One of the main challenges of all-solid-state Li-ion batteries is the restricted power density due to the poor Li-ion transport between the electrodes via the electrolyte. However, to establish what diffusional process is the bottleneck for Li-ion transport requires the ability to distinguish the various processes. The present work investigates the Li-ion diffusion in argyrodite Li6PS5Cl, a promising electrolyte based on its high Li-ion conductivity, using a combination of 7Li NMR experiments and DFT based molecular dynamics simulations. This allows us to distinguish the local Li-ion mobility from the long-range Li-ion motional process, quantifying both and giving a coherent and consistent picture of the bulk diffusion in Li6PS5Cl. NMR exchange experiments are used to unambiguously characterize Li-ion transport over the solid electrolyte-electrode interface for the electrolyte-electrode combination Li6PS5Cl-Li2S, giving unprecedented and direct quantitative insight into the impact of the interface on Li-ion charge transport in all-solid-state batteries. The limited Li-ion transport over the Li6PS5Cl-Li2S interface, orders of magnitude smaller compared with that in the bulk Li6PS5Cl, appears to be the bottleneck for the performance of the Li6PS5Cl-Li2S battery, quantifying one of the major challenges toward improved performance of all-solid-state batteries.@en

High grain-boundary resistance, Li-dendrite formation, and electrode/Li interfacial resistance are three major issues facing garnet-based solid electrolytes. Herein, interfacial architecture engineering by incorporating 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl) imide (BMP-TFSI) ionic liquid into a garnet oxide is proposed. The “soft” continuous BMP-TFSI coating with no added Li salt generates a conducting network facilitating Li+ transport and thus changes the ion conduction mode from point contacts to face contacts. The compacted microstructure suppresses Li-dendrite growth and shows good interfacial compatibility and interfacial wettability toward Li metal. Along with a broad electrochemical window larger than 5.5 V and an Li+ transference number that practically reaches unity, LiNi0.8Co0.1Mn0.1O2/Li and LiFePO4/Li solid-state batteries with the hybrid solid electrolyte exhibit superior cycling stability and low polarization, comparable to those with commercial liquid electrolytes, and excellent rate capability that is better than those of Li-salt-based ionic-liquid electrolytes.@en

Garnet-type Li7La3Zr2O12 solid electrolytes were commonly prepared by two steps solid-state reaction method, which undergoes high temperature over 1000 °C and thus inevitable for lithium volatilization and formation of secondary phases. Here, we propose a new intergrain architecture engineering of a solution method, to avoid high temperature sintering for preparing lithium halide (LiX) coated garnet-type solid electrolytes, which contain Al and Ta co-doped Li7La3Zr2O12 (Li6.75La3Zr1.75Ta0.25O12, LLZTO) synthesized at 900 °C with cubic structure. Owing to the increased relative density, the improved formability, and the altered ion transport mode from point to face conduction by LiX coating on LLZTO grains, LiX-coated LLZTO samples demonstrate a good Li dendrite suppression ability and a high ionic conductivity that is three orders of magnitude higher than pristine LLZTO. In another way, this result demonstrates the critical role of the grain boundaries on the ion transport for oxide superionic conductors. The present coating method provides a new strategy to prepare brittle solid electrolytes avoiding high temperature sintering.@en

Li6PS5X (X = Cl, Br, I) argyrodites possess high ionic conductivity but with rather scattered values due to various processing conditions. In this work, Li6PS5X solid electrolytes were prepared by solid-state sintering or mechanical alloying and optimized with or without excess Li2S. Solid-state sintering prefers excess Li2S, whereas mechanical alloying prefers stoichiometric Li2S to synthesize high-purity samples with high ionic conductivity. Solid-state sintering is also more suitable than mechanical milling for high ionic conductivity. Li6PS5Cl with the highest ionic conductivity among Li6PS5X was comprehensively characterized for electrochemical performance and air stability. MoS2/Li6PS5Cl all-solid-state batteries assembled with Li6PS5Cl-coated MoS2 as cathode and with Li6PS5Cl as solid electrolyte demonstrate high capacity and good cycling stability.@en

