Deflecting Dendrites by Introducing Compressive Stress in Li7La3Zr2O12 Using Ion Implantation.

Lithium dendrites belong to the key challenges of solid-state battery research. They are unavoidable due to the imperfect nature of surfaces containing defects of a critical size that can be filled by lithium until fracturing the solid electrolyte. The penetration of Li metal occurs along the propagating crack until a short circuit takes place. It is hypothesized that ion implantation can be used to introduce stress states into Li6.4La3Zr1.4Ta0.6O12 which enables an effective deflection and arrest of dendrites. The compositional and microstructural changes associated with the implantation of Ag-ions are studied via atom probe tomography, electron microscopy, and nano X-ray diffraction indicating that Ag-ions can be implanted up to 1 µm deep and amorphization takes place down to 650-700 nm, in good agreement with kinetic Monte Carlo simulations. Based on diffraction results pronounced stress states up to -700 MPa are generated in the near-surface region. Such a stress zone and the associated microstructural alterations exhibit the ability to not only deflect mechanically introduced cracks but also dendrites, as demonstrated by nano-indentation and galvanostatic cycling experiments with subsequent electron microscopy observations. These results demonstrate ion implantation as a viable technique to design "dendrite-free" solid-state electrolytes for high-power and energy-dense solid-state batteries.

Degradation Evolution for Li2 ZrCl6 Electrolytes in Humid Air and Enhanced Air Stability via Effective Indium Substitution.

Superionic halides have aroused interests in field of solid electrolytes such as Li2 ZrCl6 . However, they are still facing challenges including poor air stability which lacks in-depth investigation. Here, moisture instability of Li2 ZrCl6 is demonstrated and decomposition mechanism in air is clearly revealed. Li2 ZrCl6 decomposes into Li2 ZrO3 , ZrOCl2 ·xH2 O and LiCl during initial stage as halides upon moisture exposure. Later, these side products evolve into LiCl(H2 O) and Li6 Zr2 O7 after longer time exposure. More importantly, structure of destroyed halides cannot be recovered after postheating. Later, Indium is doped into Li2 ZrCl6 (9.7 × 10-5 S cm-1 ) to explore its effect on structure and properties. Crystal structure of ball-milled In-doped Li2 ZrCl6 electrolytes is converted from the Li3 YCl6 -like to Li3 InCl6 -like with increasing In content and ionic conductivity can also be enhanced (0.768-1.13) × 10-3 S cm-1 ). More importantly, good air stability of optimal Li2.8 Zr0.2 In0.8 Cl6 is achieved since halide hydrates are formed after air exposure instead of total decomposition and the hydrates can be restored to Li2.8 Zr0.2 In0.8 Cl6 after postheating. Moreover, reheated Li2.8 Zr0.2 In0.8 Cl6 after air exposure is successfully applied in solid-state LiNi0.8 Co0.1 Mn0.1 O2 /halides/Li6 PS5 Cl/Li-In battery. The results in this work can provide insights into air instability of Li2 ZrCl6 and effective strategy to regulate air stability of halides.

Cathode Interface Construction by Rapid Sintering in Solid-State Batteries.

Solid-state batteries (SSBs) are poised to replace traditional organic liquid-electrolyte lithium-ion batteries due to their higher safety and energy density. Oxide-based solid electrolytes (SEs) are particularly attractive for their stability in air and inability to ignite during thermal runaway. However, achieving high-performance in oxide-based SSBs requires the development of an intimate and robust SE-cathode interface to overcome typically large interfacial resistances. The transition interphase should be both physically and chemically active. This study presents a thin, conductive interphase constructed between lithium aluminum titanium phosphate and lithium cobalt oxide using a rapid sintering method that modifies the interphase within 10 s. The rapid heating and cooling rates restrict side reactions and interdiffusion on the interface. SSBs with thick composite cathodes demonstrate a high initial capacity of ≈120 mAh g-1 over 200 cycles at room temperature. Furthermore, the rapid sintering method can be extended to other cathode systems under similar conditions. These findings highlight the importance of constructing an appropriate SE-cathode interface and provide insight into designing practical SSBs.

