Stable Cycling Lithium−Sulfur Solid Batteries with Enhanced Li/Li10GeP2S12 Solid Electrolyte Interface StabilityEdiga Umeshbabu,† Bizhu Zheng,† Jianping Zhu,† Hongchun Wang,‡ Yixiao Li,† and Yong Yang*,†,‡

†Collaborative Innovation Center of Chemistry for Energy Materials, State Key Laboratory for Physical Chemistry of Solid Surface,College of Chemistry and Chemical Engineering, and ‡College of Energy, Xiamen University, Xiamen 361005, China

*S Supporting Information

ABSTRACT: We herein explore a facile and straightforward approachto enhance the interface stability between the lithium superionicconducting Li10GeP2S12 (LGPS) solid electrolyte and Li metal byemp l o y i n g i on i c l i q u i d s u ch a s 1 M l i t h i um b i s -(trifluoromethanesulfonyl)imide (LiTFSI)/N-methyl-N-propylpyrroli-dinium bis(trifluoromethanesulfonyl)imide (PYR13TFSI) as the inter-face modifier. The results demonstrated the presence of 1 M LiTFSI/PYR13TFSI ionic liquid; the interface stability at the electrode/solidelectrolyte (i.e., Li/LGPS) was improved remarkably by forming an insitu solid electrolyte interphase (SEI) layer. As a result, an effectivelyreduced interfacial resistance from 2021 to 142 Ω cm2 and stable Listripping/plating performance (over 1200 h at 0.038 mA cm−2 and 1000h at 0.1 mA cm−2) were achieved in the Li/LGPS/Li symmetric cells.On this basis, the Li−S solid-state batteries were further architecturedwith one of the S@C composite [where C is the ketjen black carbon (KBC) or PBX 51-type activated carbon (PBX51C) ormultiwalled carbon nanotubes (MCNTs)] cathode and the LGPS solid electrolyte. The batteries with S@KBC electrodesdelivered an excellent discharge/charge performance with a high initial discharge capacity of 1017 mA h g−1 and better stabilitythan those of the batteries with the S@PBX51C and S@MCNTs electrodes. High surface area, unique beneficial pore structure,and better particle dispersion of sulfur in the S@KBC composite facilitate high sulfur utilization and also increase the intimatecontact between the electrode and LGPS solid electrolyte during the discharge/charge process.

KEYWORDS: lithium−sulfur batteries, Li10GeP2S12 solid electrolyte, carbon materials, ionic liquid,electrode/electrolyte interface stability

1. INTRODUCTION

Replacing the flammable liquid electrolytes with incombustibleinorganic solid electrolytes (SEs) in Li−S batteries haveattracted widespread attention owing to its myriad advantages,such as safety, reliability, high energy density, long life-span,inhibition of polysulfide dissolution and the ability to preventLi dendrite growth.1−7 Moreover, the sulfur working cathode isnontoxic, earth-abundant, low-cost, and has a high theoreticalcapacity of 1675 mA h g−1.8 Nevertheless, the solid-state Li−Sbatteries (SSLSBs) possess several bottlenecks that mainlyconcentrate at the electrode/electrolyte interface region.2,9−13

The bottlenecks mainly arise from highly insulating nature ofsulfur (σ = 5 × 10−30 S/cm at 25 °C) limiting the activematerial utilization, which impedes the transfer of Li ions andelectrons, and also arise from poor compatibility and stabilityof the SEs against the electrodes (including both anode andcathode), which deteriorate the electrode/SE interface andfurther increase the interfacial resistance for mass and chargetransfer. As a result of these obstacles, the battery cells becomeinefficient and often lead to performance failure during therepeated electrochemical discharge/charge cycles. Therefore,the development of the favorable electrode/electrolyte inter-

face region, including the cathode/SE and anode/SE inSSLSBs is a key challenge to achieve better performance andlong endurance.A number of breakthroughs have been reported to increase

conductivity, sulfur utilization as well as overcome the stress/strain barriers in SSLSBs.14−19 One prevailing approach tosurmount these difficulties is unifying the sulfur with anelectrically conducting material (e.g., Cu metal or nanocarbon)and ionically conducting SE (e.g., Li3PS4) under ball-millingand/or liquid phase approach not only increasing the electron-conducting path but also enhancing the Li+ conduction pathinto the sulfur materials.6,20,21 For instance, Nagao et al.7

synthesized composite working electrodes comprising of sulfur,Li2S -P2S5 SE, and acetylene black (AB), by using hand groundwith mortar and high-energy ball-milling approaches. Inanalogy with physical mixing, the ball-milled composite asthe working electrode exhibited an excellent discharge/chargeperformance and favorable intimate electrode/electrolyte

Received: February 28, 2019Accepted: April 29, 2019Published: April 29, 2019

Research Article

www.acsami.orgCite This: ACS Appl. Mater. Interfaces 2019, 11, 18436−18447

© 2019 American Chemical Society 18436 DOI: 10.1021/acsami.9b03726ACS Appl. Mater. Interfaces 2019, 11, 18436−18447

Dow

nloa

ded

via

XIA

ME

N U

NIV

on

Aug

ust 1

, 201

9 at

03:

05:1

8 (U

TC

).Se

e ht

tps:

//pub

s.ac

s.or

g/sh

arin

ggui

delin

es f

or o

ptio

ns o

n ho

w to

legi

timat

ely

shar

e pu

blis

hed

artic

les.

contacts in SSLSBs. Yao et al.4 fabricated reduced grapheneoxide with nanosized (2 nm) sulfur coating to render theinterfacial resistance and stress/strain of the sulfur positiveelectrodes. SSLSBs by this cathode (0.4−0.5 mg cm−2

loadings) exhibit an excellent performance (capacity retentionof 830 mA h g−1 after 750 cycles at 1 C and 60 °C) and a smallinterface resistance at the electrode/electrolyte interface. Morerecently, Janek and co-workers17 developed a novel and newhot-press setup to minimize the interfacial resistances betweenthe sulfur electrode and the Li7P3S11 SE in SSLSBs. Byintroducing this methodology, the grain boundary andinterfacial resistance could minimize greatly and empower afast ion transport through the interface and bulk. Inconsequence, a high sulfur utilization of 82% (correspondingcapacity is 1370 mA h g−1) and promising cycling- and ratecapability are achieved in solid-state Li−In/Li7P3S11/S-composite batteries.To achieve SSLSBs with high energy density compared to

the contemporary conventional Li−S batteries, utilization ofthe Li metal as the anode is prerequisite as it improves the cellvoltage and specific capacity.22,23 Unfortunately, most of SEssuch as Li10GeP2S12 (LGPS), Li10SnP2S12 (LSPS), Li7P3S11,Li1.5Al0.5Ge1.5(PO4)3 (LAGP), and so forth are not compatiblewith the Li metal anode, which is a focal impediment for thebattery performance.16−18,24−27 Moreover, it has been reportedthat these SEs will undergo reduction reactions by consuminglithium ions and electrons from the lithium metal anode andform the interface layer, which is so-called the solidelectrolyte interphase (SEI) between the SE and Li metalelectrode.28 If the formed SEI layer has high lithium ionicconductivity and minimal electronic conductivity, the SEI layeracts as a protective layer to impede further reactions betweenthe Li metal and the SEs. Such kind of behavior observedusually in the LiPON, Li7P3S11, and Li6PS5Cl SEs system.29−31

However, if the SEI layer is a mixed electronic and Li ionconductor, it will continue to grow as long as contact isperpetuated between SEs and Li metal. This result in thecontinuous degradation of SEs and the growth of interfaciallayers causing capacity fading, increased resistance, and short-circuiting of the cell. The SEs of LAGP, LGPS, and LSPS arethe classical examples for this category.24,32,33

The interfacial barriers such as large interfacial resistanceand incompatibility between the Li metal and SEs have beententatively approached in several ways by many researchgroups.13,34−37 For instance, the surface amendments of SEsand/or the passivation lithium metal electrodes.34−43 Gen-erally, elements/compounds such as Si, Ge, Au, LiH2PO4, andso forth have been adopted to improve the interface betweenthe SE and Li metal.34,37,41 Another approach is alloying of thethin-film/bulk-type Li metal.13,15 For instance, a Li−In metalalloy with a voltage of 0.62 V versus Li/Li+ has beenconsidered as an anode in Li−S solid-state batteries tosuppress the reduction interface reactions of SEs.16,17 Thethird approach is an accommodation of dual-layer SEconfiguration such as LGPS@75%Li2S−24%P2S5−1%P2O5,where 75%Li2S−24%P2S5−1%P2O5 performs as the stableinterface layer against the Li anode in order to avoid thereduction of the Li metal with LGPS SE.4,19 However, theaforementioned approaches are expensive, quite complicated,and also time-consuming. In fact, some of the approaches,particularly utilization of Li−M alloy as the anode mitigate thecell voltage and thus sacrifice the energy density.

