Towards High Performance Lithium Sulfur Batteries: Upcycling of

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Towards High Performance Lithium Sulfur Batteries: Upcycling of LDPE Plastic into Sulfonated Carbon Scaffold via Microwave-promoted Sulfonation Patrick J. Kim, Harif D Fontecha, Kyungho Kim, and Vilas G. Pol ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.8b03959 • Publication Date (Web): 12 Apr 2018 Downloaded from http://pubs.acs.org on April 12, 2018

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ACS Applied Materials & Interfaces

Towards

High

Performance

Lithium

Sulfur

Batteries: Upcycling of LDPE Plastic into Sulfonated Carbon

Scaffold

via

Microwave-promoted

Sulfonation Patrick J. Kim a, Harif D. Fontecha a, Kyungho Kim b and Vilas G. Pol a*

a

Davidson School of Chemical Engineering, Purdue University, West lafayette, 47907, USA

b

School of Materials Engineering, Purdue University, West Lafayette, 47907, USA.

*Corresponding authors Prof. Vilas G. Pol (V. G. Pol) E-mail: [email protected], Tel: +1 765-494-0044

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ABSTRACT Lithium sulfur batteries have been intensively explored during last decades as nextgeneration batteries owing to the high energy density (2600 Wh kg-1) and effective cost:benefit. However, systemic challenges, mainly associated polysulfide shuttling effect and low Coulombic efficiency, plague the practical utilization of sulfur cathode electrode in battery market. In order to address the aforementioned issues, many approaches have been investigated by tailoring the surface characterisitics and porosities of carbon scaffold. In this study, we first present an effective strategy of preparing porous sulfonated carbon (PSC) from low density polyethylene (LDPE) plastic via microwave-promoted sulfonation. Microwave process not only boosts the sulfonation reaction of LDPE but also induces huge amounts of pores within the sulfonated LDPE plastic. When PSC layer was utilized as an interlayer in LiS batteries, the sulfur cathode delivered an improved capacity of 776 mAh g-1 at 0.5 C and excellent cycle retention of 79 % over 200 cycles. These are mainly attributed to two materialistic benefits of PSC: a) porous structure with high surface area, and b) negatively charged conductive scaffold. These two characteristics not only facilitate the improved electrochemical kinetics but also effectively block the diffusion of polysulfides via Coulomb interaction.


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Keywords: LDPE Plastic; Sulfonation; Microwave; Lithium-Sulfur battery; Li/Na-ion battery

1. Introduction As advanced electronic devices became an indispensable part of our daily lives, a substantial interest in the development of new materials with high energy density and low cost has grown abruptly.1-3 Elemental sulfur, as one of promising cathode materials, can offer a theoretical capacity of 1672 mAh g-1 and high energy density of 2600 W h kg-1 at a low cost, when it is coupled with metallic Li anode.2-6 However, systemic problems of lithium sulfur (Li-S) batteries are associated with polysulfide shuttling effect and poor Coulombic efficiency. In addition, insulating nature of elemental sulfur deteriorates the fast electron transport and thus leads to the poor utilization of sulfur electrode.2-4 These main challenges plague the practical utilization of sulfur cathode in commercial battery market. In order to tackle fundamental issues mentioned above, two main approaches have been intensively attempted by a) putting sulfur into meso-/microporous carbon 1, 7-11 and b) optimizing carbon scaffold with functional polymers or hydrophilic functional groups.12-21 These two strategies have shown promising results in inhibiting the polysulfide shuttling effect and enhancing the electrochemical reactions. However, each process to optimize the carbon scaffold with functional polymers and carve functional groups on the surface of carbon is too complicated and requires expensive and elaborate techniques. In addition, since nonpolar carbon itself has no chemical affinity with polar polysulfide, it is vulnerable to locally anchor the polysulfides within pores over cycles.17, 22 In these regards, the development of carbon materials, which have high porosity and chemical interaction with polysulfides, at a rational price has become a crucial part of advancing the practical utilization of Li-S cells.



