Research Article Cite This: ACS Appl. Mater. Interfaces XXXX, XXX, XXX−XXX
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All Carbon Dual Ion Batteries Zhe Hu,†,‡ Qiannan Liu,‡ Kai Zhang,§ Limin Zhou,|| Lin Li,† Mingzhe Chen,‡ Zhanliang Tao,*,† Yong-Mook Kang,§ Liqiang Mai,*,|| Shu-Lei Chou,*,†,‡ Jun Chen,† and Shi-Xue Dou‡
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†
Key Laboratory of Advanced Energy Materials Chemistry (Ministry of Education), Collaborative Innovation Center of Chemical Science and Engineering, College of Chemistry, Nankai University, Tianjin 300071, China ‡ Institute for Superconducting and Electronic Materials, University of Wollongong, Wollongong, New South Wales 2522, Australia § Department of Energy and Materials Engineering, Dongguk University-Seoul, Seoul 100-715, Republic of Korea || State Key Laboratory of Advanced Technology for Materials Synthesis and Processing, Wuhan University of Technology, Wuhan 430070, China S Supporting Information *
ABSTRACT: Dual ion batteries based on Na+ and PF6− received considerable attention due to their high operating voltage and the abundant Na resources. Here, cheap and easily obtained graphite that served as a cathode material for dual ion battery delivered a very high average discharge platform (4.52 V vs Na+/Na) by using sodium hexafluorophosphate in propylene carbonate as electrolyte. Moreover, the all-carbon dual ion batteries with graphite as cathode and hard carbon as anode exhibited an ultrahigh discharge voltage of 4.3 V, and a reversible capacity of 62 mAh·g−1 at 40 mA·g−1. Phase changes have been investigated in detail through in situ X-ray diffraction and in situ Raman characterizations. The stable structure provides long life cycling performance, and the pseudocapacitance behavior also demonstrates its benefits to the rate capability. Thus, dual ion batteries based on sodium chemistry are very promising to find their applications in future. KEYWORDS: Graphite, Hard carbon, Dual ion batteries, Anion ion batteries, Pseudocapacitance
1. INTRODUCTION
as searching for cathode materials with a high working platform and proper electrolyte. Graphite has been extensively regarded as a suitable anode material for rechargeable lithium ion batteries. Due to cointercalation of sodium ions and solvent, graphite can also be used as anode materials, but exhibits limited electrochemical performance in sodium ion batteries.11 Its stable layered structure, however, can serve as a matrix for anion groups, such as PF6−.5,12−14 At very high charging voltage (above 4 V vs Na+/Na), the PF6− anions can be inserted into graphite interlayers to form a stable structure. Thus, DIBs based on Na+ and PF6− may introduce a new route for low-cost rechargeable battery system. Zhang et al. applied 4 M LiPF6 in ethyl methyl carbonate with 2 wt % vinylene carbonate additive as the electrolyte in lithium ion based dual ion batteries.7 The high concentration of the electrolyte increased the viscosity and hindered the ionic transfer. Recent investigations on graphite as cathode dual ion batteries have also provided strong evidence that sodium based dual ion
Among all the techniques for renewable energy storage, secondary rechargeable batteries have demonstrated their capability and potential in terms of portable devices, electric vehicles, and even grid-scale energy storage stations.1 Sodium ion batteries (SIBs) have attracted much attention due to the low cost and high abundance of sodium during the past decade.2,3 Cathode materials of SIBs, however, often suffer from limited working voltage (always lower than 4.5 V vs Na+/ Na). For example, Na3V2(PO4)3 has been widely investigated as perfect sodium storage material, because of its stable cycling performance and low overpotential during charging and discharging.4,5 The output voltage is below 3.5 V, however, and the low energy and power density will limit their application. Dual-ion batteries (DIBs) based on sodium chemistry are developed and investigated because of their advantages of wide voltage window, low cost, high safety and high energy density.6−8 The use of both cations and anions of electrolyte for charge transfer on discrete electrodes ensures them high power, and the storage of two types of ions inside the electrode materials endows them high energy density with increased capacity.9,10 For sodium based DIBs, many challenges, however, still need to be further addressed, such © XXXX American Chemical Society
Received: July 22, 2018 Accepted: September 12, 2018 Published: September 12, 2018 A
DOI: 10.1021/acsami.8b11824 ACS Appl. Mater. Interfaces XXXX, XXX, XXX−XXX
Research Article
ACS Applied Materials & Interfaces
platform of 4.3 V at 40 mA·g−1 (based on the mass of graphite) which can significantly restrain the generation of dendrites. Thus, this research is expected to show the potential of graphite to act as a cathode material in all-carbon dual ion battery for the next-generation low-cost and environmentally friendly rechargeable battery.
