High Capacity, Superior Cyclic Performances in All-Solid-State Lithium

Aug 4, 2017 - All-solid-state lithium-ion batteries based on these glass-ceramic electrolytes are assembled by using Li2S nanoparticles or low-cost co...
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High Capacity, Superior Cyclic Performances in All-Solid-State Lithium-Ion Batteries Based on 78Li2S‑22P2S5 Glass-Ceramic Electrolytes Prepared via Simple Heat Treatment Yibo Zhang, Rujun Chen, Ting Liu, Yang Shen,* Yuanhua Lin, and Ce-Wen Nan* State Key Laboratory of New Ceramics and Fine Processing, School of Materials Science and Engineering, Tsinghua University, Beijing, 100084, P. R. China ABSTRACT: Highly Li-ion conductive 78Li2S-22P2S5 glass-ceramic electrolytes were prepared by simple heat treatment of the glass phase obtained via mechanical ball milling. A high ionic conductivity of ∼1.78 × 10−3 S cm−1 is achieved at room temperature and is attributed to the formation of a crystalline phase of high lithium-ion conduction. All-solidstate lithium-ion batteries based on these glass-ceramic electrolytes are assembled by using Li2S nanoparticles or low-cost commercially available FeS2 as active cathode materials and Li−In alloys as anode. A high discharge capacity of 535 mAh g−1 is achieved after at least 50 cycles for the all-solidstate cells with Li2S as cathode materials, suggesting a rather high capacity retention of 97.4%. Even for the cells using low-cost FeS2 as cathode materials, same high discharge capacity of 560 mAh g−1 is also achieved after at least 50 cycles. Moreover, the Coulombic efficiency remain at ∼99% for these all-solid-state cells during the charge−discharge cycles. KEYWORDS: lithium ion battery, 78Li2S-22P2S5, solid electrolyte, sulfide, all-solid-sate battery

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INTRODUCTION Lithium-ion batteries have been widely used as primary energy storage devices in modern electronic industries and been attracting ever-increasing attention as the most promising rechargeable energy storage devices for the emerging renewable energy industry worldwide.1−3 However, current commercial lithium batteries with flammable organic liquid electrolytes fall short of the demand for next-generation batteries which play critical roles in electronic vehicles (EVs), as well as flexible wearable electronics where batteries of intrinsic safety, higher energy density, and flexibility are highly desirable. For these reasons, all-solid-state batteries, where flammable liquid electrolyte is replaced by solid-state electrolytes, are considered the most promising approach to addressing the issues with the current lithium-ion batteries.4−6 However, the mass application of all-solid-state lithium-ion batteries as viable energy storage devices is currently limited by their rather low capacity as well as their compromised cyclic and rate performances. These issues could first be attributed to the low ionic conductivity of solid-state electrolyte as compared to their liquid counterparts. Second, the poor interfacial contacts between cathode active materials and solid electrolyte results in substantially increased interfacial resistance inside the composite cathode layer as well as at the interfaces between the composite cathode layer and solid electrolyte layer.7,8 Therefore, a superior solid electrolyte with high ionic conductivity and good interface contact with electrodes is critical to improving battery performance in allsolid-state systems.9−12 © 2017 American Chemical Society

A number of inorganic high lithium-ion conductivity solid electrolytes have been investigated. Oxide solid electrolytes like Li3xLa2/3‑xTiO3 and Li1+xAlxTi2‑x(PO4)3 exhibit a high bulk ionic conductivity of over 10−3 S cm−1 at room temperature. Yet, these solid oxide electrolytes also exhibit high grain boundary resistances and, moreover, are unstable against lithium metal.13−17 Recently, the garnet-type cubic Li7La3Zr2O12 (LLZO) shows a high room-temperature conductivity of nearly 10−3 S cm−1,18,19 while the drawback of the intricate sintering process restrains the utility of LLZO electrolytes.20,21 Meanwhile, sulfur electrolytes exhibit higher ionic conductivity, low-temperature preparation processing, better interface connection with electrodes, and much better stability against lithium metal than Ti-based oxides, and thus have been widely studied,22 though the high sensitivity to moisture affects their applications in the open air.23 Among Li2S−P2S5 glassceramic solid electrolytes, which had first been developed by Tatsumisago et al., have attracted great attention because of their room-temperature ionic conductivity of about 10−3 S cm−1 and good electrochemical stability. The high performance of the glass-ceramic electrolytes is attributed to the outstanding ionic conductive amorphous phase matrix (i.e., ∼10−4 S cm−1) and the generation of the high ionic conducting metastable phases, e.g., thio-LISICON II and III analogs, which arises from our proper heat-treatment processing. Owing to the special Received: June 4, 2017 Accepted: August 4, 2017 Published: August 4, 2017 28542

