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In-situ generated Li2S-C nanocomposite for High-Capacity and Long-Life All-Solid-State Lithium Sulfur Batteries with Ultrahigh Areal Mass Loading Hefeng Yan, Hongchun Wang, Donghao Wang, Xue Li, Zhengliang Gong, and Yong Yang Nano Lett., Just Accepted Manuscript • DOI: 10.1021/acs.nanolett.9b00882 • Publication Date (Web): 22 Apr 2019 Downloaded from http://pubs.acs.org on April 22, 2019

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In-situ generated Li2S-C nanocomposite for HighCapacity and Long-Life All-Solid-State Lithium Sulfur Batteries with Ultrahigh Areal Mass Loading Hefeng Yan,1 Hongchun Wang,1 Donghao Wang,1 Xue Li,1 Zhengliang Gong,1* and Yong Yang1,2*

1College 2State

of Energy, Xiamen University, Xiamen, Fujian 361102, P. R. China

Key Lab of Physical Chemistry of Solid Surfaces and Department of Chemistry College of

Chemistry and Chemical Engineering, Xiamen University, Xiamen, Fujian 361005, P. R. China

1 ACS Paragon Plus Environment

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ABSTRACT All-solid-state lithium-sulfur batteries (ASSLSBs) have attracted great attention due to their inherent ability to eliminate the two critical issues (polysulfide shuttle effect and safety) of traditional liquid electrolyte based Li-S batteries. However, it remains a huge challenge for ASSLSBs to achieve high areal active mass loading and high active material utilization simultaneously due to the insulating nature of sulfur and Li2S, and the large volume change during cycling. Herein, a Li2S@C nanocomposite with Li2S nanocrystals uniformly embedded in conductive carbon matrix, is in-situ generated by the combustion of lithium metal with CS2. Benefiting from its unique architecture, the Li2S@C exhibits exceptional electrochemical performance as cathode for ASSLSBs, with both ultrahigh areal Li2S loading (7 mg cm-2) and 91% of Li2S utilization (corresponding to a reversible capacity of 1067 mAh g-1). Moreover, the Li2S@C also possesses outstanding rate capability and cycling stability. High reversible capacity of 644 mAh g-1 is delivered at 2 mA cm-2 even after 700 cycles. This work demonstrates that ASSLSBs with superior electrochemical performance can be realized via rational design of the cathode structure, which provides a promising prospect to the development of ASSLSBs with practical energy density surpassing that of lithium ion batteries.

KEYWORDS: lithium-sulfur batteries, sulfide electrolyte, Li2S@C nanocomposite, cycling stability, high areal loading


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Pursuing new and innovative battery technologies beyond Li-ion batteries is highly desirable for growing demands of high-energy-density energy storage systems for transportation, renewable electricity and the grid.1,

2

Lithium-sulfur (Li-S) batteries have attracted extensive

attention as a promising next-generation energy storage technology due to their high theoretical energy density. Although significant progresses have been achieved over the last two decades, Li-S batteries with ether-based liquid electrolytes still face significant obstacles.3 Firstly, the “shuttle effect” resulting from the dissolution and diffusion of polysulfide intermediates acts as the major challenge.4-6 The intermediate discharge products lithium polysulfides (Li2Sn, 4 < n < 8) readily dissolve in ether-based electrolytes and easily diffuse from the cathode to the anode, thus serve as redox shuttle. The shuttle effect results in a series of problems such as irreversible loss of active sulfur, low Coulombic efficiency, rapid capacity fading, high self discharge and corrosion of Li anode. Secondly, the high volatile and low flash points of ether-based solvents result in significant safety risks for Li-S batteries operating at elevated temperatures. Furthermore, cycling Li metal anode in flammable ether-based electrolytes also raises serious safety concerns. Li anode is highly reactive and prone to dendrite formation, which may penetrate the separator and incite fire hazards. Therefore, the practical application of Li-S batteries utilizing ether-based electrolytes indubitably suffer from severe safety concerns.7-9 Many of the challenges described above can be addressed by using inorganic solid electrolytes.10-13 Compared with ether-based liquid electrolytes, the application of solid electrolytes to Li-S batteries will bring multiple benefits. The shuttle effect can be radically avoid via eliminating polysulfide intermediates through solid-phase Li-S redox reaction.14 In addition, solid electrolytes bring significant safety benefit due to their negligible vapor pressure and nonflammable nature. Moreover, inorganic solid electrolytes possess high lithium-ion


