Ultrahigh ionic conductivity in optimally sintered Li10.35Ge1.35P1.65S12 superionic conductor

Ultrahigh ionic conductivity in optimally sintered Li10.35Ge1.35P1.65S12 superionic conductor | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Nano Express Ultrahigh ionic conductivity in optimally sintered Li 10.35 Ge 1.35 P 1.65 S 12 superionic conductor Hao Wen, Yue Jiang, Xingang Liu, Xiaohong Zhu, Chuhong Zhang This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-79495/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Lithium superionic conductor Li 10+ δ Ge 1+ δ P 2− δ S 12 has attracted tremendous interest for advanced all-solid-state lithium ion batteries due to extremely high ionic conductivity. However, the synthetic processes reported in literature are widely divergent, resulting in an order of magnitude difference in ionic conductivities of the same material, but as far as we know, the influence of synthetic conditions on ionic conductivity has not been studied yet. Herein, we systematically investigate the influence of sintering temperature on phase composition and ionic conductivity of the Li 10+ δ Ge 1+ δ P 2− δ S 12 compounds synthesized by conventional solid-state reaction for the first time. It is found that low and high sintering temperatures lead to a low crystallinity and the formation of impurity phases, respectively. As a result, the pure Li 10.35 Ge 1.35 P 1.65 S 12 , well crystallized in space group P42/nmc, is fabricated by optimization of the solid-state reaction temperature at 580 °C and its room temperature conductivity ( 19 mS cm − 1 ) is the highest among all existing Li 10+ δ Ge 1+ δ P 2− δ S 12 solid electrolytes. Meanwhile, the microstructure of Li 10.35 Ge 1.35 P 1.65 S 12 , being very dense and uniform, is demonstrated firstly by atomic force microscopy. Nanoscience lithium superionic conductor sulfide solid electrolyte solid-state reaction lithium ion battery. Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Introduction Lithium ion batteries (LIBs) have been used as power sources for a wide range of portable electric devices because of their high energy density, light weight and long cycle life. 1 However, the safety issues, which originate from combustible and leaky organic/liquid electrolytes, are of great concern with respect to vehicle or grid applications. 2 Solid-state electrolytes are escalating to prominence as useful components in advanced LIBs technologies due to their excellent electrochemical stability, favorable mechanical properties and feasible operation over a wide temperature window. 3−‍5 Nonetheless, one major obstacle in the application of solid-state electrolytes is that their ionic conductivities are lower than 1 mS cm − 1 at room temperature. 6 In an effort to enhance the Li-ion conductivity, there have been relentless searches over the past few decades for new materials as solid electrolytes, such as crystalline (Li 3 N, LIPON (Li x PO y N z ), LISICON (Li 14 ZnGe 4 O 16 ), NASICON (Li 1 + x Al x Ti 2− x (PO 4 ) 3 ), perovskite-structured Li 3 x La 2/3− x TiO 3 and garnet-structured Li 7 La 3 Zr 2 O 12 ), glassy (Li 2 S-P 2 S 5 , Li 2 S-GeS 2 , Li 2 S-SiS 2 ) and polymer (PEO) systems. 7 – 14 Unfortunately, none of these materials possesses conductivities comparable to those of organic liquid electrolytes that are currently being used in commercial LIBs. A big step towards solving this problem has been made until the discovery of Li 10 GeP 2 S 12 (LGPS) by Kanno et al. in 2011. The lithium ionic conductor LGPS with a different crystal structure from the thio-LISICON phase shows a very high ionic conductivity of 12 mS cm − 1 at ambient temperature, which almost equals the conductivity value of 1 M LiPF 6 in the carbonate solvents. 15 It is generally believed that the high conductivity in LGPS is attributed to the fast diffusion of Li + in its crystal structure, which consists of PS 4 tetrahedra, (Ge 0.5 P 0.5 )S 4 tetrahedra, LiS 6 octahedra and LiS 4 tetrahedra, 16 – 18 and more precisely, the 3D diffusion pathways along the c channel and along the ab plane as well. 19 – 21 The appearance of LGPS prompted enormous efforts to synthesize this material, and corresponding all-solid-state batteries using this solid electrolyte were also fabricated and studied. 22 – 24 Nevertheless, the reported synthetic processes for LGPS are widely divergent, resulting in an order of magnitude change in ionic conductivities (1–12 mS cm − 1 ). 15,17,25−28 The difference of the conductivities may be caused by the varies synthetic conditions, such as calcination temperature or time, which play an crucial role to the final ionic conductivities of LGPS. However, this has not been elucidated in the published literature as far as we know. Meanwhile, it was recognized that a higher ionic conductivity can be obtained by adjusting the stoichiometric ratio of constructing elements in LGPS, i.e. the similar solid solution system Li 10+ δ Ge 1+ δ P 2− δ S 12 (0 ≤ δ ≤ 0.5). Up to now, the highest ionic conductivity of reported Li 10+ δ Ge 1+ δ P 2− δ S 12 system is 14.2 mS cm − 1 for Li 10.35 Ge 1.35 P 1.65 S 12 ( δ = 0.35) at 27 ℃, 29 but no attempt has been made to further improve its ionic conductivity by changing the synthesis condition. Therefore, in the present study, phase-pure Li 10.35 Ge 1.35 P 1.65 S 12 was synthesized by a conventional solid-state reaction method in a sealed and evacuated quartz tube. The influences of sintering temperature on the phase composition, crystallinity, grain size and ionic conductivities were systematically studied. Upon process optimization, an ultrahigh ionic conductivity was achieved, reaching as high as 19 mS cm − 1 . Experimental Section The starting materials used in this work were Li 2 S (Aldrich, > 99.98% purity), GeS 2 (Leshan China, > 99.999% purity) and P 2 S 5 (Aladdin, > 99% purity). These materials were weighed in an appropriate molar ratio, placed into a glass bottle and mixed for 30 min using a vibrating mill. All the starting materials were handled under a high purity argon atmosphere to prevent decomposition of the materials in reaction with external moisture and oxygen. The homogeneously mixed powders were then sealed in a quartz tube at 0.03 Pa (evacuated by a molecular pump, T-Station 75, Edwards) and sintered at various temperatures ranging from 550 to 600 °C in a step of 10 °C for 8 h in a furnace with 3 °C min −‍1 heating rate and 1 °C min − 1 cooling rate. After that, the pre-synthesized material was ground to a fine powder using a mortar, pressed into pellets (about 6.5 mm in diameter and 0.9 mm in thickness) under 5 MPa pressure and sealed in a quartz tube again. In order to make the grains grow equally, the pellets were finally sintered at a certain temperature of 550 °C with the same heating and cooling rates as those used in powder sintering step. Some of the sintered samples were ground