High Capacity and Superior Cyclic Performances of All-Solid-State

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High Capacity and Superior Cyclic Performances of All-SolidState Lithium Batteries Enabled by a Glass-Ceramics Solo Yibo Zhang, Rujun Chen, Ting Liu, Bingqing Xu, Xue Zhang, Liangliang Li, Yuanhua Lin, Ce-Wen Nan, and Yang Shen ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.7b18211 • Publication Date (Web): 23 Feb 2018 Downloaded from http://pubs.acs.org on February 24, 2018

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ACS Applied Materials & Interfaces

High Capacity and Superior Cyclic Performances of All-Solid-State Lithium Batteries Enabled by a Glass-Ceramics Solo Yibo Zhang, Rujun Chen, Ting Liu, Bingqing Xu, Xue Zhang, Liangliang Li, Yuanhua Lin, Ce-Wen Nan*, Yang Shen* State Key Laboratory of New Ceramics and Fine Processing, School of Materials Science and Engineering, Tsinghua University, Beijing, 100084, P. R. China E-mail: [email protected]; [email protected]

KEYWORDS All-solid-state battery, 78Li2S-22P2S5, glass-ceramic, solid electrolyte, Lithium ion battery

ABSTRACT By using highly Li-ion conductive 78Li2S-22P2S5 glass-ceramic (7822gc) as both electrolyte and active material in the composite cathode obtained via ball-milling the 7822gc with multiple carbons, a kind of monolithic all-solid-state batteries were prepared with lithium-indium foil as the anode. Such 7822gc-based monolithic batteries present stable discharge capacity of 480.3 mAh g-1 at 0.176 mA cm-2 after 60 cycles, which is three times of the previous work with the highest capacity so far among all attempts of using sulfide electrolytes as the active materials. High capacity retention of 90.6% and coulombic efficiency of higher than 99% with high active material loading of 7 mg cm-2 were also obtained. X-ray photoelectron spectroscopy was used to reveal the electrochemical reaction

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mechanisms in the 7822gc cathode.

Introduction The prevalence of the electric vehicles, wearable products and renewable electricity are greatly promoting wide applications of lithium ion batteries in the fields of energy storage.1-3

23

However, the dangerous flammable organic liquid electrolytes used in the commercial lithium-ion batteries have safety concerns with respect to vehicles or electronic products. Thus all-solid-state batteries with inorganic incombustible electrolytes exhibiting enhanced safety, higher durability and larger capacity, have been put forward to solve these safety issues and are attracting ever-increasing attention.4-6 Nevertheless, the commercialization of 56

the all-solid-state lithium-ion batteries is currently hampered for several problems, e.g., interfacial issues, compromised cyclic and rate performances. Roots of the interfacial issues and the poor cyclic performance are the poor interface contacts between solid electrolytes and electrodes, which could result in high interfacial resistance, and the low ionic conductivity of solid electrolytes compared to the liquid counterparts. 7 , 8 Therefore, a superior solid electrolyte with high ionic conductivity and low interface resistance to electrodes contacting is critical to improving battery performance in all-solid-state systems.9-12

9101112

Scores of inorganic solid electrolytes with high lithium-ion conductivity have been investigated. Among them, with the advantages of higher ionic conductivity, more convenient preparation method and better interface contacting with electrodes than oxides,


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sulfur electrolytes have been widely studied,13 though their application in the open air is restricted because of the high sensitivity to moisture. 14 Among the family of sulfur electrolytes, Li10GeP2S12