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transference number (near unity) and high mechanical strength, which is expected to inhibit the formation of Li dendrites.15, 16 Therefore, all-solid-state Li-S batteries (ASSLSBs) using a solid electrolytes are expected to have superior energy density, high cyclability and high safety. Owing to their advantages of high ionic conductivity (10-3-10-2 S/cm) and excellent formability (simply via cold pressing without high temperature sintering) at room temperature (RT), sulfidebased solid electrolytes have been widely used for ASSLSBs.17-20 In the past decade, remarkable progresses have been made on ASSLSBs.21, 22 ASSLSBs with superior electrochemical performance have been reported via the optimization of sulfur-based composite cathode.23-27 However, it is worth noting that the high discharge capacity and longterm cycling stability can only be realized at low areal mass loading of active material (normally < 2 mg cm-2) or low current density (usually < 0.5 mA cm-2) 27-31. It is highly desired to increase the areal loading of sulfur electrode and improve the rate capability in order to fulfill the high energy density potential of ASSLSBs and meet the requirements of practical application.32 Normally, the composite cathode of ASSLSBs is prepared by mechanically mixing the three phases of active material (element sulfur or Li2S), sulfide electrolyte and conductive carbon together.33,

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The mechanical mixed composite cathode structure normally has poor contact

between the insulating S/Li2S and the ionic and electronic conducting materials, which limits the electrochemical performance.35,

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Especially, the electron and ion diffusion pathways are

extended for the composite cathode with high mass loading. The poor interfacial contact between the three phases may hinder the electron and ion transport, which leads to low active material utilization and poor rate capability. Besides, the large volume change (79%) between S and Li2S during lithiation/delithiation induces giant stress and leads to formation of cracks in the electrode, which will result in the detachment of active material from the electronic/ionic-


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conducting network and rapid capacity fading. The preparation of novel composite cathode comprised of nano-sized Li2S (instead of sulfur) uniformly embedded in conductive network (such as carbon) is one of the most promising strategies to address the above technique challenges.37-39 It can simultaneously enhance the mechanical property, ionic and electronic conductivity of the composite cathode, thus significantly enhance the electrochemical performance of ASSLSBs. First, Li2S-based composite doesn’t expand during cell operation, since Li2S is already the least dense phase with the lithium incorporated.40-43 This enhances the structure stability of the composite electrode during cycling, thus improving the cycling performance. Second, the nano-sized Li2S embedded in conductive carbon can effectively reduce the diffusion pathways of both Li ions and electrons,44,

45

thus

significantly enhance the electron and ion transport, and this is particularly important for ASSLSBs to achieve high active material utilization and high rate performance. Most importantly, the compact electrode structure with much enhanced mechanical property and conductivity make it possible to achieve high areal mass loading, which is one of the critical parameters for practical application of ASSLSBs.

45, 46

However, it is highly challenging to the

synthesis of well designed Li2S/conductor nanocomposite, due to the high melting point, very low solubility in organic solvents and high sensitivity to moisture of Li2S. Han et al.47 prepared a triple-phase uniformly mixed Li2S nanocomposite via a coprecipitation and high-temperature carbonization process. The obtained nanocomposite exhibited superior electrochemical performance due to the homogeneous mixing of Li2S, solid electrolyte and carbon in nanoscale. As cathode for ASSLSBs, it delivers a high reversible capacity of 830 mAh g-1 with a high Li2S loading (∼3.6 mg cm-2) at 0.18 mA cm-2 for 60 cycles at RT. However, the rate capability of the Li2S nanocomposite cathode is still need to improve, the reversible capacity decrease to 407, 304


