The nonexistence of a paddlewheel effect in superionic conductors

Since the 1980s, the paddlewheel effect has been suggested as a mechanism to boost lithium-ion diffusion in inorganic materials via the rotation of rotor-like anion groups. However, it remains unclear whether the paddlewheel effect, defined as large-angle anion group rotations assisting Li hopping, indeed exists; furthermore, the physical mechanism by which the anion-group dynamics affect lithium-ion diffusion has not yet been established. In this work, we differentiate various types of rotational motions of anion groups and develop quaternion-based algorithms to detect, quantify, and relate them to lithium-ion motion in ab initio molecular dynamics simulations. Our analysis demonstrates that, in fact, the paddlewheel effect, where an anion group makes a large angle rotation to assist a lithium-ion hop, does not exist and thus is not responsible for the fast lithium-ion diffusion in superionic conductors, as historically claimed. Instead, we find that materials with topologically isolated anion groups can enhance lithium-ion diffusivity via a more classic nondynamic soft-cradle mechanism, where the anion groups tilt to provide optimal coordination to a lithium ion throughout the hopping process to lower the migration barrier. This anion-group disorder is static in nature, rather than dynamic and can explain most of the experimental observations. Our work substantiates the nonexistence of the long-debated paddlewheel effect and clarifies any correlation that may exist between anion-group rotations and fast ionic diffusion in inorganic materials.

Transient Ruddlesden-Popper-Type Defects and Their Influence on Grain Growth and Properties of Lithium Lanthanum Titanate Solid Electrolyte

Lithium lanthanum titanate (LLTO) perovskite is one of the most promising electrolytes for all-solid-state batteries, but its performance is limited by the presence of grain boundaries (GBs). The fraction of GBs can be significantly reduced by the preparation of coarse-grained LLTO ceramics. In this work, we describe an alternative approach to the fabrication of ceramics with large LLTO grains based on self-seeded grain growth. In compositions with the starting stoichiometry for the Li0.20La0.60TiO3 phase and with a high excess addition of Li (Li:La:Ti = 11:15:25), microstructure development starts with the formation of the layered RP-type Li2La2Ti3O10 phase. Grains with many RP-type defects initially develop into large platelets with thicknesses of up to 10 μm and lengths over 100 μm. Microstructure development continues with the crystallization of LLTO perovskite, epitaxially on the platelets and as smaller grains with thinner in-grain RP-lamellae. Theoretical calculations confirmed that the formation of RP-type sequences is energetically favored and precedes the formation of the LLTO perovskite phase. At around 1250 °C, the RP-type sequences become thermally unstable and gradually recrystallize to LLTO via the ionic exchange between the Li-rich RP-layers and the neighboring Ti and La layers as shown by quantitative HAADF-STEM. At higher sintering temperatures, LLTO grains become free of RP-type defects and the small grains recrystallize onto the large platelike seed grains via Ostwald ripening. The final microstructure is coarse-grained LLTO with total ionic conductivity in the range of 1 × 10-4 S/cm.

Halide and Sulfide Electrolytes in Cathode Composites for Sodium All-Solid-State Batteries and their Stability

Sodium all-solid-state batteries may become a novel storage technology overcoming the safety and energy density issues of (liquid-based) sodium ion batteries at low cost and good resource availability. However, compared to liquid electrolyte cells, contact issues and capacity losses due to interface reactions leading to high cell resistance are still a problem in solid-state batteries. In particular, sulfide-based electrolytes, which show very high ionic conductivity and good malleability, exhibit degradation reactions at the interface with electrode materials and carbon additives. A new group of solid electrolytes, i.e., sodium halides, shows wider potential windows and better stability at typical cathode potentials. A detailed investigation of the interface reactions of Na3SbS4 and Na2.4Er0.4Zr0.6Cl6 as catholytes in cathodes and their cycling performance in full cells is performed. X-ray spectroscopy, time-of-flight spectrometry, and impedance spectroscopy are used to study the interface of each catholyte with a transition metal oxide cathode active material. In addition, impedance measurements were used to study the separator electrolyte Na3SbS4 with the catholyte Na2.4Er0.4Zr0.6Cl6. In conclusion, cathodes with Na2.4Er0.4Zr0.6Cl6 show a higher stability at low C-rates, resulting in lower interfacial resistance and improved cycling performance.

In-Situ Formed Electron Inhibitor Enabling Dendrite-free Garnet Electrolytes: A Case Study of Fumed Silica

Ta-doped Li7La3Zr2O12 (LLZTO) solid-state electrolytes (SEs) show great promise for solid-state batteries due to its high conductivity and safety. However, one of the challenges it faces is lithium dendrite propagation upon long-term cycling. To address this issue, we propose the incorporation of fumed silica (FS) at the grain boundaries of LLZTO to modify the properties of the garnet pellet, which effectively inhibits the dendrite growth. The introduction of FS has demonstrated several beneficial effects. Firstly, it reduces the migration barrier of lithium ions, which helps prevent dendrite formation and propagation. Additionally, FS reduces the electronic conductivity of the SEs pellet, suppressing the dendrite formation. Moreover, the formed lithium silicates from FS might also be acted as electron inhibitor, thus inhibiting the lithium dendrite growth upon cycling. By investigating the use of FS as a modifier in LLZTO-based electrolytes, our study contributes to advancing dendrite-free solid-state electrolytes and thus the development of high-performance all-solid-state batteries.

Heteroionic Interfaces in Hybrid Solid-State Batteries─Current Constriction at the Interface between Different Solid Electrolytes

The requirements for suitable electrolyte materials in solid-state batteries are diverse and vary greatly depending on their role as separator or as part of the composite cathode. Hybrid cell concepts that incorporate different types of solid electrolytes are considered a promising solution to overcome the limitations of single material classes. However, the kinetics at the heteroionic interface (i.e., charge transfer) substantially affects the cell performance. Moreover, non-ideal physical contacts hinder detailed electrochemical characterization of the interface properties. Thus, we use microstructure-resolved electric network computations to explore how the impedance response of a homogeneous bilayer system is influenced by the interface morphology and the material parameters of the single solid electrolyte layers. Porous interfaces and the resulting current constriction effects give rise to signatures in the impedance spectrum that resemble that of actual migration processes. This hinders unequivocal identification of the origin of the impedance contributions. The resistance and capacitance of this geometric interface signal depend strongly on the contact area and its spatial distribution, the pore capacitance, and the local conductivities around the interface. An experimental case study of an oxide-sulfide multilayer is considered to highlight the challenges in impedance analysis and the assessment of reliable material parameters. These findings are universal and apply to any heterojunction.

Anionic Sublattices in Halide Solid Electrolytes: A Case Study with the High-Pressure Phase of Li3ScCl6

The Li3MX6 compounds (M=Sc, Y, In; X=Cl, Br) are known as promising ionic conductors due to their compatibility with typical metal oxide cathode materials. In this study, we have successfully synthesized γ-Li3ScCl6 using high pressure for the first time in this family. Structural analysis revealed that the high-pressure polymorph crystallizes in the polar and chiral space group P63mc with hexagonal close-packing (hcp) of anions, unlike the ambient-pressure α-Li3ScCl6 and its spinel analog with cubic closed packing (ccp) of anions. Investigation of the known Li3MX6 family further revealed that the cation/anion radius ratio, rM/rX, is the factor that determines which anion sublattice is formed and that in γ-Li3ScCl6, the difference in compressibility between Sc and Cl exceeds the ccp rM/rX threshold under pressure, enabling the ccp-to-hcp conversion. Electrochemical tests of γ-Li3ScCl6 demonstrate improved electrochemical reduction stability. These findings open up new avenues and design principles for lithium solid electrolytes, enabling routes for materials exploration and tuning electrochemical stability without compositional changes or the use of coatings.