15

and Li9.54Si1.74P1.44S11.7Cl0.3

16

recently reported achieved

ultrahigh ionic conductivity of more than 1.0×10-2 S cm-1. However, the utilization of the expensive element Ge and the electrochemical instability between electrolytes and low voltage anode materials such as lithium metal have restricted their applications. 17 Meanwhile, classical Li2S-P2S5 glass-ceramic solid electrolytes are still attracting great attention because of their inexpensive ingredients, high ionic conductivity of about 10-3 S cm-1 at room temperature and good electrochemical stability. Of particular interest, a high ionic conductivity of 1.7×10-2 S cm-1 and a low activation energy of 17 kJ mol-1 was achieved in 70Li2S·30P2S5 system, even though all-solid-state battery using this material has not been reported.18 Recently, we have demonstrated the usability of the 70Li2S·30P2S519 and 78Li2S·22P2S520 glass-ceramic (7822gc) electrolytes with a high conductivity of more than 1.0×10−3 S cm−1. Especially, the 7822gc prepared via a simple processing has achieved the highest conductivity of 1.78×10−3 S cm−1 in the 78Li2S·22P2S5 system. 21 , 22 High-performance all-solid-state lithium batteries with FeS2 or Li2S as cathode active materials and Li-In foil as the anode material have also been prepared to demonstrate the usability of the 7822gc electrolyte. As for the problem of poor rate performance, additive materials used to construct the ionic and electronic conduction paths in the electrode have limited the contents of active materials in the composite cathode.23-25 Thus, the capacities per gram of total composite 2425

cathode for the all-solid-state batteries are sacrificed to obtain a better power density. The



Li2S-P2S5 electrolytes contain Li2S component, which is a kind of cathode material with high theoretical capacity. Thus the electrolyte itself could be used as an active material as well. The 7822gc electrolyte might have residual Li2S crystalline phase and high conductive phase in the glass-ceramic matrix which may also have electrochemical activity. Thus both high power density and high energy density could be expected in the all-solid-state batteries with the 7822gc as both electrolyte and active cathode material. Here we report a kind of monolithic all-solid-state battery with the 7822gc as both electrolyte and cathode active material, and lithium-indium (Li-In) foil as the anode. The composite cathodes are prepared through ball-milling 7822gc and multiple carbons (MC) without any other normal active materials. Such 7822gc-based all-solid-state batteries present stable discharge capacity of 480.3 mAh g-1 at 0.176 mA cm-2 after 60 cycles, which is three times larger than the reported work with the highest capacity of all attempts of using sulfide electrolytes as the active materials as we know.23,26 High capacity retention of 90.6% and excellent coulombic efficiency higher than 99% are also obtained with high loading of 7822gc. All above effectively demonstrate the usability of this monolithic all-solid-state battery simply based on the 7822gc. Experimental Section To prepare the 7822gc electrolytes, reagent-grade chemicals P2S5 (Aldrich, 99%) and Li2S (Alfa, 99.9%) were mixed thoroughly in appropriate molar ratios. Then the mechanical milling using a high energy planetary ball mill (Fritsch Pulverisette 7) was performed for 25 hours. All the processing was carried out in a dry Ar-filled glove box with [H2O],[ O2]＜1 ppm. The obtained 78Li2S-22P2S5 glass electrolyte was grinded into powder by motor in the


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glove box, then the glass powder were heat-treated at 170 °C for 0.5 h and then 240 °C for 3h in the glove box to obtain the glass-ceramic electrolytes. The performance of 7822gc electrolytes can be found in our previous report.20 MC used as the conductive additive was prepared by ball milling Super P carbon (Timcal) (66.7 wt. %) and VGCF (vapor grown carbon fibers, SHOWA DENKO) (33.3 wt. %) together. Hong et al. have demonstrated that zero-dimensional Super P could form well electronic conduction paths in short range regions and VGCF could provide long range conduction paths. Thus, Super P and VGCF together could form a homogeneous and synergistic hierarchical conductive network.27 The composite cathodes were obtained by ball milling the mixture with 70-90 wt% the 7822gc and 30-10% wt% MC powders, and the loading of the active material 7822gc is about 7 mg cm-2. All-solid-state cells of 7822gc-MC|7822gc|Li-In (see Figure 1) were fabricated with the obtained 7822gc-MC as a working composite electrode and the 7822gc as the solid electrolyte. The electrochemical performance of all-solid-state cells were tested in a Swagelok cell, wherein the solid electrolyte and electrodes were cold-pressed inside an insulating poly(ether-ether-ketone) PEEK tube (diameter = 12 mm). Firstly, the electrolyte layer was obtained by compressing 7822gc powders at 100 MPa. Then the composite cathodes were pressed on one side of the electrolyte pellet at 150 MPa, and the Li-In foil as the anode was attached at 100 MPa on the other side. Finally, the three-layered cell pellets were pressed into a mode (3ESTC15, KEJINGSTAR, China) at 100 MPa with two stainless steel disks as current collectors on both sides. The total mass of the composite cathodes is about 10 mg. The cells were cycled using a charge-discharge measurement device (C2001A,