Since the advent of plastic products, huge amounts of plastic wastes continue to be produced and disposed into oceans and landfills without further application.23-24 Low density polyethylene (LDPE), which is predominantly used as a packaging film and takes a big portion of total plastic waste, also increasingly employed and disposed without recycling and reuse. In order to exploit the resource abundance of LDPE plastic waste and change it into more valuable materials, many attempts have been approached by converting LDPE plastic into carbon materials via a sulfonation process.23, 25-26 Pristine LDPE itself cannot produce any carbon residue or char after pyrolysis, due to its poor thermal stability and low melting temperature.23, 25 On the other hand, sulfonated-LDPE which obtains infusibility from being cross-linked with sulfonate groups can yield amorphous carbon after pyrolysis.23-25 In this study, we first present an effective strategy of preparing porous sulfonated carbon (PSC) from LDPE plastic via microwave-promoted sulfonation and demonstrate its materialistic potentials to Li-S batteries. General LDPE plastic (e.g. amazon plastic bag) was used as a carbon precursor to prepare the PSC. Sulfonation reaction not only conjugates the SO3- groups, which exhibit negative charges in the polar solvent, within LDPE chain but also facilitates the carbonization process of LDPE plastic at high temperature.27 In addition, microwave process accelerates the sulfonation reaction and induces plenty of pores within the sulfonated LDPE plastic. With the synergistic combination of sulfonation reaction and microwave process, porous carbon scaffold with sulfonate groups successfully prepared from LDPE plastic. To explore the materialistic potentials for Li-S batteries, PSCs were adopted as interlayer materials. Sulfonated groups (SO3-) are reported to have an effect on bouncing anionic polysulfides via Coulomb interaction.28 When PSC layer was employed in Li-S batteries, polysulfide shuttling effect was dramatically suppressed and electrochemical performances were substantially enhanced owing to the effective suppression of polysulfides via electrostatic repulsion and the improved electrochemical kinetics by the aid of an 4 ACS Paragon Plus Environment

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additional conductive path. To further probe the possibilities of PSC as an active material, Li/Na-ion batteries were also evaluated and showed an affordable specific capacity and excellent cycle performances with high Coulombic efficiencies.

2. Results and discussion 2.1. Preparation of porous sulfonated carbon derived from LDPE plastic Figure 1a depicts the schematic of preparing PSC from LDPE plastic via microwavepromoted sulfonation. The pristine LDPE plastic bag was soaked in sulfuric acid and irradiated by microwave for 15 min. Microwave-irradiated LDPE plastic bag become functionalized with SO3- groups after sulfonation process. After washing and drying, sulfonated LDPE plastic bags were pyrolyzed under Ar atmosphere and it became a PSC film. Figure 1b-d presents the SEM images and photographs of a pristine LDPE plastic bag, a sulfonated LDPE plastic bag, and a pyrolyzed sulfonated LDPE plastic bag. The pristine LDPE plastic with high transparency shows a flat and smooth surface without any pore and crack (Figure 1b). After sulfonation via microwave process, the color of plastic bag turned into black and morphology became irregular and crumpled (Figure 1c). Figure 1d shows pores and cracks on the surface after carbonization. This is ascribed to the contraction of sulfonated LDPE plastic bag during pyrolysis reaction, which can be seen from an inset image of a shrunk pyrolyzed sulfonated LDPE plastic bag. In order to see the distribution of carbon, oxygen, and sulfur element throughout PSC film, energy dispersive spectroscopy (EDS) mapping was performed and presented in Figure S1. Figure 1e presents the crosssectional SEM image of a pristine LDPE plastic bag, which shows a dense and compact structure with a thickness of 35 µm. After sulfonation via microwave process, huge amount 5 ACS Paragon Plus Environment


