Chemistry Design Towards a Stable Sulfide-Based Superionic Conductor Li4 Cu8 Ge3 S12

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

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

Regenerative Solid Interfaces Enhance High-Performance All-Solid-State Lithium Batteries

The performance of all-solid-state lithium batteries (ASSLBs) is significantly impacted by lithium interfacial instability, which originates from the dynamic chemical, morphological, and mechanical changes during deep Li plating and stripping. In this study, we introduce a facile approach to generate a conductive and regenerative solid interface, enhancing both the Li interfacial stability and overall cell performance. The regenerative interface is primarily composed of nanosized lithium iodide (nano-LiI), which originates in situ from the adopted solid-state electrolyte (SSE). During cell operation, the nano-LiI interfacial layer can reversibly diffuse back and forth in synchronization with Li plating and stripping. The interface and dynamic process improve the adhesion and Li+ transport between the Li anode and SSE, facilitating uniform Li plating and stripping. As a result, the metallic Li anode operates stably for over 1000 h at high current densities and even under elevated temperatures. By using metallic Li as the anode directly, we demonstrate stable cycling of all-solid-state Li-sulfur batteries for over 250 cycles at an areal capacity of >2 mA h cm-2 and room temperature. This study offers insights into the design of regenerative and Li+-conductive interfaces to tackle solid interfacial challenges for high-performance ASSLBs.

Computational approach inspired advancements of solid-state electrolytes for lithium secondary batteries: from first-principles to machine learning

The increasing demand for high-security, high-performance, and low-cost energy storage systems (EESs) driven by the adoption of renewable energy is gradually surpassing the capabilities of commercial lithium-ion batteries (LIBs). Solid-state electrolytes (SSEs), including inorganics, polymers, and composites, have emerged as promising candidates for next-generation all-solid-state batteries (ASSBs). ASSBs offer higher theoretical energy densities, improved safety, and extended cyclic stability, making them increasingly popular in academia and industry. However, the commercialization of ASSBs still faces significant challenges, such as unsatisfactory interfacial resistance and rapid dendrite growth. To overcome these problems, a thorough understanding of the complex chemical-electrochemical-mechanical interactions of SSE materials is essential. Recently, computational methods have played a vital role in revealing the fundamental mechanisms associated with SSEs and accelerating their development, ranging from atomistic first-principles calculations, molecular dynamic simulations, multiphysics modeling, to machine learning approaches. These methods enable the prediction of intrinsic properties and interfacial stability, investigation of material degradation, and exploration of topological design, among other factors. In this comprehensive review, we provide an overview of different numerical methods used in SSE research. We discuss the current state of knowledge in numerical auxiliary approaches, with a particular focus on machine learning-enabled methods, for the understanding of multiphysics-couplings of SSEs at various spatial and time scales. Additionally, we highlight insights and prospects for SSE advancements. This review serves as a valuable resource for researchers and industry professionals working with energy storage systems and computational modeling and offers perspectives on the future directions of SSE development.

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

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

Sb-doped Li10GeP2S12-type electrolyte Li10SnP2-xSbxS12 with enhanced ionic conductivity and lower lithium-ion migration barrier

Li₁₀SnP₂S₁₂ (LSPS) has been regarded as a promising solid electrolyte because of its higher ionic conductivity and lower cost. In this work, P sites of LSPS are partially substituted with Sb by the solid-phase sintering method. A series of Li₁₀SnP_2-xSb_xS₁₂ (0 ≤ x ≤ 0.4) solid electrolytes are prepared. Among them, the ionic conductivity of the Li₁₀SnP_1.8Sb_0.2S₁₂ solid electrolyte reaches 2.43 mS cm^-1. Through X-ray diffraction and refinement analysis, it is found that Sb successfully substituted part of P and increased the lattice constant. Through temperature-dependent alternating current impedance experiments and density functional theory calculations, it is found that the main reasons for the increase in ionic conductivity are the reduction of activation energy and the energy barrier of the Li⁺ migration path around Sb. The improved air stability of the electrolyte after Sb doping conforms to the Hard-Soft-Acid-Base theory. Furthermore, the assembled all-solid-state battery with Li₁₀SnP_1.8Sb_0.2S₁₂ exhibits a high specific capacity and good cycling stability than LSPS.