Synthetic Tailoring of Ionic Conductivity in Multicationic Substituted, High-Entropy Lithium Argyrodite Solid Electrolytes

Superionic conductors are key components of solid-state batteries (SSBs). Multicomponent or high-entropy materials, offering a vast compositional space for tailoring properties, have recently attracted attention as novel solid electrolytes (SEs). However, the influence of synthetic parameters on ionic conductivity in compositionally complex SEs has not yet been investigated. Herein, the effect of cooling rate after high-temperature annealing on charge transport in the multicationic substituted lithium argyrodite Li6.5[P0.25Si0.25Ge0.25Sb0.25]S5I is reported. It is demonstrated that a room-temperature ionic conductivity of ∼12 mS cm-1 can be achieved upon cooling at a moderate rate, superior to that of fast- and slow-cooled samples. To rationalize the findings, the material is probed using powder diffraction, nuclear magnetic resonance and X-ray photoelectron spectroscopy combined with electrochemical methods. In the case of moderate cooling rate, favorable structural (bulk) and compositional (surface) characteristics for lithium diffusion evolve. Li6.5[P0.25Si0.25Ge0.25Sb0.25]S5I is also electrochemically tested in pellet-type SSBs with a layered Ni-rich oxide cathode. Although delivering larger specific capacities than Li6PS5Cl-based cells at high current rates, the lower (electro)chemical stability of the high-entropy Li-ion conductor led to pronounced capacity fading. The research data indicate that subtle changes in bulk structure and surface composition strongly affect the electrical conductivity of high-entropy lithium argyrodites.

Conformal High-Aspect-Ratio Solid Electrolyte Thin Films for Li-Ion Batteries by Atomic Layer Deposition

Lithium phosphorus oxynitride (LiPON) is a state-of-the-art solid electrolyte material for thin-film microbatteries. These applications require conformal thin films on challenging 3D surface structures, and among the advanced thin-film deposition techniques, atomic layer deposition (ALD) is believed to stand out in terms of producing appreciably conformal thin films. Here we quantify the conformality (i.e., the evenness of deposition) of thin ALD-grown LiPON films using lateral high-aspect-ratio test structures. Two different lithium precursors, lithium tert-butoxide (LiOtBu) and lithium bis(trimethylsilyl)amide (Li-HMDS), were investigated in combination with diethyl phosphoramidate as the source of oxygen, phosphorus, and nitrogen. The results indicate that the film growth proceeded significantly deeper into the 3D cavities for the films grown from LiOtBu, while the Li-HMDS-based films grew more evenly initially, right after the cavity entrances. These observations can be explained by differences in the precursor diffusion and reactivity. The results open possibilities for the use of LiPON as a solid electrolyte in batteries with high-surface-area electrodes. This could enable faster charging and discharging as well as the use of thin-film technology in fabricating thin-film electrodes of meaningful charge capacity.

Concentrated Formic Acid from CO2 Electrolysis for Directly Driving Fuel Cell

The production of formic acid via electrochemical CO2 reduction may serve as a key link for the carbon cycle in the formic acid economy, yet its practical feasibility is largely limited by the quantity and concentration of the product. Here we demonstrate continuous electrochemical CO2 reduction for formic acid production at 2 M at an industrial-level current densities (i.e., 200 mA cm-2 ) for 300 h on membrane electrode assembly using scalable lattice-distorted bismuth catalysts. The optimized catalysts also enable a Faradaic efficiency for formate of 94.2 % and a highest partial formate current density of 1.16 A cm-2 , reaching a production rate of 21.7 mmol cm-2  h-1 . To assess the practicality of this system, we perform a comprehensive techno-economic analysis and life cycle assessment, showing that our approach can potentially substitute conventional methyl formate hydrolysis for industrial formic acid production. Furthermore, the resultant formic acid serves as direct fuel for air-breathing formic acid fuel cells, boasting a power density of 55 mW cm-2 and an exceptional thermal efficiency of 20.1 %.

Scalable Dry Process for Fabricating a Na Superionic Conductor-Type Solid Electrolyte Sheet

The cost reduction and mass production of oxide-based solid electrolytes are critical for the commercialization of all-solid-state batteries. In this study, an environmentally friendly, low-cost, and high-density oxide-based Na superionic conductor-type solid electrolyte sheet was fabricated via a dry process without the use of any solvent. The polytetrafluoroethylene (PTFE), used as a binder, was transformed into thin thread-like structures via shear force, resulting in a flexible solid electrolyte sheet. The solid electrolyte powder quantity was limited to 50 wt % for fabricating a uniform green sheet via the wet process. However, when the dry process was employed for green sheet fabrication, the solid electrolyte powder quantity could be increased to values exceeding 95 wt %. Therefore, the green sheets produced by using the dry process demonstrated a higher density than those fabricated by using the wet process. The binder content and particle size affected the ionic conductivity of a solid electrolyte sheet fabricated via a dry process. The sheet obtained via the blending of 3 wt % PTFE binder with a solid electrolyte powder, finely ground using a planetary ball mill, which exhibited the highest total ionic conductivity of 1.03 mS cm-1.

Benchmarking of Coatings for Cathode Active Materials in Solid-State Batteries Using Surface Analysis and Reference Electrodes

Fast and reliable evaluation of degradation and performance of cathode active materials (CAMs) for solid-state batteries (SSBs) is crucial to help better understand these systems and enable the synthesis of well-performing CAMs. However, there is a lack of well-thought-out procedures to reliably evaluate CAMs in SSBs. Current approaches often rely on X-ray photoelectron spectroscopy (XPS) for the evaluation of degradation. Unfortunately, XPS sensitivity is not very high, and minor but relevant degradation products may not be detected and distinguished. Furthermore, degradation caused by the current collector (CC) itself is usually not distinguished from CAM-induced degradation. This study uses a modified CC, which allows us to separate electrochemical degradation caused by the CC from degradation at the CAM itself. Using this CC, we present an approach using time-of-flight secondary ions mass spectrometry (ToF-SIMS) that offers high sensitivity and reliability. Principal component analysis (PCA) is applied to differentiate secondary ions as well as identify those mass fragments that correlate with degradation products. This approach also enables distinguishing between different pathways of degradation. To evaluate the kinetic performance of the samples, three-electrode rate tests are performed. Electrochemical characterization evaluates the kinetic performance of the samples under investigation. The samples are finally rated with a score that allows a reliable comparison between the different materials and offers a complete picture of the materials' characteristics in terms of electrochemical performance and degradation.

Bottom Deposition Enables Stable All-Solid-State Batteries with Ultrathin Lithium Metal Anode

Modern strides in energy storage underscore the significance of all-solid-state batteries (ASSBs) predicated on solid electrolytes and lithium (Li) metal anodes in response to the demand for safer batteries. Nonetheless, ASSBs are often beleaguered by non-uniform Li deposition during cycling, leading to compromised cell performance from internal short circuits and hindered charge transfer. In this study, the concept of "bottom deposition" is introduced to stabilize metal deposition based on the lithiophilic current collector and a protective layer composed of a polymeric binder and carbon black. The bottom deposition, wherein Li plating ensues between the protective layer and the current collector, circumvents internal short circuits and facilitates uniform volumetric changes of Li. The prepared functional binder for the protective layer presents outstanding mechanical robustness and adhesive properties, which can withstand the volume expansion caused by metal growth. Furthermore, its excellent ion transfer properties promote uniform Li bottom deposition even under a current density of 6 mA·cm-2 . Also, scanning electron microscopy analysis reveals a consistent plating/stripping morphology of Li after cycling. Consequently, the proposed system exhibits enhanced electrochemical performance when assessed within the ASSB framework, operating under a configuration marked by a high Li utilization rate reliant on an ultrathin Li.

Stable Photoelectrochemical Reactions at Solid/Solid Interfaces toward Solar Energy Conversion and Storage

Electrochemistry has extended from reactions at solid/liquid interfaces to those at solid/solid interfaces. However, photoelectrochemistry at solid/solid interfaces has been hardly reported. In this study, we achieve a stable photoelectrochemical reaction at the semiconductor-electrode/solid-electrolyte interface in a Nb-doped anatase-TiO2 (a-TiO2:Nb)/Li3PO4 (LPO)/Li all-solid-state cell. The oxidative currents of a-TiO2:Nb/LPO/Li increase upon light irradiation when a-TiO2:Nb is located at a potential that is more positive than its flat-band potential. This is because the photoexcited electrons migrate to the current collector due to the bending of the conduction band minimum toward the negative potential. The photoelectrochemical reaction at the semiconductor/solid-electrolyte interface is driven by the same principle as those at semiconductor/liquid-electrolyte interfaces. Moreover, oxidation under light irradiation exhibits reversibility with reduction in the dark. Thus, we extend photoelectrochemistry to all-solid-state systems composed of solid/solid interfaces. This extension would enable us to investigate photoelectrochemical phenomena uncleared at solid/liquid interfaces because of low stability and durability.

