Superionic Halogen-Rich Li-Argyrodites Using In Situ Nanocrystal Nucleation and Rapid Crystal Growth

A Functional Air-Stable Li9.8GeP1.7Sb0.3S11.8I0.2 Superionic Conductor for High-Performance All-Solid-State Lithium Batteries

Solid-state electrolytes (SSEs) based on sulfides have become a subject of great interest due to their superior Li-ion conductivity, low grain boundary resistance, and adequate mechanical strength. However, they grapple with chemical instability toward moisture hypersensitivity, which decreases their ionic conductivity, leading to more processing requirements. Herein, a Li9.8GeP1.7Sb0.3S11.8I0.2 (LGPSSI) superionic conductor is designed with a Li+ conductivity of 6.6 mS cm-1 and superior air stability based on hard and soft acids and bases (HSAB) theory. The introduction of optimal antimony (Sb) and iodine (I) into the Li10GeP2S12 (LGPS) structure facilitates fast Li-ion migration with low activation energy (Ea) of 20.33 kJ mol-1. The higher air stability of LGPSSI is credited to the strategic substitution of soft acid Sb into (Ge/P)S4 tetrahedral sites, examined by Raman and X-ray photoelectron spectroscopy techniques. Relatively lower acidity of Sb compared to phosphorus (P) realizes a stronger Sb-S bond, minimizing the evolution of toxic H2S (0.1728 cm3 g-1), which is ∼3 times lower than pristine LGPS when LGPSSI is exposed to moist air for 120 min. The NCA//Li-In full cell with a LGPSSI superionic conductor delivered the first discharge capacity of 209.1 mAh g-1 with 86.94% Coulombic efficiency at 0.1 mA cm-2. Furthermore, operating at a current density of 0.3 mA cm-2, LiNbO3@NCA/LGPSSI/Li-In cell demonstrated an exceptional reversible capacity of 117.70 mAh g-1, retaining 92.64% of its original capacity over 100 cycles.

Toward High-Quality Sulfide Solid Electrolytes: A Liquid-Phase Approach Featured with an Interparticle Coupled Unification Effect

Sulfide solid electrolytes (SSEs) are highly wanted for solid-state batteries (SSBs). While their liquid-phase synthesis is advantageous over their solid-phase strategy in scalable production, it confronts other challenges, such as low-purity products, user-unfriendly solvents, energy-inefficient solvent removal, and unsatisfactory performance. This article demonstrates that a suspension-based solvothermal method using single oxygen-free solvents can solve those problems. Experimental observations and theoretical calculations together show that the basic function of suspension-treatment is "interparticle-coupled unification", that is, even individually insoluble solid precursors can mutually adsorb and amalgamate to generate uniform composites in nonpolar solvents. This anti-intuitive concept is established when investigating the origins of impurities in SSEs electrolytes made by the conventional tetrahydrofuran-ethanol method and then searching for new solvents. Its generality is supported by four eligible alkane solvents and four types of SSEs. The electrochemical assessments on the former three SSEs show that they are competitive with their counterparts in the literature. Moreover, the synthesized SSEs presents excellent battery performance, showing great potential for practical applications.

Toward Achieving a High Ionic Conducting Halide Solid Electrolyte through Low-Cost Metal (Zr and Fe) and F Substitution and Their Admirable Performance in All-Solid-State Batteries