batteries will be very promising for next generation energy storage devices.15−19 Those full cells displayed high operating voltage around 4 V (vs Na+/Na) and good cycling performances. In our research, graphite as a cathode material for dual ion battery was investigated. Graphite demonstrated attractive performance with common electrolyte consisting of NaPF6 in propylene carbonate (PC). During the charging process, PF6− intercalates into the graphite interlayer, and sodium ions participate in the reaction at the counter electrode, which means both Na+ and PF6− have been involved in the electrochemical reaction (Figure 1). From the results of
2. EXPERIMENTAL SECTION Material Characterization. Graphite powder was purchased from the MTI Shenyang KJ group. The hard carbon powder was purchased from Imerys Graphite & Carbon. The crystal structure was investigated by X-ray diffraction (XRD, Cu Kα radiation) by using a D8 Advance X-ray diffractometer. Raman spectroscopy was conducted on a confocal Raman microscope (DXR, Thermo-Fisher Scientic) with an Ar-ion laser (λ = 532 nm) in ambient air. The morphology and microstructure were examined by scanning electron microscopy (SEM, JEOL JSM7500F). Electrochemical Characterization. CR2032 coin cells were used as the device to test the electrochemical performance. Natural graphite powder and poly(vinylidene fluoride) (PVDF) in a mass ratio of 9:1 were used as the cathode material, and N-methyl-2pyrrolidone (NMP) was used as the solvent to make a homogeneous mixture. Then, the slurry was pasted onto the aluminum current collector and dried at 110 °C for 10 h in vacuum. Glass fiber membrane and sodium foil were used as the separator and anode, respectively. NaPF6 and NaClO4 were used as sodium salt to prepare eletrolyte, and PC was used as solvant. The concentration of NaPF6/ PC and NaClO4/PC were 0.8 M and 1.0 M, respectively. Coin cell fabrication was conducted in a Mbraun glovebox under argon atomosphere. Charge and discharge profiles were collected with a Land battery test system, and the voltage range was set to 3.0−5.0 V (vs Na+/Na). Cyclic voltammograms (CV) and electrochemical impedance spectra (EIS) were collected on a Parstat 2273 electrochemical workstation (AMETEK). The frequency ranged from 100 mHz to 100 kHz. Fabrication of All-Carbon Full Cell. Hard carbon was mixed with PVDF in a mass ratio of 9:1 by using NMP as solvent. The slurry was pasted onto copper foil and was then dried at 110 °C for 10 h in vacuum. The coin cell fabrication was the same as for the graphite/Na half-cell, except for using preactivated hard carbon as the anode material. The capacity ratio between graphite and hard carbon was 1: (1.2−1.4). The charge and discharge voltage range was 4.8−1.5 V.
Figure 1. Schematic illustration of graphite/Na dual ion battery when charging.
electrochemical testing, the specific discharge capacity was 72 mAh·g−1, and the average discharge voltage can reach 4.52 V at 0.4 C (1 C = 93 mA·g−1). A stable reversible intercalation reaction guarantees the high capacity retention of 92.4% after 200 cycles at 2 C. In-situ Raman and in situ X-ray diffraction (XRD) characterizations demonstrated the changes in the C− C bonds and the phase conversion. For anode materials, hard carbon and other carbon nanomaterials have shown their potential in high performance sodium storage devices.20,21 Thus, all-carbon dual ion batteries including graphite and hard carbon were fabricated and showed an ultrahigh discharge
Figure 2. (a) X-ray diffraction pattern and (b) scanning electronic microscopy image of graphite. B
DOI: 10.1021/acsami.8b11824 ACS Appl. Mater. Interfaces XXXX, XXX, XXX−XXX
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ACS Applied Materials & Interfaces
Figure 3. Electrochemical performances of graphite/Na dual ion batteries.(a) Charge profiles with different electrolytes at 1C, (b) galvanostatic profiles at different current densities, (c) cycling performance, and (d) CV curve with marked pseudocapacitance contribution. CE: Coulombic efficiency.