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LAND, China) at room temperature. The cut-off voltage was 0.0 - 3.0 V (vs. Li-In), which is equivalent to 0.6 - 3.6 V (vs. Li). The capacity is based on the weight of active materials (i.e., the 7822gc in the composite electrodes). The current density was set as 0.044 mA cm−2 for the first two cycles and 0.176 mA cm−2 for the following cycles. The AC impedance measurements were performed for the cells before and after cycles using an impedance analyzer (ZAHNER-elektrik IM6) in the frequency range of 1 Hz to 8 MHz with an AC amplitude of 50 mV. X-ray diffraction patterns (XRD, Rigaku D/max-2500 diffraction meter with a Cu Kα radiation source) were obtained for the phase identification of the composite cathode samples in air at room temperature. In order to prevent from air exposure, the samples were sealed in an air-tight container covered with a polyimide thin film and mounted on the x-ray diffractometer. Scanning election microscopy (SEM, JEOLJSM-7001F) was used to observe the cross-section microstructure of the cells before and after cycles coupled with an energy dispersive spectroscopy (EDS). The surface chemistry of the 7822gc-MC cathodes was examined

by

X-ray

Photoelectron

Spectroscopy

(XPS)

using

an

ESCALAB

250Xi spectrometer. To prepare the sample for XPS test, the electrodes were charged or discharged to a certain voltage and held at that voltage for 12 h. Then the whole cells were transferred into the XPS chamber under inert conditions in a nitrogen-filled glove bag. Ar+ sputtering was performed for 180 s on the surface of the discharged and charged cathodes to remove the oxidized surface layer. XPS data were collected using an Al Kα X-ray source (1486.6eV). The working pressure of the chamber was lower than 7.0 × 10−6 mbar. All reported binding energy values are calibrated to the C 1s peak at 284.8 eV.


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Results and discussions The cycling performances of the 7822gc-MC|7822gc|Li-In all-solid-state cells cycled between 0.0 V and 3.0 V (vs. Li-In) at relatively high current density (0.176 mA cm−2) are shown in Fig. 2. Initial discharge capacity of the cells with 70wt% 7822gc-30wt% MC as the cathode is 655 mAh g-1 at 0.044 mA cm-2. The cell retains a stable discharge capacity of 480.3 mAh g-1 at 0.176 mA cm-2 after 60 cycles. High capacity retention of 90.6% during the last 50 cycles is obtained. The cells with 80wt% 7822gc-20wt% MC as the composite cathode possess an initial discharge capacity of 419 mAh g-1 at 0.044 mA cm-2. Then during the high-rate cycling, the capacity slowly increases with fluctuations to 328.9 mAh g-1 at 0.044 mA cm-2 after 60 cycles. As for the cells with 90wt% 7822gc-10wt% MC as the composite cathodes, the initial discharge capacity is only 9.2 mAh g-1 at 0.044 mA cm-2. Then the capacity keeps as low as 2.6 mAh g-1 after 60 cycles at 0.176 mA cm-2. Except for the cell with 90wt% 7822gc-10wt% MC as the composite cathodes, both the others deliver a high coulombic efficiency larger than 99% during the last 50 cycles. For the first several high-rate cycles, the relatively low coulombic efficiency and increasing capacity demonstrate that the composite cathodes need to be activated to achieve the subsequent excellent cyclic performance. The continuous rising capacity of the cell using 80wt% 7822gc-20wt% MC as the electrodes may represent a prolonged activated process. Among all attempts of using general sulfide electrolytes as the active materials as we know, the obtained high capacity is three times larger than the reported work exhibiting the highest capacity.

