Migration Barriers Research Articles

Redox-active benzoquinone-intercalated layered vanadate for high performance zinc-ion battery: Phenol-keto conversion and the anchoring effect of V-O-V host framework

• ( o -BQ) 0.25 V 2 O 5 ·0.5H 2 O and ( p -BQ) 0.25 V 2 O 5 ·0.5H 2 O (BQ = benzoquinone) were synthesized. • Rietveld refinements and HAADF-STEM reveal the successful intercalation of BQ into V 2 O 5 . • ( p -BQ) 0.25 V 2 O 5 ·0.5H 2 O shows an excellent rate performance and an ultralong cycle life. • The sandwiched BQ in layered V 2 O 5 can be prevented from leaching into the electrolyte. • DFT calculations disclose a small Zn 2+ -migration barrier in ( p -BQ) 0.25 V 2 O 5 · x H 2 O. Utilizing a facile one-step hydrothermal technique, oxygen-deficient ( o -BQ)-VO and ( p -BQ)-VO nanosheets were synthesized, which were formulated as ( o -BQ) 0.25 V 2 O 5 ·0.5H 2 O and ( p -BQ) 0.25 V 2 O 5 ·0.5H 2 O (BQ = benzoquinone), respectively. Rietveld refinements and high-angle annular dark-field (HAADF)-scanning transmission election microscope (STEM) reveal the successful intercalation of o -BQ or p -BQ into the layered V 2 O 5 with large interlayer spacings of ∼ 13.7 Å, in which all the V centers are coordinatively unsaturated due to the elongation of V-O bonds. ( p -BQ)-VO shows an excellent rate performance of 487/446/405/371/333/280 mAh g −1 at 0.1 ∼ 5 A g −1 and an ultralong cycle life with a capacity retention of 96.0 % after 4000 discharge/charge cycles at 5 A g −1 , which is due to the dual redox-activity from BQ and vanadium oxide. The phenol-keto conversion of BQ can provide extra capacity. Furthermore, the sandwiched BQ in layered V 2 O 5 can be prevented from leaching into the electrolyte. On the other hand, ( p -BQ)-VO shows better electrochemical performance than ( o -BQ)-VO, indicating that the redox property of quinone is associated with the para - or ortho -position of keto-group and their possible coordination modes with Zn 2+ . Density functional theory (DFT) calculations disclose that the deep intercalation of Zn 2+ on certain site in ( p -BQ)-VO can improve electron conductivity, giving rise to enhanced electrochemical behavior. And the Zn 2+ -migration along b axis of the ( p -BQ)-VO cell shows a small energy barrier of 0.80 eV, thus leading to the outstanding rate and cycling performances. Redox-active benzoquinone (BQ)-intercalated layered vanadate ( p -BQ) 0.25 V 2 O 5 ·0.5H 2 O exhibits excellent rate performance and ultralong cycle life in zinc-ion battery, which is due to the dual redox-activity from BQ and vanadium oxide. Furthermore, the sandwiched BQ in layered V 2 O 5 can be prevented from leaching into the electrolyte. DFT calculations disclose a small Zn 2+ -migration barrier of 0.80 eV.

Enhanced Pd/a-WO3 /VO2 Hydrogen Gas Sensor Based on VO2 Phase Transition Layer.

The utilization of clean hydrogen energy is becoming more feasible for the sustainable development of this society. Considering the safety issues in the hydrogen production, storage, and utilization, a sensitive hydrogen sensor for reliable detection is essential and highly important. Though various gas sensor devices are developed based on tin oxide, tungsten trioxide, or other oxides, the relatively high working temperature, unsatisfactory response time, and detection limitation still affect the extensive applications. In the current study, an amorphous tungsten trioxide (a-WO3 ) layer is deposited on a phase-change vanadium dioxide film to fabricate a phase transition controlled Pd/a-WO3 /VO2 hydrogen sensor for hydrogen detection. Results show that both the response time and sensitivity of the hydrogen sensor are improved greatly if increasing the working temperature over the transition temperature of VO2 . Theoretical calculations also reveal that the charge transfer at VO2 /a-WO3 interface becomes more pronounced once the VO2 layer transforms to the metal state, which will affect the migration barrier of H atoms in a-WO3 layer and thus improve the sensor performance. The current study not only realizes a hydrogen sensor with ultrahigh performance based on VO2 layer, but also provides some clues for designing other gas sensors with phase-change material.