to powders and sealed in quartz capillaries (about 0.7 mm in diameter) for X-ray diffraction (XRD) measurements, using an X-ray diffractometer under transmission mode (SmartLab3, Rigaku) with Cu Kα radiation ( λ = 1.54056 Å). Diffraction data were collected at each 0.02° step width over the 2 θ range from 10° to 60°. The surface morphology and grain size of the pellets were characterized by atomic force microscopy (AFM, Anasys AFM+). Meanwhile, some other pellets were sputtered with Au onto both sides of the pellets as electrodes by using an ion beam sputtering system (SBC-12, KYKY, Beijing) in an Ar-filled glove box for electrochemical impedance spectroscopy (EIS) measurements. This was performed with an Autolab PGSTAT302N system by applying an AC signal with amplitude of 5 mV over the frequency range from 1 MHz to 1 Hz. The ionic conductivities were deduced from AC impedance results. Results And Discussion Figure 1 shows the XRD patterns of Li 10.35 Ge 1.35 P 1.65 S 12 sintered at different temperatures in comparison to the computed result. The main phase of LGPS was observed in all these materials. Although the diffraction peaks of the 550 °C sintered sample completely coincide with the computed result, the peaks intensity is very weak, indicating poor crystallinity. As the sintering temperature is sequentially raised up to 580 °C, the diffraction peak intensity under exactly the same measurement conditions becomes gradually stronger and thus the 580 °C sample shows the best crystallinity. However, with a further increase in the sintering temperature to 590 and 600 °C, the crystallinity starts to degrade. Furthermore, other phases are noticeable in the XRD patterns and are distinctly different from those obtained in the samples sintered below 580 °C, which are confirmed to match well with γ-Li 3 PS 4 and GeS 2 via the JADE program and are marked as hollow triangle (∇) and hollow box (□) in Fig. 1 , respectively. It can be seen from the figure that the peak intensity of these impurity phases becomes stronger when the sintering temperature increases from 590 to 600 °C, revealing that heat treatment of Li 10.35 Ge 1.35 P 1.65 S 12 at high temperatures above 580 °C would lead to the formation of impurity phases like γ-Li 3 PS 4 and GeS 2 . Therefore, it is determined that the most suitable sintering temperature is 580 °C for the synthesis of Li 10.35 Ge 1.35 P 1.65 S 12 . A lower sintering temperature would result in lower crystallinity, while a higher sintering temperature would lead to the formation of impurity phases. The structural profile parameters of Li 10.35 Ge 1.35 P 1.65 S 12 sintered at 580 °C were refined by Rietveld analysis with the refinement program FullProf. Figure 2 and Table 1 provide the Rietveld refinement pattern and results. The space group P42/nmc is verified and the unit cell parameters obtained in our present work ( a = 8.7002 Å, c = 12.6274 Å) are similar to those reported in the literature. 15−‍18 Table 1 Rietveld refinement results for Li 10.35 Ge 1.35 P 1.65 S 12 sintered at 580 °C. Atom Site x y z Li1 14 h 0.24593 0.27197 0.19500 Li2 4d 0 1/2 0.94434 Li3 8f 0.23543 = x (Li3) 0 Li4 4c 0 0 0.26841 Ge1 4d 0 1/2 0.69126 P1 4d 0 1/2 0.69126 P2 2b 0 0 1/2 S1 8 g 0 0.18862 0.40801 S2 8 g 0 0.29416 0.09556 S3 8 g 0 0.70168 0.79410 Note: Space group P 4 2 / nmc (137), a = 8.7002(3) Å, c = 12.6274(5) Å, V = 955.8119 Å 3 , R p =14.2, R wp =14.9, R exp =11.5, R B =2.9, R F =2.6. AFM analysis was used here for characterization of Li 10.35 Ge 1.35 P 1.65 S 12 ’s microstructure and grain size. Figure 3 shows the two-dimensional AFM micrographs of Li 10.35 Ge 1.35 P 1.65 S 12 sintered at 550, 580 and 600 °C, respectively. For each AFM image, the area in view represents a 10 µm × 10 µm square. The roughly estimated grain size of 550 °C sintered sample is about 1–2 µm. As shown in the figure, with an increase in sintering temperature, the grain size increases gradually, and thus, a positive correlation between grain size and sintering temperature is obtained in Li 10.35 Ge 1.35 P 1.65 S 12 , like what was generally observed in many other inorganic materials. The most uniform and dense microstructure is, however, achieved in the 580 °C sintered sample. Figure 4 presents the room-temperature impedance spectra for the samples sintered at different temperatures and the high frequency parts are magnified in the inset. Similar to the widely reported results for sulfide electrolytes, these plots only exhibit an oblique line in the frequency range of 1 MHz to 1 Hz, and similarly, the horizontal intercept of oblique lines presented in Fig. 4 can be identified as the total resistance R of samples. Accordingly, the ionic conductivity is calculated as σ = L /( R × A ), where L and A are the thickness and area of the pellets, respectively. 30 Figure 5 illustrates the calculated room-temperature conductivities as a function of the sintering temperature. As shown in this figure, the conductivity increases first and then decreases with the increase in sintering temperature. When the sintering temperature is 550 °C, the obtained conductivity is 13.8 mS cm − 1 , and is close to the previously reported result. 29 Very interestingly, the highest ionic conductivity, obtained in the 580 °C sample, reaches as high as 19 mS cm −‍1 . This is the highest lithium-ion conductivity obtained experimentally at room temperature for Li 10+ δ Ge 1+ δ P 2− δ S 12 , to the best of our knowledge. However, when the sintering temperature exceeds 580 °C, the ionic conductivity decreases sharply. For example, the conductivity of the sintered sample at 600 °C (10.2 mS cm −‍1 ) is just 53.7% of the value of the 580 °C sintered one. Taking the XRD patterns into account, the crystallinity of samples peaks as the sintering temperature rises up to 580 °C. Moreover, the grain size of these samples increases with increasing the sintering temperature, as previously presented in Fig. 3 . Accordingly, the total superficial area of grains does change in the same way as grain size and the Li + migration distance among Li 10.35 Ge 1.35 P 1.65 S 12 grains changes as well, and therefore, the ionic conductivity is enhanced. Besides, the γ-Li 3 PS 4 phase, with a low ionic conductivity on the order of 10 − 4 mS cm − 1 , 31 forms in the high temperature region, which attributes to the sharp decrease of the overall conductivity. With the highest ionic conductivity as well as the best crystallinity and microstructure, it is concluded that 580 °C is the best sintering temperature for Li 10.35 Ge 1.35 P 1.65 S 12 . Conclusions In this study, the LGPS-type solid electrolytes Li 10.35 Ge 1.35 P 1.65 S 12 with high ionic conductivities have been synthesized at different sintering temperature by solid-state reaction. Either low crystallinity or phase impurity features below and above 580 ℃, respectively, both leading to a sharp decrease in ionic conductivity. As a result, an ultrahigh ionic conductivity of 19 mS cm − 1 is achieved for the 580 ℃ sintered sample, which is the highest values for all Li 10+ δ Ge 1+ δ P 2− δ S 12 solid electrolytes reported so far. Abbreviations LGPS: Li 10 GeP 2 S 12 ; PEO: polyethylene oxide Declarations Acknowledgements This work was financially supported by the Ministry of Science and Technology of China (MOST) (973 program, No. 2013CB934700) and the National Natural Science Foundation of China (Nos. 51222305 and 51673123). Authors’ contributions Hao Wen and Yue Jiang contributed equally to this study. The authors read and approved the final manuscript. Availability of data and materials All data are fully available without restriction. Competing interests The authors declare that they have no competing interests. References Goodenough JB, Kim Y (2010) Challenges for rechargeable Li batteries. Chem. Mater. 