Graphene-like Graphite as a Novel Cathode Material with a Large Capacity and Moderate Operating Potential for Dual Carbon Batteries
←
→
Page content transcription
If your browser does not render page correctly, please read the page content below
Journal of The Electrochemical
Society
OPEN ACCESS
Graphene-like Graphite as a Novel Cathode Material with a Large
Capacity and Moderate Operating Potential for Dual Carbon Batteries
To cite this article: Junichi Inamoto et al 2021 J. Electrochem. Soc. 168 010528
View the article online for updates and enhancements.
This content was downloaded from IP address 46.4.80.155 on 14/11/2021 at 06:45Journal of The Electrochemical Society, 2021 168 010528
Graphene-like Graphite as a Novel Cathode Material with a Large
Capacity and Moderate Operating Potential for Dual Carbon
Batteries
Junichi Inamoto,1,*,z Kazuhiro Sekito,1 Naoya Kobayashi,1,2 and Yoshiaki Matsuo1
1
Department of Applied Chemistry, Graduate School of Engineering, University of Hyogo, Himeji, Japan
2
NK energy frontier co., Ltd., Ikoma, Japan
Dual carbon batteries have recently attracted significant attention because of their ecofriendliness and reliability. In this study,
graphene-like graphite (GLG) was prepared by thermal reduction of graphite oxide to be used as a cathode material, and the
electrochemical PF6− anion-intercalation reaction into GLG was investigated. Decreasing the heat-treatment temperature of GLGs
from 900 °C to 600 °C resulted in increasing the reversible capacities and interlayer distances of GLG samples. Among them, GLG
synthesized at 700 °C (GLG700) showed the largest discharge capacity of 137 mAh g−1, which was much larger than that of
graphite (52 mAh g−1). Variations in the X-ray diffraction patterns and Raman spectra of GLG700 indicated that the stage number
reached 1 at 4.8 V (vs Li+/Li) while that of graphite was 2 at the same potential. This indicates that GLG could store PF6− anion in
every interlayer, which is probably one of the main causes of the larger capacity. The charge–discharge cycling test of GLG700
showed that the capacity gradually increased during cycling, and the coulombic efficiency was approximately 97% at every cycle
after the 5th cycle. These results clearly demonstrate that GLG can be used as a cathode material with a large capacity for dual
carbon batteries.
© 2021 The Author(s). Published on behalf of The Electrochemical Society by IOP Publishing Limited. This is an open access
article distributed under the terms of the Creative Commons Attribution Non-Commercial No Derivatives 4.0 License (CC BY-
NC-ND, http://creativecommons.org/licenses/by-nc-nd/4.0/), which permits non-commercial reuse, distribution, and reproduction
in any medium, provided the original work is not changed in any way and is properly cited. For permission for commercial reuse,
please email: permissions@ioppublishing.org. [DOI: 10.1149/1945-7111/abdb00]
Manuscript submitted November 17, 2020; revised manuscript received December 21, 2020. Published January 21, 2021.
Supplementary material for this article is available online
Lithium-ion batteries (LIBs) have been used in portable devices, C20+X− composition; where X− denotes the intercalated anion) charged
such as laptops and mobile phones, for more than two decades. to 5.2 V vs Li+/Li is less than 110 mAh g−1.
Currently, LIBs are used in larger scale devices such as stationary To overcome these challenges, several electrolyte solutions stable at
energy storage. The energy density and reliability of LIBs are more 5.0 V vs Li+/Li and cathode materials with larger capacity at moderate
important in large-scale devices. Lithium-containing transition metal potential were extensively investigated. Various combinations of
oxides, such as LiCoO2, have been widely used as cathode active solvents and additives as well as ionic liquids have been tested to
materials for LIBs.1,2 LiNixCoyMnzO23–6 and LiNixCoyAlzO27,8 are obtain stable electrolytes.21,26–29 Ethyl methyl carbonate-based con-
also employed in state-of-the-art LIBs because of their superior centrated electrolytes were found to be one of the promising electrolyte
energy densities. These oxides have good operating potential and solutions sufficiently stable against oxidation. Several materials, such
gravimetric capacity. However, they contain transition metals, which as hydrocarbons,30,31 metal organic frameworks,32 organic crystalline
are harmful to the environment. In addition, they release oxygen at solids,33–35 organic polymers,36,37 have been proposed as novel cathode
elevated temperatures,9–11 which results in thermal runaway that materials. However, their discharge capacity does not typically exceed
may lead to an explosion. To obtain batteries with high reliability for 110 mAh g−1. Therefore, further exploration of cathode materials is
large-scale applications, safer materials should be developed for required.