Recently, incorporation of ionic liquids (ILs) into SEs hasbecome a promising approach to improve the interfacecompatibility across the electrode and SE, owing to theirsuperior safety properties such as low vapor pressure,nonflammability, less volatility, high Li ionic conductivity,high voltage stability windows, and excellent thermal stabilitycompared to organic liquid electrolytes.12,44−46 Among theexisting ILs, the pyrrolidinium-based ILs and which consistingof the bis(trifluoromethanesulfonyl)imide (TFSI−) aniondemonstrate their applications in high-performance solid-state Li batteries.12,46 For example, Oh et al. reported thatthe incorporat ion of a smal l quant i ty of [Li -(triglyme)]+[TFSI]− solvate IL to the composite cathodecould effectively transform the contact mode from solid−solidto solid−liquid and afford an excellent Li+ conducting networkso that it could ensure intimate contact across electroactivematerial particles and the Li3PS4 SE.

45 We have also recentlydemonstrated that addition of IL such as lithium bis-(trifluoromethanesulfonyl)imide (LiTFSI)/N-methyl-N-pro-pylpyrrolidinium bis(trifluoromethanesulfonyl)imide(PYR13TFSI) on the LSPS SE surface improves the Li/LSPSinterface stability.12 The formation of an SEI layer throughdecomposition of IL is imperative in enhanced electrode/SEinterface. As a result, a small interfacial resistance and anexcellent stripping/plating stability are achieved in Li−metalsolid-state batteries. It is further interesting and challengingthat along with the enhancing Li/SEs interface, the improve-ment of the cathode/SE interface is also an imperative in orderto improve the overall cell energy density, rate capability, andcycling stability. Moreover, the effects of different hierarchicalcarbon additives on sulfur cathode performance in SSLSBshave not been reported yet.In this work, enhancement of the compatibility of lithium

superionic conducting LGPS SE with the Li metal is eventuallyachieved by promoting 1 M LiTFSI/PYR13TFSI IL as theLGPS SE surface modifier. Meanwhile, the effects of carbonadditives on sulfur composite cathodes are also studied in Li−Ssolid batteries. The systematic and comprehensive experimentresults demonstrate that the addition of a small amount of ILremarkably stabilized the LGPS SE interface with the Li metalanode by forming an in situ SEI layer on the Li metalelectrode. In consequence, a small interfacial impedance andstable Li strip/plat cycling life are achieved in Li/LGPS/Lisymmetric cells. Moreover, such a high-interface stabilizedLGPS SE combined with the S@ketjen black carbon (KBC)working electrode in Li−S solid-state batteries displayed a highcapacity and exhibited better cycle performance than the cellswith S@PBX 51-type activated carbon (PBX51C) and S@multiwalled carbon nanotube (MCNTs) electrodes.

2. EXPERIMENTAL SECTION2.1. Chemicals and Materials. In our experiments, all the

chemicals we used were of analytical grade and employed as receivedwithout further purification. LGPS SE (Hefei Kejing MaterialsTechnology Co., Ltd, China), elemental sulfur (Sinopharm ChemicalReagent Co., Ltd, China), Ketjenblack EC-600JD carbon (LionCorporation), PBX51C (Cabot Corporation), and multiwalled carbonnanotubes (Graphistrength C100, Arkema), PYR13TFSI IL (ShanghaiCheng Jie Corporation Co., Ltd., China), and LiTFSI (ZhuhaiSmoothway Electronic Materials, China).

2.2. Preparation of Sulfur@Carbon Composites. A sulfur/ketjen carbon (S@KBC) composite was fabricated by ball-millingfollowed by a thermal annealing process. Typically, the elementalsulfur and KBC (1:1 in wt) were mixed thoroughly by ball milling for

ACS Applied Materials & Interfaces Research Article

DOI: 10.1021/acsami.9b03726ACS Appl. Mater. Interfaces 2019, 11, 18436−18447

18437

0.5 h at 300 rpm and for 5 h at 500 rpm. Then, the mixture wastransferred to the ampoule, sealed in a stainless steel autoclave, andheated at 155 °C for 12 h under an argon atmosphere to achieve theS@KBC composite. Similarly, the sulfur@carbon composites such asS@PBX51C and S@MCNTs composites with 1:1 in wt wereobtained by a similar method.2.3. Preparation of 1 M LiFSI/PYR13TFSI IL. The preparation of

1 M IL such as LiTFSI salt dissolved in PYR13TFSI IL was detailed inour previous study.12 The room temperature (RT) ionic conductivityof 0.639 mS cm−1 for freshly prepared 1 M LiTFSI/PYR13TFSI ILwas measured with a DDS-307A conductivity meter.2.4. Materials Characterization. The sample X-ray diffractom-

eter (XRD) patterns were collected with XRD (Rigaku Ultima IV)employing Cu Kα (40 kV, 30 mA) as the radiation source. The SEand cathode composite samples were covered with a Mylar film tocircumvent detrimental side reactions with moist air. The phase purityand crystal lattice constants of the LGPS SE were identified by meansof Rietveld refinement analysis using the General Structure AnalysisSystem (GSAS) program. Morphology, microstructure, and elementaldistribution of the samples were performed by Hitachi S-4800 fieldemission scanning electron microscopy (SEM) equipped with anenergy-dispersive spectrometry (EDS) instrument. For SEM of LGPSand cathode composite samples, an airtight specimen holder wasutilized to fully circumvent moisture and air adulteration duringsample transfer. Transmission electron microscopy (TEM) pictureswere collected on a JEOL JEM-2100 machine. The sulfur content inthe different S@C composites was analyzed by thermogravimetricanalysis (TGA) using a STA 409 PC thermal analyzer (Netzsch,Germany). An Xplora Raman spectrometer (Horiba JY) with anexcitation laser line of 638 nm was employed to collect Raman spectraof the samples at RT. The nitrogen adsorption/desorption isothermswere obtained on a Micromeritics ASAP 2020 surface analyzer tocompute the Brunauer−Emmett−Teller (BET) surface area of thesamples. The pore size distribution plots were acquired by theBarrett−Joyner−Halenda (BJH) method. X-ray photoelectron spec-troscopy (XPS) measurements were obtained by a PHI 5000 VersaProbe III spectrometer (ULVAC-PHI, Japan) using Al Kα as the X-ray source. The observed binding energies were calibrated based onthe C 1s peak (284.8 eV).2.5. Battery Assembly. 2.5.1. Symmetric C/LGPS/C Cells. To

quantify Li ionic conductivity of LGPS SE, Li-ion blocking symmetriccells, C/LGPS/C was fabricated. For this, first 150 mg of the LGPSSE powder was cold-pressed into a dense pellet at a pressure of 360

MPa. Pressing was performed using a test cell, with a polytetrafluoro-ethylene (PTFE) cylinder body having an inner diameter of 10 mm.The carbon-coated Al foils as blocking electrodes were then laid onboth sides of the LGPS pellet by pressing at a pressure of 360 MPa.

2.5.2. Symmetric Li/LGPS/Li Cells. The symmetric Li/LGPS/Licells were fabricated as follows. First, 75 mg of the LGPS SE powderwas put in a 10 mm PTFE tube and cold-pressed at a pressure of 360MPa for 2 min. Subsequently, one drop (about 10 μL) of 1 MLiTFSI/PYR13TFSI IL was evenly spread on each side of the LGPSpellet surface and two Li metal foils with 2 mm thick were then tightlypressed by hands onto the two surfaces of the LGPS pellet to make anintimate contact between them. Similarly, the pristine Li/LGPS/Licells were also assembled by a similar procedure but no spreading ofLiTFSI/PYR13TFSI IL on the LGPS pellet surface.

2.5.3. Quasi-Solid-State S@C/LGPS/Li Cells. Quasi-solid-state S@C/LGPS/IL/Li batteries were architectured in a custom-madeSwagelok cell. Prior to cell assembly, the electrode compositeconsisting of 40 wt % of S@C (C = KBC or PBX51C or MCNTs)composite, 50 wt % LGPS SE, and 10 wt % AB was mixed with handand ground by mortar and pestle for 2 h, in order to achieve ahomogeneous mixture. For the cell assembly, 75 mg of the LGPSelectrolyte powder was placed into a 10 mm diameter mold and cold-pressed at a 360 MPa. One side of the produced SE pellet wasuniformly covered with 5 mg of the composite cathode, followed bypressing at a 360 MPa. Subsequently, one drop of 1 M IL was spreadonto the anode side of the LGPS SE pellet surface and a Li metal foilwas then attached by hand-pressing. For comparison, bare S@C/LGPS/Li solid-state cells were also prepared by a similar processwithout the addition of 1 M LiTFSI/IL. The sulfur loading in each ofthe cell is 1.28 mg cm−2.

Typical testing systems for batteries (both symmetrical and Li−Ssolid-state batteries) rely on a custom-made Swagelok-type cell systemand the cell assembly processes were conducted under an argonatmosphere in a dry glovebox (H2O and O2 <1 ppm).