22(3):587-603. Biensan P, Simon B, Peres JP, Guibert AD, Broussely M, Bodet JM, Perton F (1999) On safety of lithium-ion cells. J. Power Sources 81:906-912. Fergus JW (2010) Ceramic and polymeric solid electrolytes for lithium-ion batteries. J. Power Sources 195(15):4554-4569. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-79495","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Nano Express","associatedPublications":[],"authors":[{"id":2512374,"identity":"cf00bb99-b8c7-455f-a8eb-7f649eee556a","order_by":0,"name":"Hao Wen","email":"","orcid":"","institution":"Sichuan University - Wangjiang Campus: Sichuan University","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Hao","middleName":"","lastName":"Wen","suffix":""},{"id":2512375,"identity":"e14738f2-2103-4668-b1ff-dddb986db77c","order_by":1,"name":"Yue Jiang","email":"","orcid":"","institution":"Sichuan University - Wangjiang Campus: Sichuan University","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Yue","middleName":"","lastName":"Jiang","suffix":""},{"id":2512376,"identity":"1dd27118-fe65-4c2a-b509-000ee2652f47","order_by":2,"name":"Xingang Liu","email":"","orcid":"","institution":"Sichuan University - Wangjiang Campus: Sichuan University","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Xingang","middleName":"","lastName":"Liu","suffix":""},{"id":2512377,"identity":"07c354d7-6693-46a3-905b-521b05960ecc","order_by":3,"name":"Xiaohong Zhu","email":"","orcid":"","institution":"Sichuan University - Wangjiang Campus: Sichuan University","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Xiaohong","middleName":"","lastName":"Zhu","suffix":""},{"id":2512378,"identity":"d27a5547-8053-4b14-bc66-74f29b3ed368","order_by":4,"name":"Chuhong Zhang","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA80lEQVRIiWNgGAWjYDACCQY2GAMIKpDYRGo5Q7IWxjYitPDP7jF78HFHLYP87OZnD7/Oq5M3OMB88DYPg10eTkvunDE3nHnmOAPjnGPmxrLbDhtuOMCWbM3DkFyMS4uBRI6ZNG/bMQZmiQQzacltBxIMDvCYSfMwHEhsIKSFTSL9m7TknDqgFv5vxGipYeABMiQ/NjCDbGHDq0XiRlqZ5My2AzwSEjll0gzHDhvOPMxmbDnHIBmnFv4ZydskPrbVycnPSN8m+aOmTp7vePPDG28q7HBqgYLDPCCSGUKCHYxfPRDUgUnGHwQVjoJRMApGwUgEAHJHTgPCYyeDAAAAAElFTkSuQmCC","orcid":"https://orcid.org/0000-0002-3378-7570","institution":"Sichuan University","correspondingAuthor":true,"submittingAuthor":false,"prefix":"","firstName":"Chuhong","middleName":"","lastName":"Zhang","suffix":""}],"badges":[],"createdAt":"2020-09-17 11:31:36","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-79495/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-79495/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":2522291,"identity":"dc98673c-7a36-44f9-af41-43be51afb6d2","added_by":"auto","created_at":"2020-09-21 21:04:35","extension":"jpg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":59935,"visible":true,"origin":"","legend":"X-ray diffraction patterns for Li10.35Ge1.35P1.65S12 sintered at different temperatures (550, 560, 570, 580, 590 and 600 °C) in comparison with the computed result. The γ-Li3PS4 and GeS2 impurity phases are marked with hollow triangle () and hollow box (□), respectively.","description":"","filename":"1.jpg","url":"https://assets-eu.researchsquare.com/files/rs-79495/v1/1.jpg"},{"id":2522292,"identity":"68857f97-1241-4fd6-947c-d423a7b424f0","added_by":"auto","created_at":"2020-09-21 21:04:35","extension":"jpg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":26194,"visible":true,"origin":"","legend":"X-ray Rietveld refinement pattern for Li10.35Ge1.35P1.65S12 sintered at 580 ℃. Observed data (red dots), calculated pattern (black line), and the difference between the two (blue line) are shown. Green vertical bars indicate the positions of Bragg reflections. ","description":"","filename":"2.jpg","url":"https://assets-eu.researchsquare.com/files/rs-79495/v1/2.jpg"},{"id":2522293,"identity":"e3da2ce5-7361-4d88-8986-2cf8b5b6da31","added_by":"auto","created_at":"2020-09-21 21:04:35","extension":"jpg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":25248,"visible":true,"origin":"","legend":"Two dimensional AFM micrographs of Li10.35Ge1.35P1.65S12 sintered at (a) 550 °C, (b) 580 °C and (c) 600 °C.","description":"","filename":"3.jpg","url":"https://assets-eu.researchsquare.com/files/rs-79495/v1/3.jpg"},{"id":2522294,"identity":"e583672b-78ed-479b-b257-f9b54c7de151","added_by":"auto","created_at":"2020-09-21 21:04:35","extension":"jpg","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":41527,"visible":true,"origin":"","legend":"Room-temperature impedance spectra for the samples sintered at different temperatures. The high frequency parts are magnified in the inset.","description":"","filename":"4.jpg","url":"https://assets-eu.researchsquare.com/files/rs-79495/v1/4.jpg"},{"id":2522295,"identity":"64494df2-135f-4505-a158-9f5967a44e35","added_by":"auto","created_at":"2020-09-21 21:04:35","extension":"jpg","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":30658,"visible":true,"origin":"","legend":"Calculated conductivities at room temperature as a function of the sintering temperature for the Li10.35Ge1.35P1.65S12 samples.","description":"","filename":"5.jpg","url":"https://assets-eu.researchsquare.com/files/rs-79495/v1/5.jpg"},{"id":15669150,"identity":"d25e2e68-b36e-4a5e-9b98-cd2445529c43","added_by":"auto","created_at":"2021-11-18 13:51:48","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":316449,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-79495/v1/ffd87fbf-747b-4926-9a1d-f24f941b7d48.pdf"}],"financialInterests":"","formattedTitle":"\u003cp\u003eUltrahigh ionic conductivity in optimally sintered Li\u003csub\u003e10.35\u003c/sub\u003eGe\u003csub\u003e1.35\u003c/sub\u003eP\u003csub\u003e1.65\u003c/sub\u003eS\u003csub\u003e12\u003c/sub\u003e superionic conductor\u003c/p\u003e","fulltext":[{"header":"Introduction","content":" \u003cp\u003eLithium ion batteries (LIBs) have been used as power sources for a wide range of portable electric devices because of their high energy density, light weight and long cycle life.