positive electrodes. A new carbon material called graphene-like graphite (GLG),
Anion-intercalation reactions into graphitic carbon materials have which was recently developed by the authors,38–42 is expected to be
been recently explored as positive electrode reactions.12–15 By a good candidate for cathodes of dual carbon batteries. GLG is
substituting conventional metal oxide cathode materials with carbon synthesized through thermal reduction of graphite oxide (GO) at a
materials for LIBs, a dual carbon battery, in which carbon is used as an relatively low rate of temperature increase to avoid the exfoliation of
active material in both electrodes, can be obtained. This battery is safer graphene layers. During the thermal reduction process, most of the
and more environmentally friendly than conventional LIBs since oxygen atoms in GO are removed as CO, CO2, and H2O, which
it is free from transition metal oxides. Even before the conceptualiza- results in the formation of nanopores inside the graphene layers.38
tion of the dual carbon battery, the anion-intercalation reactions into Although the graphene layers in GLG are stacked with a three-
graphitic carbons have been extensively studied for several years. dimensional regularity similar to that of graphite, they exhibit an
Several types of anions, such as PF6−,12–16 ClO4−,17,18 BF4−,19 bis interlayer distance larger than that of graphite. When GLG was used
(trifluorimethanesulfonyl)amide,20–24 and bis(fluorosulfonyl)amide,23–25 as an anode material for LIBs, a large number of lithium ions can be
were found to electrochemically intercalate into graphitic carbons. The introduced due to the larger expansion of interlayer distance
redox potential of the reactions of these materials is generally higher compared to that of graphite, leading to a reversible capacity of
than that of conventional metal oxide cathode materials,12–25 which more than 670 mAh g−1.38 The structural changes during the Li
results in high energy densities. However, high redox potentials activate storage in GLG samples with different interlayer spacings and
unfavorable side reactions such as the oxidative decomposition of oxygen contents were investigated. The onset potential of the
electrolyte solutions. In addition, although the capacity of the graphite intercalation of lithium ions was found to be much higher than
cathodes varies with the type of anion, they are generally lower than that that observed for graphite. This was attributed to the much smaller
of LIB cathodes based on conventional transition metal oxides.12–25 For energy required for separating graphene layers of GLG compared to
example, the typical discharge capacity of a graphitic carbon (with a that of graphite. This strongly indicates that cations as well as anions
can intercalate into GLG using lower energy. Therefore, GLG is
expected to show lower potential for the anion-intercalation reaction.
*Electrochemical Society Member.
Hantel et al. also suggested that the activation potential of partially
z
E-mail: j.inamoto@eng.u-hyogo.ac.jp reduced GO for the intercalation of ions decreased with the increaseJournal of The Electrochemical Society, 2021 168 010528
in the layer distance. This was determined based on the results of the
electrochemical properties of the materials when used as cathode
materials of an electric double layer capacitor.43,44 However,
these studies focused on samples with large interlayer spacings
(−0.43 nm), but the number of intercalated anions was not clarified.
The increase in the interlayer distance of GLG possibly results in
increasing the number of intercalatable anions and achieving a
discharge capacity of more than 110 mAh g−1.
In this study, GLGs with various interlayer distances were
synthesized by changing the thermal reduction temperature. In
addition, the electrochemical intercalation behavior of anions into
the layers and the intercalation structures were carefully studied.
Experimental
To obtain graphite oxide (GO), flake graphite (Z-5F, purchased
from Ito Graphite Co. Ltd.) was oxidized based on Brodie’s
method.45,46 The detailed conditions of the experiment are described
elsewhere.38 The resulting GO was thermally reduced at 600 °C,
700 °C, 800 °C and 900 °C under vacuum to obtain GLG. Hereafter,
the GLGs synthesized at 600 °C, 700 °C, 800 °C and 900 °C are
called GLG600, GLG700, GLG800, and GLG900, respectively. The
GLGs were characterized using X-ray diffraction (XRD, D2 Phaser,
Bruker) with Cu Kα source.