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.

Surface Coordination of Garnet Fillers Improves the Organic-Inorganic Interfacial Compatibility of Composite Solid Electrolyte.

Composite solid electrolytes (CSEs) have become one of the most promising solid-state electrolytes due to their favorable safety and flexibility. However, the weak interaction between inorganic fillers and polymer matrix leads to poor organic-inorganic interfacial compatibility, which degrades the electrochemical performance of CSEs. Herein, it is demonstrated that Li6.4La3Zr1.4Ta0.6O12 (LLZTO) can be chemically bonded to the polymer matrix by surface coordination of the 1,2-dithiolane group of lipoic acid (LA) with metal atoms on the surface of LLZTO through a combination of experimental investigations and theoretical calculations. The surface coordination not only enhances the interfacial compatibility between LLZTO and the polymer matrix, but also facilitates rapid Li+ transport, which leads to the ionic conductivity of the prepared CSE (P-V-M@LLZTO) as high as 6.1 × 10-4 S cm-1 at 30 °C. The excellent interface compatibility ensures a stable cycle of Li/P-V-M@LLZTO/Li symmetrical cell for more than 3500 h. As a result, LiFePO4/P-V-M@LLZTO/Li cell delivers the discharge capacity of 161 mAh g-1 after 5 cycles with a capacity retention of 81% after 500 cycles at 0.5C under 30 °C. This work demonstrates that surface coordination is an effective strategy to solve the inherent interfacial incompatibility problem in CSEs.

Na2.5Cr0.5Zr0.5Cl6: A New Halide-Based Fast Sodium-Ion Conductor.

All-solid-state batteries employing solid electrolytes (SEs) have received widespread attention due to their high safety. Recently, lithium halides are intensively investigated as promising SEs while their sodium counterparts are less studied. Herein, a new sodium-ion conductor with a chemical formula of Na2.5Cr0.5Zr0.5Cl6 is reported, which exhibits high room temperature ionic conductivity of 0.1 mS cm-1 with low migration energy barrier of ≈0.41 eV. Na2.5Cr0.5Zr0.5Cl6 has a Fm-3m structure with 41.67 mol.% of cationic vacancies owing to the occupation of Cr (8.33 mol.%) and Zr (8.33 mol.%) ions at Na sites. Supercell calculations show that the lowest columbic energy configuration has Cr/Zr/V (where V is the vacancy) clusters in the structure. Nonetheless, the clusters have mixed effects on the sodium ion conduction pathway, based on the Bond Valence Energy Landscape calculation. A global 3D Na-ion transport percolation network can be revealed in the lowest energy supercell. Effective pathways are connected through the NaCl6 and VCl6 nodes. Besides, Raman spectroscopy and 23Na solid-state nuclear magnetic resonance spectroscopy further prove the tunable structure of the SEs with different Cr to Zr ratios. The optimization between the concentration of Na+ and vacancies is crucial to create an improved network of Na+ diffusion channels.

Transport Properties and Local Ions Dynamics in LATP-Based Hybrid Solid Electrolytes.

Hybrid solid electrolytes (HSEs), namely mixtures of polymer and inorganic electrolytes, have supposedly improved properties with respect to inorganic and polymer electrolytes. In practice, HSEs often show ionic conductivity below expectations, as the high interface resistance limits the contribution of inorganic electrolyte particles to the charge transport process. In this study, the transport properties of a series of HSEs containing Li(1+ x ) Alx Ti(2- x ) (PO4 )3 (LATP) as Li+ -conducting filler are analyzed. The occurrence of Li+ exchange across the two phases is proved by isotope exchange experiment, coupled with 6 Li/7 Li nuclear magnetic resonance (NMR), and by 2D 6 Li exchange spectroscopy (EXSY), which gives a time constant for Li+ exchange of about 50 ms at 60 °C. Electrochemical impedance spectroscopy (EIS) distinguishes a short-range and a long-range conductivity, the latter decreasing with LATP concentration. LATP particles contribute to the overall conductivity only at high temperatures and at high LATP concentrations. Pulsed field gradient (PFG)-NMR suggests a selective decrease of the anions' diffusivity at high temperatures, translating into a marginal increase of the Li+ transference number. Although the transport properties are only marginally affected, addition of moderate amounts of LATP to polymer electrolytes enhances their mechanical properties, thus improving the plating/stripping performance and processability.