\u003csup\u003e\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003e However, the safety issues, which originate from combustible and leaky organic/liquid electrolytes, are of great concern with respect to vehicle or grid applications.\u003csup\u003e\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e\u003c/sup\u003e Solid-state electrolytes are escalating to prominence as useful components in advanced LIBs technologies due to their excellent electrochemical stability, favorable mechanical properties and feasible operation over a wide temperature window.\u003csup\u003e3\u0026minus;\u0026zwj;5\u003c/sup\u003e Nonetheless, one major obstacle in the application of solid-state electrolytes is that their ionic conductivities are lower than 1 mS cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e at room temperature.\u003csup\u003e\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e\u003c/sup\u003e In an effort to enhance the Li-ion conductivity, there have been relentless searches over the past few decades for new materials as solid electrolytes, such as crystalline (Li\u003csub\u003e3\u003c/sub\u003eN, LIPON (Li\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003ePO\u003csub\u003e\u003cem\u003ey\u003c/em\u003e\u003c/sub\u003eN\u003csub\u003e\u003cem\u003ez\u003c/em\u003e\u003c/sub\u003e), LISICON (Li\u003csub\u003e14\u003c/sub\u003eZnGe\u003csub\u003e4\u003c/sub\u003eO\u003csub\u003e16\u003c/sub\u003e), NASICON (Li\u003csub\u003e1\u0026thinsp;+\u0026thinsp;\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003eAl\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003eTi\u003csub\u003e2\u0026minus;\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e(PO\u003csub\u003e4\u003c/sub\u003e)\u003csub\u003e3\u003c/sub\u003e), perovskite-structured Li\u003csub\u003e3\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003eLa\u003csub\u003e2/3\u0026minus;\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003eTiO\u003csub\u003e3\u003c/sub\u003e and garnet-structured Li\u003csub\u003e7\u003c/sub\u003eLa\u003csub\u003e3\u003c/sub\u003eZr\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e12\u003c/sub\u003e), glassy (Li\u003csub\u003e2\u003c/sub\u003eS-P\u003csub\u003e2\u003c/sub\u003eS\u003csub\u003e5\u003c/sub\u003e, Li\u003csub\u003e2\u003c/sub\u003eS-GeS\u003csub\u003e2\u003c/sub\u003e, Li\u003csub\u003e2\u003c/sub\u003eS-SiS\u003csub\u003e2\u003c/sub\u003e) and polymer (PEO) systems.\u003csup\u003e\u003cspan additionalcitationids=\"CR8 CR9 CR10 CR11 CR12 CR13\" citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e\u003c/sup\u003e Unfortunately, none of these materials possesses conductivities comparable to those of organic liquid electrolytes that are currently being used in commercial LIBs.\u003c/p\u003e \u003cp\u003eA big step towards solving this problem has been made until the discovery of Li\u003csub\u003e10\u003c/sub\u003eGeP\u003csub\u003e2\u003c/sub\u003eS\u003csub\u003e12\u003c/sub\u003e (LGPS) by Kanno et al. in 2011. The lithium ionic conductor LGPS with a different crystal structure from the thio-LISICON phase shows a very high ionic conductivity of 12 mS cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e at ambient temperature, which almost equals the conductivity value of 1\u0026nbsp;M LiPF\u003csub\u003e6\u003c/sub\u003e in the carbonate solvents.\u003csup\u003e\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e\u003c/sup\u003e It is generally believed that the high conductivity in LGPS is attributed to the fast diffusion of Li\u003csup\u003e+\u003c/sup\u003e in its crystal structure, which consists of PS\u003csub\u003e4\u003c/sub\u003e tetrahedra, (Ge\u003csub\u003e0.5\u003c/sub\u003eP\u003csub\u003e0.5\u003c/sub\u003e)S\u003csub\u003e4\u003c/sub\u003e tetrahedra, LiS\u003csub\u003e6\u003c/sub\u003e octahedra and LiS\u003csub\u003e4\u003c/sub\u003e tetrahedra,\u003csup\u003e\u003cspan additionalcitationids=\"CR17\" citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e\u003c/sup\u003e and more precisely, the 3D diffusion pathways along the \u003cem\u003ec\u003c/em\u003e channel and along the \u003cem\u003eab\u003c/em\u003e plane as well.\u003csup\u003e\u003cspan additionalcitationids=\"CR20\" citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e\u003c/sup\u003e The appearance of LGPS prompted enormous efforts to synthesize this material, and corresponding all-solid-state batteries using this solid electrolyte were also fabricated and studied.\u003csup\u003e\u003cspan additionalcitationids=\"CR23\" citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e\u003c/sup\u003e Nevertheless, the reported synthetic processes for LGPS are widely divergent, resulting in an order of magnitude change in ionic conductivities (1\u0026ndash;12 mS cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e).\u003csup\u003e15,17,25\u0026minus;28\u003c/sup\u003e The difference of the conductivities may be caused by the varies synthetic conditions, such as calcination temperature or time, which play an crucial role to the final ionic conductivities of LGPS. However, this has not been elucidated in the published literature as far as we know. Meanwhile, it was recognized that a higher ionic conductivity can be obtained by adjusting the stoichiometric ratio of constructing elements in LGPS, i.e. the similar solid solution system Li\u003csub\u003e10+\u003cem\u003eδ\u003c/em\u003e\u003c/sub\u003eGe\u003csub\u003e1+\u003cem\u003eδ\u003c/em\u003e\u003c/sub\u003eP\u003csub\u003e2\u0026minus;\u003cem\u003eδ\u003c/em\u003e\u003c/sub\u003eS\u003csub\u003e12\u003c/sub\u003e (0\u0026thinsp;\u0026le;\u0026thinsp;\u003cem\u003eδ\u003c/em\u003e\u0026thinsp;\u0026le;\u0026thinsp;0.5). Up to now, the highest ionic conductivity of reported Li\u003csub\u003e10+\u003cem\u003eδ\u003c/em\u003e\u003c/sub\u003eGe\u003csub\u003e1+\u003cem\u003eδ\u003c/em\u003e\u003c/sub\u003eP\u003csub\u003e2\u0026minus;\u003cem\u003eδ\u003c/em\u003e\u003c/sub\u003eS\u003csub\u003e12\u003c/sub\u003e system is 14.2 mS cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e for Li\u003csub\u003e10.35\u003c/sub\u003eGe\u003csub\u003e1.35\u003c/sub\u003eP\u003csub\u003e1.65\u003c/sub\u003eS\u003csub\u003e12\u003c/sub\u003e (\u003cem\u003eδ\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.35) at 27 ℃,\u003csup\u003e\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e\u003c/sup\u003e but no attempt has been made to further improve its ionic conductivity by changing the synthesis condition.\u003c/p\u003e \u003cp\u003eTherefore, in the present study, phase-pure Li\u003csub\u003e10.35\u003c/sub\u003eGe\u003csub\u003e1.35\u003c/sub\u003eP\u003csub\u003e1.65\u003c/sub\u003eS\u003csub\u003e12\u003c/sub\u003e was synthesized by a conventional solid-state reaction method in a sealed and evacuated quartz tube. The influences of sintering temperature on the phase composition, crystallinity, grain size and ionic conductivities were systematically studied. Upon process optimization, an ultrahigh ionic conductivity was achieved, reaching as high as 19 mS cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e.