Nitrile-functionalized Poly(siloxane) as Electrolytes for High-Energy-Density Solid-State Li Batteries

In the quest to replace liquid Li-ion electrolytes with safer and non-toxic solid counterparts for Li-ion batteries, polysiloxane polymers have attracted considerable attention as they offer low glass transition temperatures, stability with metallic lithium, and versatility in chemical functionalization of the backbone. Herein, we present the synthesis of Li-ion conductive polysiloxane-based polymers functionalized with 60 % nitrile groups per chain unit. The synthesis procedure is based on the reaction of poly-(dimethylsiloxane-co-methylvinylsiloxane) polymer with 2-cyanoethanethiol, followed by the addition of lithium bis (trifluoromethanesulfonyl) imide. The presented polysiloxane-based polymers exhibit exceptionally high ionic conductivity up to 0.375 mS cm-1 at 60 °C and Li+ ion transfer number of 0.73, one of the highest reported for polymer Li-ion conducting electrolytes. Their electrochemical performance was evaluated in both symmetrical and full-cell configurations to test the utility of synthesized polymers as electrolytes in Li-ion batteries.

Reducing Gases Triggered Cathode Surface Reconstruction for Stable Cathode-Electrolyte Interface in Practical All-Solid-State Lithium Batteries

The interfacial compatibility between cathodes and sulfide solid-electrolytes (SEs) is a critical limiting factor of electrochemical performance in all-solid-state lithium-ion batteries (ASSLBs). This work presents a gas-solid interface reduction reaction (GSIRR), aiming to mitigate the reactivity of surface oxygen by inducing a surface reconstruction layer (SRL) . The application of a SRL, CoO/Li2 CO3 , onto LiCoO2 (LCO) cathode results in impressive outcomes, including high capacity (149.7 mAh g-1 ), remarkable cyclability (retention of 84.63% over 400 cycles at 0.2 C), outstanding rate capability (86.1 mAh g-1 at 2 C), and exceptional stability in high-loading cathode (28.97 and 23.45 mg cm-2 ) within ASSLBs. Furthermore, the SRL CoO/Li2 CO3 enhances the interfacial stability between LCO and Li10 GeP2 S12 as well as Li3 PS4 SEs. Significantly, the experiments suggest that the GSIRR mechanism can be broadly applied, not only to LCO cathodes but also to LiNi0.8 Co0.1 Mn0.1 O2 cathodes and other reducing gases such as H2 S and CO, indicating its practical universality. This study highlights the significant influence of the surface chemistry of the oxide cathode on interfacial compatibility, and introduces a surface reconstruction strategy based on the GSIRR process as a promising avenue for designing enhanced ASSLBs.

Possibility of High Ionic Conductivity and High Fracture Toughness in All-Dislocation-Ceramics

Based on the results of numerical calculations as well as those of some related experiments which are reviewed in the present paper, it is suggested that solid electrolytes filled with appropriate dislocations, which is called all-dislocation-ceramics, are expected to have considerably higher ionic conductivity and higher fracture toughness than those of normal solid electrolytes. Higher ionic conductivity is due to the huge ionic conductivity along dislocations where the formation energy of vacancies is considerably lower than that in the bulk solid. Furthermore, in all-dislocation- ceramics, dendrite formation could be avoided. Higher fracture toughness is due to enhanced emissions of dislocations from a crack tip by pre-existing dislocations, which causes shielding of a crack tip, energy dissipation due to plastic deformation and heating, and crack-tip blunting. All-dislocation-ceramics may be useful for all-solid-state batteries.

Synthesis and Characterization of the New Li1+xAl1+xSi1-xO4 (x = 0-0.25) Solid Electrolyte for Lithium-Ion Batteries

A systematic study was performed to investigate the effect of the sintering temperature, sintering duration, and aluminum doping on the crystalline structure and ionic conductivity of the Li1+xAl1+xSi1-xO4 (LASO; x = 0-0.25) solid electrolyte. There was a strong indication that an increase in the sintering temperature and sintering time increased the ionic conductivity of the electrolyte. In particular, the doping concentration and composition ratio (Li1+xAl1+xSi1-xO4; x = 0-0.25) were found to be crucial factors for achieving high ionic conductivity. The sintering time of 18 h and lithium concentration influenced the lattice parameters of the LASO electrolyte, resulting in a significant improvement in ionic conductivity from 2.11 × 10-6 (for pristine LASO) to 1.07 × 10-5 S cm-1. An increase in the lithium concentration affected the stoichiometry, and it facilitated a smoother Li-ion transfer process since lithium served as an ion-conducting bridge between LASO grains.

Extraction Of LiCl From Low-Purity Chlorides Through Solid Electrolyte Towards High-Purity Li2 CO3 Production

Lithium carbonate (Li2 CO3 ) plays a crucial role in advancing state-of-the-art lithium-ion batteries (LIBs) for efficient energy storage. The primary source of lithium is lithium-rich brines, which have complex compositions. Conventional extraction processes from brines involve cumbersome methods that often lead to emissions and/or large volumes of wastewater. To address these environmental challenges, a novel and eco-friendly lithium extraction process under ambient pressure is necessary. In this project, we developed an electrolytic process utilizing a NASICON-type solid-state electrolyte (LATP) to extract lithium chloride from low-purity sources at a temperature of 380 °C. To reduce the melting points of the lithium sources, ZnCl2 was introduced as a fluxing agent. The electrolytic process effectively separated Li+ from other coexisting ions, but resulted in their mixture with Zn2+ . Subsequently, purification and carbonation processes were employed to produce high-purity Li2 CO3 (98.9 %). We also obtained high-purity Zn(OH)2 (>99.9 %) as a value by-product. Despite the formation of color centers that caused the LATP disk to change from white to black during the electrolytic process, it exhibited sufficient ionic conductivity for successful lithium extraction. Our environmentally friendly approach offers a promising pathway for efficient and sustainable lithium extraction, contributing to the advancement of LIB technology for energy storage applications.

Advanced High-Energy All-Solid-State Hybrid Supercapacitor with Nickel-Cobalt-Layered Double Hydroxide Nanoflowers Supported on Jute Stick-Derived Activated Carbon Nanosheets

Developing efficient, lightweight, and durable all-solid-state supercapacitors is crucial for future energy storage systems. The study focuses on optimizing electrode materials to achieve high capacitance and stability. This study introduces a novel two-step pyrolysis process to synthesize activated carbon nanosheets from jute sticks (JAC), resulting in an optimized JAC-2 material with a high yield (≈24%) and specific surface area (≈2600 m2  g-1 ). Furthermore, an innovative in situ synthesis approach is employed to synthesize hybrid nanocomposites (NiCoLDH-1@JAC-2) by integrating JAC nanosheets with nickel-cobalt-layered double hydroxide nanoflowers (NiCoLDH). These nanocomposites serve as positive electrode materials and JAC-2 as the negative electrode material in all-solid-state asymmetric hybrid supercapacitors (HSCs), exhibiting remarkable performance metrics. The HSCs achieve a specific capacitance of 750 F g-1 , a specific capacity of 209 mAh g-1 (at 0.5 A g-1 ), and an energy density of 100 Wh kg-1 (at 250 W kg-1 ) using PVA/KOH solid electrolyte, while maintaining outstanding cyclic stability. Importantly, a density functional theory framework is utilized to validate the experimental findings, underscoring the potential of this novel approach for enhancing HSC performance and enabling the large-scale production of transition metal-based layered double hydroxides.

Quasi-Solid-State All-V2 O5 Battery

Solid-state symmetrical battery represents a promising paradigm for future battery technology. However, its development is hindered by the deficiency of high-performance bipolar electrodes and compatible solid electrolytes. Herein, a quasi-solid-state all-V2 O5 battery constructed by a binder-free carbon fabric-V2 O5 nanowires@graphene (CVOG) bipolar electrode and a softly cross-linked polyethylene oxide-based solid polymer electrolyte (SPE) is reported. The synergetic effect of nano-structuring of V2 O5 , hierarchical conductive network, and graphene wrapping endows the CVOG electrode with boosted reaction kinetics and suppressed vanadium dissolution. The cathodic and anodic reactions of CVOG are decoupled by electrochemical analysis, conceiving the feasibility of constructing all-V2 O5 full battery. In manifesting the solid-state all-V2 O5 battery, the robust and elastic SPE exhibits high ionic conductivity, tight/self-adaptable electrolyte-electrode contact, and a low charge-transfer barrier. The resultant solid-state full battery exhibits a high reversible capacity of 158 mAh g-1 at 0.1 C, good capacity retention of over 61% from 0.1 C to 2 C, and remarkable cycling stability of 77% capacity retention after 1000 cycles at 1 C, which surpass other solid-state symmetrical batteries. Hence, this work provides a practice of high-performance solid-state batteries with symmetrical configuration and is constructive for next-generation battery technology.