Point Defects Stability, Hydrogen Diffusion, Electronic Structure, and Mechanical Properties of Defected Equiatomic γ(U,Zr) from First-Principles.

At present, many experimental fast reactors have adopted alloy nuclear fuels, for example, U-Zr alloy fuels. During the neutron irradiation process, vacancies and hydrogen (H) impurity atoms can both exist in U-Zr alloy fuels. Here, first-principles density functional theory (DFT) is employed to study the behaviors of vacancies and H atoms in disordered-γ(U,Zr) as well as their impacts on the electronic structure and mechanical properties. The formation energy of vacancies and hydrogen solution energy are calculated. The effect of vacancies on the migration barrier of hydrogen atoms is revealed. The effect of vacancies and hydrogen atom on densities of states and elastic constants are also presented. The results illustrate that U vacancy is easier to be formed than Zr vacancy. The H interstitial prefers the tetrahedral site. Besides, U vacancy shows H-trap ability and can raise the H migration barrier. Almost all the defects lead to decreases in electrical conductivity and bulk modulus. It is also found that the main effect of defects is on the U-5f orbitals. This work provides a theoretical understanding of the effect of defects on the electronic and mechanical properties of U-Zr alloys, which is an essential step toward tailoring their performance.

First-principles study of vacancy defects in TiVTa and TiVTaNb concentrated solid-solution alloys

The formation and migration energies of vacancy defects are studied systematically by first-principal calculations method in three concentrated solid-solution alloys (CSAs), namely equimolar TiVTa alloy, TiVTa50 alloy with Ta content increased to 50%, and equimolar TiVTaNb alloy. It is found that the vacancy formation and migration in TiVTaNb alloy are more difficult than that in TiVTa and TiVTa50 alloys. The TiVTa alloy has the larger local lattice distortion than TiVTa50 and TiVTaNb alloys, which would lead to an irregular energy landscape and make it easier to form vacancies. Vacancies are easily formed in Ti-rich environments and the trend reverses for in V-rich environments in these three alloys, originating from the large local lattice distortion in Ti-rich environments and strong binding interactions between Ti atoms and vacancies. Ti atoms with the largest size tend to migrate to neighboring vacancies in these three alloys. The addition of Nb enhances the electron interactions between atoms in TiVTaNb alloy. Compared to TiVTa and TiVTa50 alloys, the migration barrier of atoms diffusing into vacancies in TiVTaNb alloy is improved due to the combination of strong electron interactions between atoms and lattice distortion. It is implied that the influence of alloy element combination on vacancy formation and migration energies may be greater than that of alloy element content in Ti-V-Ta and Ti-V-Ta-Nb alloys. These results provide fundamental insights into the defects evolution of CSAs with body-centered cubic (bcc) structure and supply the scientific basis for the composition design of bcc CSAs.

