Garnet Solid Electrolyte Protected Li-Metal Batteries - ACS Publications

May 12, 2017 - Department of Materials Science and Engineering, University of Maryland, College Park, Maryland 20742, United States. •S Supporting ...
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Garnet Solid Electrolyte Protected Li-Metal Batteries Boyang Liu,†,‡,§ Yunhui Gong,†,‡,§ Kun Fu,†,‡,§ Xiaogang Han,†,‡ Yonggang Yao,†,‡ Glenn Pastel,†,‡ Chunpeng Yang,†,‡ Hua Xie,†,‡ Eric D. Wachsman,*,†,‡ and Liangbing Hu*,†,‡ †

University of Maryland Energy Research Center, University of Maryland, College Park, Maryland 20742, United States Department of Materials Science and Engineering, University of Maryland, College Park, Maryland 20742, United States

‡

S Supporting Information *

ABSTRACT: Garnet-type solid state electrolyte (SSE) is a promising candidate for high performance lithium (Li)-metal batteries due to its good stability and high ionic conductivity. One of the main challenges for garnet solid state batteries is the poor solid−solid contact between the garnet and electrodes, which results in high interfacial resistance, large polarizations, and low efficiencies in batteries. To address this challenge, in this work gel electrolyte is used as an interlayer between solid electrolyte and solid electrodes to improve their contact and reduce their interfacial resistance. The gel electrolyte has a soft structure, high ionic conductivity, and good wettability. Through construction of the garnet/gel interlayer/electrode structure, the interfacial resistance of the garnet significantly decreased from 6.5 × 104 to 248 Ω cm2 for the cathode and from 1.4 × 103 to 214 Ω cm2 for the Li-metal anode, successfully demonstrating a full cell with high capacity (140 mAh/g for LiFePO4 cathode) over 70 stable cycles in room temperature. This work provides a binary electrolyte consisting of gel electrolyte and solid electrolyte to address the interfacial challenge of solid electrolyte and electrodes and the demonstrated hybrid battery presents a promising future for battery development with high energy and good safety. KEYWORDS: solid state electrolyte, garnet, gel electrolyte, interfacial impedance, Li-metal battery film batteries.32 Among different kinds of inorganic SSEs, garnet Li7La3Zr2O12 (LLZO) is a promising type of electrolyte for Li-metal batteries33−35 for its high lithium-ion conductivity (10−4 to 10−3 S/cm)29 and the best electrochemical stability against metallic Li.35,36 The high electrochemical stability with Li metal of garnet gives the garnet battery intrinsic stability and high safety with Li-metal anode compared to batteries using other oxide and sulfide SSEs.37−39 The main challenge for garnet electrolytes in Li-metal batteries is the high interfacial resistance between garnet and both the cathode and the anode.40−43 One reason for the high interfacial resistance is the poor contact between garnet and electrodes, as both materials are hard solids, and it is difficult to contact them together with fully wetting.44,45 High interfacial resistance due to poor contact results in a large overpotential during cycling. There are effective methods for interfacial engineering between Li metal and liquid electrolytes,46,47 but they are difficult to be applied for SSE to solve the contact issues. Current strategies to reduce the interfacial resistance for SSE mainly focus on introducing interfacial layers such as metal/metal oxide (Au, Si, Al, or Al2O3) or dry polymer between the SSE and electrodes, which are effective but need

1. INTRODUCTION Lithium-ion battery technology has developed significantly in the last few decades.1−3 Pure lithium (Li) metal has the highest specific capacity (3860 mAh/g) and the lowest electrochemical potential (−3.04 V vs standard hydrogen electrode) in comparison to any other lithium-ion anode materials.4−6 One critical challenge associated with lithium metal anodes is the formation of metal dendrites in liquid electrolyte systems that can penetrate polymer separators and cause both safety concerns and performance decay in long-term cycling applications.7−15 Solid state electrolytes (SSEs) have been recognized as a solution to deter Li dendrite formation by acting as a strong, impenetrable barrier.16 SSEs generally have a wide electrochemical stability voltage window and a high elastic modulus to prevent Li dendrite penetration17 and improve safety.13,18−20 As one type of SSE, inorganic solid state electrolytes have particularly high elastic modulus, stability, and safety.21−30 Various types of inorganic SSEs have been reported, including sulfide-type, oxide-type, and oxynitride-type materials.21−26 Sulfide and oxide SSEs such as Li10GeP2S12 and LISICON (lithium super ionic conductor) respectively, have high ionic conductivity (10−2 to 10−3 S/cm) but are electrochemically unstable against Li-metal.30,31 Oxynitride SSEs such as LiPON (Li2.88PO3.73N0.14) are electrochemically stable against Li-metal but suffer from low ionic conductivity (10−6 S/cm), so they are applicable only for thin© 2017 American Chemical Society