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and 202 mAh g-1 at 0.36, 0.72 and 1.44 mA cm-2, respectively. In this work, we presented a unique Li2S@C nanocomposite cathode prepared through the combustion of lithium metal with CS2 to in-stiu form a carbon wrapped nano-sized Li2S particles, and the Li2S@C nanocomposite were then mixed with sulfide electrolyte Li7P3S11 (LPS) and acetylene black (AB) by high energy ball milling to form a mixed ionic and electronic conducting network. The in-situ formed carbon matrix can intimately wrap on the Li2S nanoparticles, which not only significantly improves the electronic conductivity but also effectively inhibits the aggregation of Li2S and accommodates the large volume change of Li2S during cycling. Meanwhile, the nano-sized Li2S particles can shorten the diffusion lengths of Li ions and mitigate the stress upon lithiation/delithiation. Furthermore, the uniformly distributed ionic and electronic conductive networks formed by ball milling facilitate the formation of nanoscale percolation network, which significantly increases the electrochemically active surface area. As a result, the Li2S@C nanocomposite cathode with very high areal Li2S loading exhibited excellent electrochemical performance with high specific capacity, good rate capability as well as outstanding cycling performance. Figure 1a shows the X-ray diffraction (XRD) patterns of the as-obtained Li2S@C nanocomposite. All the peaks can be indexed by the cubic Li2S structure with the space group of Fd3m. The main diffraction peaks of Li2S@C at 2θ = 27.0°, 31.3°, 44.8°, 53.1° and 55.7° can be indexed to the diffraction from the (111), (200), (220), (311) and (222) planes of crystal Li2S, respectively. No impurity peaks can be observed except for Li2S phase, indicating that high pure Li2S@C was successfully prepared by the combustion of lithium metal with CS2. The morphology and nanometric structure of the Li2S@C were characterized by scanning electron micrographs (SEM) and transmission electron microscopy (TEM). As shown in Figure


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1b, Li2S@C adopts an interwoven architecture that consists of in-stiu formed nano-sized Li2S interlaced with conductive carbon forming a unique porous nanocomposite structure. From TEM image (Figure 1c), we can clearly see that the nano-sized Li2S particles with a diameter of 50100 nm are uniformly embedded and well-isolated in carbon matrix. Figure 1d shows highresolution transmission electron microscopy (HRTEM) image of the Li2S nanoparticles, where the lattice fringe is determined to be 0.202 nm corresponding to the (220) lattice plane of cubic Li2S. Raman spectroscopy (Figure S1a) displays well defined G band and D band at 1,570 and 1,350 cm-1, respectively, indicating that carbon is in situ generated when combustion lithium metal with CS2. The HRTEM image (Figure S1b) shows that a 10-20 nm amorphous carbon layer is coated on the surface of Li2S nanocrystal. The electronic conductivity of Li2S@C was determined to be 2.9×10-8 S/cm by using the d.c. polarization method, which is about five orders of magnitude higher than that of pure Li2S (~×10-13 S/cm).5 Figure S2a shows the XRD pattern of the prepared LPS solid electrolyte. XRD results indicate the successfully synthesis of pure phase LPS glass-ceramic.48,

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All the diffraction peaks

observed can be identified as the Li7P3S11 with triclinic centrosymmetric space group P-1.50 Figure S3 shows the SEM images of LPS powder and the surface of LPS electrolyte pellet prepared by cold-pressed process. The as obtained LPS electrolyte prepared by high-energy ball milling is composed of irregular particles with particle size of 0.5-2 μm. The electrolyte pellet prepared by cold-press exhibits compact structure and smoother surface. This indicates that dense LPS solid electrolyte can be achieved by room-temperature pressure sintering, which is consistent with the previous experimental reports.51 The ionic conductivity of the cold-pressed LPS solid electrolyte was measured to be 1.7 × 10-3 S cm-1 (Figure S2b). Figure 2 shows the SEM image and element mapping images of the as-obtained Li2S@C-


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LPS-AB composite prepared by high-energy ball milling. It is clear that a layer of glass like LPS is uniformly coated on the Li2S nanoparticles, while the incorporation of LPS induces a more compact structure due to its room-temperature sintering nature. According to the element mapping images, the elements of C, P, and S are uniformly distributed in the Li2S@C-LPS-AB composite, suggesting the uniform distribution of Li2S@C, LPS and AB within the composite. The electrochemical performance of the Li2S@C-LPS-AB composite cathode was evaluated using all-solid-state lithium batteries with LPS as electrolyte and Li-In alloy as anode at both 60 °C and RT. Commercial Li2S-LPS-AB composite cathode was also measured in the same fashion for comparison. In addition, the effects of areal active mass loading (from 1.75 to 7 mg cm-2) on the electrochemical performance were also evaluated. The mass ratio of Li2S in the composite cathode is 38 wt %, which is much higher than the previously reported values.31, 32, 37, 39