of pores was induced through a sulfonated LDPE film, which led to the increase of thickness six times higher (215 µm) than a pristine separator (Figure 1f). This is attributed to the intense generation of bubbles by a rapid increase of temperature of sulfuric acid. In order to ascertain and compare the effect of heating rate on the formation of pores, solvothermal reaction was carried out with a LDPE plastic. The sulfonated LDPE plastic, which was prepared by solvothermal reaction, showed a dense and compact structure without noticeable pores inside the film (Figure S2). During the carbonization, polymeric portion of sulfonated LDPE plastic started to decompose and it became a shrunk sulfonated carbon with a thickness of 150 µm (Figure 1g). In contrast, pristine LDPE plastic did not yield any residual carbon after pyrolysis (Figure S3). These results directly show that sulfonation via microwave process can effectively facilitate the crosslinking of LDPE plastic with solfonate groups (SO3-) in a short time and thus enables the carbonization reaction under inert atmosphere. To analyze the porosity and pore distribution of PSC, Brunauer-Emmett-Teller (BET) analysis was performed and presented in Figure S4. The PSC exhibits a high surface area as high as 570 m2 g-1 and large pore distribution ranging from 1 to 5 nm.


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Figure 1. Characterization of PSC. (a) Procedure to prepare the pyrolyzed sulfonated LDPE; Top SEM views and photographs of (b) a pristine LDPE, (c) a sulfonated LDPE, and (d) a pyrolyzed sulfonated LDPE; cross-sectional SEM views of (e) a pristine LDPE, (f) a sulfonated LDPE, and (g) a pyrolyzed sulfonated LDPE.

2.2. Characterization of sulfonated LDPE plastic In order to investigate the characteristics of sulfonated LDPE plastic and ascertain how thermal properties (melting point) change in terms of reaction time, DSC and TGA 7 ACS Paragon Plus Environment


studies were carried out (Figure 2). Figure 2a presents the DSC profiles for a pristine LDPE plastic, sulfonated LDPE plastic bags with different microwave reaction time (8 min and 15 min). The pristine LDPE plastic shows a distinct melting endothermic peak at around 115 oC. In contrast, sulfonated plastic treated with 15 min of microwave irradiation did not show any peak and curvature from room temperature to 200 oC, implying that LDPE plastic was fully cross-linked with sulfonate groups at this condition and the melting peak of sulfonated LDPE disappeared.25 For the sulfonated plastic sample with 8 min of microwave irradiation, it still shows a broad peak of melting point at around 115 oC, indicating the insufficient crosslinking reaction with sulfuric acid.25 Thermal gravimetric analysis (TGA) was performed under the Ar flow to check the degree of sulfonation and the approximate yield of remaining carbon when temperature reaches 800 oC (Figure 2b). The TGA curve for a pristine LDPE plastic showed an abrupt drop to nearly zero at 500oC, implying that there is no residue of carbon due to the LDPE decomposition with gaseous product formation. In case of a partially sulfonated plastic (8 min of microwave treatment), it showed the initial decrease of weight from 110 to 200 oC by the loss of functional (sulfonate) groups on LDPE and the second decrease of weight around 500 oC by the degradation of un-sulfonated LDPE.25 Then, it reached a relatively low yield (22 wt%) of pyrolyzed sulfonated carbon. In contrast, the fully sulfonated LDPE plastic (15 min of microwave treatment) presented a gradual decrease of weight up to 800 oC and achieved 50 % of carbon residue at 800 oC, not showing the dramatic decrease of weight around 400 oC. Extrapolating from the above results, at least 15 min of microwave reaction is required to fully crosslink the LDPE plastic with sulfonate groups and to get a high yield of carbonized sulfonated LDPE.29


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Figure 2 Characterization of LDPE according to the degree of sulfonation. (a) DSC profile and (b) TGA analysis for a pristine LDPE, a partially sulfonated LDPE, and a fully sulfonated LDPE.