73 Parenting Experiences of Families of Refugee Background in the Greater Toronto Area: A Formative Study

Abstract Background As of date, the world is experiencing its highest levels of human displacement, with many families resettling in Canada. While there is an understanding that families of refugee background have complex, multigenerational mental health, and developmental needs, little is known about whether their parenting needs are met adequately in Canada after resettlement nor how COVID-19 related restrictions have further complicated their resettlement experience. Objectives To gather data about the facilitators and barriers that impact the parenting experience of families of refugee background in the Greater Toronto Area (GTA) in the context of their children’s unique developmental and resettlement needs. Design/Methods This was a qualitative, community-based participatory research study. All data was collected from August 2019 to July 2020. In-depth interviews (IDIs) were conducted with caregivers of refugee background and healthcare providers that work closely with this population. Data were recorded, transcribed, and coded by two independent coders and a peer-debriefing strategy was used to verify the coding approach. Results In total, 20 IDIs were conducted (7 caregivers, 13 care providers). Six key themes were identified: (1) Mental Health and Healthcare Access, (2) Language, (3) Navigating Canadian Systems, (4) Finances, (5) Cultural Dimensions of Caregiving, and (6) Advocacy and Agency. The caregivers and healthcare providers agreed that language is a migration barrier, housing and financial stability are challenging to obtain, and that families struggle to self-advocate. There was disagreement as to how families and healthcare providers viewed healthcare access: caregivers reported that they have good access, but the providers cited that there are still barriers, including health literacy and cultural differences. While caregivers believe they are well supported by the government, healthcare providers believe more funding and education on the families’ rights are necessary. Finally, although most caregivers describe Canada as welcoming, healthcare providers highlighted more incidences of misunderstandings and gaps within the system that may allow families to fall through the cracks. Conclusion Our study describes the unique facilitators and barriers to the resettlement, healthcare access, and lived experiences of families of refugee background raising children within the GTA.

Long-lifespan benzoquinone-intercalated vanadium oxide with vacancies and disorders on the (00l) facets for efficient sodium-ion battery: A facile approach to Na+ capture and pre-sodiation

Via a facile one-step hydrothermal method, it was synthesized (m-BQ)0.15V2O5·0.5H2O (m-BQ = m-benzoquinone) (denoted as (m-BQ)-VO) three-dimensional (3D) porous hierarchical microflowers, which possesses a large (001) lattice spacing of 13.7 Å with crystalline vacancies and disorders on the (00l) facets. Rietveld refinement and high-angle annular dark field-scanning transmission election microscopy (HAADF-STEM) of (m-BQ)-VO unveil that the successful intercalation of m-BQ into layered V2O5 leads to the elongation of V-O bonds. As a result, the V centers of the sample are unsaturated with structural oxygen vacancies, and the V-O-V bilayer is split into two V-O-V monolayers with the (001) facet as the division plane. Consequently, upon lower-temperature annealing, the dehydrated sample can deliver a high initial capacity of 252 mAh/g at 0.05 A/g with excellent capacity retentions of 90 % over 210 cycles at 0.1 A/g, and 87 % over 2100 cycles at 2 A/g, respectively, in which no apparent phase change is observed. It is associated with the large interlayer channel with a lower Na+ migration barrier of 0.48 eV. And the anchoring effect of layered V-O-V framework can prevent the leaching of m-BQ into electrolyte. Furthermore, the redox-active m-BQ can provide extra capacity, whose affinity towards Na+ can induce the partial inclusion of Na+ ions in the sample even only immersion in Na+ solution undisturbed under room temperature, giving rise to improved electron conductivity and a facile approach to pre-sodiation, as evidenced by density functional theory (DFT) calculations.

Impurity influence on the hydrogen diffusivity in B2–TiFe

The projector augmented-wave method within the electron density functional theory is used for calculations of the hydrogen absorption energy and its migration barriers in the doped B2–TiFe. An analytical expression for the temperature-dependent diffusion coefficients of the hydrogen in the doped alloy is derived using Landman's method. An approach for estimation of the average jump rates of hydrogen that are necessary for calculations of the diffusion coefficient in the doped alloys is developed. The activation energy of hydrogen diffusion and the pre-exponential factor are estimated. The effect of impurities on the hydrogen diffusion in the alloy is discussed.