Figure S4 shows the cyclic voltammogram (CV) curves of the Li2S@C-LPS-AB composite

cathode in ASSLSBs at 60 °C. In the initial anodic scan, an obvious oxidation peak around 2.6 V vs. Li+/Li is observed, corresponding to the extraction of lithium from Li2S. One remarkable reduction peak at ~1.8 V is observed during the cathodic process due to the reduction of element sulfur back to Li2S. The oxidation peak shifts to lower potential (~2.4 V) and the peak intensity increases in the subsequent cycles, corresponding to the activation process, which will be further discussed in the following section. Figure 3a shows the voltage profiles of Li2S@C-LPS-AB composite cathode in ASSLSBs with a moderate Li2S loading of ~1.75 mg cm-2 at 0.2 mA cm-2 at 60 °C. It displays one single charge and discharge plateau at around 2.3V (2.45 V at the first charge) and 2.1V (vs. Li+/Li), consisting with the typical solid-to-solid binary phase transition (between Li2S and S) behavior observed in ASSLSBs.27 This is different from the solid-liquid-solid two dual-phase transition


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behavior observed in traditional Li-S batteries with liquid electrolytes, which shows two characteristic discharge plateaus at 2.3 V and 2.1 V and charge plateaus at 2.35 V and 2.45 V, indicating the two stage reduction processes from elemental sulfur to liquid lithium polysulfides (Li2Sn, 4 < n < 8), and from these polysulfides to solid Li2S2/Li2S.42, 52, 53 The high charge plateau at the first cycle, which shifts to low voltage (~2.3 V) in subsequent cycles, is due to the initial potential barrier associated with the electrochemical activation of insulating Li2S. This activation phenomenon is widely observed in Li-S batteries using Li2S based cathode.54, 55 According to the previously reports, a large potential barrier (around 1 V) has to be overcome for the pristine Li2S electrode during the initial charge process, in order to conquer the barrier of delithiation of insulating Li2S (which is caused by the direct conversion of Li2S into S8). In general, a high charge cut-off voltage (~3.5-4.0 V) and a low charge rate have to be used for Li2S based cathode, in order to fully convert Li2S into sulfur during the first charging.41,

56

Figure S5 shows the

comparison of the first charge–discharge curves of the Li2S@C and commercial Li2S electrodes. It can be seen the Li2S@C electrode displays an obviously lower initial potential barrier (only about 0.15 V) compared with commercial Li2S electrode, indicating the benefit of the nanocomposite architecture in reducing the charge transfer overpotential. The low initial potential barrier is also confirmed by the charge/discharge equilibrium potential curves determined by the galvanostatic intermittent titration method (Figure S6). Furthermore, the cell also shows low overpotential (< 0.2 V) for all-solid-state batteries, indicating the fast redox reaction kinetics of Li2S@C. The small initial potential barrier and low overpotenial can be attributed to the unique nanocompostie architecture of Li2S@C cathode with Li2S nanoparticles dispersed uniformly in carbon matrix, which greatly enhances the conductivity and largely reduces Li-ion/electron transport pathways. The Li2S@C exhibits a high initial charge capacity


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of 1209 mAh g-1, which is very close to fully convert Li2S into sulfur (with a theoretical capacity of 1166 mAh g-1). The charge capacity is slightly higher than theoretical value, which can be attributed to the side reaction of sulfide solid electrolyte Li7P3S11.57, 58 It delivers a high discharge capacity of 955 mAh g-1 with 80% Coulombic efficiency upon the following discharge. The Li2S@C-LPS-AB composite cathode also exhibits excellent cycling stability (Figure 3b). The capacity gradually increases from 955 to 1186 mAh g-1 during the initial several cycles, and the Coulombic efficiency is slightly higher than 100%, corresponding to the activation of initial formed sulfur. After the activation of the first several cycles, the capacities are maintained at around 1100 mAh g-1 for 100 cycles with high Coulombic efficiency (close to 100%). The surface morphologies of the Li2S@C-LPS-AB composite cathode before cycling and after 100 cycles were characterized using SEM. As shown in Figure S7, no obvious change is observed in the electrode's morphology, suggesting the good structural stability of the Li2S@C-LPS-AB composite cathode. Electrochemical impedance spectroscopy (EIS) spectra of the cell with Li2S@C nanocomposite cathode after different cycles were collected in order to understand the activation process (Figure S8). All the Nyquist plots at different cycles show a depressed semicircle at high frequency region with a slope tail at low frequency region. The first intercept with the real axis (at high frequency) is related to the ohmic resistance (Ro) of the cell from the solid electrolyte and electrode. The semicircle is assigned to the interfacial resistance (Ri) and charge transfer resistance (Rct) in parallel with double-layer capacitance (Cdl), and the low frequency slope tail is related to Li-ion diffusion in the bulk material. The ohmic resistance doesn’t change upon the whole cycle process, indicating the great stability of the LPS solid electrolyte and the low stress/strain within the cathode during cycling. A continuous increase in the ohmic resistance was reported for sulfur cathode based ASSLSBs due to the stress/strain within ASSLSBs