Received: March 18, 2017 Accepted: May 12, 2017 Published: May 12, 2017 18809

DOI: 10.1021/acsami.7b03887 ACS Appl. Mater. Interfaces 2017, 9, 18809−18815

Research Article

ACS Applied Materials & Interfaces

suitable for most commercially employed cathode materials. Compared to that of dry polymer employed in hybrid batteries,51,57 our design has a smaller interfacial resistance at room temperature and can be easily adopted for current battery manufacturing processes. Due to the hybrid design with gel electrolyte as the interlayer between the garnet SSE and the active electrodes, the interfacial resistances of garnet SSE with electrodes significantly decreased from 6.5 × 104 to 248 Ω cm2 for the garnet/cathode interface and from 1.4 × 103 to 214 Ω cm2 for the garnet/Li interface. Our results show that the symmetric cells with gel/garnet/gel hybrid electrolyte and Li metal can cycle with stable stripping and plating profiles with a low overpotential, which is indicative of a stable interface between the garnet SSE and metallic Li anode. Because minimal amounts of liquid electrolyte are stored in the gel interlayers, batteries with the gel/garnet/gel hybrid electrolyte demonstrate stable long-term cycling performance and safety and do not suffer from leakage issues as do conventional batteries with liquid electrolytes or hybrid batteries with SSEs employing unbounded liquid electrolytes as interlayers.58,59 The hybrid electrolyte design with gel interlayers is an important surface engineering strategy to decrease the overall interfacial resistance against electrodes while maintaining safe and scalable Li-metal batteries with high performance.

high temperatures for manufacturing or battery cycling, respectively.45,48−52 Compared with these techniques, gel electrolyte interlayers, composed of polymer and liquid electrolyte, are more scalable for battery manufacturing and application processes. The flexible and soft gel can form continuous contact between garnet SSE and solid electrodes, and the high ionic conductivity of the gel at room temperature adds almost zero bulk resistance to the battery.53−56 In this work, gel electrolyte was used as interlayers between garnet SSE and the electrodes to decrease the garnet SSE interfacial resistance against cathode and Li-metal anode (Figure 1a). Figure 1b shows a schematic of the Li-metal

Figure 1. Schematic of hybrid battery with gel interfaces. (a) Schematic of the interface improvement using gel interlayers. Without the gel interlayers, the garnet SSE and electrode have poor interfacial contact. With the gel interlayers, the contact between electrodes and SSE is improved. (b) Schematic of the battery design with hybrid gel/ garnet electrolyte.

2. RESULTS AND DISCUSSION 2.1. Characterization of Hybrid Electrolyte. Garnet Li7La2.75Ca0.25Zr1.75Nb0.25O12 (LLCZNO) disks have a rough surface, as shown in the scanning electron microscope (SEM) image (Figure 2a). The rough and hard surface of the garnet leads to poor contact against the electrode layers. The zoomed in cross-sectional SEM image of a garnet LLCZNO disk shows dense grain structures (Figure 2b) as a result of the 12 h of high temperature sintering during the synthesis process. The densification of the LLCZNO is also quantitatively evaluated

battery design using the gel/garnet SSE hybrid electrolyte. The gel electrolyte used in this study is a combination of a porous PVDF−HFP polymer matrix and a controlled amount of liquid electrolyte stored inside the polymer. The gel electrolyte has good ionic conductivity (5 × 10−4 S/cm) and is electrochemically stable in the voltage range of 0−4.5 V vs Li+/Li, which is

Figure 2. Structural and electrochemical characterizations of LLCZNO garnet and gel electrolyte. (a) Cross-sectional SEM image of LLCZNO garnet disk. Inset is a photo image of the garnet disk. (b) Zoomed in cross-sectional SEM image of the LLCZNO garnet disk. (c) Top view SEM image of PVDF−HFP polymer matrix. (d) XRD pattern comparison of the LLCZNO garnet disk and standard Li5La3Nb2O12 with cubic garnet phase. (e) EIS plots of the LLCZNO disks with different thicknesses of 1000 and 150 μm. (f) Cyclic voltammetry of the gel electrolyte between Li and Ti electrodes. 18810