beneficial for the cycling and rate properties.23−26 Then, the capacitance-type contribution was calculated using SI Equations S1−S3. It was found that half of the capacity came from fast intercalation process. Electrochemical impedance spectroscopy (EIS) was conducted when the cell was at 4.5 V (state of discharge) at the first and second cycles (SI Figure S2). The results demonstrate that, after the initial cycle activation, the charge transfer resistance (Rct) decreases and the slope of the linear part in the low frequency region is close to 90°, which means that the reaction consists of not only the redox reaction, but also a supercapacitance contribution. This is in accordance with the CV analysis. During the intercalation process, there exists a stage evolution mechanism and the products are named as stage-n graphite intercalation compounds (GICs), where n equals the number of graphite layers between two adjacent intercalate planes (Figure 4a). The in situ Raman characterization was conducted to measure the effects of PF6− on the bounded layers and to find the n value of the final charge product as shown in Figure 4b. Hexagonal graphite consists of a unique layered structure, and the Raman-active vibration mode E2g corresponds to the peak at around 1580 cm−1.27 The E2g vibration mode is derived from the strong C−C stretch vibration called G band, which indicates the degree of graphitization. During the charging process, with the continuous intercalation, the G band peak is split, and a new shoulder peak appears at ∼1602 cm−1 (E2g )́ , indicating that the intercalated PF6− ions have changed the chemical environment of the adjacent graphite layers.28 As the intensity of E2g peak drops, the E2g ́ peak forms increasing intensity. In the fully charged state, however, the E2g peak still exists, but the intensity is lower than that of E2g ,́ which means that the final charge product is not a stage-1 GIC. That is also the reason
3. RESULTS AND DISCUSSION The graphite powders show typical XRD diffraction peaks, as shown in Figure 2a. The (002) peak appears at 26.4°, and the corresponding d-spacing is 0.335 nm. The average particle size of the graphite powders is about 10 μm from the SEM image in Figure 2b. Figure 3a shows the comparison of charge profiles of graphite/Na cells using 0.8 M NaPF6/PC and 1 M NaClO4/ PC as electrolytes. Results show that it is more stable to use NaPF6/PC electrolyte and the PF6− can be intercalated into the graphite interlayers.22 The coin cell using 1 M NaClO4/PC as electrolyte, however, come across side reaction near 5V (vs Na+/Na), which hinders its use in DIBs.Then, further electrochemical investigations on graphite/Na cells using NaPF6/PC as electrolyte were conducted, and the results are shown in Figure 3b−d. Figure 3b displays the charge and discharge plots at 0.4, 1, 2, 3, 5, and 6 C, and the specific discharge capacities are 72, 58, 57, 55, 50, and 46 mAh·g−1, respectively. This excellent rate capability is attributed to the good electronic conductivity of graphite. The specific power density and specific energy density can reach 2550 W·kg−1 and 325 Wh·kg−1, respectively. The average discharge voltage is 4.52 V at 0.4 C and the small over potential of 0.14 V (0.4 C) also makes it very competitive in practical use. The cycling performance was also tested and is shown in Figure 3c. The capacity retention at 1 and 2 C is 92.5% and 92.4%, respectively. The initial Coulombic efficiency (CE) of the cell cycled at 1 C is 78.3%. After few cycles’ activation, the CE is close to 100%. The cyclic voltammetry (CV) curves at different sweep rates are summarized in Supporting Information (SI) Figure S1 and Figure 3d. According to previous reports, pseudocapacitance has always been found in layered structure materials and nanostructures during cycling, and is C
DOI: 10.1021/acsami.8b11824 ACS Appl. Mater. Interfaces XXXX, XXX, XXX−XXX
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ACS Applied Materials & Interfaces