2.6. Electrochemical Measurements. The electrochemicalimpedance spectroscopy (EIS) measurements of the cells wereperformed on a VersaSTAT MV multichannel potentiostat/galvanostat instrument with frequency range from 1 Hz to 1 MHz.The galvanostatic charge/discharge (GCD) measurements wereperformed on a multichannel battery test system (LAND CT-2001A Wuhan, China). The galvanostatic lithium plating/strippingcycling was conducted on Li/LGPS/Li cells at fixed biased currentdensities of 0.038 and 0.1 mA cm−2 by periodically charging for 1 h

Figure 1. (A) SEM image, (B) Raman spectrum, (C) X-ray Rietveld refinement patterns, and (D) Nyquist plot of the LGPS SE.

ACS Applied Materials & Interfaces Research Article

DOI: 10.1021/acsami.9b03726ACS Appl. Mater. Interfaces 2019, 11, 18436−18447

18438

and discharging for 1 h. Discharge and charge measurements of theS@C cathodes in Li−S quasi-solid-state batteries were recorded atdifferent current densities (1 C = 1670 mA g−1) and the cut-offvoltages for discharge and charge were 1.5 and 3.0 V (vs Li/Li+). Theapplied current density was computed based on the sulfur content inthe composite cathode. The electrochemical measurements of the as-assembled cells were performed at RT.

3. RESULTS AND DISCUSSION

3.1. Characterization of LGPS and S@C Composites.The SEM image of LGPS SE powder unveils nonuniformsurface morphology with a clear aggregation of the particles inthe range of micron scale (Figure 1A). The Raman spectrum ofthe LGPS SE is shown in Figure 1B. The peaks at around 175and 278 cm−1 are attributed to deformation of the PS4

3− unit.47

The peak seemed at 415 cm−1, mainly comes from the Ge−S−Ge stretching, and the other peak appeared at 420 cm−1 is thestretching of the PS4

3− unit. The peak marked at 384 cm−1 isascribed to the (GeS0.5S3)

3− unit with a nonbridging sulfur.48

According to Martin’s report, Li+−S− stretching vibration isfound at 363 cm−1.49 In addition, the representative peaksfound at 550 and 573 cm−1, due to asymmetric vibrations ofthe PS4

3− and P2S74− units.48 The crystal structure and phase

purity of the LGPS were further determined from the powderXRD pattern and Rietveld refinement, as shown in Figure 1C.The as-obtained results demonstrate that the LGPS SE consistsof a tetragonal crystal structure with a space group of P42/nmc(137) and the corresponding lattice constants are a = b =8.696 Å and c = 12.607 Å, which are in good agreement withthe earlier published literature.26,50

To determine the Li ionic conductivity (σLi) of the LGPSelectrolyte, ac impedance analysis was performed on C/LGPS/C symmetric cells at RT within the frequency range from 1 Hzto 1 MHz, as shown in Figure 1D. It is obvious that theNyquist plot consists of a clear semicircle at a high frequencyrange and a vertical capacitive tail at low frequency is attributedto contribution of the interface between the Li-ionic conductorand blocking carbon electrodes.12,51 The intercept at real axis(Z′) in the high frequency region can be accredited to the bulkresistance (Rbulk) of the LGPS SE whereas the depressed arccorresponding to the grain boundary response. The totalresistance, Rtotal (bulk and grain boundary contributions), ofthe LGPS SE is 62.3 Ω, estimated from the low-frequencyintercept. The Li ionic conductivity (σLi) of the LGPS SE canbe determined from the total resistance by the equation, σLi =l/(Rtotal × a), where l and a represent the thickness and area ofthe LGPS SE pellet, respectively. The computed total Li ionicconductivity of the LGPS SE is 2.04 × 10−3 S cm−1, which iscomparably lower than the literature reported value of 12 ×10−3 S cm−1.26 In general, the ionic conductivity of SEs greatlydepends on synthesis conditions (which can largely influencethe amount of impurities) and hot/cold pressing conditions ofthe SE pellets, thus, varying the ionic conductivity of our LGPSSE.The powder XRD patterns of sulfur, carbon blacks, and

sulfur@carbon composites are given in Figures 2A and S1. Asexpected, the broad diffraction peaks centered at about 24.3°and 43.2°, which correspond to the (002) and (100) facets ofamorphous carbon.52 However, in all the S@C composites, nopronounced diffraction peaks of sulfur as compared to standardcrystalline sulfur, implying that sulfur is in a highly dispersedstate inside the pores of carbon. At 155 °C, the sulfur meltsand is fully confined into porous of the carbon frameworks.53

The salient feature to note is that high-energy ball-millingcaused a high degree of dispersion and exfoliation of carbon, asreflected by the pronounced decrease in graphitic peakintensity in all three S@C composites compared to thepristine carbons (Figure S1).52 The comparison Raman spectraof the different S@C composites in Figure 2B exhibit twoprominent peaks at around 1315 (D-band) and 1590 cm−1 (G-band), which are accredited to the defects/disordered carbonand ordered sp2 graphitized carbon, respectively.4,54 In allsamples, the intensity of the D-band is greater than that of theG-band owing to existence of the defects induced by sulfurinfiltration into the porous carbon matrix. Moreover, the basicfeatures of the sulfur exhibit well-defined Raman bands at 153,218, 244, 435, and 471 cm−1 (Figure 2B).55 In contrast withsulfur, the S@C composites do not exhibit those Raman bandsbecause the sulfur is in a highly dispersed state in thecomposite.54 Further, TGA profiles for all three S@Ccomposite samples confirmed that the sulfur content is almost50 wt % (Figure S2).The morphology and microstructure of the prepared S@C

composite samples were examined by SEM (Figure 3). Therepresentative images of S@KBC in Figure 3A,B display thehomogenous mixing of sulfur and KBC with an abundantmesoporous structure. The pictures of S@PBX51C (Figure3C,D) and S@MCNTs (Figure 3E,F) also signify good mixingof sulfur and carbon components but no significant porousstructure. To further better understand the microstructure andinteraction between sulfur and carbon particles in the S@KBCcomposite, TEM was performed. The combined results ofTEM and EDS mapping images for the S@KBC sample areshown in Figure 4A−D. As shown in Figure 4A,B, the sulfurparticles with the size range of 10−20 nm sizes are welladhered on the surface of ketjen carbon and uniformlydistributed throughout the carbon skeleton in the composite.The EDS mapping of carbon and sulfur further confirms thehealthy distribution of sulfur in the mesoporous carbonframework (Figure 4C,D). The XPS analysis was performed

Figure 2. (A) Comparison powder XRD patterns and (B) Ramanspectra of sulfur and different sulfur@carbon composites.

ACS Applied Materials & Interfaces Research Article

DOI: 10.1021/acsami.9b03726ACS Appl. Mater. Interfaces 2019, 11, 18436−18447

18439

on the S@KBC composite to determine the surface chemicalbonding state of sulfur. The high-resolution S 2p spectrum canbe deconvoluted into two peaks at about 164.3 eV (2p3/2) and165.4 eV (2p1/2) is ascribed to the characteristic peaks ofelemental sulfur (Figure 4E).56 The high-resolution C 1sspectrum shows peaks at about 284.8, 285.4, and 286.3 eV,which can be attributed to the CC/C−C, C−OH and CO functional groups, respectively, for the KBC (Figure 4F).56

The surface textural characteristics of the S@C compositepowders were determined by N2 adsorption/desorptionisotherms. The isotherms of the different carbon materialsand their sulfur composites are shown in Figure 5 and pore sizedistribution plots of the corresponding samples are depicted in

the insets. The computed BET specific surface areas for thepristine carbons of KBC, PBX51C, and MCNTs are 1390,1124, and 198 m2 g−1, respectively. However, after infiltrationof sulfur into these carbons significantly reduces the surfaceareas to 115, 65, and 19 m2 g−1 for S@KBC, S@PBX51C, andS@MCNTs samples. The large attenuation in surface areas ofthe composites is found due to the blocking of carbon pores bylarge-sized sulfur particles. Moreover, it can be seen from theBJH plots (insets of Figure 5) that the pristine carbonmaterials exhibit broad pore size distribution while after mixingthe sulfur in carbon materials reduces the pore size distributionrange, suggesting pores of the carbon materials are filled by thesulfur. Nonetheless, the large specific surface area and favorablemesoporous structure of the S@KBC composite is advanta-geous in that it presumably facilitates the increase of theinterface at the electrode/SE that allows the smooth chargetransfer with the LGPS SE.The positive electrode is a composite, residing a mixture of

one of the prepared S@C (where C is KBC or PBX51C orMCNTs) composites, AB (electronic conduction additive),and LGPS SE (Li+ conduction additive), obtained in two steps.First, the S@C composite was obtained through ball-millingand subsequent heating. The as-obtained S@C composite wasthen mixed with LGPS and AB by hand ground with themortar and pestle for at least 2 h, so as to obtain the evenlymixed S@C/LGPS/AB composite. Figure S3 signifies thepowder XRD patterns of the S@KBC/LGPS/AB compositecathode at first and after three days of preparation. There is noobvious side reaction in the prepared composite even after 3days, implying good stability of the composite. The SEMpicture of the composite cathode is shown in Figure S4A. Itcan be seen that sulfur, carbon, and LGPS components areevenly dispersed and contact firmly, which is highly beneficialand endows balanced prodigious electronic and ionicconductivity of the composite. Moreover, the size reductionand homogeneous dispersion of sulfur and carbon in thecomposite could increase sulfur utilization during thedischarge/charge process, leading to a better electrochemicalperformance with robust rate and long endurance. The EDSimages were carried out in order to have a deeper look at thecomposite cathode (Figure S4). The results confirm thepresence of C, S, Ge, and P in the composite, which furthersuggests the uniform mixing of sulfur, carbon, and SE in thecomposite cathode powder.