Exploration of advanced anode materials is a highly relevant research topic for next generation lithium-ion batteries. Here, we report severe lattice distorted MoS2 nanosheets with a flower-like morphology prepared with PEG400 as additive, which acts not only as surfactant but importantly, also as reactant. Notably, in the absence of a carbon-related incorporation/decoration, it demonstrates superior electrochemical performance with a high reversible capacity, a good cycling stability, and an excellent rate capability, originated from the advantages of synthesized MoS2 including enlarged interlayer spacing, 1T-like metallic behavior, and coupling of Mo–O–C (and Mo–O) hetero-bonds. PEG-assisted synthesis is believed applicable to other anode materials with a layered structure for lithium-ion batteries.@en

Solid-state batteries potentially offer increased lithium-ion battery energy density and safety as required for large-scale production of electrical vehicles. One of the key challenges toward high-performance solid-state batteries is the large impedance posed by the electrode-electrolyte interface. However, direct assessment of the lithium-ion transport across realistic electrode-electrolyte interfaces is tedious. Here we report two-dimensional lithium-ion exchange NMR accessing the spontaneous lithium-ion transport, providing insight on the influence of electrode preparation and battery cycling on the lithium-ion transport over the interface between an argyrodite solid-electrolyte and a sulfide electrode. Interfacial conductivity is shown to depend strongly on the preparation method and demonstrated to drop dramatically after a few electrochemical (dis)charge cycles due to both losses in interfacial contact and increased diffusional barriers. The reported exchange NMR facilitates non-invasive and selective measurement of lithium-ion interfacial transport, providing insight that can guide the electrolyte-electrode interface design for future all-solid-state batteries.@en

The high Li-ion conductivity of the argyrodite Li6PS5Cl makes it a promising solid electrolyte candidate for all-solid-state Li-ion batteries. For future application, it is essential to identify facile synthesis procedures and to relate the synthesis conditions to the solid electrolyte material performance. Here, a simple optimized synthesis route is investigated that avoids intensive ball milling by direct annealing of the mixed precursors at 550 °C for 10 h, resulting in argyrodite Li6PS5Cl with a high Li-ion conductivity of up to 4.96 × 10-3 S cm-1 at 26.2 °C. Both the temperature-dependent alternating current impedance conductivities and solid-state NMR spin-lattice relaxation rates demonstrate that the Li6PS5Cl prepared under these conditions results in a higher conductivity and Li-ion mobility compared to materials prepared by the traditional mechanical milling route. The origin of the improved conductivity appears to be a combination of the optimal local Cl structure and its homogeneous distribution in the material. All-solid-state cells consisting of an 80Li2S-20LiI cathode, the optimized Li6PS5Cl electrolyte, and an In anode showed a relatively good electrochemical performance with an initial discharge capacity of 662.6 mAh g-1 when a current density of 0.13 mA cm-2 was used, corresponding to a C-rate of approximately C/20. On direct comparison with a solid-state battery using a solid electrolyte prepared by the mechanical milling route, the battery made with the new material exhibits a higher initial discharge capacity and Coulombic efficiency at a higher current density with better cycling stability. Nevertheless, the cycling stability is limited by the electrolyte stability, which is a major concern for these types of solid-state batteries.@en

Sulfide solid electrolytes possess high ionic conductivity and moderate dendrite suppression capability, but rather poor compatibility against oxide cathodes and metallic Li. Here, we report O-doped Li6PS5Br as solid electrolyte synthesized by a facile solid-state sintering. Different from other O-incorporated sulfides, the O atoms in Li6PS5-xOxBr prefer to substitute the S atoms at free S2− sites rather than those at the PS4 tetrahedra. Remarkably, without deteriorating the ionic conductivity, this inorganic solid electrolyte with O doping exhibits comprehensively enhanced properties including excellent dendrite suppression capability, superior electrochemical and chemical stability against Li metal as well as high voltage oxide cathodes, and good air stability. Li(Ni0.8Co0.1Mn0.1)O2 and LiCoO2-based all-solid-state batteries with Li6PS4.7O0.3Br electrolyte deliver high specific capacity, superior rate capability, and outstanding cycling stability accompanied with low interfacial resistivity. This type of inorganic solid electrolytes is promising for all-solid-state batteries with high energy density.@en