2.3. Analysis of sulfonated LDPE and pyrolyzed sulfonated LDPE To ascertain the materialistic characteristics of sulfonated LDPE plastic and pyrolyzed sulfonated LDPE plastic, Raman spectroscopy was carried out (Figure 3a). Raman spectrum of a pristine plastic bag presents peaks of LDPE, corresponding to the anisotropic parts (1439 cm-1) and amorphous parts (1294 and 1062 cm-1).30 After sulfonation, it showed two main broad peaks at 1352 cm-1 and 1575 cm-1, indicating that sulfonation via microwave process leads to form sp2 carbon networks.31 Pyrolyzed sulfonated LDPE displayed analogous but shifted and sharp peaks at 1324 cm-1 (D) and 1597 cm-1 (G), indicating the turbostratic phase of carbon.32 For the confirmation of crystallinity of sulfonated LDPE and pyrolyzed sulfonated LDPE, X-ray diffraction (XRD) measurement was performed (Figure 3b). The pyrolyzed sulfonated LDPE presents two diffraction peaks around 22° (002) and 43° (100), representing reflection peaks of graphitic lattice, whereas the sulfonated LDPE does 9 ACS Paragon Plus Environment


not show analogous peaks associated with graphitic phase.32 This implies that sulfonated LDPE before pyrolysis has no carbon structure before carbonization. In order to determine the presence of sulfonate groups within the pyrolyzed sulfonated LDPE, Fourier-transform infrared spectra analysis (FT-IR) was performed. Figure 3b showed an overall FT-IR spectrum of carbonized sulfonated plastic ranging from 4000 to 400 cm-1. It shows a peak around 3350 cm-1 corresponding to OH stretching bond and a few more peaks ranging from 600 to 1800 cm-1. Magnified FT-IR spectrum clearly shows the sharp peaks of sulfonate groups derived from the pyrolysis of sulfonated LDPE plastic (Figure 3c-d).27 This strongly supports that sulfonated groups still remained even after carbonization at a high temperature of 900 oC. Sulfonated groups (SO3-) are reported to exhibit negative charges in the polar solvent.28 Zeta potential measurement was carried out with a pyrolyzed sulfonated LDPE to ascertain the influence of sulfonated groups on the net electrostatic charges in the aqueous solvent. Figure S5 presents a zeta potential distribution of pyrolyzed sulfonated LDPE, exhibiting high negative charge of -53.7 mV. The above result directly corroborates that sulfonated groups which are chemically cross-linked with carbon can influence on the electrical charge in the polar solvent.


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Figure 3. Structural analysis and surface characteristics. (a) Raman spectra for a pristine LDPE, a sulfonated LDPE, and a pyrolyzed sulfonated LDPE; (b) XRD curve of a sulfonated LDPE, and a pyrolyzed sulfonated LDPE; (c-d) FT-IR spectrum for a pyrolyzed sulfonated LDPE.

2.4. Electrochemical performances of PSC as an interlayer material in Li-S batteries Scheme 1 illustrates the role of PSC with negative charges on curbing the diffusion of anionic polysulfides (Sn2-) via repulsive interaction. During the discharge, polysulfide species dissolve out of sulfur cathode electrode and then start to diffuse towards Li anode 11 ACS Paragon Plus Environment