Figure 3. SEM images of (A,B) S@KBC, (C,D) S@PBX51C, and (E,F) S@MCNTs composite samples at different magnifications.

Figure 4. (A,B) TEM and (C,D) EDS mapping images of the S@KBC composite; core-level XPS spectra of (E) S 2p and (F) C 1s ofthe S@KBC composite sample.

ACS Applied Materials & Interfaces Research Article

DOI: 10.1021/acsami.9b03726ACS Appl. Mater. Interfaces 2019, 11, 18436−18447

18440

Figure 5. N2 adsorption/desorption isotherms of pristine carbons of (A) KBC, (C) PBX51C, and (E) MCNTs and their composites with sulfur:(B) S@KBC, (D) S@PBX51C, and (F) S@MCNTs. In sets show the corresponding BJH pore size distribution plots.

Figure 6. Photographs (top views) of the LGPS SE pellet surface (A) without and (B) with 1 M LiTFSI/PYR13TFSI (1 M LiTFSI/IL) IL. (C)Nyquist profiles for the Li/LGPS/Li symmetric cells with and without 1 M LiTFSI/PYR13TFSI IL, and (D) time evolution of impedance responseof the Li/LGPS/Li cell with 1 M LiTFSI/IL at various storage times.

ACS Applied Materials & Interfaces Research Article

DOI: 10.1021/acsami.9b03726ACS Appl. Mater. Interfaces 2019, 11, 18436−18447

18441

3.2. Electrochemical Studies. 3.2.1. Li/LGPS/Li Sym-metric Cells. To quantify the effect of IL such as LiTFSI/PYR13TFSI on the Li/LGPS interface and lithium plating/stripping cycling stability, symmetric Li/LGPS/Li cells wereassembled with or without addition of IL. Figure 6A,Brepresents photographs of the pelletized LGPS SE surfacewithout and with IL. As seen in Figure 6C, the Nyquist plots ofthe Li/LGPS/Li symmetric cells, assembled without and withthe addition of 1 M IL. The Nyquist profiles of two differentLi/LGPS/Li symmetric cells show a clear difference in theirsemicircles, representing different resistances of the cells.Usually, the first intercept at the real part (Z′) of the data inthe high frequency is attributable to the bulk resistance, Rbulk.

57

The semicircle at the medium frequency region is regarded tothe interfacial resistance, Rintf, which essentially poised ofcharge-transfer resistance, Rct, and passivation layer resistance,Rsei.

58 The resulting impedance data of the cells were simulatedwith the modal circuit, as shown in the inset of Figure 6C. Itcan be noticed that the Li/LGPS/Li cells modified with 1 M ILdeliver remarkably a small interfacial resistance of 142 Ω cm2

than that of the unmodified Li/LGPS/Li cells (∼2021 Ω cm2).It is worth noting that the interfacial resistance of IL-modifiedLGPS SE is well comparable to or better than the reportedsulfide- and oxide-based SEs.12,36,59−63

To determine the dynamic interface stability between the IL-modified LGPS SE and Li metal, the ac impedance test wascarried out on the Li/LGPS/Li symmetric cell stored for 15days at RT. Figure 6D illustrates the variation of the interfacialimpedance of 1 M LiTFSI/IL-modified Li/LGPS/Li sym-metric cells with time evolution under open circuit voltage. It isevident that with the increase of time, the bulk resistance, Rbulk,value is almost constant, demonstrating that the ionicconductivity of the SE does not change with increased storagetime. However, there is a marked change in interface charge-transfer resistance, Rintf, first a sharp jump with time in first 3days, and it could keep constant eventually over 15 days,implying a formation of a stable interface across the LGPS SEand Li metal electrode as a result of the addition of IL. The

initial increase in resistance is due to the growth of thepassivation layer which becomes stable with increase in time.64

We further carried out “Li strip/plate test” to evaluate thedynamical interface stability and lithium ion transportcapability across the LGPS SE and Li metal interface. Figure7A,B shows the time-dependent plating/striping voltageprofiles of the Li/LGPS/Li cells at 0.038 and 0.1 mA cm−2.It can be seen from that the Li/LGPS/Li symmetric cellsmodified with 1 M IL show a flat and highly stable stripping/plating profiles with a small overpotential of ±37.5 mV at0.038 mA cm−2 (Figure 7A). Even after prolonged 1200 h, thecell unveils a stable and flat voltage profiles, signifying aremarkable improvement in cycling stability. As the currentdensity increases to 0.1 mA cm−2 (Figure 7B), the over-potential of the Li stripping/plating remains smaller anddelivers exceptionally stable cycle performance for at least 1000h. In stark contrast, a spike in overpotential with prolongedtime is observed in unmodified Li/LGPS/Li cells because ofthe unstable interface where the interfacial resistance (Rintf)rises quickly with time (Figure 7A). We further performedSEM images on the LGPS SE pellet surface after long-termstripping/plating cycles (Figure 7C,D). It can be clearlyobserved that 1 M IL can efficiently protect from theunfavorable side reactions between the LGPS SE and Limetal during stripping and plating cycles, thus, the smoothsurface morphology with no significant chemical reactions hasbeen observed between them (Figure 7C). While in theabsence of IL (Figure 7D), the surface of LGPS SE hassignificant voids and moreover, the SE surface is highly reactedwith the Li metal during charge/discharge cycling leading to ablack color.The improved interface stability of the Li/LGPS with

reduced impedance and excellent cycle stability in IL-modifiedLi/LGPS/Li cells is attributed to the following aspects.12,65 Inthe solid−liquid hybrid electrolyte system, that is, IL-modifiedLGPS SE symmetric cells, (i) IL facilitates a good ionicconducting network and also change the contact mode fromsolid−solid to solid−liquid which empowers the intimate

Figure 7. (A) Galvanostatic cycling curves of Li/LGPS/Li cells with and without 1 M LiTFSI/IL at a current density of 0.038 mA cm−2, and (B)the Li/LGPS/Li cell with 1 M LiTFSI/IL at 0.1 mA cm−2. SEM images obtained after long-term Li stripping/platting cycles for the Li/LGPS/Lisymmetric cells (C) with and (D) without 1 M LiTFSI/IL IL at a current density of 0.038 mA cm−2.

ACS Applied Materials & Interfaces Research Article

DOI: 10.1021/acsami.9b03726ACS Appl. Mater. Interfaces 2019, 11, 18436−18447

18442

interface contact between LGPS SE and Li metal.65 (ii) ILssuch as LiTFSI/PYR13TFSI increase the Li/LGPS interfacestability by the in situ formation of the interface layer on the Limetal surface through the putrefaction of ILs.12,66 The as-formed dense and stable SEI layer further inhibits the chemicalreactions that occur at the LGPS SE-contacting Li metal andthus helps to increase the related properties of the cells. While,in the absence of IL in Li/LGPS/Li symmetric cells, the Li/LGPS interface is intrinsically unstable and attributing to thegradual decomposition of the LGPS SE, leading to theformation of the interface layer consisting low ionicconductivity materials (such as Li2S and Li3P, etc.) and amixed ion-electron conductive Li−Ge layer,32 thus increasingthe interfacial resistance and reduced electrochemical stability.3.2.2. Quasi-Solid-State Li−S Cells. The effect of the

addition of IL on improving SSLSB performance was probed atambient temperature by using GCD and EIS techniques.46