The high lithium conductivity of argyrodite Li6PS5Cl makes it an attractive candidate as solid electrolyte in all solid-state Li batteries. Aiming at an optimal preparation strategy the structure and conductivity upon different mechanical milling times is investigated. Li6PS5Cl material with high ionic conductivity of 1.1·10−3 S/cm was obtained by milling for 8 hours at 550 rpm followed by a heat-treatment at 550 °C. All solid-state Li-S batteries were assembled, combining the Li6PS5Cl solid electrolyte, with a carbon-sulfur mixture as positive electrode and Li, Li-Al and Li-In as negative electrode. An optimum charge/discharge voltage window between 0.4 and 3.0 V vs. Li-In was obtained by CV experiments and galvanostatic cycling displays a very large capacity around 1400 mAh/g during the first cycles, decreasing below 400 mAh/g after 20 cycles. Impedance spectroscopy suggests that the origin of the capacity fading is related to an increasing electrode-electrolyte interface resistance.@en

Exploration of advanced solid electrolytes with good interfacial stability toward electrodes is a highly relevant research topic for all-solid-state batteries. Here, we report PCL/SN blends integrating with PAN-skeleton as solid polymer electrolyte prepared by a facile method. This polymer electrolyte with hierarchical architectures exhibits high ionic conductivity, large electrochemical windows, high degree flexibility, good flame-retardance ability, and thermal stability (workable at 80 °C). Additionally, it demonstrates superior compatibility and electrochemical stability toward metallic Li as well as LiFePO4 cathode. The electrolyte/electrode interfaces are very stable even subjected to 4.5 V at charging state for long time. The LiFePO4/Li all-solid-state cells based on this electrolyte deliver high capacity, outstanding cycling stability, and superior rate capability better than those based on liquid electrolyte. This solid polymer electrolyte is eligible for next generation high energy density all-solid-state batteries.@en

The increased safety associated with all-solid-state batteries using inorganic ceramic electrolytes make it a promising technology, with potential to replace current commercial battery systems. The key challenges to realize this technology are the development of new solid electrolytes with high ionic conductivity and optimization of the ionic transport pathways across the multiple phases of the battery. In this study an optimal composition of the argyrodite i.e. Li6PS5Cl0.5Br0.5 is synthesized via the mechanical milling method. This material possesses a higher bulk ionic conductivity and reduced activation energy than the single halogen doped argyrodites i.e. Li6PS5X (X = Cl and Br), assessed by temperature-dependent impedance spectroscopy and Nuclear Magnetic Resonance (NMR) relaxometry. A combined X-ray and neutron diffraction analysis reveals an influence of the composition and distribution of halogen atoms on the Li-ion conductivity. All-solid-state batteries fabricated using Li2S as cathode show a high reversible capacity of 820 mAh g−1 for up to 30 cycles. In addition, the Li-ion diffusion across the interface between the Li2S cathode and Li6PS5Cl0.5Br0.5 electrolyte is probed by exchange NMR spectroscopy. It reveals that Li-ion diffusion across this interface was the main factor limiting the performance of Li6PS5Cl0.5Br0.5 in the battery, despite its high bulk ionic conductivity.@en

A comprehensive research coupling experiment and computation has been performed to understand the phase transition of Na3SbS4 and to synthesize cubic Na3SbS4 (c-Na3SbS4), a high temperature phase of Na3SbS4 that is difficult to be preserved when cooled down to ambient temperature. The formation of c-Na3SbS4 is verified by Rietveld refinement, nuclear magnetic resonance spectroscopy as well as electrochemical impedance spectroscopy. Unlike tetragonal Na3SbS4 (t-Na3SbS4) appearing phase transition at high temperature, c-Na3SbS4 is stable not just at room temperature but also sustaining thermal cycling up to at least 200 °C. Both experiment and theoretical calculation reveal that the ionic conductivity of c-Na3SbS4 is higher than that of t-Na3SbS4, though the values are in the same order of magnitude. Both structures allow fast ion transport. All-solid-state cells with c-Na3SbS4 solid electrolyte demonstrate superior Coulombic efficiency, high specific capacity, and relatively good cycling stability. Na3SbS4 solid electrolyte is promising for all-solid-state sodium-ion batteries.@en