Recently, the halide solid electrolyte (SE) system has been widely used in lithium solid-state batteries due to their specific properties, such as the high electrochemical stability window that prevents any side reaction with the electrode/electrolyte interface. Conspicuously, the halide SE possesses very low ionic conductivity values in the range (0.2-0.5) mS cm-1. In this work, we enhance the ionic conductivity of Li3YCl6 SE by the substitution of low-cost Fe and Zr elements on the Y-site and F on the Cl site, in which the electrolyte is prepared through high-energy ball milling without a heat treatment process. The structural analysis reveals that the prepared halide SEs showed the pure phase of the Li3YCl6 tetragonal crystal structure and were free from impurity phases. In the prepared composition, the Li2.4Y0.4Zr0.6Cl6 and Li2.4Y0.4Zr0.6Cl5.85F0.15 electrolyte exhibited a higher ionic conductivity of 2.05 and 1.45 mS cm-1, respectively, than Li3YCl6 (0.26 mS cm-1). Interestingly, the Li2.4Y0.4Zr0.6Cl5.85F0.15 electrolyte possesses a better electrochemical stability window of 1.29-3.9 V than Li2.4Y0.4Zr0.6Cl6 (2.1-3.79 V). Moreover, the electrochemical results revealed that the assembled solid-state battery using Li2.4Y0.4Zr0.6Cl6 and Li2.4Y0.4Zr0.6Cl5.85F0.15 electrolyte demonstrated the higher initial Coulombic efficiency of 84.7 and 87%, respectively, than Li3YCl6 of 82.6%. We consider Li2.4Y0.4Zr0.6Cl5.85F0.15 to be an important electrolyte candidate in all-solid-state batteries.

Argyrodite-Li6PS5Cl/Polymer-based Highly Conductive Composite Electrolyte for All-Solid-State Batteries

Solid-state batteries (SSBs) that incorporate the argyrodite-Li6PS5Cl (LPSCl) electrolyte hold potential as substitutes for conventional lithium-ion batteries (LIBs). However, the mismatched interface between the LPSCl electrolyte and electrodes leads to increased interfacial resistance and the rapid growth of lithium (Li) dendrites. These factors significantly impede the feasibility of their widespread industrial application. In this study, we developed a composite electrolyte of the LPSCl/polymer to enhance the contact between the electrolyte and electrodes and suppress dendrite formation at the grain boundary of the LPSCl ceramic. The monomer, triethylene glycol dimethacrylate (TEGDMA), is utilized for in situ polymerization through thermal curing to create the argyrodite LPSCl/polymer composite electrolyte. Additionally, the ball-milling technique was employed to modify the morphology and particle size of the LPSCl ceramic. The ball-milled LPSCl/polymer composite electrolyte demonstrates slightly higher ionic conductivity (ca. 2.21 × 10-4 S/cm) compared to the as-received LPSCl/polymer composite electrolyte (ca. 1.65 × 10-4 S/cm) at 25 °C. Furthermore, both composite electrolytes exhibit excellent compatibility with Li-metal and display cycling stability for up to 1000 h (375 cycles), whereas the as-received LPSCl and ball-milled LPSCl electrolytes maintain stability for up to 600 h (225 cycles) at a current density of 0.4 mA/cm2. The SSB with the ball-milled LPSCl/polymer composite electrolyte delivers high specific discharge capacity (138 mA h/g), Coulombic efficiency (99.97%), and better capacity retention at 0.1C, utilizing the battery configuration of coated NMC811//electrolyte//Li-Indium (In) at 25 °C.

A Review on Engineering Design for Enhancing Interfacial Contact in Solid-State Lithium-Sulfur Batteries

The utilization of solid-state electrolytes (SSEs) presents a promising solution to the issues of safety concern and shuttle effect in Li-S batteries, which has garnered significant interest recently. However, the high interfacial impedances existing between the SSEs and the electrodes (both lithium anodes and sulfur cathodes) hinder the charge transfer and intensify the uneven deposition of lithium, which ultimately result in insufficient capacity utilization and poor cycling stability. Hence, the reduction of interfacial resistance between SSEs and electrodes is of paramount importance in the pursuit of efficacious solid-state batteries. In this review, we focus on the experimental strategies employed to enhance the interfacial contact between SSEs and electrodes, and summarize recent progresses of their applications in solid-state Li-S batteries. Moreover, the challenges and perspectives of rational interfacial design in practical solid-state Li-S batteries are outlined as well. We expect that this review will provide new insights into the further technique development and practical applications of solid-state lithium batteries.