Figure 8A reveals a schematic representation of a quasi-SSLSBfabricated with the sulfur composite consisting of S@C, LGPSSE, and AB as the positive electrode, LGPS as SE, and Li metalas the anode, respectively. At the anode side of LGPS, the SEsurface was uniformly covered with a drop of 1 M LiTFSI/PYR13TFSI IL so as to improve the interface stability andsuppress adverse side reactions between the lithium metal andLGPS SE. Figure 8B represents the first charge/dischargecurves for different S@C composite cathodes in Li−S solidbatteries at 83.5 mA g−1. The first discharge capacities for thecells with S@KBC, S@PBX51C, and S@MCNTs electrodesare 1068, 783 and 677 mA h g−1, respectively, and theirretained reversible capacities after 25th cycles are 868, 375, and218 mA h g−1 (Figure 8C). Among these composite cathodes,the S@KBC shows enhanced discharge specific capacity andhigh cycle stability during the charge/discharge process.In order to gain a better insight into the effects of carbon

additives on the electrochemical properties of the S@Ccomposites, EIS was carried out in the frequency range of 1Hz to 1 MHz and the results are displayed in Figure 8D. Thesolid symbols denote the experiment data and the thick line

represents the fitting data with the equivalent circuit, as shownin the inset. The fitting results of three different compositeelectrodes are shown in Table 1. All the Nyquist profiles

comprise a clear semicircle at a high-frequency region and anear vertical line along the Z″ in the low-frequency region. Theintercept at x-axis (at Z′) in the high-frequency region signifiesthe bulk resistance (Rbulk) of the LGPS SE.5 This value isalmost same for all three electrodes owing to the presence ofsame kind of LGPS SE. The clear semicircle in the middle-frequency region reflects the Rct and Rintf between the electrodeand the electrolyte.67 The linear part in the lower frequencyregion reflects diffusion impedance, Wo.

55 In comparison,among all three electrodes, the S@KBC had a smaller diameterof the semicircle indicating that low charge transfer resistanceand interfacial resistance than those of the S@PBX51C andS@MCNTs. Therefore, the batteries with S@KBC as thecathode exhibited an excellent discharge/charge performanceand better cycling stability. The large surface area, indis-pensable pore structure, and good sulfur particle dispersion inthe S@KBC composite are highly responsible for achievinghigh sulfur utilization and favorable intimate interface contactleading to fast charge-transfer rate at the electrode/electrolyteinterface.Further, we have chosen the sulfur/KBC (S@KBC)

composite to in-depth analysis in Li−S solid batteries. Figure9A illustrates initial five discharge/charge profiles of the S@KBC/LGPS/IL/Li solid-state battery under a fixed currentdensity of 83.5 mA g−1. The cell delivered very high discharge

Figure 8. (A) Schematic diagram of the quasi-solid-state lithium−sulfur battery. Comparison of the (B) galvanostatic discharge/charge profiles,(C) cycling performances, and (D) Nyquist plots for the different sulfur/carbon composite electrodes in quasi-SSLSBs. Galvanostatic discharge/charge profiles and cycling stability measurements are obtained at a current density of 83.5 mA g−1.

Table 1. Fitting Results of the Different Sulfur@CarbonComposite Cathodes in Quasi-SSLSBs

electrodematerial

SE resistance, RSE(Ω cm2)

interfacial resistance, Rif(Ω cm2)

S@KBC 11.15 29.86S@PBX51C 11.81 56.81S@MCNTs 11.48 64.55

ACS Applied Materials & Interfaces Research Article

DOI: 10.1021/acsami.9b03726ACS Appl. Mater. Interfaces 2019, 11, 18436−18447

18443

capacities of 1017 and 912 mA h g−1, respectively, at 1st and5th cycles. The discharge capacity of the S@KBC composite ismuch better than the reported several S@C compositeelectrodes in SSLSBs (Table S1).14,15,68−71 It is notable thatthe discharge and charge curves of the solid-state cell exhibit asingle voltage plateau in their potential profiles, as it undergoesa solid-phase Li−S redox reaction (S8 + 16Li+ ↔ 8Li2S +16e−),46 suggesting that no polysulfide dissolution.16,55 In theliterature, a plenty of reports showed similar discharge/chargeprofiles of SSLSBs with sulfide SEs such as glass/glass-ceramicLi2S−P2S5, LGPS, and Li6PS5Cl.

4,9,46,55,72 As seen fromderivative plots of the corresponding cell in Figure 9B, theredox peaks at about 2.30 and 2.07 V are observed during thecharge and discharge processes, which are corresponding tolithiation and delithiation processes of sulfur in theelectrode.16,71 The other peak located at around 2.18 V duringdischarge can be related to the solid-electrolyte contribution.Kanno et al. observed a similar kind of redox behavior incharge/discharge curves of SSLSBs with utilization of thio-LISICON Li3.25Ge0.25P0.75S4 SE.16 An additional broadreduction peak looked at 1.85 V during the first dischargecycle, attributed to some irreversible reactions occurring during

the initial cycle, which might be related to the decompositionof LGPS.73,74

Figure 9C shows the second cycle lithiation/delithiationprofiles of the S@KBC cathode at vacillate current densities,ranging from 50 to 200 mA g−1. It can be seen that thedischarge capacities decline gradually with the increase incurrent density. The cell can be delivered a discharge specificcapacity as high as 1068 mA h g−1 at 50 mA g−1 and remainedabout 652 mA h g−1 (i.e., 61% with respect to the initialcapacity) even at a high applied current of 200 mA g−1

indicates good rate capability of the cell. It is furthermentioning that as the current increases to higher values of167 and 200 mA g−1, the voltage gap between the dischargeand charge plateau is increased as a result of polarizationassociated with higher current density. Further, the long-termgalvanostatic cycling test for the S@KBC composite electrodewas performed over 50 cycles at a constant current of 83.5 mAg−1 (Figure 9D). The capacity of the cell gradually diminisheswith increase in the cycle number, and the capacity retentionsfor 25, 35, and 50th cycles are 95.2, 90.6 and 82.6%,respectively. These values are calculated after the 5th cycleonward. Even though the capacity diminishes with cycling is

Figure 9. (A) Galvanostatic discharge/charge profiles and (B) the corresponding derivative curves for the S@KBC composite in SSLSBs under acurrent density of 83.5 mA g−1 and (C) the 2nd cycle discharge/charge profiles at different current densities and (D) long-term cyclingperformance of SSLSB with the S@KBC composite electrode.

Figure 10. (A) Galvanostatic discharge/charge curves of the S@KBC composite as the cathode in Li−S state−state batteries without the additionof 1 M LiTFSI/PYR13TFSI IL. (B) Comparison Nyquist plots of the S@KBC electrode in Li−S solid-state batteries with and without 1 M LiTFSI/PYR13TFSI IL; inset shows the enlarged high-frequency view.

ACS Applied Materials & Interfaces Research Article

DOI: 10.1021/acsami.9b03726ACS Appl. Mater. Interfaces 2019, 11, 18436−18447

18444

more pronounced in the last cycles (mainly 25−50 cycles) butwe noticed that the capacity fades even within 25 cycles. Thiscan be attributed to the formation of polysulfide species whichresult in large volume changes of the electrode.64,72 Never-theless, the cell maintained a reversible discharge capacity ashigh as of 726 mA h g−1 at the end of the 50th cycle.Moreover, the Coulombic efficiency of the corresponding cellincreases in the first few cycles and could keep constanteventually; however, it did not exceed 97%, implying someirreversibility of the battery reaction.Further, we have fabricated solid-state batteries without the

addition of 1 M IL of LiTFSI/PYR13TFSI to confirm whetherIL can suppress adverse side reactions between LGPS SE andLi metal or not and we measured the GCD profiles at aconstant current of 83.5 mA g−1 (Figure 10A). The initialdischarge capacity of the cell is merely 405 mA h g−1, while thereversible specific capacity is found to be as low as 50 mA hg−1, which can be attributed to the unstable interface betweenthe LGPS SE and Li metal anode because of favoring the sidereactions between them during the discharge/charge process;as a result, broad plateaus are found within the appliedpotential window.4,75 Further, we performed EIS spectra of thecorresponding cells in order to assess the decrease in resistancewith the addition of 1 M LiTFSI/PYR13TFSI IL (Figure 10B).A comparatively large interface impedance of 69 Ω cm2 can befound in the pristine S@KBC/LGPS/Li cell (without theaddition of IL) than that of the cells modified with IL which isabout 29.8 Ω cm2 that is, the resistance decreases by 57%. Theunstable Li/LGPS interfacial is ascribed to the gradualspontaneous reaction between the LGPS SE and Li metal,which leads to the formation of interphases consisting of Li2S,Li3P, and Li−Ge alloy, as a result, high interfacial resistance isachieved in unmodified SE-based cells.32 Therefore, theaddition of a small amount of 1 M LiTFSI/PYR13TFSI IL atthe anode side of the LGPS pellet surface can remarkablyincrease the battery performance in terms of specific capacity,cyclability, and interfacial resistance of the S@C/LGPS/Lisolid cell due to the enriched interface stability at theelectrode/electrolyte (Li/LGPS) interface.