DOI: 10.1021/acsami.7b06038 ACS Appl. Mater. Interfaces 2017, 9, 28542−28548

Research Article

ACS Applied Materials & Interfaces

glass-ceramic pellets were obtained by compressing the glass-ceramic powders at 150 MPa. 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 samples at room temperature. In order to prevent air exposure, the samples were sealed in an airtight container covered with a polyimide thin film and mounted on the X-ray diffractometer. Scanning election microscopy (SEM, JEOL, JSM-7001F) was used to observe the surface and cross-section microstructure of the pellets. The ionic conductivities of all samples were measured using the pelletized samples with 12 mm in diameter and about 0.8 mm in thickness in an insulating poly(ether ether ketone) (PEEK) tube. Two stainless steel disks were attached to the pellets as current collectors. The AC impedance measurements were performed for the cells using an impedance analyzer (ZAHNER-elektrik IM6) in the frequency range of 1 Hz to 8 MHz with an AC amplitude of 50 mV. The Li-ion conduction activation energy (Ea) was calculated from the Arrhenius plot of the relationship between the total ionic conductivity and temperature. The testing temperature was controlled by an environmental chamber (Cincinnati Sub-Zero MCB-1.2-AC) from −20 to 40 °C. The electrochemical stability of the obtained samples was evaluated by cyclic voltammetry. An electrochemical cell of the glass-ceramic electrolyte pellet was fabricated by using a stainless steel disk and lithium foil as working and counter electrodes. A cyclic voltammogram was obtained using a potentio-/galvanostat (CHI760, Chenhua, China) at a scanning rate of 1 mV s−1 in the range from −0.5 to 5 V. For illustration, all-solid-state Li−S cells were fabricated with the high conductivity 78Li2S·22P2S5 glass-ceramic sample as the solid electrolyte. For cells with FeS2 as active material, FeS2 (Alfa, 99.9%) powders (30 wt %), the 78Li2S·22P2S5 glass-ceramic electrolyte (60 wt %), Super P carbon (Timcal) (6.7 wt %), and VGCF (vapor grown carbon fibers, Showa Denko) (3.3 wt %) were ball milled and used as the composite cathode. As for cells using Li2S as active material, nanosized Li2S was prepared as reported by Wu et al.32 The composite cathode (about 5 mg) was pressed on one side of the electrolyte at 150 MPa and the lithium−indium (Li−In) foil as the anode was attached at 100 MPa on the other side. Finally, the three-layered cells were pressed into a mode (3ESTC15, Kejingstar, China) at 100 MPa with two stainless steel disks as current collectors on both sides. The cells were cycled using a charge−discharge measurement device (C2001A, LAND, China) at room temperature. The cutoff voltage was 0.0−3.0 V (vs Li−In), which is equivalent to 0.6−3.6 V (vs Li). The current density of the first cycle was 0.018 mA cm−2 and the current density of the other cycles was set to be 0.044 mA cm−2. In particular, the cutoff voltage was 0.0−4.2 V (vs Li−In) for the cells with Li2S as active material for the first cycle.

