Academia.eduAcademia.edu

Figure 3 – uploaded by Mohammed Matouq

See full PDFdownloadDownload figure
Figure 3. a) Raman spectroscopy measurements of pristine and sonicated vein graphite flakes. b, c) Galvanostatic charge-discharge voltage curves and cyclic stability of pristine and sonicated vein graphite flakes measured without and with CCCV protocol at the current density of 100 mAg™ using an anolyte with 1.3:1 (AICI;/EMIMCI) molar ratio. Notably, although we have also attempted to prepare AICI,- saturated anolytes with r=2.3, at such a high AICI;/EMIMCI molar ratio AICI, was not fully soluble in the IL even at a high temperature of 150°C. Consequently, the electrochemical performance of vein graphite was performed, employing only IL with r= 2.1. As illustrated in Figure 4a, the higher the acidity of chloroaluminate ionic liquid leads to lower voltage and capacity. The average discharge voltages and capacities at r =1.3, 2.0, and 2.1 were 1.99, 1.73, 1.71 V vs. AP*/Al, and 116, 108, and 103mAhg™', respectively. However, the cycling stability tests of vein graphite measured with IL with r=2.1 show high capacity retention in excess of 105 mAg™' for at least 50 cycles with a Coulombic efficiency of 93-97% (Fig- ure 4b). We note that by the increasing r we observed a significant lowering of the Coulombic efficiency, which is associated with the intensified oxidation of the tungsten current collector in IL anolyte.23465

Figure 3 a) Raman spectroscopy measurements of pristine and sonicated vein graphite flakes. b, c) Galvanostatic charge-discharge voltage curves and cyclic stability of pristine and sonicated vein graphite flakes measured without and with CCCV protocol at the current density of 100 mAg™ using an anolyte with 1.3:1 (AICI;/EMIMCI) molar ratio. Notably, although we have also attempted to prepare AICI,- saturated anolytes with r=2.3, at such a high AICI;/EMIMCI molar ratio AICI, was not fully soluble in the IL even at a high temperature of 150°C. Consequently, the electrochemical performance of vein graphite was performed, employing only IL with r= 2.1. As illustrated in Figure 4a, the higher the acidity of chloroaluminate ionic liquid leads to lower voltage and capacity. The average discharge voltages and capacities at r =1.3, 2.0, and 2.1 were 1.99, 1.73, 1.71 V vs. AP*/Al, and 116, 108, and 103mAhg™', respectively. However, the cycling stability tests of vein graphite measured with IL with r=2.1 show high capacity retention in excess of 105 mAg™' for at least 50 cycles with a Coulombic efficiency of 93-97% (Fig- ure 4b). We note that by the increasing r we observed a significant lowering of the Coulombic efficiency, which is associated with the intensified oxidation of the tungsten current collector in IL anolyte.23465

Related Figures (3)

