Rechargeable solid-state batteries (SSBs) offer tremendous promise as a safe and energy-dense storage technology for use in electric transportation, robotics, and portable electronics. Lithium argyrodites (e.g., Li 7 PS 6 , and its halogen-doped derivatives) have emerged as a lucrative class of solid-state electrolytes (SSEs) for SSBs owing to their high Li-ion conductivity (~10 -3 S/cm), good elastic stiffness (~30 GPa), and low flammability. Meanwhile, sulfide-based solid electrolytes such as Na 3 SbS 4 (NSS) also showcase substantial potential for SSBs with their high theoretical specific capacity, enhanced safety, and abundance of resources. Despite their promise, both lithium and sodium-based SSBs remain far from commercialization due to lack of atomic-scale understanding of ion-conduction, charge transport, structural evolution, and interfacial reactions (e.g., dendrite growth, electrolyte decomposition etc.). Here we employ a combination of density functional theory calculations, ab initio molecular dynamics simulations, and nudged elastic band calculations to understand ion transport mechanism in chemically doped lithium argyrodites and NSS. In lithium-based systems, using accurate materials modeling, we design fluorine-containing argyrodite electrolytes that offers enhanced Li-ion conduction facilitated by unique Li-disorder induced by fluorine and other halogen co-dopants. Our results show the opening up of new pathways for Li inter-cage hops in these fluorine -containing argyrodite electrolytes which increases the Li-ion conductivity. In the case of sodium-based systems, we focus on atomic-scale mechanisms underlying Na-ion conduction in the presence of cation dopants. Ab initio molecular dynamics simulations reveal the significant impact of cation dopants on NSS, where the introduction of charge-compensating Na-vacancies enhances Na-ion conduction. The size of the cation dopant is found to be a critical factor, with examples such as Ca-doped NSS (r Ca 2+ / r Na + = 0.98) showing a conductivity approximately 10 times that of pristine NSS, while larger Ba 2+ as a dopant (r Ba 2+ / r Na + = 1.35) hinders Na-ion hops due to local strain, resulting in a Na-ion conductivity ~5 times that of NSS. We will discuss these results in the context of accelerating design of novel solid-state electrolytes for long-lived, stable, and high-energy density SSBs.

Solid composite electrolytes (SCEs) have attracted serious attention for solid-state Li metal batteries. In particular, SCEs that incorporate inorganic sulfide into polymer electrolytes provide a feasible approach to address the air sensitivity and (electro)chemical instability of sulfides. Nevertheless, there is still little research on pairing sulfide-SCEs with high-voltage cathodes. In this work, reports on efforts to synthesize and compare SCEs that embedding sulfides (Li7PS6 and Li3PS4) into PVDF/HFP polymer using a strong polar solvent (DMF). Two sulfides show distinct behaviors when dispersed in the DMF solvent. The Li7PS6-SCE exhibits an ionic conductivity of 2.5 x 10-4 S cm-1 at room temperature, higher than the Li3PS4-SCE (1.75 x 10-4 S cm-1). Moreover, Li7PS6-SCE displays better electrochemical cycling performance in solid-state Li metal batteries with LiNi1/3Mn1/3Co1/3O2 (NMC 111) cathode.. When increasing upper cut-off voltages from 4.0 to 4.4 V, Li| Li7PS6-SCE |NMC111 cells deliver higher discharge capacities but exhibit worse cycling stability. Interface analysis using X-ray photoelectron spectroscopy (XPS) reveals the formation of LiF under a high voltage of 4.4 V, while t not present with 4.0 V. This work explores the synthesis of SCEs with different sulfides in a strong polar solvent and highlights the interface reactions between sulfide/PVDF-HFP SCEs with oxide cathodes. Sulfide-polymer solid composite electrolyte (SCE) membranes are prepared for two sulfides (Li7PS6 and Li3PS4) incorporated into PVDF/HFP polymer electrolytes using a strong polar solvent (DMF). Li7PS6-SCE exhibits better room temperature ionic conductivity than that of Li3PS4-SCE. When increasing upper cut-off voltages from 4.0 to 4.4 V, Li| Li7PS6-SCE |NMC111 cells deliver higher discharge capacities but exhibit worse cycling stability. image

