Ultrahigh “Relative Energy Density” and Mass Loading of Carbon Cloth Anodes for K-Ion Batteries

Abstract

Open AccessCCS ChemistryCOMMUNICATION1 Feb 2021Ultrahigh "Relative Energy Density" and Mass Loading of Carbon Cloth Anodes for K-Ion Batteries Junpeng Xie, Jinliang Li, Xiaodan Li, Hang Lei, Wenchen Zhuo, Xibo Li, Guo Hong, Kwun Nam Hui, Likun Pan and Wenjie Mai Junpeng Xie Siyuan Laboratory, Guangdong Provincial Engineering Technology Research Center of Vacuum Coating Technologies and New Materials, Department of Physics, Jinan University, Guangzhou 510632 Institute of Applied Physics and Materials Engineering (IAPME), University of Macau. Department of Physics and Chemistry, Faculty of Science and Technology, University of Macau, Macao SAR 999078 , Jinliang Li *Corresponding authors: E-mail Address: [email protected] E-mail Address: [email protected] Siyuan Laboratory, Guangdong Provincial Engineering Technology Research Center of Vacuum Coating Technologies and New Materials, Department of Physics, Jinan University, Guangzhou 510632 , Xiaodan Li Siyuan Laboratory, Guangdong Provincial Engineering Technology Research Center of Vacuum Coating Technologies and New Materials, Department of Physics, Jinan University, Guangzhou 510632 , Hang Lei Siyuan Laboratory, Guangdong Provincial Engineering Technology Research Center of Vacuum Coating Technologies and New Materials, Department of Physics, Jinan University, Guangzhou 510632 Department of Chemistry, Jinan University, Guangzhou 510632 , Wenchen Zhuo Siyuan Laboratory, Guangdong Provincial Engineering Technology Research Center of Vacuum Coating Technologies and New Materials, Department of Physics, Jinan University, Guangzhou 510632 Department of Chemistry, Jinan University, Guangzhou 510632 , Xibo Li Siyuan Laboratory, Guangdong Provincial Engineering Technology Research Center of Vacuum Coating Technologies and New Materials, Department of Physics, Jinan University, Guangzhou 510632 , Guo Hong Institute of Applied Physics and Materials Engineering (IAPME), University of Macau. Department of Physics and Chemistry, Faculty of Science and Technology, University of Macau, Macao SAR 999078 , Kwun Nam Hui Institute of Applied Physics and Materials Engineering (IAPME), University of Macau. Department of Physics and Chemistry, Faculty of Science and Technology, University of Macau, Macao SAR 999078 , Likun Pan Shanghai Key Laboratory of Magnetic Resonance, School of Physics and Electronic Science, East China Normal University, Shanghai 200062. and Wenjie Mai *Corresponding authors: E-mail Address: [email protected] E-mail Address: [email protected] Siyuan Laboratory, Guangdong Provincial Engineering Technology Research Center of Vacuum Coating Technologies and New Materials, Department of Physics, Jinan University, Guangzhou 510632 https://doi.org/10.31635/ccschem.020.202000203 SectionsSupplemental MaterialAboutAbstractPDF ToolsAdd to favoritesDownload CitationsTrack Citations ShareFacebookTwitterLinked InEmail Mass loading and potential plateau are the two most important issues of potassium (K)-ion batteries (KIBs), but they have long been ignored in previous studies. Herein, we report a simple and scalable method to fabricate acidized carbon clothes (A-CC) as high mass loading (13.1 mg cm−2) anode for KIBs, which achieved a reversible areal-specific capacity of 1.81 mAh cm−2 at 0.2 mA cm−2. Besides, we have proposed the concept of "relative energy density" to reasonably evaluate the electrochemical performance of the anode. According to our calculation method, the A-CC electrode exhibited an ultrahigh relative energy density of 46 Wh m−2 in the initial charge process and remained at 40 Wh m−2 after 50 cycles. Furthermore, we performed the operando Raman spectroscopy (ORS) to investigate the K-ion storage mechanism. We believe that our work might provide a new guideline for the evaluation of anode performance, thereby, opening an avenue for the development of commercial anode. Download figure Download PowerPoint Introduction Nowadays, lithium (Li)-ion batteries (LIBs) are being used extensively in portable electric products and electric vehicles.1–4 Driven by the challenges of limited and expensive Li resources, potassium (K)-ion batteries (KIBs) have taken the privilege over LIBs on account of their accessibility and low-cost K resources.5–7 Unfortunately, the oversized radius of K-ion compared with Li-ion hinders the plating–stripping process, which ultimately results in sluggish diffusion kinetics.8 Such behavior not only destroys the inherent material structure but also ruins the electrochemical performance for KIBs.9 Therefore, it is significant to explore compatible host materials for reversible K-ion intercalation and deintercalation10,11. Carbonaceous materials have aroused great concern in KIBs, due to their abundant resources, environmental friendliness, and accessibility.12–17 Considerable progress has been made in carbon-based KIB fields. Ji's group14 found that K-ion could insert into graphite in a nonaqueous electrolyte, with the graphite exhibiting a reversible specific capacity of 273 mAh g−1 at 7 mA g−1, approaching the theoretical capacity for K-ion storage. Also, Pint's group18 reported that N-doping could increase the K-ion storage capacity of graphene at 350 mAh g−1 at 50 mA g−1. Further, Xiong's group19 prepared N/O dual-doped hierarchical porous hard carbon for KIBs, delivering high reversible capacities of 365 mAh g−1 at 25 mA g−1. Nevertheless, the hidden problems for further industrial applications should not be ignored. Firstly, electrochemical performance, in the most reported materials, is based only on the low mass loading evaluations (usually less than 1 mg cm−2), which is far from the practical industrial requirement (more than 10 mg cm−2). Besides, as the critical parameters in practical battery production, the areal and volumetric capacities are frequently overlooked in KIBs. Most importantly, some anode materials always exhibit high charging potential, resulting in lower energy density after fabrication of the full battery. Accordingly, numerous works need to be achieved to realize industrialization in KIBs. Herein, we present a two-step method for the preparation of acidized carbon clothes (A-CC) to obtain a desirable improvement of the kinetic progress and K-ion storage performance. After facile processing, a free-standing A-CC electrode, with its high mass loading (∼13.1 mg·cm−2), exhibited a high reversible areal-specific capacity of 1.81 mAh·cm−2 at a current density of 0.2 mA·cm−2, which could even be doubled by simple electrode stacking to achieve a two-fold areal capacity. In order to reflect the practical benefits of the A-CC electrode, a "relative energy density" (ER) assessment was presumed to evaluate the performance by considering the requirement of both low potential plateau and large anode capacity. Benefiting from the slight oxygen decorated, both the battery rate performance and ER of the carbon clothes were improved. Besides, we employed the operando Raman spectra (ORS) of the A-CC electrode during different potassiation–depotassiation process, used to investigate the K-ion storage mechanism. Materials and Methods Materials and synthesis Pristine carbon clothes (P-CC; WOS1009, CeTech Co., Taichung City, Taiwan) were cut into 2 × 10 cm pieces and immersed in a 120 mL mixture of concentrated sulfuric acid, concentrated nitric acid, and deionized water with a volumetric ratio of 1∶1∶1. Then the mixture was sealed and transferred into an electric oven at 70 °C for 24 h. The crude intermediate sample was washed and dried after cooling. Subsequently, the A-CC was synthesized successfully by heating in a muffle furnace at 500 °C for 2 h with a heating rate of 10 °C min−1. Characterization The samples were characterized by obtaining its morphology and structure information via the conduction of scanning electron microscopy (SEM; Zeiss Ultra 55, JEOL Ltd., Beijing, China), transmission electron microscope (TEM; JEOL 2100 F), X-ray diffraction (XRD; Rigaku, MiniFlex600, Beijing, China) with Cu Kα radiation and Raman spectrometer (T64000, Horiba Scientific, Eindhoven, Netherlands) with a wavelength of 532 nm, X-ray photoelectron spectrometry (Thermo Fisher Scientific, Shanghai, China) with Al Kα radiation, Fourier-transform infrared spectrometer (FTIR; NEXUS 670, Nicolet, Madison, WI, USA). The Brunauer–Emmett–Teller (BET) specific surface areas were obtained using a nitrogen adsorption