The GLGs were mixed with acetylene black (AB) and polytetra-
fluoroethylene (PTFE) at a weight ratio of 90:5:5. The same process
was also conducted using graphite (Z-5F). Next, the two the Figure 1. XRD patterns of GLG600, GLG700, GLG800, and GLG900.
mixtures were thinned down to form self-standing electrodes at a
loading weight of approximately 32 mg cm−2. Three-electrode cells
were constructed using these electrodes as the working electrodes oxygen atoms might electrostatically attract carbon atoms in the
along with lithium metal counter and reference electrodes. neighboring layers, resulting in a slightly smaller interlayer distance
Approximately 5 ml of LiPF6/ethyl methyl carbonate (EMC, compared to graphite. These results prove the successful synthesis of
3 mol dm−3) was used as an electrolyte solution. For charge– GLGs with various interlayer distances, which was conducted by
discharge measurements, constant current at 10 mA g−1 was applied changing the temperature of the thermal treatment.
at 2.0–4.8 V vs Li+/Li of cut-off voltage. Figure 2a shows the charge–discharge curves of GLGs and
In addition to the above described charge–discharge measure- graphite. The electrochemical intercalation and deintercalation of
ments, XRD and Raman spectroscopy of GLG charged to various PF6− into and from GLGs occurred successfully. During the
potential and discharged to 2.0 V was conducted to analyze the charging process, the increase in the potential of GLGs was more
intercalation structures of GLG at each potential during the charge- gradual than that of graphite. Among GLGs, the charge capacity
–discharge tests. The cells were deconstructed in Ar-filled grove box increased with the decrease in the interlayer distance, which was
and the electrodes were transferred to an air-tight sample holder to 149, 150, 179, and 214 mAh g−1 for GLG600, GLG700, GLG800,
conduct these tests under inert atmosphere. To investigate the and GLG900, respectively. These values were much larger than
intercalated species in sheet-type GLGs with no AB and PTFE, that of graphite (55 mAh g−1). The discharge capacities of
charged and discharged electrodes were examined using attenuated GLG600, GLG700, GLG800, and GLG900 were 137, 137,
total reflection Fourier transform infrared spectroscopy (ATR-IR). 131, and 134 mAh g−1, respectively, which are much larger
The samples were extracted from the cell in Ar-filled glove box and than that (52 mAh g−1) of graphite. It should be emphasized that
washed with dimethyl carbonated (DMC) and then dried for 3 d in the capacities of GLGs were larger than the values reported in the
the glove box before starting measurements. The measurement was literature for graphitic carbons with various anions.12–25 Since the
conducted under ambient air immediately after extracting the discharge capacities of all GLGs were similar, despite the large
electrodes from the glove box in order to avoid their decomposition. variation in charge capacity, the GLG with smaller interlayer
distance exhibited larger coulombic efficiency. The coulombic
Results and Discussion efficiencies of GLG600, GLG700, GLG800, and GLG900 were 92%,
Electrochemical properties of GLGs with various interlayer 91%, 73%, and 63%, respectively. Thus, the coulombic efficiencies of
distances.—Figure 1 shows the XRD patterns of GLG600, GLG700, GLG600 and GLG700 are comparable to that of graphite (94%).
GLG800, and GLG900. The 002 diffraction peaks of GLG shifted to Concerning lithium-ion intercalation reaction into graphitic carbons, the
higher 2θ values with the increase in the thermal treatment oxygen-containing groups lower coulombic efficiency. On the other
temperatures, indicating a decrease in the interlayer distance. The hand, GLG600 which contain largest number of oxygens showed the
interlayer distances of GLG600, GLG700, GLG800, and GLG900 highest efficiency for PF6− intercalation. This is because the oxygen-
were examined at 0.358, 0.340, 0.337, and 0.332 nm, respectively. containing groups in GLGs did not activate oxidation of electrolyte
The decrease in the distance can be explained as follows: there were solution and irreversibly trap the anions. Figure 2b shows the dQ/dV
repulsion forces between the remaining oxygen atoms in the curves calculated from the charge–discharge curves. The figure
neighboring graphene layers of GLG, leading to the expansion of indicated that the onset potentials of GLGs increased in the following
the interlayer distance. Since the remining oxygen atoms decreased order: GLG600 < GLG800 ⩽ GLG700 < GLG900 < graphite. Except
with the increase in the temperature, the repulsion force weakened, for graphite, the order was roughly consistent with that of the interlayer
and the interlayer distance became similar to that of graphite distance. In the discharging process, the curves show that the mean
(0.335 nm). Although it seems strange that GLG900 exhibited a discharge potential decreased with the increase in the interlayer
lower value than that of graphite, a similar result was obtained in the distance. These results indicate that the weaker interaction between
authors’ previous study.39 The number of oxygen atoms in GLG900 the layers led to a lower redox potential in the anion-intercalation
was too small to cause a strong repulsion force. Furthermore, the reaction. As mentioned, GLG600 and GLG700 exhibited a coulombicJournal of The Electrochemical Society, 2021 168 010528
Figure 3. XRD patterns of pristine GLG700 (a), and that charged to 4.38 V
(b), 4.51 V (c), 4.58 V (d), 4.80 V (e), and discharged to 2.0 V (f) during the
initial cycle. The 00 l index attributable to each peak was denoted with stage
number in round brackets.