Borohydride and halide dual-substituted lithium argyrodites

Solid electrolyte is a crucial component of all-solid-state batteries, with sulphide solid electrolytes such as lithium argyrodite being closest to commercialization due to their high ionic conductivity and formability. In this study, borohydride/halide dual-substituted argyrodite-type electrolytes, Li7-α-βPS6-α-β(BH4)αXβ (X = Cl, Br, I; α + β ≤ 1.8), have been synthesized using a two-step ball-milling method without post-annealing. Among the various compositions, Li5.35PS4.35(BH4)1.15Cl0.5 exhibits the highest ionic conductivity of 16.4 mS cm-1 at 25 °C when cold-pressed, which further improves to 26.1 mS cm-1 after low temperature sintering. The enhanced conductivity can be attributed to the increased number of Li vacancies resulting from increased BH4 and halide occupancy and site disorder. Li symmetric cells with Li5.35PS4.35(BH4)1.15Cl0.5 demonstrate stable Li plating and stripping cycling for over 2,000 hours at 1 mA cm-2, along with a high critical current density of 2.1 mA cm-2. An all-solid-state battery prepared using Li5.35PS4.35(BH4)1.15Cl0.5 as the electrolyte and pure Li as the anode exhibits an initial coulombic efficiency of 86.4%. Although these electrolytes have limited thermal stability, it shows a wide compositional range while maintaining high ionic conductivity.

High-Entropy Lithium Argyrodite Solid Electrolytes Enabling Stable All-Solid-State Batteries

Superionic solid electrolytes (SEs) are essential for bulk-type solid-state battery (SSB) applications. Multicomponent SEs are recently attracting attention for their favorable charge-transport properties, however a thorough understanding of how configurational entropy (ΔSconf ) affects ionic conductivity is lacking. Here, we successfully synthesized a series of halogen-rich lithium argyrodites with the general formula Li5.5 PS4.5 Clx Br1.5-x (0≤x≤1.5). Using neutron powder diffraction and 31 P magic-angle spinning nuclear magnetic resonance spectroscopy, the S2- /Cl- /Br- occupancy on the anion sublattice was quantitatively analyzed. We show that disorder positively affects Li-ion dynamics, leading to a room-temperature ionic conductivity of 22.7 mS cm-1 (9.6 mS cm-1 in cold-pressed state) for Li5.5 PS4.5 Cl0.8 Br0.7 (ΔSconf =1.98R). To the best of our knowledge, this is the first experimental evidence that configurational entropy of the anion sublattice correlates with ion mobility. Our results indicate the possibility of improving ionic conductivity in ceramic ion conductors by tailoring the degree of compositional complexity. Moreover, the Li5.5 PS4.5 Cl0.8 Br0.7 SE allowed for stable cycling of single-crystal LiNi0.9 Co0.06 Mn0.04 O2 (s-NCM90) composite cathodes in SSB cells, emphasizing that dual-substituted lithium argyrodites hold great promise in enabling high-performance electrochemical energy storage.

Halogen chemistry of solid electrolytes in all-solid-state batteries

All-solid-state batteries (ASSBs) using solid-state electrolytes, replacing flammable liquid electrolytes, are considered one of the most promising next-generation electrochemical energy storage devices because of their improved, inherent safety and energy density. A family of solid electrolytes incorporating halogens has attracted attention because of their potentially high ionic conductivity, good deformability and wide electrochemical windows. Although progress has been made for halogen-containing solid electrolytes (HSEs) in ASSBs, challenges in the preparations, characterizations and low-cost industrial scalability remain. In this Review, we focus on the development of halide battery chemistry, the preparation, modification and properties of HSEs, and issues with HSEs in ASSBs. The chemical action of halogen and ion transport mechanisms are discussed. Moreover, the main challenges and future development directions of halide-based ASSBs are discussed to pave the way for practical applications of HSEs for next-generation rechargeable batteries.

Optimizing milling and sintering parameters for mild synthesis of highly conductive Li5.5PS4.5Cl1.5 solid electrolyte

The Li5.5PS4.5Cl1.5 electrolyte gains significant attention due to its ultrahigh ionic conductivity and cost-effectiveness in halogen-rich lithium argyrodite solid electrolytes. The conventional synthetic method for obtaining the electrolyte involves mechanical milling followed by post-annealing. However, these synthesis methods typically involve high milling speeds, elevated temperatures, and prolonged durations, resulting in both high energy consumption and potential damage to the electrolyte. In this study, we successfully obtained Li5.5PS4.5Cl1.5 with a high conductivity of 7.92 mS cm-1 using a milling speed of 400 rpm and annealing at 400 °C for 5 hours. When incorporated into a Li4Ti5O12-based all-solid-state battery, this electrolyte demonstrates stable cycling performance across varying temperatures.