apparatus (Biaode-Kubo X1000, Beijing, China). Electrochemical measurement Generally, the electrochemical performance was tested by CR2032 coin half-cell at room temperature. The samples were used directly as working electrodes after cutting into circles with a 14 mm diameter. The mass loading of A-CC electrodes was ∼ 13.1 mg cm−2. For the graphite electrode, we mixed with the natural graphite, super P carbon black and carboxymethyl cellulose at a ratio of 8∶1∶1 in water to form a slurry, then coated it onto a Cu foil and dried at 100 °C for 12 h in a vacuum oven. After that, the electrode was cut into a circle with a 14 mm diameter. The different mass loading of the graphite electrodes were obtained by the optimization of the thickness during the coating process. K metal, glass fiber (Whatman), and 1 M KPF6 in 1∶1 by volume of propylene carbonate (PC) and ethylene carbonate (EC) were utilized as counter electrodes, separators, and electrolyte, respectively. The half-cell was assembled in an argon (Ar)-filled glove box (Etelux Lab2000) with H2O and O2 < 0.1 ppm. Galvanostatic charge–discharge process was recorded by a battery testing system (BTS 4000; Neware Tech. Ltd., Kowloon Bay, Hong Kong) with a potential range of 0.01–3.0 V (vs K+/K). Cyclic voltammetry (CV) measurements were conducted on an electrochemical workstation (CHI 1030 C, Chenhua, Shanghai, China) in the potential window between 0.01 and 3.0 V at a sweep rate of 0.2 mV s−1. Electrochemical impedance spectroscopy (EIS) was recorded by an electrochemical workstation (Veras STAT3-400, Princeton, Beijing, China) with a frequency range of 0.01 Hz–0.1 MHz. Operando Raman spectra testing system consisting of Raman spectrometer (532 nm laser) with per-Raman spectrum in voltage internal of 0.1 V, electrochemical workstation (CV test at 0.6 mV s−1), a computer, and an Operando Raman cell (Tianjin Aida Hengsheng Sci. & Tech. Co. Ltd., China) was utilized with A-CC electrode, separator, and K metal with a hole in the middle. All the Operando Raman spectra information collected was raw, untreated data. Results and Discussion The typical A-CC synthesis method is shown in Figure 1a. After acidifying and annealing process, P-CC could be converted readily into A-CC. In Figure 1b, this facile two-step synthesis led to the achievement of a free-standing electrode after cutting into small circles without any current collector and electrode preparation process. This simple experimental design elevated the electric conductivity in the entire electrode and also avoided the complicated electrode preparation process, thereby, decreasing the liberation of harmful pollutants and minimizing the production cost. Figure 1c displays the SEM image of A-CC, which shows the braided-fabric structure inherited from the P-CC. Locally ordered structure and random orientation in graphene layers were observed in the TEM image, featuring a typical hard carbon (Figure 1d). Raman spectra of both P-CC and A-CC corroborate D band at ∼ 1339 cm−1 and G band at ∼ 1579 cm−1, as shown in Figure 1e. The peak intensity ratio of D and G band, ID/IG, was utilized to assess the defect level of carbon materials.20 The higher value of ID/IG in A-CC (1.04) indicated that the A-CC electrode exhibited higher distortion structure, compared with P-CC (1.00). The slight increase of disorder structure might be derived from the modification of the carbon cloth's surface during acidization that could have damaged the original structure of carbon cloth, resulting in a higher distortion structure.21,22 This increase in disordered structure could facilitate the K-ion striping–plating process. In addition, 2D bands at 2680 cm−1 in both spectra were detected, related to a second-zone boundary phonon mode for graphene, and displayed low degrees of ordering in both electrodes. In Supporting Information Figure S1, the XRD patterns of both P-CC and A-CC exhibited similar amorphous structures with two broad peaks attributable to (002) and (100), thereby, demonstrating that the acidified treatment of the carbon cloth did not change its bulk property. To validate the surface property of P-CC and A-CC further, we obtained the XPS spectra of C 1s and O 1s, presented in Figure 1f-g. Both of the C 1 s