We introduce a quasi-solid-state electrolyte lithium-sulfur (Li–S) battery (QSSEB) based on a novel Li-argyrodite solid-state electrolyte (SSE), Super P–Sulfur cathode, and Li-anode. The cathode was prepared using a water-based carboxymethyl cellulose (CMC) solution and styrene butadiene rubber (SBR) as the binder while Li6PS5F0.5Cl0.5 SSE was synthesized using a solvent-based process, via the introduction of LiF into the argyrodite crystal structure, which enhances both the ionic conductivity and interface-stabilizing properties of the SSE. Ionic liquids (IL) were prepared using lithium bis(trifluoromethyl sulfonyl)imide (LiTFSI) as the salt, with pre-mixed pyrrolidinium bis(trifluoromethyl sulfonyl)imide (PYR) as solvent and 1,3-dioxolane (DOL) as diluent, and they were used to wet the SSE–electrode interfaces. The effect of IL dilution, the co-solvent amount, the LiTFSI concentration, the C rate at which the batteries are tested and the effect of the introduction of SSE in the cathode, were systematically studied and optimized to develop a QSSEB with higher capacity retention and cyclability. Interfacial reactions occurring at the cathode–SSE interface during cycling were also investigated using electrochemical impedance spectroscopy, cyclic voltammetry, and X-ray photoelectron spectroscopy supported by ab initio molecular dynamics simulations. This work offers a new insight into the intimate interfacial contacts between the SSE and carbon–sulfur cathodes, which are critical for improving the electrochemical performance of quasi-solid-state lithium–sulfur batteries.

Sodium chalcogenide ionic conductors are attractive candidates as solid electrolytes (SEs) in solid-state Na metal batteries. They show the advantages of high ionic conductivity of 10-4-10- 2 S cm- 1 at room temperature and great chemical stability in air. However, simple and efficient approaches for the scalable synthesis of chalco-genide solid electrolytes (SEs) are required. In this work, we report a solvent-free mixing to form dry interme-diate products, which are subjected to different treatments (electron-beam assisted method or low temperature heating (& LE;150 degrees C)) to produce pure phase of Na3SbS4-ySey (0 & LE; y & LE; 2) chalcogenides. Heavy Se-doping in Na3SbS4 results in the tetragonal-to -cubic phase transition as well as a significant change of Sb-S bonding in Raman spectra. Among all chalcogenide SEs, Na3SbS3Se showed the highest ionic conductivity of 3.75 x 10-4 S cm-1 at room temperature, 47% higher than that of pristine Na3SbS4. Moreover, the Se-dopant also enhanced the electrochemical stability towards Na metal in solid-state batteries. The solid-state Na||FeS2 battery with Na3SbS3Se SE displayed long-term cycling ability up to 1,000 cycles within the voltage window of 1.0-2.7 V and retained a specific discharge capacity of 105 mAh g-1 after 600 cycles. This technique promotes the practical applications of chalcogenide SEs in solid-state Na batteries.

Sulfide-type argyrodite solid electrolytes (SEs) with halide doping have attracted serious interests. While other halides (Cl, Br) have been found to enhance Li-ion transport in argyrodites, the direct synthesis and without post-processing to produce highly conductive Li6PS5I has been rarely investigated. In this work, we report the direct synthesis of highly conductive Li6PS5I with an impressive ionic conductivity of 2.5 × 10-4 S cm-1 at room temperature through a solvent-based method. Moreover, by introducing F- to partially replace I-, hybrid-doped argyrodites Li6PS5FxI1-x (x = 0.25, 0.5, and 0.75) have been synthesized, and Li6PS5F0.25I0.75 achieves the highest conductivity of 3.5 x 10-4 S cm-1 due to F- and I- dual dopants facilitate faster Li-transport as indicated by density functional theory (DFT) calculations. With higher F-content in argyrodites, Li6PS5F0.75I0.25 displays the best electrochemical stability towards Li metal, as evidenced by long-term stable cycling in Li symmetric cells up to 1,100 hours. Solid-state Li metal batteries with active cathode of Li4Ti5O12 (LTO) display an initial specific capacity of 140 mAh g-1 and remains at 105 mAh g-1 after 200 cycles, suggesting great battery cycling performance. This research expands new compositions in argyrodite SE family and promotes the development of solid-state Li metal batteries.

