Structure of amorphous Ag/Ge/S alloys: experimentally constrained density functional study

Solid ionic conductors – a review. The conductivity of solid electrolytes, like that of liquid electrolytes, is determined by the concentration and mobility of the mobile ions. There are solid electrolytes in which all particles of one particular type are mobile and the mobility of these ions is as great as that in molten salts or liquid electrolyte solutions. A partial lattice of the otherwise solid crystal is then in a quasimolten state. The conductivity itself now has values as in salt melts or concentrated liquid electrolyte solutions. The solid electrolyte has then reached the maximum value for the ionic partial conductivity. Important solid electrolytes with high ionic conductivities are discussed.

In recent years, much effort has been pursued in developing solid state electrolytes for Li-ion batteries and beyond. While advances have been made in this field, challenges still exist. A few excellent review papers have been published discussing the mechanism and synthesis of solid state electrolytes with some examples of reducing the interfacial resistances between particles, which provide useful information to understand solid state chemistry underlying the electrolytes. Different from previous overview, this talk will categorize different solid state electrolytes according to their applications including Li-ion batteries, Li-air, Li-S batteries and Li metal protection. Both fundamental science and practical applications will be discussed and the energy density will be projected to compare with state-of-art Li-ion batteries.

<p indent="0mm">Since the commercialization of lithium-ion batteries in the 1990s, lithium-ion batteries have been successfully applied in portable electronics, electric vehicles, and grid energy storage. Although current organic liquid electrolytes have high ionic conductivities, they are inherently flammable, volatile, and prone to leakage. Moreover, severe side reactions and dendrite growth on the surface of the lithium anode during the charge-discharge process can cause safety hazards, which greatly impede their applications in lithium metal batteries. Solid electrolytes, including inorganic solid electrolytes and polymer electrolytes, are regarded as effective alternatives to organic liquid electrolytes for the construction of lithium metal batteries with high energy density and safety. Among them, solid polymer electrolytes offer excellent flexibility, processability, and interfacial compatibility over inorganic solid electrolytes, and they are extraordinarily promising for lithium metal batteries with high energy density and safety. Ideal solid polymer electrolytes should have following features: (1) High ionic conductivity (&gt; <sc>10 ^–4 S cm ^–1) </sc> at room temperature; (2) high lithium ion transference number (~1) to reduce the concentration polarization and improve the rate performance of batteries; (3) intimate contact at the electrode/electrolyte interfaces; (4) wide electrochemical window <sc>(&gt;4.5 V</sc> vs. Li/Li ⁺) to match high-voltage cathodes and improve the energy density of batteries; (5) good mechanical stability to resist processing, buffer electrode volume change and inhibit dendrite growth; (6) good thermal stability to withstand environmental changes. Generally, the ionic conductivity of pure solid polymer electrolytes at room temperature is low <sc>(~10 ^–6 S cm ^–1). </sc> Researchers have tried to improve the ionic conductivities by adjusting the lithium salt concentration, such as developing “polymer-in-salt” solid electrolytes. However, increasing the concentration of lithium salt leads to the deterioration of the mechanical strength. Strategies such as developing novel lithium salts, modifying polymer matrix, and incorporating inorganic fillers into solid polymer electrolytes are proposed to promote ionic conductivities of solid polymer electrolytes. In particular, composite polymer electrolytes, fabricated by dispersing a certain amount of inorganic fillers into solid polymer electrolytes, have improved ionic conductivities without sacrificing their mechanical performances. Poor interfacial property between electrodes and electrolytes is also a critical issue for solid polymer electrolytes. On one hand, poor and uneven solid/solid contacts at the electrode/electrolyte interfaces lead to high resistance and sluggish ionic transport kinetics. Furthermore, the volume change of the positive and negative electrodes in the charge/discharge process deteriorates the interfacial contacts, blocks the ion and electron transport through the interfaces, and greatly reduces the electrochemical reaction kinetics. On the other hand, the electrochemical windows of solid polymer electrolytes are usually narrow <sc>(＜4.5 V).</sc> During cycling, redox reactions are prone to occur at the electrode/electrolyte interfaces, causing battery failure. Solid polymer electrolytes have also poor thermal and mechanical stabilities. Therefore, design and synthesis of polymer-based solid electrolytes with excellent comprehensive performances and construction of fast and stable ion transport channels at the electrolyte/electrode interfaces are of great significance for the successful development of solid-state lithium metal batteries. This paper presents a brief review of the research progress in solid polymer electrolytes from two aspects: Improving the ionic conductivities of solid polymer electrolytes and enhancing the interfacial performance at electrolyte/electrode interfaces. First, targeted optimization strategies on ionic conductivities of solid polymer electrolytes, including constructing continuously aligned ionic transport paths and shortening the ionic transport distance, are summarized. Second, interface optimization strategies, including constructing wetting interfaces and synthesizing asymmetric electrolytes, are presented to reduce the interface resistance and improve the interfacial contact. Finally, perspectives on the development of solid polymer electrolytes and high-performance solid-state lithium metal batteries are discussed, and key research directions and advanced test methods are proposed. This review may provide a comprehensive understanding and further guidance for not only the material design of solid polymer electrolytes, but also the structural design of lithium metal batteries with favorable electrochemical and interfacial performances.