DOI: 10.1021/acsami.7b03887 ACS Appl. Mater. Interfaces 2017, 9, 18809−18815

Research Article

ACS Applied Materials & Interfaces

Figure 3. Impedance analysis of symmetric cells with hybrid electrolyte. (a) EIS of a cathode/gel/cathode symmetric cell. (b) EIS of a SS/gel/SSE/ gel/SS symmetric cell. (c) EIS of a cathode/gel/SSE/gel/cathode symmetric cell. (d) EIS plot of a Li/gel/Li symmetric cell. (e) EIS plot of Li/gel/ SSE/gel/Li symmetric cell. (f) Comparison of the SSE/electrode interfacial areal specific resistance (ASR) with and without the gel interlayers.

between SSE and the electrodes and reduce the interfacial resistance. 2.2. Analysis of the Interfacial Impedance of the Hybrid Electrolyte. The impedance analysis of symmetric cells with garnet/gel hybrid electrolyte is shown in Figure 3. Figure 3a shows the impedance profile of a cathode/gel/ cathode symmetric cell. The bulk resistance of the cell is small because of the highly conductive gel layer. The semicircle in the middle frequency region corresponds to the charge transfer resistance (Rct) on interface, which is about 70 Ω cm2 for each side, as calculated with equivalent circuit simulations shown in the Supporting Information, Figure S2. The small Rct proves that the gel and cathode have good interfacial contact. In the low frequency region is the diffusion impedance in the cathode. The impedance profile of a stainless steel (SS)/gel/SSE/gel/SS symmetric cell contains the bulk and grain boundary impedances of the garnet SSE in the high frequency region, the interfacial Rct in middle frequency region, and the diffusion impedance in low frequency region (Figure 3b). The Rct between the gel and SS is almost zero (Supporting Information, Figure S1), so all of the Rct in a SS/gel/SSE/gel/SS symmetric cell comes from gel/SSE interfaces, which is about 155 Ω cm2 for each side, calculated from the corresponding fitting result in the Supporting Information, Figure S2. This resistance is close to the Rct of the cathode/gel interface, which means that the gel/SSE and cathode/gel interfaces have similar contact performance. The EIS plot of cathode/gel/SSE/gel/cathode symmetric cell describes the interfacial resistance between cathode and SSE with gel interlayer (Figure 3c). The impedance curve contains the bulk and grain boundary impedances of the garnet SSE in the high frequency region, the interfacial Rct between garnet SSE and cathode in the middle frequency region, and the diffusion impedance of the cathode in the low frequency region. The total interfacial Rct in the cathode/gel/SSE/gel/cathode

by Archimedes method to be 92%. The dense garnet structure enables a homogeneous current distribution and prevents lithium-metal dendrites from penetrating through the electrolyte during cycling with a limited current density.45 The porous structure of the PVDF−HFP polymer matrix as shown in the SEM image (Figure 2c) helps the polymer absorb and contain liquid electrolyte to form a gel electrolyte with high ionic conductivity. The X-ray diffraction (XRD) pattern of garnet LLCZNO matches that of the cubic phase garnet Li5La3Nb2O12, which indicates that LLCZNO has the cubic garnet phase with Li-ion conductivity higher than that of the tetragonal garnet phase (Figure 2d). The electrochemical impedance spectroscopies (EIS) of LLCZNO disks were tested with gold electrodes on both sides and show high conductivity of the garnet (Figure 2e). The semicircle in the high frequency portion of the impedance spectroscopy curve represents the bulk resistance and the grain boundary resistance of LLCZNO.60 The LLCZNO disks with different thicknesses have the same bulk conductivity of around 2 × 10−4 S/cm, which is high for solid state electrolytes. Figure 2f is the cyclic voltammetry (CV) plot of the Li/gel/ Ti system. The flatness of the CV curve in the voltage range of 0−4.5 V, except the Li stripping and platting peaks, suggests that the gel electrolyte is electrochemically stable from 0 to 4.5 V vs Li+/Li. In addition, the garnet LLCZNO is electrochemically stable from 0 to 6 V vs Li+/Li;61 therefore, the hybrid electrolyte design is stable in the voltage range of 0−4.5 V vs Li+/Li. This wide stable voltage range makes the hybrid electrolyte suitable for lithium-metal anode with numerous cathode materials. The areal specific resistance and ionic conductivity of the gel with 40 μm thickness are 8 Ω cm2 and 5 × 10−4 S/cm, respectively, which are measured from the EIS of a simple symmetric cell with stainless steel plates, as seen in the Supporting Information, Figure S1. This soft and highly ionically conductive gel electrolyte can improve the contact 18811

