New Amorphous Oxy-Sulfide Solid Electrolyte Material: Anion Exchange, Electrochemical Properties, and Lithium Dendrite Suppression via In Situ Interfacial Modification

Improved air-stability and conductivity in the 75Li2S·25P2S5 solid-state electrolyte system: the role of Li7P3S11

Doping modification is regarded as a simple and effective method for increasing the ionic conductivity and air stability of solid state electrolytes. In this work, a series of (100-x)(0.75Li2S·0.25P2S5)·xP2O5 (mol%) (x = 0, 1, 2, 3 and 4) glass-ceramic electrolytes were synthesized by a two-step ball milling technique. Various characterization techniques (including powder X-ray diffraction, Raman and solid-state nuclear magnetic resonance) have proved that the addition of P2O5 can stimulate 75Li2S·25P2S5 system to generate the high ionic conductivity phase Li7P3S11. Through the doping optimization strategy, 98(0.75Li2S·0.25P2S5)·2P2O5 glass-ceramic (2PO) not only had a 3.6 times higher ionic conductivity than the undoped sample but also had higher air stability. Its ionic conductivity remained in the same order of magnitude after 10 minutes in the air. We further investigated the reasons why 2PO has a relatively high air stability using powder X-ray diffraction and scanning electron microscopy in terms of crystal structure degradation and morphology changes. In comparison to the undoped sample, the high ionic conductivity phases (β-Li3PS4 and Li7P3S11) of 2PO were better preserved, and less impurity and unknown peaks were generated over a short period of exposure time. In addition, the morphology of 2PO only changed slightly after 10 minutes of exposure. Despite the fact that the particles aggregated significantly after several days of exposure, 2PO tended to form a protective layer composed of S8, which might allow some particles to be shielded from attack by moisture, slowing down the decay of material properties.

Effects of LiPON Incorporation on the Structures and Properties of Mixed Oxy-Sulfide-Nitride Glassy Solid Electrolytes

Glassy solid electrolytes (GSEs) are promising solid electrolytes in the development of all solid-state batteries. Mixed oxy-sulfide nitride (MOSN) GSEs combine the high ionic conductivity of sulfide glasses, the excellent chemical stability of oxide glasses, and the electrochemical stability of nitride glasses. However, the reports on the synthesis and characterization of these novel nitrogen containing electrolytes are quite limited. Therefore, the systematic incorporation of LiPON during glass synthesis was used to explore the effects of nitrogen and oxygen additions on the atomic-level structures in the glass transition (T_g) and crystallization temperature (T_c) of MOSN GSEs. The MOSN GSE series 58.3Li₂S + 31.7SiS₂ + 10[(1 - x)Li_0.67PO_2.83 + x LiPO_2.53N_0.314], x = 0.0, 0.06, 0.12, 0.2, 0.27, 0.36, was prepared by melt-quench synthesis. Differential scanning calorimetry was used to determine the T_g and T_c values of these glasses. Fourier transformation-infrared, Raman, and magic angle spinning nuclear magnetic resonance spectroscopies were used to examine the short-range order structures of these materials. X-ray photoelectron spectroscopy was conducted on the glasses to further understand the bonding environments of the doped nitrogen. Finally, N and S elemental analyses were used to confirm the composition of these GSEs. These results are used to elucidate the structure of these glasses and to understand the thermal property impact oxygen and nitrogen doping in these GSEs.

Tremella-like Vanadium Tetrasulfide as a High-Performance Cathode Material for Rechargeable Aluminum Batteries

Rechargeable aluminum batteries (RABs) are gaining widespread attention for large-scale energy storage applications as a result of their high energy densities, high security, and abundance. The key to sustain the progress of RABs lies in the quest for the proper cathode materials with prominent capacity and reversible cycle life. Herein, we propose a tremella-like VS₄ as a cathode material aiming to tackle this problem. Obtained from a morphology modification process, VS₄ with a unique nanosheet structure provides sufficient active sites for intercalation and conversion reactions, shortens the transport paths for charge carrier ions, and facilitates the infiltration process for electrolyte. The RAB with the VS₄ cathode exhibits excellent electrochemical performance, including outstanding specific capacity (407.9 mAh g^-1) and stable cycling performance (∼300 cycles at a high current density). The energy storage mechanism has been comprehensively investigated and is confirmed to be a combination of the intercalation/deintercalation of Al³⁺ and AlCl₄^- ions and conversion reaction by various techniques and DFT calculation. Our study not only provides a peculiar and simple strategy for the rational design of metal sulfide cathode materials with high capacity and long-term stability but also proposes a specific energy storage mechanism that guides the development of cathode materials of RABs in the future.