Dynamic Response of Ion Transport in Nanoconfined Electrolytes

Ion transport in nanoconfined electrolytes exhibits nonlinear effects caused by large driving forces and pronounced boundary effects. An improved understanding of these impacts is urgently needed to guide the design of key components of the electrochemical energy systems. Herein, we employ a nonlinear Poisson-Nernst-Planck theory to describe ion transport in nanoconfined electrolytes coupled with two sets of boundary conditions to mimic different cell configurations in experiments. A peculiar nonmonotonic charging behavior is discovered when the electrolyte is placed between a blocking electrode and an electrolyte reservoir, while normal monotonic behaviors are seen when the electrolyte is placed between two blocking electrodes. We reveal that impedance shapes depend on the definition of surface charge and the electrode potential. Particularly, an additional arc can emerge in the intermediate-frequency range at potentials away from the potential of zero charge. The obtained insights are instrumental to experimental characterization of ion transport in nanoconfined electrolytes.

In Situ Constructing Robust and Highly Conductive Solid Electrolyte with Tailored Interfacial Chemistry for Durable Li Metal Batteries

Employing nanofiber framework for in situ polymerized solid-state lithium metal batteries (SSLMBs) is impeded by the insufficient Li+ transport properties and severe dendritic Li growth. Both critical issues originate from the shortage of Li+ conduction highways and nonuniform Li+ flux, as randomly-scattered nanofiber backbone is highly prone to slippage during battery assembly. Herein, a robust fabric of Li0.33 La0.56 Ce0.06 Ti0.94 O3-δ /polyacrylonitrile framework (p-LLCTO/PAN) with inbuilt Li+ transport channels and high interfacial Li+ flux is reported to manipulate the critical current density of SSLMBs. Upon the merits of defective LLCTO fillers, TFSI- confinement and linear alignment of Li+ conduction pathways are realized inside 1D p-LLCTO/PAN tunnels, enabling remarkable ionic conductivity of 1.21 mS cm-1 (26 °C) and tLi+ of 0.93 for in situ polymerized polyvinylene carbonate (PVC) electrolyte. Specifically, molecular reinforcement protocol on PAN framework further rearranges the Li+ highway distribution on Li metal and alters Li dendrite nucleation pattern, boosting a homogeneous Li deposition behavior with favorable SEI interface chemistry. Accordingly, excellent capacity retention of 76.7% over 1000 cycles at 2 C for Li||LiFePO4 battery and 76.2% over 500 cycles at 1 C for Li||LiNi0.5 Co0.2 Mn0.3 O2 battery are delivered by p-LLCTO/PAN/PVC electrolyte, presenting feasible route in overcoming the bottleneck of dendrite penetration in in situ polymerized SSLMBs.

Clarifying the Dopant Local Structure and Effect on Ionic Conductivity in Garnet Solid-State Electrolytes for Lithium-Ion Batteries

The high Li-ion conductivity and wide electrochemical stability of Li-rich garnets (Li7La3Zr2O12) make them one of the leading solid electrolyte candidates for solid-state batteries. Dopants such as Al and Ga are typically used to enable stabilization of the high Li+ ion-conductive cubic phase at room temperature. Although numerous studies exist that have characterized the electrochemical properties, structure, and lithium diffusion in Al- and Ga-LLZO, the local structure and site occupancy of dopants in these compounds are not well understood. Two broad 27Al or 69,71Ga resonances are often observed with chemical shifts consistent with tetrahedrally coordinated Al/Ga in the magic angle spinning nuclear magnetic resonance (MAS NMR) spectra of both Al- and Ga-LLZO, which have been assigned to either Al and/or Ga occupying 24d and 96h/48g sites in the LLZO lattice or the different Al/Ga configurations that arise from different arrangements of Li around these dopants. In this work, we unambiguously show that the side products γ-LiAlO2 and LiGaO2 lead to the high frequency resonances observed by NMR spectroscopy and that both Al and Ga only occupy the 24d site in the LLZO lattice. Furthermore, it was observed that the excess Li often used during synthesis leads to the formation of these side products by consuming the Al/Ga dopants. In addition, the consumption of Al/Ga dopants leads to the tetragonal phase formation commonly observed in the literature, even after careful mixing of precursors. The side-products can exist even after sintering, thereby controlling the Al/Ga content in the LLZO lattice and substantially influencing the lithium-ion conductivity in LLZO, as measured here by electrochemical impedance spectroscopy.

High precision of sign language recognition based on In2O3 transistors gated by AlLiO solid electrolyte

In recent years, the synaptic properties of transistors have been extensively studied. Compared with liquid or organic material-based transistors, inorganic solid electrolyte-gated transistors have the advantage of better chemical stability. This study uses a simple, low-cost solution technology to prepare In2O3 transistors gated by AlLiO solid electrolyte. The electrochemical performance of the device is achieved by forming a double electric layer and electrochemical doping, which can mimic basic functions of biological synapses, such as excitatory postsynaptic current (EPSC), paired-pulse promotion (PPF), and spiking time-dependent plasticity (STDP). Furthermore, complex synaptic behaviors such as Pavlovian classical conditioning and the Morse code "QINGDAO" are successfully emulated. With a 95 % identification accuracy, an artificial neural network based on transistors is built to recognize sign language and enable sign language interpretation. Additionally, the handwriting digit's identification accuracy is 94 %. Even with various levels of Gaussian noise, the recognition rate is still above 84 %. The above findings demonstrate the potential of In2O3/AlLiO TFT in shaping the next generation of artificial intelligence. .

Accelerating the Search for New Solid Electrolytes: Exploring Vast Chemical Space with Machine Learning-Enabled Computational Calculations

Discovering new solid electrolytes (SEs) is essential to achieving higher safety and better energy density for all-solid-state lithium batteries. In this work, we report machine learning (ML)-assisted high-throughput virtual screening (HTVS) results to identify new SE materials. This approach expands the chemical space to explore by substituting elements of prototype structures and accelerates an evaluation of properties by applying various ML models. The screening results in a few candidate materials, which are validated by density functional theory calculations and ab initio molecular dynamics simulations. The shortlisted oxysulfide materials satisfy key properties to be successful SEs. The advanced screening method presented in this work will accelerate the discovery of energy materials for related applications.

Typology of Battery Cells - From Liquid to Solid Electrolytes

The field of battery research is bustling with activity and the plethora of names for batteries that present new cell concepts is indicative of this. Most names have grown historically, each indicative of the research focus in their own time, e.g. lithium-ion batteries, lithium-air batteries, solid-state batteries. Nevertheless, all batteries are essentially made of two electrode layers and an electrolyte layer. This lends itself to a systematic and comprehensive approach by which to identify the cell type and chemistry at a glance. The recent increase in hybridized cell concepts potentially opens a world of new battery types. To retain an overview of this dynamic research field, each battery type is briefly discussed and a systematic typology of battery cells is proposed in the form of the short and universal cell naming system AAM XEBCAM (AAM: anode active material; X: L (liquid), G (gel), PP (plasticized polymer), DP (dry polymer), S (solid), H (hybrid); EB: electrolyte battery; CAM: cathode active material). This classification is based on the principal ion conduction mechanism of the electrolyte during cell operation. Even though the presented typology initiates from the research fields of lithium-ion, solid-state and hybrid battery concepts, it is applicable to any battery cell chemistry.