DOI: 10.1021/acsami.7b03887 ACS Appl. Mater. Interfaces 2017, 9, 18809−18815

Research Article

ACS Applied Materials & Interfaces symmetric cell is 248 Ω cm2 for each side, approximately the sum of gel/cathode interfacial Rct and gel/SSE interfacial Rct, both of which show up in middle frequency range. The EIS plot of cathode/SSE/cathode symmetric cell without interfacial modification and made by directly coating the cathode slurry on the garnet SSE shows that the total Rct of cathode/SSE/ cathode symmetric cell without gel interlayer is about 1.3 × 105 Ω cm2. The huge resistance is evidence of poor contact between SSE and cathode materials, which can be solved with gel interlayer in the hybrid design between the garnet SSE and the cathode. The EIS plot of a Li/gel/Li symmetric cell shows that the Rct of gel/Li interfaces is 90 Ω cm2 (Figure 3d), which is close to the gel/cathode interfacial resistance. This means that the contact between gel and Li anode is as good as the contact between gel and cathode. The EIS plot of Li/gel/SSE/gel/Li symmetric cell contains the bulk resistance and the grain boundary resistance of the garnet SSE in high frequencies, the interfacial Rct between garnet SSE and Li-metal in middle frequencies, and the diffusion impedance in low frequencies (Figure 3e). From the corresponding equivalent circuit fitting (Supporting Information, Figure S2), the total interfacial Rct on one interface in the Li/gel/SSE/gel/Li symmetric cell is 214 Ω cm2. To compare, the total resistance of a Li/SSE/Li symmetric cell with Li metal directly melted on the garnet is about 1400 Ω cm2 for one side. Therefore, gel interlayer made an 85% interfacial resistance decrease for the Li/garnet interface. The resistances of all interfaces in the Li/gel/SSE/gel/Li and cathode/gel/SSE/gel/cathode cells are presented in Table 1.

2.3. Electrochemical Performance of the Hybrid Solid−Gel Electrolyte. The electrochemical performances of lithium symmetric cells and full cells with gel/garnet hybrid electrolyte are shown in Figure 4. The total areal specific

Table 1. Impedance of the Electrode/SSE/Electrode Symmetric Cell Components with and without Gel Interlayersa

Figure 4. Electrochemical performances of gel/SSE/gel hybrid electrolyte in symmetric and full cells. (a) Voltage profile of Li stripping and platting in a Li/gel/SSE/gel/Li symmetric cell with constant current for 15 h. (b) EIS plot of the cell before and after cycling. (c) EIS of a LiFePO4/gel/SSE/gel/Li cell. (d) Charge and discharge voltage profiles of a LiFePO4/SSE/Li cell at a current density of 170 mA/g. (e) Discharge capacity of the LiFePO4/gel/SSE/ gel/Li cell at a current density of 170 mA/g.

cell with/without gel cathode/SSE/cathode with gel

cathode/SSE/cathode without gel Li/SSE/Li with gel

Li/SSE/Li without gel a

component SSE SSE/gel interface cathode/gel interface total cathode/SSE interface total SSE SSE/gel interface Li/gel interface total Li/SSE interface total

equivalent circuit parts

resistance (Ω cm2)