Exploring the Cathode Active Materials for Sulfide-Based All-Solid-State Lithium Batteries with High Energy Density.

All-solid-state lithium batteries (ASSLBs) are considered promising alternatives to current lithium-ion batteries that employ liquid electrolytes due to their high energy density and enhanced safety. Among various types of solid electrolytes, sulfide-based electrolytes are being actively studied, because they exhibit high ionic conductivity and high ductility, which enable good interfacial contacts in solid electrolytes without sintering at high temperatures. To improve the energy density of the sulfide-based ASSLBs, it is essential to increase the loading of active material in the composite cathode. In this study, the Ni-rich LiNix Coy Mn1-x-y O2 (NCM) materials are explored with different Ni content, particle size, and crystalline form to probe suitable cathode active materials for high-performance ASSLBs with high energy density. The results reveal that single-crystalline LiNi0.82 Co0.10 Mn0.08 O2 material with a small particle size exhibits the best cycling performance in the ASSLB assembled with a high mass loaded cathode (active mass loading: 26 mg cm-2 , areal capacity: 5.0 mAh cm-2 ) in terms of discharge capacity, capacity retention, and rate capability.

Intercepting Dendrite Growth With a Heterogeneous Solid Electrolyte for Long-Life All-Solid-State Lithium Metal Batteries.

The application of lithium metal anode in all-solid-state batteries has the potential to achieve both high energy density and safety performance. However, the presence of serious dendrite issues hinders this potential. Here, the ion transport pathways and orientation of dendrite growth are regulated by utilizing the differences of ionic conductivity in heterogeneous electrolytes. The in situ formed Li-Ge alloy phases from the spontaneous reaction between Li10GeP2S12 and the attracted dendrites greatly enhance the ability to resist dendrite growth. As an outcome, the heterogeneous electrolyte achieves a high critical current density of 2.1 mA cm-2 and long-term stable symmetrical battery operation (0.3 mA cm-2 for 17 000 h and 1.0 mA cm-2 for 2000 h). Besides, due to the superior interfacial stability and low interface impedance between the heterogeneous electrolyte and lithium anode, the Li||LiNi0.8Co0.1Mn0.1O2 full battery exhibits great cycling stability (80.5% after 500 cycles at 1.0 mA cm-2) and rate performance (125.4 mAh g at 2.0 mA cm-2). This work provides a unique strategy of interface regulation via heterogeneous electrolytes design, offering insights into the development of state-of the-art all-solid-state batteries.

An Effective Catholyte for Sulfide-Based All-Solid-State Batteries Utilizing Gas Absorbents.

All-solid-state batteries (ASSBs) possess the advantage of ensuring safety while simultaneously maximizing energy density, making them suitable for next-generation battery models. In particular, sulfide solid electrolytes (SSEs) are viewed as promising candidates for ASSB electrolytes due to their excellent ionic conductivity. However, a limitation exists in the form of interfacial side reactions occurring between the SSEs and cathode active materials (CAMs), as well as the generation of sulfide-based gases within the SSE. These issues lead to a reduction in the capacity of CAMs and an increase in internal resistance within the cell. To address these challenges, cathode composite materials incorporating zinc oxide (ZnO) are fabricated, effectively reducing various side reactions occurring in CAMs. Acting as a semiconductor, ZnO helps mitigate the rapid oxidation of the solid electrolyte facilitated by an electronic pathway, thereby minimizing side reactions, while maintaining electron pathways to the active material. Additionally, it absorbs sulfide-based gases, thus protecting the lithium ions within CAMs. In this study, the mass spectrometer is employed to observe gas generation phenomena within the ASSB cell. Furthermore, a clear elucidation of the side reactions occurring at the cathode and the causes of capacity reduction in ASSB are provided through density functional theory calculations.