Lithium hydroxide halides, as a family of lithium-ion conductive materials, have a promising potential on the application of solid state electrolytes. In this work, we have synthesized orthohombic Li2OHI through a facile mechanochemical method. The obtained sample exhibits a higher lithium-ion conductivity than solid sintering, which can be attributed to the high purity and crystallinity obtained from ball milling. Ball milling can avoid the phase segregation of Li2OHI at high temperature and promote the sufficient eutectic reaction of binary system, which can be widely used in the synthesis of other materials with low melting points.

The application of solid-state electrolytes is one of the effective approaches to address the safety issues of lithium-ion batteries. From a manufacturing perspective, 3D printing based on direct ink writing (DIW) has attracted unprecedented interest due to its high design freedom and convenient fine-scale control. In this study, Li[Formula: see text]Al[Formula: see text]Ti[Formula: see text](PO4)3 (LATP) electrolyte nanoparticles were dispersed in polyethylene oxide (PEO) polymer to form a printable electrolyte ink, and a composite solid-state electrolyte was subsequently fabricated via DIW. The results show that the composite electrolyte ink containing 2 wt.% LATP exhibits the optimal rheological properties at room temperature. The addition of LATP nanofillers effectively enhances the structural stability, thermal stability, and electrochemical performance of the polymer electrolyte. The ionic conductivity of the printed composite solid-state electrolyte membrane is increased to 5.62 × 10[Formula: see text] S ⋅ cm[Formula: see text]. The NCA/graphite solid-state lithium-ion battery assembled with this electrolyte displays a specific discharge capacity of 236 mAh g[Formula: see text] at a 0.1 C rate, and exhibits excellent electrochemical reversibility and cycle stability. This multi-shaped, printable ink technology opens up new pathways for the manufacturing of scalable energy storage devices.

Epoxy resin is widely used as electrical insulation material and its electrical degradation is significantly influenced by ionic conduction. However, the theoretical understanding of ionic transfer in epoxy is limited. In this study, sodium ion (Na <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> ) mobility and chloride ion (Cl <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−</sup> ) mobility in epoxy resin are computed using the molecular dynamics (MD) simulation, and their electric field dependence and temperature dependence are discussed. The calculated ionic mobility is consistent with the experimental results. The ionic mobility and its Arrhenius activation energy of Cl <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−</sup> are, respectively, larger and smaller than those of Na <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> . The MD results also suggest that the effect of free volume on ionic conduction is small. To further analyze the ion transport mechanism, the interaction energy between the ion and surrounding epoxy molecules when the ion is at a stable “trap” site and a “barrier” site for ion is calculated. The results show that the potential barrier for ion transportation in epoxy resin is smaller for Cl <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−</sup> than Na <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> , and hence, the Cl <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−</sup> ion mobility is larger than Na <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> . Furthermore, the effect of water in epoxy on ionic mobility is computed. The computed ionic mobility is larger for the water-containing system. This is because hydration inhibits the bonding between the ions and epoxy molecules. A comparison is also conducted between the MD computed mobility and the mobility calculated by a classical ionic conduction theory. This study reveals the relationship between the microscopic interactions of the ion and surrounding molecules and the macroscopic ionic mobility in epoxy.