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induced by repeated volume change during cycling, which can generate cracks in both electrode and the electrolyte.27 Meanwhile, the interfacial and charge transfer resistances continuously decrease during the first twenty cycles and then maintain stable in the following cycles. EIS results are consistent with galvanostatic cycling performance, suggesting the activation process during cycling is closely related to the decrease in interfacial and charge transfer resistances. The activation process will be prolonged at high current density or RT due to the sluggish reaction kinetics. It will take about 40-50 cycles to active the cell and realize the highest capacity when cycled at a high current density of 1 mA cm-2 at 60 °C, or at 0.2 mA cm-2 at RT (Figure S9a and S10). The activation process can be significantly reduced when cycled at 0.2 mA cm-2 at 60 °C (Figure S9b). A high reversible capacity of 903 mAh g-1 and good cycling stability can be obtained at a 1 mA cm-2 after only 10-cycles activation process at 0.2 mA cm-2 at 60 °C. Therefore, for the electrochemical cycling tests at high current density or RT, the cells were first activated by precycling at low current density of 0.2 mA cm-2 at 60 °C for 10 cycles, in order to reduce the prolonged activation process. Moreover, the Li2S@C nanocomposite also demonstrates excellent rate performance (Figure 3c). When the current density increases from 0.2 mA cm-2 (114 mA g-1) to 0.5, 1.0, 1.5 and 2.0 mA cm-2 (1142 mA g-1), the capacity only slightly decreases from 1186 to 1040, 937, 870 and 800 mAh g-1, respectively. The capacity of 800 mAh g-1 at 2.0 mA cm-2 corresponds to 65% of its capacity at 0.2 mA cm-2. When the current density is returned back to 0.2 mA cm-2, the capacity of Li2S@C nanocomposite can fully recover to 1186 mAh g-1 and maintain stable for 100 cycles. Comparatively, for the commercial Li2S cathode, the rate capability is very poor even though a high reversible capacity of 930 mAh g-1 can be achieved at a low current density of 0.2 mA cm-2. The capacity dramatically decreases from 930 to 750, 520, 360 and 160 mAh g-1


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with the current density increases from 0.2 mA cm-2 to 0.5, 1.0, 1.5 and 2.0 mA cm-2, respectively. Figure 3d shows the charge-discharge profiles of the Li2S@C at various current densities. It is clear the cell polarization just slightly increases with increasing the chargedischarge current density, indicating the low charge transfer resistance, which is beneficial to high rate performance. The rate performance of Li2S@C nanocomposite is significantly better than commercial and other Li2S/sulfur based cathodes previously reported in the literatures.29, 37, 39

Figure 4a shows the long-term cycling performance of the Li2S@C at a high current density of

2 mA cm-2. It exhibits a stable capacity around 680 mAh g-1, and excellent long-term cycling stability with a high capacity retention of 93% after 700 cycles at a high current density of 2 mA cm-2. The Coulombic efficiency is close to 100% over the course of cycling, suggesting the good reversibility. The corresponding charge-discharge curves at different cycles are shown in Figure 4b. It shows that the charge-discharge curves are almost identical without obvious voltage drop over extended cycles. Room temperature cyclability is very important to the practical application of ASSLSBs. The electrochemical performances of the Li2S@C nanocomposite at room temperature (RT) were also investigated and the results are shown in Figure 4c and 4d. As can be seen, the Li2S@C nanocomposite can also deliver high capacity and good cycling stability even at RT. It exhibits a high capacity of 790 mAh g-1 with capacity retention of ∼94% after 100 cycles with the Li2S loading of 1.75 mg cm-2 at 0.5 mA cm-2 at RT. High areal active mass loading is one of the most critical factors for ASSLSBs to achieve its high energy density potential and fulfill the requirements of practical implementation. The impact of areal Li2S loading on the electrochemical performance of the Li2S@C nanocomposite was evaluated. Figure 5a displays the typical voltage profiles after activation of the Li2S@C