spectra exhibited the characteristic peaks at 290.7, 286.8, 285.1, and 284.8 eV, attributable to COOH, C=O, C–OH, and C–C/C=C bond, respectively.19 Meanwhile, three peaks located at 532.0, 533.3, and 536.1 eV were decomposed in both O 1s spectra and were assigned to C–O, C=O and COOH bonds, respectively.16 However, the intensity of fingerprint peaks at C=O in A-CC was enhanced after the acid treatment, demonstrating that the oxygen content increased on the surface of A-CC, compared with the prototype P-CC. Besides, FTIR spectra were employed to verify the XPS results. The characteristic absorption peaks of A-CC at 1587 and 1637 cm−1, shown in Figure 1h indicate the stretching vibration of the functional group of COOH and C=O.23 Compared with P-CC, the signal intensity peaks of A-CC exhibited an increase of C=O (at 1637 cm−1), and decrease of COOH (at 1587 cm−1) and C–O (at 1087 cm−1), indicating that the COOH and C–O groups were converted into C=O group due to the slight oxidation in the acidification process.23,24 The slight oxygen decoration on the surface of the carbon cloth was helpful as an improvement of the electrochemical performance, especially, in the rate performance.25 Supporting Information Figure S2 shows the nitrogen adsorption–desorption isotherms of P-CC and A-CC, respectively. According to the calculation by the BET method, the specific surface areas of P-CC and A-CC were 1.42 and 3.00 m2 g−1, respectively, demonstrating slight carbon cloth improvement of the A-CC after acidification, which should be attributable to some created pores on the carbon surface. Indeed, such a slight upgrade in the specific surface area is not the key factor for the enhancement of the electrochemical performance. Figure 1 | (a) Scheme of the A-CC synthetic process, (b) photograph, (c) SEM image, and (d) TEM image of A-CC. Insets in (c) and (d) are the enlarged SEM and TEM images of A-CC. (e) Raman spectra, (f) C1s XPS spectra, (g) O1s XPS spectra, and (h) FTIR spectra of P-CC and A-CC. SEM, scanning electron microscopy; TEM, transmission electron microscopy; XPS, X-ray photoelectron spectroscopy; FTIR, Fourier-transform infrared spectroscopy. Download figure Download PowerPoint Mass loading is a crucial technical parameter for industrial production, which is often ignored in basic frontier researches. Our A-CC electrode exhibited a high mass loading of 13.1 mg cm−2, almost the same as P-CC electrode (13.9 mg cm−2). To evaluate the electrochemical performance of such high mass loading samples after acidification, cycling performance in mass, areal, and volumetric specific capacities at 0.2 mA cm−2 were achieved, as shown in Supporting Information Figure S3a and Figure 2a and 2b. The corresponding coulombic efficiencies of P-CC and A-CC electrodes are provided in Supporting Information Figure S4. We observed that the P-CC electrode delivered an initial reversible areal-specific capacity of 1.56 mAh cm−2 (volumetric specific capacity of 54.0 mAh cm−3) and remained at 1.47 mAh cm−2 (volumetric specific capacity of 50.9 mAh cm−3) after 50 cycles. After acidizing, the reversible areal-specific capacity of A-CC electrode was improved to 1.81 mAh cm−2 (volumetric specific capacity of 65.6 mAh cm−3 and mass-specific capacity of 136 mAh g−1) and maintained at 1.59 mAh cm−2 (volumetric specific capacity of 57.4 mAh cm−3 and mass-specific capacity of 119 mAh g−1), hence, displaying a better cycling performance, compared with P-CC electrode. Supporting Information Figure S5 shows the EIS spectra of P-CC and A-CC electrodes before and after the cycles. Although the Rct of the A-CC electrode was slightly higher than that of P-CC before the cycling procedure, the Rct of the A-CC after 50 cycles was lower than that of the P-CC electrode, indicating that the decorated oxygen could promote ionic migration during the potassiation and depotassiation process. These results proved that our free-standing A-CC electrode, with high mass loading, still exhibited desirable electrochemical performance for K-ion storage, although it was difficult to compare the P-CC electrode with a low mass loading with the performance of our A-CC electrode. Generally, the natural graphite exhibits excellent electrochemical performance for