Superior Lithium-Ion Storage at Room and Elevated Temperature in

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Superior Lithium-ion Storage at Room and Elevated Temperature in an Industrial Woodchip Derived Porous Carbon Ryan A Adams, Arthur D. Dysart, Roberto Esparza, Salvador Acuña, Samrudhi R Joshi, Aaron Cox, David Mulqueen, and Vilas G. Pol Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.6b01786 • Publication Date (Web): 25 Jul 2016 Downloaded from http://pubs.acs.org on July 27, 2016

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Industrial & Engineering Chemistry Research

Superior Lithium-ion Storage at Room and Elevated Temperature in an Industrial Woodchip Derived Porous Carbon Ryan A. Adams,a Arthur D. Dysart,a Roberto Esparza,a† Salvador Acuña,b Samrudhi R. Joshi,a‡ Aaron Cox,c David Mulqueen,c Vilas G. Pol*a a) School of Chemical Engineering, Purdue University, West Lafayette, IN 47907, USA b) Universidad Politécnica de Querétaro, Carretera Estal 420 S/N, El Rosario, 76240 Qro., Mexico c) Sure Carbon Holdings, 215 Cumberland St, Kingsport, TN 37660, USA * Corresponding Author Email: [email protected]

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Abstract: An industrial pyrolysis process converted loblolly pine tree woodchips into porous carbonaceous particles that is tested as promising lithium ion battery anode. Sure Carbon Holdings, TN Company demonstrated scalability for the KOH activation and pyrolysis process by producing hundreds of kilograms of carbon from the sustainable wood precursor. Material characterization reveals amorphous carbon structure, with 1580 m2/g BET surface area and 0.883 cc/g pore volume. Galvanostatic cycling was performed at C/10 rate in a half cell (carbon vs. Li+/Li), achieving a stable capacity of 700 mAh/g and 1000 mAh/g at 22°C and 50°C, respectively. Cycling at 50°C increases lithium ion diffusion rates into the electroactive carbon but lowers the coulombic efficiency and long-term cell cyclability due to electrolyte degradation. Electrochemical impedance spectroscopy studies reveal the decreased charge transfer and diffusional resistance in porous carbon electrode compared to conventional graphite, making it an attractive anode material for lithium ion batteries.

Keywords: Li-ion Anode ∙ Porous carbon ∙ Sustainable biomass ∙ High temperature cycling


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1. Introduction Since its commercialization, lithium ion batteries (LIBs) have become the lead performing rechargeable battery technology, with high energy density and reasonable cyclability 1–3. LIBs are typically used and suitable for handheld electronics; however, large-scale applications in electric vehicles and stationary electrical energy storage systems require improved performance 4. Though the engineering aspects of conventional LIBs have improved dramatically, the electroactive materials, LiCoO2 cathode and graphite anode, still limit the maximum energy density of the batteries. Graphite has a theoretical capacity of 372 mAh/g and poor rate capabilities due to the 2dimensional intercalation mechanism in several micron thick particles limiting lithium diffusion 5. The low operating voltage (< 0.3 V) of graphite results in safety concerns due to lithium plating and dendrite formation during cycling, which can cause thermal runaway and short circuiting 6. High current densities increase solid electrolyte interface (SEI) and dendrite formation, limiting high power applications with graphite 6. Thus, development of alternative anode materials with improved electrochemical performance and safety at reasonable cost is necessary in demanding LIB technology. Biomass-derived carbons have shown great promise in LIBs due to advantages of higher operating potential, superior conductivity, and improved capacity. Aside from intercalation in the graphitic layers, Li ions can be stored by chemisorption of surface heteroatoms (such as O and N) and physisorption in pores and interfacial regions, resulting in increased capacities

7–10

. Many

precursors have been investigated, including carbon derived from olive stone, rice husk, peat moss, algae, peanut skin, banana peel, eggplant, mushroom, and pollen as anode material for LIBs and sodium ion batteries

11–19

. Biomass-derived carbon properties are determined by the precursor’s

composition and structure, typically resulting in high surface areas, porosities, and unique


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morphologies such as sheets, fibers, and spheres 18,20–22. Some drawbacks of most biomass derived carbon anodes is poor first cycle coulombic inefficiency due to excessive SEI formation and irreversible Li trapping, as well as significant voltage hysteresis between charge and discharge curves

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. Industrial implementation of these materials could be difficult due to costs associated

with methodical collection/recycling, and chemical treatment to the feedstock and produced carbon.