structure with high conducting microcrystalline phases homogeneously dispersed in the glass phase matrix, lithium ions could transport better through the high conducting phases with lower barrier.24−27 However, the previous work is far from exhaustive and more detailed studies on specific composition and treatment process are still in demand to achieve higher ionic conductivity and better battery performance. Of particular interest, a recent report presented an extremely high ionic conductivity of 1.7 × 10−2 S cm−1 and a low activation energy of 17 kJ mol−1 in 70Li2S·30P2S5 system, even though no allsolid-state battery was prepared using this material.28 However, the preparation process of the high-conduction sulfur electrolyte reported before is complicated and time-consuming, where tube sealing, quenching, and intricate sintering processes are required. High-performance sulfur electrolytes with a simple synthetic process and effective all-solid-state Li−S batteries based on the solid electrolytes have seldom been reported.29,30 Here we report a high-conduction crystalline phase similar in structural to thio-LISICON II analog, formed by simple crystallization of the ball-milled 78Li2S·22P2S5 glass powder. The impact of different heat-treatment processes has also been studied. Finally, by simple heat-treatment process without tube sealing, quenching, or any other complex sintering process, the glass-ceramics with high conductivity of 1.78 × 10−3 S cm−1 at room temperature were obtained. To the best of our knowledge, this is the highest conductivity in the composition of 78Li2S·22P2S5 electrolytes ever reported.26,31,34 Even by Li2SO4 doping, ball milling at high temperature, or some other sophisticated modification, the ionic conductivity obtained by previous work is still only about 1.0 × 10−3 S cm−1, which is lower than our result. Using this high-conduction glass-ceramic as electrolyte, and Li2S and FeS2 as the cathode active substances, we prepared all-solid-state Li−S batteries with excellent performance and effectively demonstrated the viability of these glass-ceramic electrolytes prepared via simple heat treatment.

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EXPERIMENTAL SECTION

78Li2S·22P2S5 glass-ceramic electrolytes were prepared from reagentgrade chemicals, P2S5 (Aldrich, 99%) and Li2S (Alfa, 99.9%). To obtain glass-phase electrolytes, the starting materials were mixed thoroughly in appropriate molar ratios, and then mechanical milling was performed for 25 h using a high-energy planetary ball mill (Fritsch Pulverisette 7). All the processes were carried out in a dry Ar-filled glovebox with [H2O],[ O2] < 1 ppm. The nucleation temperature of the glass samples was dominated from the differential thermal analysis (DTA) measurement (TGA/ DSC 1 STAR system, METTLER TOLEDO). The glass samples were sealed in an Al2O3 pan. The pan was heated in the DTA apparatus to temperatures of 300 °C at 10 °C min−1. The glass-ceramic samples were prepared further by heat treatment of the glass samples. The obtained glass samples were grinded into powder. Then the glass-phase powder was wrapped with aluminum foil and a two-step heat-treatment process was adopted to get the final sample. The power was heated at 150, 160, 170, 180 °C separately for 0.5 h, and then at 220, 230, 240, 250 °C for 3 h separately in the glovebox. The samples treated at different temperature are named 150−220, 160−230, 170−240, and 180−250, in which the numbers represent their heat-treatment temperature. For comparison, the powder was also cold-pressed in the glovebox or sealed under vacuum in a quartz tube. Then the glass-phase pellets were also wrapped with aluminum foil and heated at 170 °C for 0.5 h and then 240 °C for 3 h directly in the glovebox. The sealed samples were subjected to the same heat-treatment process in an electric furnace. All the densified

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RESULTS AND DISCUSSION Structure and Composition. In order to determine the optimum heat-treatment temperature of the 78Li2S-22P2S5 glass, the DTA curves of the glass were obtained as shown in

Figure 1. DTA curves of the ball-milled 78Li2S·22P2S5 glass. 28543

DOI: 10.1021/acsami.7b06038 ACS Appl. Mater. Interfaces 2017, 9, 28542−28548

Research Article

ACS Applied Materials & Interfaces

Figure 2. XRD pattern of 78Li2S·22P2S5 ball-milled glass and heattreated glass ceramic. The impure phase in the sample could be indexed to Li2S, Li7PS6 and some unknown phase. (a) Glass-ceramics heat-treated directly in the glovebox at different temperature and (b) ball-milled glass and glass-ceramics heat-treated through different methods.

