Composite Solid Polymer Electrolyte with Garnet Nanosheets in Poly

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Composite Solid Polymer Electrolyte with Garnet Nanosheets in Poly(ethylene oxide) Shufeng Song, Yongmin Wu, Weiping Tang, Fan Deng, Jianyao Yao, Zongwen Liu, Rongjie Hu, * Alamusi, Zhaoyin Wen, Li Lu, and Ning Hu ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.9b00143 • Publication Date (Web): 01 Mar 2019 Downloaded from http://pubs.acs.org on March 4, 2019

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ACS Sustainable Chemistry & Engineering

Composite Solid Polymer Electrolyte with Garnet Nanosheets in Poly(ethylene oxide) Shufeng Song,*, † Yongmin Wu,  Weiping Tang, Fan Deng,† Jianyao Yao, † Zongwen Liu,§ Rongjie Hu,∥ Alamusi,∥ Zhaoyin Wen,& Li Lu,#,% and Ning Hu*, † , ‡

†College

of Aerospace Engineering, Chongqing University, 174 Shazhengjie Road,

Chongqing 400044, P.R. China. State

Key Laboratory of Space Power-sources Technology, Shanghai Institute of Space

Power-Sources, 2965 Dongchuan Road, Shanghai 200245, P.R. China. §Australian

Centre for Microscopy and Microanalysis, The University of Sydney, NSW

2006, Australia. ∥College

of Manufacturing Science and Engineering, Southwest University of Science

and Technology, 59 Qinglong Road, Mianyang 621010, P.R. China.

ACS Paragon Plus Environment

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ACS Sustainable Chemistry & Engineering 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

&CAS

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Key Laboratory of Materials for Energy Conversion, Shanghai Institute of

Ceramics, Chinese Academy of Sciences, 1295 Dingxi Road, Shanghai 200050, P.R. China. #Materials

Science Group, Department of Mechanical Engineering, National University

of Singapore, 21 Lower Kent Ridge Road, Singapore 117575. %National

University of Singapore Suzhou Research Institute, 377 Linquan Road,

Suzhou 215000, P.R. China. ‡State

Key Laboratory of Coal Mine Disaster Dynamics and Control, Chongqing

University, 174 Shazhengjie Road, Chongqing 400044, P.R. China.

*Corresponding author.

E-mail addresses: [email protected] (S.F. Song), [email protected] (N. Hu)

KEYWORDS: Garnet nanosheet, PEO, composite polymer electrolyte, conductivity.

ABSTRACT: Solid electrolytes potentially provide safety, Li dendrites blocking, as well as electrochemical stability in Li-metal batteries. Large efforts have been devoted to disperse


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ceramic nanoparticles in poly(ethylene oxide) (PEO) matrix to improve the ions transport. However, it is challengeable to create efficient framework for ions transport with nanoparticles. Here we report for the first time garnet nanosheets to provide interconnected Li-ions transport pathway in a PEO matrix. The garnet nanosheet fillers would not only facilitate ions transport but also enhance ionic conductivity in comparison with their nanoparticle counterparts. A composite solid polymer electrolyte containing 15 wt.% garnet nanosheets exhibits a practically useful conductivity of 3.6×10-4 S cm-1 at room temperature. Besides, the composite electrolyte can robustly isolate Li dendrites in symmetric

lithium

metal-composite

electrolyte

battery

during

reversible

Li

dissolution/deposition at relatively low temperature of 40 oC. The symmetric cell with composite electrolyte shows flat voltage and low interfacial resistance over galvanostatic cycling 200 h at a current density of 0.1 mA cm-2. A solid-state Li/LiFePO4 battery with the composite polymer electrolyte exhibits a capacity of 98.1 mAh g-1 and a capacity retention of 97.5% after 30 cycles at temperature of 40 oC. This finding provides a strategy to explore superionic conductors.


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INTRODUCTION

The need for efficient and safe energy storage technology revives solid-state-electrolytesconstructed batteries.1,2 Rechargeable solid-state polymer batteries represent an excellent choice as electrochemical device characterized by outstanding safety and highenergy density, since the polymer electrolytes serving for lithium batteries from the pioneering work of Armand et al.3 Classical polymer electrolytes are consisting of lithium salt and poly(ethylene oxide) (PEO).4 Unfortunately, PEO suffers from crystallization below 60 oC, but ions conduction is a behavior of an amorphous structure. The roomtemperature conductivities of polymer electrolytes consisting of PEO-lithium salt, i.e., PEO-LiClO4, are only around 10-8 S cm-1.5 On the other hand, the useful conductivity level of 10-4 S cm-1 is only delivered at temperature range of 60-80 oC.6 Therefore, considerable efforts have been devoted to inhibit PEO crystallization and realize environmental operation. Blending liquid plasticizers within PEO matrix is an initial but effective approach to improve the conductivity.7,8 Unfortunately, the conductivity enhancement is at the