Insights into interfacial chemistry of Ni-rich cathodes and sulphide-based electrolytes in all-solid-state lithium batteries

All-solid-state lithium batteries (ASSLBs) have attracted increasing attention recently because they are more safe and have higher energy densities than conventional lithium-ion batteries. In particular, ASSLBs composed of Ni-rich cathodes, sulphide-based solid-state electrolytes (SSEs) and lithium metal anodes have been regarded as the most competitive candidates. Ni-rich cathodes possess high operating potential, high specific energy and low cost, and sulphide-based SSEs have excellent ionic conductivity comparable to that of liquid electrolytes. However, severe parasitic reactions and chemo-mechanical issues hinder their practical application. Herein, the structure, ionic conductivity, chemical or electrochemical stability and mechanical property of sulphide-based SSEs are introduced. Critical interfacial problems between Ni-rich cathodes and sulphide-based SSEs, including chemical or electrochemical parasitic reactions, space charge layer effect, mechanical stress and contact loss, are summarised. The corresponding solutions including coating layer construction and structure design are expounded. Finally, the remaining challenges are discussed, and perspectives are outlined to provide guidelines for the future development of ASSLBs.

Investigation into Structural Variation from 3D to 1D and Strong Second Harmonic Generation of the AHgPS4 (A+ = Na+, K+, Rb+, Cs+) Family

The continuous exploration of multinary chalcogenide semiconductors has provided a variety of new functional materials. In this paper, four new quaternary chalcogenides AHgPS₄ (A⁺ = Na⁺, K⁺, Rb⁺, Cs⁺) have been prepared by solid-state syntheses. These findings complement the lack of research on this quaternary system. Influenced by the size effect of cations and the coordination mode of Hg, the four compounds crystallize in four different space groups [NaHgPS₄, P4̅n2; KHgPS₄, Pnn2; RbHgPS₄, P2₁/n; CsHgPS₄, P2₁2₁2₁] and show an interesting evolution from a 3D framework structure to a 1D chain structure. Moreover, all of these compounds feature noncentrosymmetric (NCS) structures except for RbHgPS₄. The materials exhibit wide band gaps of 2.7 eV < E_g < 3.0 eV. The NCS- related second-harmonic-generation (SHG) property of NaHgPS₄ and KHgPS₄ was also studied. They display strong powder SHG responses (3.14 × AgGaS₂ for NaHgPS₄; 4.15 × AgGaS₂ for KHgPS₄), which indicate their intriguing potential as IR nonlinear-optical materials. Moreover, first-principles theoretical calculations were performed to understand the structure-property relationships of these materials.

Superior All-Solid-State Batteries Enabled by a Gas-Phase-Synthesized Sulfide Electrolyte with Ultrahigh Moisture Stability and Ionic Conductivity

Sulfide solid electrolytes (SEs) are recognized as one of the most promising candidates for all-solid-state batteries (ASSBs), due to their superior ionic conductivity and remarkable ductility. However, poor air stability, complex synthesis process, low yield, and high production cost obstruct the large-scale application of sulfide SEs. Herein, a one-step gas-phase synthesis method for sulfide SEs with oxide raw materials in ambient air, completely getting rid of the glovebox and thus making large-scale production possible, is reported. By adjusting substituted elements and concentrations, the ionic conductivity of Li_{4- x} Sn_{1- x} M_x S₄ can reach 2.45 mS cm^-1 , which represents the highest value among all reported moist-air-stable and recoverable lithium-ion sulfide SEs reported. Furthermore, ASSBs with air/water-exposed and moderate-temperature-treated Li_3.875 Sn_0.875 As_0.125 S₄ even maintains superior performances with the highest reversible capacity (188.4 mAh g^-1 ) and the longest cycle life (210 cycles), which also breaks the record. Therefore, it may become one of the most critical breakthroughs during the development of sulfide ASSBs toward its practical application and commercialization.