Figure 4. AC impedance spectra of the 78Li2S·22P2S5 ball-milled glass and heat-treated glass ceramic at room temperature. (a) Glassceramics heat-treated directly in the glovebox at different temperature and (b) ball-milled glass and glass-ceramics heat-treated through different methods.

sample except for some small peaks assigned to row materials Li2S. As displayed in Figure 2a, XRD patterns for the powder samples heat-treated at different temperature in the glovebox are similar. Formation of a new crystalline phase similar in structural to thio-LISICON II analog with sharp diffraction peaks near 17.7°, 25.8°, and 29.7° was observed.24 As the heattreatment temperature increased, peak intensity increased and width narrowed. In addition, the peak at 17.7° transformed from double peaks for the 150−220 and 160−230 samples to a single sharp peak for the 170−240 and 180−250 samples. Some weak peaks assigned to Li7PS6 also can be observed, whose intensity minimized for the 170−240 sample. Meanwhile, as shown in Figure 2b, the new crystalline phase similar to thio-LISICON II analog and the Li7PS6 phase were also observed for the powder and pellet samples, which were heat-treated directly in the glovebox. A slight intensity increase and peak width narrowing for the phase similar to thioLISICON II analog were observed for the powder sample annealed in the glovebox. As for the sealed pellet sample, another unknown phase with diffraction peaks near 19.1°, 21.6°, and 23.8° appeared in addition to the previous discussed phases. Meanwhile, the peak intensity of Li7PS6 phase increased and the peak intensity of the new phase similar to thioLISICON II analog slightly decreased. As we can see, the simple two-step heat treatment directly in the glovebox promotes the crystallization of the new phase similar to thioLISICON II analog for all the samples after annealing. A highest peak intensity of the new crystalline phase similar to thio-LISICON II analog and a weakest peak intensity of other

Figure 3. SEM images of (a) the surface and (b) cross section of the 78Li2S·22P2S5 glass ceramic.

Figure 1. Two crystallization peaks appeared at 136 and 178 °C. The width of the peak at 136 °C was much narrower than the one at 178 °C. The full width at half-maximum of the peak at 178 °C was 26 °C. The nucleation rate is maximized at a temperature near the middle of the temperature range where nucleation occurs, and the intensity of the DTA crystallization peak, (δT)p, is proportional to the number of nuclei in the glass.33 The maximum nucleation rate was achieved at the first peak temperature, so the first annealing temperature was chosen around 160 °C. Then the crystal fast grew at the higher temperature. Based on the DTA results and by considering the rather big peak width, the 78Li2S-22P2S5 glass samples were heat-treated using a two-step process for the transformation of glass to glass-ceramic electrolytes, i.e., a first step at about 160 °C for nucleation and a second step at about 230 °C for grain growth. Figure 2 shows the XRD patterns of the 78Li2S·22P2S5 ballmilled glass and glass-ceramics after heat treatment. As shown in Figure 2b, only halo patterns appear in the glass-phase 28544

DOI: 10.1021/acsami.7b06038 ACS Appl. Mater. Interfaces 2017, 9, 28542−28548

Research Article

ACS Applied Materials & Interfaces

Table 1. Ionic Conductivity of Glass-Ceramics Heat-Treated Directly in the Glove Box at Different Temperature sample

150−220

160−230

170−240

180−250

ionic conductivity (S cm‑1)

1.16 × 10−03

1.31 × 10−03

1.78 × 10−03

1.25 × 10−03

Table 2. Ionic Conductivity of Ball-Milled Glass and Glass-Ceramics Heat-Treated through Different Methods sample

glass

powder-glovebox

pellet-glovebox

pellet-sealing

ionic conductivity (S cm‑1)

3.22 × 10−04

1.78 × 10−03

1.66 × 10−03

1.01 × 10−03

Figure 5. Typical Arrhenius plot of the ionic conductivity of the 78Li2S·22P2S5 glass ceramic.