Table I. Stage number and sandwich thickness of GLG700 inter-
calation compounds at each potential calculated from Fig. 3.
Potential/V Stage number Sandwich thickness ds/nm
4.38 5/4 0.810/0.788
4.51 3/2 0.808/0.776
4.58 2/1 0.810/0.767
4.80 1 0.765
2.0 4/5 0.775/0.794
(intercalated gallery heights) of each sample were calculated from
the XRD results and summarized in Table I. The calculation method
was referred to the literature,47 and the detailed procedure for the
attribution was described in Table SI. During the charging process,
the stage number decreased as the potential increased. The 002 peak
indicated that a stage-5 or a stage-4 intercalation compound was
obtained at 4.38 V. However, it was difficult to determine the exact
stage number since there was no other peak except for the main
Figure 2. (a) Charge-discharge curves of GLGs and graphite at the initial peak, and a small difference was observed in the sandwich thickness
cycle. (b) dQ/dV curves calculated from the charge-discharge curves. The between stage-5 and −4 compounds. Considering that the charge
potentials were referred to Li+/Li. capacity (35 mAh g−1) obtained at 4.38 V was 4.3 times smaller than
that (150 mAh g−1) obtained at 4.80 V, the intercalation compound
was probably a two-phase compound resulting from the coexistence
efficiency comparable to that of graphite, and the mean discharge of stages 5 and 4. At 4.58 V, a weak peak was observed around 2θ =
potential of GLG700 was higher than that of GLG600. Thus, GLG700 32° in the middle position between 004 peak of stage-2 compound
was considered the most promising material among GLGs. Therefore, and 003 peak of stage-1 compound. It was previously reported that if
further investigation of the anion-intercalation reaction into GLG700 intercalation compound has both stage-n and -m compounds
was conducted and discussed in the following sections. collectively piled along the c-axis, the peak will occur at the
intermediate position between those of stage-n and -m compounds.
Structural analysis of GLG during charge–discharge reac- Therefore, the intercalation compound obtained at 4.58 V was
tions.—XRD and Raman spectroscopy were carried out to investi- probably composed of both stage-2 and stage-1 compounds. At
gate the structural changes during the charge and discharge test of 4.8 V, the weak peak around 2θ = 34° was close to the 003 peak of
GLG. Figure 3 shows XRD patterns of GLG700 charged to 4.38, stage-1 compound and no other peak was observed; thus, the
4.51, 4.58, and 4.80 V and then discharged to 2.0 V. The 002 peak, intercalation compound was mainly composed of stage-1 compound.
which corresponds to the pristine GLG700, shifted to a lower value Figure S1 (available online at stacks.iop.org/JES/168/010528/
as the potential increased, indicating an increase in the interlayer mmedia) shows the XRD patterns of other GLGs and graphite at
spacing. The possible stage numbers and sandwich thicknesses various potentials during charge and discharge for comparison. TheJournal of The Electrochemical Society, 2021 168 010528
Figure 4. Raman spectra of GLG700 during the initial charge and discharge.
