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Article

Porous Activated Carbons Derived from Coffee Waste for Use as Functional Separators in Lithium-Sulfur Batteries

by
Jae-Hoon Shin
†,
Yu-Yeon Park
†,
Sang-Hyun Moon
,
Ji-Hwan Kim
,
Jae-Sung Jang
,
Sung-Beom Kim
,
Seong-Nam Lee
and
Kyung-Won Park
*
Department of Chemical Engineering, Soongsil University, Seoul 06978, Korea
*
Author to whom correspondence should be addressed.
†
These authors contributed equally to this work.
Energies 2022, 15(21), 7961; https://doi.org/10.3390/en15217961
Submission received: 27 September 2022 / Revised: 20 October 2022 / Accepted: 24 October 2022 / Published: 27 October 2022
(This article belongs to the Section D2: Electrochem: Batteries, Fuel Cells, Capacitors)
Browse Figures
Versions Notes

Abstract

:
A novel approach has been proposed for improving the performance of lithium-sulfur batteries (LSBs) with a carbon-based material as an interlayer between the cathode and separator. With this method, the cross-over of lithium polysulfides (LiPS) to the anode is suppressed, increasing reutilization of the sulfur cathode. In this study, activated carbons (ACs) were prepared using coffee waste as a carbon source and potassium hydroxide (KOH) as an activation agent at various reaction temperatures ranging from 500 to 800 °C. With the rise in heating temperature, the specific surface areas, micro-surface areas, and micro-pore volumes of the AC samples gradually increased. In particular, the AC sample prepared at 800 °C and used as a functional separator for LSB exhibited improved capacity and cycling performance while suppressing the LiPS shuttle effect.

1. Introduction

Lithium-sulfur batteries (LSBs) are promising energy sources that can electrochemically convert chemical energy into electrochemical energy and vice versa because of their high theoretical capacity of 1675 mAh g−1, high energy density of 2600 Wh kg−1, and abundant resource of sulfur as an active material [1,2,3]. However, sulfur cathodes exhibit a low electrical conductivity of 5 × 10−30 S·cm−1 at 25 °C and high solubility in ether-based electrolytes [4,5]. Furthermore, LSBs have drawbacks such as electrical isolation of the sulfur cathode and dissolution of lithium polysulfides (LiPS) during the conversion process [6,7,8]. Problems associated with LSBs can lead to high polarization, low Coulombic efficiency, and rapid capacity decay [9,10,11]. In particular, LiPS (Li2Sx (4 ≤ x ≤ 8), generated during charging/discharging, are highly soluble in electrolytes, thereby decreasing the number of active materials at the cathode [12,13,14]. Moreover, the dissolved LiPS are transported through the separator to the Li anode in the so-called “shuttle effect” of LiPS. The separator and Li anode may be covered by LiPS, producing insoluble Li2S or Li2S2 insulating layers on the surface of the separator and anode, thereby deteriorating the LSB performance [15,16].
Thus, a novel approach has been proposed for improving the performance of LSBs with insertion of a carbon-based material as a functional separator between the cathode and separator. It suppresses the cross-over of LiPS to the anode and increases reutilization of the sulfur cathode [17,18]. Carbon-based functional separator materials, such as multi-walled carbon nanotubes and reduced graphene oxide, display the high electrical conductivity and improved physical adsorption properties of LiPS [19,20,21,22]. Furthermore, the physical adsorption ability of carbon-based materials, based on van der Waals forces, can block the diffusion of LiPS in the initial cycle. In general, carbons with micropores and mesopores provide high specific surface areas and facilitate Li+ ion diffusion [23,24,25]. The specific surface areas, micro surface areas, micropore volumes, and pore sizes of template carbons were compared with activated carbon (Table 1). In particular, carbon prepared using coffee waste has been utilized in various electrochemical applications [26,27,28]. Carbons derived from the coffee waste (Coffee extract, CAS 84650-00-0) have several advantages, such as eco-friendliness, low-cost, a well-defined porous structure, a fairly high surface area, and high electrical conductivity [29]. Shen et al. reported that the Li-S cell fabricated using activated carbon prepared from puffed corn showed enhanced electrochemical performance (787.6 mAh g−1@0.5C) [30]. Furthermore, the carbon derived from coconut shell was applied to the Li-S cell and exhibited a high discharge capacity (846 mAh g−1@0.5C) [31]. In this study, activated carbon (AC) samples were simply prepared using coffee waste as a carbon source and potassium hydroxide (KOH) as an activation agent at various reaction temperatures ranging from 500 to 800 °C. The AC samples exhibited amorphous crystals and well-formed porous structures with high specific surface areas. Specifically, the AC sample prepared at 800 °C was used as a functional separator material for LSBs and delivered the highest capacity and improved cycling performance because of its porous structure and high specific surface area.

