Graphene Regulated Ceramic Electrolyte for Solid-State Sodium Metal

Subscriber access provided by UNIV OF BARCELONA

Energy, Environmental, and Catalysis Applications

Graphene Regulated Ceramic Electrolyte for Solid-State Sodium Metal Battery with Superior Electrochemical Stability Edward Matios, Huan Wang, Chuanlong Wang, Xiaofei Hu, Xuan Lu, Jianmin Luo, and Weiyang Li ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.8b19519 • Publication Date (Web): 10 Jan 2019 Downloaded from http://pubs.acs.org on January 12, 2019

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 24 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Applied Materials & Interfaces

Graphene Regulated Ceramic Electrolyte for Solid-State Sodium Metal Battery with Superior Electrochemical Stability Edward Matios,† Huan Wang,† Chuanlong Wang,† Xiaofei Hu,† Xuan Lu,† Jianmin Luo,† Weiyang Li†,*

†Thayer

School of Engineering, Dartmouth College, 14 Engineering Drive, Hanover, New

Hampshire 03755, USA *To

whom correspondence may be address. E-mail: [email protected]

1 ACS Paragon Plus Environment

ACS Applied Materials & Interfaces 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Abstract

Employing solid ceramic electrolyte in sodium (Na) metal batteries enables safe and costeffective energy storage solution towards the advent of sustainable energy. Nevertheless, the development of solid-state Na batteries is hindered by the large interfacial charge transfer resistance between electrodes and solid electrolyte. Here, a novel and scalable design approach is utilized to significantly reduce the interfacial resistance through the direct growth of graphenelike interlayer on Na+ superionic conductor (NASICON) ceramic electrolyte, resulting in a tenfold decrease of interfacial resistance. Benefiting from the graphene regulated NASICON, extremely stable Na plating/stripping cycling performance using solid electrolyte at a current density up to 1 mA/cm2 with a cycling capacity of 1 mAh/cm2 for 500 cycles (1000 hours) is demonstrated for the first time. The surface of Na electrode after 1000 hours of cycling remained smooth because of uniform Na+ flux across graphene-coated-NASICON/Na interface enabled by the abundant graphene defects network for efficient Na+ transport. Solid-state room temperature battery consists of graphene-regulated NASICON electrolyte, Na3V2(PO4)3 cathode and Na anode delivered a reversible initial capacity of 108 mAh/g at 1C current density for 300 cycles with 85% capacity retention, far superior than the battery with pristine NASICON. This work can be a valuable contribution towards a safe and stable solid-state Na metal battery system, and provide insights for solid-state lithium metal batteries as well.

KEYWORDS: Solid ceramic electrolyte, solid-state battery, sodium metal anode, graphene interlayer, stable cycling


Page 2 of 24

Page 3 of 24 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


INTRODUCTION Rechargeable sodium (Na) based battery can be a cost-effective successor of lithium (Li) ion battery owing to the natural abundance of Na resource and high capacity of metallic Na anode.1-5 Conventional Na batteries rely on liquid electrolytes, which offer the benefits of high ionic conductivity (~10−2 S/cm) and excellent wettability with electrode surface. However, liquid electrolytes pose critical safety issue that arises from their flammable organic solvent component and Na dendrite formation upon repeated electrochemical charge/discharge cycles. Solid electrolytes not only can eliminate the abovementioned safety concerns, they can also enhance electrochemical stability, broaden operating temperature range and prolong cycling life.6-11 The two greatest commercialization challenges for solid electrolyte lie in the relatively inferior ionic conductivity (~10−4 S/cm) and large interfacial resistance between electrolyte and electrode. Altering the chemical composition of solid electrolytes via doping with appropriate cations can enhance the intrinsic ionic conductivity by increasing the concentration of charge carriers and tailoring the size of the ionic transport channel.12,13 Meanwhile, various optimization techniques for reducing interfacial resistance have been reported, including maximizing the contact area by nanocomposite electrodes,14,15 surface chemistry modification on solid electrolyte for better wettability with electrode,16-18 and liquid-solid hybrid electrolytes.19-22 Nevertheless, all-solidstate batteries still face stagnant advancements due to the limited effectiveness of the abovementioned approaches. Amongst the known solid electrolytes for Na battery systems, Na+ superionic conductor, also known as NASICON (Na3Zr2Si2PO12) ceramic electrolyte discovered by Goodenough et al. in 1976 remains to be the most promising material because of its high ionic conductivity and excellent electrochemical and thermal stability.23-26 However, the pairing of pristine NASICON with high-capacity metallic Na anode gives rise to large NASICON/Na interfacial resistance and poor interface wettability that result in non-uniform Na+ flux across the interface.27-29 Specifically, Na tends to plate preferentially along the grain boundaries of NASICON where the Na+ flux is locally intensified, leading to detrimental dendrite-like nucleation on Na anode over repeated charge/discharge cycles as schematically illustrated in Figure 1a.11,16 Theoretically, a homogeneous and stable interlayer with superior Na anode compatitability and ion conductivity can facilitate uniform Na+ flux across the interface, therefore effectively decrease the interfacial resistance and suppress unregulated dendrite-like Na formation during cycling.29,30 Past research 3 ACS Paragon Plus Environment