Theoretical design of Na-rich anti-perovskite as solid electrolyte: The effect of cluster anion in stability and ionic conductivity

The next-generation solid-state batteries need safe and efficient solid-state electrolytes. However, the conventional solid-state electrolytes materials often suffer from low ionic conductivity. The emerging anti-perovskites are potential solid electrolytes materials for their rich cations and tunable crystal structure. Here, the first-principles density functional theory (DFT) calculations are employed to investigate the stability, electronic properties, elastic constants and the ions migration of sodium-rich anti-perovskite Na3SA (A ​= ​AlF4¯, ClO4¯, ICl4¯, IO4¯). Calculations show that the clusters substitution at anion position A of Na3SA displays larger band gap and faster Na ion transport than that of halogen anions (e.g., Cl, Br, I). Among them, the band gaps of Na3SAlF4 and Na3SClO4 exceed 3.5 ​eV, which indicates their excellent electrochemical stability. The AlF4¯ cluster exhibits high sodium ion conductivity (6.55 ​× ​10-2 ​S ​cm-1), low activation energy (0.19 ​eV) and small migration barrier (0.46 ​eV) according to the ab initio molecular dynamics (AIMD) simulations and transition states study. Molecular dynamics simulations suggest that the enhanced ionic conductivity is due to the rotation of cluster ions which promotes the migration of sodium ions; moreover, the large volume created by anion clusters leads to larger lattices which is also benefit for fast ion transport. Therefore, this work designs Na-rich anti-perovskite with high ionic conductivity by substitution of anion clusters and also provides the Na ion transport mechanism for reference in solid-state electrolytes.

Zn/Mg Dual Dopant Strategy to Enhance Sodium Ion Conductivity in Na3Zr2Si2PO12

Sodium-based all-solid-state batteries (ASSBs) are economically feasible alternatives to lithium-based batteries that show high potential to provide energy storage systems that are safe and possess high energy density in an ever-increasing energy demand around the globe. Among the many sodium-ion conducting solid electrolytes (that are integral to developing an ASSB), monoclinic-structured Na3Zr2Si2PO12 (part of the NASICON-family of compounds) are promising materials that exhibit high ionic conductivity in the range of 0.67 mS/cm. However, to be as effective as liquid electrolytes, the innate low grain boundary conductivity in Na3Zr2Si2PO12 needs to be resolved. In this work, by adopting a strategic co-doping of the Zr-site by divalent Zn2+ and Mg2+-ions, the bulk and grain boundary conductivities were improved concomitantly in Na3Zr2Si2PO12. With a general stoichiometry of Na3+2(x+y)Zr2-xZnxMgySi2PO12, an enhanced total ionic conductivity (bulk + grain boundary) of 2.8 mS/cm at room temperature was achieved with an optimum composition of x = 0.2 and y = 0.125. A considerable increase in the grain boundary conductivity from 0.3 mS/cm for undoped Na3Zr2Si2PO12 to 4.4 mS/cm for Zn/Mg-co-doped Na3Zr2Si2PO12 contributed to such improvement in its total ionic conductivity. In addition, increase in bulk conductivity was down to the structural transformation from monoclinic (C 2/c) of Na3Zr2Si2PO12 to rhombohedral (R-3c) crystal structure as observed from the significant peak shifts in the X-ray diffraction patterns of the Zn/Mg-co-doped Na3Zr2Si2PO12 samples. To understand the effect of co-doping Zn2+- and Mg2+-ions were investigated by comparing its structural and impedance characteristics to that of the undoped-, Zn2+- and Mg2+-doped Na3Zr2Si2PO12 (single dopant), as shown in Fig. 1 (a) and (b). The inclusion of dual dopants in the Na3Zr2Si2PO12 structure had a significant effect on the migration barrier (around 0.22 eV) for ionic conduction relative to 0.33 eV obtained from undoped Na3Zr2Si2PO12. Additionally, the migration barriers for bulk and the grain boundary conduction were resolved by studying the impedance properties at lower temperatures (21 oC to –40 oC). Although, there was considerable increase in the ionic conductivity after doping with divalent ions, the electronic conductivity of the system remained unaffected (in the range of 10–8 S/cm) indicating that the system can withstand relatively higher critical current densities. To understand the Na stripping and plating characteristics, symmetric cells were assembled with the dual-doped Na3Zr2Si2PO12 as a solid electrolyte sandwiched between sodium metal. Exhibiting an area specific resistance at the sodium-electrolyte interface as low as 34 Ω cm2, stable Na cycling was observed for 25 cycles at different current densities ranging from 0.05 mA/cm2 to 0.3 mA/cm2 recorded at room temperature (as shown in Fig. 1 (c)).Dendrite growth, resulting in a cell-shortage, was observed at current density of 0.35 mA/cm2 for the Zn/Mg-doped Na3Zr2Si2PO12. The results presented in this work shows the potential of dual doping Na3Zr2Si2PO12 crystal structure to attain high sodium ion conducting solid electrolyte for ASSBs. Figure 1 (a) X-ray diffraction profiles and (b) ionic conductivities for undoped-, Zn2+-, Mg2+- and dual Zn2+/Mg2+-doped Na3Zr2Si2PO12 and (c) Na cycling characteristics of dual Zn2+/Mg2+-doped Na3Zr2Si2PO12 as the solid-state electrolyte. Figure 1