owing to different concentration gradient. As a physical and Coulomb barrier and an additional current collector, PSC/separator effectively curbs the diffusion of anionic polysulfides via repulsive interaction and further reactivate the trapped polysulfide species throughout the additional conductive path.33 The electrochemical performances of Li-S cell with a pristine PP separator, a Carbon/separator, and a PSC/separator were evaluated and presented in Figure 4. The sulfur cathode with areal sulfur loading mass (~ 2mg cm-2) was prepared by referring previous study.34 Each Carbon/separator and PSC/separator was fabricated by laminating the slurry, composed of 80 wt% carbon (or PSC) and 20 wt% PVdF binder onto the pristine PP separator. To exclude the size effect of carbon material as an interlayer material, similar sized carbon material derived from biomass (biodegradable packing peanut) was utilized as a comparison (Figure S6).35 Figure 4a presents initial voltage profiles of each cell at a current density of 0.5 C. The sulfur cathode with a pristine separator exhibited a specific discharge capacity of 909 mAh g-1. When a Carbon/separator and a PSC/separator were employed in Li-S cells, the capacity of each cell increased to 962 mAh g-1 and 979 mAh g-1, respectively. These are ascribed to the increased utilization of sulfur by an aid of additional carbon current collector. Interestingly, the cycle retention of each electrode showed huge differences (Figure 4b). After 200 cycles, the sulfur cathode electrode (with a pristine separator) decayed to 311 mAhg-1 (34.2 % of initial capacity) due to the serious loss of active sulfur materials during repetitive cycles. In contrast, the sulfur cathode with a PSC/separator delivered a high capacity of 776 mAh g-1 at 0.5C rate with a retention of 79 % after 200 cycles, which is much higher than the cycle retention of the sulfur cathode electrode with a Carbon/separator (59.8 %, after 200 cycles). This is ascribed to the two main benefits of PSC for polysulfide blocking: a) electrostatic repulsion by negatively charged sulfonated groups and b) physical blocking of polysulfide by an aid of porous structured PSC. These two advantages of PSC 12 ACS Paragon Plus Environment

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facilitate an effective confinement of polysulfide species within the cathodic area and thus enhance the electrochemical performances of Li-S batteries. Figure 4c presents the rate performances of electrodes at current densities from 0.2 C to 2 C. The sulfur cathode showed relatively poor rate capabilities owing to the inherently poor electrical conductivity of sulfur and the harsh diffusion of polysulfides out of sulfur cathode. When Carbon/separator and PSC/separator were introduced, the low conductivity of sulfur cathode was complemented by an addition carbon current collector and thus this led to the improvement of rate capability. At 2C, the sulfur cathode with a PSC/separator delivered a higher capacity of 766 mAh g-1, as comparison with the sulfur cathode with a Carbon/separator (681 mAh g-1); this is ascribed to the effective prevention of polysulfide shuttling by electrostatic repulsion. For further characterizing the interfacial resistance between separator and sulfur cathode, electrochemical impedance spectroscopy (EIS) measurements were performed (Figure 4d). The Ohmic resistances of sulfur cathode, sulfur cathode with a Carbon/separator, and sulfur cathode with a PSC/separator show analogous values of 5.1 Ω, 4.6 Ω, and 4.6 Ω, respectively. The diameter of semicircle, corresponding to the charge transfer resistance, of the sulfur cathode with a pristine separator and the sulfur cathode with a Carbon/separator exhibited similar value of 121 Ω. Interestingly, the sulfur cathode with a PSC/separator showed the smallest charge transfer resistance (95.5 Ω) among three electrodes. Extrapolating from this result, it could be confirmed that polysulfide shuttling is highly impacting on the polarization resistance and the carbon scaffold with sulfonate groups can facilitate much improved reaction kinetics between carbon interlayer and sulfur cathode.



Scheme 1. The role of PSC/separator in Li-S cells. Schematic illustration depicts the role of PSC/separator during the discharge (Li2S formation). Pristine separator Carbon/Separator PSC/Separator

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Figure 4. Electrochemical characterization for Li-S batteries. The performance of sulfur cathode electrode with a pristine separator, a Carbon/separator, and a PSC/separator were evaluated. (a) Initial voltage profiles; (b) cycle performances; (c) rate capabilities; (d) Nyquist plots of each electrode.