Protective NaSICON Interlayer between a Sodium-Tin Alloy Anode and Sulfide-Based Solid Electrolytes for All-Solid-State Sodium Batteries

This paper presents a suitable combination of different sodium solid electrolytes to surpass the challenge of highly reactive cell components in sodium batteries. The focus is laid on the introduction of ceramic Na3.4Zr2Si2.4P0.6O12 serving as a protective layer for sulfide-based separator electrolytes to avoid the high reactivity with the sodium metal anode. The chemical instability of the anode|sulfide solid electrolyte interface is demonstrated by impedance spectroscopy, X-ray photoelectron spectroscopy, and scanning electron microscopy. The Na3.4Zr2Si2.4P0.6O12 disk shows chemical stability with the sodium metal anode as well as the sulfide solid electrolyte. Impedance analysis suggests an electrochemically stable interface. Electron microscopy points to a reaction at the Na3.4Zr2Si2.4P0.6O12 surface toward the sulfide solid electrolyte, which does not seem to affect the performance negatively. The results presented prove the chemical stabilization of the anode-separator interface using a Na3.4Zr2Si2.4P0.6O12 interlayer, which is an important step toward a sodium all-solid-state battery. Due to the applied pressure that is mandatory for battery cells with sulfide-based cathode composite, the use of a brittle ceramic in such cells remains challenging.

One Stone, Three Birds: An Air and Interface Stable Argyrodite Solid Electrolyte with Multifunctional Nanoshells

Li6 PS5 Cl (LPSC) solid electrolytes, based on Argyrodite, have shown potential for developing high energy density and safe all-solid-state lithium metal batteries. However, challenges such as interfacial reactions, uneven Li deposition, and air instability remain unresolved. To address these issues, a simple and effective approach is proposed to design and prepare a solid electrolyte with unique structural features: Li6 PS4 Cl0.75 -OF0.25 (LPSC-OF0.25 ) with protective LiF@Li2 O nanoshells and F and O-rich internal units. The LPSC-OF0.25 electrolyte exhibits high ionic conductivity and the capability of "killing three birds with one stone" by improving the moist air tolerance, as well as the interface compatibility between the anode or cathode and the solid electrolyte. The improved performance is attributed to the peculiar morphology and the self-generating and self-healing interface coupling capability. When coupled with bare LiCoO2 , the LPSC-OF0.25 electrolyte enables stable operation under high cutoff voltage (≈4.65 V vs Li/Li+ ), thick cathodes (25 mg cm-2 ), and large current density (800 cycles at 2 mA cm-2 ). This rationally designed solid electrolyte offers promising prospects for solid-state batteries with high energy and power density for future long-range electric vehicles and aircrafts.

Effect of the Degree of Li3PO4 Vapor Dissociation on the Ionic Conductivity of LiPON Thin Films

Thin films of solid-state lithium-ion electrolytes show promise for use in small-sized autonomous power sources for micro- and nanoelectronic elements. The high rate of vacuum-plasma synthesis (~0.5 μm/h) of lithium phosphor-oxynitride (LiPON) films with an ionic conductivity of ~2·10-6 S/cm is achieved through anodic evaporation of Li3PO4 in a low-pressure arc. The microstructure and ionic conductivity of LiPON films are influenced by the proportion of free lithium in the vapor flow. This paper presents the results of a study on the plasma composition during anodic evaporation of Li3PO4 in a discharge with a self-heating hollow cathode and a crucible anode. A method is proposed for adjusting the free lithium concentration in the gas-vapor (Li3PO4 + N2/Ar) discharge plasma based on changing the frequency of collisions of electrons with Li3PO4 vapor in the anodic region of the discharge. It is demonstrated that an increase in the proportion of free lithium in the flow of deposited particles leads to an enhancement in the concentration and mobility of lithium ions in the deposited films and, subsequently, an improvement in the ionic conductivity of LiPON films.

Order-Disorder Phase Transition and Ionic Conductivity in a Li2B12H12 Solid Electrolyte

Temperature-induced phase transitions and ionic conductivities of Li2B12H12 and LiCB11H12 were simulated with the use of machine learning interatomic potentials based on van der Waals-corrected density functional theory (rev-vdW-DF2 functional). The simulated temperature of order-disorder phase transition, lattice parameters, diffusion, ionic conductivity, and activation energies are in good agreement with experimental data. Our simulations of Li2B12H12 uncover the importance of the reorientational motion of the [B12H12]2- anion. In the ordered α-phase (T < 625 K), these anions have well-defined orientations, while in the disordered β-phase (T > 625 K), their orientations are random. In vacancy-rich systems, its complete rotation was observed, while in the ideal crystal, the anions display limited vabrational motion, indicating the static nature of the phase transition without dynamic disordering. The use of machine learning interatomic potentials has allowed us to study large systems (>2000 atoms) in long (nanosecond-scale) molecular dynamics runs with ab initio quality.

Silicon-Based Solid-State Batteries: Electrochemistry and Mechanics to Guide Design and Operation

Solid-state batteries (SSBs) are promising alternatives to the incumbent lithium-ion technology; however, they face a unique set of challenges that must be overcome to enable their widespread adoption. These challenges include solid-solid interfaces that are highly resistive, with slow kinetics, and a tendency to form interfacial voids causing diminished cycle life due to fracture and delamination. This modeling study probes the evolution of stresses at the solid electrolyte (SE) solid-solid interfaces, by linking the chemical and mechanical material properties to their electrochemical response, which can be used as a guide to optimize the design and manufacture of silicon (Si) based SSBs. A thin-film solid-state battery consisting of an amorphous Si negative electrode (NE) is studied, which exerts compressive stress on the SE, caused by the lithiation-induced expansion of the Si. By using a 2D chemo-mechanical model, continuum scale simulations are used to probe the effect of applied pressure and C-rate on the stress-strain response of the cell and their impacts on the overall cell capacity. A complex concentration gradient is generated within the Si electrode due to slow diffusion of Li through Si, which leads to localized strains. To reduce the interfacial stress and strain at 100% SOC, operation at moderate C-rates with low applied pressure is desirable. Alternatively, the mechanical properties of the SE could be tailored to optimize cell performance. To reduce Si stress, a SE with a moderate Young's modulus similar to that of lithium phosphorous oxynitride (∼77 GPa) with a low yield strength comparable to sulfides (∼0.67 GPa) should be selected. However, if the reduction in SE stress is of greater concern, then a compliant Young's modulus (∼29 GPa) with a moderate yield strength (1-3 GPa) should be targeted. This study emphasizes the need for SE material selection and the consideration of other cell components in order to optimize the performance of thin film solid-state batteries.

Low Interfacial Resistance and Superior Suppression to Li-Dendrite Penetration Facilitated by Air-Stable and Mechanically Robust Al/Mg-Co-Doped Li-La-Zirconate as Electrolyte for Li-Based Solid-State Cells

In the context of usage as a solid electrolyte (SE) for Li-based solid-state cells, the interfacial characteristics of Li-La-zirconate (LLZO) with the electrodes and the mechanical properties of LLZO influence the overall impedance and stability. In this regard, the newly developed air-stable Al/Mg-co-doped LLZO has been found to possess greater resistance to crack propagation (by ∼31%) and fracture stress (by ∼52%), along with elevated hardness and stiffness, as compared to simply Al-doped LLZO. Furthermore, as directly visualized via cross-section electron microscopy at the Li/LLZO interfaces, the air-stability, along with mechanical robustness of Al/Mg-co-doped LLZO, facilitates the complete absence of impurity phase and cracks at the Li/LLZO interface, unlike for the simply Al-doped LLZO. These result in a very low area specific resistance for the Li/"Al/Mg-co-doped LLZO" interface of ∼9 Ω cm2, which is ∼3 times lower than that at the Li/"Al-doped LLZO" interface and is also among the lowest reported to date for Li/LLZO interfaces, that too sans any surface/interfacial coating/engineering. Galvanostatic Li-plating/stripping cycles indicate that the critical current density toward initiating Li-dendrite nucleation/propagation is higher in the case of Al/Mg-co-doped LLZO SE, viz., ∼0.45 mA/cm2, than for the Al-doped counterpart (viz., ∼0.25 mA/cm2). Furthermore, Li-stripping/plating cycles @ 0.1 mA/cm2 have revealed outstanding stability of polarization voltage up to at least 100 cycles upon using Al/Mg-codoped LLZO as the SE, in contrast to the instability right from the 36th cycle onward with the Al-doped LLZO. This indicates superior suppression toward Li-dendrite nucleation/propagation by the Al/Mg-codoped LLZO, unlike by Al-doped LLZO, as also directly visualized via cross-section electron microscopy post-cycling. The air-stability induced a clean Li/LLZO interface (viz., good contact), which, together with the mechanical robustness of Al/Mg-codoped LLZO, resulted in the very low interfacial resistance and excellent suppression toward Li-dendrite nucleation/propagation, leading to high CCD and very stable long-term Li-stripping/plating. Overall, in addition to highlighting the notable advantages offered by the Al/Mg-co-doped LLZO solid electrolyte, the insights obtained as part of this work are expected to lead to the successful and facile development of high-performance solid-state Li-based cells.