Solid-state sodium (Na) batteries (SSSBs) using sulfide-based solid electrolytes (SSEs) hold tremendous promise due to their high theoretical specific capacity, enhanced safety and abundant resources. However, detrimental interfacial issues between SSEs and Na metal present a major challenge to the advancement of sulfide-based SSSBs. To address interfacial issues, we demonstrate an efficient approach by incorporating an ionic liquid electrolyte ((PYR/Na)TFSI) as interlayer to stabilize the Na metal/SSE interface. The presence of the (PYR/Na) TFSI interlayer enables the formation of a stable solid electrolyte interphase (SEI) to prevent the harmful reactions and inhibit Na dendrites. Combination of ab initio molecular dynamics simulations and X-ray photoelectron spectroscopy reveale that this stable SEI is largely composed of reduced products of TFSI-, such as NaF and CF3. As a result, the symmetric cells exhibited stable Na plating/striping cycling for 300 h at 0.1 mA cm(-2). In addition, FeS2||Na quasi-solid-state batteries delivered an impressive specific capacity of over 300 mAh g(-1) under the current density of 20 mA g(-1) at room temperature. Under a higher current density (100 mA g(-1)), such batteries performed with long-term cycling stability and maintained a specific capacity of around 103 mAh g(-1) after 330 cycles. This work demonstrates the novel perspective of using an ionic liquid interlayer to address interfacial issues, contributing to the advancement of high-performance SSSBs for the next-generation energy storage systems.

Solid-state lithium metal batteries (SSLMBs) that utilize novel solid electrolytes (SEs) have garnered much attention because of their potential to yield safe and high-energy-density batteries. Sulfide-based argyrodite-class SEs are an attractive option because of their impressive ionic conductivity. Recent studies have shown that LiF at the interface between Li and SE enhances electrochemical stability. However, the synthesis of F-doped argyrodites has remained challenging because of the high temperatures used in the state-of-the-art solid-state synthesis methods. In this work, for the first time, we report F-doped Li5+yPS5Fy argyrodites with a tunable doping content and dual dopants (F-/Cl- and F-/Br-) that were synthesized through a solvent-based approach. Among all compositions, Li6PS5F0.5Cl0.5 exhibits the highest Li-ion conductivity of 3.5 × 10-4 S cm-1 at room temperature (RT). Furthermore, Li symmetric cells using Li6PS5F0.5Cl0.5 show the best cycling performance among the tested cells. X-ray photoelectron spectroscopy and ab initio molecular dynamics simulations revealed that the enhanced interfacial stability of Li6PS5F0.5Cl0.5 SE against Li metal can be attributed to the formation of a stable solid electrolyte interphase (SEI)-containing conductive species (Li3P), alongside LiCl and LiF. These findings open new opportunities to develop high-performance SSLMBs using a novel class of F-doped argyrodite electrolytes.