4. CONCLUSIONSIn summary, with the purpose of addressing the problems ofinterface stability across the Li-conducting LGPS SE and Limetal anode, an exceptionally small amount of IL-modifiedLGPS SE-based Li/Li symmetric cells was assembled andstudied their performance in Li metal batteries. Meanwhile, theadditive effects of carbon materials on the performance of Li−Scell chemistry are also investigated thoroughly. With enabling 1M LiTFSI/PYR13TFSI IL, exceptionally improved the interfacestability at the Li/LGPS SE by forming an in situ SEI layer. Asa consequence, remarkably improved interface stability of theLGPS SE with the Li metal anode in Li/LGPS/Li symmetriccells. The interfacial resistance has been achieved as low as of142 Ω cm2 and stable Li stripping/plating performance over1200 h at 0.038 mA cm−2 and 1000 h at 0.1 mA cm−2.Moreover, the Li−S solid-state battery architecture with theS@KBC positive electrode and surface-stabilized LGPS SEdelivered excellent charge/discharge performance and a smallinterfacial resistance compared to that of S@PBX51C and S@MCNTs electrodes. For instance, the S@KBC electrodeexhibits initial discharge capacity as high as of 1017 mA hg−1 at 83.5 mA cm−2 and retains greater than 750 mA h g−1

even after 50 cycles. Featuring beneficial properties such as

high specific surface area, indispensable pore structure, anduneven sulfur particle dispersion in the S@KBC composite aresubstantial in achieving high sulfur utilization and favorableintimate interface contact between the active electrode materialand LGPS SE. The results, herein, demonstrate a promisingmethod in improving the anodic interface problems and Li−Ssolid battery performance using IL-modified sulfide-type LGPSSEs.

■ ASSOCIATED CONTENT*S Supporting InformationThe Supporting Information is available free of charge on theACS Publications website at DOI: 10.1021/acsami.9b03726.

Powder XRD patterns and TGA profiles of the differentS@C composites and XRD, SEM, and EDS mapping ofS@KBC-LGPS-AB composite (PDF)

Electrochemical chemical performance (PDF)

■ AUTHOR INFORMATIONCorresponding Author*E-mail: yyang@xmu.edu.cn. Phone/Fax: + 86 592 2185753.ORCIDEdiga Umeshbabu: 0000-0003-4233-5565Bizhu Zheng: 0000-0002-2744-394XNotesThe authors declare no competing financial interest.

■ ACKNOWLEDGMENTSThis work was financially supported by the National KeyResearch and Development Program of China (grant nos.2016YFB0901502 and 2018YFB0905400) and NationalNatural Science Foundation of China (grant nos.21761132030, 21621091 and 21473148).

■ REFERENCES(1) Janek, J.; Zeier, W. G. A Solid Future for Battery Development.Nat. Energy 2016, 1, 16141.(2) Yue, J.; Yan, M.; Yin, Y.-X.; Guo, Y.-G. Progress of the InterfaceDesign in All-Solid-State Li-S Batteries. Adv. Funct. Mater. 2018, 28,1707533.(3) Umeshbabu, E.; Zheng, B.; Yang, Y. Recent Progress in All-Solid-State Lithium−Sulfur Batteries Using High Li-Ion ConductiveSolid Electrolytes. Electrochem. Energy Rev. 2019, DOI: 10.1007/s41918-019-00029-3.(4) Yao, X.; Huang, N.; Han, F.; Zhang, Q.; Wan, H.; Mwizerwa, J.P.; Wang, C.; Xu, X. High-Performance All-Solid-State Lithium-SulfurBatteries Enabled by Amorphous Sulfur-Coated Reduced GrapheneOxide Cathodes. Adv. Energy Mater. 2017, 7, 1602923.(5) Xu, R.; Wu, Z.; Zhang, S.; Wang, X.; Xia, Y.; Xi, X.; Huang, X.;Tu, J. Construction of All-Solid-State Batteries based on a Sulfur-Graphene Composite and Li9.54Si1.74P1.44S11.7Cl0.3 Solid Electrolyte.Chem.Eur. J. 2017, 23, 13950−13956.(6) Suzuki, K.; Mashimo, N.; Ikeda, Y.; Yokoi, T.; Hirayama, M.;Kanno, R. High Cycle Capability of All-Solid-State Lithium-SulfurBatteries Using Composite Electrodes by Liquid-Phase andMechanical Mixing. ACS Appl. Energy Mater. 2018, 1, 2373−2377.(7) Nagao, M.; Hayashi, A.; Tatsumisago, M. Sulfur-CarbonComposite Electrode for All-Solid-State Li/S Battery with Li2S-P2S5Solid Electrolyte. Electrochim. Acta 2011, 56, 6055−6059.(8) Ji, X.; Lee, K. T.; Nazar, L. F. A Highly Ordered NanostructuredCarbon-Sulphur Cathode for Lithium-Sulphur Batteries. Nat. Mater.2009, 8, 500−506.

ACS Applied Materials & Interfaces Research Article

DOI: 10.1021/acsami.9b03726ACS Appl. Mater. Interfaces 2019, 11, 18436−18447

18445

(9) Zhao, Q.; Zheng, J.; Archer, L. Interphases in Lithium-SulfurBatteries: Toward Deployable Devices with Competitive EnergyDensity and Stability. ACS Energy Lett. 2018, 3, 2104−2113.(10) Yu, X.; Manthiram, A. Electrode-Electrolyte Interfaces inLithium-Sulfur Batteries with Liquid or Inorganic Solid Electrolytes.Acc. Chem. Res. 2017, 50, 2653−2660.(11) Kobayashi, T.; Inada, T.; Sonoyama, N.; Yamada, A.; Kanno, R.All Solid-State Batteries Using Super Ionic Conductor, Thio-Lisicon-Electrode/Electrolyte interfacial Design. MRS Online Proc. Libr. 2004,835, K11.1.(12) Zheng, B.; Zhu, J.; Wang, H.; Feng, M.; Umeshbabu, E.; Li, Y.;Wu, Q.-H.; Yang, Y. Stabilizing Li10SnP2S12/Li Interface via an in SituFormed Solid Electrolyte Interphase Layer. ACS Appl. Mater.Interfaces 2018, 10, 25473−25482.(13) Sakuma, M.; Suzuki, K.; Hirayama, M.; Kanno, R. Reactions atthe electrode/electrolyte interface of all-solid-state lithium batteriesincorporating Li-M (M = Sn, Si) alloy electrodes and sulfide-basedsolid electrolytes. Solid State Ionics 2016, 285, 101−105.(14) Agostini, M.; Aihara, Y.; Yamada, T.; Scrosati, B.; Hassoun, J. ALithium-Sulfur Battery Using a Solid, Glass-type P2S5-Li2S electrolyte.Solid State Ionics 2013, 244, 48−51.(15) Choi, H. U.; Jin, J. S.; Park, J.-Y.; Lim, H.-T. PerformanceImprovement of All-Solid-State Li-S Batteries with OptimizingMorphology and Structure of Sulfur Composite Electrode. J. Alloy.Comp. 2017, 723, 787−794.(16) Suzuki, K.; Kato, D.; Hara, K.; Yano, T.-A.; Hirayama, M.;Hara, M.; Kanno, R. Composite Sulfur Electrode Prepared by High-Temperature Mechanical Milling for Use in An All-Solid-StateLithium-Sulfur Battery with a Li3.25Ge0.25P0.75S4 Electrolyte. Electro-chim. Acta 2017, 258, 110−115.(17) Busche, M. R.; Weber, D. A.; Schneider, Y.; Dietrich, C.;Wenzel, S.; Leichtweiss, T.; Schroder, D.; Zhang, W.; Weigand, H.;Walter, D.; Sedlmaier, S. J.; Nazar, L. F.; Janek, J.; Janek, J. In SituMonitoring of Fast Li-Ion Conductor Li7P3S11 Crystallization Inside aHot-Press Setup. Chem. Mater. 2016, 28, 6152−6165.(18) Kobayashi, T.; Imade, Y.; Shishihara, D.; Homma, K.; Nagao,M.; Watanabe, R.; Yokoi, T.; Yamada, A.; Kanno, R.; Tatsumi, T. AllSolid-State Battery with Sulfur Electrode and Thio-LISICONElectrolyte. J. Power Sources 2008, 182, 621−625.(19) Lin, Z.; Liu, Z.; Fu, W.; Dudney, N. J.; Liang, C. LithiumPolysulfidophosphates: A Family of Lithium-Conducting Sulfur-RichCompounds for Lithium-Sulfur Batteries. Angew. Chem., Int. Ed. 2013,52, 7460−7463.(20) Nagata, H.; Chikusa, Y. All-Solid-State Lithium-Sulfur Batterywith High Energy and Power Densities at the Cell Level. EnergyTechnol. 2016, 4, 484−489.(21) Hao, F.; Han, F.; Liang, Y.; Wang, C.; Yao, Y. ArchitecturalDesign and Fabrication Approaches for Solid-State Batteries. MRSBull. 2018, 43, 775−781.(22) Hao, Y.; Wang, S.; Xu, F.; Liu, Y.; Feng, N.; He, P.; Zhou, H. ADesign of Solid-State Li-S Cell with Evaporated Lithium Anode toEliminate Shuttle Effects. ACS Appl. Mater. Interfaces 2017, 9, 33735−33739.(23) Unemoto, A.; Yasaku, S.; Nogami, G.; Tazawa, M.; Taniguchi,M.; Matsuo, M.; Ikeshoji, T.; Orimo, S.-i. Development of Bulk-typeAll-Solid-State Lithium-Sulfur Battery Using LiBH4 Electrolyte. Appl.Phys. Lett. 2014, 105, 083901.(24) Hartmann, P.; Leichtweiss, T.; Busche, M. R.; Schneider, M.;Reich, M.; Sann, J.; Adelhelm, P.; Janek, J. Degradation ofNASICON-Type Materials in Contact with Lithium Metal:Formation of Mixed Conducting Interphases (MCI) on SolidElectrolytes. J. Phys. Chem. C 2013, 117, 21064−21074.(25) Kato, Y.; Hori, S.; Saito, T.; Suzuki, K.; Hirayama, M.; Mitsui,A.; Yonemura, M.; Iba, H.; Kanno, R. High-Power All-Solid-StateBatteries Using Sulfide Superionic Conductors. Nat. Energy 2016, 1,16030.(26) Kamaya, N.; Homma, K.; Yamakawa, Y.; Hirayama, M.; Kanno,R.; Yonemura, M.; Kamiyama, T.; Kato, Y.; Hama, S.; Kawamoto, K.;