Sodium-Stuffed Open-Framework Quaternary Chalcogenide Built with (Cu2Ga6S18)16- Ribbons Cross-Linked by Unusual Linear Cu(I) Pillars

A quaternary compound, Na₁₅Cu₃Ga₆S₁₈, the first member in the A-Cu-Ga-S (A = alkali metal) series, has been synthesized from a solid-state metathesis reaction between Na₆Ga₂S₆ and CuCl as well as from a combination of Na₂S, Ga, Cu, and S. The compound crystallizes in a monoclinic crystal system, space group C2/c, and represents a unique open-framework structure with channels filled with eight crystallographically distinct Na ions. The anionic framework is built up of infinite chains of corner-shared GaS₄ tetrahedra fused together by an edge-shared dimer of CuS₄ tetrahedra forming one-dimensional ribbons of (Cu₂Ga₆S₁₈)^16-, which are cross-linked by linearly coordinated S-Cu-S linkages resulting in a three-dimensional network with tunnels filled with Na atoms. Optical band gap measurements show that the compound has a direct band gap of 3.00 eV that is in good agreement with the theoretical band gap derived from density functional theory calculations. Band structure calculations further indicate that the states near the Fermi level are dominated by tetrahedral Cu⁺(d) and S(p) states resulting from the antibonding interactions, while s-d hybridization is prevalent in linear Cu⁺ coordination. Ionic conductivity measurements show that the compound has a room-temperature Na ion conductivity of 2.72 × 10^-5 mS/cm with an activation energy of 0.68 eV, which corroborates well the nudged elastic band calculations.

Recent Development of Mg Ion Solid Electrolyte

Although the successful deployment of lithium-ion batteries (LIBs) in various fields such as consumer electronics, electric vehicles and electric grid, the efforts are still ongoing to pursue the next-generation battery systems with higher energy densities. Interest has been increasing in the batteries relying on the multivalent-ions such as Mg²⁺, Zn²⁺, and Al³⁺, because of the higher volumetric energy densities than those of monovalent-ion batteries including LIBs and Na-ion batteries. Among them, magnesium batteries have attracted much attention due to the promising characteristics of Mg anode: a low redox potential (−2.356 V vs. SHE), a high volumetric energy density (3,833 mAh cm⁻³), atmospheric stability and the earth-abundance. However, the development of Mg batteries has progressed little since the first Mg-ion rechargeable battery was reported in 2000. A severe technological bottleneck concerns the organic electrolytes, which have limited compatibility with Mg anode and form an Mg-ion insulating passivation layer on the anode surface. Consequently, beneficial to the good chemical and mechanical stability, Mg-ion solid electrolyte should be a promising alternative to the liquid electrolyte. Herein, a mini review is presented to focus on the recent development of Mg-ion solid conductor. The performances and the limitations were also discussed in the review. We hope that the mini review could provide a quick grasp of the challenges in the area and inspire researchers to develop applicable solid electrolyte candidates for Mg batteries.

New quaternary chalcogenide Ba4HgAs2S10 originating from the combination of linear [HgS2]2− and tetrahedral [AsS4]3− modules

A new quaternary chalcogenide Ba₄HgAs₂S₁₀ is constructed by combining linear HgS₂²⁻ and tetrahedral AsS₄³⁻ modules.

Two rare-earth-based quaternary chalcogenides EuCdGeQ4 (Q = S, Se) with strong second-harmonic generation

Two RE-based quaternary metal chalcogenides EuCdGeQ₄ (Q = S, Se) are discovered. They possess many attractive properties as preferred IR NLO materials including large band gaps, phase-matched intense SHG and congruent melting behavior.