The Impact of Intergrain Phases on the Ionic Conductivity of the LAGP Solid Electrolyte Material Prepared by Spark Plasma Sintering

Li1.5Al0.5Ge1.5(PO4)3 (LAGP) is a promising oxide solid electrolyte for all-solid-state batteries due to its excellent air stability, acceptable electrochemical stability window, and cost-effective precursor materials. However, further improvement in the ionic conductivity performance of oxide solid-state electrolytes is hindered by the presence of grain boundaries and their associated morphologies and composition. These key factors thus represent a major obstacle to the improved design of modern oxide based solid-state electrolytes. This study establishes a correlation between the influence of the grain boundary phases, their 3D morphology, and compositions formed under different sintering conditions on the overall LAGP ionic conductivity. Spark plasma sintering has been employed to sinter oxide solid electrolyte material at different temperatures with high compacity values, whereas a combined potentiostatic electrochemical impedance spectroscopy, 3D FIB-SEM tomography, XRD, and solid-state NMR/materials modeling approach provides an in-depth analysis of the influence of the morphology, structure, and composition of the grain boundary phases that impact the total ionic conductivity. This work establishes the first 3D FIB-SEM tomography analysis of the LAGP morphology and the secondary phases formed in the grain boundaries at the nanoscale level, whereas the associated 31P and 27Al MAS NMR study coupled with materials modeling reveals that the grain boundary material is composed of Li4P2O7 and disordered Li9Al3(P2O7)3(PO4)2 phases. Quantitative 31P MAS NMR measurements demonstrate that optimal ionic conductivity for the LAGP system is achieved for the 680 °C SPS preparation when the disordered Li9Al3(P2O7)3(PO4)2 phase dominates the grain boundary composition with reduced contributions from the highly ordered Li4P2O7 phases, whereas the 27Al MAS NMR data reveal that minimal structural change is experienced by each phase throughout this suite of sintering temperatures.

Fluorine-Substituted Halide Solid Electrolytes with Enhanced Stability toward the Lithium Metal

The high ionic conductivity and good oxidation stability of halide-based solid electrolytes evoke strong interest in this class of materials. Nonetheless, the superior oxidative stability compared to sulfides comes at the expense of limited stability toward reduction and instability against metallic lithium anodes, which hinders their practical use. In this context, the gradual fluorination of Li2ZrCl6-xFx (0 ≤ x ≤ 1.2) is proposed to enhance the stability toward lithium-metal anodes. The mechanochemically synthesized fluorine-substituted compounds show the expected distorted local structure (M2-M3 site disorder) and significant change in the overall Li-ion migration barrier. Theoretical calculations reveal an approximate minimum energy path for Li2ZrCl6-xFx (x = 0 and 0.5) with an increase in the Li+ migration energy barrier for Li2ZrCl5.5F0.5 in comparison to Li2ZrCl6. However, it is found that the fluorine-substituted compound exhibits substantially lower polarization after 800 h of lithium stripping and plating owing to enhanced interfacial stability against the lithium metal, as revealed by density functional theory and ex situ X-ray photoelectron spectroscopy, thanks to the formation of a fluorine-rich passivating interphase.

Layered Polymer Stacking for Stable Interfaces and Dendrite Growth Inhibition in All-Solid-State Lithium Batteries

To improve the ionic conductivity and cycling stability of solid-state lithium batteries based on poly(ethylene oxide) (PEO) electrolytes, we developed a sandwich-structured composite polymer electrolyte (sandwich-CPE) PEO-TiN/PEO-LiYF4/PEO-TiN. The sandwich-CPE delivers a high ionic conductivity of 1.7 × 10-4 S cm-1 at 30 °C and a wide potential window of 0 to 5.0 V (vs Li/Li+). Adding PEO-TiN leads to the formation of Li3N between Li and sandwich-CPE during cycling, which effectively reduces the level of Li dendrite formation. Additionally, PEO-TiN acts as a sacrificial layer to stop the entry of Li dendrites into the interlayer PEO-LiYF4. Using the sandwich-CPE, LiFePO4 retains a reversible capacity of 113.8 mA h g-1 at 30 °C after 300 cycles under 0.5 C. For high-voltage cells, LiNi0.5Co0.2Mn0.3O2 retains a capacity retention of 71.4% at 45 °C after 300 cycles under 0.2 C among 3.0-4.3 V, while Li3V2(PO4)3 delivers an initial discharge capacity of 108.1 mA h g-1 at 60 °C and retains 81.6% after 500 cycles under 1 C among 2.8-4.4 V. These results demonstrate the strong electrochemical compatibility of the sandwich-CPE, enabling high reversible capacity and good cycling stability for solid-state Li batteries with different cathodes at different temperatures and current rates.

Temperature and Pressure Effects on Unrecoverable Voids in Li Metal Solid-State Batteries

All-solid-state batteries (ASSB) can potentially achieve high gravimetric and volumetric energy densities (900 Wh/L) if paired with a lithium metal anode and solid electrolyte. However, there is a lack in critical understanding about how to operate lithium metal cells at high capacities and minimize unwanted degradation mechanisms such as dendrites and voids. Herein, we investigate how pressure and temperature influence the formation and annihilation of unrecoverable voids in lithium metal upon stripping. Stack pressure and temperature are effective means to initiate creep-induced void filling and decrease charge transfer resistances. Applying stack pressure enables lithium to deform and creep below the yield stress during stripping at high current densities. Lithium creep is not sufficient to prevent cell shorting during plating. Three-electrode experiments were employed to probe the kinetic and morphological limitations that occur at the anode-solid electrolyte during high-capacity stripping (5 mAh/cm2). The role of cathode-LLZO interface, which dictates cyclability and capacity retention in full cells, was also studied. This work elucidates the important role that temperature (external or in situ generated) has on reversible operation of solid-state batteries.

Solid Hybrid Electrolyte Featuring a Vertically Aligned Li6.4La3.0Zr1.4Ta0.6O12 Membrane for All-Solid-State Lithium Batteries

All-solid-state lithium batteries (ASSLBs) with enhanced safety are considered one of the most promising substitutes for liquid electrolyte-based Li-ion batteries. However, many properties of solid electrolytes, such as ionic conductivity, film formability, and electrochemical, mechanical, thermal, and interfacial stability need to be improved for their practical application. In this study, a vertically aligned Li_6.4La_3.0Zr_1.4Ta_0.6O₁₂ (LLZO) membrane with finger-like microvoids was prepared using processes involving phase inversion and sintering. A hybrid electrolyte was then obtained by infusing the LLZO membrane with a solid polymer electrolyte based on poly(ε-caprolactone). The solid hybrid electrolyte (SHE) was a flexible thin film with high ionic conductivity, superior electrochemical stability, high Li⁺ transference number, enhanced thermal stability, and improved Li metal electrode-solid electrolyte interfacial stability. A solid-state Li/LiNi_0.78Co_0.10Mn_0.12O₂ cell assembled with the hybrid electrolyte exhibited good cycling performance, in terms of discharge capacity, cycling stability, and rate capability. Accordingly, the SHE using a vertically aligned LLZO membrane is a promising solid electrolyte for realizing safe, high-performance ASSLBs.

Oriented Porous NASICON 3D Framework via Freeze-Casting for Sodium-Metal Batteries

Sodium-metal batteries are promising candidates for low-cost, large-format energy storage systems. However, sodium-metal batteries suffer from high interfacial resistance between the electrodes and the solid electrolyte, leading to poor electrochemical performance. We demonstrate a sodium superionic conductor (NASICON) with an oriented porous framework of sodium aluminum titanium phosphate (NATP) fabricated by the freeze-casting technique, which shows excellent properties as a solid electrolyte. Using X-ray computed tomography, we confirm the uniform low-tortuosity channels present along the thickness of the scaffold. We infiltrated the porous NATP scaffolds with sodium vanadium phosphate (NVP) cathode nanoparticles achieving mass loadings of ∼3-4 mg cm^-2, which enables short sodium ion diffusion path lengths. For the resulting hybrid cell, we achieved a capacity of ∼90 mAh g^-1 at a specific current of 50 mA g^-1 (∼300 Wh kg^-1) for over 100 cycles with ∼94% capacity retention. Our study offers valuable insights for the design of hybrid solid electrolyte-cathode active material structures to achieve improved electrochemical performance through low-tortuosity ion transport networks.