Figure 7. Cycle performance Li2S-based cathode |78Li2S·22P2S5|Li−In all-solid-state cells. (a) Charge, discharge capacity, and Coulombic efficiency as a function of the cycle number at the current of 0.05 mA cm−2. (b) Corresponding discharge−charge voltage profiles of the cells at first, 10th, and 50th cycles.

Figure 6. Stability window for the first cyclic voltammogram of the 78Li2S·22P2S5 glass ceramic.

150−220 sample to as high as 1.78 × 10−3 S cm−1 for the 170− 240 sample, as shown in Figure 4a. The substantial enhancement in ionic conductivity is attributed to the formation of a new high-conduction phase similar to thio-LISICON II analog in the 78Li2S·22P2S5 glass-ceramic electrolytes after annealing. However, owing to the increased content of the impure phase Li7PS6, the conductivity of the 180−250 sample decreased to only 1.25 × 10−3 S cm−1. As shown in Figure 4b, benefiting from the formation of the new crystalline phase similar to thio-LISICON II analog, the conductivity increased to 1.66 × 10−3 S cm−1 for the pellets electrolytes heat-treated in the glovebox. The ionic conductivity of the sealed pellet sample also increased, but less, to 1.01 × 10−3 S cm−1, which was resulted from the appearance of the unknown new phase and the Li7PS6 phase. The ionic conductivity of over 10−3 S cm−1 is the highest ionic conductivity ever achieved in 78Li2S·22P2S5 glass-ceramic electrolytes.26,31,34 The activation energy (Ea) of the 78Li2S· 22P2S5 glass-ceramic electrolytes is then determined from the temperature dependence of the ionic conductivity as shown in Figure 5. By fitting the Arrhenius plots to the equation: σ ∝

impure phases were obtained simultaneously in the sample heat-treated at 170 °C for 0.5 h and then at 240 °C for 3 h. Figure 3 shows the surface (a) and cross-section (b) morphology of the 78Li2S·22P2S5 glass-ceramic pellets. It could be seen obviously that good particle contacting was achieved in the glass-ceramic electrolyte, though some cracks in the boundary area can be observed because only cold pressing without sintering process were adopted. The two-step heat treatment effectively turned the ball-milling glass into the glassceramic phase and dense electrolyte pellets were obtained through cold pressing. Electrochemical Properties. The lithium ionic conductivities of the 78Li2S·22P2S5 solid electrolytes are determined from the AC impedance spectra at room temperature shown in Figure 4 and the values are shown in Tables 1 and 2. Notably, the 170−240 sample and the powder-glovebox sample are the same one, and were named differently for better comparison. The lithium-ion conductivity of the ball-milling glass was 3.22 × 10−4 S cm−1. After directly annealing in the glovebox at different temperature, the ionic conductivity of the glassceramic samples increased from 1.16 × 10−3 S cm−1 for the 28545

