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The mechanism of Li+ transport through the solid electrolyte interphase (SEI), a passivating film on electrode surfaces, has never been clearly elucidated despite its overwhelming importance to Li-ion battery operation and lifetime. The present paper develops a multiscale theoretical methodology to reveal the mechanism of Li+ transport in a SEI film. The methodology incorporates the boundary conditions of the first direct diffusion measurements on a model SEI consisting of porous (outer) organic and dense (inner) inorganic layers (similar to typical SEI films). New experimental evidence confirms that the inner layer in the ~20 nm thick model SEI is primarily crystalline Li2CO3. Using density functional theory, we first determined that the dominant diffusion carrier in Li2CO3 below the voltage range of SEI formation is excess interstitial Li+. This diffuses via a knock-off mechanism to maintain higher O-coordination, rather than direct-hopping through empty spaces in the Li2CO3 lattice. Mesoscale diffusion equations were then formulated upon a new two-layer/two-mechanism model: pore diffusion in the outer layer and knock-off diffusion in the inner layer. This diffusion model predicted the unusual isotope ratio 6Li+/7Li+ profile measured by TOF-SIMS, which increases from the SEI/electrolyte surface and peaks at a depth of 5 nm, and then gradually decreases within the dense layer. With no fitting parameters, our approach is applicable to model general transport properties, such as ionic conductivity, for SEI films on the surface of other electrodes, from the atomic scale to the mesoscale, as well as aging phenomenon. [ABSTRACT FROM AUTHOR]

Cathode coatings have received extensive attention due to their ability to delay electrochemical performance degradation in lithium-ion batteries. However, the development of cathode coatings possessing high ionic conductivity and good interfacial stability with cathode materials has proven to be a challenge. Here, we performed first-principles computational studies on the phase stability, thermodynamic stability, and ionic transport properties of LiMXO 4 F (M-X = Al-P and Mg-S) used as cathode coatings. We find that the candidate coatings are thermodynamically metastable and can be synthesized experimentally. The coating materials possess high oxidative stability, with the materials predicted to decompose above 4.2 V, suggesting that they have good electrochemical stability under a high-voltage cathode. In addition, the candidate coatings exhibit significant chemical stability when in contact with oxide cathodes. Finally, we have studied the Li-ion transport paths and migration barriers of LiMXO 4 F (M-X = Al-P and Mg-S) and calculated the low migration barriers to be 0.19 and 0.09 eV, respectively. Our findings indicate that LiMXO 4 F (M-X = Al-P and Mg-S) are promising cathode coatings, among which LiAlPO 4 F has been experimentally confirmed. The theoretical cathode coating computational methods presented here can be extended to the solid-state battery system.

Silicon monoxide (SiO) is considered as one of the most promising anode material candidates for next-generation high-energy-density lithium ion batteries (LIBs) due to its high specific capacity and relatively lower volume expansion than that of Si. However, a large number of irreversible products are formed during the first charging and discharging process, resulting in a low initial Coulombic efficiency (ICE) of SiO. Herein, we report an economical and convenient method to increase the ICE of SiO without sacrificing its specific capacity by a solid reaction between magnesium silicide (Mg 2 Si) and micron-sized SiO. The reaction product (named MSO) exhibits a unique core-shell structure with uniformly distributed Mg 2 SiO 4 and Si as the shell and disproportionated SiO as the core. MSO exhibits a superior ICE and a high reversible capacity of 81.7% and 1306.1 mAh g -1 , respectively, which can be further increased to 88.7% and 1446.4 mAh g -1 after carbon coating, and improved cyclic stability compared to bare SiO. This work provides a simple yet effective strategy to address the low ICE issue of SiO anode materials to promote the practical application of SiO.

Fast ion conduction in solid-state matrices constitutes the foundation for a wide spectrum of electrochemical systems that use solid electrolytes (SEs), examples of which include solid-state batteries (SSBs), solid oxide fuel cells (SOFCs), and diversified gas sensors. Mixing different solid conductors to form composite solid electrolytes (CSEs) introduces unique opportunities for SEs to possess exceptional overall performance far superior to their individual parental solids, thanks to the abundant chemistry and physics at the new interfaces thus created. In this review, we provide a comprehensive and in-depth examination of the development and understanding of CSEs for SSBs, with special focus on their physiochemical properties and mechanisms of ion transport therein. The origin of the enhanced ionic conductivity in CSEs relative to their single-phase parents is discussed in the context of defect chemistry and interfacial reactions. The models/theories for ion movement in diversified composites are critically reviewed to interrogate a general strategy to the design of novel CSEs, while properties such as mechanical strength and electrochemical stability are discussed in view of their perspective applications in lithium metal batteries and beyond. As an integral component of understanding how ions interact with their composite environments, characterization techniques to probe the ion transport kinetics across different temporal and spatial time scales are also summarized.

An economic and facile method was urgently required for the degradation of SF 6 to replace the high-energy excitation treatment. Both theoretical calculations and experimental observations were conducted to reveal the synergy of Cr/Fe/Si composites on a new technique of SF 6 degradation through reacting silicon dioxide. Density functional theory (DFT) calculations show that strong adsorption of SF 6 on Cr 2 O 3 , and then the fast F/O exchange between CrF 3 and Fe 2 O 3 (energy barrier was 1.45 eV) as well as FeF 3 and SiO 2 (energy barrier was 1.69 eV) enhanced mediated efficiency from SF 6 to SiF 4 . The fluorine (F) migration between solid interfaces in Cr 2 O 3 &Fe 2 O 3 @SBA15 was responsible for efficient SF 6 removal. The F migration route was composed of SF 6 to CrF 3 , CrF 3 to FeF 3 , and FeF 3 to SiF 4 with the lowest thermodynamic driving. Enhanced specific accumulative converted amount (SACA) of SF 6 on Cr 2 O 3 &Fe 2 O 3 @SBA15 was achieved and the highest SACA was 13.98 mmol/g within 7 h, significantly higher than that on Fe 2 O 3 @SBA15 (5.74 mmol/g) and Cr 2 O 3 @SBA15 (2.71 mmol/g). Moreover, X-ray diffractometry and X-ray photoelectron spectroscopy were performed to support DFT calculations, including ion intensities detected using mass spectroscopy and composition analysis of the mediator during the reaction. Therefore, our work put forward a novel approach for economic and efficient SF 6 decomposition through reacting with silicon dioxide under the mediation of Cr 2 O 3 &Fe 2 O 3 . This method was also potentially used in effective degradation of refractory non-metal halides.