R0, R1, C1 R2, CPE1

127 200

R3, CPE2

48

N/A N/A

623 ∼6.5 × 104

N/A R0, R1, C1 R2, CPE1

∼1.3 × 105 171 135

R3, CPE2 N/A N/A N/A

79 599 1400 3000

resistance of the Li/gel/SSE/gel/Li symmetric cell was stable during long period galvanostatic cycling (Figure 4a). The inset of Figure 4a shows that the resistance was constant during each cycle, which indicates long-term electrochemical stability of the gel interlayer. Figure 4b shows the interfacial resistances of the cell before and after cycling for 15 h, which was almost constant and changed slightly from 1000 to 1100 Ω cm2. This confirms that the gel interface was stable and maintained a small resistance during Li cycling. Figures 4c−e show the cycling performances of a full cell with a gel/garnet hybrid electrolyte, metallic Li anode, and LiFePO4 cathode. The cell was charged and discharged at 1 C rate (170 mAh/g) for 70 cycles at room temperature. Figure 4c is the EIS plot of the battery before cycling. The Rct was about 650 Ω cm2, which was close to the sum of garnet/Li anode interfacial resistance and garnet/cathode interfacial resistance. The charge and discharge curves showed stable voltage plateaus with constant overpotentials of about 0.2 V during 70 charge and discharge cycles at a current density of 170 mA/g (Figure 4d). The stable overpotential is attributed to the high stability of the gel/garnet/gel electrolyte. Figure 4e shows the discharge capacity and Coulombic efficiency of the full cell, which were around 140 mAh/g and 93% for the 70 cycles. The stable discharge capacity of battery over a long period indicates that

The equivalent circuits are in the Supporting Information, Figure S2.

As a conclusion, gel interlayer can significantly reduce the interfacial Rct between the LLCZNO solid state electrolyte and the electrodes, including both cathodes and Li-metal anodes. Figure 3f concludes the interfacial resistance decrease with the gel interlayers. The interfacial resistance between cathode and garnet SSE was dramatically decreased from 6.5 × 104 to 248 Ω cm2 after applying the gel interlayers. The interfacial resistance between the Li-metal anode and garnet SSE also decreased from 1400 to 214 Ω cm2 after applying gel interlayers. 18812

DOI: 10.1021/acsami.7b03887 ACS Appl. Mater. Interfaces 2017, 9, 18809−18815

Research Article

ACS Applied Materials & Interfaces

small round films with an area of 0.2 cm2 and immersed into 1 M LiPF6 in 1:1 ethylene carbonate (EC):diethyl carbonate (DEC) liquid electrolyte for 1 min to be fully soaked by electrolyte, and the excess liquid on the surface of the membrane was moved away by wipers. Material Characterization. Phase analysis of the LLCZNO garnet disks was performed by XRD on a D8 Advanced with LynxEye and SolX (Bruker AXS, WI, USA) using a Cu Kα radiation source operated at 40 kV and 40 mA. The morphology of the microstructures of asprepared LLCZNO garnet disks and PVDF−HFP membranes was examined by a field emission scanning electron microscope (FE-SEM, JEOL 2100F). Battery Fabrication and Electrochemical Test. The interfacial impedance was measured for both the Li/SSE interface and the LiFePO4 cathode/SSE interface. The lithium-metal electrodes were pressed and punched from a Li belt (Sigma-Aldrich) into round disks with an area of 0.2 cm2 and a thickness 0.5 mm. To make the cathode, LiFePO4, carbon black, and polyvinylidene difluoride (PVDF) were dissolved in N-methyl-2-pyrrolidone (NMP) with a mass ratio 3:2:1 and mixed into slurry. The slurry was coated on aluminum foil and then dried at 100 °C in an oven for 12 h. After drying, the cathodes were cut into round disks with an area of 0.2 cm2 and immersed in 1 M LiPF6 in 1:1 EC:DEC liquid electrolyte before testing, and the surplus liquid electrolyte was wiped away. Battery assembly and electrochemical tests were done in an argon filled glovebox. CV of the Li/gel/Ti cell was tested with a voltage range of −0.3 to 4.5 V with a scan rate of 1 mV/s. Symmetric cells were made for the EIS test. The schematic of the cell for each test is in the corresponding EIS plot. The electrodes, gel membranes, and garnet disks were pressed together in sequence by clips, with one stainless steel disk on each side of the cell. The electrochemical performances of the cells were tested by a BioLogic tester. EIS tests of the symmetrical cells have a voltage amplitude of 10 mV and a frequency range of 0.1 Hz to 1 MHz. Constant current cycling of Li/SSE/Li with gel interface layers used the same assembly method as with the EIS test and was conducted with a current density of 0.125 mA/cm2 with a period of 10 min. The EIS of the cell before cycling and after cycling for 15 h was measured and compared. The Li/SSE/LiFePO4 full cell with gel interfaces was made by pressing the garnet, gel, and electrode layers together in a CR2016 coin cell and sealing by epoxy. This cell was cycled with a constant current of 50 μA/cm2 in the voltage range of 2−4.2 V.

the interfacial layer is electrochemically stable. The increment of capacity in the first few cycles is possibly because of an improvement to the electrolyte/electrode interface during cycling. The relatively low Coulombic efficiency can be attributed to the liquid electrolyte in gel affected by the environmental humidity due to the nonideal packaging by coincell cases and epoxy. This issue can be solved with a better packaging technique. However, this battery with a gel/garnet hybrid electrolyte can stably cycle at room temperature because of the small resistance and the stability of the electrolyte against Li metal. The hybrid gel/garnet electrolyte can be used for scalable development of future Li-metal full cells with small overpotentials and improved safety and stability.