Figure 1. Schematic of the charging process of AGDIB comprising AICI3- saturated anolyte with an excess of AICI;. In typical anolytes used for AGDIBs, only AI,Cl,- ions enable the aluminum electroplating, which occurs, consequently, in acidic chloroaluminate melts (i.e., the molar ratio (r) of AICI, to EMIMCI > 1).°°3" Hence the specific charge-storage capacity of the acidic melts is a function of the Al,Cl, ion concentration in the ionic liquid. Towards getting an increased charge-storage capacity of anolytes, in this work, we present an AIDIB concept using an AICl;-saturated AICI;/EMIMCI (1-ethyl-3-meth- ylimidazolium chloride) anolyte with an excess of AICI; powder (r=2.1) for keeping constant acidity during AIDIB charging (Figure 1). The studied anolyte exhibits a high theoretical capacity of 52 mAhg™' owing to the increased content of the
Figure 1. Schematic of the charging process of AGDIB comprising AICI3- saturated anolyte with an excess of AICI;. In typical anolytes used for AGDIBs, only AI,Cl,- ions enable the aluminum electroplating, which occurs, consequently, in acidic chloroaluminate melts (i.e., the molar ratio (r) of AICI, to EMIMCI > 1).°°3" Hence the specific charge-storage capacity of the acidic melts is a function of the Al,Cl, ion concentration in the ionic liquid. Towards getting an increased charge-storage capacity of anolytes, in this work, we present an AIDIB concept using an AICl;-saturated AICI;/EMIMCI (1-ethyl-3-meth- ylimidazolium chloride) anolyte with an excess of AICI; powder (r=2.1) for keeping constant acidity during AIDIB charging (Figure 1). The studied anolyte exhibits a high theoretical capacity of 52 mAhg™' owing to the increased content of the
Figure 2. a) The charge-storage capacity of AICI,/EMIMCI anolyte versus its acidity (r). b) Comparison of the calculated cell-level capacities of AGDIB: comprising AICI;/EMIMCI anolyte of different acidities. The curves are computed from Eq. S22 published in the Supporting information of Ref. [49]. Generally, chloroaluminate ionic liquids are defined as mixtures of AICI, and other Cl” based salts such as, for instance, commonly used 1-ethyl-3-methylimidazolium chloride (EMIM). The mixture turns liquid at room temperature because of the acid-base reaction between AICI, (Lewis acid) and Cl” (Lewis base), yielding AICI, anions charge-balanced with, for example, EMIM~ cations. The excess of AICI; over EMIMCI results in the formation of acidic ionic liquid formulations containing Al,Cl, . Aluminum electrodeposition from chloroaluminate ionic liquids has been comprehensively studied in the past, leading to the conclusion that solely AI,Cl, anions (not AICI, ) allows the electroplating of Al.2*“" Consequently, aluminum does not plate from neutral/basic melts (equal/excess molar amount of EMIMCI to AICI,). Hence the concentration of Al,Cl, ions in chloroaluminate IL must be proportional to the capacity of the graphite. Specifically, for four Al,Cl, ions that are reduced at the negative electrode, three AICI, anions concomitantly intercalate into the graphite positive electrode. The charging of AGDIB stops when there are only AICI, ions left in the chloroaluminate IL, that correspond to the neutral melt formulation (AICI;/EMIMCI = 1), or when the maximum capacity of the graphite cathode is reached. In this context, hypotheti- cally, any current collector supporting the aluminum electro- plating of Al in chloroaluminate IL or coated with a thin seeding layer of Al film, can be used in AGDIBs instead of Al foil“?! Figure 2a illustrates the impact of the AICI,:EMIMCI molar ratio (r) on the charge storage capacity of the Hence, following the above-mentioned consideration, the theoretical capacities of AICl,-saturated IL anolytes with an excess of AICI; can be increased, for instance, by up to ca. 52 and 58mAhg™" for r=2.1 and 2.3, accordingly. The latter improves the cell-level capacity of AGDIB of up to 36 and 39 mAhg"', respectively (assuming charge-storage capacity of graphite of ca. 120 mAhg™') as compared to IL formulation with r=1.3 or 2.0 [C,., =16 mAhg™ (r=1.3); C.., =34 mAhg"! (r= 2), Figure 2b]. It should be noted, however, that an increase in r often leads to a concomitant decrease in graphite capacity and the average discharge voltage,°“*! as is apparent from the electrochemical measurements, which will be discussed in the next section.
Figure 2. a) The charge-storage capacity of AICI,/EMIMCI anolyte versus its acidity (r). b) Comparison of the calculated cell-level capacities of AGDIB: comprising AICI;/EMIMCI anolyte of different acidities. The curves are computed from Eq. S22 published in the Supporting information of Ref. [49]. Generally, chloroaluminate ionic liquids are defined as mixtures of AICI, and other Cl” based salts such as, for instance, commonly used 1-ethyl-3-methylimidazolium chloride (EMIM). The mixture turns liquid at room temperature because of the acid-base reaction between AICI, (Lewis acid) and Cl” (Lewis base), yielding AICI, anions charge-balanced with, for example, EMIM~ cations. The excess of AICI; over EMIMCI results in the formation of acidic ionic liquid formulations containing Al,Cl, . Aluminum electrodeposition from chloroaluminate ionic liquids has been comprehensively studied in the past, leading to the conclusion that solely AI,Cl, anions (not AICI, ) allows the electroplating of Al.2*“" Consequently, aluminum does not plate from neutral/basic melts (equal/excess molar amount of EMIMCI to AICI,). Hence the concentration of Al,Cl, ions in chloroaluminate IL must be proportional to the capacity of the graphite. Specifically, for four Al,Cl, ions that are reduced at the negative electrode, three AICI, anions concomitantly intercalate into the graphite positive electrode. The charging of AGDIB stops when there are only AICI, ions left in the chloroaluminate IL, that correspond to the neutral melt formulation (AICI;/EMIMCI = 1), or when the maximum capacity of the graphite cathode is reached. In this context, hypotheti- cally, any current collector supporting the aluminum electro- plating of Al in chloroaluminate IL or coated with a thin seeding layer of Al film, can be used in AGDIBs instead of Al foil“?! Figure 2a illustrates the impact of the AICI,:EMIMCI molar ratio (r) on the charge storage capacity of the Hence, following the above-mentioned consideration, the theoretical capacities of AICl,-saturated IL anolytes with an excess of AICI; can be increased, for instance, by up to ca. 52 and 58mAhg™" for r=2.1 and 2.3, accordingly. The latter improves the cell-level capacity of AGDIB of up to 36 and 39 mAhg"', respectively (assuming charge-storage capacity of graphite of ca. 120 mAhg™') as compared to IL formulation with r=1.3 or 2.0 [C,., =16 mAhg™ (r=1.3); C.., =34 mAhg"! (r= 2), Figure 2b]. It should be noted, however, that an increase in r often leads to a concomitant decrease in graphite capacity and the average discharge voltage,°“*! as is apparent from the electrochemical measurements, which will be discussed in the next section.
Figure 4. a) Galvanostatic charge-discharge voltage curves of sonicated vein graphite flakes measured at a current density of 100 mAg” in AICI, :EMIMCI ionic liquid with r= 1.3, 2.0, and 2.1. b) Cycling stability measurements of sonicated vein graphite flakes measured at a current density of 100 mAg' in AICI,/ EMIMCL ionic liquid with r= 2.0 and 2.1. Cycling stability measurements at higher currents of 500 mAg”' are shown in Figure $4.
Figure 4. a) Galvanostatic charge-discharge voltage curves of sonicated vein graphite flakes measured at a current density of 100 mAg” in AICI, :EMIMCI ionic liquid with r= 1.3, 2.0, and 2.1. b) Cycling stability measurements of sonicated vein graphite flakes measured at a current density of 100 mAg' in AICI,/ EMIMCL ionic liquid with r= 2.0 and 2.1. Cycling stability measurements at higher currents of 500 mAg”' are shown in Figure $4.
Related topics:
Environmental Science
580 California St., Suite 400
San Francisco, CA, 94104
© 2025 Academia. All rights reserved