In this paper, we report the investigation on structural, electrical, dielectric properties, and ion dynamics of novel blend polymer electrolyte matrix (PEO-PEI) complexed with sodium hexafluorophosphate salt. All the solid polymer electrolyte films have been synthesized via solution cast method. The SPE films were characterized by the X-ray diffraction, field emission scanning electron microscope, impedance-dielectric spectroscopy, and thermogravimetric analysis. The morphology of the SPE alters with salt addition and confirms the blend polymer complex formation. The FTIR analysis evidenced the complex formation, and increase in the fraction of free ions is achieved. The ionic conductivity exhibits a maximum at the stoichiometric ratio O/Na = 10 and follows the Arrhenius behavior. The fraction of free ions is maximum for the SPE film with the highest ionic conductivity. The optimum electrolyte possesses a voltage stability window of about 4 V, excellent thermal stability up to 380 °C, and high ionic transference number (~ 1). The complex permittivity and conductivity have been simulated in whole frequency window to extract relaxation time and dielectric strength. The dielectric constant and relaxation time exhibited sequentially a maximum and minimum for the SPE film with the highest ionic conductivity. The loss tangent peak shifts toward high frequency with addition of salt, and it infers the faster ion dynamics in the polymer matrix. Then the ion transport parameters number density of charge carriers (n), ion mobility (μ), and diffusion coefficient (D) have been obtained by three methods (FTIR, impedance spectroscopy, and loss tangent method) and are in absolute correlation with the impedance results. An ion transport mechanism has been proposed based on experimental findings.

Solid-state proton-conductive electrolytes operating at intermediate temperatures (i.e., 100-300 °C) offer numerous advantages for electrochemical devices, for example, faster electrode kinetics. Solid acids (MxHy(AO4)z, where M = Cs, Rb, K, Li, or NH4; A = S, Se, P, or As) have attracted considerable attention as electrolytes for intermediate temperature devices.[1] LiH2PO4 is an interesting material with potential for high conductivity over a wide temperature range. However, high conductivities were reported using a specialized setup, such as a closed system with high water vapor pressure (2 bar at 200 °C),[2] which is difficult for many researchers to access. In this study, we developed a self-standing electrolyte membrane of an H3PO4-containing LiH2PO4 and quartz fiber (QF) matrix, which exhibited a high conductivity (21-28 mS cm−1) over a broad and comparatively low temperature range (100-200 °C) under ambient pressure. A novel polymerization and hydrolysis (PH) treatment was employed to synthesize this membrane.A simple mixture of LiH2PO4 and H3PO4 was used as precursors and heating-induced phosphate polymerization resulted in a unique glassy sol formation that could be reshaped easily (Fig. 1a). X-ray diffraction and Raman spectroscopies revealed that the subsequent regeneration of LiH2PO4 from the phosphate polymer hydrosol upon hydrolysis was responsible for the high ionic conductivity. The infiltrating amount of H3PO4 in the electrolyte was optimized to achieve the maximum conductivity (Fig. 1b). It is also found that the conductivity of LiH2PO4-based electrolytes is sensitive to humidity (Fig. 1c). It is expected that a highly conductive interface forms between the LiH2PO4 particles that contain H3PO4 and H2O, contributing significantly to the electrolyte's high conductivity. Thermogravimetric (TG) analysis further revealed the electrolyte's high hygroscopicity—the ability to absorb water from the atmosphere at temperatures exceeding 100°C. This property may explain its consistent conductivity performance over a wide temperature range.The key factors contributing to the high conductivity of this electrolyte can be summarized as follows: 1) adequate salts embedded in the membrane through PH treatment, 2) the incorporation of extra H3PO4 on LiH2PO4 and 3) humid conditions. The scalability of the PH synthesis process was demonstrated by successfully forming a 100 mm Φ QF sheet with uniform conductivities through the sheet.In summary, this study presents a novel synthesis method for the LiH2PO4-based solid acid electrolyte and offers valuable insights into its proton conduction mechanism. Reference: [1] S. M. Haile et al., Nature, 2001, 410, 910.[2] R. W. Berg et al., Ionics, 2021, 27, 703. Figure 1