efforts to implement such an interlayer on ceramic electrolyte include the employment of polymer layer,16 applying molten metal on ceramic electrolyte,18 and coating a layer of metal oxide using relatively expensive method of atomic layer deposition.31 This motivated us to solve the challenges of large interfacial resistance and non-uniform plated Na for solid-state Na metal batteries through a facile and scalable approach. Graphene, with its unique properties of chemical inertness,32 mechanical flexibility33 and structural rigidness,34 has attracted great interests in various energy storage applications. Our recent study demonstrated the use of ultrathin graphene film coating on Na metal as a stable artificial solid electrolyte interphase (SEI) layer in conventional liquid electrolyte to suppress the dendrite growth, in which the graphene defects network act as an efficient Na+ transport pathway.35 Therefore, graphene can be a promising interlayer for solid-state Na metal batteries to improve Na+ conductivity between the ceramic electrolyte and Na metal. The abundantly distributed defects network on graphene-like interlayer can enable uniform Na+ flux across the electrode/electrolyte interface, circumventing the preferential Na metal plating along the grain boundaries of NASICON and therefore suppress dendrite growth. However, direct growth of graphene on ceramic electrolyte has not yet been reported, largely due to the non-catalytic nature of ceramic electrolyte.36 Meanwhile, achieving stable Na stripping/plating cycling performance using a ceramic electrolyte is rather challenging at a current density beyond 0.25 mA/cm2, and no successful effort has been reported. In this study, we report the direct growth of ultrathin graphene-like layer on NASICON ceramic electrolyte, hereafter referred as G-NASICON, to significantly decrease the interfacial resistance, improve Na plating/stripping cycling stability and enable uniform Na plating. Figure 1b depicts the process of graphene-like layer grown on the NASICON pellet as a stable interlayer to minimize the unregulated dendrite-like Na formation on Na anode after repeated stripping/plating cycles. Graphene growth on NASICON was carried out in a chemical vapor deposition (CVD) system (see methods for detail). CVD growth of graphene materials towards energy-related applications is highly attractive due to the outstanding properties of graphene materials, as well as the scalability of CVD method. CVD method is considered scalable and facile because the equipment involved (tube furnace, etc) can be scaled up to industrial standard scale, and the CVD procedure is a one-step process that grows 2D materials directly on substrates in relatively short time. 37-39 The formation mechanism of graphene-like layer on the 4 ACS Paragon Plus Environment

Page 4 of 24

Page 5 of 24 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


ceramic substrate is based on the carbothermic reduction occurring at ceramic surface to initiate nucleation and growth.40-42 CVD growth time was controlled accordingly to obtain the optimized thickness that yields the lowest interfacial resistance, as thicker graphene-like layer that covers the entire surface of NASICON pellet can result in battery short circuit due to the electronically conductive nature of graphene material. The photos of the as-prepared NASICON and GNASICON are presented in Figure S1. Optimized graphene-like layer on NASICON effectively decreases the NASICON/Na interfacial resistance more than ten-fold, from 524 Ω cm2 to 46 Ω cm2. The Na/G-NASICON/Na symmetric cells delivered remarkably stable Na stripping/plating cycling behavior at a current density of 1 mA/cm2 with 1 mAh/cm2 capacity over 1000 hours that, to the best of our knowledge, represents the best performance in solid-state Na symmetric cell systems. Furthermore, room temperature solid-state Na metal batteries with stable cycling performance and high Coulombic efficiency are demonstrated. Hence, our works provide new insight to realize next-generation high energy density and safe solid-state batteries. RESULTS AND DISCUSSION X-ray diffraction (XRD) was used to examine the crystalline structure of NASICON with and without graphene-like layer coating, as shown in Figure 2a. The XRD spectra indicate that the crystal structure of NASICON remains unchanged after the growth of graphene-like layer on its surface. The XRD spectra of both NASICON and G-NASICON exhibit the characteristic phase peaks of the NASICON crystal structure, which is in good agreement with prior studies.12,13,16 Note that because the NASICON ceramic particles were synthesized by highenergy ball milling method in ZrO2 container, traceable ZrO2 phase peaks at around 28 degree and 31.5 degree can be observed in the XRD spectra, which is consistent with the previous study that also utilized high-energy ball milling using ZrO2 container for NASICON synthesis.12 As shown in Figure S2, the scanning electron microscope (SEM) image of the as-synthesized NASICON exhibits the surface morphology of aggregated ceramic particles. The revealed surface morphology of the pristine NASICON synthesized by high-energy ball milling method here is similar to that of previously reported NASICON surface morphology prepared by the same method.12 The higher magnification SEM images of G-NASICON and NASICON in Figure S3-4 both show the densely packed ceramic grains structure and boundaries, which is



critical for sufficient ionic conductivity.23 Also, the energy-dispersive X-ray spectroscopy (EDS) spectrum of NASICON shows the expected weight percent of each element (Figure S5). The Raman spectrum of G-NASICON reveals the three characteristic graphene peaks of D band (defects) at around 1360 cm-1, G band (sp2 hybridized carbon) at around 1580 cm-1 and a relatively weak and broad 2D band (second-order vibrational) at around 2700 cm-1 (Figure 2b). The Raman spectrum exhibits the same characteristic peaks and intensities as the previous reports on graphene-like layer grown on insulating substrate.36,43 Our growth temperature was optimized to be at 750°C on non-catalytic ceramic NASICON, while conventional graphene growth temperature on catalytic metal substrate (e.g. copper) is above 850 °C. Past studies concluded that lowering the graphene growth temperature can introduce more point and line defects that serve as fast Na+ diffusion pathway.44,45 Thus, the lower growth temperature we used here promoted the formation of abundant defects in the as-grown graphene-like coating, leading to relatively intense D peak and weak 2D peak in the Raman spectrum of G-NASICON. In our case, the abundant defects in the graphene-like layer are highly advantageous for uniform Na+ flux across the interface, and therefore prevent preferential Na plating along the grain boundaries of NASICON ceramic particles and effectively suppress Na dendrite growth.35 The thickness of graphene-like layer coating on NASICON was estimated by depth profiling analysis via a combination of Argon (Ar) ion sputtering and X-ray photoelectron spectroscopy (XPS) measurement.46 The depth profiling was operated to achieve the calibrated sputtering rate of 1 nm per min in silicon dioxide (SiO2), and the XPS measurement was set to take place every 15 seconds during the sputtering process. The carbon (C) intensity measured by XPS corresponds to the presence of graphene-like layer on NASICON and was normalized with respect to zirconium (Zr) intensity. Hence, the relative C intensity decreased as Ar ion continuously sputtered away the graphene-like layer on NASICON. The thickness of the graphene-like layer coating is estimated to be around 4 nm, which is determined by the sputtering time at which the relatively intensity of C drops to < 1%, as shown in Figure 2c. For reference, the other elemental intensities from XPS depth profiling, namely Na, Si, P and O are presented in Figure S6 and they all exhibit a trend similar to that of Zr. The CVD procedure was precisely controlled by keeping the precursor gas flow rate and the furnace temperature constant (see method for detail), and the growth rate of the graphene-like interlayer is linearly proportional to the growth time.39 Therefore, based on the XPS depth profiling analysis that 6 ACS Paragon Plus Environment