Figure 5. ATR FT-IR spectra of pristine GLG700, and that charged and
discharged in 3 mol dm−3 LiPF6/EMC, along with 3 mol dm−3 LiPF6/EMC
other GLGs showed the same tendency, i.e., a decrease in the stage and pure EMC.
number with the increase in the potential until it reached 1 at a
potential equal to or less than 4.8 V. In particular, GLG600 reached
stage-1 even at 4.51 V. On the other hand, the stage number of 1624 cm−1. It was previously reported in the literature that the
graphite intercalation compound (GIC) at 4.8 V remained 2, graphene layers with and without neighboring intercalant layer(s)
indicating that GLGs can intercalate larger number of PF6− anions. showed peaks at 1624 and 1594 cm−1, respectively.48 This peak shift
These results explain the larger charge capacity of GLGs compared indicates that a stage-2 or -1 compound was formed, which is
to graphite. Although GLG900 has smaller interlayer distance than consistent with the XRD results. In the discharged sample, peaks
graphite, it showed much larger capacity in Fig. 2a. One of the were observed at 1594 and 1624 cm−1. The peak at 1624 cm−1 was
causes of this larger capacity was this smaller stage number of slightly weaker than that at 1594 cm−1, which suggests that the stage
GLG900 at 4.8 V, which is possibly derived from difference in number of the discharged GLG700 was 4 or 5. This is also consistent
density of state (DOS) of valence band. To clarify origin of the with the XRD results.
smaller stage number, the DOS of GLGs will be investigated using To clarify the intercalated species in charged and discharged
X-ray emission spectroscopy and/or ultraviolet photoelectron spec- GLG700, ATR-FTIR tests were conducted. Figure 5 shows the FT-
troscopy in our next study. IR spectra of pristine, charged, and discharged GLG700 along with
In the spectra of discharged GLG700, the peak did not return to those of LiPF6/EMC (3 mol dm−3) and pure EMC. PF6− anion was
the initial position, indicating that some of the intercalated anions previously reported to have two IR active vibration modes (ν3 and
were not completely deintercalated. The calculation revealed that ν4) showing absorption peaks at 554 and 835 cm−1, respectively. In
the discharged GLG was a stage-4 or −5 compound. When stage-4 addition, the ion–ion interaction between PF6− and Li+ activates the
and -5 compounds have the same configuration and density of IR inactive vibration mode (ν1), resulting in an absorption peak at
intercalants as that of stage-1 compound, the capacities of stage-4 774 cm−1.49,50 These ν3, ν1, and ν4 peaks were observed at 556, 742,
and -5 compounds can be estimated based on the capacity of and 845 cm−1 in the spectrum of LiPF6/EMC (3 mol dm−3). In the
stage-1 compound (150 mAh g−1) to be 37.5 and 30 mAh g−1, charged GLG700 spectrum, clear peaks around 556 and 845 cm−1
respectively. However, the irreversible capacity of GLG700 was were observed as well as small ones around 889, 929, 982, 1177, and
only 14 mAh g−1, which was considerably smaller than these values. 1288 cm−1. The former two peaks are due to PF6− ions, indicating
Therefore, it was suggested that the density of the remaining that the anions were intercalated into GLG. Most of the latter peaks
intercalants was lower than that of stage-1 compound. GLG600, were also observed in the spectra of LiPF6/EMC (3 mol dm−3) and
GLG800, and GLG900 also showed similar behaviors in terms of the EMC. Several solvent molecules were reported to be co-intercalated
variations of XRD patterns after discharge, while graphite after into graphite with the PF6− or BF4− ions.27,51 This strongly suggests
discharge exhibited similar pattern to that of the pristine graphite. that they are also included in GLG. In the discharged GLG700, weak
This indicates that it is intrinsically difficult to deintercalate all the peaks were observed at 556 and 845 cm−1. This indicates that some
intercalated anions from GLG, which leads to a slightly lower of the PF6− ions remained in the interlayer space of GLG, which was
coulombic efficiency. also suggested by the results of XRD and Raman measurements.