Seasonal migration and habitat use of adult barbel (Barbus barbus) and nase (Chondrostoma nasus) along a river stretch of the Austrian Danube River

Migration patterns and habitat use of adult barbel (Barbus barbus) and nase (Chondrostoma nasus) were monitored by radio telemetry over a period of 13 months along a 58-km-long section of the Austrian part of the Danube River. The study site is confined upstream and downstream by two hydropower plants, and contains a larger tributary, the Pielach River. Telemetry transmitters were implanted into fish caught in this tributary after spawning in June (25 individuals per species). The results show that both species use the entire available width and depth spectrum of the Danube along the full migratable river length. Nase had an average home range of 22.4 km, while that of barbel was 34.4 km. The habitat use of the two species differs significantly. While the nase was primarily encountered in the free-flowing section, barbel mainly used deep areas of the impoundment during the year. Nase showed a distinct site fidelity to certain areas in the free-flowing reach which were periodically revisited. During the spawning season, distinct homing behavior was observed in both species. All seven nase that could still be detected during the spawning season returned to the tributary (homing rate 100%). Six homing nase migrated up to the first migration barrier in the tributary but did not pass the existing fish passage facility. In contrast, only nine barbel returned to spawn in the tributary (homing rate 50%), while nine barbel were most likely using a spawning location in the head of impoundment section. Homing fish entered the tributary during darkness.

Visible-light irradiation improved resistive switching characteristics of a 2D Cs2Pb(SCN)2I2-Based memristor device

Two-dimensional (2D) perovskite materials show enormous potential in optoelectronic applications owing to their exceptional thermal stability and unique lattice structures. However, research into anion-substituted 2D perovskites is relatively rare, particularly in the photoelectric information storage field. Here, an anion-based 2D perovskite Cs2Pb(SCN)2I2 film with high orientation and high thermal-stability is achieved by simple low-temperature solution processing and the memristor of Al/Cs2Pb(SCN)2I2/FTO is established. The experimental evidence shows that: 1) In the absence of light irradiation, memristors present typical bipolar resistance switching behaviour with On/Off resistance ratio (>103) and reliable retention (>104 s); 2) By introducing light irradiation, it can achieve a more dependable memristor with decreased RS fluctuation and improved cycling endurance. In addition, by modifying the compliance current (Icc), it can realize multi-level storage function of memories with good high temperature endurance. Finally, the logic gate function is also demonstrated with these cells. The operational principles of memristor devices are comprised of the charge trapping and conductive filament mechanisms. The light irradiation reduces the ion migration barrier and enhances the conductivity of perovskite films, thus limiting the excessive growth of conductive filaments. This work offers the groundwork for creating anionic two-dimensional perovskite photoelectric memristor devices.