\u003c/p\u003e "},{"header":"Experimental Section","content":" \u003cp\u003eThe starting materials used in this work were Li\u003csub\u003e2\u003c/sub\u003eS (Aldrich, \u0026gt;\u0026thinsp;99.98% purity), GeS\u003csub\u003e2\u003c/sub\u003e (Leshan China, \u0026gt;\u0026thinsp;99.999% purity) and P\u003csub\u003e2\u003c/sub\u003eS\u003csub\u003e5\u003c/sub\u003e (Aladdin, \u0026gt;\u0026thinsp;99% purity). These materials were weighed in an appropriate molar ratio, placed into a glass bottle and mixed for 30\u0026nbsp;min using a vibrating mill. All the starting materials were handled under a high purity argon atmosphere to prevent decomposition of the materials in reaction with external moisture and oxygen. The homogeneously mixed powders were then sealed in a quartz tube at 0.03\u0026nbsp;Pa (evacuated by a molecular pump, T-Station 75, Edwards) and sintered at various temperatures ranging from 550 to 600\u0026nbsp;\u0026deg;C in a step of 10\u0026nbsp;\u0026deg;C for 8\u0026nbsp;h in a furnace with 3\u0026nbsp;\u0026deg;C min\u003csup\u003e\u0026minus;\u0026zwj;1\u003c/sup\u003e heating rate and 1\u0026nbsp;\u0026deg;C min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e cooling rate. After that, the pre-synthesized material was ground to a fine powder using a mortar, pressed into pellets (about 6.5\u0026nbsp;mm in diameter and 0.9\u0026nbsp;mm in thickness) under 5\u0026nbsp;MPa pressure and sealed in a quartz tube again. In order to make the grains grow equally, the pellets were finally sintered at a certain temperature of 550\u0026nbsp;\u0026deg;C with the same heating and cooling rates as those used in powder sintering step.\u003c/p\u003e \u003cp\u003eSome of the sintered samples were ground to powders and sealed in quartz capillaries (about 0.7\u0026nbsp;mm in diameter) for X-ray diffraction (XRD) measurements, using an X-ray diffractometer under transmission mode (SmartLab3, Rigaku) with Cu Kα radiation (\u003cem\u003eλ\u003c/em\u003e\u0026thinsp;=\u0026thinsp;1.54056\u0026nbsp;\u0026Aring;). Diffraction data were collected at each 0.02\u0026deg; step width over the 2\u003cem\u003eθ\u003c/em\u003e range from 10\u0026deg; to 60\u0026deg;. The surface morphology and grain size of the pellets were characterized by atomic force microscopy (AFM, Anasys AFM+). Meanwhile, some other pellets were sputtered with Au onto both sides of the pellets as electrodes by using an ion beam sputtering system (SBC-12, KYKY, Beijing) in an Ar-filled glove box for electrochemical impedance spectroscopy (EIS) measurements. This was performed with an Autolab PGSTAT302N system by applying an AC signal with amplitude of 5\u0026nbsp;mV over the frequency range from 1\u0026nbsp;MHz to 1\u0026nbsp;Hz. The ionic conductivities were deduced from AC impedance results.\u003c/p\u003e "},{"header":"Results And Discussion","content":"\u003cp\u003eFigure \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e shows the XRD patterns of Li\u003csub\u003e10.35\u003c/sub\u003eGe\u003csub\u003e1.35\u003c/sub\u003eP\u003csub\u003e1.65\u003c/sub\u003eS\u003csub\u003e12\u003c/sub\u003e sintered at different temperatures in comparison to the computed result. The main phase of LGPS was observed in all these materials. Although the diffraction peaks of the 550\u0026nbsp;\u0026deg;C sintered sample completely coincide with the computed result, the peaks intensity is very weak, indicating poor crystallinity. As the sintering temperature is sequentially raised up to 580\u0026nbsp;\u0026deg;C, the diffraction peak intensity under exactly the same measurement conditions becomes gradually stronger and thus the 580\u0026nbsp;\u0026deg;C sample shows the best crystallinity. However, with a further increase in the sintering temperature to 590 and 600\u0026nbsp;\u0026deg;C, the crystallinity starts to degrade. Furthermore, other phases are noticeable in the XRD patterns and are distinctly different from those obtained in the samples sintered below 580\u0026nbsp;\u0026deg;C, which are confirmed to match well with \u0026gamma;-Li\u003csub\u003e3\u003c/sub\u003ePS\u003csub\u003e4\u003c/sub\u003e and GeS\u003csub\u003e2\u003c/sub\u003e via the JADE program and are marked as hollow triangle (\u0026nabla;) and hollow box (□) in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e, respectively. It can be seen from the figure that the peak intensity of these impurity phases becomes stronger when the sintering temperature increases from 590 to 600\u0026nbsp;\u0026deg;C, revealing that heat treatment of Li\u003csub\u003e10.35\u003c/sub\u003eGe\u003csub\u003e1.35\u003c/sub\u003eP\u003csub\u003e1.65\u003c/sub\u003eS\u003csub\u003e12\u003c/sub\u003e at high temperatures above 580\u0026nbsp;\u0026deg;C would lead to the formation of impurity phases like \u0026gamma;-Li\u003csub\u003e3\u003c/sub\u003ePS\u003csub\u003e4\u003c/sub\u003e and GeS\u003csub\u003e2\u003c/sub\u003e. Therefore, it is determined that the most suitable sintering temperature is 580\u0026nbsp;\u0026deg;C for the synthesis of Li\u003csub\u003e10.35\u003c/sub\u003eGe\u003csub\u003e1.35\u003c/sub\u003eP\u003csub\u003e1.65\u003c/sub\u003eS\u003csub\u003e12\u003c/sub\u003e. A lower sintering temperature would result in lower crystallinity, while a higher sintering temperature would lead to the formation of impurity phases.\u003c/p\u003e\n\u003cp\u003eThe structural profile parameters of Li\u003csub\u003e10.35\u003c/sub\u003eGe\u003csub\u003e1.35\u003c/sub\u003eP\u003csub\u003e1.65\u003c/sub\u003eS\u003csub\u003e12\u003c/sub\u003e sintered at 580\u0026nbsp;\u0026deg;C were refined by Rietveld analysis with the refinement program FullProf. Figure\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e and Table\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e provide the Rietveld refinement pattern and results. The space group P42/nmc is verified and the unit cell parameters obtained in our present work (\u003cem\u003ea\u003c/em\u003e\u0026thinsp;=\u0026thinsp;8.7002\u0026nbsp;\u0026Aring;, \u003cem\u003ec\u003c/em\u003e\u0026thinsp;=\u0026thinsp;12.6274\u0026nbsp;\u0026Aring;) are similar to those reported in the literature.\u003csup\u003e15\u0026minus;\u0026zwj;18\u003c/sup\u003e\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;\u003c/p\u003e\n\u003cdiv class=\"gridtable\"\u003e\n\u003ctable id=\"Tab1\" border=\"1\"\u003e\u003ccaption\u003e\n\u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e\n\u003cdiv class=\"CaptionContent\"\u003e\n\u003cp\u003eRietveld refinement results for Li\u003csub\u003e10.35\u003c/sub\u003eGe\u003csub\u003e1.35\u003c/sub\u003eP\u003csub\u003e1.65\u003c/sub\u003eS\u003csub\u003e12\u003c/sub\u003e sintered at 580\u0026nbsp;\u0026deg;C.