Realizing long-cycling all-solid-state Li-In||TiS2 batteries using Li6+xMxAs1-xS5I (M=Si, Sn) sulfide solid electrolytes

Inorganic sulfide solid-state electrolytes, especially Li₆PS₅X (X = Cl, Br, I), are considered viable materials for developing all-solid-state batteries because of their high ionic conductivity and low cost. However, this class of solid-state electrolytes suffers from structural and chemical instability in humid air environments and a lack of compatibility with layered oxide positive electrode active materials. To circumvent these issues, here, we propose Li_6+xM_xAs_1-xS₅I (M=Si, Sn) as sulfide solid electrolytes. When the Li_6+xSi_xAs_1-xS₅I (x = 0.8) is tested in combination with a Li-In negative electrode and Ti₂S-based positive electrode at 30 °C and 30 MPa, the Li-ion lab-scale Swagelok cells demonstrate long cycle life of almost 62500 cycles at 2.44 mA cm^-2, decent power performance (up to 24.45 mA cm^-2) and areal capacity of 9.26 mAh cm^-2 at 0.53 mA cm^-2.

Lithium Superionic Conduction in BH4 -Substituted Thiophosphate Solid Electrolytes

Compared with conventional liquid electrolytes, solid electrolytes can better improve the safety properties and achieve high-energy-density Li-ion batteries. Sulfide-based solid electrolytes have attracted significant attention owing to their high ionic conductivities, which are comparable to those of their liquid counterparts. Among them, Li thiophosphates, including Li-argyrodites, are widely studied. In this study, Li thiophosphate solid electrolytes containing BH₄ ^- anions are prepared via a simple and fast milling method even without heat treatment. The synthesized materials exhibit a high ionic conductivity of up to 11 mS cm^-1 at 25 °C, which is much higher than reported values. To elucidate the mechanism behind, the thiophosphate local structure, whose effect on the ionic conductivity remains unclear to date, is investigated. Raman and solid-state NMR spectroscopies are performed to identify the thiophosphate local structure in the sulfide samples. Based on the analysis results, the ratios of the different thiophosphate units in the prepared electrolyte samples are determined. It is found that the thiophosphate local structure can be varied by changing the amount of LiBH₄ and the milling conditions, which significantly impact the ionic conductivity. The all-solid-state cell with the prepared solid electrolyte exhibits superior cycle and rate performances.

Grain Boundary Electronic Insulation for High-Performance All-Solid-State Lithium Batteries

Sulfide electrolytes with high ionic conductivities are one of the most highly sought for all-solid-state lithium batteries (ASSLBs). However, the non-negligible electronic conductivities of sulfide electrolytes (≈10^-8  S cm^-1 ) lead to electron smooth transport through the sulfide electrolyte pellets, resulting in Li dendrite directly depositing at the grain boundaries (GBs) and serious self-discharge. Here, a grain-boundary electronic insulation (GBEI) strategy is proposed to block electron transport across the GBs, enabling Li-Li symmetric cells with 30 times longer cycling life and Li-LiCoO₂ full cells with three times lower self-discharging rate than pristine sulfide electrolytes. The Li-LiCoO₂ ASSLBs deliver high capacity retention of 80 % at 650 cycles and stable cycling performance for over 2600 cycles at 0.5 mA cm^-2 . The innovation of the GBEI strategy provides a new direction to pursue high-performance ASSLBs via tailoring the electronic conductivity.