Page 6 of 24

Page 7 of 24 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


reveals 4-nm-thick graphene-like interlayer over 30 mins of CVD growth time, the growth rate of the graphene-like interlayer can be estimated to be around 8 nm per hour. The XPS spectra of G-NASICON reveal an obvious shift to lower for Zr, Si, and phosphorus (P) elements (Figure 2d-f). The Zr 3d5/2 peak at 184.82 eV and 3d3/2 peak at 182.18 eV in NASICON shifted, respectively, to 183.78 eV and 181.15 eV in G-NASICON. The Si 2p peaks shifted from 102.31 eV in NASICON to 101.24 eV in G-NASICON. Similarly, the P 2p peak at 133.16 eV in NASICON shifted to 132.08 eV in G-NASICON. Meanwhile, there is no obvious O 2p binding energy shift in G-NASICON as compared to pristine NASICON (Figure S7). The XPS peak shifts of Zr, Si, and P in G-NASICON imply that NASICON surface was slightly reduced by the hydrogen-contained carrier gas during CVD process. Previous study by Goodenough’s group observed this similar phenomenon that slightly electrochemical reduced NASICON improves its interfacial electrochemical stability.16 The transmission electron microscope (TEM) images of G-NASICON are displayed in Figure 2g-h. Here, the graphene-like interlayer uniformly coating on NASICON can be visually observed in Figure 2g, and the boundary between NASICON and graphene-like interlayer can be easily identified. Moreover, the lattice spacing of NASICON ceramic particle and graphene-like interlayer thickness of around 3-4 nm can be clearly observed in Figure 2h. Meanwhile, the TEM imaging of pristine NASICON ceramic particle is presented in Figure S8 for comparison. Without the presence of graphene-like interlayer, the edge of NASICON ceramic particle can be clearly defined under TEM imaging. The interfacial resistances of as-prepared NASICON and G-NASICON were quantified by AC impedance spectroscopy. To maximize data consistency and identify the contribution of graphene-like layer towards interfacial resistance, AC impedance spectroscopy measurements were carried out with the cells assembled from the same batch of sintered NASICON pellets. Figure 3a presents the Nyquist plot of Au/G-NASICON/Au, Na/G-NASICON/Na and Na/NASICON/Na symmetric cells, and Figure 3b summarizes the corresponding interfacial resistances. For Au/G-NASICON/Au symmetric cell that utilized Au as ion-blocking electrodes, the total electrolyte area specific resistance (ASR) of bulk plus grain boundary (ASRb+gb) is 164 Ω cm2.31,47 Similarly, the total electrolyte ASRb+gb of NASICON is 167 Ω cm2 (Figure S9). Thus, the total ionic conductivity of the as-prepared NASICON and G-NASICON are both around 0.6 mS/cm, which is in good agreement with previous studies.13,16,25 The total cell ASRb+gb/interface of 7 ACS Paragon Plus Environment


NASICON interpreted from the low-frequency x-intercept of Na symmetric cell is around 1215 Ω cm2. ASRb+gb/interface is contributed by resistances from bulk and grain boundary of NASICON, plus the two NASICON/Na interfaces.31,47 Therefore, the ASRinterface on either side of the NASICON/Na interface is calculated by subtracting total electrolyte resistance ASRb+gb from total cell resistance ASRb+gb/interface, then divided by two. Hence, the effective NASICON/Na ASRinterface is 524 Ω cm2. Similarly, the total cell ASRb+gb/interface for G-NASICON is determined to be 257 Ω cm2, and thus the ASRinterface of G-NASICON/Na interface is 46 Ω cm2. Therefore, the AC impedance spectroscopy data clearly indicate that the graphene-like layer grown on NASICON decreases ASRinterface substantially from 524 to 46 Ω cm2, and this greatly facilitates Na+ conduction across the G-NASICON/Na interface. The Na plating/stripping cycling stability of the as-prepared NASICON and GNASICON was systematically investigated by Na symmetric cells. Figure 4a compares the voltage profiles of Na/G-NASICON/Na and Na/NASICON/Na symmetric cells cycling at a current density of 0.5 mA/cm2 with a capacity of 1 mAh/cm2 over 1000 hours. Na/GNASICON/Na symmetric cell delivered an extremely stable Na plating/stripping behavior with an average overpotential of around 0.12 V. In comparison, the voltage profile of Na/NASICON/Na symmetric cell was very unstable with an average overpotential of around 0.25 V. At an even higher current density of 1 mA/cm2 (Figure 4b), Na/G-NASICON/Na symmetric cell still maintained its consistently stable cycling behavior with an overpotential of around 0.25 V for 1000 hours, whereas Na/NASICON/Na symmetric cell exhibited a large overpotential of around 0.5 V and noticeably worse voltage hysteresis. The comparison can be more clearly observed in the enlarged voltage profile of the initial and final ten cycles respectively, as shown in Figure 4c-d. To the best of our knowledge, the performance of Na/GNASICON/Na demonstrates the highest current density and lowest voltage overpotential in previously reported all-solid-state NASICON symmetric cell systems.12,16 The cycling performance of Na/NASICON/Na symmetric cells were electrochemically unstable with severe voltage hysteresis, while Na/G-NASICON/Na symmetric cells showcased extremely stable voltage profiles without any fluctuation. Furthermore, voltage profiles of Na/G-NASICON/Na and Na/NASICON/Na symmetric cells cycling at a current density of 2 mA/cm2 with a capacity of 2 mAh/cm2 (Figure S10) demonstrate the superiority of G-NASICON in enabling extremely stable voltage profiles for Na/G-NASICON/Na cell under an even higher current density of 2 8 ACS Paragon Plus Environment