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nanocomposite with different areal Li2S loading at 0.2 mA cm-2 at 60 °C. It shows that high reversible capacity can still be obtained at a high areal Li2S loading. While the Li2S loading increases from 1.75 to 7 mg cm-2, the cell exhibits excellent capacity retention ability. There is no obvious overpotential increase when the Li2S loading increases from 1.75 to 7 mg cm-2, indicating the outstanding electrochemical activity of Li2S@C nanocomposite even with a high areal Li2S loading. It is worth noting that the Li2S@C nanocomposite still exhibits exceptionally high reversible capacity of 1066 mAh g-1 (corresponding to an areal capacity of 8.54 mA h cm-2 and 91% of the theoretical capacity) even with an ultrahigh Li2S loading of 7 mg cm-2. The Li2S@C nanocomposite also shows good cycling stability at Li2S loading of 7 mg cm-2, with stable capacity and high Coulombic efficiency (close to 100%) for 30 cycles (Figure 5b). To the best of our knowledge, the Li2S@C nanocomposite with a high areal Li2S loading of 7 mg cm-2 provides an areal capacity of 8.54 mAh cm-2, which is the highest compared with all prior reported ASSLSBs. Besides, outstanding rate capability can also be obtained for the Li2S@C nanocomposite cathode with a high areal Li2S loading of 3.5 mg cm-2 (Figure 5c). It was able to charge-discharge at an exceptional high current density up to 5 mA cm-2. The cell shows reversible capacities of 819, 677, 592, 531, 429, 361 and 282 mAh g-1 at the current density of 0.5, 1.0, 1.5, 2.0, 3.0, 4.0 and 5.0 mA cm-2, respectively. Furthermore, the Li2S@C nanocomposite cathode with Li2S loading of 3.5 mg cm-2 can still delivers a high capacity of 1039 mAh g-1 at 0.2 mA cm-2 even at RT (Figure S11). Figure 5d shows the available capacity at different areal active mass loading and current density of this work as a comparison with the state-of-the-art ASSLSBs reported in the literatures. The data obtained for the Li2S@C nanocomposite are marked with red circles. A more detailed comparison of electrochemical performance including cell design and operating conditions is listed in Table 1. Apparently, the


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performance of Li2S@C nanocomposite is more attractive in term of high areal Li2S loading, as well as rate capability and cycling stability than that of Li2S/sulfur based cathodes reported in the recent literatures. In summary, this work demonstrated the Li2S@C-LPS-AB nanocomposite cathode achieving ultrahigh areal Li2S loading and high Li2S utilization simultaneously for ASSLSBs. Conductive carbon and Li2S nanocrystals are in situ generated simultaneously when combustion lithium metal with CS2, resulting the unique Li2S@C nanocomposite architecture. The in-situ generated carbon intimately wrapped on the nano-sized Li2S particles, which greatly enhances the electronic conductivity, effectively prohibits the aggregation of Li2S nanoparticles and accommodates the large volume change of Li2S during cycling. Since the Li2S nanocrystals must nucleate with carbon at the same time, a nanoscale percolation network can be formed to offer effective pathways for both electrons and ions, and alleviate the stress/strain during lithiation/delithiation. Therefore, the Li2S@C nanocomposite cathode exhibits excellent electrochemical performance with high capacity, as well as outstanding rate capability and cycling stability. It delivered a high reversible capacity of 1186 mAh g-1 at 0.2 mA cm-2 with a Li2S loading of 1.75 mg cm-2. Moreover, it exhibited high reversible capacity of 692 mAh g-1 and superior long-term cycling performance with high capacity retention of 93% after 700 cycles even at a high current density of 2 mA cm-2. Most importantly, the unique architecture characteristics of Li2S@C nanocomposite facilitate the achievement of ultrahigh areal Li2S loading (7 mg cm-2) and high Li2S utilization of 91% simultaneously. This work provides a facile and effective strategy to overcome the key challenges for ASSLSBs to fulfill the high energy density potential and meet the requirements of practical application.