Enabling all-solid-state Li-ion batteries requires solid electrolytes with high Li ionic conductivity and good electrochemical stability. Following recent experimental reports of Li3 YCl6 and Li3 YBr6 as promising new solid electrolytes, we used first principles computation to investigate the Li-ion diffusion, electrochemical stability, and interface stability of chloride and bromide materials and elucidated the origin of their high ionic conductivities and good electrochemical stabilities. Chloride and bromide chemistries intrinsically exhibit low migration energy barriers, wide electrochemical windows, and are not constrained to previous design principles for sulfide and oxide Li-ion conductors, allowing for much greater freedom in structure, chemistry, composition, and Li sublattice for developing fast Li-ion conductors. Our study highlights chloride and bromide chemistries as a promising new research direction for solid electrolytes with high ionic conductivity and good stability.

The present work is an effort to study the effects of Li doping on the structural and transport properties of the solid polymer electrolyte, poly-ethelene oxide (PEO) (molecular weight, 200,000). Li-doped PEO was synthesized by treating PEO with n-Butyllithium in hexane for different doping concentrations. It is seen that the crystallinity of the doped PEO decreases on increasing the Li doping concentration and XRD and FTIR studies support this observation. FESEM images give better details of surface morphology of doped PEO samples. The TGA curves of PEO and Li-doped PEO samples reveal the weight loss region, and it is observed that the weight loss process of the solid polymer electrolyte is gradual rather than abrupt, contrary to the case of liquid electrolytes. The purity and the electrochemical stability of the samples were established by cyclic voltammetry studies. Impedance measurements were carried out to estimate the ionic conductivity of Li-doped PEO samples. The present value of ionic conductivity observed at room temperature in Li-doped PEO is about five orders higher than that of pure PEO and is quite close to that of liquid electrolytes. It is inferred that, ionic conductivity of the sample is increasing on increasing the Li doping concentration due to enhanced charge carrier density and flexibility of the doped sample structure. The ionic mobility and ionic transport are significantly improved by the less crystallinity and higher flexibility of the Li-doped PEO samples which in turn are responsible for the enhanced ionic conductivity observed.

We use a microscopically motivated generalized Langevin equation (GLE) approach to link the vibrational density of states (VDOS) to the dielectric response of orientational glasses (OGs). The dielectric function calculated based on the GLE is compared with experimental data for the paradigmatic case of two OGs: freon-112 and freon-113, around and just above T_{g}. The memory function is related to the integral of the VDOS times a spectral coupling function γ(ω_{p}), which tells the degree of dynamical coupling between molecular degrees of freedom at different eigenfrequencies. The comparative analysis of the two freons reveals that the appearance of a secondary β relaxation in freon-112 is due to cooperative dynamical coupling in the regime of mesoscopic motions caused by stronger anharmonicity (absent in freon-113) and is associated with the comparatively lower boson peak in the VDOS. The proposed framework brings together all the key aspects of glassy physics (VDOS with the boson peak, dynamical heterogeneity, dissipation, and anharmonicity) into a single model.