Mitsui, A. A Lithium Superionic Conductor. Nat. Mater. 2011, 10,682−686.(27) Yu, C.; van Eijck, L.; Ganapathy, S.; Wagemaker, M. Structureand Electrochemical Performance of the Argyrodite Li6PS5Cl SolidElectrolyte for Li-ion Solid State Batteries. Electrochim. Acta 2016,215, 93−99.(28) Kasemchainan, J.; Bruce, P. G. All-Solid-State Batteries andtheir Remaining Challenges. Johnson Matthey Technol. Rev. 2018, 62,177−180.(29) Schwobel, A.; Hausbrand, R.; Jaegermann, W. InterfaceReactions between LiPON and Lithium Studied by in-situ X-rayPhotoemission. Solid State Ionics 2015, 273, 51−54.(30) Wenzel, S.; Weber, D. A.; Leichtweiss, T.; Busche, M. R.; Sann,J.; Janek, J. Interphase Formation and Degradation of Charge TransferKinetics between a Lithium Metal Anode and Highly CrystallineLi7P3S11 Solid Electrolyte. Solid State Ionics 2016, 286, 24−33.(31) Wenzel, S.; Sedlmaier, S. J.; Dietrich, C.; Zeier, W. G.; Janek, J.Interfacial Reactivity and Interphase Growth of Argyrodite SolidElectrolytes at Lithium Metal Electrodes. Solid State Ionics 2018, 318,102−112.(32) Wenzel, S.; Randau, S.; Leichtweiß, T.; Weber, D. A.; Sann, J.;Zeier, W. G.; Janek, J. Direct Observation of the Interfacial Instabilityof the Fast Ionic Conductor Li10GeP2S12 at the Lithium Metal Anode.Chem. Mater. 2016, 28, 2400−2407.(33) Wenzel, S.; Leichtweiss, T.; Kruger, D.; Sann, J.; Janek, J.Interphase Formation on Lithium Solid Electrolytes-An In SituApproach to Study Interfacial Reactions by Photoelectron Spectros-copy. Solid State Ionics 2015, 278, 98−105.(34) Ogawa, M.; Kanda, R.; Yoshida, K.; Uemura, T.; Harada, K.High-Capacity Thin Film Lithium Batteries with Sulfide SolidElectrolytes. J. Power Sources 2012, 205, 487−490.(35) Chen, K.; Yamamoto, K.; Orikasa, Y.; Uchiyama, T.; Ito, Y.;Yubuchi, S.; Hayashi, A.; Tatsumisago, M.; Nitta, K.; Uruga, T.;Uchimoto, Y. Effect of introducing interlayers into electrode/electrolyte interface in all-solid-state battery using sulfide electrolyte.Solid State Ionics 2018, 327, 150−156.(36) Shao, Y.; Wang, H.; Gong, Z.; Wang, D.; Zheng, B.; Zhu, J.; Lu,Y.; Hu, Y.-S.; Guo, X.; Li, H.; Huang, X.; Yang, Y.; Nan, C.-W.; Chen,L. Drawing a Soft Interface: An Effective Interfacial ModificationStrategy for Garnet-Type Solid-State Li Batteries. ACS Energy Lett.2018, 3, 1212−1218.(37) Liu, Y.; Li, C.; Li, B.; Song, H.; Cheng, Z.; Chen, M.; He, P.;Zhou, H. Germanium Thin Film Protected Lithium AluminumGermanium Phosphate for Solid-State Li Batteries. Adv. Energy Mater.2018, 8, 1702374.(38) Nagao, M.; Hayashi, A.; Tatsumisago, M.; Kanetsuku, T.;Tsuda, T.; Kuwabata, S. In Situ SEM Study of a Lithium Depositionand Dissolution Mechanism in a Bulk-Type Solid-State Cell with aLi2S-P2S5 Solid Electrolyte. Phys. Chem. Chem. Phys. 2013, 15,18600−18606.(39) Kato, A.; Hayashi, A.; Tatsumisago, M. Enhancing Utilizationof Lithium Metal Electrodes in All-Solid-State Batteries by InterfaceModification with Gold Thin Films. J. Power Sources 2016, 309, 27−32.(40) Hayashi, A.; Ohtomo, T.; Mizuno, F.; Tadanaga, K.;Tatsumisago, M. All-solid-state Li/S batteries with highly conductiveglass-ceramic electrolytes. Electrochem. Commun. 2003, 5, 701−705.(41) Zhang, Z.; Chen, S.; Yang, J.; Wang, J.; Yao, L.; Yao, X.; Cui, P.;Xu, X. Interface Re-Engineering of Li10GeP2S12 Electrolyte andLithium Anode for All-Solid-State Lithium Batteries with UltralongCycle Life. ACS Appl. Mater. Interfaces 2018, 10, 2556−2565.(42) Chien, P.-H.; Feng, X.; Tang, M.; Rosenberg, J. T.; O’Neill, S.;Zheng, J.; Grant, S. C.; Hu, Y.-Y. Li Distribution Heterogeneity inSolid Electrolyte Li10GeP2S12 upon Electrochemical Cycling Probedby 7Li MRI. J. Phys. Chem. Lett. 2018, 9, 1990−1998.(43) Wu, J.-F.; Pu, B.-W.; Wang, D.; Shi, S.-Q.; Zhao, N.; Guo, X.;Guo, X. In Situ Formed Shields Enabling Li2CO3-Free SolidElectrolytes: A New Route to Uncover the Intrinsic Lithiophilicity