Figure 4 shows Raman spectra of pristine GLG700 and that Additional peaks were observed at 787, 1014, 1094, and 1258 cm−1,
charged to 4.8 V and discharged to 2.0 V. In all samples, the D and which are attributed to electrolyte solution. It was difficult to
G bands around 1350 cm−1 and 1590 cm−1, which are attributed to determine the location of the residual PF6− ions in the interlayer
the disordered graphitic region and ordered region, respectively, space of GLG even at 2.0 V. Since GLG contains oxygen atoms
were observed. The peak position of the G band was a bit higher than introduced within its graphene layers in the form of C–O–C, the
the standard value for graphitic carbons (1580 cm−1).48 This peak residual PF6− ions might strongly interact with positively charged
shift can be attributed to the action of the oxygen atoms remaining in carbon atoms bonded to electronegative oxygen atoms. These results
the graphene layers of GLG700. In the charged sample, the peak at revealed that a large number of PF6− ions can reversibly intercalate/
1594 cm−1 almost disappeared and a new peak was observed at deintercalate into/from GLG, respectively, with a small number ofJournal of The Electrochemical Society, 2021 168 010528
Figure 7. Variations of XRD patterns of GLG700 during the 20-cycle
charge-discharge test.
residual PF6− ions at 2.0 V, which is the main cause of the
irreversible capacity.
Cycling properties of GLG.—Finally, charge–discharge cycling
test of GLG700 was conducted. Figures 6a and 6b show the
charge–discharge curves the variations in the dQ/dV curves during
the cycles corresponding to the charge–discharge curves. While the
intercalation started at a potential higher than 4 V at the initial cycle,
it significantly dropped at the second cycle. This is probably caused
by the irreversibly remained PF6− anion in GLG700, which expands
interlayer distance. In addition, the dQ/dV curves clearly showed that
the peak observed at 4.0 V in the second cycle gradually shifted to a
lower potential during the cycles, and that the capacity under 4.0 V
increased. On the other hand, the peak at 4.25 V slightly shifted to a
lower potential with the increase in the dQ/dV value. During the
discharge process, the shapes of the discharge curves above 3.0 V
did not change over 20 cycles. On the other hand, under 3.0 V, the
capacity increased with the increase in the cycle number. These
results were more pronounced on the dQ/dV curves. The charge and
discharge capacities and coulombic efficiency during 20 cycles were
summarized in Fig. 6c. It clearly showed that the reversible capacity
and the coulombic efficiency were enhanced during cycling, and the
efficiency reached approximately 97% after the 5th cycle. These
results in Fig. 6 indicated that electrochemical properties of GLG700
was enhanced during cycling.
To clarify the cause of the change in the electrochemical
properties of GLG700 during cycling, variations of XRD during
the cycling test was conducted. Figure 7 shows XRD patterns of
GLG700 at charged and discharged state at the 1st, 2nd, and 20th
cycle, along with pristine GLG700. After the 2nd charge, the 002
peak emerged at lower angle compared to that at the first charge. In
addition, a new peak was observed at 2θ = 34.8 degree, which was
corresponding to 003 reflection of the stage-1 intercalation com-
pound. In addition, the peak shift and 003 peak were also observed at
the 20th cycle. Therefore, the number of intercalated anions
increased compared to the initial cycle. For GLG700 after the 2nd
Figure 6. (a) Charge-discharge curves, (b) dQ/dV curves, and (c) charge- and 20th discharge, the main peak was observed at slightly lower
discharge capacity and coulombic efficiency of GLG700 electrode during 20 angle than that after the 1st discharge. It indicated that GLG 700
cycles. after the 2nd and 20th cycle had larger number of remaining PF6−Journal of The Electrochemical Society, 2021 168 010528
anions than that after the 1st cycle. Since the reversible capacity and 8. M. Guilmard, C. Pouillerie, L. Croguennec, and C. Delmas, Solid State Ionics, 160,
coulombic efficiency increased with cycle number increasing, the 39 (2003).
number of intercalated PF6− anions at the charged state was largely 9. J. R. Dahn, E. W. Fuller, M. Obrovac, and U. V. Sacken, Solid State Ionics, 69, 265
(1994).
increased compared to the number of the remaining ones at the 10. J. Jiang, K. W. Eberman, L. J. Krause, and J. R. Dahn, J. Electrochem. Soc., 152,
discharged state during cycling. A566 (2005).
In conclusion, the discharge capacity of GLG700 reached 11. Y. Wang, J. Jiang, and J. R. Dahn, Electrochem. Commun., 9, 2534 (2007).
approximately 140 mAh g−1 at the 20th cycle, which is comparable 12. J. A. Seel and J. R. Dahn, J. Electrochem. Soc., 147, 892 (2000).