A Low-Cost Liquid-Phase Method of Synthesizing High-Performance Li6PS5Cl Solid-Electrolyte

Li₆PS₅Cl is an extensively studied sulfide-solid-electrolyte for developing all-solid-state lithium batteries. However, its practical application is hindered by the high cost of its raw material lithium sulfide (Li₂S), the difficulty in its massive production, and its substandard performance. Herein we report an economically viable and scalable method, denoted as "de novo liquid phase method", which enables in synthesizing high-performance Li₆PS₅Cl without using commercial Li₂S but instead in situ making Li₂S from cheap materials of lithium chloride (LiCl) and sodium sulfide. LiCl, a raw material needed for making both Li₂S and Li₆PS₅Cl, can be added at a full-scale in the beginning and unrequired to separate when making the intermediate Li₃PS₄. Such a consecutive feature makes this method time-efficient; and the excess amount of LiCl in the step of making Li₂S also facilitates removing the byproduct of sodium chloride via the common ion effect. The materials cost of this method for Li₆PS₅Cl is ∼ $55/kg, comparable with the practical need of $50/kg. Moreover, the obtained Li₆PS₅Cl shows high ionic conductivity and outstanding cyclability in full battery tests, that is, ∼2 mS/cm and >99.8% retention for 400+ cycles at 1 C, respectively. Thus, this innovative method is expected to pave the way to develop practical sulfide-solid-electrolytes for all-solid-state lithium batteries.

Ionic Conductivity of Nanocrystalline and Amorphous Li10GeP2S12: The Detrimental Impact of Local Disorder on Ion Transport

Solids with extraordinarily high Li⁺ dynamics are key for high performance all-solid-state batteries. The thiophosphate Li₁₀GeP₂S₁₂ (LGPS) belongs to the best Li-ion conductors with an ionic conductivity exceeding 10 mS cm^–1 at ambient temperature. Recent molecular dynamics simulations performed by Dawson and Islam predict that the ionic conductivity of LGPS can be further enhanced by a factor of 3 if local disorder is introduced. As yet, no experimental evidence exists supporting this fascinating prediction. Here, we synthesized nanocrystalline LGPS by high-energy ball-milling and probed the Li⁺ ion transport parameters. Broadband conductivity spectroscopy in combination with electric modulus measurements allowed us to precisely follow the changes in Li⁺ dynamics. Surprisingly and against the behavior of other electrolytes, bulk ionic conductivity turned out to decrease with increasing milling time, finally leading to a reduction of σ_20°C by a factor of 10. ³¹P, ⁶Li NMR, and X-ray diffraction showed that ball-milling forms a structurally heterogeneous sample with nm-sized LGPS crystallites and amorphous material. At −135 °C, electrical relaxation in the amorphous regions is by 2 to 3 orders of magnitude slower. Careful separation of the amorphous and (nano)crystalline contributions to overall ion transport revealed that in both regions, Li⁺ ion dynamics is slowed down compared to untreated LGPS. Hence, introducing defects into the LGPS bulk structure via ball-milling has a negative impact on ionic transport. We postulate that such a kind of structural disorder is detrimental to fast ion transport in materials whose transport properties rely on crystallographically well-defined diffusion pathways.

A Nanoscale Design Approach for Enhancing the Li-Ion Conductivity of the Li10GeP2S12 Solid Electrolyte

The discovery of the lithium superionic conductor Li10GeP2S12 (LGPS) has led to significant research activity on solid electrolytes for high-performance solid-state batteries. Despite LGPS exhibiting a remarkably high room-temperature Li-ion conductivity, comparable to that of the liquid electrolytes used in current Li-ion batteries, nanoscale effects in this material have not been fully explored. Here, we predict that nanosizing of LGPS can be used to further enhance its Li-ion conductivity. By utilizing state-of-the-art nanoscale modeling techniques, our results reveal significant nanosizing effects with the Li-ion conductivity of LGPS increasing with decreasing particle volume. These features are due to a fundamental change from a primarily one-dimensional Li-ion conduction mechanism to a three-dimensional mechanism and major changes in the local structure. For the smallest nanometric particle size, the Li-ion conductivity at room temperature is three times higher than that of the bulk system. These findings reveal that nanosizing LGPS and related solid electrolytes could be an effective design approach to enhance their Li-ion conductivity.

