Inorganic solid electrolytes, in comparison with their liquid counterparts, have more potential in varioust ypes of batteries due to their dual roles of ion transportation and separation. For all-solid-state batteries, solide lectrolytes bring several advantages, [1][2][3][4][5][6] such as enhanced safety,i ncreased energy density,s olid device integration, and packaging;t hese expand the operation temperature range and potentially improve cycling stabilitya nd lifetime. Moreover,i norganic solid electrolytes are also beneficial for lithium-ion batteries and lithium-air batteries, in which they functiona se ither surface modification layers or lithium-ion conductors. [7,8] In principle, ideal solid electrolytes are expected to have several features: [9][10][11][12][13][14] 1) fast ion dynamics and negligible electronic conductivity (minimum ionic conductivity of 10 À4 Scm À1 at room temperature for practical consideration);2 )a wide electrochemical potential window for battery cycling;3 )ane xceptional mechanical strength to suppress lithium dendrite growth;4 )excellent thermal stability during the cycling processes;and 5) asimple and low cost synthetic process for large-scale applications.Generally,i norganic lithium superionic conductors are divided into three categories:o xides, sulfides, and phosphates. Suc-cessfule xamples in oxidesi nclude garnet oxides, [15,16] perovskite-type oxides, [17,18] and antiperovskite oxides. [19][20][21] Sulfide solid electrolytes include Li 2 SÀP 2 S 5 , [22,23] Li 3 PS 4 , [24][25][26] Li 7 P 3 S 11 , [27,28] Li 7 PS 6 ,a nd Li 6 PS 5 X( X = Cl, Br). [29][30][31] Popular phosphate solid electrolytes include sodium superionic conductor (NaSICON)structured lithium-ion conductors, [32][33][34][35][36] such as LiTi 2 (PO 4 ) 3 (LTP), Li 1 + x Al x Ti 2Àx (PO 4 ) 3 (LATP), and Li 1 + x Al x Ge 2Àx (PO 4 ) 3 (LAGP). Many exciting discoveries of these materials have been summarized in important review papers. [2,6,[37][38][39][40] NaSICON-type solid electrolytes, such as LATP and LAGP, have marked advantages compared with sulfides and oxides: they display chemicals tabilityi na ir and/or water,a re low cost and low toxicity,a nd have great electrochemical stability with the added benefito fe asy preparation. [2,36,38] They also exhibit attractive ionic conductivities of 10 À4 -10 À3 Scm À1 at room temperature. Such features have recently caused renewed interest in these NaSICON-structured materials and much effort has been devoted to the investigation of this type of solid electrolyte, especiallyL ATPa nd LAGP.T his manuscript reviewsr ecent progress in LATP and LAGP solid electrolytes, with as pecific focus on synthetic approaches and their effects on the crystal structures, conductive properties, and applications. Herein, general synthetic methods for LATP and LAGP solid electrolytes are first introduced, followed by ac omparison of the crystal structures, phase purities, and ionic conductivities that result from different approaches. Later,t he applications of LATP and LAGP in ful...

Strongly anharmonic low-energy phonons enable the fast diffusion of Na ions in the solid-state electrolyte compound Na3PS4.

Solid electrolytes are the key to realize future solid-state batteries that show the advantages of high energy density and intrinsic safety. However, most solid electrolytes require long time and energy-consuming synthesis conditions of either extended ball milling or high-temperature solid-state reactions, impeding practical applications of solid electrolytes for large-scale systems. Here, we report a new and rapid liquid-based synthetic method for preparing a high-purity Li7PS6 solid electrolyte through the stoichemical reaction of Li3PS4 and Li2S. This method relies on facile and low-cost solution-based soft chemistry to complete chemical reaction in extensively short time (2 h). The prepared Li7PS6 solid electrolyte shows a high phase purity, an impressive ionic conductivity (0.11 mS cm–1), and a reasonable electrochemical stability with a metallic lithium anode. Our results highlight the use of an economic and nontoxic solvent to quickly synthesize a Li7PS6 solid electrolyte, which would promote the development of solid-state batteries for next-generation energy storage systems.

Inorganic Na-ion superionic conductors play a vital role in all-solid-state Na batteries that operate at room temperature. Sodium thioantimonate (Na3SbS4), a popular sulfide-based solid electrolyte, has attracted serious attention due to its advantages of high ionic conductivity at room temperature and impressive chemical stability under ambient conditions. Much research detailing Na3SbS4 focused on its synthetic approaches and interfacial stability against Na metal, yet, there is limited information elucidating a fundamental understanding of the Na-ion diffusion mechanisms in Na3SbS4 with different crystal structures (e.g., tetragonal and cubic). Herein, we combine real-time electrochemical impedance measurements with theoretical simulations based on density functional theory and  in situ quasi-elastic neutron scattering to study the Na-ion conductive properties of Na3SbS4 during its phase transition from a tetragonal to cubic structure. Although there is a slight change in the lattice parameters, the energy barrier for Na-ion diffusion in the tetragonal structure was determined to be much larger (5–10 times) than that in the cubic structure from both theoretical and experimental perspectives. The high degree of symmetry in cubic Na3SbS4 leads to less interatomic correlations between Na and S­(Sb) atoms, a shorter jump distance (2.85 Å), and a larger diffusion coefficient. This research provides insight into understanding the Na-ion diffusion in solid electrolytes with phase transitions and provides fundamental guidance for designing novel solid-state Na-ion conductors.