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expense of mechanical property and compatibility with lithium electrodes. The ionic conductivities and mechanical properties are particularly improved by compositing oxide nanoparticles within PEO matrix. The addition of ceramic particles fillers has been demonstrated to hinder PEO crystallization. The inactive ceramic fillers, such as Al2O3, TiO2, ZrO2, and SiO2, have been added to the PEO matrix, as inspired by the pioneer work of Scrosati et al.9 Ionic conductivity is enhanced to 10-5 S cm-1, but still far away from the practically useful value.10-12 Cui et al.13 developed the composite electrolyte by in-situ dispersing silica nanospheres in PEO matrix, showing largely extended electrochemical stability, again, the conductivity is approximately 10-5 S cm-1 at room temperature. On the other hand, it is well known that the conductivity of PEO can be enhanced by plastic additive of ionic liquid, but at the cost of mechanical stability of the membrane.14 We

reported

PEO-ceramic

nanoparticle

filler-ionic

liquid

composite

polymer

electrolytes.15,16 An interaction is activated between PEO, ceramic nanoparticle filler, and ionic liquid by mechanochemical reaction, demonstrating superior conductivity of 10-4 S cm-1.


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Recently, active ceramic fillers, such as hectorite, laponite, and montmorillonite, have been investigated for PEO base polymer electrolytes.17 In this regard, PEO chains intercalate within the organoclay platelets and solvate lithium ions. However, low conductivities are typically observed in these categories.18 To address this issue, inorganic lithium ceramic electrolytes have been served as the active fillers within PEO matrix. The influence of garnet-type and NASICON-type active fillers, such as Li7La3Zr2O12, Li1.5Al0.5Ge1.5(PO4)3, and Li1.3Al0.3Ti1.7(PO4)3 on conductivities of PEO base polymer electrolytes has been largely studied.19-23 In this case, ionic conductivity is typically increased to 10-5-10-4 S cm-1, and voltage stability of the PEO base polymer electrolyte is further enhanced. It is believed that the particle size has great influence on the conductivity. Li et al. 24 reported garnet nanoparticles with small particle size, ~40 nm favoring Li-ion transport within PEO matrix due to the percolation effect. The ceramic nanoparticles are generally obtained by mechanically milling. In this context, the particle size is limited and not uniform, the morphology is irregular, all of which are detrimental to the conductivity enhancement. Ceramic nanofibers are believed to be much more pronounced as fillers to enhance conductivity. Cui et al. 25 reported addition of perovskite


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Li0.33La0.557TiO3 nanowire to polyacrylonitrile-LiClO4 polymer electrolyte to improve the conductivity. Reversible capacity of 329.2 mAh g-1 is demonstrated in a lithium vanadium cell consisting of solid polymer electrolyte of V2O5 nanowires and PEO at 17 mA g-1.26 Hu

et al.

27

reported 3D garnet nanofiber networks incorporated with PEO-LiTFSI,

demonstrating promising conductivity of 2.5×10-4 S cm-1. Very recently, Hu’s group has reported composite electrolyte based on design of a flexible garnet textile, which realizes stable Li cycling and very high active material loading of 10.8 g cm-2, demonstrating the advantages of lithium conductive ceramics using in composite polymer electrolytes.28 In addition, a hybrid solid electrolyte prepared by distributing garnet Li7La3Zr2O12 particles into PVDF-HFP matrix delivers good electrochemical performance.29

Ceramic nanoparticles, one-dimensional, and three-dimensional fillers have been reported, whereas two-dimensional active ceramic fillers are ignored. Herein, we first report garnet nanosheets and present positive electrochemical performance. We synthesized the garnet nanosheets via co-precipitation with graphene oxide (GO) template. A novel composite solid polymer electrolyte is fabricated by dispersing the


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nanosheet

fillers

within

hybrid

PEO-LiClO4-EmimFSI.

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Typically,

garnet

Li6.5La3Zr1.5Nb0.5O12 is selected because of its good electrochemical performance and low annealing temperature.30 In this work, we contrast the nanosheet-dispersed composite electrolytes with the nanoparticle-dispersed ones.

EXPERIMENTAL SECTION

Garnet nanosheets were prepared by a co-precipitation method with GO as a template. A garnet composition of Li6.5La3Zr1.5Nb0.5O12 was selected for study. LiNO3, ZrO(NO3)2xH2O, La(NO3)36H2O, and NbCl5 in ethanol were dissolved in deionized water to form garnet precursors. A 20 wt% excess LiNO3 raw material was used to compensate for lithium volatilization during calcination. GO was synthesized via the improved method.31 Then GO solution (typically, 4.9 mg mL-1) was added into the garnet precursors and dispersed by ultrasound for 30 min. The weight ratio of GO to garnet was 0.2. This solution was then chemically precipitated by adding ammonium solution. The pH is carefully manipulated to be 8, 9.5, and 11. The GO@garnet precursors were collected by centrifuging and washing with deionized water to remove residual nitrate ions