Page 8 of 24

Page 9 of 24 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


mA/cm2, whereas Na/NASICON/Na cell suffers even far more severe voltage hysteresis under the same current density. SEM characterization was carried out to reveal the surface morphology of Na metal electrodes disassembled from Na/NASICON/Na and Na/G-NASICON/Na symmetric cells after cycling at a current density of 1 mA/cm2 and 1 mAh/cm2 capacity for 1000 hours. Non-uniform morphology and cracks can be evidently observed on Na electrode from Na/NASICON/Na symmetry cell (Figure 4e). Non-uniform plated Na can be evidently observed on Na electrode obtained from after-cycled Na/NASICON/Na symmetry cell due to preferential Na plating along NASICON grain boundaries and non-uniform Na+ flux across NASICON/Na interface. On the other hand, the surface morphology of Na metal electrode from Na/G-NASICON/Na symmetry cell (Figure 4f) is significantly smoother, implying uniform Na+ flux across C-NASICON/Na interface during stripping/plating cycling. These phenomena clearly indicate that the graphenelike interlayer between NASICON ceramic pellet and Na metal effectively improves the interfacial electrochemical stability, facilitates uniform Na+ flux across interface and minimizes rough dendrite-like Na formation after many stripping/plating cycles. The interfacial resistances of Na/G-NASICON/Na and Na/NASICON/Na symmetric cells after 10 cycles and 100 cycles at a current density of 1 mA/cm2 and 1 mAh/cm2 capacity are presented in Figure S11-12, respectively. After only 10 cycles, the interfacial resistance of Na/NASICON/Na increased more than three folds from 1200 Ω cm2 to 3700 Ω cm2, while interfacial resistance of Na/GNASICON/Na increased from 260 Ω cm2 to 350 Ω cm2. The interfacial resistance of Na/NASICON/Na and Na/G-NASICON/Na after 100 cycles further increased to 4200 Ω cm2 and 390 Ω cm2, respectively. The above results further elucidate the critical role of graphene-like interlayer and its abundantly distributed defects network in facilitating uniform Na+ flux across G-NASICON/Na interface that greatly decreases the interfacial resistance before and during Na plating/stripping cycling. Meanwhile, NASICON/Na interfacial contact is inevitably exacerbated during cycling due to Na dendrite growth arising from the preferential Na plating along pristine NASICON grain boundaries. Moreover, XRD (Figure S13) and XPS (Figure S14-16) analysis on G-NASICON and NASICON after 100 cycles at a current density of 1 mA/cm2 and 1 mAh/cm2 capacity in Na/Na symmetric cells are identical to G-NASICON and NASICON before cycling, reaffirming NASICON is chemically stable and did not undergo phase change upon cycling.



To evaluate the electrochemical performance of G-NASICON as a solid ceramic electrolyte, solid-state batteries were assembled with Na3V2(PO4)3 (NVP) as cathode, metallic Na as anode and G-NASICON as electrolyte. NASICON-structured NVP is considered as a promising high voltage Na cathode with a theoretical specific capacity of around 118 mAh/g.48-50 The XRD spectrum of the as-prepared NVP cathode synthesized by solid-state reaction method is shown in Figure S17, in which all the diffraction peaks agreed well with the simulation derived from the NASICON framework.48-50 Solid ceramic electrolyte studies reported thus far have relied on small amount of liquid electrolyte (LE) or even ionic liquid on the composite cathode side as wetting agent to improve the interfacial contact for solid-state battery operating at room temperature,13, 18, 31 and this challenge requires forthcoming innovative solutions to be resolved. Herein, to improve the interfacial contact between G-NASICON and NVP cathode, a tiny amount (5 µL/cm2) conventional additive-free LE of 1M NaPF6 in ethylene carbonate (EC) and diethyl carbonate (DEC) was added as on the cathode side during coin cell assembly. Figure 5a displays the cycling performance of NVP/LE/G-NASICON/Na solid-state battery at a current rate of 1C at room temperature, with the charge/discharge voltage curves shown in the inset. NVP/LE/G-NASICON/Na battery delivered a reversible initial capacity of 108 mAh/g, and 85% capacity retention (~92 mAh/g) after 300 cycles with nearly 100% Coulombic efficiency. Furthermore, the performance of NVP/LE/G-NASICON/Na cell is more superior to the previous modified NASICON study that utilized the same LE and cell configuration.13 In contrast, the control experiment of NVP/LE/NASICON/Na (Figure S18-19) and NVP/LE/Na (Figure S20-21) that uses Celgard separator with abovementioned LE showcased rapid capacity decay and very unstable voltage profiles under the same condition. One can observe that even without graphene-like interlayer coating on NASICON, NVP/LE/NASICON/Na still delivered better cycling performance than that of NVP/LE/Na due to the outstanding electrochemical stability of NASICON ceramic electrolyte that helps to suppress dendrite growth to some extent, therefore illustrating the advantage of employing a ceramic electrolyte over conventional liquid electrolyte and polymer separator. Unlike pristine NASICON that is subject to Na dendrite formation along its grain boundaries leading to nonuniform Na plating/stripping and rapid capacity loss in NVP/LE/NASICON/Na, G-NAISOCON used in NVP/LE/G-NASICON/Na solid-state battery delivered outstanding cycling stability.


Page 10 of 24

Page 11 of 24 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


This further demonstrates the critical role of graphene-like interlayer between NASICON/Na interface that enables remarkably uniform Na plating/stripping and capacity retention. The rate performance of NVP/LE/G-NASICON/Na is shown in Figure 5b, with average discharge capacities of 113 mAh/g, 108 mAh/g, 103 mAh/g and 96 mAh/g achieved at current densities of 0.5C, 1C, 2C and 5C, respectively. The inset depicts the charge-discharge curves of the initial cycle at different current rates, exhibiting consistent and low voltage overpotential. An average discharge capacity of 109 mAh/g was retained as the current density returned to 0.5C. Moreover, the average Coulombic efficiency throughout the rate performance was above 99.5% at various current rates, hence the solid-state batteries demonstrated efficient Na plating/stripping and stable electrochemical reaction across the Na/G-NASICON interface. Figure 5c shows the electrochemical performance of the NVP/G-NASICON/Na all-solid-state battery cycling with a current rate of 0.1C at 80 °C. A high discharge capacity of 106 mAh/g can be obtained for the initial cycle, with gradual capacity decay caused by the inferior interfacial contact between cathode materials and solid ceramic electrolyte compared to the case with small amount of LE. This performance of NVP/G-NASICON/Na all-solid-state battery is nevertheless superior to NVP/NASICON/Na all-solid-state battery cycling under the same condition (Figure S22) due to the presence of graphene-like interlayer facilitating uniform Na+ across the interfaces. Additionally, Nyquist plots of all-solid-state NVP/G-NASICON/Na and NVP/NASICON/Na cells before cycling as well as after 10 cycles at a current density of 0.1C at 80 °C are presented in Figure S23, with substantial lower interfacial resistance measured in NVP/G-NASICON/Na than that of NVP/NASICON/Na that once again demonstrating the effectiveness of GNASICON in improving interfacial conductivity. CONCLUSIONS In summary, we established a scalable and facile approach to regulate NASICON with direct growth of graphene-like interlayer on its surface, where abundantly distributed defects network on graphene-like interlayer can enable uniform Na+ flux across the electrode/electrolyte interface, preventing the preferential Na metal plating along the grain boundaries of NASICON and therefore suppressing dendrite growth. As a result, G-NASICON managed to effectively reduce the large NASICON/Na interfacial resistance by tenfold from 524 Ω cm2 to 46 Ω cm2. Compared to Na/NASICON/Na symmetric cells, Na/G-NASICON/Na symmetric cells exhibited 11 ACS Paragon Plus Environment