2. Experimental

2.1. Synthesis of Activated Carbons (ACs) Derived from Coffee Waste

Activated carbon (AC) was prepared using an activation process with coffee waste (Blended Milky Way, CAS 84650-00-0) and KOH (95%, SAMCHUN, Seoul, Korea) powder. Specifically, 2 g of coffee waste and 3 g of KOH flakes were mixed homogeneously in a mortar. The heat treatment was conducted with the mixed powder in an alumina tube at various temperatures ranging from 500 to 800 °C under N2 gas atmosphere for 30 min. To remove impurities such as K and K2CO3, the heated samples were washed with 2 L deionized (DI) water and stirred in 2 M HCl solution for 12 h. The samples were completely washed with DI water to adjust the pH to 7.0 and dried in a vacuum oven at 50 °C for 12 h.

2.2. MWCNT/S as a Cathode

The MWCNT/S cathode for a functional separator was prepared using a multi-wall carbon nanotube (MWCNT, GRAPHENE SUPERMARKET, Ronkonkoma, NY, USA) and sulfur (S, 99.98%, Sigma Aldrich, St. Louis, MI, USA). For acid-treatment of MWCNT, 2 g of MWCNT powder was stirred in HCl (35%, 10 mL) and HNO3 (60%, 30 mL) at 60 °C for 2 h. The acid-treated MWCNT was washed with DI water several times and dried in an oven at 50 °C for 12 h. The acid-treatment of MWCNT can increase the polarity of MWCNT and support the effective adsorption of MWCNT with polar polysulfides. MWCNT and sulfur were mixed with a weight ratio of 2:8 and ground. The mixture was transferred to a Teflon-lined autoclave and heated at 155 °C for 12 h.

2.3. Materials Characterization

The crystal structure was confirmed by X-ray diffraction (XRD, D2 PHASER, Bruker AXS, Madison, WI, USA) with Ni filter and Cu Kα X-ray source (λ = 0.154 nm). Raman spectroscopy (Leica DM2700 M, Leica Microsystems, Wetzlar, Germany) was performed with a Nd:YAG laser (λ = 532 nm) in the waver number range of 800–2000 cm−1. The shape and composition of the samples were observed using field emission scanning electron microscopy (FE-SEM, GeminiSEM 300, ZEISS, Oberkochen, Germany) and energy dispersive X-ray spectroscopy (EDX, XFlash Detector 6), respectively. The specific surface areas and pore structures of the samples were characterized using an N2 adsorption/desorption analyzer (Micromeritics ASAP 2020) according to the BET (Brunauer–Emmett–Teller) theory and BJH (Barrett–Joyner–Halenda) method. The degassing temperature was 200 °C in air. The presence of impurities in the activated carbon samples was confirmed by thermal gravimetric analysis (TGA, TGA 2-XP1, METTLER TOLEDO, Columbus, OH, USA) in the temperature range from 25 to 800 °C under an air ambience. The Li2S6 adsorption capability of the samples was measured by UV/VIS spectroscopy (UV/VIS spectrophotometer, V-650, JASCO, Oklahoma City, OK, USA).