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and impurities, and drying overnight at 100 oC in air. Next, the GO@garnet precursors were calcined at 750 and 800 oC for 2 h in air to remove GO and to obtain garnet nanosheets. The synthesis of garnet nanoparticles was similar with that procedure of the nanosheets except GO addition. PEO (Mw=100,0000) and LiClO4 were dried respectively at 50 and 100 oC. The scale of [EO] to Li was 10 : 1, the weight of 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide (EmimFSI) was 50% of the PEO weight, and the ceramic filler weight ranged from 5 wt.% to 35 wt.% of the PEO weight. A mixture of PEO, LiClO4, EmimFSI, and ceramic filler was ball-milled with high speed (SPEX SamplePrep 8000M) for 1 h. The mixture was subsequently spread on PTFE substrate and a membrane was obtained and kept in an inert glove box after dried at 50 oC in vacuum. X-ray diffraction (Bruker AXS D2) and SEM (JEOL 7610F) were performed to determine the phases and morphologies of the garnet electrolytes. The composition distribution of the elements was evaluated using ICP-OES (Thermo Fisher Scientific, iCAP 6300 Duo). To obtain the clear solution, the garnet samples were dissolved in aqua regia at 100 oC over 12 h in a sealed autoclave. The ionic conductivity was measured from 1 MHz to 1


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Hz (Autolab, 302N) in a cell sandwiching the composite electrolyte between stainless steels. The symmetric Li/composite solid electrolyte battery was prepared in a glove box.

Composite electrolyte, lithium metal, and composite cathode were used to construct solid lithium batteries. The composite cathode was prepared by mixing LiFePO4, Super P, PEO and LiTFSI at a ratio of weight of 60 : 10 : 20 : 10 in acetonitrile and was coating on Al current collector, and the active material mass loading in the cathode was about 1.0 mg cm-2. The composite electrolyte was consisting of 15 wt.% nanosheets obtained at calcining temperature of 800 oC.

RESULTS AND DISCUSSION GO-assisted wet-chemical conditions have been reported to synthesize large-size twodimensional nanomaterials.32,33 In the present work, we have successfully developed large-size nanosheets with cubic garnet structure by using GO as a template under coprecipitation conditions. Figure 1 schematically shows the procedure to synthesize garnet nanosheets. First, garnet precursors are uniformly mixed with GO, resulting in attraction of positive ions on the surface of GO, owing to the electrostatic attraction. The co-


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precipitation is generated by careful manipulation of pH after the attraction process, which will lead to a very thin garnet precursor layer on the surface of GO (GO@garnet precursors). Finally, the GO@garnet precursors are annealed in air, during which GO is sacrificed and the garnet nanosheets can be gained. On the other hand, the garnet nanoparticles are obtained by the same co-precipitation conditions, but without GO template. As shown in Figure 1, we further fabricate a composite solid polymer electrolyte filled with the garnet nanosheets, and make a comparison with garnet nanoparticle-filled electrolyte.


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Figure 1. Schematic diagram of preparation of garnet nanosheets, together with the comparison of composite solid polymer electrolytes consisting of garnet nanosheets nanoparticles.

The XRD patterns of garnet nanosheets and nanoparticles which were calcined at 750, 800, and 850 °C for 2 h are gave in Figure 2. In Figure 2a, the garnet nanoparticles that were calcined at 750 °C display a mixed structure of cubic and tetragonal phases, and the tetragonal phase is converted to cubic phase after calcining at 800 °C, accompanied by some impurity of Li2ZrO3. The garnet nanosheets that were calcined at 750 °C display cubic phase (PDF: 45-0109) and slight impurity of Li2ZrO3.34 The crystalline of cubic garnet is becoming distinct as the calcined temperature increasing to 800 and 850 °C, the impurity of Li2ZrO3 is also disappeared at higher calcined temperature and more than 750 °C. It is demonstrated that the GO not only regulates the garnet morphologies, but also decreases the calcination temperature of cubic phase. The as-prepared garnet precursors are always produced in an aggregated state when using co-precipitation, which in turn aggravating grain coalescence when calcining temperature ramps up. On


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the contrary, the GO is utilized as sacrificial template and to absorb the garnet precursors. The GO sheets will prevent the aggregation of the precursors. The efficient dispersion of the precursors is important to obtain nanostructured garnet. Further, the combustion of sacrificial GO at high temperature is helpful to crush the coalesced grains. On this basis, we hypothesized that garnet using GO sacrificial template, could result in fine grains and facilitate the reaction and prefer the cubic phase. The SEM images also display smaller grains of garnet with GO than that of without GO. Chan et al. 35 also reported that the nanoscaled ligaments facilitate the formation of cubic garnet phase using cellulosic fibers as templates. The dependent of phase evolution of garnet nanosheets on pH value is demonstrated, and the results of phase formation are showed in Figure 2b. To synthesize the garnet nanosheets by using GO template, three pH values of 8, 9.5, and 11 are performed. All of the samples display cubic garnet phases with calcination temperature of 800 oC and calcination time of 2 hours. It is noted that some impurity of Li2ZrO3 appeared with low pH value of 8 or high pH value of 11, the medium pH value of 9.5 is adaptive for formation of single cubic phase. Furthermore, with low pH, such as 8 and 7, the obtained weight of calcined powder was much lower than that of designed


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Page 14 of 37

composition. With pH of above 9, the obtained weight of calcined powder matched very well with that of designed composition. The calcined powder displays single cubic garnet phase by using GO template, owing to the even adsorption of garnet metal ions on the GO surface before co-precipitation, although the low pH is not enough to precipitate all of the garnet metal ions.