Local Structure in Disordered Melilite Revealed by Ultrahigh Field 71Ga and 139La Solid-State Nuclear Magnetic Resonance Spectroscopy.

Multinuclear Nuclear Magnetic Resonance (NMR) spectroscopy of quadrupolar nuclei at ultrahigh magnetic field provides compelling insight into the short-range structure in a family of fast oxide ion electrolytes with La1+xSr1-xGa3O7+0.5x melilite structure. The striking resolution enhancement in the solid-state 71Ga NMR spectra measured with the world's unique series connected hybrid magnet operating at 35.2 T distinctly resolves Ga sites in four- and five-fold coordination environments. Detection of five-coordinate Ga centers in the site-disordered La1.54Sr0.46Ga3O7.27 melilite is critical given that the GaO5 unit accommodates interstitial oxide ions and provides excellent transport properties. This work highlights the importance of ultrahigh magnetic fields for the detection of otherwise broad spectral features in systems containing quadrupolar nuclei and the potential of ensemble-based computational approaches for the interpretation of NMR data acquired for site-disordered materials.

Chemistry Aspects and Designing Strategies of Flexible Materials for High-Performance Flexible Lithium-Ion Batteries.

In recent years, flexible and wearable electronics such as smart cards, smart fabrics, bio-sensors, soft robotics, and internet-linked electronics have impacted our lives. In order to meet the requirements of more flexible and adaptable paradigm shifts, wearable products may need to be seamlessly integrated. A great deal of effort has been made in the last two decades to develop flexible lithium-ion batteries (FLIBs). The selection of suitable flexible materials is important for the development of flexible electrolytes self-supported and supported electrodes. This review is focused on the critical discussion of the factors that evaluate the flexibility of the materials and their potential path toward achieving the FLIBs. Following this analysis, we present how to evaluate the flexibility of the battery materials and FLIBs. We describe the chemistry of carbon-based materials, covalent-organic frameworks (COFs), metal-organic frameworks (MOFs), and MXene-based materials and their flexible cell design that represented excellent electrochemical performances during bending. Furthermore, the application of state-of-the-art solid polymer and solid electrolytes to accelerate the development of FLIBs is introduced. Analyzing the contributions and developments of different countries has also been highlighted in the past decade. In addition, the prospects and potential of flexible materials and their engineering are also discussed, providing the roadmap for further developments in this fast-evolving field of FLIB research.

Enhancing mechanical properties of composite solid electrolyte by ultra-high molecular weight polymers.

Composite solid electrolytes combining the advantages of inorganic and polymer electrolytes are considered as one of the promising candidates for solid-state lithium metal batteries. Compared with ceramic-in-polymer electrolyte, polymer-in-ceramic electrolyte displays excellent mechanical strength to inhibit lithium dendrite. However, polymer-in-ceramic electrolyte faces the challenges of lack of flexibility and severely blocked Li+transport. In this study, we prepared polymer-in-ceramic film utilizing ultra-high molecular weight polymers and ceramic particles to combine flexibility and mechanical strength. Meanwhile, the ionic conductivity of polymer-in-ceramic electrolytes was improved by adding excess lithium salt in polymer matrix to form polymer-in-salt structure. The obtained film shows high stiffness (10.5 MPa), acceptable ionic conductivity (0.18 mS cm-1) and high flexibility. As a result, the corresponding lithium symmetric cell stably cycles over 800 h and the corresponding LiFePO4cell provides a discharge capacity of 147.7 mAh g-1at 0.1 C without obvious capacity decay after 145 cycles.

Piperazinium Poly(Ionic Liquid)s as Solid Electrolytes for Lithium Batteries.

