and efficient purification of silicon through ultrasonic-Cu catalyzed chemical leaching.

The present study proposed a novel and efficient ultrasonic-Cu catalyzed chemical leaching (U-CuCCL) method to purify large-sized industrial silicon powders. Different from the traditional ultrasonic-HF (U-HF) leaching method, U-CuCCL and U-CuCCL combined rapid thermal processing (U-CuCCL + RTP) were performed to investigate the efficiency of removing the main impurities Fe, Al, Ca, Ti, Ni, V, Cu, and Mn. The evolution of typical precipitates phases on the surface of silicon before and after leaching were observed and analyzed by electron probe micro analyzer. The results show that the impurities removal can be significantly improved under the ultrasonically strengthen process, especially the U-CuCCL process shows a high-efficient impurities removal efficiency. After the U-CuCCL, the etched silicon powders accompanied with numerous porous structure are obtained which is beneficial for the removal of impurities. Notably, it was found that the rapid thermal processing is beneficial for the residual impurities diffuse to the porous layer surface and the purity of silicon powder can be significantly increased from 99.3% to 99.995%.