23,26

The excellent performance is also comparable with those for all-solid-state

cells with metal sulfides or Li2S as the cathodes,28-30 and our monolithic all-solid-state cells 2930



even have higher loading of active materials (about 7 mg cm-2) and better capacity retention. For further illustration, Fig. 2 (b) shows the charge-discharge curves of 7822gc-MC|7822gc|Li-In cells with 70wt% 7822gc-30wt% MC as the cathodes. It should be noted that the current density of the 2nd cycle is 0.044 mA cm−2 and for the others is 0.176 mA cm−2. Overlapping of the 10th and the 60th discharge curves demonstrates the good cycling performance with little attenuation during the galvanostatic cycling. High capacity and well retention without rapid degradation clearly indicate that charge-discharge reaction of the 78Li2S-22P2S5 system active material is reversible. The rate capabilities of the 7822gc-MC|7822gc|Li-In all-solid-state cells with three types of composite cathodes cycled between 0.0 V and 3.0 V (vs. Li-In) at room temperature are compared in Fig. 3 (a). The discharge capacity of the cell with 70wt% 7822gc-30wt% MC as the cathodes is the highest, which achieves 646 mAh g-1 for the first full cycle at 0.044 mA cm−2. The capacity retention of this cell is 64.9% at 0.352 mA cm−2 (407 mAh g-1) with respect to the initial capacity. When the tested current decreases back to 0.044 mA cm−2, the discharge capacity obtains a high capacity retention of 94.5% (592 mAh g-1). While for the cell with 80wt% 7822gc-20wt% MC as the cathodes, the capacity is 426 mAh g-1 at 0.044 mA cm−2. And the cells retains 59.8% of their capacity at 0.352 mA cm−2 (i.e., 235 mAh g-1). When the current goes back to 0.044 mA cm−2, the capacity retention is 89.5% (351 mAh g-1). The discharge capacity of the cell with 90wt% 7822gc-10wt% MC as the cathodes is rather low, only 6.7 mAh g-1 for the first full cycle at 0.044 mA cm−2. The capacity retention of this cell is only 26.9% at 0.352 mA cm−2 (i.e., 1.8 mAh g-1). When the current decreases back to 0.044 mA cm−2, the discharge capacity slowly increases to 8.0


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mAh g-1 at 0.044 mA cm-2. Among all these composite cathodes, the 70wt% 7822gc-30wt% MC electrodes exhibit the best performance, which possess the highest capacity and the best capacity retention after high-rate cycling. The comparison illustrates that sufficient electric conductive paths are important for satisfactory performance of the 7822gc-MC composite cathodes, because the 7822gc owns poor electronic conductivity and well ionic conductivity. Well electronic conductive paths are rather essential to inspire the capacity potential of the 7822gc. The discharge-charge voltage profiles of the 7822gc-MC|7822gc|Li-In cells with 70wt% 7822gc-30wt% MC as the cathodes are presented in Fig. 3 (b). Two plateaus at about 1.8 V and 2.3 V during the charge process and another two at about 1.3 V and 0.6 V during the discharge process are observed. Among them the plateaus at 1.8 V and 1.3 V have also been observed by Hakari et al., which mainly attribute to the electrochemical reaction of the glass matrix itself as active material.23 The other two plateaus may relate to the Li2S crystal phase or some other materials generated during the discharge process. Both of these two reactions contribute to the high capacity of 646.1 mAh g-1 at 0.044 mA cm−2. We separate the discharge process into two parts. The regions with voltage higher than 0.7 V are called region I and with voltage lower than 0.7 V are called region II. By comparing the cell cycling on different rates, we can see that the speed of the capacity attenuation contributed by region I and II is different. As the current density increases from 0.044 mA.cm−2 to 0.352 mA cm−2, the discharge capacity above 0.7 V decreases from 360 mAh g-1 to 310 mAh g-1. High capacity retention of 86.1% is achieved. While the capacity below 0.7 V rapidly decreases from 290 mAh g-1 to 110 mAh g-1 and only 37.9% of the initial capacity is