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. Graphite has advantages of a synthesis pathway from petroleum coke and can be

extracted via mining, thus widely available and already associated with industrial processes 23–25. Loblolly pines are the second most common tree in the United States, the primary species for renewable industrial logging, and have been explored as bio-oil

26,27

. This article demonstrates

industrial production of the porous carbons from the ubiquitous biomass feedstock in an environmentally benign and renewable way. SureCarbon, an industrial collaborator, produced hundreds of kilograms of high surface area porous carbon from woodchip biomass that was tested as a promising anode for lithium ion batteries at room and elevated temperature. This carbon also has applications in activated carbon sorbents for pollution control, solid bio-fuel, and CO2 sequestration. Scheme 1 demonstrates industrial woodchip carbon treatment and porous carbon production, with subsequent incorporation into a Li-ion full cell to power a LED. Thorough morphological and structural characterization is carried out for porous carbon, followed by electrochemical studies at room and elevated temperatures.


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KOH Activation

Loblolly Pine Woodchips

Pyrolysis

Cell Assembly

Li-ion Battery

Porous Carbon

Scheme 1. Woodchip derived carbon anode industrial process and implementation into full cell construction to power purple LED.

2. Experimental Methods 2.1 Materials Synthesis Woodchip precursor was obtained from loblolly pine trees (Pinus taeda) and activated for 96 hours via aqueous KOH soaking in a 1:4 (woodchip: KOH) mass ratio. The woodchip was then filtered, air dried, and pyrolyzed at 850°C in N2 atmosphere for 3 hours to activate the impregnated KOH. The material was ground into a fine powder using a mortar and pestle and then underwent an additional pyrolysis step at 600°C for 2 hours in Argon to clean the sample and remove impurities. Finally, it was air activated at 300°C for 6 hours. Artificial graphite as comparison material was purchased from MTI Corporation and utilized without further treatment. 2.2 Materials Characterization


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Powder X-ray diffraction technique was utilized to characterize the crystallinity of porous carbon using the Bragg-Brentano method (Rigaku SmartLab X-Ray Diffractometer). A Cu−Kα Xray source (λ = 0.154 nm) was used to obtain the spectra (2θ = 10−80°) at a scanning rate of 5°/minute. Raman measurements were taken with a 532-nm laser (Thermo Scientific DXR Raman Microscope). Surface area analysis (Quantachrome NOVA 2200e) of porous carbon was performed using nitrogen sorption isotherm measurements at 77 K. Carbon samples were degassed for 12 hours at 300°C prior to measurements. Multipoint specific surface area calculations were performed using the linear portion (P/P0 = 0.05−0.3) of the Brunauer−Emmett−Teller model. Pore size and volume distribution curves were generated using Density Functional Theory analysis. Transmission electron microscope images of porous carbon were taken using the FETEM mode of a Titan 80-300 kV Environmental Transmission Electron Microscope. Scanning electron microscopy (FE-SEM) images of the woodchip derived carbon samples were recorded using a Hitachi S-4800 microscope. 2.3 Electrochemical Characterization Electrodes were prepared by taking a ratio of 80 wt. % active material (porous carbon derived from woodchip), 10 wt. % acetylene black conductive material (Timcal Super C65), and 10 wt. % polymer binder, polyvinylidene fluoride (PVDF) with N-Methyl-2-pyrrolidone (NMP), as solvent. Addition of conductive additive to carbon anodes has shown improvement in cycle life, electrochemical reaction rates, and a decrease in first cycle loss due to improved electrodeelectrolyte contact 28. The slurry was mixed for 20 minutes using Thinky mixer and coated onto a copper foil using a doctor-blade. The laminate was dried in a vacuum oven at 80°C for 12 hours and 12 mm diameter electrodes were punched out with an active material density of about 1.5 mg/cm2. Full cell construction was conducted utilizing commercial LiCoO2 to power light emitting


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diode (LED). Electrochemical tests and cycling are performed on a coin-type 2032 half-cell with lithium metal as the counter electrode. Celgard 2500 polypropylene was used as separator and 1 M LiPF6 in a 1:1:1 mixture of ethylene carbonate (EC)/dimethyl carbonate (DMC)/diethyl carbonate (DEC) with 1% wt. vinylene carbonate was utilized as electrolyte. Cells were assembled in a high-purity Argon glovebox (99.998%) with oxygen and water sensors ensuring O2 and H2O concentrations of

Superior Lithium-Ion Storage at Room and Elevated Temperature in

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