significantly improved Na plating/stripping cycling behavior at a current density up to 1 mA/cm2 with 1 mAh/cm2 capacity for 1000 hours. The G-NASICON effectively decreased the Na plating/stripping voltage potential by half compared to its pristine NASICON counterpart. Furthermore, the surface of Na electrode after 1000 hours of cycling remained smooth because of uniform Na+ flux across G-NASICON/Na interface enabled by the abundant graphene defects network for efficient Na+ transport pathway. Solid-state batteries using G-NASICON electrolyte delivered outstanding cycling performance and rate capability. At 1C current density, NVP/LE/G-NASICON/Na battery delivered a high reversible initial capacity of 108 mAh/g with 85% capacity retention (~92 mAh/g) after 300 cycles at nearly 100% Coulombic efficiency. In contrast, the control experiment of NVP/LE/NASICON/Na showcased inferior performance with rapid capacity decay and very unstable voltage profiles. Our strategy can potentially be extended to other solid-state electrolytes and other 2D material coating for high energy and safe solid-state Na metal as well as Li metal batteries. METHODS NASICON Ceramic Electrolyte Synthesis. Na3Zr2Si2PO12 NASICON solid electrolyte was synthesized through solid-state reaction combined with mechanochemical process. Stoichiometric ratio of ZrO2 (Sigma-Aldrich, ≥ 99.9%), Na2CO3 (Sigma-Aldrich, ≥ 99.5%), SiO2 (Sigma-Aldrich, ≥ 99%) and NH4H2PO4 (Sigma-Aldrich, ≥ 98%) were mixed accordingly for solid-state reaction in a high energy ball mill (SPEX SamplePrep 8000 M Mixer) within zirconium oxide container for 2 hours. To prevent overheating of the sample, ball milling was paused for 15 minutes at the end of every hour. Next, the ball milled NASICON precursor powder was calcinated at 950 °C for 8 hours in open air, and subsequently ball milling again for 2 hours. The grounded powder was then pressed into pellets with 12.7 mm diameter and 0.75 mm thickness under a pressure of 500 MPa, and sintered at 1200 °C for 12 hours. Graphene-Like Layer Growth on NASICON. Growth of graphene-like layer on NASICON was carried out by chemical vapor deposition (CVD) method with acetonitrile (CH3CN, Alfa Aesar, 99%) as the liquid precursor. NASICON pellets were placed inside 1-inchdiameter quartz tube of a tube furnace, where graphene-like interlayer subsequently forms on the entire surface of NASICON pellets including edges. The system was purged by a vacuum pump to reach base pressure of around 1 Pa and subsequently filled with forming gas (95% Ar and 5% 12 ACS Paragon Plus Environment

Page 12 of 24

Page 13 of 24 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


H2) until reaching the atmospheric pressure. The temperature of the system was raised slowly to 750 oC with a continuous flow of forming gas at a flow rate of 200 sccm. Forming gas was rerouted to pass through the acetonitrile liquid precursor reservoir as the system temperature reached the terminal temperature of 750 oC. After 30 minutes of graphene growth, the furnace was naturally cooled down to room temperature. The thickness of graphene-like layer can be adjusted by changing forming gas flow rate or/and growth time. Here, acetonitrile molecules are thermally decomposed into hydrocarbon reactive species that promote the nucleation and growth of graphene-like carbon layers on a ceramic substrate. Na3V2(PO4)3 Cathode Material. Na3V2(PO4)3 cathode was synthesized by a solid-state reaction with a stoichiometric mixture of NaH2PO4 (Sigma-Aldrich, ≥ 98%) and V2O3 (Alfa Aesar, 99.4%) to be ball milled for 2 h and dried in the vacuum oven at 100 °C for 8 hours. Next, the dried Na3V2(PO4)3 powder was sintered at 950 °C for 16 hours within Argon environment. The final compositions of the cathode material are 80 wt% Na3V2(PO4)3 active material, 10 wt% carbon black and 10 wt% PVDF binder. The average mass loading of the Na3V2(PO4)3 active material for battery testing is 1.5 mg/cm2. Material Characterization. The crystal structure of NASICON was analyzed by a Rigaku (Model Number: 007) X-ray diffractometer. Surface morphology of NASICON and after-cycled Na electrodes was characterized by a Thermo Scientific Scios scanning electron microscope. Raman spectra were acquired from a Horiba labRAM HR Evolution Raman spectrometer with 532 nm excitation. X-ray photoelectron spectroscopy (XPS) analysis was conducted on PHI Versaprobe II scanning XPS with monochromatic 1486.7 X-ray source. Depth profiling was carried out by a combination of Ar ion sputtering and XPS measurement at every 15 seconds, in which the Argon ion sputtering to achieve the calibrated sputtering rate of 1 nm per min in SiO2. The depth profiling was operated and the XPS measurement was set to take place every 15 seconds during the sputtering process. Ar ion sputtering was set to be 0.5 kV and 0.5 μA over a 2 x 2 mm area. The thickness of the graphene-like layer was estimated from the calibrated sputtering rate of 1 nm per min in SiO2 and the sputtering time at which the normalized intensity of C decreases to below 1%.43 Electrochemical Measurement. The ionic conductivity test was carried out by an electrochemical workstation (VMP3, Bio-Logic Science Instruments) by sputtering gold film on both sides of the ceramic pellets as ion-blocking electrodes. AC impedance spectroscopy 13 ACS Paragon Plus Environment