13. J. R. Dahn and J. A. Seel, J. Electrochem. Soc., 147, 899 (2000).
to the practical capacity of LiCoO2. The coulombic efficiency, 97% 14. T. Ishihara, M. Koga, H. Matsumoto, and M. Yoshio, Electrochem. Solid State Lett.,
at the 5th cycle, was as good as that of graphite. These results proved 10, A74 (2007).
that GLG can be used as a cathode active material in dual carbon 15. H. Wang and M. Yoshio, Electrochem. Commun., 8, 1481 (2006).
16. W. Märkle, N. Tran, D. Goers, M. E. Spahr, and P. Novák, Carbon, 47, 2727
batteries. (2009).
17. D. Alliata, R. Kötz, O. Haas, and H. Siegenthaler, Langmuir, 15, 8483 (1999).
Conclusions 18. D. Alliata, P. Häring, O. Haas, R. Kötz, and H. Siegenthaler, Electrochem.
−
Commun., 1, 5 (1999).
Electrochemical PF6 intercalation behaviors of GLG was 19. W. Ruch, M. Hahn, F. Rosciano, M. Holzapfel, H. Kaiser, W. Scheifele, B. Schmitt,
investigated using XRD, Raman, and FT-IR spectroscopies. The P. Novák, R. Kötz, and A. Wokaun, Electrochim. Acta, 53, 1074 (2007).
reversible capacity of PF6− intercalation/deintercalation into/from 20. W. Yan and M. Lerner, J. Electrochem. Soc., 148, D83 (2001).
21. T. Placke, O. Fromm, S. F. Lux, P. Bieker, S. Rothernel, H.-W. Meyer, S. Passerini,
GLG, respectively, (131–137 mAh g−1) was larger than that of and M. Winter, J. Electrochem. Soc., 159, A1755 (2012).
graphite (52 mAh g−1) and the reported values with higher upper 22. S. Rothermel, P. Meister, G. Schmuelling, O. Fromm, H.-W. Meyer, S. Nowak,
cut-off potential for various anions (110 mAh g−1). The decrease in M. Winter, and T. Placke, Energy Environ. Sci., 7, 3412 (2014).
the thermal reduction temperature of GLG from 900 °C to 600 °C 23. T. Fukutsuka, F. Yamane, K. Miyazaki, and T. Abe, J. Electrochem. Soc., 163,
A499 (2016).
resulted in an increase in the interlayer distance and reversible 24. K. Beltrop, P. Meister, S. Klein, A. Heckmann, M. Grünebaum, H.-D. Wiemhöfer,
capacity. The coulombic efficiencies of GLG600 and GLG700 (92% M. Winter, and T. Placke, Electrochim. Acta, 209, 44 (2016).
and 91%) were similar to that of graphite (94%). The redox potential 25. Y. Kondo, Y. Miyahara, T. Fukutsuka, K. Miyazaki, and T. Abe, Electrochem.
of GLGs was lower than that of graphite, which can aid in Commun., 100, 26 (2019).
26. A. Heckmann, J. Thienenkamp, K. Beltrop, M. Winter, G. Brunklaus, and
suppressing the oxidative decomposition of the electrolyte solution. T. Placke, Electrochim. Acta, 260, 514 (2018).
XRD and Raman spectroscopy indicated that GLG700 formed 27. J. A. Read, J. Phys. Chem. C, 119, 8438 (2015).
statge-1 intercalation compound at 4.8 V, while graphite reached 28. R. Nozu, E. Suzuki, O. Kimura, N. Onagi, and T. Ishihara, Electrochim. Acta, 332,
stage-2 at the same potential. The lower stage of the intercalation 135238 (2020).
29. H. Fan, L. Qi, M. Yoshio, and H. Wang, Solid State Ionics, 304, 107 (2017).
compound is probably one of the main causes of the larger capacity. 30. I. A. Rodríguez-Pérez, Z. Jian, P. K. Waldenmaier, J. W. Palmisano, R. S. Chandrabose,
In addition, XRD, Raman, and FT-IR spectroscopies indicated that X. Wang, M. M. Lerner, R. G. Carter, and X. Ji, ACS Energy Lett., 1, 719 (2016).
the discharged GLG700 still contained a small number of PF6− 31. I. A. Rodríguez-Pérez, C. Bommier, D. D. Fuller, D. P. Leonard, A. G. Williams,
anions, which was probably the main cause of the irreversible and X. Ji, ACS Appl. Mater. Interfaces, 10, 43311 (2018).