Poly(ionic liquid)s combine the unique properties of ionic liquids (ILs) within ionic polymers holding significant promise for energy storage applications. It is reported here the synthesis and characterization of a new family of poly(ionic liquid)s synthesized from cationic piperazinium ionic liquid monomers. The cationic poly(acrylamide piperazinium) in combination with sulfonamide anions like bis(trifluoromethanesulfonyl) imide (TFSI) and bis(fluorosulfonyl) imide (FSI) are characterized as solid polymer electrolytes. The polymer electrolytes in combination with pyrrolidonium ILs and LiFSI show high ionic conductivity, 5×10-3 S cm-1 at 100 °C. Piperazinium polymer electrolytes show excellent compatibility with lithium metal reversible plating and stripping at high current density and low temperature 40 °C.

A theoretical perspective on solid-state ionic interfaces.

Solid-state ionic conductors find application across various domains in materials science, particularly showcasing their significance in energy storage and conversion technologies. To effectively utilize these materials in high-performance electrochemical devices, a comprehensive understanding and precise control of charge carriers' distribution and ionic mobility at interfaces are paramount. A major challenge lies in unravelling the atomic-level processes governing ion dynamics within intricate solid and interfacial structures, such as grain boundaries and heterophases. From a theoretical viewpoint, in this Perspective article, my focus is to offer an overview of the current comprehension of key aspects related to solid-state ionic interfaces, with a particular emphasis on solid electrolytes for batteries, while providing a personal critical assessment of recent research advancements. I begin by introducing fundamental concepts for understanding solid-state conductors, such as the classical diffusion model and chemical potential. Subsequently, I delve into the modelling of space-charge regions, which are pivotal for understanding the physicochemical origins of charge redistribution at electrified interfaces. Finally, I discuss modern computational methods, such as density functional theory and machine-learned potentials, which offer invaluable tools for gaining insights into the atomic-scale behaviour of solid-state ionic interfaces, including both ionic mobility and interfacial reactivity aspects. This article is part of the theme issue 'Celebrating the 15th anniversary of the Royal Society Newton International Fellowship'.

Atomic-Resolution Electron Microscopy Unravelling the Role of Unusual Asymmetric Twin Boundaries in the Electron-Beam-Sensitive NASICON-Type Solid Electrolyte.

An atomic-scale understanding of the role of nonperiodic features is essential to the rational design of highly Li-ion-conductive solid electrolytes. Unfortunately, most solid electrolytes are easily damaged by the intense electron beam needed for atomic-resolution electron microscopy observation, so the reported in-depth atomic-scale studies are limited to Li0.33La0.56TiO3- and Li7La3Zr2O12-based materials. Here, we observe on an atomic scale a third type of solid electrolyte, Li1.3Al0.3Ti1.7(PO4)3 (LATP), through minimization of damage induced by specimen preparation. With this capability, LATP is found to contain large amounts of twin boundaries with an unusual asymmetric atomic configuration. On the basis of the experimentally determined structure, the theoretical calculations suggest that such asymmetric twin boundaries may considerably promote Li-ion transport. This discovery identifies a new entry point for optimizing ionic conductivity, and the method presented here will also greatly benefit the mechanistic study of solid electrolytes.

Toluene Tolerated Li9.88GeP1.96Sb0.04S11.88Cl0.12 Solid Electrolyte toward Ultrathin Membranes for All-Solid-State Lithium Batteries.

Sulfide solid electrolyte membranes employed in all-solid-state lithium batteries generally show high thickness and poor chemical stability, which limit the cell-level energy density and cycle life. In this work, Li9.88GeP1.96Sb0.04S11.88Cl0.12 solid electrolyte is synthesized with Sb, Cl partial substitution of P, S, possessing excellent toluene tolerance and stability to lithium. The formed SbS43- group in Li9.88GeP1.96Sb0.04S11.88Cl0.12 exhibits low adsorption energy and reactivity for toluene molecules, confirmed by first-principles density functional theory calculation. Using toluene as the solvent, ultrathin Li9.88GeP1.96Sb0.04S11.88Cl0.12 membranes with adjustable thicknesses can be well prepared by the wet coating method, and an 8 µm thick membrane exhibits an ionic conductivity of 1.9 mS cm-1 with ultrahigh ionic conductance of 1860 mS and ultralow areal resistance of 0.68 Ω cm-2 at 25 °C. The obtained LiCoO2|Li9.88GeP1.96Sb0.04S11.88Cl0.12 membrane|Li all-solid-state lithium battery shows an initial reversible capacity of 125.6 mAh g-1 with a capacity retention of 86.3% after 250 cycles at 0.1 C under 60 °C.

