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Article Cite This: ACS Omega 2018, 3, 17520−17527
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Amorphous Carbon Chips Li-Ion Battery Anodes Produced through Polyethylene Waste Upcycling ́ ez-Salas,†,‡,§ Palanisamy Manikandan,† Salvador Francisco Acuña Guzmań ,§ Saúl Villagom and Vilas G. Pol*,† †
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Davidson School of Chemical Engineering, Purdue University, 480 W Stadium Avenue, 47907 West Lafayette, Indiana, United States ‡ Universidad Tecnológica de Querétaro, Av. Pie de la Cuesta 2501, 76148 Santiago de Querétaro, Querétaro, Mexico § Centro de Ingeniería y Desarrollo Industrial, Av. Playa Pie de la Cuesta 702, 76125 Santiago de Querétaro, Querétaro, Mexico ABSTRACT: Remediation process produces high-value functional material from low-cost or valueless waste feedstock. Current research demonstrates an innovative solvothermal approach to effectively react sulfuric acid on polyethylene (PE) chains, modifying the PE at a moderate temperature. In this process, the polymer undergoes a cross-linking step above 120 °C, whereas above 500 °C, it transforms into turbostratic carbon structures. Scanning electron micrographs confirmed the free-standing carbon sheet architecture. Raman spectroscopy and X-ray diffraction verified the amorphous/disordered sp2/sp3 hybrid carbon structure in the produced carbons. A high Brunauer−Emmett−Teller surface area of 752.3 and 673.5 m2/g for low-density PE-derived carbon (LDPE-C) and high-density PE-derived carbon (HDPE-C), respectively, was recorded. Thermogravimetric analysis analysis established a total mass retention of 50 and 46% for LDPE and HDPE, respectively, from sulfonated materials. Li-ion battery composite anode comprising LDPE-C and HDPE-C, with a binder and a carbon additive (vs lithium), produced 230 and 350 mA h/g specific capacities for LDPE-C and HDPE-C, respectively, when cycled at room temperature at C/5 rate. Elevated temperature (50 °C) battery cycling produced 290 and 440 mA h/g specific capacities for LDPE-C and HDPE-C, respectively, at C/5 rate. On the basis of the literature survey, this is the first report, which demonstrates that a solvothermal sulfonation process followed by thermal treatment successfully converts waste LDPE and HDPE plastic bags to functional energy-storing carbons.
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INTRODUCTION Globally, around 300 million tons of plastic were produced in 2013 to fulfill the growing demand.1 Soon after, most of the used plastic (>85%) makes its way to landfill and oceans, where it takes hundreds of years to decompose into small fragments.2 As plastic slowly degrades with sunlight, it becomes smaller and starts releasing toxic chemicals into the environment.3 This approach disturbs our ecosystem. In 2014, Eriksen et al. estimated that at least 5.25 trillion plastic particles weighing around 269 000 tons4 are submerged or floating in the sea. Currently, there is an unsustainable trend, where waste plastics are shipped for recycling to countries with lower environmental standards.1 However, this approach is not economical, appealing, or benign for our environment and the overall ecosystem. Typically, closed-loop recycling approach is used in most thermoplastics because energy recovery from plastics is very poor, air emission controls are needed, and byproduct ash could be hazardous. Moreover, polyethylene (PE) with colorants, dyes, labels, and sticky additives5 increases the difficulty in recycling. PE has been proposed for more than © 2018 American Chemical Society
four decades as a low cost (1 $/kg) carbon precursor with a high (86%) carbon content. In 1972, Saglio et al. pyrolyzed saturated chlorinated6 PE to obtain carbon. Zhang and Sun produced carbon fibers7 by reacting ultrahigh molecular weight PE with H2SO4 acid at 180 °C followed by carbonization in the He atmosphere at 1100 °C, yielding 55 wt % carbon fibers. Recently, Hameed et al. prepared microporous8 carbon with high-density PE (HDPE) using H2SO4 at 120 °C and carbonization at 1150 °C under a N2 atmosphere, obtaining a 51.9 wt % yield. However, with the former methods, carbon was produced in limited quantities without potential applications. Hydrothermal carbonization is known to produce carbonaceous materials from biomass precursors using water.9−12 Because of self-generated pressures at low temperatures in a hydrothermal system, it resembles the natural process of coal formation.9 Previously, dry autoclaving of PE (thermolysis Received: September 5, 2018 Accepted: November 28, 2018 Published: December 17, 2018 17520
DOI: 10.1021/acsomega.8b02290 ACS Omega 2018, 3, 17520−17527
ACS Omega
Article
with a 633 nm laser; a low laser power of 2 mW was used to avoid sample burning/modification. X-ray diffraction (XRD) patterns were collected using a Riguka SmartLab X-ray diffractometer operated at 40 kV and 40 mA with a Cu Kα radiation source (λ = 0.154 nm); the samples were measured from 10° to 80° with a scan rate of 2.5° per minute. Surface area analysis of black carbon powders/sheets was performed in a Quantachrome Instruments analyzer after outgassing the materials at 300 °C for 24 h. Thermogravimetric analysis (TGA) was performed using a thermal analyzer system (i1000, IS Inc.) with flowing argon gas (99.997%) at a heating rate of 10 °C min−1 from room temperature to 1000 °C. Electrochemical Tests. Lithium-ion battery anode electrodes were prepared with 80% of waste PE-derived carbons, 10% of polyvinylidene difluoride (KYNAR HSV900, Arkema Inc.) binder, and 10% of carbon black additive (TIMCAL Super P Li). The composite slurry was homogenized for 20 min by employing a Thinky planetary mixture in the presence of seven to eight drops of N-methylpyrrolidone at a constant speed of around 8000 rpm. Using the Dr. Blade technique,17 the slurries were deposited on a battery-grade copper foil using an MTI laminate coater with approximately 40 μm thickness, and the obtained foils were dried overnight at 80 °C. Electrodes of 12 mm diameter were punched out, and CR-2032-type half-coin cells (MTI Corp) were assembled in a high-purity argon glovebox (NEXUS II Vacuum Atmospheres Co.) with