measurement was done by Na symmetric cells, in which typical 2032-type coin cells assembled with two identical metallic Na electrodes in Argon-filled glove box (Mbraun). The electrolyte consisted of 1M sodium hexafluorophosphate (NaPF6, Sigma-Aldrich) in ethylene carbonate (EC) and diethyl carbonate (DEC) (1:1 by volume, Sigma-Aldrich) without any additives. Na stripping/plating cycling test was performed on a standard battery tester (CT2001A, Wuhan LAND Electronics Co., Ltd). ASSOCIATED CONTENT Supporting Information. Details about additional characterization and electrochemical performance of batteries made from G-NASICON and as-prepared NASICON electrolytes. AUTHOR INFORMATION Corresponding Author *Email: [email protected] Author Contributions E.M., H.W. and W.L. conceived the idea. E.M. conducted the NASICON synthesis, graphene coating and characterization. E.M. carried out the electrochemical tests. E.M. and W.L. co-wrote the paper. All the authors discussed the results and commented on the manuscript.

Notes The authors declare no competing financial interests.

ACKNOWLEDGMENT The authors greatly acknowledge the support from Young Investigator Program funded by US Air Force Office of Scientific Research under award FA9550-17-1-0184, and support from the start-up funds at Thayer School of Engineering, Dartmouth College. The authors also would like to thank Dr. Min Li for his generous help on the XPS measurement.


Page 14 of 24

Page 15 of 24 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


REFERENCES (1)

Yang, Z.; Zhang, J.; Kintner-meyer, M. C. W.; Lu, X.; Choi, D.; Lemmon, J. P.; Liu, J. Electrochemical Energy Storage for Green Grid. Chem. Rev. 2011, 111, 3577–3613.

(2)

Dunn, B.; Kamath, H.; Tarascon, J.-M. Electrical Energy Storage for the Grid: A Battery of Choices. Science 2011, 334, 928–935.

(3)

Larcher, D.; Tarascon, J.-M. Towards Greener and More Sustainable Batteries for Electrical Energy Storage. Nat. Chem. 2014, 7, 19–29.

(4)

Grey, C. P.; Tarascon, J. M. Sustainability and in Situ Monitoring in Battery Development. Nat. Publ. Gr. 2017, 16, 45–56.

(5)

Chu, S.; Cui, Y.; Liu, N. The Path towards Sustainable Energy. Nat. Mater. 2016, 16, 16– 22.

(6)

Manthiram, A.; Yu, X.; Wang, S. Lithium Battery Chemistries Enabled by Solid-State Electrolytes. Nat. Rev. Mater. 2017, 2, 16103.

(7)

Kerman, K.; Luntz, A.; Viswanathan, V.; Chiang, Y.-M.; Chen, Z. Review—Practical Challenges Hindering the Development of Solid State Li Ion Batteries. J. Electrochem. Soc. 2017, 164, 1731–1744.

(8)

Sun, C.; Liu, J.; Gong, Y.; Wilkinson, D. P.; Zhang, J. Recent Advances in All-Solid-State Rechargeable Lithium Batteries. Nano Energy 2017, 33, 363–386.

(9)

Kim, J.; Yoon, K.; Park, I.; Kang, K. Progress in the Development of Sodium-Ion Solid Electrolytes. Small Methods 2017, 1700219, 1–12.

(10)

Bachman, J. C.; Muy, S.; Grimaud, A.; Chang, H. H.; Pour, N.; Lux, S. F.; Paschos, O.; Maglia, F.; Lupart, S.; Lamp, P.; Giordano, L.; Yang, S. H. Inorganic Solid-State Electrolytes for Lithium Batteries: Mechanisms and Properties Governing Ion Conduction. Chem. Rev. 2016, 116, 140–162.

(11)

Goodenough, J. B.; Singh, P. Review—Solid Electrolytes in Rechargeable Electrochemical Cells. J. Electrochem. Soc. 2015, 162, 2387–2392.

(12)

Song, S.; Duong, H. M.; Korsunsky, A. M.; Hu, N.; Lu, L. A Na+ Superionic Conductor for Room-Temperature Sodium Batteries. Sci. Rep. 2016, 6, 32330.

(13)

Zhang, Z.; Zhang, Q.; Shi, J.; Chu, Y. S.; Yu, X.; Xu, K.; Ge, M.; Yan, H.; Li, W.; Gu, L.; Hu, Y.S.; Li, H.; Yang, X.Q.; Chen, L.; Huang, X. A Self-Forming Composite Electrolyte for Solid-State Sodium Battery with Ultralong Cycle Life. Adv. Energy Mater. 2017, 7, 1– 11.



(14)

Seh, Z. W.; Sun, Y.; Zhang, Q.; Cui, Y. Designing High-Energy Lithium-Sulfur Batteries. Chem. Soc. Rev. 2016, 45, 5605-5634.

(15)

Sun, Y.; Lee, H. W.; Seh, Z. W.; Zheng, G.; Sun, J.; Li, Y.; Cui, Y. Lithium Sulfide/Metal Nanocomposite as a High-Capacity Cathode Prelithiation Material. Adv. Enery Mater. 2016, 6, 1600154.

(16)

Zhou, W.; Li, Y.; Xin, S.; Goodenough, J. B. Rechargeable Sodium All-Solid-State Battery. ACS Cent. Sci. 2017, 3, 52–57.

(17)

Tian, H.; Seh, Z. W.; Yan, K.; Fu, Z.; Tang, P.; Lu, Y.; Zhang, R.; Legut, D.; Cui, Y.; Zhang, Q. Theoretical Investigation of 2D Layered Materials as Protective Films for Lithium and Sodium Metal Anodes. Adv. Mater. 2017, 7, 1602528.

(18)

Luo, W.; Gong, Y.; Zhu, Y.; Li, Y.; Yao, Y.; Zhang, Y.; Fu, K. K.; Pastel, G.; Lin, C. F.; Mo, Y.; Wachsman, E.; Hu, L. Reducing Interfacial Resistance between Garnet-Structured Solid-State Electrolyte and Li-Metal Anode by a Germanium Layer. Adv. Mater. 2017, 29, 1–7.