Amorphous Phase Induced Lithium Dendrite Suppression in Glass-Ceramic Garnet-Type Solid Electrolytes

Lithium metal-based solid-state batteries (SSBs) have attracted much attention due to their potentially higher energy densities and improved safety compared with lithium-ion batteries. One of the most promising solid electrolytes, garnet-type Li₇La₃Zr₂O₁₂ (LLZO), has been investigated intensively in recent years. It enables the use of a lithium metal anode, but its application is still challenging because of lithium dendrites that grow at voids, cracks, and grain boundaries of sintered bodies during cycling of the battery cell. In this work, glass-ceramic Ta-doped LLZO produced in a unique melting process was investigated. Upon cooling, an amorphous phase is generated intrinsically, whose composition and fraction are adjusted during the process. Herein, it was set to about 4 wt % containing Li₂O and a Li₂O-SiO₂ phase. During sintering, it was shown to segregate into the grain boundaries and decrease porosity via liquid phase sintering. Sintering temperature and sintering time were found to be reduced compared with the LLZO fabricated by a solid-state reaction while maintaining high density and ionic conductivity. The glass-ceramic sintered at 1130 °C for 0.5 h showed a room-temperature ionic conductivity of 0.64 mS cm^-1. Most importantly, the evenly distributed amorphous phase along the grain boundaries effectively hinders lithium dendrite growth. Besides mechanically blocking pores and voids, it helps to prevent inhomogeneous distribution of current density. The critical current density (CCD) of the Li|LLZTO|Li symmetric cell was determined as 1.15 mA cm^-2, and in situ lithium plating experiments in a scanning electron microscope revealed superior dendrite stability properties. Therefore, this work provides a promising strategy to prepare a dense and dendrite-suppressing solid electrolyte for future implementation in SSBs.

Understanding the Influence of Li7La3Zr2O12 Nanofibers on Critical Current Density and Coulombic Efficiency in Composite Polymer Electrolytes

Composite polymer electrolytes (CPEs) are attractive materials for solid-state lithium metal batteries, owing to their high ionic conductivity from ceramic ionic conductors and flexibility from polymer components. As with all lithium metal batteries, however, CPEs face the challenge of dendrite formation and propagation. Not only does this lower the critical current density (CCD) before cell shorting, but the uncontrolled growth of lithium deposits may limit Coulombic efficiency (CE) by creating dead lithium. Here, we present a fundamental study on how the ceramic components of CPEs influence these characteristics. CPE membranes based on poly(ethylene oxide) and lithium bis(trifluoromethanesulfonyl)imide (PEO-LiTFSI) with Li₇La₃Zr₂O₁₂ (LLZO) nanofibers were fabricated with industrially relevant roll-to-roll manufacturing techniques. Galvanostatic cycling with lithium symmetric cells shows that the CCD can be tripled by including 50 wt % LLZO, but half-cell cycling reveals that this comes at the cost of CE. Varying the LLZO loading shows that even a small amount of LLZO drastically lowers the CE, from 88% at 0 wt % LLZO to 77% at just 2 wt % LLZO. Mesoscale modeling reveals that the increase in CCD cannot be explained by an increase in the macroscopic or microscopic stiffness of the electrolyte; only the microstructure of the LLZO nanofibers in the PEO-LiTFSI matrix slows dendrite growth by presenting physical barriers that the dendrites must push or grow around. This tortuous lithium growth mechanism around the LLZO is corroborated with mass spectrometry imaging. This work highlights important elements to consider in the design of CPEs for high-efficiency lithium metal batteries.

A New Sodium Thioborate Fast Ion Conductor: Na 3 B 5 S 9

We report a new sodium fast-ion conductor, Na3B5S9, that exhibits a high Na ion total conductivity of 0.80 mS∙cm-1 (sintered pellet; cold-pressed pellet = 0.21 mS∙cm-1). The structure consists of corner-sharing B10S20 supertetrahedral clusters, which create a framework that supports 3D Na ion diffusion channels. The Na ions are well-distributed in the channels and form a disordered sublattice spanning five Na crystallographic sites. The combination of structural elucidation via single crystal X-ray diffraction and powder synchrotron X-ray diffraction at variable temperatures, solid-state nuclear magnetic resonance spectra and ab initio molecular dynamics simulations reveal high Na-ion mobility (predicted conductivity: 0.96 mS∙cm-1) and the nature of the 3D diffusion pathways. Notably, the Na ion sublattice orders at low temperatures, resulting in isolated Na polyhedra and thus much lower ionic conductivity. This highlights the importance of a disordered Na ion sublattice - and existence of well-connected Na ion migration pathways formed via face-sharing polyhedra - in dictating Na ion diffusion.

Aqueous Cold Sintering of Li-Based Compounds

Aqueous cold sintering of two lithium-based compounds, the electrolyte Li_6.25La₃Zr₂Al_0.25O₁₂ (LLZAO) and cathode material LiCoO₂ (LCO), is reported. For LLZAO, a relative density of ∼87% was achieved, whereas LCO was sintered to ∼95% with 20 wt % LLZAO as a flux/binder. As-cold sintered LLZAO exhibited a low total conductivity (10^-8 S/cm) attributed to an insulating grain boundary blocking layer of Li₂CO₃. The blocking layer was reduced with a post-annealing process or, more effectively, by replacing deionized water with 5 M LiCl during cold sintering to achieve a total conductivity of ∼3 × 10^-5 S/cm (similar to the bulk conductivity). For LCO-LLZAO composites, scanning electron microscopy and X-ray computer tomography indicated a continuous LCO matrix with the LLZAO phase evenly distributed but isolated throughout the ceramics. [001] texturing during cold sintering resulted in an order of magnitude difference in electronic conductivity between directions perpendicular and parallel to the c-axis at room temperature. The electronic conductivity (∼10^-2 S/cm) of cold sintered LCO-LLZAO ceramics at room temperature was comparable to that of single crystals and higher than those synthesized via either conventional sintering or hot pressing.

Preparation of Metal-Oxide-Doped Li7P2S8Br0.25I0.75 Solid Electrolytes for All-Solid-State Lithium Batteries

The all-solid-state lithium battery (ASSB) has received great attention due to its greater safety than the conventional lithium-ion battery (LIB). Sulfide-based inorganic solid electrolytes are an important component to fabricate the ASSB. But to attain a better performance, the ionic conductivity and electrochemical stability of the sulfide-based solid electrolytes need to be improved. In this work, we prepared the metal-oxide-doped/mixed Li₇P₂S₈I_0.75Br_0.25 lithium superionic conductors by a dry ball-milling process. The high ionic conductivity was achieved by a low-temperature (200 °C) heat-treatment process. The metal-oxide-doped Li₇P₂S₈I_0.75Br_0.25 solid electrolyte exhibited a higher ionic conductivity value of 7.3 mS cm^-1 at room temperature than the bare Li₇P₂S₈I_0.75Br_0.25 solid electrolyte. The structural characteristics of the prepared solid electrolytes were studied by solid NMR and laser Raman analysis. The electrochemical stability of the prepared solid electrolyte was studied by cyclic voltammetry and DC charge-discharge analysis. The addition of metal oxide increased the electrochemical stability and dry-air stability of the Li₇P₂S₈I_0.75Br_0.25 solid electrolyte. The Ta₂O₅-doped Li₇P₂S₈I_0.75Br_0.25 solid electrolyte was stable even after 300 charge-discharge DC cycles and also 100 h of dry-air exposure. Further, the Ta₂O₅-doped Li₇P₂S₈I_0.75Br_0.25 solid electrolyte-based ASSB exhibited a high discharge capacity value of 184 mA h g^-1 at 0.1 C rate with 66% initial cycle Coulombic efficiency.