The high Li-ion conductivity of the Li7P3S11 sulfide-based solid electrolyte makes it a promising candidate for all-solid-state lithium batteries. The Li-ion transport over electrode-electrolyte and electrolyte-electrolyte interfaces, vital for the performance of solid-state batteries, is investigated by impedance spectroscopy and solid-state NMR experiments. An all-solid-state Li-ion battery is assembled with the Li7P3S11 electrolyte, nano-Li2S cathode and Li-In foil anode, showing a relatively large initial discharge capacity of 1139.5 mAh/g at a current density of 0.064 mA/cm2 retaining 850.0 mAh/g after 30 cycles. Electrochemical impedance spectroscopy suggests that the decrease in capacity over cycling is due to the increased interfacial resistance between the electrode and the electrolyte. 1D exchange 7Li NMR quantifies the interfacial Li-ion transport between the uncycled electrode and the electrolyte, resulting in a diffusion coefficient of 1.70(3)⋅10−14 cm2/s at 333 K and an energy barrier of 0.132 eV for the Li-ion transport between Li2S cathode and Li7P3S11 electrolyte. This indicates that the barrier for Li-ion transport over the electrode-electrolyte interface is small. However, the small diffusion coefficient for Li-ion diffusion between the Li2S and the Li7P3S11 suggests that these contact interfaces between electrode and electrolyte are relatively scarce, challenging the performance of these solid-state batteries.@en

The ultrafast ionic conductivity of Li 6 PS 5 Br, which is higher than 1 mS cm -1 at room temperature, makes it an attractive candidate electrolyte for the all-solid-state Li-S battery. A simple synthesis route with an easy scale up process is critical for practical applications. In this work, the highest room temperature ionic conductivity (2.58 × 10 -3 S cm -1 ) of Li 6 PS 5 Br is obtained by an optimal annealing temperature in a simple solid-state reaction method. Neutron diffraction and XRD show that the origin of the highest ionic conductivity is due to the higher purity, smaller mean lithium ion jumps and the optimal Br ordering over 4a and 4c sites. All-solid-state Li-S batteries using a S-C composite cathode in combination with the optimized Li 6 PS 5 Br electrolyte and Li-In anode show high (dis)charge capacities. Different cycling modes (charge-discharge and discharge-charge) reveal that the capacity of the S-C-Li 6 PS 5 Br/Li 6 PS 5 Br/Li-In battery arises from both the active S-C composite and the Li 6 PS 5 Br in the cathode mixture. The contribution of the latter is verified from all-solid-state batteries using Li 6 PS 5 Br and its analogues as active materials. Ex situ XRD and electrochemical performance results show that the contribution of capacity from Li 6 PS 5 Br in the cathode mixture may be associated with the decomposition product Li 2 S, while the Li 6 PS 5 Br in the bulk solid electrolyte layer is stable during cycling. @en

The presented thesis aims at understanding the relationship between the synthesis procedure of argyrodite Li6PS5X (X=Br, Cl) solid electrolytes and the resulting structure, morphology, and solid-state battery performance. Specifically, argyrodite solid electrolytes in combination with Li2S positive electrodes were investigated using X-ray and neutron diffraction, impedance spectroscopy and solid state NMR.@en

Based on its high Li-ion conductivity, argyrodite Li6PS5Br is a promising solid electrolyte for all-solid-state batteries. However, more understanding is required on the relation between the solid electrolyte conductivity and the solid-state battery performance with the argyrodite structure, crystallinity and particle size that depend on the synthesis conditions. In the present study, this relationship is investigated using neutron and X-ray diffraction to determine the detailed structure and impedance as well as 7Li solid state NMR spectroscopy to study the Li-ion kinetics. It is found that depending on the synthesis conditions the distribution of the Br dopant over the crystallographic sites in Li6PS5Br is inhomogeneous, and that this may be responsible for a larger mobile Li-ion fraction at the interface regions in the annealed argyrodite materials. Comparing the bulk and interface properties of the differently prepared Li6PS5Br materials, it is proposed that optimal solid-state battery performance requires a different particle size for the solid electrolyte only region and the solid electrolyte in the cathode mixture. In the electrolyte region, the grain boundary resistance is minimized by annealing the argyrodite Li6PS5Br resulting in relatively large crystallites. In the cathode mixture however, additional particle size reduction of the Li6PS5Br is required to provide abundant Li6PS5Br-Li2S interfaces that reduce the resistance of this rate limiting step in Li-ion transport. Thereby the results give insight in how to improve solidstate battery performance by controlling the solid electrolyte structure. @en