From the XRD data, only one phase at a time is discovered, except for the marked region in Figure 4c. At very close to 5 V, a platform corresponding to the transformation between stage4 and stage-5 is found, which means that the final charge products are a mixture of two stage GICs. During the discharging process, there is a reverse phase transformation. Finally, the GICs are transformed to graphite, and the typical peak of the (002) crystal planes reappears, indicating the good reversibility of the graphite/Na cell even at such high working voltage. The electrochemical performances of all-carbon full cell based on graphite cathode and hard carbon anode using NaPF6/PC electrolyte are summarized in Figure 5. SI Figure S4 shows the typical charge and discharge curves of the hard carbon half-cell. Both the charge and the discharge platforms are in the low voltage region, which makes it a good choice for fabricating high voltage full cells. The capacity of the hard carbon half-cell is about 200 mAh·g−1 at 40 mA·g−1. From Figure 5, the average charge and discharge voltage is 4.55 and 4.3 V at 40 mA·g−1, respectively. The specific energy density is 252 Wh·kg−1 based on the cathode materials, and the energy density of a real battery device can be estimated to reach 63 Wh·kg−1. The high output voltage contributes to the high energy density and makes it very competitive for renewable energy storage.
Figure 4. Electrochemical reaction mechanism of graphite/Na dual ion battery. (a) Schematic illustration of stage-n GICs, (b) in situ Raman data, with corresponding (c) charge−discharge profile and (d) in situ XRD characterization.
why the capacity of a graphite/Na cell is ∼70 mAh·g−1. Then, during the discharge process, the E2g ́ peak gradually weakens and finally disappears, indicating the reversible nature of the electrochemical reaction. In-situ Raman spectroscopy can prove the intercalation of PF6− into the graphite layers and the change in the C−C bonds, but in order to know the details of the PF6 − stable sites in the GICs, in situ XRD characterization was applied to the graphite/Na cell. As expected, the in situ XRD patterns obviously exhibit the stage conversion and changes in the interlayer distance during cycling, as shown in Figure 4c and d. During the charging process, the main (002) peak of graphite gradually moves left, and new peaks at around 20° and 30° appear. According to Bragg’s law: d(00n) = Ic /l
(1)
d = λ /(2sin θ )
(2)
l = 1/((sin θ(00(n + 1))/sin θ00n) − 1)
(3)
ds = Ic − 0.335 × (n − 1)
(4)
4. CONCLUSION The above results indicate the potential of graphite to be a high voltage cathode material for dual ion batteries, and the fabricated full cell coupled with hard carbon also demonstrates its advantages in high output voltage. By optimizing the electrolyte, the NaPF6/PC electrolyte has proved to be the best electrolyte for this battery system. The in situ characterization proves the intercalation process and a good reversibility for graphite/Na dual ion batteries. Graphite can also adopt Na+ as anode materials, but during the reaction the Na always couples with the electrolyte molecule and cointercalate into the carbon matrix, which will damage the graphite structure and shorten the cycling life.11,29,30 The PF6− anion group intercalation, however, only induces small lattice changes of the GICs compared to sodium indicating the good cycling behavior. The only issue is the decomposition of electrolyte, but it is likely to be solved by further investigation on the electrolyte optimization. In addition, graphite is far more outstanding than any other organic compounds which also possess the anion
where d is the d-spacing value, Ic is the identity period along the c-axis, θ is the measured Bragg angle, and ds is the d-spacing of the expanded intercalate layers. The Ic, n, and ds for stage 4− 7 can be calculated, and the results are summarized in SI Figure S3. The different stage-n GICs have been indexed in Figure 4c. At the beginning of the charging process, the stage changes very rapidly, and the indexed n value is higher than 8.