remained. When the cells cycle at high current density (0.352 mA cm−2), about 73.8% of the cycling capacity comes from region I. While when the current density is as low as 0.044 mA cm−2, about 44.6% of the cycling capacity comes from region II. Thus at low current density, the capacity contributed by region II is comparable to that of region I. While operated at higher current density, region II would provide little recyclable energy and even lose the electrochemical activity. To balance both high capacity and high rate, the current is set at 0.176 mA cm−2 for the galvanostatic cycling test mentioned above. EIS measurements are performed to further understand the well electrochemical performances of the 7822gc-MC composite cathodes. The Nyquist plots of the all-solid-state cells with 70wt% 7822gc-30wt% MC as the composite cathodes at room temperature are shown in Fig. 4. The total impedance of the all-solid-state battery before cycle is 46 Ω, which is similar to that for the 7822gc electrolyte layer itself. The initial interface impedance of the cells is rather low. While after the 10th cycle, the total impedance of the battery increases to about 130 Ω. The variation of the impedance related to the composite cathode/electrolyte interface is much larger than the one for the electrolyte/Li-In interface. 20,31

After subsequent 50 more cycles, the total impedance of the all-solid-state battery

merely increases about 20 Ω. As the rate of the deterioration of the interfacial impedance keeps slow, the cells could successfully maintain a high capacity and high coulombic efficiency after 60 cycles. Fig. 5 shows the XRD of the 70wt% 7822gc-30wt% MC composite cathodes before and after 60 cycles. Comparing with the 7822gc electrolyte, no new peaks are observed in the composite cathodes. It suggests that no new crystal phase is formed after ball-milling


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treatment. However, the peak intensity of the high conductivity phase in the composite cathodes is greatly reduced owing to the existence of a large volume fraction of MC which only shows halo patterns in the XRD testing. The weak peaks assigned to Li7PS6 in the 7822gc were even hard to distinguish in the composite cathodes. Similar XRD patterns were observed for the composite cathodes before and after 60 cycles, which indicates that no new crystal phase is generated during the cycle. Meanwhile, when we carefully examine the XRD result near 28°, as shown in fig. S1. We can find that the peak assigned to Li2S at 26.8° disappeared in the sample before cycle. But the same peak appeared in the composite cathode after the 60th discharge process. We believe that the remained Li2S phase in the 7822gc finally become part of the glass matrix during the ball milling mixing process. As a result, no Li2S phase could be found in the composite cathode before cycle. However, new Li2S phase is generated during the discharge process, leading to the reappearance of the Li2S peak in the sample after 60 cycles. The XRD result coincides with the discharge-charge voltage profiles, which demonstrates that the materials generated during the discharge process lower than 0.7 V is Li2S crystal phase. Fig. 6 shows the cross-sectional microstructure of the cells before and after 60 cycles, which concentrates on the interface between the composite cathode and the electrolyte. Fig. 6 (a) shows the sample before cycle, and Fig. 6 (b) and (c) are EDS mappings of carbon and sulfur. The interface between the composite cathodes and the electrolytes is difficult to distinguish in Fig. 6 (a). Through observing the element mappings, the area with carbon or sulfur enriched can be identified as the composite cathodes or the electrolytes layer with ease. Both of these two layers are compressed tightly. The intimate physical contact of the