\u003c/p\u003e\n\u003c/div\u003e\n\u003c/caption\u003e\n\u003cthead\u003e\n\u003ctr style=\"height: 35px;\"\u003e\n\u003cth style=\"height: 35px;\" align=\"left\"\u003e\n\u003cp\u003eAtom\u003c/p\u003e\n\u003c/th\u003e\n\u003cth style=\"height: 35px;\" align=\"left\"\u003e\n\u003cp\u003eSite\u003c/p\u003e\n\u003c/th\u003e\n\u003cth style=\"height: 35px;\" align=\"left\"\u003e\n\u003cp\u003e\u003cem\u003ex\u003c/em\u003e\u003c/p\u003e\n\u003c/th\u003e\n\u003cth style=\"height: 35px;\" align=\"left\"\u003e\n\u003cp\u003e\u003cem\u003ey\u003c/em\u003e\u003c/p\u003e\n\u003c/th\u003e\n\u003cth style=\"height: 35px;\" align=\"left\"\u003e\n\u003cp\u003e\u003cem\u003ez\u003c/em\u003e\u003c/p\u003e\n\u003c/th\u003e\n\u003c/tr\u003e\n\u003c/thead\u003e\n\u003ctbody\u003e\n\u003ctr style=\"height: 35px;\"\u003e\n\u003ctd style=\"height: 35px;\" align=\"left\"\u003e\n\u003cp\u003eLi1\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"height: 35px;\" align=\"left\"\u003e\n\u003cp\u003e14\u0026nbsp;h\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"height: 35px;\" align=\"left\"\u003e\n\u003cp\u003e0.24593\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"height: 35px;\" align=\"left\"\u003e\n\u003cp\u003e0.27197\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"height: 35px;\" align=\"left\"\u003e\n\u003cp\u003e0.19500\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr style=\"height: 35px;\"\u003e\n\u003ctd style=\"height: 35px;\" align=\"left\"\u003e\n\u003cp\u003eLi2\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"height: 35px;\" align=\"left\"\u003e\n\u003cp\u003e4d\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"height: 35px;\" align=\"left\"\u003e\n\u003cp\u003e0\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"height: 35px;\" align=\"left\"\u003e\n\u003cp\u003e1/2\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"height: 35px;\" align=\"left\"\u003e\n\u003cp\u003e0.94434\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr style=\"height: 35px;\"\u003e\n\u003ctd style=\"height: 35px;\" align=\"left\"\u003e\n\u003cp\u003eLi3\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"height: 35px;\" align=\"left\"\u003e\n\u003cp\u003e8f\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"height: 35px;\" align=\"left\"\u003e\n\u003cp\u003e0.23543\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"height: 35px;\" align=\"left\"\u003e\n\u003cp\u003e= \u003cem\u003ex\u003c/em\u003e(Li3)\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"height: 35px;\" align=\"left\"\u003e\n\u003cp\u003e0\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr style=\"height: 35px;\"\u003e\n\u003ctd style=\"height: 35px;\" align=\"left\"\u003e\n\u003cp\u003eLi4\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"height: 35px;\" align=\"left\"\u003e\n\u003cp\u003e4c\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"height: 35px;\" align=\"left\"\u003e\n\u003cp\u003e0\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"height: 35px;\" align=\"left\"\u003e\n\u003cp\u003e0\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"height: 35px;\" align=\"left\"\u003e\n\u003cp\u003e0.26841\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr style=\"height: 35px;\"\u003e\n\u003ctd style=\"height: 35px;\" align=\"left\"\u003e\n\u003cp\u003eGe1\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"height: 35px;\" align=\"left\"\u003e\n\u003cp\u003e4d\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"height: 35px;\" align=\"left\"\u003e\n\u003cp\u003e0\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"height: 35px;\" align=\"left\"\u003e\n\u003cp\u003e1/2\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"height: 35px;\" align=\"left\"\u003e\n\u003cp\u003e0.69126\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr style=\"height: 35px;\"\u003e\n\u003ctd style=\"height: 35px;\" align=\"left\"\u003e\n\u003cp\u003eP1\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"height: 35px;\" align=\"left\"\u003e\n\u003cp\u003e4d\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"height: 35px;\" align=\"left\"\u003e\n\u003cp\u003e0\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"height: 35px;\" align=\"left\"\u003e\n\u003cp\u003e1/2\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"height: 35px;\" align=\"left\"\u003e\n\u003cp\u003e0.69126\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr style=\"height: 35px;\"\u003e\n\u003ctd style=\"height: 35px;\" align=\"left\"\u003e\n\u003cp\u003eP2\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"height: 35px;\" align=\"left\"\u003e\n\u003cp\u003e2b\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"height: 35px;\" align=\"left\"\u003e\n\u003cp\u003e0\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"height: 35px;\" align=\"left\"\u003e\n\u003cp\u003e0\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"height: 35px;\" align=\"left\"\u003e\n\u003cp\u003e1/2\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr style=\"height: 35px;\"\u003e\n\u003ctd style=\"height: 35px;\" align=\"left\"\u003e\n\u003cp\u003eS1\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"height: 35px;\" align=\"left\"\u003e\n\u003cp\u003e8\u0026nbsp;g\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"height: 35px;\" align=\"left\"\u003e\n\u003cp\u003e0\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"height: 35px;\" align=\"left\"\u003e\n\u003cp\u003e0.18862\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"height: 35px;\" align=\"left\"\u003e\n\u003cp\u003e0.40801\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr style=\"height: 35px;\"\u003e\n\u003ctd style=\"height: 35px;\" align=\"left\"\u003e\n\u003cp\u003eS2\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"height: 35px;\" align=\"left\"\u003e\n\u003cp\u003e8\u0026nbsp;g\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"height: 35px;\" align=\"left\"\u003e\n\u003cp\u003e0\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"height: 35px;\" align=\"left\"\u003e\n\u003cp\u003e0.29416\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"height: 35px;\" align=\"left\"\u003e\n\u003cp\u003e0.09556\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr style=\"height: 35px;\"\u003e\n\u003ctd style=\"height: 35px;\" align=\"left\"\u003e\n\u003cp\u003eS3\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"height: 35px;\" align=\"left\"\u003e\n\u003cp\u003e8\u0026nbsp;g\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"height: 35px;\" align=\"left\"\u003e\n\u003cp\u003e0\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"height: 35px;\" align=\"left\"\u003e\n\u003cp\u003e0.70168\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"height: 35px;\" align=\"left\"\u003e\n\u003cp\u003e0.79410\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr style=\"height: 42px;\"\u003e\n\u003ctd style=\"height: 42px;\" colspan=\"5\" align=\"left\"\u003e\n\u003cp\u003eNote: Space group \u003cem\u003eP\u003c/em\u003e4\u003csub\u003e2\u003c/sub\u003e/\u003cem\u003enmc\u003c/em\u003e (137), \u003cem\u003ea\u0026thinsp;=\u003c/em\u003e\u0026thinsp;8.7002(3) \u0026Aring;, \u003cem\u003ec\u003c/em\u003e\u0026thinsp;=\u0026thinsp;12.6274(5) \u0026Aring;, \u003cem\u003eV\u003c/em\u003e\u0026thinsp;=\u0026thinsp;955.8119 \u0026Aring;\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e3\u003c/span\u003e\u003c/sup\u003e, \u003cem\u003eR\u003c/em\u003e\u003csub\u003ep\u003c/sub\u003e=14.2, \u003cem\u003eR\u003c/em\u003e\u003csub\u003ewp\u003c/sub\u003e=14.9, \u003cem\u003eR\u003c/em\u003e\u003csub\u003eexp\u003c/sub\u003e=11.5, \u003cem\u003eR\u003c/em\u003e\u003csub\u003eB\u003c/sub\u003e=2.9, \u003cem\u003eR\u003c/em\u003e\u003csub\u003eF\u003c/sub\u003e=2.6.