Figure 5. (a) The charge and discharge curves and (b) cycling performances of Graphite/hard carbon dual ion battery at 40 mA·g−1 and 100 mA· g−1. D
DOI: 10.1021/acsami.8b11824 ACS Appl. Mater. Interfaces XXXX, XXX, XXX−XXX
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ACS Applied Materials & Interfaces
(4) Fang, Y.; Xiao, L.; Ai, X.; Cao, Y.; Yang, H. Hierarchical carbon framework wrapped Na3V2(PO4)3 as a superior high-rate and extended lifespan cathode for sodium-ion batteries. Adv. Mater. 2015, 27, 5895−5900. (5) Jian, Z.; Han, W. Z.; Lu, X.; Yang, H. X.; Hu, Y. S.; Zhou, J.; Zhou, Z. B.; Li, J. Q.; Chen, W.; Chen, D. F.; Chen, L. Q. Superior Electrochemical Performance and Storage Mechanism of Na3V2(PO4)3 Cathode for Room-Temperature Sodium-Ion Batteries. Adv. Energy Mater. 2013, 3, 156−160. (6) Li, Q.; Qiao, Y.; Guo, S.; Jiang, K.; Li, Q.; Wu, J.; Zhou, H. Both Cationic and Anionic Co-(de)intercalation into a Metal-Oxide Material. Joule 2018, 2, 1134−1145. (7) Zhang, X.; Tang, Y.; Zhang, F.; Lee, C.-S. A Novel AluminumGraphite Dual-Ion Battery. Adv. Energy Mater. 2016, 6, 1502588. (8) Read, J. A.; Cresce, A. V.; Ervin, M. H.; Xu, K. Dual-Graphite Chemistry Enabled by a High Voltage Electrolyte. Energy Environ. Sci. 2014, 7, 617−620. (9) Jiang, C.; Fang, Y.; Lang, J.; Tang, Y. Integrated Configuration Design for Ultrafast Rechargeable Dual-Ion Battery. Adv. Energy Mater. 2017, 7, 1700913. (10) Chan, C. Y.; Lee, P.-K.; Xu, Z.; Yu, D. Y. W. Designing HighPower Graphite-Based Dual-Ion Batteries. Electrochim. Acta 2018, 263, 34−39. (11) Jache, B.; Adelhelm, P. Use of Graphite as a Highly Reversible Electrode with Superior Cycle Life for Sodium-Ion Batteries by Making Use of Co-Intercalation Phenomena. Angew. Chem., Int. Ed. 2014, 53, 10169−10173. (12) Lin, M. C.; Gong, M.; Lu, B.; Wu, Y.; Wang, D. Y.; Guan, M.; Angell, M.; Chen, C.; Yang, J.; Hwang, B. J.; Dai, H. An Ultrafast Rechargeable Aluminium-Ion Battery. Nature 2015, 520, 325−8. (13) Seel, J. A.; Dahn, J. R. Electrochemical Intercalation of PF6 into Graphite. J. Electrochem. Soc. 2000, 147, 892−898. (14) Noel, M.; Santhanam, R. Electrochemistry of Graphite Intercalation Compounds. J. Power Sources 1998, 72, 53−65. (15) Qin, P.; Wang, M.; Li, N.; Zhu, H.; Ding, X.; Tang, Y. BubbleSheet-Like Interface Design with an Ultrastable Solid Electrolyte Layer for High-Performance Dual-Ion Batteries. Adv. Mater. 2017, 29, 1606805. (16) Zhu, H.; Zhang, F.; Li, J.; Tang, Y. Penne-Like MoS2/Carbon Nanocomposite as Anode for Sodium-Ion-Based Dual-Ion Battery. Small 2018, 14, 1703951. (17) Sheng, M.; Zhang, F.; Ji, B.; Tong, X.; Tang, Y. A Novel TinGraphite Dual-Ion Battery Based on Sodium-Ion Electrolyte with High Energy Density. Adv. Energy Mater. 2017, 7, 1601963. (18) Fan, L.; Liu, Q.; Chen, S.; Xu, Z.; Lu, B. Soft Carbon as Anode for High-Performance Sodium-Based Dual Ion Full Battery. Adv. Energy Mater. 2017, 7, 1602778. (19) Ma, R.; Fan, L.; Chen, S.; Wei, Z.; Yang, Y.; Yang, H.; Qin, Y.; Lu, B. Offset Initial Sodium Loss To Improve Coulombic Efficiency and Stability of Sodium Dual-Ion Batteries. ACS Appl. Mater. Interfaces 2018, 10, 15751−15759. (20) Hou, H.; Banks, C. E.; Jing, M.; Zhang, Y.; Ji, X. Carbon Quantum Dots and Their Derivative 3D Porous Carbon Frameworks for Sodium-Ion Batteries with Ultralong Cycle Life. Adv. Mater. 