(19)

Li, Y.; Xu, B.; Xu, H.; Duan, H.; Lü, X.; Xin, S.; Zhou, W.; Xue, L.; Fu, G.; Manthiram, A.; Goodenough, J.B. Hybrid Polymer/Garnet Electrolyte with a Small Interfacial Resistance for Lithium-Ion Batteries. Angew. Chemie - Int. Ed. 2017, 56, 753–756.

(20)

Yu, X.; Bi, Z.; Zhao, F.; Manthiram, A. Polysulfide-Shuttle Control in Lithium-Sulfur Batteries with a Chemically/Electrochemically Compatible NASICON-Type Solid Electrolyte. Adv. Energy Mater. 2016, 6, 1601392.

(21)

Wang, L.; Wang, Y.; Xia, Y. A High Performance Lithium-Ion Sulfur Battery Based on a Li2S Cathode Using a Dual-Phase Electrolyte. Energy Environ. Sci. 2015, 8, 1551–1558.

(22)

Li, N.; Weng, Z.; Wang, Y.; Li, F.; Cheng, H.-M.; Zhou, H. An Aqueous Dissolved Polysulfide Cathode for Lithium–sulfur Batteries. Energy Environ. Sci. 2014, 7, 3307– 3312.

(23)

Goodenough, J. B.; Hong, H. Y. P.; Kafalas, J. A. Fast Na+-Ion Transport in Skeleton Structures. Mater. Res. Bull. 1976, 11, 203–220.

(24)

Baur, W. H.; Dygas, J. R.; Whitmore, D. H.; Faber, J. Neutron powder diffraction study and ionic conductivity of Na2Zr2SiP2O12 and Na3Zr2Si2PO12. Solid State lonics 1986, 18, 935–943.

(25)

Bohnke, O.; Ronchetti, S.; Mazza, D. Conductivity Measurements on NASICON and NASICON-Modified Materials. Solid State Ionics 1999, 122, 127–136.

(26)

Boilot, J. P.; Collin, G.; Colomban, P. Crystal Structure of the True NASICON: Na3Zr2Si2PO12. Mater. Res. Bull. 1987, 22, 669–676. 16 ACS Paragon Plus Environment

Page 16 of 24

Page 17 of 24 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(27)

Ren, Y.; Shen, Y.; Lin, Y.; Nan, C. W. Direct Observation of Lithium Dendrites inside Garnet-Type Lithium-Ion Solid Electrolyte. Electrochem. commun. 2015, 57, 27–30.

(28)

Sudo, R.; Nakata, Y.; Ishiguro, K.; Matsui, M.; Hirano, A.; Takeda, Y.; Yamamoto, O.; Imanishi, N. Interface Behavior between Garnet-Type Lithium-Conducting Solid Electrolyte and Lithium Metal. Solid State Ionics 2014, 262, 151–154.

(29)

Zhou, W.; Wang, S.; Li, Y.; Xin, S.; Manthiram, A.; Goodenough, J. B. Plating a Dendrite-Free Lithium Anode with a Polymer/Ceramic/Polymer Sandwich Electrolyte. J. Am. Chem. Soc. 2016, 138, 9385–9388.

(30)

Hood, Z. D.; Wang, H.; Samuthira Pandian, A.; Keum, J. K.; Liang, C. Li2OHCl Crystalline Electrolyte for Stable Metallic Lithium Anodes. J. Am. Chem. Soc. 2016, 138, 1768–1771.

(31)

Han, X.; Gong, Y.; Fu, K. (Kelvin); He, X.; Hitz, G. T.; Dai, J.; Pearse, A.; Liu, B.; Wang, H.; Rubloff, G.; Mo, Y.; Thangadurai, V.; Wachsman, E.; Hu, L. Negating Interfacial resistance in Garnet-Based Solid-State Li Metal Batteries. Nat. Mater. 2016, 16, 572–579.

(32)

O’Hern, S. C.; Boutilier, M. S. H.; Idrobo, J. C.; Song, Y.; Kong, J.; Laoui, T.; Atieh, M.; Karnik, R. Selective Ionic Transport through Tunable Subnanometer Pores in SingleLayer Graphene Membranes. Nano Lett. 2014, 14, 1234–1241.

(33)

Kim, K. S.; Zhao, Y.; Jang, H.; Lee, S. Y.; Kim, J. M.; Kim, K. S.; Ahn, J. H.; Kim, P.; Choi, J. Y.; Hong, B. H. Large-Scale Pattern Growth of Graphene Films for Stretchable Transparent Electrodes. Nature 2009, 457, 706–710.

(34)

Lee, C.; Wei, X.; Kysar, J. W.; Hone, J. Measurement of the Elastic Properties and Intrinsic Strength of Monolayer Graphene. Science 2008, 321, 385–388.

(35)

Wang, H.; Wang, C.; Matios, E.; Li, W. Critical Role of Ultrathin Graphene Films with Tunable Thickness in Enabling Highly Stable Sodium Metal Anodes. Nano Lett. 2017, 17, 6808–6815.

(36)

Rümmeli, M. H.; Bachmatiuk, A.; Scott, A.; Börrnert, F.; Warner, J. H.; Hoffman, V.; Lin, J. H.; Cuniberti, G.; Büchner, B. Direct Low-Temperature Nanographene CVD Synthesis over a Dielectric Insulator. ACS Nano 2010, 4, 4206–4210.

(37)

Chen, K.; Shi, L.; Zhang, Y.; Liu, Z. Scalable Chemical-Vapour-Deposition Growth of Three-Dimensional Graphene Materials Towards Energy-Related Applications. Chem. Soc. Rev. 2018, 47, 3018-3036.

(38)

Obraztsov, A. Making Graphene on a Large Scale. Nat. Nanotech. 2009, 4, 212–213.

(39)

Li, X.; Magnuson, C W.; Venugopal, A.; Tromp, R M.; Hannon, J B.; Vogel, E M.; Colombo, L.; Ruoff, R S. Large-area graphene single crystals grown by low-pressure 17 ACS Paragon Plus Environment


chemical vapor deposition of methane on copper. J. Am. Chem. Soc. 2011, 133, 28162819. (40)

Zhou, M.; Lin, T.; Huang, F.; Zhong, Y.; Wang, Z.; Tang, Y.; Bi, H.; Wan, D.; Lin, J. Highly Conductive Porous Graphene/ceramic Composites for Heat Transfer and Thermal Energy Storage. Adv. Funct. Mater. 2013, 23, 2263–2269.