Sulfide-based lithium (Li)-ion conductors represent one of the most popular solid electrolytes (SEs) for solid-state Li metal batteries (SSLMBs) with high safety. However, the commercial application of sulfide SEs is significantly limited by their chemical instability in air and electrochemical instability with electrode materials (metallic Li anode and oxide cathodes). To address these difficulties, here, we design and successfully demonstrate a novel sulfide-incorporated composite electrolyte (SCE) through the combination of inorganic sulfide Li argyrodite (Li7PS6) with poly­(vinylidenefluoride-co-hexafluoropropylene) (PVDF-HFP) polymer. In this composite structure, Li7PS6 is embedded in PVDF-HFP polymer matrix, making the SCE flexible and air-stable and achieve great chemical and electrochemical stability. Meanwhile, the presence of sulfide facilitates Li-ion transport in SCE, leading to a superior room-temperature ionic conductivity of 1.1 × 10–4 S cm–1. Using the SCE with enhanced stability while maintaining high conductivity, Li||Li symmetric cells achieved stable cycling up to 1000 h at 0.2 mA cm–2. In addition, LiFePO4 (LFP)||SCE||Li cells can deliver an impressive specific capacity of 160 mAh g–1 over 150 cycles. These features indicate that Li7PS6/PVDF-HFP SCE is a promising candidate to contribute to the practical development of SSLMBs.

Utilizing Li-ion conductors as solid electrolytes is essential in solid-state lithium (Li) batteries (SSLBs), which is a promising solution for the next-generation electrochemical energy storage systems that require high energy and high levels of safety. Among various Li-ion conductors, Li1.5Al0.5Ti1.5(PO4)3 (LATP), a NASICON-type ceramic, has attracted intensive attention due to its advantages of air stability and fast Li+ conductivity. However, to reach a decent ionic conductivity and reduce grain boundary resistance, LATP requires high temperatures for densification, which is time-consuming and expensive for large-scale applications. Herein, we report a simple solution-casting synthesis for new composite solid electrolytes by embedding LATP ceramic into a PVdF–HFP matrix. In the LATP/PVdF–HFP composite solid membranes, the NASICON-type crystal structure of LATP is well maintained. Without taking any additional liquid electrolyte absorption, the prepared composite solid electrolytes with 10 wt % LATP show the highest ionic conductivity of 2.3 × 10–4 S cm–1 at room temperature, three times higher than that of polymer electrolyte (7.1 × 10–5 S cm–1). In addition, the Li||LiFePO4 (LFP) battery with LATP/PVdF–HFP composite electrolyte exhibits enhanced cycling performance of both capacity and stability as compared to the polymer electrolyte-based battery.

Solid-state lithium metal batteries (SSLMBs) that utilize novel solid electrolytes (SEs) have garnered much attention because of their potential to yield safe and high-energy-density batteries. Sulfide-based argyrodite-class SEs are an attractive option because of their impressive ionic conductivity. Recent studies have shown that LiF at the interface between Li and SE enhances electrochemical stability. However, the synthesis of F-doped argyrodites has remained challenging because of the high temperatures used in the state-of-the-art solid-state synthesis methods. In this work, for the f irst time, we report F-doped Li 5+y PS 5 F y argyrodites with a tunable doping content and dual dopants (F − /Cl − and F − /Br − ) that were synthesized through a solvent-based approach. Among all compositions, Li 6 PS 5 F 0.5 Cl 0.5 exhibits the highest Li-ion conductivity of 3.5 × 10 −4 S cm −1 at room temperature (RT). Furthermore, Li symmetric cells using Li 6 PS 5 F 0.5 Cl 0.5 show the best cycling performance among the tested cells. X-ray photoelectron spectroscopy and ab initio molecular dynamics simulations revealed that the enhanced interfacial stability of Li 6 PS 5 F 0.5 Cl 0.5 SE against Li metal can be attributed to the formation of a stable solid electrolyte interphase (SEI)-containing conductive species (Li 3 P), alongside LiCl and LiF. These findings open new opportunities to develop high-performance SSLMBs using a novel class of F-doped argyrodite electrolytes.

All-solid-state batteries that employ superionic solid conductor potentially enable the broadening of battery operation in harsh environments, such as under subzero temperatures and even lower. The solid electrolyte as the key component requires structural stability, high-efficiency of ion transportation channels, and low activation energy to maintain the fast-ionic conduction against temperature drop. Herein, we use 3D superionic conductor Na 3 SbS 4 as a model to investigate the structure and conductive mechanism at extremely low temperature. Cryogenic in situ neutron and X-ray diffractions reveal that Na 3 SbS 4 maintains a stable tetragonal crystal structure and the anisotropic lattice contraction upon cooling. The dimensions of the S-gate (represented by the S−S pair length) that Na ions hop through in the 3D transportation network is found to maintain open sizes in the xy-plane, contributing to the low activation energy and impressive ionic conductivity. The Na-ion transportation network is demonstrated to be directionally accessible at the extremely low temperature, which reveals the ion conductive mechanism at broadened temperature range in the view of structure. These findings provide valuable guidance in the search for materials as promising solid electrolyte in solidstate batteries to fulfill harsh environmental needs.