The chemical compositions of the nanosheets calcining at 800 oC are analyzed using ICP-OES. The molar ratio of the elements Li+ : Zr4+ : Nb5+ is 6.59 : 1.3 : 0.55. A lower Zr4+ content than the nominal composition is obtained, which is probably duo to the imperfect dissolution of oxides containing Zr4+ ions even in aqua regia solution. The Li+ and Nb5+ contents agree with the nominal composition, indicating that the excess of Li precursor compensates for lithium volatilization at calcining temperature of 800 oC.


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Figure 2. Phase structure of garnet nanosheets and nanoparticles under different calcination temperature and pH. (a) XRD patterns of the garnet precursors calcined at temperature of 750, 800, and 850 oC for 2 h, with and without GO template. (b) XRD patterns of the garnet precursors by using GO template calcined at the temperature of 800 oC for 2 h, under pH of 8, 9.5, and 11.

The garnet precursors with and without GO, were calcined at 750, 800, and 850 oC for 2h. The morphologies of garnet nanosheets and nanoparticles were examined by SEM (Figure 3a-h). The SEM image of calcined garnet powder without GO shows that the obtained garnet particles are about 0.5-1.0 μm in size (Figure 3a). These particles are actually the aggregation of nanoparticles of about 30-50 nm. This can be found in the


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magnified image (Figure 3e). The influence of calcining temperature on the morphology of nanosheets with GO template is studied. As shown in Figure 3b~h, garnet prepared by templating on GO can offer sheet-like morphology consists of numerous interconnected primary particles. It seems that the calcining temperature has no prominent influence on the morphology, but the size of nanosheets is dependent on the calcining temperature. As shown in Figure 3b & f, the nanosheets are about 1-2 μm in size and consist of primary particles in the size of 5-10 nm after calcined at 750 oC. In Figure 3c & g, the typical nanosheets size is about 1-5 μm after calcined at 800 oC, and each nanosheet is composed of primary particles of 10-20 nm in size. As shown in Figure 3d & h, the morphology shows nanosheets in the size of 5-10 μm as the calcined temperature ramps up to 800 oC, and high-temperature treatment coarsens the primary particles to be about 20-50 nm in size. TEM observations also reveal the two-dimensional morphologies of the calcined garnet with GO, as shown in Figure 3i-l, demonstrating effective templating of


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GO

in

the

formation

of

garnet

nanosheets.

Figure 3. Morphological characterizations of garnet nanosheets and nanoparticles. (a & e) SEM and magnified images of garnet nanoparticles annealed at 800 oC. (b & f) SEM and magnified images of garnet nanosheets annealed at 750 oC. (c & g) SEM and magnified images of garnet nanosheets annealed at 800 oC. (d & h) SEM and magnified images of garnet nanosheets annealed at 850 oC. (i) TEM image of GO. (j) TEM image of garnet nanosheets annealed at 800 oC under pH of 8. (k) TEM image of garnet


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nanosheets annealed at 800 oC under pH of 9.5. (l) TEM image of garnet nanosheets annealed at 800 oC under pH of 11.

The electrochemical impedance spectroscopy (EIS) was used to evaluate electrical property of the present composite electrolytes. Figure 4a presents the representative Nyquist profiles of the composite solid electrolytes filled with garnet nanosheets sandwiched between stainless steels at room temperature. The EIS profile shows a semicircle indicating a bulk relaxation, and an inclined line indicating a double layer capacitance.36 The interception of inclined line on Z’ is used to calculate the total conductivity. The 15 wt. %-garnet-nanosheet composite electrolyte possesses the superior ambient-temperature conductivity of 3.6×10-4 S cm-1, demonstrating four orders of magnitude higher than that of PEO-LiClO4 (~2×10-8 S cm-1).37 Thus our composite solid polymer electrolyte containing garnet nanosheets exhibits practically useful ionic conductivity. The composite electrolytes containing 15 wt. % and 25 wt.% garnet nanoparticles present similar room-temperature conductivities of 1.2×10-4 S cm-1 and 1.0×10-4 S cm-1, respectively. Therefore, the composite electrolyte consisting of garnet


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nanosheet possesses much higher conductivity compared with the nanoparticle-filled electrolyte, which is about three times (Figure 4b). As seen in Figure 4b, ionic conductivity of the present material is enhanced at 5 wt.% and achieves the maximum at 15 wt.%, following a significant decline at 25 wt%, which is consistent with the percolation behaviour.38 It is verified that the garnet nanosheet fillers exhibit superior conductivity enhancement to their particle counterparts. The lithium ions should pass through many particle−particle junctions in the nanoparticle-filled polymer electrolytes, while the junction cross might be decreased in the nanosheet-filled polymers due to the high aspect ratio of nanosheets.25 On the other hand, the dispersion of nanofillers is important to decrease the PEO crystallinity and thus a smaller size of the nanosheet is desired as larger sheets are harder to be dispersed.