2.4. Electrochemical Measurements

To fabricate an functional separator structure for LSB, the AC sample was mixed at a weight ratio of 9:1 (AC:polyvinylidene fluoride (PVDF, Alfa Aesar, Ward Hill, MA, USA)) in N-methyl-2-pyrrolidone (NMP, Samchun). The paste was evenly applied on a polypropylene (PP, Celgard 2400) separator using a doctor blade method. The coated separator was dried in a vacuum oven at 50 °C for 12 h and cut to a diameter of 19 mm. The mass loading of the AC sample on the coated separator was 0.70 mg cm−2. In addition, to fabricate the cathode for LSBs, MWCNT/S (80 wt%) as an active material was mixed homogeneously in NMP using a paste mixer with super P (10 wt%, Alfa Aesar) and PVDF (10 wt%) as the conducting agent and binder, respectively. The slurry was applied using the doctor blade method onto aluminum foil and then dried in a vacuum oven at 50 °C for 48 h. The dried foil was cut to a diameter of 13 mm. The load amount of sulfur was 2.0–2.1 mg cm−2. Coin cells (size 2032, Hohsen Corporation, Osaka, Japan) for LSBs were assembled in an Ar-filled glove box with a sulfur cathode on aluminum-foil, a Li metal anode, and sample-coated polypropylene as a functional separator. The electrolyte was prepared by dissolving 1.0 M lithium bis(trifluoromethanesulfonyl)imide (LiTFSI, Aldrich) and 0.2 M LiNO3 (Alfa Aesar) in a 1:1 volume ratio of 1,3-dioxolane (DOL, TCI chemical, Tokyo, Japan) and 1,2-dimethoxyethane (DME, TCI Chemical). The ratio of electrolyte to S was 15 μL mg−1. Charge–discharge curves were obtained at a current density of 0.5 C with a battery tester (WBCS3000Le, WonATech Co. Ltd., Seoul, Korea) in 1.8–2.6 V vs. Li/Li+.