Lithium-Sulfur (Li-S) batteries stand out to be one of the most promising candidates to meet the current energy storage requirement, with its natural abundance of materials, high theoretical capacity of 1672 mAhg-1, high energy density of 2600 Whkg-1, and low cost and lower environmental impact. Sulfur itself (S8), Li2S2 and Li2S formed during the discharge process, are electrical insulators and hence reduce the active material utilization and the electronic conductivity of the cathode affecting the battery performance. Combining of Carbon Super P (SP) with sulfur in cathode formulation is used to overcome these issues. In Liquid electrolyte batteries, polysulfides formed while charging and discharging, easily dissolve in liquid electrolyte and the resulting polysulfide shuttling leads to poor coulombic efficiency and cyclability. Liquid electrolytes used in the conventional Li-S batteries are easy to flow and become flammable. Further, Lithium dendrites piercing through separator causing short circuit paths leads to safety concerns. Replacement of the liquid electrolyte by a solid-state electrolyte (SSE) proves to be a strategy to overcome above mentioned issues. Sulfide based solid electrolytes have received greater attention due to their higher ionic conductivity, compatible interface with sulfur-based cathodes, and lower grain boundary resistance. Novel Li6PS5F0.5Cl0.5 due to its remarkable ionic conductivity of 3.5 x 10-4 S cm-1 makes it an excellent candidate for use in a Li-S solid state battery. However, the interface between SSEs and cathodes has become a challenge to be addressed in all solid-state Li-S batteries due to the rigidity of the participating surfaces. A hybrid electrolyte containing of SSE coupled with a small amount of ionic liquid at the interface, has been employed to improve the interface contact of the SSE with the electrodes. Cathode formulation consisting of sulfur as the active material, Super P as the conductive carbon black, acetylene carbon black as conductive carbon additive, with water based carboxymethyl cellulose (CMC) solution and Styrene butadiene rubber (SBR) as the binder was successfully developed. Thermo gravimetric analysis (TGA) studies of the cathode were carried out by the thermo gravimetric analyzer TA 2050 under N2 gas flow of 100 ml/min. Cathode surface morphology was characterized using the Field emission gun scanning electron microscope (FEI), TESCAN scanning electron microscope with energy dispersive X-ray spectroscopy (EDAX). Using a solvent-based process, Li6PS5F0.5Cl0.5 and Li6PS5F0.5Cl2 SSE were synthesized via the introduction of LiF into the argyrodite crystal structure, which enhances both the ionic conductivity and interface-stabilizing properties of the SSE. Relevant Ionic Liquids (IL) were prepared using Lithium bis(trifluoromethyl sulfonyl)imide (LiTFSI) as salt, with premixed pyrrolidinium bis(trifluoromethyl sulfonyl)imide (PYR) as solvent and 1,3-dioxolane (DOL) as diluent. SP-S cathode with 0.70 mgcm-2 sulfur loading was punched into disks of 2.0 cm2. SSE was pressed into 150 mg pellets using a stainless-steel tank. During the assembly, SSE was wetted with total of 40 μl of IL (LiTFSI dissolved in PYR and DOL solution) from both ends using a micropipette. 2032 type coin cells of Quasi-solid-state Li-S batteries (QSSLSB) consisting of SP-S based composite cathodes, Li anodes and novel Li6PS5F0.5Cl0.5 SSE were tested with an ionic liquid wetting both electrode-SSE interfaces. All the QSSLSB were cycled at 30 °C between 1.0 V and 2.8 V using an 8 channel Arbin battery testing system. Effect of IL dilution, co-solvent amount, LiTFSI concentration and C rate at which the batteries are tested, were systematically studied and optimized to develop a QSSLSB with higher capacity retention and cyclability. Optimum batteries had initial discharge capacity >1100 mAh/g and discharge capacity >400 mAh/g after 100 cycles at the C rate of C/10 with a significant coulombic efficiency. 40 μl of LiTFSI (2M) dissolved in PYR:DOL(1:1) IL was found to be optimum for high performance QSSEBs with low sulfur loading of 0.7 mg/cm2. From the C rate performance study QSSEBs have shown improved stability with the higher current rates. Next, cathodes with higher sulfur loading were studied and for sulfur loading > 4 mgcm-2, initial discharge capacity >950 mAh/g and 400 mAh/g after 60 cycles at C/20 rate were achieved with 40 μl of IL consisting of LiTFSI (3M) dissolved in PYR:DOL(1:3) for the SSE Li6PS5F0.5Cl2. Further testing is underway to improve the performance at high C rate for higher loading by incorporating SSE in the cathode to realize QSSLSB with higher capacity with improved cycle retention.

Strongly anharmonic low-energy phonons enable the fast diffusion of Na ions in the solid-state electrolyte compound Na 3 PS 4 .