32. M. L. Aubrey and J. R. Long, J. Am. Chem. Soc., 137, 13594 (2015).
capacity. The cycling test of GLG700 showed good cyclability and 33. É. Deunf, P. Jiménez, D. Guyomard, F. Dolhem, and P. Poizot, Electrochem.
coulombic efficiency. These results clearly demonstrate that GLG Commun., 72, 64 (2016).
has large capacity and a good cyclability for the PF6− intercalation 34. M. Yao, H. Sano, H. Ando, and T. Kiyobayashi, Sci. Rep., 5, 10962 (2015).
reaction. Thus, GLG could be used as cathode material for dual 35. É. Deunf, P. Moreau, É. Quarez, D. Guyomard, F. Dolhem, and P. Poizot, J. Mater.
Chem. A, 4, 6131 (2016).
carbon batteries. 36. X. Dong, H. Yu, Y. Ma, J. L. Bao, D. G. Truhlar, Y. Wang, and Y. Xia, Chem. Eur.
J., 23, 2560 (2017).
Acknowledgments 37. M. Walter, K. V. Kravchyk, C. Böfer, R. Widmer, and M. V. Kovalenko, Adv.
Mater., 30, 1705644 (2018).
This work was partially supported by the Advanced Low 38. Q. Cheng, Y. Okamoto, M. Tsuji, N. Tamura, S. Maruyama, and Y. Matsuo, Sci.
Carbon Technology Research and Development Program (ALCA: Rep., 7, 14782 (2017).
39. Y. Matsuo, J. Taninaka, K. Hashiguchi, T. Sasaki, Q. Cheng, Y. Okamoto, and
JPMJAL140) of the Japan Science and Technology Agency (JST). N. Tamura, J. Power Sources, 396, 134 (2018).
40. Y. Matsuo, S. Maruyama, Q. Cheng, Y. Okamoto, and N. Tamura, Tanso, 281, 2
ORCID (2018).
41. Y. Matsuo, T. Sasaki, S. Maruyama, J. Inamoto, Y. Okamoto, and N. Tamura,
Junichi Inamoto https://orcid.org/0000-0002-1159-361X J. Electrochem. Soc., 165, A2409 (2018).
Yoshiaki Matsuo https://orcid.org/0000-0002-3808-5375 42. J. Inamoto, S. Maruyama, Y. Matsuo, S. Uchida, K. Maeda, and M. Ishikawa,
Electrochemistry, 87, 260 (2019).
References 43. M. M. Hantel, T. Kaspar, R. Nesper, A. Wokaun, and R. Kötz, Electrochem.
Commun., 13, 90 (2011).
1. K. Mizushima, P. C. Jones, P. J. Wiseman, and J. B. Goodenough, Mat. Res. Bull., 44. M. M. Hantel, T. Kaspar, R. Nesper, A. Wokaun, and R. Kötz, Chem. Eur. J., 18,
15, 783 (1980). 9125 (2012).
2. T. Ohzuku and A. Ueda, J. Electrochem. Soc., 141, 2972 (1994). 45. B. C. Brodie, Ann. Chim. Phys., 59, 466 (1860).
3. T. Ohzuku and Y. Makimura, Chem. Lett., 30, 744 (2001). 46. T. Nakajima and Y. Matsuo, Carbon, 32, 469 (1994).
4. T. Ohzuku and Y. Makimura, Chem. Lett., 30, 642 (2001). 47. M. S. Dresselhaus and G. Dresselhaus, Adv. Phys., 51, 1 (2002).
5. Z. Lu, L. Y. Beaulieu, R. A. Donaberger, C. L. Thomas, and J. R. Dahn, J. Electrochem. 48. Y. Wang, D. C. Alsmeyer, and R. L. McCreery, Chem. Mater., 2, 557 (1990).
Soc., 149, A778 (2002). 49. C. M. Burba and R. Frech, J. Phys. Chem. B, 109, 15161 (2005).
6. N. Yabuuchi and T. Ohzuku, J. Power Sources, 119–121, 171 (2003). 50. A. V. Cresce et al., Phys. Chem. Chem. Phys., 19, 574 (2017).
7. C. Delmas and I. Saadoune, Solid State Ionics, 53–56, 370 (1992). 51. Y. Huang and H. Wang, J. Electrochem. Soc., 166, A3838 (2019).You can also read