DOI: 10.1021/acsami.7b06038 ACS Appl. Mater. Interfaces 2017, 9, 28542−28548

Research Article

ACS Applied Materials & Interfaces

1454 mAh g−1 and discharge capacity of 647 mAh g−1 at a low cycling rate of ∼0.01 C. While during the following ten cycles of higher rate (∼0.03 C), the discharge capacity increases from 378 mAh g−1 to 549 mAh g−1 with the Coulombic efficiency decreases from 117.5% to 102.7%. The capacity of the cell then maintains stable and even achieves a discharge capacity of 535 mAh g−1 after the 50 cycle and the Coulombic efficiency keeps above 98.5% during the cycles. The discharge capacity of the 11th cycle is highest during the galvanostatic cycling, and after that a high capacity retention of 97.4% from the 11th cycle to the 50th one is achieved. Figure 7b shows charge−discharge curves of the Li2S-based cathode |78Li2S·22P2S5|Li−In cell. As seen, the charge and discharge curves for the 10th and 50th cycle almost overlap, suggesting superior cyclic performance during the galvanostatic cycling. High capacity and excellent capacity retention are thus achieved in the all-solid-state cells with Li2S as cathodes.28,29,35 These all-solid-state cells even outperform all-solid-state lithium-ion batteries with commercial LiCoO2 as active materials and other sulfides as solid electrolytes.31,36 By replacing Li2S in the composite cathodes with low-cost commercially available FeS2, another all-solid-state cell (FeS2based cathode |78Li2S·22P2S5|Li−In) with similar structure is assembled via identical procedures. Figure 8a shows the cycle performance of the all-solid-state cell with commercial FeS2 as active material. For the first charge−discharge cycle at low rate of 0.02 C, the all-solid-state cell exhibits a high charge capacity of 1236 mAh g−1 and discharge capacity of 1136 mAh g−1. During the follow higher-rate cycles (about 0.05 C), the capacity slowly decreases and stabilizes at ∼560 mAh g−1 after 50 cycles and the Coulombic efficiency keeps above 96% during all the cycle. This trend could also be readily distinguished in the charge−discharge curves shown in Figure 8b. As seen, the very mild decrease in capacity could be observed from charge and discharge curves for the 40th and 50th cycles, suggesting a stable cyclic performance after intensive galvanostatic cycling. To the best of our knowledge, this is the highest capacity, capacity retention, and Coulombic efficiency ever achieved in all-solid-state cells using commercial FeS2 as cathode active material.37 It is also worth noting that the discharge capacity and Coulombic efficiency of our all-solid-state lithium-ion batteries are even comparable to those of the all-solid-state cells using nanocrystalline FeS2 or other metal sulfide nanoparticles as cathode material.38−40 Note that the charge capacities exhibited by the two types of all-solid-state cells in the first cycle are even higher than the theoretical capacity of the active cathode materials employed, i.e., 1170 mAh g−1 for Li2S and 900 mAh g−1 for FeS2. These ultrahigh charge capacities could be attributed to the sulfide glass-ceramic electrolyte in the composite cathodes which could also act as active cathode materials and may contribute to the enhanced total capacity. 41,42 However, considering the relatively low capacity (lower than 100 mAh g−1) achieved and high content of electronic conductive agent (30 wt % of the composite cathode) necessary to inspire the capacity potential of the electrolyte materials, the capacity contribution of the electrolyte should be rather limited in our work. The Coulombic efficiency of the cells is rather low for the first cycle, but after several cycles, the Coulombic efficiency gradually increases and even maintains above 99% for the following cycles for both cells. All these results prove that 78Li2S·22P2S5 glass-ceramic is a promising candidate as solid electrolyte for all-solid-state Li−S batteries. Further enhance-

Figure 8. Cycle performance FeS2-based cathode |78Li2S·22P2S5|Li− In all-solid-state cells. (a) Charge, discharge capacity, and Coulombic efficiency as a function of the cycle number at the current of 0.05 mA cm−2. (b) Corresponding discharge−charge voltage profiles of the cells at second, 40th, and 50th cycles.

exp(−Ea/kT), Ea of ∼0.31 eV is determined. It is a suitable activation energy for sulfur electrolytes with conductivity higher than 10−3 S cm−1.25−27 The first cyclic voltammogram of the high-conduction 78Li2S·22P2S5 glass ceramic electrolytes was shown in Figure 6 which indicates the stability window. Lithium deposition (Li+ + e− → Li) and dissolution (Li → Li+ + e−) reactions are observed as redox peaks at around 0 V vs Li/Li+ in the voltammogram. The 78Li2S·22P2S5 glass-ceramic electrolytes exhibit high stability against the lithium metal electrode as evidenced by the almost unity Coulombic efficiency in the reactions. Meanwhile, there are no any other reactions apart from lithium deposition and resolution in the potential range from −0.5 to 5 V vs Li/Li+. Although a conceivable decomposition reaction in sulfides is the oxidation of sulfide ions, they are immobile in solids and thus do not diffuse to the electrode surface to be oxidized.13,23 Therefore, the 78Li2S· 22P2S5 glass-ceramic electrolytes possess a wide electrochemical window of more than 5 V. In order to further evaluate the performance of the 78Li2S· 22P2S5 electrolytes, all-solid-state Li−S cells were prepared with sulfides as cathode and Li−In alloys as anode. The cycle performance of the all-solid-state cells was shown in Figure 7 and Figure 8. The cells were operated at a current density of 0.018 mA cm−2 for the first cycle and 0.044 mA cm−2 for the following cycles. The cutoff voltage was 0.0−3.0 V (vs Li−In). As shown in Figure 7a, during the first cycle of the all-solidstate Li−S cell, Li2S-based cathode|78Li2S·22P2S5|Li−In (with nanosized Li2S as active material) exhibits a charge capacity of 28546