To demonstrate the advantages of composite electrolytes, the properties of ceramic Li6.5La3Zr1.5Nb0.5O12, polymer PEO-LiClO4-50 wt.% EmimFSI, and composite PEOLiClO4-15 wt.% nanosheet-50 wt.% EmimFSI are compared. As seen in Figure 4c, the room-temperature ionic conductivity of ceramic Li6.5La3Zr1.5Nb0.5O12 is about 5×10-4 S cm-


19


1,

Page 20 of 37

higher than those of polymer PEO-LiClO4-50 wt.% EmimFSI and composites PEO-

LiClO4-15 wt.% nanosheets-50 wt.% EmimFSI. The highly conductive ceramic filler is advantageous to the conduction of composite electrolyte. It is notable that the ceramic pellet is stiff and brittle, and is hard to use in solid-state batteries, while the flexibility of the composite electrolyte is a superiority. We have clarified the influence of the calcining temperature on the morphologies of nanosheets. To further demonstrate the influence of morphology on the properties of the composites. Three types of composites of PEOLiClO4-15 wt.% nanosheets-50 wt.% EmimFSI are prepared, where the nanosheets are obtained at 750, 800, and 850 oC respectively. As can be seen in Figure 4c, the composite with nanosheet that is obtained at 800 oC possesses highest conductivity of 3.6×10-4 S cm-1, better than polymer PEO-LiClO4-50 wt.% EmimFSI. The conductivity of composite with nanosheet obtaining at 750 oC is higher than that of composite with nanosheet obtaining at 850 oC. The enhancement of conductivity for smaller-size fillers owes possibly to the conductive interfacial transport between the filler grains and the polymer matrix. In the present work, the size of nanosheets is enlarged with the increased temperature. On the other hand, the nanosheet exhibits impurity of Li2ZrO3 at temperature


20

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of 750 oC, though smallest size. The impurity hinders carrier mobility. On contrary, the nanosheet presents single cubic phase and smaller size at temperature of 800 oC, thus leading to superior electrical conductivity. Figure 4d exhibits the Arrhenius curve of electrical conductivity of the composite electrolyte PEO-LiClO4-50 wt.% EmimFSI with 15 wt.% nanosheets obtained at 800 oC. The activation energy is calculated with Arrhenius equation: 𝐸𝑎

(1)

σ = Aexp( ― 𝑘𝑇)

where Ea, , T, A, and k are activation energy, electrical conductivity, absolute temperature,

pre-exponential factor, and Boltzmann constant, respectively. Ea is

calculated to be 0.33 eV, which is lower than that of PEO-LLZ composite electrolyte, and is close to that of PEO-LLZ composite electrolyte with plasticizer succinonitrile in the high temperature range.39 The presence of highly conductive ionic liquid EmimFSI is also beneficial to the ions conduction thus relatively low activation energy.


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Figure 4. Conductive performance of composite solid electrolytes. (a) EIS profiles of the composite electrolytes filled with 5-35 wt.% garnet nanosheets. (b) Conductivity comparison of the composite electrolytes filled with garnet nanosheets and nanoparticles. (c) EIS profiles of ceramic Li6.5La3Zr1.5Nb0.5O12, polymer PEO10-LiClO4-50 wt.%, and composite electrolytes filled with 15 wt.% garnet nanosheets calcined at 750, 800, and


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850 oC. (d) Arrhenius plot of the 15 wt.% -garnet-nanosheet composite electrolyte calcined at 800 oC.

Symmetric lithium metal-composite electrolyte cell is fabricated to assess the mechanical stability of the composite solid polymer electrolyte containing 15 wt.% garnet nanosheets against Li dendrites. As seen in Figure 5a, the symmetric cell is cycling over 200 h at 0.1 mA cm-2 and 40 oC. The charge and discharge processes were periodically conducted for 1.0 h. The positive and negative voltages represent Li stripping and plating, respectively. The Li/composite/Li symmetric battery shows smooth plating/stripping voltages (inset in Figure 5a). A small voltage fluctuation is observed throughout the longterm cycling (Figure 5a). This is might be because of the temperature fluctuation and/or the insufficient interfacial quality between composite electrolyte and lithium metal during the repeating process of Li stripping/plating, illustrated by the EIS plots of the battery before and after cycling for 200 h (Figure 5b). The low-frequency depressive semicircle indicates the interfacial behavior between composite electrolyte and lithium metal. The high-frequency semicircles represents the impedance of composite electrolyte. The


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interfacial resistance between electrolyte and metallic lithium is increased during cycling, indicated by the lower-frequent semicircles. The interfacial resistance is increased from 480 Ω cm2 to 530 Ω cm2 after cycling. This is might be because the low temperature of 40 oC

is insufficient to soften the composite solid electrolyte to wet the lithium metal. The

high-frequency semicircles indicate relatively stable bulk impedance of the composite solid electrolyte during cycling. A bulk resistance of 45 Ω cm2 for the composite electrolyte is obtained. The relatively stable voltage and interfacial impedance demonstrate good performance of the composite electrolyte. The highly chemically/electrochemically stable and conductive ceramic fillers will prevent the interfacial reactions between lithium metal and PEO, which can achieve stable interfaces and long-term cycling.40


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Figure 5. Electrochemical performance of the composite solid polymer electrolyte containing 15 wt.% garnet nanosheets performed in the symmetric Li/electrolyte/Li cell. (a) Galvanostatic cycling of Li/electrolyte/Li cell at 0.1 mA cm-2 and 40 oC. The inset is local view of voltage profiles at 20-24 h and 180-184 h. (b) Nyquist plots of the composite solid polymer symmetric cell before cycling and after cycling at 0.1 mA cm-2 for 200 h.