K-ion storage in a low mass loading, which has been proven in previous reports.14,26 Therefore, we also provide the different mass loading graphite electrode for comparison with our A-CC electrode, as shown in Supporting Information Figure S6. We found that all of the natural graphite electrodes still exhibited low mass-specific capacity, and their capacities decay more rapidly with the increase in mass loading. This result indicated that the high mass loading electrode was difficult to obtain for high-performance K-ion storage. Compared with the mass-specific capacity, our free-standing electrode exhibited better K-ion storage performance (including high mass loading and cyclic stability). To further measure the electrochemical performance, the rate performance in mass, areal, and volumetric specific capacities of A-CC and P-CC were measured, as shown in Supporting Information Figure S3b and Figure 2c and 2d, we found that A-CC electrode exhibited 1.93, 1.76, 1.51, and 0.98 mAh cm−2 (the corresponding volumetric specific capacities are 70.4, 64.2, 55.1, and 35.8 mAh cm−3) at a current density of 0.1, 0.2, 0.5, and 1.0 mA cm−2, respectively, which were higher than that of the P-CC electrode (the areal specific capacities are 1.83, 1.63, 1.22, 0.74 mAh cm−2 and the corresponding volumetric specific capacities are 63.8, 57.0, mAh This result indicated that the slight oxygen decorated on the surface of A-CC could the K-ion diffusion which to its rate performance. To the of carbon cloth surface further, we obtained SEM images of P-CC and A-CC electrodes before and after the cycles. shown in Supporting Information Figure and observed some in P-CC after the by the of electrolyte, which might and their oxidation However, compared with P-CC, the surface structure of A-CC remained the same before and after the cycles. This cycling of A-CC might be attributable to the of the decorated oxygen that and the of Figure 2 | (a) and (b) volumetric specific capacities of P-CC and A-CC during different cycles at a current density of 0.2 mA (c) areal and (d) volumetric specific capacities of P-CC and A-CC electrodes at a different current density from 0.1 to 1.0 mA cm−2. Download figure Download PowerPoint for mass loading, the high energy density in practical production is achieved by anode materials with low charge–discharge To the charge–discharge in initial cycles were In Figure a broad peak between and 0.01 V is by the intercalation of K-ion and of peak at V was after the initial indicating that was a great charge plateau in this from the materials with large specific surface our A-CC with low specific surface area with the of a peak at Supporting Information Figure shows the at different sweep We found that the peaks to a high potential with an increased sweep rate due to the electrochemical from an of charge on the electrode at high current Figure displays charge–discharge of the A-CC electrode at 0.1 mA cm−2. We observed that the capacity at low potential V Such behavior a significant in energy density of a full battery in of anode We a and charge potential in a capacity V and respectively. Figure | (a) Cyclic voltammetry (CV) of A-CC electrode at a sweep rate of 0.2 mV (b) charge–discharge of A-CC electrode at a current density of 0.1 mA (c) areal ER of A-CC electrode at the charge and (d) of ER of P-CC and A-CC electrodes at the initial and charge (e) cycling performance of a electrode at a current density of 1 mA (f) of ER of A-CC electrode and electrode in the charge process. Download figure Download PowerPoint We the electrochemical performance of the anode material more and by the concept of "relative energy which not only the specific capacity but also the charge–discharge potential plateau of the anode materials, and an evaluation of the electrochemical performance in the of working The corresponding are as P K V V and are relative energy specific capacity, potential, and relative potential of K V respectively. The is the potential in the process, and the is also the charging potential in the charging process. is the different value between and The corresponding typical is shown in Figure on the areal and volumetric ER of A-CC and P-CC electrode at the charge and process were as shown in Figure