DOI: 10.1021/acsami.7b06038 ACS Appl. Mater. Interfaces 2017, 9, 28542−28548

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(7) Mizuno, F.; Hayashi, A.; Tadanaga, K.; Tatsumisago, M. High Rate Performances of All-Solid-State In/LiCoO2, Cells with the Li2SP2S5, Glass-Ceramic Electrolytes. Solid State Ionics 2006, 177, 2731− 2735. (8) Tatsumisago, M. Glassy Materials Based on Li2S for All-SolidState Lithium Secondary Batteries. Solid State Ionics 2004, 175, 13−18. (9) Mercier, R.; Malugani, J. P.; Fahys, B.; Robert, G. Superionic Conduction in Li2S-P2S5-LiI-glasses. Solid State Ionics 1981, 5, 663− 666. (10) Zhu, Y.; He, X.; Mo, Y. Origin of Outstanding Stability in the Lithium Solid Electrolyte Materials: Insights from Thermodynamic Analyses Based on First-Principles Calculations. ACS Appl. Mater. Interfaces 2015, 7, 23685−23693. (11) Minami, K.; Hayashi, A.; Ujiie, S.; Tatsumisago, M. Structure and Properties of Li2S-P2S5-P2S3, Glass and Glass-ceramic Electrolytes. J. Power Sources 2009, 189, 651−654. (12) Hayashi, A.; Hama, S.; Morimoto, H.; Tatsumisago, M.; Minami, T. Preparation of Li2S-P2S5 Amorphous Solid Electrolytes by Mechanical Milling. J. Am. Ceram. Soc. 2001, 84, 477−479. (13) Chen, K.; Huang, M.; Shen, Y.; Lin, Y.; Nan, C. W. Improving Ionic Conductivity of Li0.35La0.55TiO3 Ceramics by Introducing Li7La3Zr2O12 Sol into the Precursor Powder. Solid State Ionics 2013, 235, 8−13. (14) Chen, K.; Huang, M.; Shen, Y.; Lin, Y.; Nan, C. W. Enhancing Ionic Conductivity of Li0.35La0.55TiO3 Ceramics by Introducing Li7La3Zr2O12. Electrochim. Acta 2012, 80, 133−139. (15) Ma, C.; Chen, K.; Liang, C.; Nan, C. W.; Ishikawa, R.; More, K.; Chi, M. Atomic-scale Origin of the Large Grain-boundary Resistance in Perovskite Li-ion-conducting Solid Electrolytes. Energy Environ. Sci. 2014, 7, 1638. (16) Arbi, K.; Rojo, J. M.; Sanz, J. Lithium Mobility in Titanium Based NASICON Li1+xTi2−xAlx(PO4)3 and LiTi2−xZrx(PO4)3 Materials Followed by NMR and Impedance Spectroscopy. J. Eur. Ceram. Soc. 2007, 27, 4215−4218. (17) Knauth, P. Inorganic Solid Li Ion Conductors: an Overview. Solid State Ionics 2009, 180, 911−916. (18) Inaguma, Y.; Chen, L.; Itoh, M.; Nakamura, T. Candidate Compounds with Perovskite Structure for High Lithium Ionic Conductivity. Solid State Ionics 1994, 70-71, 196−202. (19) Chen, R. J.; Huang, M.; Huang, W. Z.; Shen, Y.; Lin, Y. H.; Nan, C. W. Effect of Calcining and Al Doping on Structure and Conductivity of Li7La3Zr2O12. Solid State Ionics 2014, 265, 7−12. (20) Cheng, L.; Wu, C. H.; Jarry, A.; Chen, W.; Ye, Y.; Zhu, J.; Kostecki, R.; Persson, K.; Guo, J.; Salmeron, M.; Chen, G.; Doeff, M. Interrelationships Among Grain Size, Surface Composition, Air Stability, and Interfacial Resistance of Al-substituted Li7La3Zr2O12 Solid Electrolytes. ACS Appl. Mater. Interfaces 2015, 7, 17649−17655. (21) Ohta, S.; Kobayashi, T.; Asaoka, T. High Lithium Ionic Conductivity in the Garnet-Type Oxide Li7La3(Zr2‑xNbx)O12(x = 0− 2). J. Power Sources 2011, 196, 3342−3345. (22) Tatsumisago, M.; Nagao, M.; Hayashi, A. Recent Development of Sulfide Solid Electrolytes and Interfacial Modification for All-SolidState Rechargeable Lithium Batteries. Journal of Asian Ceramic Societies 2013, 1, 17−25. (23) Kamaya, N.; Homma, K.; Yamakawa, Y.; Hirayama, M.; Kanno, R.; Yonemura, M.; Kamiyama, T.; Kato, Y.; Hama, S.; Kawamoto, K.; Mitsui, A. A Lithium Superionic Conductor. Nat. Mater. 2011, 10, 682−686. (24) Hayashi, A.; Hama, S.; Minami, T.; Tatsumisago, M. Formation of Superionic Crystals from Mechanically Milled Li2S-P2S5 Glasses. Electrochem. Commun. 2003, 5, 111−114. (25) Mizuno, F.; Hayashi, A.; Tadanaga, K.; Tatsumisago, M. New, Highly Ion-conductive Crystals Precipitated from Li2S-P2S5 Glasses. Adv. Mater. 2005, 17, 918−921. (26) Trevey, J.; Jang, J. S.; Jung, Y. S.; Stoldt, C. R.; Lee, S. H. Glassceramic LiS-PS Electrolytes Prepared by a Single Step Ball Billing Process and Their Application for All-Solid-State Lithium-ion Batteries. Electrochem. Commun. 2009, 11, 1830−1833.