\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003c/tbody\u003e\n\u003c/table\u003e\n\u003c/div\u003e\n\u003cp\u003e\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eAFM analysis was used here for characterization of Li\u003csub\u003e10.35\u003c/sub\u003eGe\u003csub\u003e1.35\u003c/sub\u003eP\u003csub\u003e1.65\u003c/sub\u003eS\u003csub\u003e12\u003c/sub\u003e\u0026rsquo;s microstructure and grain size. Figure\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e shows the two-dimensional AFM micrographs of Li\u003csub\u003e10.35\u003c/sub\u003eGe\u003csub\u003e1.35\u003c/sub\u003eP\u003csub\u003e1.65\u003c/sub\u003eS\u003csub\u003e12\u003c/sub\u003e sintered at 550, 580 and 600\u0026nbsp;\u0026deg;C, respectively. For each AFM image, the area in view represents a 10\u0026nbsp;\u0026micro;m\u0026thinsp;\u0026times;\u0026thinsp;10\u0026nbsp;\u0026micro;m square. The roughly estimated grain size of 550\u0026nbsp;\u0026deg;C sintered sample is about 1\u0026ndash;2\u0026nbsp;\u0026micro;m. As shown in the figure, with an increase in sintering temperature, the grain size increases gradually, and thus, a positive correlation between grain size and sintering temperature is obtained in Li\u003csub\u003e10.35\u003c/sub\u003eGe\u003csub\u003e1.35\u003c/sub\u003eP\u003csub\u003e1.65\u003c/sub\u003eS\u003csub\u003e12\u003c/sub\u003e, like what was generally observed in many other inorganic materials. The most uniform and dense microstructure is, however, achieved in the 580\u0026nbsp;\u0026deg;C sintered sample.\u003c/p\u003e\n\u003cp\u003eFigure\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e presents the room-temperature impedance spectra for the samples sintered at different temperatures and the high frequency parts are magnified in the inset. Similar to the widely reported results for sulfide electrolytes, these plots only exhibit an oblique line in the frequency range of 1\u0026nbsp;MHz to 1\u0026nbsp;Hz, and similarly, the horizontal intercept of oblique lines presented in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e can be identified as the total resistance \u003cem\u003eR\u003c/em\u003e of samples. Accordingly, the ionic conductivity is calculated as \u003cem\u003e\u0026sigma;\u003c/em\u003e\u0026thinsp;=\u0026thinsp;\u003cem\u003eL\u003c/em\u003e/(\u003cem\u003eR\u003c/em\u003e\u0026thinsp;\u0026times;\u0026thinsp;\u003cem\u003eA\u003c/em\u003e), where \u003cem\u003eL\u003c/em\u003e and \u003cem\u003eA\u003c/em\u003e are the thickness and area of the pellets, respectively.\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e30\u003c/span\u003e\u003c/sup\u003e\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eFigure\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003e illustrates the calculated room-temperature conductivities as a function of the sintering temperature. As shown in this figure, the conductivity increases first and then decreases with the increase in sintering temperature. When the sintering temperature is 550\u0026nbsp;\u0026deg;C, the obtained conductivity is 13.8 mS cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, and is close to the previously reported result.\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e29\u003c/span\u003e\u003c/sup\u003e Very interestingly, the highest ionic conductivity, obtained in the 580\u0026nbsp;\u0026deg;C sample, reaches as high as 19 mS cm\u003csup\u003e\u0026minus;\u0026zwj;1\u003c/sup\u003e. This is the highest lithium-ion conductivity obtained experimentally at room temperature for Li\u003csub\u003e10+\u003cem\u003e\u0026delta;\u003c/em\u003e\u003c/sub\u003eGe\u003csub\u003e1+\u003cem\u003e\u0026delta;\u003c/em\u003e\u003c/sub\u003eP\u003csub\u003e2\u0026minus;\u003cem\u003e\u0026delta;\u003c/em\u003e\u003c/sub\u003eS\u003csub\u003e12\u003c/sub\u003e, to the best of our knowledge. However, when the sintering temperature exceeds 580\u0026nbsp;\u0026deg;C, the ionic conductivity decreases sharply. For example, the conductivity of the sintered sample at 600\u0026nbsp;\u0026deg;C (10.2 mS cm\u003csup\u003e\u0026minus;\u0026zwj;1\u003c/sup\u003e) is just 53.7% of the value of the 580\u0026nbsp;\u0026deg;C sintered one. Taking the XRD patterns into account, the crystallinity of samples peaks as the sintering temperature rises up to 580\u0026nbsp;\u0026deg;C. Moreover, the grain size of these samples increases with increasing the sintering temperature, as previously presented in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e. Accordingly, the total superficial area of grains does change in the same way as grain size and the Li\u003csup\u003e+\u003c/sup\u003e migration distance among Li\u003csub\u003e10.35\u003c/sub\u003eGe\u003csub\u003e1.35\u003c/sub\u003eP\u003csub\u003e1.65\u003c/sub\u003eS\u003csub\u003e12\u003c/sub\u003e grains changes as well, and therefore, the ionic conductivity is enhanced. Besides, the \u0026gamma;-Li\u003csub\u003e3\u003c/sub\u003ePS\u003csub\u003e4\u003c/sub\u003e phase, with a low ionic conductivity on the order of 10\u003csup\u003e\u0026minus;\u0026thinsp;4\u003c/sup\u003e mS cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e,\u003csup\u003e31\u003c/sup\u003e forms in the high temperature region, which attributes to the sharp decrease of the overall conductivity. With the highest ionic conductivity as well as the best crystallinity and microstructure, it is concluded that 580\u0026nbsp;\u0026deg;C is the best sintering temperature for Li\u003csub\u003e10.35\u003c/sub\u003eGe\u003csub\u003e1.35\u003c/sub\u003eP\u003csub\u003e1.65\u003c/sub\u003eS\u003csub\u003e12\u003c/sub\u003e.