Ultrafast Synthesis of I-Rich Lithium Argyrodite Glass-Ceramic Electrolyte with High Ionic Conductivity

Lithium argyrodites are one of the most promising sulfide electrolytes due to their high ionic conductivity and ductile feature. Among them, Li₆ PS₅ I (LPSI) exhibits better stability against Li metal but a rather low ionic conductivity (only ≈10^-6 S cm^-1 ) because of the absence of S^2- /I^- disorder. Herein, argyrodite Li_{6- x} PS_{5- x} I_{1+ x} glass-ceramic electrolytes with high iodine content are synthesized using ultimate-energy mechanical alloying method. S^2- /I^- disorder is successfully introduced into the system by doping LiI during this one-pot process. Determined by ⁶ Li magic angle spinning nuclear magnetic resonance and ab initio molecular dynamics simulations, the introduction of iodine promotes Li⁺ inter-cage jumps, leading to an enhanced long-range Li⁺ conducting. The Li_5.6 PS_4.6 I_1.4 glass-ceramic electrolyte (LPSI_1.4 -gc) possesses high ionic conductivity (2.04 mS cm^-1 ) and excellent stability against Li metal. The Li symmetric cell with the LPSI_1.4 -gc electrolyte demonstrates ultralong cycling stability over 3200 h at 0.2 mA cm^-2 . LiCoO₂ /Li₆ PS₅ Cl/Li all-solid-state battery applying LPSI_1.4 -gc as the anode interlayer also presents prominent cycling and rate performance. This work provides a novel type of electrolyte with high ionic conductivity and stability against Li metal.

All-Solid-State Lithium-Ion Batteries with Oxide/Sulfide Composite Electrolytes

Li_6.3La₃Zr_1.65W_0.35O₁₂ (LLZO)-Li₆PS₅Cl (LPSC) composite electrolytes and all-solid-state cells containing LLZO-LPSC were fabricated by cold pressing at room temperature. The LPSC:LLZO ratio was varied, and the microstructure, ionic conductivity, and electrochemical performance of the corresponding composite electrolytes were investigated; the ionic conductivity of the composite electrolytes was three or four orders of magnitude higher than that of LLZO. The high conductivity of the composite electrolytes was attributed to the enhanced relative density and the rule of mixture for soft LPSC particles with high lithium-ion conductivity (~10⁻⁴ S·cm⁻¹). The specific capacities of all-solid-state cells (ASSCs) consisting of a LiNi_0.8Co_0.1Mn_0.1O₂ (NCM811) cathode and the composite electrolytes of LLZO:LPSC = 7:3 and 6:4 were 163 and 167 mAh·g⁻¹, respectively, at 0.1 C and room temperature. Moreover, the charge–discharge curves of the ASSCs with the composite electrolytes revealed that a good interfacial contact was successfully formed between the NCM811 cathode and the LLZO-LPSC composite electrolyte.

Quantitative determination of lithium depletion during rapid cycling in sulfide-based all-solid-state batteries

We propose a promising electrochemical analysis tool based on the distribution of relaxation times (DRT) to quantify interfacial resistances towards a comprehensive understanding of complex solid-state interfacial phenomena in sulfide-based all-solid-state batteries (ASSBs). Using DRT-assisted impedance analysis, we identify a new resistance component in the range of 10²-10³ Hz of 3.5 and 0.9 Ω in the absence and presence of a LiNbO₃ layer, respectively, at 1C-rate. Experimental and computational studies confirm that this interfacial resistance results from lithium depletion in sulfide solid electrolytes. Furthermore, we expect our approach to provide new insights into complex interfacial phenomena in ASSBs.

Functionalized Sulfide Solid Electrolyte with Air-Stable and Chemical-Resistant Oxysulfide Nanolayer for All-Solid-State Batteries

Sulfide solid electrolytes (SEs) with high Li-ion conductivities (σ_ion) and soft mechanical properties have limited applications in wet casting processes for commercial all-solid-state batteries (ASSBs) because of their inherent atmospheric and chemical instabilities. In this study, we fabricated sulfide SEs with a novel core-shell structure via environmental mechanical alloying, while providing sufficient control of the partial pressure of oxygen. This powder possesses notable atmospheric stability and chemical resistance because it is covered with a stable oxysulfide nanolayer that prevents deterioration of the bulk region. The core-shell SEs showed a σ_ion of more than 2.50 mS cm^-1 after air exposure (for 30 min) and reaction with slurry chemicals (mixing and drying for 31 min), which was approximately 82.8% of the initial σ_ion. The ASSB cell fabricated through wet casting provided an initial discharge capacity of 125.6 mAh g^-1. The core-shell SEs thus exhibited improved powder stability and reliability in the presence of chemicals used in various wet casting processes for commercial ASSBs.