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2.5. Visual verification of polysulfide suppression effect of each separator In order to visually verify the effect of PSC/separator on the inhibition of polysulfide shuttling, polysulfide diffusion experiments were performed and accounted (Figure 5). The electrolyte diffusion tests and polysulfide (Li2S8) solution were prepared by referring previous studies.18, 34 The diffusion tests are composed of separator, fresh electrolyte and polysulfide (Li2S8) solution. As soon as each diffusion test was placed into the vial with fresh electrolyte, there was no noticeable color change. After 24 hours, fresh electrolyte displayed very different color due to the dissimilar diffusion rate of polysulfide throughout separator. The diffusion tester inserted with a PSC/separator showed the lightest color of fresh electrolyte among three cells, indicating that PSC layer has a substantial effect on curbing the diffusion of polysulfide (Figure 5c). As for the diffusion tester inserted with a Carbon/separator, it exhibited a lighter color than that inserted with a pristine separator but a darker color than that inserted with a PSC/separator (Figure 5a-b). This implies that carbon layer somewhat has an effect on curbing the polysulfide diffusion but has a less protective effect than PSC layer. Extrapolating from this result, it can be inferred that the diffusion rate of polysulfide out of separator is in inverse proportion to the cycle stability of each electrode, which is well matched to the obtained cycle performances.



Figure 5. Demonstration of polysulfide diffusion test. The polysulfide diffusion tester inserted with a) pristine separator, b) Carbon/separator, and c) PSC/separator.

3. Conclusions In this article, we first report a strategy of preparing porous sulfonated carbon (PSC) from LDPE plastic via a microwave-promoted sulfonation and demonstrate its materialistic potentials to Li-S batteries. Microwave process not only boosts sulfonation reaction of LDPE and but also generates huge amounts pores within the LDPE plastic. After sulfonation via microwave, high mass yield of sulfonated LDPE is observed; this presents an optimistic potential of LDPE as a carbon source. When PSC was employed as an interlayer material for 16 ACS Paragon Plus Environment

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Li-S cells, the sulfur cathode with areal sulfur loading mass (~2 mg cm-2) delivered an improved capacity of 979 mAh g-1 at 0.5C and cycle performances of the sulfur cathode were dramatically improved over 200 cycles, with a retention of 79 % of initial capacity. These are mainly attributed to two materialistic benefits of PSC: a) porous structure with high surface area, and b) negatively charged conductive scaffold. These two characteristics not only facilitate the improved electrochemical kinetics but also effectively curb the diffusion of polysulfides via Coulomb interaction. Unlike the previous approach to synthesize the carbon materials from pyrolysis of biomass waste, the strategy to use LDPE plastic waste as a carbon source and utilize it as an excellent carbon scaffold for energy storage devices provides a new guideline to manage the environmental and energy issues altogether. Expansively, our approach of functionalizing the LDPE plastic via microwave treatment can be extended to other polymeric materials and help to advance the development of practical carbon materials with high surface area.

4. Experimental Section

4.1. Preparation of sulfonated LDPE and pyrolyzed sulfonated LDPE First, a pristine LDPE plastic bag was soaked into sulfuric acid and placed inside the microwave. Microwave is specially designed for the chemical reactions with reflux system to condense the reaction solvents. Microwave was turned on and off to maintain a reaction temperature between 100 to 120 oC, which was measured by an infrared thermometer. After sulfonation reaction, the flake-shaped solid product was thoroughly washed with fresh DI water and dried in vacuum oven at 80ºC overnight. Sulfonated LDPE sample was heated up with 5ºC min-1 heating rate to 900 ºC under Ar atmosphere and was maintained for 2 hours.



Then, it was naturally cooled to room temperature. A water trap was connected to the outlet of furnace tube to limit and capture toxic emissions.