ACS Applied Materials & Interfaces Research Article

DOI: 10.1021/acsami.9b03726ACS Appl. Mater. Interfaces 2019, 11, 18436−18447

18446

of Garnet Electrolytes for Dendrite-Free Li-Metal Batteries. ACS Appl.Mater. Interfaces 2019, 11, 898−905.(44) Zhou, D.; Liu, R.; Zhang, J.; Qi, X.; He, Y.-B.; Li, B.; Yang, Q.-H.; Hu, Y.-S.; Kang, F. In Situ Synthesis of Hierarchical Poly(ionicliquid)-based Solid Electrolytes for High-Safety Lithium-Ion andSodium-Ion Batteries. Nano Energy 2017, 33, 45−54.(45) Oh, D. Y.; Nam, Y. J.; Park, K. H.; Jung, S. H.; Cho, S.-J.; Kim,Y. K.; Lee, Y.-G.; Lee, S.-Y.; Jung, Y. S. Excellent Compatibility ofSolvate Ionic Liquids with Sulfide Solid Electrolytes: TowardFavorable Ionic Contacts in Bulk-Type All-Solid-State Lithium-IonBatteries. Adv. Energy Mater. 2015, 5, 1500865.(46) Cao, Y.; Zuo, P.; Lou, S.; Sun, Z.; Li, Q.; Huo, H.; Ma, Y.; Du,C.; Gao, Y.; Yin, G. A Quasi-Solid-State Li-S Battery with HighEnergy Density, Superior Stability and Safety. J. Mater. Chem. A 2019,7, 6533−6542.(47) Sang, L.; Haasch, R. T.; Gewirth, A. A.; Nuzzo, R. G. Evolutionat the Solid Electrolyte/Gold Electrode Interface during LithiumDeposition and Stripping. Chem. Mater. 2017, 29, 3029−3037.(48) Hassoun, J.; Verrelli, R.; Reale, P.; Panero, S.; Mariotto, G.;Greenbaum, S.; Scrosati, B. A Structural, Spectroscopic andElectrochemical Study of a Lithium Ion Conducting Li10GeP2S12Solid Electrolyte. J. Power Sources 2013, 229, 117−122.(49) Seo, I.; Martin, S. W. Structural Properties of Lithium Thio-Germanate Thin Film Electrolytes Grown by Radio FrequencySputtering. Inorg. Chem. 2011, 50, 2143−2150.(50) Weber, D. A.; Senyshyn, A.; Weldert, K. S.; Wenzel, S.; Zhang,W.; Kaiser, R.; Berendts, S.; Janek, J.; Zeier, W. G. Structural Insightsand 3D Diffusion Pathways within the Lithium Superionic ConductorLi10GeP2S12. Chem. Mater. 2016, 28, 5905−5915.(51) Rosero-Navarro, N. C.; Miura, A.; Tadanaga, K. CompositeCathode Prepared by Argyrodite Precursor Solution Assisted byDispersant Agents for Bulk-type All-Solid-State Batteries. J. PowerSources 2018, 396, 33−40.(52) Xu, J.; Shui, J.; Wang, J.; Wang, M.; Liu, H.-K.; Dou, S. X.;Jeon, I.-Y.; Seo, J.-M.; Baek, J.-B.; Dai, L. Sulfur-GrapheneNanostructured Cathodes via Ball-Milling for High-PerformanceLithium-Sulfur Batteries. ACS Nano 2014, 8, 10920−10930.(53) Zhang, S.; Zheng, M.; Lin, Z.; Li, N.; Liu, Y.; Zhao, B.; Pang,H.; Cao, J.; He, P.; Shi, Y. Activated carbon with ultrahigh specificsurface area synthesized from natural plant material for lithium-sulfurbatteries. J. Mater. Chem. A 2014, 2, 15889−15896.(54) Yang, X.; Zhu, W.; Cao, G.; Zhao, X. Preparation of ReducedCarbon-Wrapped Carbon-Sulfur Composite as Cathode Material ofLithium-Sulfur Batteries. RSC Adv. 2015, 5, 93926−93936.(55) Xu, R.-C.; Xia, X.-H.; Li, S.-H.; Zhang, S.-Z.; Wang, X.-L.; Tu,J.-P. All-Solid-State Lithium−Sulfur Batteries Based on A Newlydesigned Li7P2.9Mn0.1S10.7I0.3 Superionic Conductor. J. Mater. Chem. A2017, 5, 6310−6317.(56) Gao, F.; Qu, J.; Zhao, Z.; Qiu, J. Efficient Synthesis ofGraphene/Sulfur Nanocomposites with High Sulfur Content andtheir Application as Cathodes for Li-S Batteries. J. Mater. Chem. A2016, 4, 16219−16224.(57) Li, Y.; Chen, X.; Dolocan, A.; Cui, Z.; Xin, S.; Xue, L.; Xu, H.;Park, K.; Goodenough, J. B. Garnet Electrolyte with an UltralowInterfacial Resistance for Li-Metal Batteries. J. Am. Chem. Soc. 2018,140, 6448−6455.(58) Lin, Y.; Li, J.; Lai, Y.; Yuan, C.; Cheng, Y.; Liu, J. A WiderTemperature Range Polymer Electrolyte for All Solid-State LithiumIon Batteries. RSC Adv. 2013, 3, 10722−10730.(59) Yamada, T.; Ito, S.; Omoda, R.; Watanabe, T.; Aihara, Y.;Agostini, M.; Ulissi, U.; Hassoun, J.; Scrosati, B. All Solid-StateLithium-Sulfur Battery Using a Glass-Type P2S5-Li2S Electrolyte:Benefits on Anode Kinetics. J. Electrochem. Soc. 2015, 162, A646−A651.(60) Sun, Y.; Yan, W.; An, L.; Wu, B.; Zhong, K.; Yang, R. A FacileStrategy to Improve the Electrochemical Stability of a Lithium IonConducting Li10GeP2S12 Solid Electrolyte. Solid State Ionics 2017,301, 59−63.

(61) Xu, X.; Hou, G.; Nie, X.; Ai, Q.; Liu, Y.; Feng, J.; Zhang, L.; Si,P.; Guo, S.; Ci, L. Li7P3S11/Poly(ethylene oxide) Hybrid SolidElectrolytes with Excellent Interfacial Compatibility for All-Solid-StateBatteries. J. Power Sources 2018, 400, 212−217.(62) Xu, R.; Han, F.; Ji, X.; Fan, X.; Tu, J.; Wang, C. InterfaceEngineering of Sulfide Electrolytes for All-Solid-State LithiumBatteries. Nano Energy 2018, 53, 958−966.(63) Wang, C.; Zhao, Y.; Sun, Q.; Li, X.; Liu, Y.; Liang, J.; Li, X.;Lin, X.; Li, R.; Adair, K. R.; Zhang, L.; Yang, R.; Lu, S.; Sun, X.Stabilizing Interface Between Li10SnP2S12 and Li metal by molecularlayer deposition. Nano Energy 2018, 53, 168−174.(64) Chen, L.; Fan, L.-Z. Dendrite-free Li Metal Deposition in All-Solid-State Lithium Sulfur Batteries with Polymer-in-Salt PolysiloxaneElectrolyte. Energy Storage Mater. 2018, 15, 37−45.(65) Sun, B.; Liu, K.; Lang, J.; Fang, M.; Jin, Y.; Wu, H. Ionic LiquidEnabling Stable Interface in Solid State Lithium Sulfur BatteriesWorking at Room Temperature. Electrochim. Acta 2018, 284, 662−668.(66) Guo, Q.; Han, Y.; Wang, H.; Xiong, S.; Li, Y.; Liu, S.; Xie, K.New Class of LAGP-Based Solid Polymer Composite Electrolyte forEfficient and Safe Solid-State Lithium Batteries. ACS Appl. Mater.Interfaces 2017, 9, 41837−41844.(67) Yubuchi, S.; Uematsu, M.; Deguchi, M.; Hayashi, A.;Tatsumisago, M. Lithium-Ion-Conducting Argyrodite-Type Li6PS5X(X = Cl, Br, I) Solid Electrolytes Prepared by a Liquid-PhaseTechnique Using Ethanol as a Solvent. ACS Appl. Energy Mater. 2018,1, 3622−3629.(68) Tanibata, N.; Tsukasaki, H.; Deguchi, M.; Mori, S.; Hayashi,A.; Tatsumisago, M. A novel Discharge-Charge Mechanism of a S-P2S5 Composite Electrode Without Electrolytes in All Solid- State Li/S Batteries. J. Mater. Chem. A 2017, 5, 11224−11228.(69) Machida, N.; Kobayashi, K.; Nishikawa, Y.; Shigematsu, T.Electrochemical Properties of Sulfur as Cathode Materials in a Solid-State Lithium Battery with Inorganic Solid Electrolytes. Solid StateIonics 2004, 175, 247−250.(70) Marmorstein, D.; Yu, T. H.; Striebel, K. A.; McLarnon, F. R.;Hou, J.; Cairns, E. J. Electrochemical performance of lithium/sulfurcells with three different polymer electrolytes. J. Power Sources 2000,89, 219−226.(71) Suzuki, K.; Kato, D.; Hara, K.; Yano, T.; Hirayama, M.; Hara,M.; Kanno, R. Composite Sulfur Electrode for All-Solid-StateLithium-Sulfur Battery with Li2S-GeS2-P2S5-based Thio-LISICONSolid Electrolyte. Electrochemistry 2018, 86, 1−5.(72) Wang, S.; Zhang, Y.; Zhang, X.; Liu, T.; Lin, Y.-H.; Shen, Y.; Li,L.; Nan, C.-W. High-Conductivity Argyrodite Li6PS5Cl SolidElectrolytes Prepared via Optimized Sintering Processes for All-Solid-State Lithium-Sulfur Batteries. ACS Appl. Energy Mater. 2018,10, 42279−42285.(73) Han, F.; Zhu, Y.; He, X.; Mo, Y.; Wang, C. ElectrochemicalStability of Li10GeP2S12 and Li7La3Zr2O12 Solid Electrolytes. Adv.Energy Mater. 2016, 6, 1501590.(74) Sun, Y.; Suzuki, K.; Hara, K.; Hori, S.; Yano, T.-a.; Hara, M.;Hirayama, M.; Kanno, R. Oxygen Substitution Effects in Li10GeP2S12Solid Electrolyte. J. Power Sources 2016, 324, 798−803.(75) Han, F.; Gao, T.; Zhu, Y.; Gaskell, K. J.; Wang, C. A BatteryMade from a Single Material. Adv. Mater. 2015, 27, 3473−3483.

ACS Applied Materials & Interfaces Research Article

DOI: 10.1021/acsami.9b03726ACS Appl. Mater. Interfaces 2019, 11, 18436−18447

18447