3. Results and Discussion

In this study, we synthesized porous AC from coffee waste using the KOH activation mechanism as follows [33,34]:
Coffee waste + 2KOH → Coffee waste + K2O + H2O
Coffee waste + H2O → Char; C + H2O + Tar
C + H2O → H2 + CO
C + 4KOH → K2O + 3H2 + K2CO3 (600 °C)
K2CO3 → K2O + CO2 (700 °C)
2C + K2CO3 → 2K +3CO (700 °C)
C + K2O → 2K + CO (800 °C)
Coffee waste was thermally decomposed into carbon through the physical activation process, i.e., carbonization (step (1)–(3)). In step (1), KOH is dehydrated into potassium oxide (K2O) and water (H2O), and the main components of coffee waste, such as cellulose, hemicellulose, and lignin, are distorted and cracked. In step (2) and (3), the pores are formed via the gas (tar or CO) emission. Lignocellulosic materials are aromatized into char through a thermal decomposition process at 450~500 °C (steps (1)–(3)). In step (4)–(7), the additional thermal decomposition occurs, which corresponds to the chemical activation process, drastically increasing specific surface areas and pore volumes. In step (4), the interaction between KOH and carbon at 600 °C produces K2O and potassium carbonate (K2CO3). Moreover, the K2CO3 formed in step (4) is partially decomposed into K2O and carbon dioxide (CO2) at ~700 °C (step (5)). At 700–800 °C, K2O and K2CO3 formed in step (4) react with carbon to produce metallic potassium and carbon monoxide (CO) (steps (6) and (7)). Hence, according to the KOH activation mechanism, with increasing activation temperature, the physical (step (1)–(3)) and chemical (step (4)–(7)) activation processes can induce the increased specific surface area and pore size. At 500 °C, lignin, one of the main components of coffee waste, may be incompletely carbonized. Figure 1 shows SEM images of the samples prepared with coffee waste at different reaction temperatures ranging from 500 to 800 °C (AC-500, AC-600, AC-700, and AC-800). Specifically, it was found that a porous carbon structure could be formed via etching in steps (4) and (5) through (6) and (7). With increasing reaction temperatures, the KOH activation processes (steps (6) and (7)) could be improved, thus forming a more porous AC structure. The specific surface areas and pore structures of the AC samples are compared in Figure 2 and Table 2. The samples exhibited type-I N2 isotherms, implying a microporous structure. As the reaction temperature increased from 500 to 800 °C, the specific surface areas, micro-surface area, and micro-pore volumes gradually increased. However, the samples prepared at 800 °C, at which the KOH etching process that occurred most actively, had the highest specific surface area (~1940 m2 g−1) and a significantly increased meso-surface area.
Figure 3 shows the XRD patterns of the AC-500, AC-600, AC-700, and AC-800 samples. In general, for the carbon crystal structure, the main peaks corresponding to the (002) and (101) planes appear at ~23.0° and ~43.5°, respectively [35]. All samples exhibited broad carbon peaks with lower angle shifts, compared to a typical carbon structure, without impurities (K2O, K2CO3, and K) being generated during the thermal activation process. The broad peaks of the samples may result from pores or defects in the carbon structure caused by the KOH activation process [36,37,38]. It was reported that more nanoporous structures exhibited an increased intensity of XRD peaks at ~10° [39,40]. In this study, as reaction temperature increased, the samples became more nanoporous. Raman spectroscopy analysis was performed to further characterize the crystal structures of the samples (Figure 4a). All samples contained characteristic peaks corresponding to the D- and G-bands of the carbon structure, which are associated with defects and a graphitic structure, respectively, at ~1350 and ~1580 cm−1, respectively [41]. Specifically, the broad peaks and high intensity ratios of the D- to G-bands (ID/IG) indicate that pure carbon structures without any other phases such as K2O, K2CO3, and K could be formed by the KOH activation process with coffee waste. In addition, the ID/IG values of AC-500, AC-600, AC-700, and AC-800 were determined to be 0.84, 0.81, 0.92, and 0.87, respectively, indicating that AC samples are graphitic carbon materials. The presence of impurities in the samples was confirmed by the thermogravimetric analysis (TGA) in the temperature range of 25–800 °C in an air (Figure 4b). The evaporation of water molecules was observed from 25 to 150 °C with a weight loss of 8%. Overall, the single weight loss from 150 to 600 °C, indicative of oxidation of the pure carbon structure, demonstrates that the carbon structure with a single phase was formed without impurities and other phases.
Figure 5 shows the SEM-EDX mapping data of the AC-500, AC-600, AC-700, and AC-800 samples. The compositions of main elements corresponding to C, O, and N were 78–83%, 8–13%, and 6–8%, respectively. The impurities such as K2O and K2CO3 were found to be completely removed out in the samples via leaching and washing processes. In addition, the presence of N indicates the formation of N-doped activated carbon through heat treatment under the N2 atmosphere.