Two-dimensional (2D) Ti 3 C 2 MXene has attracted great attention in electrochemical energy storage devices (supercapacitors and lithium-ion and sodium-ion batteries) due to its excellent electrical conductivity as well as high volumetric capacity. Nevertheless, a previous study showed that multivalent Mg 2+ ions cannot reversibly insert into MXene, resulting in a negligible capacity. Here, we demonstrate a simple strategy to achieve high magnesium storage capability for Ti 3 C 2 MXene by preintercalating a cationic surfactant, cetyltrimethylammonium bromide (CTAB). Density functional theory simulations verify that intercalated CTA + cations reduce the diffusion barrier of Mg 2+ on the MXene surface, resulting in the significant improvement of the reversible insertion/deinsertion of Mg 2+ ions between MXene layers. Consequently, the MXene electrode exhibits a desirable volumetric specific capacity of 300 mAh cm -3 at 50 mA g -1 as well as outstanding rate performance. This work endows MXene material with an application in electrochemical energy storage and, simultaneously, introduces magnesium battery materials as a member.

We demonstrate that (NH 4 ) 2 Si 0.5 Ti 0.5 P 4 O 13 is an excellent proton conductor. The crystallographic information concerning the hydrogen positions is unraveled from neutron-powder-diffraction (NPD) data for the first time. This study shows that all the hydrogen atoms are connected though H bonds, establishing a two-dimensional path between the [(Si 0.5 Ti 0.5 )P 4 O 13 2- ] n layers for proton diffusion across the crystal structure by breaking and reconstructing intermediate H-O═P bonds. This transient species probably reduces the potential energy of the H jump from an ammonium unit to the next neighboring NH 4 + unit. Both theoretical and experimental results support an interstitial-proton-conduction mechanism. The proton conductivities of (NH 4 ) 2 Si 0.5 Ti 0.5 P 4 O 13 reach 0.0061 and 0.024 S cm -1 in humid air at 125 and 250 °C, respectively. This finding demonstrates that (NH 4 ) 2 Si 0.5 Ti 0.5 P 4 O 13 is a promising electrolyte material operating at 150-250 °C. This work opens up a new avenue for designing and fabricating high-performance inorganic electrolytes.

The improved ionic conductivity (1.64 × 10(-4) S cm(-1) at room temperature) and excellent electrochemical stability of nanoporous β-Li3PS4 make it one of the promising candidates for rechargeable all-solid-state lithium-ion battery electrolytes. Here, elastic properties, defect thermodynamics, phase diagram, and Li(+) migration mechanism of Li3PS4 (both γ and β phases) are examined via the first-principles calculations. Results indicate that both γ- and β-Li3PS4 phases are ductile while γ-Li3PS4 is harder under volume change and shear stress than β-Li3PS4. The electrochemical window of Li3PS4 ranges from 0.6 to 3.7 V, and thus the experimentally excellent stability (>5 V) is proposed due to the passivation phenomenon. The dominant diffusion carrier type in Li3PS4 is identified over its electrochemical window. In γ-Li3PS4 the direct-hopping of Lii(+) along the [001] is energetically more favorable than other diffusion processes, whereas in β-Li3PS4 the knock-off diffusion of Lii(+) along the [010] has the lowest migration barrier. The ionic conductivity is evaluated from the concentration and the mobility calculations using the Nernst-Einstein relationship and compared with the available experimental results. According to our calculated results, the Li(+) prefers to transport along the [010] direction. It is suggested that the enhanced ionic conductivity in nanostructured β-Li3PS4 is due to the larger possibility of contiguous (010) planes provided by larger nanoporous β-Li3PS4 particles. By a series of motivated and closely linked calculations, we try to provide a portable method, by which researchers could gain insights into the physicochemical properties of solid electrolyte.

For specific application to an uncooled infrared detector, VO2 thin films should have a series of characteristics including purposefully chosen polymorphs, accurate stoichiometry, phase stabilization, a high temperature-coefficient of resistance (TCR), and suitable square-resistance. This work reports controllable preparation of high-performance VO2 films via post annealing of a sandwich-structured V2O5/metal (V, W)/V2O5 multilayer precursor, which was deposited by RF magnetron sputtering. This sandwich structure can dynamically regulate oxygen contents and doping element levels in the films, enabling us to achieve accurate regulation of stoichiometry and polymorphs. The precursor films undergo a B to M phase transition depending on the quantity of the metal layers. At the thickness of the metal layer below a limitation, the resulting film after heat treatment was VO2 (B), and above the limitation, the product was VO2 (M). The optical modulation of the VO2 (M) in the near-infrared region can be tuned from 1.2 to 39.8% (ΔT2000 nm). TCR values can range from -1.89 to -4.29%/K and the square-resistances at room temperature (R0) from 69.68 to 12.63 kΩ. The simplicity in phase regulation of the present method and the superior optical and electrical properties of the films may allow its wide applications in thermo-opto-electro sensing devices.