(41)

Porwal, H.; Grasso, S.; Reece, M. J. Review of Graphene–ceramic Matrix Composites. Adv. Appl. Ceram. 2013, 112, 443–454. Large-Area Graphene Single Crystals Grown by Low-Pressure Chemical Vapor Deposition of Methane on Copper.

(42)

Hwang, J.; Shields, V. B.; Thomas, C. I.; Shivaraman, S.; Hao, D.; Kim, M.; Woll, A. R.; Tompa, G. S.; Spencer, M. G. Epitaxial Growth of Graphitic Carbon on C-Face SiC and Sapphire by Chemical Vapor Deposition (CVD). J. Crystal. Growth 2010, 312, 3219– 3224.

(43)

Ferrari, a. Raman Spectroscopy of Graphene and Graphite: Disorder, Electron–phonon Coupling, Doping and Nonadiabatic Effects. Solid State Commun. 2007, 143, 47–57.

(44)

Li, X.; Cai, W.; An, J.; Kim, S.; Nah, J.; Yang, D.; Piner, R.; Velamakanni, A.; Jung, I.; Tutuc, E.; Banerjee, S.; Colombo, L.; Ruoff, R.S. Large Area Synthesis of High Quality and Uniform Graphene Films on Copper Foils. Science 2009, 324, 1312–1314.

(45)

Gao, T.; Song, X.; Du, H.; Nie, Y.; Chen, Y.; Ji, Q.; Sun, J.; Yang, Y.; Zhang, Y.; Liu, Z. Temperature-Triggered Chemical Switching Growth of in-Plane and Vertically Stacked Graphene-Boron Nitride Heterostructures. Nat. Commun. 2015, 6,

(46)

Seh, Z. W.; Sun, J.; Sun, Y.; Cui, Y. A Highly Reversible Room-Temperature Sodium Metal Anode. ACS Cent. Sci. 2015, 1, 449–455.

(47)

Huggins, R. A. Advanced Batteries (Materials Science Aspects); Springer: New York, USA, 2008.

(48)

Jian, Z.; Han, W.; Lu, X.; Yang, H.; Hu, Y. S.; Zhou, J.; Zhou, Z.; Li, J.; Chen, W.; Chen, D.; Chen, Li. Superior Electrochemical Performance and Storage Mechanism of Na3V2(PO4)3 Cathode for Room-Temperature Sodium-Ion Batteries. Adv. Energy Mater. 2013, 3, 156–160.

(49)

Saravanan, K.; Mason, C. W.; Rudola, A.; Wong, K. H.; Balaya, P. The First Report on Excellent Cycling Stability and Superior Rate Capability of Na3V2(PO4)3 for Sodium Ion Batteries. Adv. Energy Mater. 2013, 3, 444–450.

(50)

Zhu, C.; Song, K.; Van Aken, P. A.; Maier, J.; Yu, Y. Carbon-Coated Na3V2(PO4)3 Embedded in Porous Carbon Matrix: An Ultrafast Na-Storage Cathode with the Potential of Outperforming Li Cathodes. Nano Lett. 2014, 14, 2175–2180.


Page 18 of 24

Page 19 of 24 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 1. (a) Schematic diagram illustrates the formation of non-uniform and dendrite-like morphology on Na anode after repeated stripping and plating cycles with pristine NASICON solid ceramic electrolyte. (b) The presence of a CVD-grown stable graphene-like interlayer effectively suppressed the dendrite-like Na formation, resulting in uniform plated Na anode after repeated stripping and plating cycles.




Page 20 of 24

Page 21 of 24 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 2. (a) The XRD spectra of the NASICON and G-NASICON. (b) The Raman spectra of NASICON with and without graphene-like coating. (c) The Normalized XPS signals of C and Zr on G-NASICON during Ar ion sputtering for estimating graphene-like coating thickness. The XPS spectra of (d) Zr, (e) P, and (f) Si for NASICON and G-NASICON. (g) and (h) are the TEM images of G-NASICON, revealing the graphene-like layer coating on NASICON electrolyte.

Figure 3. (a) The Nyquist plot of Au/G-NASICON/Au, Na/G-NASICON/Na and Na/NASICON/Na symmetric cells. (b) The bar chart with the respective electrolyte resistance, cell resistance and interfacial resistance of NASICON with and without graphene-like layer coating.



Figure 4. (a) The Na stripping/plating cycling stability test of Na symmetric cells with GNASICON and NASICON, respectively, at a current density of 0.5 mA/cm2 with a capacity of 1 mAh/cm2 over 1000 hours (250 cycles), and (b) at a current density of 1 mA/cm2 with a capacity of 1 mAh/cm2 over 1000 hours (500 cycles). (c) 1st to 10th cycles and (d) 490th to 500th cycles of Na symmetric cells at 1 mA/cm2 with a capacity of 1 mAh/cm2. The SEM images of the Na metal electrode disassembled from (e) Na/NASICON/Na and (f) Na/G-NASICON/Na symmetry cells after 1000 hours (500 cycles) at 1 mA/cm2 and 1 mAh/cm2. The scale bar is 40 μm. 22 ACS Paragon Plus Environment

Page 22 of 24

Page 23 of 24 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 5. (a) The electrochemical cycling performance of NVP/LE/G-NASICON/Na solid-state battery discharge capacity at a current rate of 1C at room temperature; the inset displays the galvanostatic charging/discharging curves of the 1st, 150th and 300th cycles. (b) Rate performance of NVP/LE/G-NASICON/Na solid-state battery discharge capacity at current rates of 0.5C, 1C, 2C and 5C at room temperature; the inset displays the galvanostatic charging/discharging curves of the last cycle for each C rate. (c) The cycling performance of the NVP/G-NASICON/Na allsolid-state battery at a current rate of 0.1C at 80 °C; the inset displays the galvanostatic charging/discharging curves of the 1st and 30th cycles.



TOC


Page 24 of 24

Graphene Regulated Ceramic Electrolyte for Solid-State Sodium Metal

Recommend Documents