Polarization switching induced by domain wall sliding in two-dimensional ferroelectric monochalcogenides

The ability to switch between distinct states of polarization comprises the defining property of ferroelectrics. However, the microscopic mechanism responsible for switching is not well understood and theoretical estimates based on coherent monodomain switching typically overestimates experimentally determined coercive fields by orders of magnitude. In this work we present a detailed first principles characterization of domain walls (DWs) in two-dimensional ferroelectric GeS, GeSe, SnS and SnSe. In particular, we calculate the formation energies and migration barriers for 180∘ and 90∘ DWs, and then derive a general expression for the coercive field assuming that polarization switching is mediated by DW migration. We apply our approach to the materials studied and obtain good agreement with experimental coercive fields. The calculated coercive fields are up to two orders of magnitude smaller than those predicted from coherent monodomain switching in GeSe, SnS and SnSe. Finally, we study the optical properties of the compounds and find that the presence of 180∘ DWs leads to a significant red shift of the absorption spectrum, implying that the density of DWs may be determined by means of simple optical probes.

Long-Term Evolution of Vacancies in Large-Area Graphene.

Devices based on two-dimensional (2D) materials such as graphene and molybdenum disulfide have shown extraordinary potential in physics, nanotechnology, and electronics. The performances of these applications are heavily affected by defects in utilized materials. Although great efforts have been spent in studying the formation and property of various defects in 2D materials, the long-term evolution of vacancies is still unclear. Here, using a designed program based on the kinetic Monte Carlo method, we systematically investigate the vacancy evolution in monolayer graphene on a long-time and large spatial scale, focusing on the variation of the distribution of different vacancy types. In most cases, the vacancy distribution remains nearly unchanged during the whole evolution, and most of the evolution events are vacancy migrations with a few being coalescences, while it is extremely difficult for multiple vacancies to dissolve. The probabilities of different categories of vacancy evolutions are determined by their reaction rates, which, in turn, depend on corresponding energy barriers. We further study the influences of different factors such as the energy barrier for vacancy migration, coalescence, and dissociation on the evolution, and the coalescence energy barrier is found to be dominant. These findings indicate that vacancies (also subnanopores) in graphene are thermodynamically stable for a long period of time, conducive to subsequent characterizations or applications. Besides, this work provides hints to tune the ultimate vacancy distribution by changing related factors and suggests ways to study the evolution of other defects in various 2D materials.

Hydrogen trapping energetics at BCC iron-helium interfaces

Density functional theory (DFT) calculations have been performed to assess the trapping and segregation strength of hydrogen (H) to helium (He) interfaces in BCC (Fe) as a function of He density and surface orientation. The He density ranges from 0 to 2 He/V which corresponds to equilibrium bubbles that are expected to form in the structural components in a fusion reactor environment. The DFT calculations consist of a slab of BCC metal and an initial lattice of FCC He. We report on the binding energy of H to these interfaces as well as the migration barriers into and away from the surface, which together provide information on the de-trapping energy for H at He bubbles. It was found that the binding energy of H to He-Fe interfaces decreases with increasing He density. Migration barriers are also modified due to the He density, which are sensitive to the surface orientation as well as the diffusion pathway. These results provide valuable first-principles energetics that are necessary for higher-order, mesoscale models, and provide insight into the extent to which He bubbles may trap tritium in fusion structural materials.

SiS2 monolayer: An auspicious alkali-ion anode material with high specific capacity and ultrafast ion diffusion

Over the past few years, two-dimensional materials using as electrode of metal-ion batteries have attracted extensive attentions due to its excellent performance. Very recently, a novel monolayer (ML) SiS 2 with hexa-coordinated atomic conformation has been proposed. In this work, the capability of ML SiS 2 used as anode for Li, Na, and K-ions batteries has been comprehensive appraised via first-principles calculations. Our finding shown that the whole adsorption system is stable, and after adsorbing Li, Na and K atoms, the ML SiS 2 changes from semiconductivity to metallicity . In particular, Li, Na, and K-ions prefer disperse along the path I in ML SiS 2 and the corresponding migration barrier height are 0.210, 0.130 and 0.076 eV, respectively. Consequently, ML SiS 2 exhibits high rate performance. Besides, the maximum storage capacity of ML SiS 2 used as Li, Na, and K-ion batteries anode material are 581.280, 435.960 and 435.960 mAh/g, and the nominal open-circuit voltages for Li, Na, and K-ion batteries are 0.460, 0.380 and 0.620 V, respectively. These prominent properties indicate that ML SiS 2 is an auspicious metal-ion anode material. • The binding energy of metal atoms adsorbed on ML SiS 2 is negative. • The Li, Na, and K-ions tend to diffuse along the path I in ML SiS 2 . • Maximum capacity of Li, Na, and K-ions batteries are 581.280, 435.960 and 435.960 mA h/g. • The OCV for Li, Na, and K-ions batteries is 0.460, 0.380, and 0.620 V, respectively.