To characterize the LiPS adsorption capability of the samples, UV-vis spectroscopy tests were conducted (Figure 6). The samples (40 mg) were added to 50 mM Li2S6 solutions (50 mL) and stored at room temperature for 12 h. After the 12 h adsorption test, the UV-vis absorption spectra were measured in the wavelength range of 250–500 nm to investigate the concentration of Li2S6 remaining in the solutions. Typically, absorbance peaks corresponding to S62- species are observed at 260, 280, 300, and 340 nm [42,43]. In this study, the order of the Li2S6 absorption peak intensity was AC-500 > AC-600 > AC-700 > AC-800, whereas the order of the adsorption capability of the samples was AC-800 > AC-700 > AC-600 > AC-500. Hence, the AC-800, which has the highest specific surface area and a significantly increased meso-surface area, exhibited the best LiPS adsorption properties, which could block the migration of LiPS [44].
Figure 7 shows CVs of the assembled coin cells with the AC functional separators (0.70 mg cm−2 of the AC sample) and MWCNT/S cathode (2.0–2.1 mg cm−2) measured in the potential range of 1.8–2.6 V vs Li/Li+ at a scan rate of 0.01 mV s−1. All the AC samples exhibited characteristic peaks corresponding to reduction reactions and oxidation reactions of solid S8 to polysulfide Li2Sx (1 ≤ n ≤ 8). During discharging, the 1st reduction peaks were observed at 2.28–2.30 V, transforming solid S8 to soluble polysulfide (4 ≤ x ≤ 8), and the 2nd reduction peaks were observed at 2.05–2.07 V, transforming soluble polysulfide (4 ≤ x ≤ 8) to insoluble Li2Sx (1 ≤ x ≤ 2). During charging, two distinct oxidation peaks were observed at 2.29–2.32 and 2.37–2.40 V, respectively, transforming insoluble Li2S2/Li2S to ring-type S8 [45]. However, with the rise in heating temperature, the peak areas associated with electrochemical reactions of LiPS gradually increased. As previously mentioned, as the heating temperature increased from 500 to 800 °C, the specific surface areas, micro-surface areas, and micro-pore volumes gradually increased. The AC-800 with the highest specific surface area and meso-surface area exhibited the largest CV area, which could result from the electrochemical response of LiPS adsorbed in the porous carbon structure [46].
Characteristic charge-discharge curves of the Li/S cells with the AC samples as functional separators and a pristine PP separator were measured at a current density of 0.1 C in the potential range of 1.8–2.6 V vs Li/Li+ (Figure 8a). All cells have two plateaus at 2.2–2.4 and 2.0–2.1 V, observed during discharging [47]. The first plateau represents the electrochemical reduction of solid-state S8 to long chain polysulfide (4 ≤ x ≤ 8), corresponding to 25% of the theoretical capacity of sulfur. In the 2nd plateau, long-chain polysulfide (4 ≤ x ≤ 8) is electrochemically reduced to short chain polysulfide (Li2Sx (1 ≤ x ≤ 2)), contributing to 75% of the theoretical capacity of sulfur [48,49]. On the contrary, during charging, Li2S2 and Li2S in the first plateau are oxidized to soluble long-chain polysulfide (4 ≤ x ≤ 8) and soluble long-chain polysulfides (4 ≤ x ≤ 8) in the 2nd plateau are oxidized to solid-state S8, which are identical to oxidation- and reduction-related peaks in the CVs [50,51]. The initial discharge capacities of the Li/S cells with PP, AC-500, AC-600, AC-700, and AC-800 were 738, 897, 944, 977, and 992 mAh g−1, respectively. Compared to the PP separator, the high electrical conductivity of the AC samples as the functional separators can lead to high capacities and improved redox reaction rates [52]. In particular, the porous structure of the AC samples can facilitate Li+ ion transport and increase the reaction sites, thereby enhancing the electrochemical performance [53]. The capacity of the Li/S cells increased with increasing heating temperature. The increased electrochemical reaction corresponding to LiPS adsorbed in the porous carbon structures may be attributed to the increased specific surface areas, micro-surface areas, and micro-pore volumes with increasing heating temperature [54]. Hence, AC-800 with the highest specific surface area and meso-surface area exhibited the highest discharge capacity. Figure 8b shows the cycling performance of the Li/S cells measured at 0.1 C for 100 cycles. The discharge capacities of the Li/S cells with AC-500, AC-600, AC-700, and AC-800 measured at 100 cycles were 610, 645, 698, and 767mAh g−1, respectively. The retentions of the Li/S cells with AC-500, AC-600, AC-700, and AC-800 measured at 100 cycles were 68%, 68%, 71%, and 77%, respectively. All the Li/S cells exhibited ~100% Coulombic efficiency. The cycling performance of the Li/S cells was recorded at a higher current density of 0.5 C for 100 cycles (Figure 8c). The first discharge capacities of the Li/S cells with PP separator, AC-500, AC-600, AC-700, and AC-800 were 252, 649, 670, 673, and 719 mAh g−1, respectively. The retentions of the Li/S cells with AC-500, AC-600, AC-700, and AC-800 as the functional separators after 100 cycles were 63%, 81%, 88%, and 92%, respectively. As a result, AC-800, with an improved porous structure significantly maintained the electrochemical reaction of LiPS, thus suppressing the LiPS shuttle effect.