and Supporting Information and The ER of A-CC electrode achieved 46 Wh m−2 Wh in the initial charge process and at 40 Wh m−2 Wh after 50 cycles. In addition, the concept of "relative energy was also derived from the charging energy density by energy The relative energy could also be used to evaluate the of the "relative and "relative Generally, high relative energy could the energy of KIBs. Supporting Information and the relative energy of both A-CC and P-CC electrode. We that the electrode exhibited a relative energy of ∼ after the initial For we have provided the ER of P-CC and A-CC electrode in the initial and 50 cyclic charge as shown in Figure which that A-CC electrode exhibited higher relative energy density than that of P-CC electrode. Figure | for the of the relative energy density (ER) of (a) ER and (b) charge Download figure Download PowerPoint We further the of high mass loading electrode by the electrochemical performance of the electrode, which was by two A-CC electrodes, as shown in Figure and Supporting Information Figure The electrode delivered an areal-specific capacity of mAh cm−2 volumetric specific capacity of mAh cm−3) after 50 and at a high current density of 1 mA cm−2 even with a mass loading of mg cm−2. In Figure the ER of Wh m−2 Wh and in A-CC electrode at 1.0 mA cm−2 was at the cyclic charge process, indicating that the A-CC electrode exhibited excellent with high mass loading for KIBs. Supporting Information Figure shows the EIS spectra of A-CC with a and electrode the Supporting The impedance of A-CC of the electrode was than that of a electrode, which was to the between the two electrodes. we the practical K-ion storage in low potential without an using an operando Raman Figure shows the of the operando Raman spectra testing and Supporting Information and also the of the operando testing and the practical testing Figure is a of the operando Raman spectra A-CC electrode in the initial Our results that the A-CC electrodes of D and G band were located at and cm−1 at the respectively. After to 0.01 V, the D and G bands to a lower of and cm−1, respectively. The of D band might be related to by of and some of For the of the G band, the and the of the of groups were After the depotassiation process, the D band and the G band to and cm−1, that the A-CC electrode exhibited excellent and the of the D and G band at a different charge–discharge from the operando Raman spectra, demonstrating that the ratio of ID/IG value also from to in the potassiation process. The decrease of intensity from the of with K-ion which was to the of limited by the After the depotassiation process, the ID/IG value was from to indicating that the electrode exhibited of K-ion and was that the structure of the carbon cloth to a more ordered structure in the potassiation process and then to disordered structure in the depotassiation process. This result indicated that the K-ion into the after in the disordered carbon to at a specific the the of also with the process of the graphite been Figure | (a) of operando Raman testing (b) operando Raman spectra of A-CC electrode in the at a sweep rate of 0.6 mV s−1. The ID/IG value of operando Raman spectra in the (c) potassiation process and (d) depotassiation process. Download figure Download PowerPoint We obtained the A-CC electrode by a acidified treatment as anode for KIBs. Benefiting from the free-standing structure and high mass loading (13.1 mg cm−2), the A-CC electrode exhibited a high areal reversible specific capacity of 1.81 mAh cm−2 and volumetric reversible specific capacity of 65.6 mAh cm−3 at a current density of 0.2 mA cm−2. The electrode mg cm−2) also delivered a high reversible areal-specific capacity of mAh cm−2 at a high current density of 1.0 mA cm−2. Besides, for an calculation method to evaluate the of the low potential plateau was In this our sample delivered an ultrahigh relative energy density of 46 Wh m−2 Wh Further, operando Raman spectrometry was conducted to investigate the K-ion storage which the of graphene of A-CC electrode during K-ion process. We believe that our work an avenue to more practical KIB industrialization in of a low potential plateau and high mass loading. 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