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ASSOCIATED CONTENT Supporting Information. XRD patterns and AC impedance spectra of the Li7P3S11 glass ceramic solid electrolyte; SEM images of Li7P3S11 solid electrolyte; Raman spectra and HRTEM image of Li2S@C nanocomposite; CV of the Li2S@C ASSLSBs; Comparison of the first charge–discharge curves of the Li2S@C and commercial Li2S electrodes; Charge/discharge GITT curves of Li2S@C nanocomposite cathode; SEM images of the surface of Li2S@C-LPS-AB composite cathode before and after 100 cycle; EIS spectra of the Li2S@C based ASSLSBs after different cycles; Cycling performances of the Li2S@C nanocomposite at high current density without and with precycling activation at 0.2 mA cm-2 at 60 oC; Cycling performances of the Li2S@C nanocomposite at 0.2 mA cm-2 at RT without precycling activation at 60 oC; The typical charge/discharge curve and cycling performances of the Li2S@C based ASSLSBs with Li2S loading around 3.5 mg cm-2 at RT (PDF)

AUTHOR INFORMATION

Corresponding Author *E-mail: [email protected]. *E-mail: [email protected]. ORCID Zhengliang Gong: 0000-0003-4671-4044 Yong Yang: 0000-0002-9928-7165 15 ACS Paragon Plus Environment

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Notes The authors declare no competing financial interest.

ACKNOWLEDGMENTS This work was supported by the National Key R&D Program of China (Grants No. 2018YFB0905400 and 2016YFB0901500), the National Natural Science Foundation of China (Grants No. 21875196, 21761132030 and U1732121) and the Science and Technology Planning Projects of Fujian Province, China (Grant No. 2019H0003).


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Figure 1. The structural and morphology characterization of the as obtained Li2S@C nanocomposite. (a) XRD pattern, (b) SEM image, (c) TEM image, showing nano-sized Li2S particles are uniformly embedded in conductive carbon matrix, and (d) High-resolution TEM (HRTEM) image.


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Figure 2. (a) SEM image and (b) elemental mapping images of the Li2S@C-LPS-AB nanocomposite cathode.


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Figure 3. Electrochemical performance of the Li2S@C nanocomposite in ASSLSBs with areal Li2S loading of ~1.75 mg cm-2 at 60 °C. (a) Charge/discharge curves and (b) cycling performance at 0.2 mA cm-2, (c) rate performance and (d) corresponding voltage profiles under different current densities.


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Figure 4. Cycling performances of the Li2S@C nanocomposite in ASSLSBs with areal Li2S loading of ~1.75 mg cm-2. (a) Long-term cycling performances and (b) voltage profiles at different cycles under a high current density of 2.0 mA cm-2 at 60 °C, (c) cycling performances and (d) voltage profiles at different cycles under current density of 0.5 mA cm-2 at RT.


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Figure 5. Electrochemical performances of the Li2S@C nanocomposite with high areal active mass loading at 60 °C. (a) Typical voltage profiles with areal Li2S loading from 1.75 mg cm-2 to 7 mg cm-2, (b) cycling performances under a high Li2S loading of 7 mg cm-2, (c) rate performance with Li2S loading of 3.5 mg cm-2, and (d) the comparison of electrochemical performance of the Li2S@C nanocomposite with the state-of-the-art ASSLSBs reported in the literatures. A more detailed comparison of electrochemical performance including cell design and operating conditions can be found in Table 1.


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Table 1. Detailed comparison of the electrochemical performance of the Li2S@C nanocomposite with the state-of-the-art ASSLSBs reported in the literatures including cell design and operating conditions. Active material

Content (%)

Loading (mg cm-2)

Current density (mA cm-2)

Cycle life (cycle)

Capacity after Cycling (mA h g-1)

Cut-off voltage (V) vs. Li

Remarks Reference

Li2S Li2S Li2S Li2S Li2S Li2S Li2S Li2S Li2S Sulfur Sulfur Sulfur

38 38 38 38 36 36 65 25 15 25 12 25

1.75 1.75 3.5 7 3.6 3.6 0.2 3.18 5.7 1 0.4-0.5 0.8

0.5 2 0.2 0.2 0.18 0.36 0.02 0.064 0.067 0.44 0.7 0.08

100 700 10 30 60 5 100 10 10 1000 750 60

748 644 (60°C) 1047 1073 (60°C) 830 406 600 (60°C) 700 700 834 830 (60°C) 394

1.5-3.0 1.5-3.0 1.5-3.0 1.5-3.0 1.0-3.6 1.0-3.6 1.5-2.8 0.6-3.6 1.0-3.6 0.6-3.6 1.5-2.8 1.0-3.0

This work This work This work This work


[47] [47] [29] [37] [39] [24] [27] [31]

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A Table of Contents (TOC) graphic


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