Low-Temperature Sintering of a Garnet-Type Li6.5La3Zr1.5Ta0.5O12 Solid Electrolyte and an All-Solid-State Lithium-Ion Battery

Garnet-type Ta-substituted Li₇La₃Zr₂O₁₂ materials attract considerable attention as solid electrolytes for use in future oxide-based all-solid-state lithium-ion batteries owing to their superior ionic conductivity and chemical and electrochemical stabilities. However, high-temperature sintering above 1000 °C, which is needed to realize high lithium-ion conductivity, results in the formation of insulating interface impurities at the electrode-electrolyte interface. Herein, the low-temperature sintering of the Li_6.5La₃Zr_1.5Ta_0.5O₁₂ (LLZT) solid electrolyte at a remarkably low temperature of 400 °C was demonstrated using the submicrometer-sized garnet-type LLZT fine powder sample prepared at 600 °C through a reaction of Li₂O and La_2.4Zr_1.2Ta_0.4O₇. The lithium-ion conductivity at 25 °C was 4.54 × 10^-5 S cm^-1 without any additives through low-temperature sintering at 400 °C. In addition, the preliminary battery performance of the oxide-based all-solid-state LiNi_1/3Co_1/3Mn_1/3O₂-Li₄Ti₅O₁₂ full-battery cell fabricated at 400 °C using the present LLZT fine powder sample as the solid electrolyte was demonstrated.

LiNi0.6Co0.2Mn0.2O2 Cathode-Solid Electrolyte Interfacial Behavior Characterization Using Novel Method Adopting Microcavity Electrode

Due to the limitations of organic liquid electrolytes, current development is towards high performance all-solid-state lithium batteries (ASSLBs). For high performance ASSLBs, the most crucial is the high ion-conducting solid electrolyte (SE), with a focus on interface analysis between SE and active materials. In the current study, we successfully synthesized the high ion-conductive argyrodite-type (Li₆PS₅Cl) solid electrolyte, which has 4.8 mS cm^-1 conductivity at room temperature. Additionally, the present study suggests the quantitative analysis of interfaces in ASSLBs. The measured initial discharge capacity of a single particle confined in a microcavity electrode was 1.05 nAh for LiNi_0.6Co_0.2Mn_0.2O₂ (NCM622)-Li₆PS₅Cl solid electrolyte materials. The initial cycle result shows the irreversible nature of active material due to the formation of the solid electrolyte interphase (SEI) layer on the surface of the active particle; further second and third cycles demonstrate high reversibility and good stability. Furthermore, the electrochemical kinetic parameters were calculated through the Tafel plot analysis. From the Tafel plot, it is seen that asymmetry increases gradually at high discharge currents and depths, which rise asymmetricity due to the increasing of the conduction barrier. However, the electrochemical parameters confirm the increasing conduction barrier with increased charge transfer resistance.

Interface Analysis of LiCl as a Protective Layer of Li1.3Al0.3Ti1.7(PO4)3 for Electrochemically Stabilized All-Solid-State Li-Metal Batteries

Regardless of the superiorities of Li_1.3Al_0.3Ti_1.7(PO₄)₃ (LATP), such as stability against oxygen and moisture, high ionic conductivity, and low activation energy, its practical application in all-solid-state lithium metal batteries is still impeded by the formation of ionic-resistance interphase layers. Upon contact with Li metal, electron migration from Li to LATP causes the reduction of Ti⁴⁺ in LATP. As a result, an ionic-resistance layer will be formed at the interface between the two materials. Applying a buffer layer between them is a potential measure to mitigate this problem. In this study, we analyzed the potential role of LiCl to protect the LATP solid electrolyte through a first-principle study-based density functional theory (DFT) calculation. Density-of-states (DOS) analysis on the Li/LiCl heterostructure reveals the insulating roles of LiCl in preventing electron flow to LATP. The insulating properties begin at depths of 4.3 and 5.0 Å for Li (001)/LiCl (111) and Li (001)/LiCl (001) heterostructures, respectively. These results indicate that LiCl (111) is highly potential to be applied as a protecting layer on LATP to avoid the formation of ionic resistance interphase caused by electron transfer from the Li metal anode.

Sn-Substituted Argyrodite Li6PS5Cl Solid Electrolyte for Improving Interfacial and Atmospheric Stability

Sulfide-based solid electrolytes exhibit good formability and superior ionic conductivity. However, these electrolytes can react with atmospheric moisture to generate H₂S gas, resulting in performance degradation. In this study, we attempted to improve the stability of the interface between Li metal and an argyrodite Li₆Ps₅Cl solid electrolyte by partially substituting P with Sn to form an Sn-S bond. The solid electrolyte was synthesized via liquid synthesis instead of the conventional mechanical milling method. X-ray diffraction analyses confirmed that solid electrolytes have an argyrodite structure and peak shift occurs as substitution increases. Scanning electron microscopy and energy-dispersive X-ray spectroscopy analyses confirmed that the particle size gradually increased, and the components were evenly distributed. Moreover, electrochemical impedance spectroscopy and DC cycling confirmed that the ionic conductivity decreased slightly but that the cycling behavior was stable for about 500 h at X = 0.05. The amount of H₂S gas generated when the solid electrolyte is exposed to moisture was measured using a gas sensor. Stability against atmospheric moisture was improved. In conclusion, liquid-phase synthesis could be applied for the large-scale production of argyrodite-based Li6PS5Cl solid electrolytes. Moreover, Sn substitution improved the electrochemical stability of the solid electrolyte.

Progress and Perspective of Glass-Ceramic Solid-State Electrolytes for Lithium Batteries

The all-solid-state lithium battery (ASSLIB) is one of the key points of future lithium battery technology development. Because solid-state electrolytes (SSEs) have higher safety performance than liquid electrolytes, and they can promote the application of Li-metal anodes to endow batteries with higher energy density. Glass-ceramic SSEs with excellent ionic conductivity and mechanical strength are one of the main focuses of SSE research. In this review paper, we discuss recent advances in the synthesis and characterization of glass-ceramic SSEs. Additionally, some discussions on the interface problems commonly found in glass-ceramic SSEs and their solutions are provided. At the end of this review, some drawbacks of glass-ceramic SSEs are summarized, and future development directions are prospected. We hope that this review paper can help the development of glass-ceramic solid-state electrolytes.

Lithium-Ion Glass Gating of HgTe Nanocrystal Film with Designed Light-Matter Coupling

Nanocrystals' (NCs) band gap can be easily tuned over the infrared range, making them appealing for the design of cost-effective sensors. Though their growth has reached a high level of maturity, their doping remains a poorly controlled parameter, raising the need for post-synthesis tuning strategies. As a result, phototransistor device geometry offers an interesting alternative to photoconductors, allowing carrier density control. Phototransistors based on NCs that target integrated infrared sensing have to (i) be compatible with low-temperature operation, (ii) avoid liquid handling, and (iii) enable large carrier density tuning. These constraints drive the search for innovative gate technologies beyond traditional dielectric or conventional liquid and ion gel electrolytes. Here, we explore lithium-ion glass gating and apply it to channels made of HgTe narrow band gap NCs. We demonstrate that this all-solid gate strategy is compatible with large capacitance up to 2 µF·cm^-2 and can be operated over a broad range of temperatures (130-300 K). Finally, we tackle an issue often faced by NC-based phototransistors:their low absorption; from a metallic grating structure, we combined two resonances and achieved high responsivity (10 A·W^-1 or an external quantum efficiency of 500%) over a broadband spectral range.

Microstructure of the Li-Al-O Second Phases in Garnet Solid Electrolytes

The microstructure of the Li₇La₃Zr₂O₁₂ (LLZO) garnet solid electrolyte is critical for its performance in all-solid-state lithium-ion battery. During conventional high-temperature sintering, second phases are generated at the grain boundaries due to the reaction between sintering aids and LLZO, which have an enormous effect on the performances of LLZO. However, a detailed structure study of the second phases and their impact on physical properties is lacking. Here, crystal structures of the second phases in LLZO pellets are studied in detail by transmission electron microscopy. Three different crystal structures of Li-Al-O second phases, γ-LiAlO₂, α-Li₅AlO₄, and β-Li₅AlO₄ were identified, and atomic-scale lattice information was obtained by applying low-dose high-resolution imaging for these electron-beam-sensitive second phases. On this basis, the structure-property relationship of these structures was explored. It was found that sintering aids with a higher Li/Al ratio are beneficial to form Li-rich second phases, which result in more highly ionic conductive LLZO.