Solid-State Li-Ion Batteries Operating at Room Temperature Using New Borohydride Argyrodite Electrolytes

Using a new class of (BH₄)⁻ substituted argyrodite Li₆PS₅Z_0.83(BH₄)_0.17, (Z = Cl, I) solid electrolyte, Li-metal solid-state batteries operating at room temperature have been developed. The cells were made by combining the modified argyrodite with an In-Li anode and two types of cathode: an oxide, Li_xMO₂ (M = ⅓ Ni, ⅓ Mn, ⅓ Co; so called NMC) and a titanium disulfide, TiS₂. The performance of the cells was evaluated through galvanostatic cycling and Alternating Current AC electrochemical impedance measurements. Reversible capacities were observed for both cathodes for at least tens of cycles. However, the high-voltage oxide cathode cell shows lower reversible capacity and larger fading upon cycling than the sulfide one. The AC impedance measurements revealed an increasing interfacial resistance at the cathode side for the oxide cathode inducing the capacity fading. This resistance was attributed to the intrinsic poor conductivity of NMC and interfacial reactions between the oxide material and the argyrodite electrolyte. On the contrary, the low interfacial resistance of the TiS₂ cell during cycling evidences a better chemical compatibility between this active material and substituted argyrodites, allowing full cycling of the cathode material, 240 mAhg⁻¹, for at least 35 cycles with a coulombic efficiency above 97%.

Advances in Materials Design for All-Solid-state Batteries: From Bulk to Thin Films

All-solid-state batteries (SSBs) are one of the most fascinating next-generation energy storage systems that can provide improved energy density and safety for a wide range of applications from portable electronics to electric vehicles. The development of SSBs was accelerated by the discovery of new materials and the design of nanostructures. In particular, advances in the growth of thin-film battery materials facilitated the development of all solid-state thin-film batteries (SSTFBs)—expanding their applications to microelectronics such as flexible devices and implantable medical devices. However, critical challenges still remain, such as low ionic conductivity of solid electrolytes, interfacial instability and difficulty in controlling thin-film growth. In this review, we discuss the evolution of electrode and electrolyte materials for lithium-based batteries and their adoption in SSBs and SSTFBs. We highlight novel design strategies of bulk and thin-film materials to solve the issues in lithium-based batteries. We also focus on the important advances in thin-film electrodes, electrolytes and interfacial layers with the aim of providing insight into the future design of batteries. Furthermore, various thin-film fabrication techniques are also covered in this review.

Understanding the Origin of Enhanced Li-Ion Transport in Nanocrystalline Argyrodite-Type Li6PS5I

Argyrodite-type Li₆PS₅X (X = Cl, Br) compounds are considered to act as powerful ionic conductors in next-generation all-solid-state lithium batteries. In contrast to Li₆PS₅Br and Li₆PS₅Cl compounds showing ionic conductivities on the order of several mS cm^-1, the iodine compound Li₆PS₅I turned out to be a poor ionic conductor. This difference has been explained by anion site disorder in Li₆PS₅Br and Li₆PS₅Cl leading to facile through-going, that is, long-range ion transport. In the structurally ordered compound, Li₆PS₅I, long-range ion transport is, however, interrupted because the important intercage Li jump-diffusion pathway, enabling the ions to diffuse over long distances, is characterized by higher activation energy than that in the sibling compounds. Here, we introduced structural disorder in the iodide by soft mechanical treatment and took advantage of a high-energy planetary mill to prepare nanocrystalline Li₆PS₅I. A milling time of only 120 min turned out to be sufficient to boost ionic conductivity by 2 orders of magnitude, reaching σ_total = 0.5 × 10^-3 S cm^-1. We followed this noticeable increase in ionic conductivity by broad-band conductivity spectroscopy and ⁷Li nuclear magnetic relaxation. X-ray powder diffraction and high-resolution ⁶Li, ³¹P MAS NMR helped characterize structural changes and the extent of disorder introduced. Changes in attempt frequency, activation entropy, and charge carrier concentration seem to be responsible for this increase.