4. Conclusions

In summary, the AC samples were prepared using coffee waste as the carbon source and KOH as the activation agent at various reaction temperatures. The AC samples exhibited amorphous crystals and well-defined porous structures with high specific surface areas. With increasing heating temperature, the specific surface areas, micro-surface areas, and micro-pore volumes of the AC samples gradually increased. In particular, the AC sample prepared at 800 °C and used as a functional separator material for LSB exhibited the highest capacity and improved cycling performance, thereby suppressing the LiPS shuttle effect because of its improved porous structure.

Author Contributions

J.-H.S.: Conceptualization, Methodology, Formal analysis. Y.-Y.P.: Formal analysis, Data curation, Writing—original draft. S.-H.M.: Investigation, Data curation. J.-H.K.: Data curation. J.-S.J.: Data curation. S.-B.K.: Data curation. S.-N.L.: Data curation. K.-W.P.: Conceptualization, Supervision, Writing—review & editing. All authors have read and agreed to the published version of the manuscript.

Funding

This research was supported by the National Research Foundation of Korea (2020R1A2C2010510, 2020R1A6A1A03044977).

Data Availability Statement

The data can be shared up on request.

Conflicts of Interest

The authors declare no conflict of interest.

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Figure 1. SEM images of the activated carbon (AC) samples prepared with coffee waste at different reaction temperatures from 500 to 800 °C. (a) AC-500; (b) AC-600; (c) AC-700; (d) AC-800 of low magnification SEM images; (e) AC-500; (f) AC-600 ; (g) AC-700; (h) AC-800 of high magnification SEM images.
Figure 1. SEM images of the activated carbon (AC) samples prepared with coffee waste at different reaction temperatures from 500 to 800 °C. (a) AC-500; (b) AC-600; (c) AC-700; (d) AC-800 of low magnification SEM images; (e) AC-500; (f) AC-600 ; (g) AC-700; (h) AC-800 of high magnification SEM images.
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Figure 2. The N2 isotherms of AC-500, AC-600, AC-700, and AC-800.
Figure 2. The N2 isotherms of AC-500, AC-600, AC-700, and AC-800.
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Figure 3. The XRD patterns of AC-500, AC-600, AC-700, and AC-800.
Figure 3. The XRD patterns of AC-500, AC-600, AC-700, and AC-800.
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Figure 4. (a) Raman spectra (D- and G-bands represent defects and a graphitic structure, respectively.) and (b) TGA curves of the AC samples.
Figure 4. (a) Raman spectra (D- and G-bands represent defects and a graphitic structure, respectively.) and (b) TGA curves of the AC samples.
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Figure 5. SEM-EDX mapping images of elements such as C, O, N, K, and Cl (a) AC-500, (b) AC-600, (c) AC-700, and (d) AC-800.
Figure 5. SEM-EDX mapping images of elements such as C, O, N, K, and Cl (a) AC-500, (b) AC-600, (c) AC-700, and (d) AC-800.
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Figure 6. UV-vis absorbance spectra of the AC samples as the functional separators.
Figure 6. UV-vis absorbance spectra of the AC samples as the functional separators.
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Figure 7. CVs of the AC samples measured in the potential range of 1.8–2.6 V vs Li/Li+ at a scan rate of 0.01 mV s−1.