The solid Li/LiFePO4 battery assembled with the composite solid electrolytes was charged to 4.0 V and discharged to 2.0 V at 0.05C and 40 oC. Figure 6a illustrates the capacity-voltage plots of the 1st, 15th, and 30th cycle of the Li/LiFePO4 cell. The cell exhibits typical potential plateaus around 3.3 V and 3.5 V at 0.05C, representing discharge and charge of LiFePO4, respectively. The 1st, 15th, and 30th discharge capacity is 98.1 mAh g-1, 98.1 mAh g-1 and 95.6 mAh g-1, respectively. That is below the theoretical capacity of LiFePO4, which might be because of the low working temperature and insufficient interfacial contact between electrodes and electrolyte. On the hand, the capacity retention is 97.5% after 30 cycles, indicating good cycling stability. The discharge capacity is relatively stable and the coulombic efficiency is maintained at ＞ 96%


25


Page 26 of 37

throughout cycling (Figure 6b). The electrochemically stable composite solid electrolyte may inhibit harmful interfacial side reactions between the electrodes and electrolyte, leading to relatively good cycling property.

Figure 6. (a) Capacity-voltage plots of the LiFePO4/composite electrolyte/Li cell at 0.05C and 40 oC. (b) Cycling performance of LiFePO4/composite electrolyte/Li cell at 0.05C and 40 oC.

CONCLUSIONS In conclusion, garnet nanosheets have been successfully fabricated by using GO as a template via co-precipitation condition for the first time. The garnet nanosheets construct


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an interconnected structure that offers continuous Li-ions transport pathway and affords structural robustness to the polymer framework. The findings clarify the positive effect of garnet nanosheets on the electrical performance of polymer electrolyte, compared with their counterparts of nanoparticles. 15 wt.% -garnet-nanosheet composite electrolyte demonstrates promising room-temperature conductivity of 3.6×10-4 S cm-1, among the best reported value to date. Moreover, the composite electrolyte can robustly isolate Li dendrites in a symmetric Li metal-composite electrolyte battery upon reversible cycling at a current density of 0.1 mA cm-2 over 200 h and temperature of 40 oC. The relatively stable voltage, bulk impedance, and low interfacial resistance demonstrate good performance of the composite electrolyte. The solid-state Li/LiFePO4 cell exhibits an initial discharge capacity of 98.1 mAh g-1 and a capacity retention of 97.5% after 30 cycles at a current rate of 0.05C and temperature of 40 oC. The present work first constructs, to our best knowledge, two-dimensional Li-conducting ceramic materials dispersion in PEO matrix, demonstrating potential to Li-metal batteries.

AUTHOR INFORMATION


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*Corresponding author.

E-mail addresses: [email protected] (S.F. Song), [email protected] (N. Hu)

Notes The authors declare no competing financial interest.

ACKNOWLEDGMENTS This work is supported by the National Natural Science Foundation of China (No. 51702030 and No. 11632004, and No. U1864208), Shanghai Aerospace Science and Technology Innovation Fundation (No. SAST2017-137), Chongqing University, the Fundamental Research Funds for the Central Universities (No. 2018CDXYHK0016), the Key Program for International Science and Technology Cooperation Projects of the Ministry of Science and Technology of China (No. 2016YFE0125900).

REFERENCES (1) Sun, C. W.; Liu, J.; Gong, Y. D.; Wilkinson D. P.; Zhang, J. J. Recent advances in all-solid-state rechargeable lithium batteries. Nano Energy 2017, 33, 363-386.


28

Page 29 of 37 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


(2) Hou, H. D.; Xu, Q. K.; Pang, Y. K.; Li, L.; Wang, J. L.; Zhang, C.; Sun, C. W. Efficient storing energy harvested by triboelectrical nanogenerators using a safe and durable allsolid-state sodium-ion battery. Adv. Sci. 2017, 4, 1700072. (3) Armand, M. B.; Chabagno, J.-M.; Duclot, M. J. In fast ion transport in solids: electrodes and electrolytes. North-Holland, New York, 1979, 131-136. (4) Lightfoot, P.; Mehta, M. A.; Bruce, P. G. Crystal-structure of the polymer electrolyte poly(ethylene oxide)3 LiCF3SO3. Science 1993, 262, 883-885. (5) Fullerton-Shirey, S. K.; MaranHas, J. K. Effect of LiClO4 on the structure and mobility of PEO-based solid polymer electrolytes. Macromolecules 2009, 42, 2142-2156. (6) Zardalidis, G.; Ioannou, E.; Pispas, S.; Floudas, G. Relating structure, viscoelasticity, and local mobility to conductivity in PEO/LiTf electrolytes. Macromolecules 2013, 46, 2705-2714. (7) Kim, Y. T.; Smotkin, E. S. The effect of plasticizers on transport and electrochemical properties of PEO-based electrolytes for lithium rechargeable batteries. Solid State Ionics 2002, 149, 29-37.