ment of the energy storage performances of the all-solid-state cells based on 78Li2S·22P2S5 glass-ceramics may lie in the increase in the ionic conductivity of the solid electrolytes and in the optimization of the processing and assembly of the all-solidstate batteries.

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CONCLUSIONS High-performance 78Li2S·22P2S5 glass-ceramic electrolytes have been prepared via a simple heat-treatment method. High ionic conductivity of 1.78 × 10−3 S cm−1 is achieved in these glass-ceramic electrolytes at room temperature, which is attributed to the nucleation of thio-LISICON II analogue crystallites from the glass during annealing. The impact of different heat-treatment process has also been studied. All-solidstate lithium-ion batteries based on these glass-ceramic electrolytes are assembled by using Li2S nanoparticles or lowcost commercially available FeS2 as active cathode materials and Li−In alloys as anode. A high discharge capacity of 535 mAh g−1 is achieved after at least 50 cycles for the all-solid-state cells with Li2S as cathode materials, suggesting a rather high capacity retention of 97.4%. Even for the cells using low-cost FeS2 as cathode materials, the same high discharge capacity of 560 mAh g−1 is also achieved after at least 50 cycles. Moreover, the Coulombic efficiency remained at ∼99% for these all-solid-state cells during the charge−discharge cycles.

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AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected]. Tel.: +86-1062794855; fax: +86-10-62772507. *E-mail: [email protected]. ORCID

Yang Shen: 0000-0002-1421-0629 Author Contributions

The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by the NSF of China (grant no. 51572141, 51532002, 51625202).

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REFERENCES

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DOI: 10.1021/acsami.7b06038 ACS Appl. Mater. Interfaces 2017, 9, 28542−28548