electrode and the electrolyte guarantees the high initial cycling capacity of the cells. Fig. 6 (d) shows the cell after 60 cycles, and Fig. 6 (e) and (f) are corresponding EDS mappings of carbon and sulfur. High structural integrity between the electrode and the electrolyte can also be observed in Fig. 6 (d). Without the help of element mapping, the interface is also very hard to be discerned. Even after 60 cycles, both of the composite cathode and the electrolyte layer are still dense. With the help of element mappings, the area of the composite cathode and the electrolyte can also be distinguished by carbon or sulfur enrichment. The interface contact maintains the sound condition as that before cycle, which guarantees the high cycling capacity and great capacity retention. Although good physical contact of the interface between the composite cathode and electrolyte after cycle is observed, possible poor chemical contact or space charge layer may have an impact, which results in the increase of the interface impedance and the attenuation of the cycling capacity. To reveal the electrochemical reaction mechanisms of the 7822gc-MC electrode in the all-solid-state cells, XPS was used to characterize the electrodes at various charged or discharged states. Fig. 7 (a) shows the discharge–charge voltage profiles of the cells using 70wt% 7822gc-30wt% MC as the cathodes for the first two cycles. The electrodes at fresh state, first fully charged (to 3.0 V), first discharged to 0.64 V, first fully discharged (to 0.0 V), second charged to 1.85 V, and second fully charged (to 3.0 V), are respectively named as states 1 to 6, as shown in Fig. 7 (a). Fig. S2 shows the XPS spectra of S 2p for the samples. The spectra for the states 1, 3 and 5 are similar, which represent the initiate state of the composite cathodes. Similar XPS spectra of S 2p are also observed for the states 2 and 6, which represent the charge state. The XPS spectra of S 2p for the state 4 shows the discharge


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state. Fig. 7 (b)-(d) compare the XPS spectra of S 2p for the states 1, 2 and 4, which represent the composite cathodes at fresh, fully charged and fully discharged states. The corresponding spectra are fitted with spin-orbit coupled 2p 3/2 and 2p 1/2 doublets, constrained at 1.18 eV separation with a characteristic 2:1 area ratio and equal full-width at half maximum. The results indicate that the cathodes at different states exhibit a main peak around ≈ 163 eV. The detailed fitting for the main peak of interest results in two peaks at ≈ 163.3 eV and ≈ 162.1 eV, respectively. However, considering the difficulty of distinguishing either of them for the complicated chemical environment of S in the 7822gc samples (e.g. peaks at 164 eV (S8 ring), 163.5 eV (bridging sulfur: P-S-P) and 162.2 eV (non-bridging sulfur: P=S)32 in the glass-ceramic matrix, high conductive phase and lithium sulfides), they are denoted as a high binding energy (B.E.) peak (at ≈ 163.3 eV) and a low B.E. peak (at ≈ 162.1 eV).23,33 Nevertheless, another new B.E. peak (at ≈ 160.2 eV) is observed in the sample of fully discharged states. It represents an electron-rich sulfur species whose B.E. is similar to that of S2- in bulk Li2S (at ≈ 159.8 eV). 34 So it is denoted as S2-. The electronegativity difference of cations that are bonded with S could tell a general trend of their B.E. positions (S-S > P-S-P > P=S > Li-S). Additionally, the peak would shift to higher binding energy as the oxidation state of S increases. Li2S with a sulfur oxidation state of -2 is always located in the lowest B.E. peak. These results allow us to use the area ratio of the low B.E. peak or the S2- peak to the high B.E. peak to speculate the reaction mechanism in the 7822gc cathodes (Table 1). The area ratio of the low to high B.E. peak decreases from 3.31:1 for the fresh 7822gc electrode to 1.65:1 after charged to 3.0 V, which indicates that the oxidation of sulfur ( from P=S to P-S-P and S-S) occurs during the charge process. While