29


Page 30 of 37

(8) Fan, L. Z.; Maier, J. Composite effects in poly(ethylene oxide)-succinonitrile based all-solid electrolytes. Electrochem. Commun. 2006, 8, 1753-1756. (9) Croce, F.; Appetecchi, G. B.; Persi, L.; Scrosati, B. Nanocomposite polymer electrolytes for lithium batteries. Nature 1998, 394, 456-458. (10) Croce, F.; Curini, R.; Martinelli, A.; Persi, L.; Ronci, F.; Scrosati, B. J. Physical and chemical properties of nanocomposite polymer electrolytes. Phys. Chem. B 1999, 103, 10632-10638. (11) Ji, K. S.; Moon, H. S.; Kim, J. W.; Park, J. W. Role of functional nano-sized inorganic fillers in poly(ethylene) oxide-based polymer electrolytes. J. Power Sources 2003, 117, 124-130. (12) Zhou, W. D.; Gao, H. C.; Goodenough, J. B. Cross-linked chitosan as a polymer network binder for an antimony anode in sodium-ion batteries. Adv. Energy Mater. 2016,

6, 1501802. (13) Lin, D. C.; Liu, W.; Liu, Y. Y.; Lee, H. R.; Hsu, P. C.; Liu, K.; Cui, Y. High ionic conductivity of composite solid polymer electrolyte via in situ synthesis of monodispersed SiO2 nanospheres in poly(ethylene oxide). Nano Lett. 2016, 16, 459-465.


30

Page 31 of 37 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


(14) Shin, J. H.; Henderson, W. A.; Passerini, S. Ionic liquids to the rescue? Overcoming the ionic conductivity limitations of polymer electrolytes. Electrochem.

Commun. 2003, 5, 1016-1020. (15) Song, S. F.; Yang, S.; Zheng, F.; Zeng, K. Y.; Duong, H. M.; Savilov, S. V.; Aldoshin, S. M.; Hu, N.; Lu, L. Poly(ethylene oxide)-immobilized ionogel with high ionic liquid loading and superior ionic conductivity. J. Electrochem. Soc. 2016, 163, A2887A2889. (16) Song, S. F.; Kotobuki, M.; Zheng, F.; Xu, C. H.; Savilov, S. V.; Hu, N.; Lu, L. A hybrid polymer/oxide/ionic-liquid solid electrolyte for Na-metal batteries. J. Mater. Chem.

A 2017, 5, 6424-6431. (17) Walls, H. J.; Riley, M. W.; Singhal, R. R.; Spontak, R. J.; Fedkiw, P. S.; Khan, S. Nanocomposite electrolytes with fumed silica and hectorite clay networks: Passive versus active fillers. Adv. Funct. Mater. 2003, 13, 710-717. (18) Hayamizu, K., Aihara, Y.; Arai, S.; Martinez, C. G. Pulse-gradient spin-echo H-1, Li-7, and F-19 NMR diffusion and ionic conductivity measurements of 14 organic electrolytes containing LiN(SO2CF3)(2). J. Phys. Chem. B 1999, 103, 519-524.


31


Page 32 of 37

(19) Li, Y. T.; Xu, B.; Xu, H.; Duan, H.; Lu, 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. Chem. Int. Ed. 2017, 56, 753-756. (20) Wang, C.; Yang, Y.; Liu, X.; Zhong, H.; Xu, H.; Xu, Z.; Shao, H.; Ding, F. Suppression of lithium dendrite formation by using LAGP-PEO (LiTFSI) composite solid electrolyte and lithium metal anode modified by PEO (LiTFSI) in all-solid-state lithium batteries. ACS Appl. Mater. Interfaces 2017, 9, 13694-13702. (21) Chen, R.; Zhang, Y.; Liu, T.; Xu, B.; Lin, Y.; Nan, C. W.; Shen, Y. High capacity, superior cyclic performances in all-solid-state lithium-ion batteries based on 78Li(2)S22P(2)S(5) glass-ceramic electrolytes prepared via simple heat treatment. ACS Appl.

Mater. Interfaces 2017, 9, 9654-9661. (22) Zhao, Y.; Huang, Z.; Chen, S.; Chen, B.; Yang, J.; Zhang, Q.; Ding, F.; Chen, Y.; Xu, X. X. A promising PEO/LAGP. hybrid electrolyte prepared by a simple method for allsolid-state lithium batteries. Solid State Ionics 2016, 295, 65-71.


32

Page 33 of 37 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


(23) Ban, X. Y.; Zhang, W. Q.; Chen, N.; Sun, C. W. A high-performance and durable poly(ethylene oxide)-based composite solid electrolyte for all solid-state lithium battery.