Experimental and MD simulation investigation on thermophysical properties of binary/ternary mixtures of 1-butyl-3-methylimidazolium trifluoromethanesulfonate with molecular solvents

Ion migration is a key phenomenon that influences the performance and stability of metal halide perovskite solar cells (PSCs). In this work, we systematically study how ion mobility evolves under thermal stress at 85 °C, using capacitance-frequency (C-f) spectroscopy measured in the dark. Aided by drift-diffusion simulations, we demonstrate that the measured C-f spectra cannot be reproduced using a single anion density with a unique ion mobility, particularly in the low-frequency domain where nonideal behavior emerges. A double-Gaussian distribution of anion mobilities provides a substantially better fit even for fresh devices and remains necessary after prolonged aging under thermal stress. This evolution suggests that heat stress not only influences the redistribution of mobile ions but also induces morphology-related changes, such as interface modifications and interlayer degradation, which collectively alter the electrochemical response of the device. Furthermore, the experimental hysteresis index (HI) for fresh and aged devices cannot be captured by assuming a single ion mobility, indicating that a distribution of ion mobilities is necessary to fully describe hysteresis behavior. These findings elucidate the complex ion dynamics under thermal stress and point toward the presence of distinct ionic populations contributing to device behavior, with implications for improving PSC stability.

Battery safety is increasingly at the forefront of consumer concerns, especially regarding electric vehicles. Current lithium ion battery technology utilizes liquid electrolytes, which have very high ionic conductivities but are extremely flammable. To improve safety, researchers are investigating replacing liquid electrolytes in lithium ion batteries with solid electrolytes. A promising approach is the use of solid polymer composite electrolytes where lithium conductive ceramic powders are dispersed into polymer electrolyte matrix. These materials are intended to improve lithium conductivities and mechanical properties relative to pure polymer electrolyte, lower manufacturing and battery cell construction costs relative to using pure ceramic electrolytes, and eliminate volatile and flammable electrolyte solvents. Currently, the archetypal polymer matrix used in composite electrolytes is polyethylene oxide (PEO). When mixed with lithium salts, such as lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), and ceramics, such as Li7La3Zr2O12 (LLZO), PEO based composites have conductivities (~10-7 S/cm at room temperature) that are still insufficient for today’s applications. In addition, PEO tends to crystallize and has poor oxidative stability (decomposition ca. 4V). We are exploring poly(polyethylene glycol methyl ether methacrylate) (PEGMA) and polyethylene carbonate (PEC) as alternatives to PEO to address issues with crystallization and oxidative stability, respectively. Composite electrolytes are fabricated by blending bulk polymer with LiTFSI and LLZO powders. We have formed rubbery PEGMA-based composites with comparable conductivities (~10-7 S/cm at room temperature, 70 vol% polymer, 10:1 ethylene oxide:lithium). Lithium symmetric cycling was observed to be stable over 250 hours at 1C. We have also recently formed stand-alone PEC based composites with high conductivities (~10-6 S/cm at room temperature, 60 vol% polymer, 10:1 ethylene carbonate:lithium). Investigations into the origin of this high conductivity and measurements of electrochemical stability are currently underway.

The application of solid-state electrolytes in Li batteries is hampered by the occurrence of Li-dendrite-caused short circuits. To avoid cell failure, the electrolytes can only be stressed with rather low current densities, severely restricting their performance. As grain size and pore distributions significantly affect dendrite growth in ceramic electrolytes such as Li7 La3 Zr2 O12 and its variants; here, a "detour and buffer" strategy to bring the superiority of both coarse and fine grains into play, is proposed. To validate the mechanism, a coarse/fine bimodal grain microstructure is obtained by seeding unpulverized large particles in the green body. The rearrangement of coarse grains and fine pores is fine-tuned by changing the ratio of pulverized and unpulverized powders. The optimized bimodal microstructure, obtained when the two powders are equally mixed, allows, without extra interface decoration, cycling for over 2000h as the current density is increased from 1.0 mA·cm-2 , and gradually, up to 2.0 mA·cm-2 . The "detour and buffer" effects are confirmed from postmortem analysis. The complex grain boundaries formed by fine grains discourage the direct infiltration of Li. Simultaneously, the coarse grains further increase the tortuosity of the Li path. This study sheds light on the microstructure optimization for the polycrystalline solid-state electrolytes.