after the 7822gc is discharged to 0.0 V, the ratio increases back to as high as 7.21:1, which means the reduction of S. Meanwhile, the S2- peak appears during the discharge process. The area ratio of the S2- to the high B.E. peak increases from zero to 5.56:1 during discharging. It demonstrates that the sulfide ion further reduces during the discharge process and transform from low or high B.E. state to S2- state. The generation of S2- state mainly provides the extra discharge capacity of the cell between the voltages ranging from 0.7 V to 0.0 V (region II), which has also been confirmed by the XRD test and the discharge-charge voltage profiles. The reduction from P-S-P or S-S to P=S in the glass matrix contributes to the discharge capacity of the cell with voltage higher than 0.7 V (region I). These results confirm that the electrode performance of the 7822gc could be attributed to both the oxidation and reduction of the P=S, P-S-P and S-S state, as well as the formation and decomposition of the S2- state within the 7822gc material. Both the glass matrix and the new generated Li2S give rise to the high discharge capacity of the 7822gc and the good cycling performance of the all-solid-state batteries enabled by a glass-ceramics solo. Conclusions High-performance monolithic all-solid-state cells using the 7822gc as both electrolyte and active material of the composite cathode have been prepared. The cathode is prepared via ball-milling the 7822gc with MC which constructs well electron conduction paths so as to inspire the capacity potential of the 7822gc. The monolithic 7822gc-MC|7822gc|Li-In cells exhibit an initial discharge capacity of 654.5 mAh g-1 at 0.044 mA cm-2, and retain a stable discharge capacity of 480.3 mAh g-1 at 0.176 mA cm-2 after 60 cycles, which is three times larger than the reported work with the highest capacity of all attempts of using sulfide


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electrolytes as the active materials as we know. The impedance of the cells increase rather slowly with well overlapping of the discharge curves during the cycles. High capacity retention of 90.6% and coulombic efficiency of higher than 99% with ultra-high active material loading of 7 mg cm-2 are obtained. Our results show that providing enough electron conduction paths, the use of the 7822gc as both an active material and ionic conduction path in the composite electrode is effective for increasing capacity of the cells. The XPS analysis of the electrochemical reaction mechanisms of the cells demonstrates that the electrode performance of the 7822gc could be attributed to both the oxidation and reduction of the P=S, P-S-P and S-S state in the glass matrix, as well as the formation and decomposition of the S2within the 7822gc. Corresponding Author *E-mail: [email protected];(Y.S.); [email protected](C.W.N.) Author Contributions The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript.

ACKNOWLEDGMENT This work was supported by the NSF of China (grant No. 51532002). Supporting Information XRD pattern of the composite cathodes near 28° and XPS spectra of S 2p for the composite cathodes at different states.



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Table and Figure list: Table 1. XPS binding energies of high B.E. peak (Ehigh), low B.E. peak (Elow) and S2- peak (E S2-) of S 2p spectra and the area ratio of Elow or E S2- peak to Ehigh peak in 70wt% 7822gc-30wt% MC cathodes. Figure 1. Schematic configuration of the monolithic cell 7822gc-MC|7822gc|Li-In. Yellow polyhedrons denote the 7822gc particles, and dark dots and rods denote the MC particles. Figure 2. Cycling performance of x wt% 7822gc-(100-x) wt% MC|7822gc|Li-In all-solid-state cells. (a) Charge, discharge capacity and coulombic efficiency as a function of the cycle number at the current of 0.176 mA cm-2. (b) The corresponding discharge-charge voltage profiles of the cells using 70wt% 7822gc-30wt% MC as the electrodes at 2nd, 10th and 60th cycles. Figure 3. Rate performance of x wt% 7822gc-(100-x) wt% MC|7822gc|Li-In all-solid-state cells. (a) Charge and discharge capacity under different cyclic currents (i.e., 0.044, 0.088, 0.176, 0.352, and 0.044 mA cm-2) as a function of the cycle number. (b) The corresponding discharge-charge voltage profiles at different currents of the cells using 70wt% 7822gc-30wt% MC as the electrodes. Figure 4. Nyquist plots for the cells with 70wt% 7822gc-30wt% MC as the electrodes before cycle, after 10th and 60th cycles. Figure 5. XRD pattern of 7822gc electrolyte material and the composite cathodes before and after 60 cycles. The phases in the samples can be indexed to Li2S, Li7PS6 and the high