All‐solid‐state sodium (Na) batteries (ASSSBs) using sulfide‐based solid electrolytes (SEs) have attracted intensive attention due to their superior safety, high energy density, and low cost. However, the interfacial issue is one of the biggest challenges to achieve high‐performance sulfide‐based ASSSBs due to the serious reactions between active Na metal and sulfide SEs at the interface. To address the interfacial challenges, a simple and efficient approach by introducing a phase transition polymer electrolyte as an interlayer to stabilize the interface is proposed. Na 3 SbS 4 as a model sulfide SE is used to demonstrate the interlayer strategy to stabilize the interface by preventing the detrimental reactions and inhibiting Na dendrites. As a result, stable Na plating/stripping is observed in Na symmetric cells under the current density of 0.1 mA cm −2 . Moreover, ASSSBs with Na metal and TiS 2 electrode deliver long‐term stability over 300 cycles remaining a specific capacity above 100 mAh g −1 , and FeS 2 ||Na cells exhibit an impressive specific capacity of up to 200 mAh g −1 after the 20th cycles. This study demonstrates an efficient strategy to address interfacial challenges between sulfide SEs and Na metal, which contributes to the development of ASSSBs in next‐generation energy storage systems.

Solid-state Li-ion conductors are of broad interest in electrochemical energy storage, especially in solid-state Li batteries that serve as a promising alternative for the next-generation safe and high-energy-density batteries. Exploring solid-state superionic conductors is significant for the development of solid-state Li batteries with high performance. Herein, we report a disordered rock-salt (A(1)B(1))-structured solid electrolyte (Li0.625Al0.125H0.25)(Cl0.75O0.25) (abbr. LAHCO) that was synthesized using Li2OHCl and LiAlCl4 as precursors. Neutron diffraction reveals that Li, Al, and H atoms occupy the A sites and O and Cl atoms occupy the B sites in the A(1)B(1) structure for pure LAHCO. The LAHCO compound with excess LiAlCl4 shows the highest Li+ ionic conductivity of similar to 10(-4) S cm(-1) at room temperature due to the disordering induced by configurational entropy as well as the entropy of mixing. Moreover, LAHCO-LiAlCl4 solid electrolyte exhibits a stable polarization voltage under a current density of 5-50 mu A cm(-2) in Li symmetric cells. This work not only explicates the importance of Li-ion conductors with a rock-salt structure but also contributes toward the development of solid-state Li-ion conductors for broad applications.

In solid-state lithium (Li)-metal batteries (SSLMBs), sulfide-based Li-ion conductors represent one of the most popular solid electrolytes (SEs). However, the development of sulfide-based SSLMBs is significantly hampered by interfacial issues including large solid-solid contact resistance and serious side reactions at the SE/electrode interface. To address these issues, here, we demonstrated a simple and efficient strategy by using LiCl-rich argyrodite Li6PS5Cl (Li6PS5Cl-LiCl) SE and trace amount of propylene carbonate (PC) at the SE/electrode interface to facilitate the formation of stable and robust solid electrolyte interphase (SEI). The formed SEI not only serves as a buffer layer to passivate the interfacial reactions and suppress Li dendrite growth, but also acts as a bridge for Li-ion conduction to reduce the contact resistance. As a result, the Li parallel to Li symmetric cell exhibited long-term electrochemical cycling stability over 1000 h at a current density of 0.2 mA cm(-2). Furthermore, the assembled Li parallel to Li4Ti5O12 (LTO) batteries delivered a specific capacity of 175 mAh g(-1) at 0.2 C, and remained an excellent specific capacity of 116 mAh g(-1) after 200 cycles at a high current rate of 1 C. These features indicate a feasible strategy to enhance the interfacial property of high-performance SSLMBs. (C) 2020 Elsevier Ltd. All rights reserved.