3. CONCLUSIONS In summary, we used gel interlayers to address the high interfacial resistance of garnet solid electrolyte with electrodes, and the results indicate that the hybrid binary electrolyte consisting of solid electrolyte and gel electrolyte can effectively protect Li metal and help extend the cycle life of Li-metal batteries. Gel electrolyte has a soft structure, high ionic conductivity, and a wide electrochemically stable voltage window, which can provide good wettability with rigid solid electrolyte and electrodes. The gel interlayer decreases the interfacial resistances of garnet from 6.5 × 104 to 248 Ω cm2 against the cathode, and from 1.4 × 103 to 214 Ω cm2 against the Li-metal anode. A full cell consisting of the hybrid binary electrolyte, LiFePO4 cathode, and Li-metal anode was demonstrated, and the cell exhibited a high capacity (140 mAh/g for LiFePO4 at 1 C rate) and stable cycling performance over 70 cycles at room temperature. This work has successfully addressed the interfacial challenge of solid electrolyte and electrodes using a scalable approach for convenient integration with current battery fabrication processes. The demonstrated hybrid battery presents a useful improvement toward batteries with high energy density and improved safety using garnet solid electrolyte.

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MATERIALS AND METHODS

ASSOCIATED CONTENT

S Supporting Information *

Synthesis of the LLCZNO Disks. The garnet Li7La2.75Ca0.25Zr1.75Nb0.25O12 powders were synthesized by a sol−gel method. Precursors LiNO3 (99%, Alfa Aesar), La(NO3)3·6H2O (99%, Alfa Aesar), Ca(NO3)2·4H2O (99.9%, Sigma-Aldrich), NbCl5 (99%, Alfa Aesar), and zirconium(IV) propoxide (70 wt % in 1-propanol, Sigma-Aldrich) were dissolved into ethanol, with stoichiometric amounts and 10 wt % extra LiNO3, and the solution was stirred until clear. Then, pure acetic acid was added with a volume ratio 1:4 to the solution. The ethanol solvent was evaporated under 100 °C to get the gel precursors. The gel was heated at 350 °C to get dry precursor powders, and those were then heated at 800 °C for 10 h to get garnet powders. The powders were ball milled for 48 h and then pressed into cylindrical disks. The area of the disks is 0.5 cm2 after sintering at 1050 °C for 12 h. The as-synthesized disks were polished with sand paper to reduce the thickness to between 400 and 450 μm and washed with isopropyl alcohol (IPA). Synthesis of the PVDF−HFP-Based Gel Electrolyte. PVDF− HFP-based gel electrolyte was made by first dissolving 0.25 g of PVDF−HFP (Sigma-Aldrich) into a mixture of 4.5 g of acetone and 0.25 g of ethanol under mechanical stirring for 1 h to get a homogeneous solution. The solution was then cast onto a flat aluminum foil, and the solvent was evaporated in a constant 80% humidity chamber at 25 °C. The samples were dried under vacuum at 60 °C for 5 h, after which a homogeneous freestanding membrane was obtained. The thickness of the PVDF−HFP membrane is around 40 μm. The as-prepared porous PVDF−HFP membrane was cut into

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsami.7b03887. Impedance of gel electrolyte, equivalent circuits of the symmetric cells, and impedances of the garnet/cathode and garnet/Li symmetric cells without gel interlayers (PDF)

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AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected]. *E-mail: [email protected]. ORCID

Chunpeng Yang: 0000-0001-7075-3356 Eric D. Wachsman: 0000-0002-0667-1927 Liangbing Hu: 0000-0002-9456-9315 Author Contributions §

B.L., Y.G., and K.F. contributed equally to this work.

Notes

The authors declare no competing financial interest. 18813

DOI: 10.1021/acsami.7b03887 ACS Appl. Mater. Interfaces 2017, 9, 18809−18815

Research Article

ACS Applied Materials & Interfaces

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ACKNOWLEDGMENTS This work was supported by the U.S. Department of Energy, DOE EERE contract DEEE0006860. We acknowledge the support of the Maryland NanoCenter and its FabLab and AimLab.

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