J. Phys. Chem. C 2018, 122, 9852-9858. (24) Zhang, J.; Zhao, N.; Zhang, M.; Li, Y.; Chu, P.; Guo, X.; Di, Z.; Wang, X.; Li, H. Flexible and ion-conducting membrane electrolytes for solid-state lithium batteries: Dispersion of garnet nanoparticles in insulating polyethylene oxide. Nano Energy 2016,

28, 447-454. (25) Liu, W.; Liu, N.; Sun, J.; Hsu, P.; Li, Y.; Lee, H.; Cui, Y. Ionic conductivity enhancement of polymer electrolytes with ceramic nanowire fillers. Nano Lett. 2015, 15, 2740-2745. (26) Zhang, Y.; Lai, J. Y.; Gong, Y. D.; Hu, Y. M.; Liu, J.; Sun, C. W.; Wang, Z. L. A safe high-performance all-solid-state lithium-vanadium battery with a freestanding V2O5 nanowire composite paper cathode. ACS Appl. Mater. Interfaces 2016, 8, 34309-34316. (27) Fu, K.; Gong, Y.; Dai, J.; Gong, A.; Han, X.; Yao, Y.; Wang, C.; Wang, Y.; Chen, Y.; Yan, C.; Li, Y.; Wachsmana, E. D.; Hu, L. B. Flexible, solid-state, ion-conducting


33


Page 34 of 37

membrane with 3D garnet nanofiber networks for lithium batteries. Proc. Natl. Acad. Sci. 2016, 113, 7094-7099. (28) Gong, Y. H.; Fu, K.; Xu, S. M.; Dai, J. Q.; Hamann, T. R.; Zhang, L.; Hitz, G. T.; Fu, Z. Z.; Ma, Z. H.; McOwen, D. W.; Han, X. G.; Hu, L. B.; Wachsman, E. D. Lithium-ion conductive ceramic textile: A new architecture for flexible solid-state lithium metal batteries. Mater. Today 2018, 21, 594-601. (29) Zhang, W. Q.; Nie, J. H.; Li, F.; Wang, Z. L.; Sun, C. W. A durable and safe solidstate lithium battery with a hybrid electrolyte membrane. Nano Energy 2018, 45, 413-419. (30) Ohta, S.; Kobayashi, T.; Asaoka, T. High lithium ionic conductivity in the garnettype oxide Li7-XLa3(Zr2-X, Nbx)O12 (X=0-2). J. Power Sources 2011, 196, 3342-3345. (31) Marcano, D. C.; Kosynkin, D. V.; Berlin, J. M.; Sinitskii, A.; Sun, Z.; Slesarev, A.; Alemany, L. B.; Lu, W.; Tour, J. M. Improved synthesis of graphene oxide. ACS Nano 2010, 4, 4806-4814. (32) Zhao, H.; Zhu, Y.; Li, F.; Hao, R.; Wang, S.; Guo, L. A generalized strategy for the synthesis of large-size ultrathin two-dimensional metal oxide nanosheets. Angew. Chem.

Int. Ed. 2017, 56, 1-6.


34

Page 35 of 37 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


(33) Wu, G.; Shen, Q.; Yu, H.; Zhao, T.; Lu, C.; Liu, A. Reduced graphene oxide encapsulated Cu2O with controlled crystallographic facets for enhanced visible-light photocatalytic degradation. Funct. Mater. Lett. 2017, 10, 1750034. (34) Qin, S.; Zhu, X.; Jiang, Y.; Ling, M.; Hu, Z.; Zhu, J. Extremely dense microstructure and enhanced ionic conductivity in hot-isostatic pressing treated cubic garnet-type solid electrolyte of Ga2O3-doped Li7La3Zr2O12. Funct. Mater. Lett. 2018, 11, 1850029. (35) Gordon, Z. D.; Yang, T.; Morgado, G. B. G.; Chan, C. K. Preparation of nano- and microstructured garnet Li7La3Zr2O12 solid electrolytes for Li-ion batteries via cellulose templating. ACS Sustain. Chem. Eng. 2016, 4, 6391-6398. (36) Song, S.; Dong, Z.; Deng, F.; Hu, N. Lithium superionic conductors Li10MP2O12 (M = Ge, Si). Funct. Mater. Lett. 2018, 11, 1850039. (37) Wen, Z. Y.; Wu, M.; Itoh, T.; Kubo, M.; Lin, Z. X.; Yamamoto, O. Effects of alumina whisker in (PEO)(8)-LiClO4-based composite polymer electrolytes. Solid State Ionics 2002, 148, 185-191. (38) Roman, H. E.; Bunde, A.; Dieterich, W. Conductivity of dispersed ionic conductorsA percolation model with 2 critical-points. Phys. Rev. B 1986, 34, 3439-3445.


35


Page 36 of 37

(39) Zha, W.; Chen, F.; Yang, D.; Shen, Q.; Zhang, L. High-performance Li6.4La3Zr1.4Ta0.6O12/poly(ethylene oxide)/succinonitrile composite electrolyte for solidstate lithium batteries. J. Power Sources 2018, 397, 87-94. (40) Chen, L.; Li, Y. T.; Peng, S.; Fan, L. Z.; Nan, C. W.; Goodenough, J. B. PEO/garnet composite electrolytes for solid-state lithium batteries: From “ceramic-in-polymer” to “polymer-in-ceramic”. Nano Energy 2018, 46, 176-184.

For Table of Contents Use Only


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Graphene oxide-templated lithium garnet nanosheets promise composite solid polymer electrolytes impressive electrochemical performance.


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Composite Solid Polymer Electrolyte with Garnet Nanosheets in Poly

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