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conductivity phase. Figure 6. (a) Cross-sectional SEM image of the cells, and EDS mappings of (b) carbon and (c) sulfur in the same area, before cycles; (d)-(f) are respectively SEM image, and EDS mappings of carbon and sulfur after 60 cycles. Figure 7. (a) The discharge–charge voltage profiles of the cells using 70wt% 7822gc-30wt% MC as the electrodes for the first two cycles. The deconvoluted S 2p core XPS spectra of the composite cathodes at the states: (b) 1 at the fresh state, (c) 2 first fully charged (to 3.0 V), and (d) 4 first fully discharged (to 0.0 V).



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Table 1. XPS binding energies of high B.E. peak (Ehigh), low B.E. peak (Elow) and S2- peak (E S2-) of S 2p spectra and the area ratio of Elow or E S2- peak to Ehigh peak in 70wt% 7822gc-30wt% MC cathodes.

Samples

E S2[eV]

Elow S 2p3/2 [eV]

Ehigh S 2p3/2 [eV]

Area ratio

Fresh

-

162.23

163.46

3.31:1

Charged

-

162.03

163.35

Discharged

161.6

160.23

162.9


1.65:1 7.21:1

5.56:1

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Figure 1. Schematic configuration of the monolithic cell 7822gc-MC|7822gc|Li-In. Yellow polyhedrons denote the 7822gc particles, and dark dots and rods denote the MC particles.



Figure 2. Cycling performance of x wt% 7822gc-(100-x) wt% MC|7822gc|Li-In all-solid-state cells. (a) Charge, discharge capacity and coulombic efficiency as a function of the cycle number at the current of 0.176 mA cm-2. (b) The corresponding discharge-charge voltage profiles of the cells using 70wt% 7822gc-30wt% MC as the electrodes at 2nd, 10th


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and 60th cycles.

.

Figure 3. Rate performance of x wt% 7822gc-(100-x) wt% MC|7822gc|Li-In all-solid-state cells. (a) Charge and discharge capacity under different cyclic currents (i.e., 0.044, 0.088, 0.176, 0.352, and 0.044 mA cm-2) as a function of the cycle number. (b) The corresponding discharge-charge voltage profiles at different currents of the cells using 70wt% 7822gc-30wt% MC as the electrodes.



Figure 4. Nyquist plots for the cells with 70wt% 7822gc-30wt% MC as the electrodes before cycle, after 10th and 60th cycles.

Figure 5. XRD pattern of 7822gc electrolyte material and the composite cathodes before and after 60 cycles. The phases in the samples can be indexed to Li2S, Li7PS6 and the high conductivity phase.


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Figure 6. (a) Cross-sectional SEM image of the cells, and EDS mappings of (b) carbon and (c) sulfur in the same area, before cycles; (d)-(f) are respectively SEM image, and EDS mappings of carbon and sulfur after 60 cycles.



Figure 7. (a) The discharge–charge voltage profiles of the cells using 70wt% 7822gc-30wt% MC as the electrodes for the first two cycles. The deconvoluted S 2p core XPS spectra of the composite cathodes at the states: (b) 1 at the fresh state, (c) 2 first fully charged (to 3.0 V), and (d) 4 first fully discharged (to 0.0 V).


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Graphical TOC


High Capacity and Superior Cyclic Performances of All-Solid-State

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