2015, 27, 7861−7866. (21) Hou, H.; Shao, L.; Zhang, Y.; Zou, G.; Chen, J.; Ji, X. LargeArea Carbon Nanosheets Doped with Phosphorus: A High-Performance Anode Material for Sodium-Ion Batteries. Advanced Science 2017, 4, 1600243. (22) Wang, H.; Yoshio, M. Suppression of PF6− Intercalation into Graphite by Small Amounts of Ethylene Carbonate in Activated Carbon/Graphite Capacitors. Chem. Commun. 2010, 46, 1544−1546. (23) Muller, G. A.; Cook, J. B.; Kim, H.-S.; Tolbert, S. H.; Dunn, B. High performance pseudocapacitor based on 2D layered metal chalcogenide nanocrystals. Nano Lett. 2015, 15, 1911−1917. (24) Zhang, K.; Park, M.; Zhou, L.; Lee, G.-H.; Shin, J.; Hu, Z.; Chou, S.-L.; Chen, J.; Kang, Y.-M. Cobalt-Doped FeS2 Nanospheres with Complete Solid Solubility as a High-Performance Anode
intercalation mechanism, in terms of conductivity, working voltage, and raw material cost.31−33 In conclusion, graphite that used as a cathode material for dual ion batteries has demonstrated good cycling stability and high power density. The proper selection of NaPF6/PC electrolyte makes the battery function good and safe. The pseudocapacitance also facilitates ion absorption, leading to high rate capability. The in situ Raman and in situ XRD characterizations demonstrate the phase changes from graphite to a mixture of stage-4 GICs and stage-5 GICs at 5.0 V, which also can be reversed in the fully discharged state. The allcarbon dual ion battery shows ultrahigh voltage, which is suitable for the demands of electric and hybrid electric vehicles. Thus, we hope that this research can shed light on graphite as a high voltage cathode material in dual ion batteries for future investigations.
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ASSOCIATED CONTENT
* Supporting Information S
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsami.8b11824.
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Pseudocapacitance contribution. CVs at different sweep rates and EIS data of graphite/Na cell. The values of d(00n), ds, and Ic for stage-n GICs. Charge and discharge curves of hard carbon/Na cell (PDF)
AUTHOR INFORMATION
Corresponding Authors
*(Z.T.) E-mail:
[email protected]. *(L.M.) E-mail:
[email protected]. *(S.-L.C.) E-mail:
[email protected]. ORCID
Zhe Hu: 0000-0001-7652-6939 Liqiang Mai: 0000-0003-4259-7725 Shu-Lei Chou: 0000-0003-1155-6082 Jun Chen: 0000-0001-8604-9689 Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS The research is supported by Australian Research Council through a Linkage Project (LP120200432), the Commonwealth of Australia through the Automotive Australia 2020 Cooperative Research Centre (Auto CRC) and the National key R&D Program (2016YFB0901502) NFSC (51771094). K. Zhang would like to thank the Korea Research Fellowship Program of the NRF, which was funded by the Ministry of Science and ICT; the number for this grant is 2016H1D3A1906790. We thank Dr. Tania Silver for critical reading of the manuscript.
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REFERENCES
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DOI: 10.1021/acsami.8b11824 ACS Appl. Mater. Interfaces XXXX, XXX, XXX−XXX
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DOI: 10.1021/acsami.8b11824 ACS Appl. Mater. Interfaces XXXX, XXX, XXX−XXX