Halide-doped lithium argyrodites (Li6PS5X, X = Cl, Br or I) are one class of the most promising solid electrolyte candidates for solid-state Li batteries. However, similar to other superionic conductors, Li6PS5X argyrodites are mostly synthezied through high temperature solid-state reactions. Herein, we employ a solvent-based method to synthesize Li6PS5X argyrodites and study the halide doping (type and concentration) effect on their structure and properties. Using ethanol as the solvent medium, Li6PS5X and Li6PS5Cl center dot xLiCl (0 <= x <= 2) materials with precise composition control were achieved. The liquid-synthesized Li6PS5Cl showed the best ionic conductivity of 0.34 mS cm(-1) at room temperature, followed by Li6PS5Br, with Li6PS5I being the worst. Interestingly, excess Cl content further increased the ionic conductivity of Li6PS5Cl center dot LiCl up to 0.53 mS cm(-1) at room temperature and 5 mS cm(-1) at 90 degrees C. In addition, the Li4Ti5O12/Li cell with Li6PS5Cl center dot LiCl solid electrolyte exhibited higher specific capacity (135 mAh g(-1)) than that of Li6PS5Cl-based cell (110 mAh g(-1)) at 0.2C. These results highlight a solventbased synthesis method with precise composition control to study the halogen ion's effect on the structure and properties of lithium argyrodites, which would promote the development of lithium argyrodite solid electrolytes for applications in all-solid-state Li batteries.

The utilization of solid electrolyte (SE) to suppress lithium (Li) dendrites is promising but still far from satisfactory due to the inhomogeneous Li plating/stripping. Here, we demonstrated a novel strategy to inhibit Li dendrites via regulating Li-ion flux in SE by using vertically aligned channels. The ion-insulating walls facilitated uniform distribution of Li-ion flux through the channels, leading to a homogeneous Li deposition, thus alleviating Li dendrite formation. As a result, symmetric cells with this SE exhibited excellent long-term stability (1000 h) against Li metal. In addition, Li4Ti5O12 (LTO)/Li cell with the developed SE achieved good battery performance over 100 cycles. The mechanism for dendrite suppression was further investigated by phase-field simulation. This work provides a novel strategy by manipulating uniform Li-ion flux to fabricate SE to inhibit Li dendrites and facilitates the development of high-performance rechargeable Li batteries.

Sulfide-based lithium (Li)-ion conductors represent one of the most popular solid electrolytes (SEs) for solid-state Li metal batteries (SSLMBs) with high safety. However, the commercial application of sulfide SEs is significantly limited by their chemical instability in air and electrochemical instability with electrode materials (metallic Li anode and oxide cathodes). To address these difficulties, here, we design and successfully demonstrate a novel sulfide-incorporated composite electrolyte (SCE) through the combination of inorganic sulfide Li argyrodite (Li7PS6) with poly(vinylidenefluoride-co-hexafluoropropylene) (PVDF-HFP) polymer. In this composite structure, Li7PS6 is embedded in PVDF-HFP polymer matrix, making the SCE flexible and air-stable and achieve great chemical and electrochemical stability. Meanwhile, the presence of sulfide facilitates Li-ion transport in SCE, leading to a superior room-temperature ionic conductivity of 1.1 × 10-4 S cm-1. Using the SCE with enhanced stability while maintaining high conductivity, Li||Li symmetric cells achieved stable cycling up to 1000 h at 0.2 mA cm-2. In addition, LiFePO4 (LFP)||SCE||Li cells can deliver an impressive specific capacity of 160 mAh g-1 over 150 cycles. These features indicate that Li7PS6/PVDF-HFP SCE is a promising candidate to contribute to the practical development of SSLMBs.

Solid electrolytes are the key to realize future solid-state batteries that show the advantages of high energy density and intrinsic safety. However, most solid electrolytes require long time and energy-consuming synthesis conditions of either extended ball milling or high-temperature solid-state reactions, impeding practical applications of solid electrolytes for large-scale systems. Here, we report a new and rapid liquid-based synthetic method for preparing a high-purity Li7PS6 solid electrolyte through the stoichemical reaction of Li3PS4 and Li2S. This method relies on facile and low-cost solution-based soft chemistry to complete chemical reaction in extensively short time (2 h). The prepared Li7PS6 solid electrolyte shows a high phase purity, an impressive ionic conductivity (0.11 mS cm-1), and a reasonable electrochemical stability with a metallic lithium anode. Our results highlight the use of an economic and nontoxic solvent to quickly synthesize a Li7PS6 solid electrolyte, which would promote the development of solid-state batteries for next-generation energy storage systems.