4.2. Fabrication of the PSC/separator and Carbon/separator The slurry for PSC/separator was prepared by mixing 80 wt% ball-milled PSC and 20 wt% polymeric binder (PVDF) in the organic solvent (N-Methyl-2-pyrrolidone (nMP)). Then, PSC slurry was casted onto the pristine PP separator followed by overnight drying at 50 oC. Asfabricated PSC/separator was cut into circular shape and employed as an interlayer for Li-S batteries. We tried to minimize the loading mass of carbon on separator, not to significantly influence on overall energy density.36-37 The areal loading mass of PSC in PSC/separator is ~1.2 mg cm-2. The preparation for Carbon/separator followed the same procedure as PSC/separator.

4.3. Preparation of sulfur cathode and the assembly of Li-S battery. The slurry for sulfur cathode electrode was prepared by homogenizing 120 mg sulfur, 60 mg Super P, 20 mg PVdF in nMP solvent via slurry mixer (Thinky). Then, the slurry was casted on the Al foil, followed by being dried at conventional oven (at 50 oC) overnight in order to fully get rid of nMP solvent. Once electrode was fully dried, electrode was cut in circular shape with a diameter of 12 mm to fabricate the Li-S cell. The areal sulfur loading mass of sulfur cathode is ~2.0 mg cm-2. Li metal disc (MTI) was used as an anode electrode and electrolyte, which was used in this study was 1 M lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) in the bi-solvent of 1,3-dioxolane (DIOX) and 1,2-dimethoxyethane (DME) (v:v) dissolved with 1 % LiNO3. The analogous amount of electrolyte was used to fabricate cells to perform comparative study. In order to further investigate the materialistic potentials of PSC as an anode, Li/Na ion batteries were evaluated and presented in Figure S7. 18 ACS Paragon Plus Environment

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4.4. Characterizations The morphologies of PSC flakes was observed by field emission scanning electron microscope (FEI NOVA NanoSEM 450). The morphology of PSC/separator was further observed by SEM (Figure S8). DSC and TGA study (TA Instruments Q20 instrument) were performed at a scan rate of 5 °C min-1. Raman spectra for a pristine LDPE, a sulfonated LDPE, and a pyrolyzed sulfonated LDPE were collected by Thermo Scientific DXR Raman microscope. X-ray diffraction (XRD, Rigaku SmartLab X-ray diffractometer) study was carried out to characterize the crystalline phase of sulfonated LDPE and pyrolyzed sulfonated LDPE. The galvanostatic discharge-charge tests, cycle performances and rate performances of each cell were tested by a MTI battery cycle tester. The EIS study of sulfur cathode with a pristine PP separator, a Carbon/separator, and PSC/separator were tested by potentiostat instrument (Gamry Ref 600). The EIS studies were carried out after one cycle (discharge/charge) of cells.38 The FTIR spectrum (FT-IR-4200) of PSC was recorded in the range from 4000 to 400 cm-1.

CORRESPONDING AUTHORS *E-mail: [email protected]

CONFLICT OF INTEREST The authors declare no conflict of interest.

ACKNOWLEDGEMENTS This work was funded by Naval Enterprise Partnership Teaming with Universities for National Excellence (NEPTUNE) at Purdue Center for Power and Energy Research ( grant 19 ACS Paragon Plus Environment


number N00014-15-1-2833). The Li-S cell part of this work was supported by the Assistant Secretary for Energy Efficiency and Renewable Energy, Office of Vehicle Technologies of the U.S. Department of Energy under contract no. DE-EE0006832. The authors acknowledges additional financial support from Purdue University as well as Davidson School of Chemical Engineering.

SUPPORTING INFORMATION

EDS mapping image of ball-milled PSC, SEM image of pyrolyzed sulfonated LDPE prepared by a solvo-thermal method, Photographs of pristine LDPE plastic bag before and after pyrolysis, BET anaylsis of PSC, Zeta potential curve of PSC, SEM image of carbon (packing peanut derived carbon), Li-/Na ion battery performance of PSC, SEM image of PSC/separator.

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Towards High Performance Lithium Sulfur Batteries: Upcycling of

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