Alternate Crystal Structure Achieving Ionic Conductivity above 1 mS cm-1 in Cost-Effective Zr-Based Chloride Solid Electrolytes.

The realization of practical, commercial all-solid-state Li batteries requires the solid electrolyte to possess not only high ionic conductivity (above 1 mS cm-1 at 25 °C) but also low cost (below $50/kg). Unlike most of the present solid electrolytes, the recently reported Zr-based chloride solid electrolytes generally cost less than $50/kg, but their ionic conductivities at 25 °C are below 1 mS cm-1. Here, a Li-ion conductivity of 1.35 mS cm-1 at 25 °C and an estimated material cost of $11.09/kg are achieved simultaneously in a Li3Zr0.75OCl4 solid electrolyte. Unlike other Zr-based chloride systems, Li3Zr0.75OCl4 does not exhibit the trigonal structure, but is isostructural with Li3ScCl6, whose monoclinic structure allows for much faster ion transport. With such desirable characteristics, the all-solid-state cell formed by LiNi0.8Mn0.1Co0.1O2 and Li3Zr0.75OCl4 shows a capacity retention above 80.9% for 700 cycles at 25 °C and 5 C (975 mA g-1).

A Cost-Effective Sulfide Solid Electrolyte Li7P3S7.5O3.5 with Low Density and Excellent Anode Compatibility.

The commercialization of all-solid-state Li batteries (ASSLBs) demands solid electrolytes with strong cost-competitiveness, low density (for enabling satisfactory energy densities), and decent anode compatibility (the need for cathode compatibility can be circumvented by the cathode coating techniques that are widely applied in sulfide-based ASSLBs). However, none of the reported oxide, sulfide, or chloride solid electrolytes meets these requirements simultaneously. Here, we design a Li7P3S7.5O3.5 (LPSO) solid electrolyte, which shows a combination of all the aforementioned characteristics. The synthesis of this material does not need the expensive Li2S, so the raw materials cost is only $14.42/kg, which, unlike most solid electrolytes, lies below the $50/kg threshold for commercialization. The density of LPSO is 1.70 g cm-3, considerably lower than those of the oxide (typically above 5 g cm-3) and chloride (around 2.5 g cm-3) solid electrolytes. Besides, LPSO also shows excellent anode compatibility. The Li|LPSO|Li cell cycles stably with a potential of ~50 mV under 0.1 mA cm-2 for over 4200 h at 25 °C, and the all-solid-state pouch cell with the Si anode shows a capacity retention of 89.29 % after 200 cycles under 88.6 mA g-1 at 60 °C.

Superionic Conduction in K3SbS4 Enabled by Cl-Modified Anion Lattice.

All-solid-state potassium batteries emerge as promising alternatives to lithium batteries, leveraging their high natural abundance and cost-effectiveness. Developing potassium solid electrolytes (SEs) with high room-temperature ionic conductivity is critical for realizing efficient potassium batteries. In this study, we present the synthesis of K2.98Sb0.91S3.53Cl0.47, showcasing a room-temperature ionic conductivity of 0.32 mS/cm and a low activation energy of 0.26 eV. This represents an increase of over two orders of magnitude compared to the parent compound K3SbS4, marking the highest reported ionic conductivity for non-oxide potassium SEs. Solid-state 39K magic-angle-spinning nuclear magnetic resonance on K2.98Sb0.91S3.53Cl0.47 reveals an increased population of mobile K+ ions with fast dynamics. Ab initio molecular dynamics (AIMD) simulations further confirm a delocalized K+ density and significantly enhanced K+ diffusion. This work demonstrates diversification of the anion sublattice as an effective approach to enhance ion transport and highlights K2.98Sb0.91S3.53Cl0.47 as a promising SE for all-solid-state potassium batteries.