Silicon Carbide Derived from Coal Gangue and Multi-Source Solid Wastes for Lithium-Ion Battery Anodes

MaterialCoal gangue samples were collected from the Hecaogou Coal Mine in northern Shaanxi Province, China. Waste tire pyrolysis carbon black was purchased from Shaanxi Hongrui Rubber Products Co., Ltd. Coal-oil co-refining residues were obtained from Shaanxi Yanchang Petroleum Group. The chemical reagents of analytical grade, including hydrochloric acid (HCl) and hydrofluoric acid (HF) were purchased from Sinopharm Chemical Reagent Co., Ltd and used for material washing and purification. Kerosene and 2-octanol (C8H18O) were purchased from Macklin and used as the collector and frother for coal gangue flotation. Commercial 3C-SiC (Macklin, 99.9% metal basis, D50 = 500 nm) was used for comparison and labeled as Com-SiC when assessing the SiC samples as anode materials.Material characterizationThe three carbon sources were subjected to proximate analysis in accordance with the Chinese National Standard GB/T 212-2008. Elemental analysis (EA) for C, H, O, N, and S was conducted on an elementar vario Micro cube elemental analyzer. The samples were combusted at 1150°C under an oxygen atmosphere for complete oxidation. The resulting gases were separated by adsorption-desorption chromatography and detected by a thermal conductivity detector (TCD). X-ray fluorescence (XRF) spectroscopy was performed using a Zetium (Philips Analytical) spectrometer equipped with a Rh tube as the excitation source. The morphology of the silicon carbide (SiC) material was characterized by scanning electron microscopy (SEM, Thermo Fisher Quattro S) and transmission electron microscopy (TEM, JEOL JEM-2100F) operated at 200 kV. Energy dispersive spectroscopy (EDS) was obtained with an EDAX Elite Plus detector. Graphitic and defect structures were investigated by Raman spectroscopy (LabRAM HR Evolution, HORIBA, France) with a 532 nm excitation laser. Crystalline structures were analyzed by X-ray diffraction (XRD) on a diffractometer (Bruker D8 Advance, Germany) with a Cu Kα radiation source. Their surface area and pore size distribution were determined by N2 physisorption using a gas adsorption analyzer (Quantachrome Autosorb iQ). The specific surface area (SSA) was calculated using the Braunner-Emmett-Teller method. Their pore volume was calculated using the density functional theory method. Surface chemical properties were studied by X-ray photoelectron spectroscopy (XPS) using an analyzer (Thermo Fisher Scientific K-Alpha, America) with an Al Kα X-ray source (1486.6 eV).Electrode fabricationThe electrochemical performances of FC-SiC, TC-SiC, RC-SiC, and Com-SiC were evaluated using CR2032 battery. These batteries were assembled in an argon-filled glove box with controlled oxygen and moisture levels (≤ 0.1 ppm). The slurries comprise a mixture of active material (SiC), conductive additives (conductive carbon black), binders (polyvinylidene fluoride (PVDF, Sigma-Aldrich) at the mass ratio of 7:2:1. They were dissolved in N-methyl-2-pyrrolidone (NMP, Sigma-Aldrich) and mixed using a planetary mixer. The resulting slurry was then coated onto a copper foil current collector and dried overnight at 60℃ under vacuum. The dried electrode was punched into 12 mm diameter discs, with the active material mass loading controlled at approximately 1.5 mg·cm-2. Lithium metal foil was used as the counter electrode. The electrolyte consisted of 1 M LiPF6 in a mixed solvent of diethyl carbonate (DEC) and ethylene carbonate (EC, 1:1 by volume) with 5vol% fluoroethylene carbonate (FEC) additive, and the polypropylene membrane was employed as the separator.Electrochemical testsCycling and rate performance were tested by a battery test system (CT2001A, Rand Corporation, Wuhan, China) with a voltage range of 0.01-3.00 V (vs. Li/Li⁺). The cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) tests were performed by a CHI760F electrochemical workstation (Shanghai Chenhua, China). CV tests were carried out at scan rates ranging from 0.10 to 1.00 mV·s-1. EIS measurements were recorded over a frequency range of 10-2 to 105 Hz with an AC amplitude of 5 mV. Galvanostatic intermittent titration technique (GITT) tests were implemented at a current density of 0.1 mA·g-1, with a pulse duration of 5 min and a relaxation interval of 1 h.