The development of high-performance all-solid-state batteries relies on charge transport in solid electrolytes, where transport across grain boundaries often limits their bulk conductivity. The argyrodite Li 6 PS 5 X (X = Cl, Br) solid electrolyte has a high conductivity; however, macroscopic diffusion in this material involves complex jump processes, which leads to an underestimation of the activation energy. Using a comprehensive frequency- and temperature-dependent analysis of the spin-lattice relaxation rates, a complete estimation of Li self-diffusion is demonstrated. Another experimental challenge is quantifying the impact of grain boundaries on the total bulk conductivity. Li 6 PS 5 Cl and Li 6 PS 5 Br have identical crystalline structures, but with 6 Li MAS NMR, their resonance peaks have different chemical shifts. Exploiting this with two-dimensional 6 Li- 6 Li exchange NMR on a mixture of Li 6 PS 5 Br and Li 6 PS 5 Cl, we observe Li exchange between particles of these two materials across grain boundaries, allowing direct and unambiguous quantification of this often limiting process in solid-state electrolytes. @en

All-solid-state Li-ion batteries promise safer electrochemical energy storage with larger volumetric and gravimetric energy densities. A major concern is the limited electrochemical stability of solid electrolytes and related detrimental electrochemical reactions, especially because of our restricted understanding. Here we demonstrate for the argyrodite-, garnet- and NASICON-type solid electrolytes that the favourable decomposition pathway is indirect rather than direct, via (de)lithiated states of the solid electrolyte, into the thermodynamically stable decomposition products. The consequence is that the electrochemical stability window of the solid electrolyte is notably larger than predicted for direct decomposition, rationalizing the observed stability window. The observed argyrodite metastable (de)lithiated solid electrolyte phases contribute to the (ir)reversible cycling capacity of all-solid-state batteries, in addition to the contribution of the decomposition products, comprehensively explaining solid electrolyte redox activity. The fundamental nature of the proposed mechanism suggests this is a key aspect for solid electrolytes in general, guiding interface and material design for all-solid-state batteries.@en

Tetragonal and cubic phase Na3PS4 sodium electrolytes were successfully prepared by a relatively low rotation speed mechanical milling (400 rpm) route, aiming at homogeneous materials. The influence of the mechanical milling and annealing on the structure and ionic conductivity are studied by XRD and impedance spectroscopy, giving insight into the optimal mechanical synthesis conditions. Fourier analysis of the XRD data, compared to DFT based MD simulations reflects the diffusion pathway, where the simulations indicate a vacancy induced high bulk Na-ion mobility in both cubic and tetragonal phases. 23Na solid-state NMR relaxation experiments were applied to investigate the Na-ion bulk diffusion in both the cubic and tetragonal phases, showing reasonable agreement with the MD simulation results. The MD simulations indicate that the bulk mobility of both phases may be further improved by introducing more Na vacancies. The macroscopic ionic conductivity probed by impedance spectroscopy is much smaller than that predicted by the bulk Na-ion mobility, in particular for the tetragonal phase, suggesting a large impact of amorphous phase fractions and/or grain boundaries on the macroscopic Na-ion conductivity. In particular in the less crystalline cubic phase, the amorphous fraction present as a consequence of the lower annealing temperature suggests that this phase may lead to a decrease in grain boundary resistance, which may be further exploited to improve the performance of all solid state Na-ion batteries with the Na3PS4 solid electrolyte.@en

It is a highly relevant topic concerning how to improve the electrochemical performance of anode materials for the next generation lithium-ion batteries (LIBs). Herein, for the first time, we report a facile and controllable approach to modify MoS 2 nanosheets, a typical 2D material, as an anode material for advanced LIBs via oxygen plasma engineering. An oxygen plasma treatment not only generates vacancies/defects but also incorporates heteroatom doping to form Mo–O–C bonds. This unique hybrid specialty enables the oxygen-plasma-treated MoS 2 to achieve superior electrochemical performance with high reversible capacities, a long-term cycle life, and good rate capabilities. The plasma-assisted modification is believed to be applicable for other 2D materials as an efficient anode for energy storages. @en