Figure 7. CVs of the AC samples measured in the potential range of 1.8–2.6 V vs Li/Li+ at a scan rate of 0.01 mV s−1.
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Figure 8. (a) Characteristic charge-discharge curves of the Li/S cells with AC samples as functional separators and a pristine PP separator measured at a current density of 0.1 C of the first cycle in the potential range of 1.8–2.6 V vs. Li/Li+. (b) Cycling performance of the Li/S cells recorded at a current density of 0.1 C for 100 cycles (The transparent dots are Coulombic efficiencies of the samples). (c) Cycling performance of the Li/S cells recorded at a current density of 0.5 C for 100 cycles.
Figure 8. (a) Characteristic charge-discharge curves of the Li/S cells with AC samples as functional separators and a pristine PP separator measured at a current density of 0.1 C of the first cycle in the potential range of 1.8–2.6 V vs. Li/Li+. (b) Cycling performance of the Li/S cells recorded at a current density of 0.1 C for 100 cycles (The transparent dots are Coulombic efficiencies of the samples). (c) Cycling performance of the Li/S cells recorded at a current density of 0.5 C for 100 cycles.
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Table
Table 1. Comparison of specific surface areas, micro surface areas, micropore volumes, and pore sizes of the templated carbons and activated carbon determined from the N2 isotherms.
Table 1. Comparison of specific surface areas, micro surface areas, micropore volumes, and pore sizes of the templated carbons and activated carbon determined from the N2 isotherms.
SampleBET Surface Area
(m2 g−1)		Micro Surface Area
(m2 g−1)		Micropore Volume
(cm3 g−1)		Median Pore Width
(nm)		Ref.
Alumina-
Sodium dodecyl sulfate		288160.686.5[32]
Zeolite16645971.01.3[32]
Silica Gel74000.655.7[32]
Activated carbon18646900.871.8[31]
Table
Table 2. Comparison of specific surface areas and pore structures of the AC samples determined from the N2 isotherms.
Table 2. Comparison of specific surface areas and pore structures of the AC samples determined from the N2 isotherms.
SampleBET Surface Area
(m2 g−1)		Micro Surface Area
(m2 g−1)		Micropore Volume
(cm3 g−1)		Median Pore Width
(nm)
AC-500761 ± 11.89629 ± 9.790.24 ± 0.0050.54 ± 0.003
AC-6001054 ± 17.42938 ± 6.700.36 ± 0.0060.51 ± 0.001
AC-7001464 ± 25.261295 ± 12.540.49 ± 0.0040.54 ± 0.001
AC-8001940 ± 32.771470 ± 35.380.58 ± 0.020.61 ± 0.003
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Shin, J.-H.; Park, Y.-Y.; Moon, S.-H.; Kim, J.-H.; Jang, J.-S.; Kim, S.-B.; Lee, S.-N.; Park, K.-W. Porous Activated Carbons Derived from Coffee Waste for Use as Functional Separators in Lithium-Sulfur Batteries. Energies 2022, 15, 7961. https://doi.org/10.3390/en15217961

AMA Style

Shin J-H, Park Y-Y, Moon S-H, Kim J-H, Jang J-S, Kim S-B, Lee S-N, Park K-W. Porous Activated Carbons Derived from Coffee Waste for Use as Functional Separators in Lithium-Sulfur Batteries. Energies. 2022; 15(21):7961. https://doi.org/10.3390/en15217961

Chicago/Turabian Style

Shin, Jae-Hoon, Yu-Yeon Park, Sang-Hyun Moon, Ji-Hwan Kim, Jae-Sung Jang, Sung-Beom Kim, Seong-Nam Lee, and Kyung-Won Park. 2022. "Porous Activated Carbons Derived from Coffee Waste for Use as Functional Separators in Lithium-Sulfur Batteries" Energies 15, no. 21: 7961. https://doi.org/10.3390/en15217961

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