\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;\u003c/p\u003e"},{"header":"Conclusions","content":" \u003cp\u003eIn this study, the LGPS-type solid electrolytes Li\u003csub\u003e10.35\u003c/sub\u003eGe\u003csub\u003e1.35\u003c/sub\u003eP\u003csub\u003e1.65\u003c/sub\u003eS\u003csub\u003e12\u003c/sub\u003e with high ionic conductivities have been synthesized at different sintering temperature by solid-state reaction. Either low crystallinity or phase impurity features below and above 580 ℃, respectively, both leading to a sharp decrease in ionic conductivity. As a result, an ultrahigh ionic conductivity of 19 mS cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e is achieved for the 580 ℃ sintered sample, which is the highest values for all Li\u003csub\u003e10+\u003cem\u003eδ\u003c/em\u003e\u003c/sub\u003eGe\u003csub\u003e1+\u003cem\u003eδ\u003c/em\u003e\u003c/sub\u003eP\u003csub\u003e2\u0026minus;\u003cem\u003eδ\u003c/em\u003e\u003c/sub\u003eS\u003csub\u003e12\u003c/sub\u003e solid electrolytes reported so far.\u003c/p\u003e "},{"header":"Abbreviations","content":"\u003cp\u003eLGPS: Li\u003csub\u003e10\u003c/sub\u003eGeP\u003csub\u003e2\u003c/sub\u003eS\u003csub\u003e12\u003c/sub\u003e; PEO: polyethylene oxide\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAcknowledgements\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis work was financially supported by the Ministry of Science and Technology of China (MOST) (973 program, No. 2013CB934700) and the National Natural Science Foundation of China (Nos. 51222305 and 51673123).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthors\u0026rsquo; contributions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eHao Wen and Yue Jiang contributed equally to this study. The authors read and approved the final manuscript.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAvailability of data and materials\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAll data are fully available without restriction.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting interests\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare that they have no competing interests.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eGoodenough JB, Kim Y (2010) Challenges for rechargeable Li batteries. Chem. Mater. 22(3):587-603.\u003c/li\u003e\n\u003cli\u003eBiensan P, Simon B, Peres JP, Guibert AD, Broussely M, Bodet JM, Perton F (1999) On safety of lithium-ion cells. J. Power Sources 81:906-912.\u003c/li\u003e\n\u003cli\u003eFergus JW (2010) Ceramic and polymeric solid electrolytes for lithium-ion batteries. J. 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Mater. 17(7):918-921.\u003c/li\u003e\n\u003cli\u003eAldissi M (2001) Multi-layered polymer electrolytes towards interfacial stability in lithium ion batteries. J. Power Sources 94(2):219-224.\u003c/li\u003e\n\u003cli\u003eAdachi GY, Imanaka N, Aono H (1996) Fast Li\u003csup\u003e+\u003c/sup\u003e conducting ceramic electrolytes. Adv. Mater. 8(2):127-135.\u003c/li\u003e\n\u003cli\u003eKayama N, Homma K, Yamakawa Y, Hirayama M, Kanno R, Yonemura M, Kamiyama T, Kato Y, Hama S, Kawamoto K, Mitsui A (2011) A lithium superionic conductor. Nat. Mater. 10:682-686.\u003c/li\u003e\n\u003cli\u003eOng SP, Richards WD, Miara L, Lee HS, Ceder G (2013) Phase stability, electrochemical stability and ionic conductivity of the Li\u003csub\u003e10\u0026plusmn;1\u003c/sub\u003eMP\u003csub\u003e2\u003c/sub\u003eX\u003csub\u003e12\u003c/sub\u003e (M = Ge, Si, Sn, Al or P, and X = O, S or Se) family of superionic conductors. Energy Environ. 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Technol. 29(3):193\u0026ndash;\u003c/li\u003e\n\u003cli\u003eHomma K, Yonemura M, Kobayashi T, Nagao M, Hirayama M, Kanno R (2011) Crystal structure and phase transitions of the lithium ionic conductor Li\u003csub\u003e3\u003c/sub\u003ePS\u003csub\u003e4\u003c/sub\u003e. Solid State Ionics 182(1):53\u0026ndash;\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"lithium superionic conductor, sulfide, solid electrolyte, solid-state reaction, lithium ion battery.","lastPublishedDoi":"10.21203/rs.3.rs-79495/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-79495/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eLithium superionic conductor Li\u003csub\u003e10+\u003cem\u003eδ\u003c/em\u003e\u003c/sub\u003eGe\u003csub\u003e1+\u003cem\u003eδ\u003c/em\u003e\u003c/sub\u003eP\u003csub\u003e2\u0026minus;\u003cem\u003eδ\u003c/em\u003e\u003c/sub\u003eS\u003csub\u003e12\u003c/sub\u003e has attracted tremendous interest for advanced all-solid-state lithium ion batteries due to extremely high ionic conductivity. However, the synthetic processes reported in literature are widely divergent, resulting in an order of magnitude difference in ionic conductivities of the same material, but as far as we know, the influence of synthetic conditions on ionic conductivity has not been studied yet. Herein, we systematically investigate the influence of sintering temperature on phase composition and ionic conductivity of the Li\u003csub\u003e10+\u003cem\u003eδ\u003c/em\u003e\u003c/sub\u003eGe\u003csub\u003e1+\u003cem\u003eδ\u003c/em\u003e\u003c/sub\u003eP\u003csub\u003e2\u0026minus;\u003cem\u003eδ\u003c/em\u003e\u003c/sub\u003eS\u003csub\u003e12\u003c/sub\u003e compounds synthesized by conventional solid-state reaction for the first time. It is found that low and high sintering temperatures lead to a low crystallinity and the formation of impurity phases, respectively. As a result, the pure Li\u003csub\u003e10.35\u003c/sub\u003eGe\u003csub\u003e1.35\u003c/sub\u003eP\u003csub\u003e1.65\u003c/sub\u003eS\u003csub\u003e12\u003c/sub\u003e, well crystallized in space group P42/nmc, is fabricated by optimization of the solid-state reaction temperature at 580\u0026nbsp;\u0026deg;C and its room temperature conductivity (\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003e19\u003c/span\u003e mS cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) is the highest among all existing Li\u003csub\u003e10+\u003cem\u003eδ\u003c/em\u003e\u003c/sub\u003eGe\u003csub\u003e1+\u003cem\u003eδ\u003c/em\u003e\u003c/sub\u003eP\u003csub\u003e2\u0026minus;\u003cem\u003eδ\u003c/em\u003e\u003c/sub\u003eS\u003csub\u003e12\u003c/sub\u003e solid electrolytes. Meanwhile, the microstructure of Li\u003csub\u003e10.35\u003c/sub\u003eGe\u003csub\u003e1.35\u003c/sub\u003eP\u003csub\u003e1.65\u003c/sub\u003eS\u003csub\u003e12\u003c/sub\u003e, being very dense and uniform, is demonstrated firstly by atomic force microscopy.\u003c/p\u003e","manuscriptTitle":"Ultrahigh ionic conductivity in optimally sintered Li10.35Ge1.35P1.65S12 superionic conductor","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2020-09-21 21:04:33","doi":"10.21203/rs.3.rs-79495/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"d13d27fc-aa10-4c35-8354-f2403c47482a","owner":[],"postedDate":"September 21st, 2020","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[{"id":568303,"name":"Nanoscience"}],"tags":[],"updatedAt":"2020-09-27T23:13:03+00:00","versionOfRecord":[],"versionCreatedAt":"2020-09-21 21:04:33","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-79495","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-79495","identity":"rs-79495","version":["v1"]},"buildId":"7rjqhiLT3MXkJMwkYKINL","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}