Enhancing the Interfacial Stability of the Li2S-SiS2-P2S5 Solid Electrolyte toward Metallic Lithium Anode by LiI Incorporation

Chalcogenide solid-state electrolytes (SEs) have been regarded as promising candidates for lithium dendrite suppression due to their high ionic conductivity, suitable mechanical strength, and large Li⁺ ion transference number. However, the wide applications of SEs in pragmatic all-solid-state batteries are still retarded by their limited interface stability, which leads to lithium dendrite growth and formation of interphase with high resistance. In addition, the interphase evolution mechanism between SEs and metallic Li anodes remains unclear. Herein, this work demonstrates that the interfacial stability of Li₂S-SiS₂-P₂S₅ SEs can be effectively enhanced by tuning the interphase through LiI incorporation. This strategy contributes to a high ionic conductivity of the SEs and electronic insulation interphase containing LiI. Thus, the 70(60Li₂S-28SiS₂-12P₂S₅)-30 LiI SEs prepared by melt-quenching exhibit a high ionic conductivity of 1.74 mS cm^-1 at room temperature and a larger critical current density of 1.65 mA cm^-2 at 65 °C. The cycling life of the symmetric Li|SEs|Li cell is up to 200 h without significant resistance growth at 0.1 mA cm^-2 at room temperature. This enhanced interface stability is revealed to originate from the in situ-formed LiI within the interphase, which prevents continual SEs degradation and suppresses lithium dendrite growth. This work provides a vital understanding of interphase evolution, which is valuable for designing SEs with long cycling stability.

Enhancing Moisture Stability of Sulfide Solid-State Electrolytes by Reversible Amphipathic Molecular Coating

The all-solid-state battery (ASSB) is a promising next-generation energy storage technology for both consumer electronics and electric vehicles because of its high energy density and improved safety. Sulfide solid-state electrolytes (SSEs) have merits of low density, high ionic conductivity, and favorable mechanical properties compared to oxide ceramic and polymer materials. However, mass production and processing of sulfide SSEs remain a grand challenge because of their poor moisture stability. Here, we report a reversible surface coating strategy for enhancing the moisture stability of sulfide SSEs using amphipathic organic molecules. An ultrathin layer of 1-bromopentane is coated on the sulfide SSE surface (e.g., Li₇P₂S₈Br_0.5I_0.5) via Van der Waals force. 1-Bromopentane has more negative adsorption energy with SSEs than H₂O based on first-principles calculations, thereby enhancing the moisture stability of SSEs because the hydrophobic long-chain alkyl tail of 1-bromopentane repels water molecules. Moreover, this amphipathic molecular layer has a negligible effect on ionic conductivity and can be removed reversibly by heating at low temperatures (e.g., 160 °C). This finding opens a new pathway for the surface engineering of moisture-sensitive SSEs and other energy materials, thereby speeding up their deployment in ASSBs.

Synthesis and Growth Mechanism of SiS2 Rods

The SiS₂ rods exhibit a significant anisotropy property applied in a special field such as in the one of all-solid-state lithium-ion batteries and so on. In this work, the orthorhombic SiS₂ rods with high chemical/phase purity were prepared by an elemental method, either through a boiling or a steaming process, at 1023-1073 K for 3 h and under the saturated S-vapor pressure (2.57-3.83 MPa) in a closed sealed-tube system. The composition, crystal structure, morphology, and growth mechanism were investigated. Results showed that the growth orientation of SiS₂ along the <0 0 1> is intrinsically governed by the crystal structure motif. It could exist in both processes and the latter tends to show in macroscopic morphology. Using the pressure-temperature diagram, structure refinement, pole figures, image analyses, and so forth, factors influencing the purity and growth of SiS₂ rods were concluded from the thermodynamics and kinetics viewpoints.