Ion pumping synergy with atomic anchoring for dendrite-free Zn anodes

• Ion pumping synergy with atomic anchoring is first proposed for Zn anodes. • The TCNQ@Zn foils effectively avoid 2D diffusion on the exposed Zn (101) surface. • The TCNQ@Zn foils induce 3D diffusion deposited on Zn (002) plane. • The TCNQ@Zn cells cycle over 2000 h under 1, 5, and 10 mA cm −2 . • The full cells maintain a capacity decay rate of only 0.03% over 1000 cycles. The practical application of aqueous Zn-ion batteries (AZIBs) has been limited by the notorious dendrite growth and side reactions of Zn anode, despite their high theoretical capacity, low cost, and intrinsic safety in large-scale energy storage. Herein, the tetracyanoquinodimethane anions (TCNQ 2− ) modified Zn anode (TCNQ@Zn) is fabricated via in-situ interfacial etching of Zn by TCNQ, which induces more exposure of Zn (101) planes. Benefitting from the abundant cyano group of TCNQ 2− , the TCNQ 2− can serve as an ion pump to continuously pump Zn 2+ in electrolyte for uniform Zn nucleation deposition on the exposed (101) surface. Simultaneously, owing to the significantly higher migration barrier on TCNQ 2− modified Zn (101) than (002), the 2D diffusion on the Zn (101) can be effectively inhibited, inducing 3D diffusion on Zn (002) to form the ordered (002) deposition orientation. These ordered Zn (002) textures significantly restrain the Zn dendrite formation and passivation reaction. Due to the synergistic effects of surficial ion pumping and atomic anchoring, the TCNQ@Zn anode exhibits remarkable cycling stability over 2000 h at different current densities (1, 5, and 10 mA cm −2 ). This work provides new theoretical guidance for highly stable reversible Zn metal anodes. TCNQ@Zn anode is fabricated by in situ interfacial reaction, which shows TCNQ 2− modified surface with a high proportion of Zn (101). Ion pumping synergy with atomic anchoring effect enable cells to cycle over 2000 h at 1, 5 and 10 mA cm −2 .

Enabling the fast sodium ions diffusion by constructing reduced graphene oxide/TiO2/MXenes tandem architecture for durable sodium ions battery

• The reduced graphene oxide/TiO 2 / Ti 3 C 2 F 2 with tandem architecture is proposed. • The rGO/TiO 2 /Ti 3 C 2 F 2 has exhibited the enhanced conductivity. • The theory calculation features that the Na + migration barrier of rGO/TiO 2 /Ti 3 C 2 F 2 can be significantly reduced. • The high Na + storage capacity and long-term cyclic stability of rGO/TiO 2 /Ti 3 C 2 F 2 has been demonstrated. In this work, a combined strategy of in-situ growth and sonication is proposed to prepare the reduced graphene oxide/TiO 2 /Ti 3 C 2 F 2 (rGO/TiO 2 /Ti 3 C 2 F 2 ) nanoflakes for enhanced sodium-ion batteries (SIBs). The rGO/TiO 2 /Ti 3 C 2 F 2 nanoflakes with the thickness of 3.806 nm exhibits the tandem nanostructure, which benefits to alleviate the aggregation of rGO and TiO 2 /Ti 3 C 2 F 2 layers, restrict the volume expansion of TiO 2 and improve the conductivity of whole electrode. Remarkably, the density functional calculation proves that the Na + migration barrier of rGO/TiO 2 /Ti 3 C 2 F 2 can be greatly decreased by introducing rGO. Moreover, the low charge transfer resistance is associated with rGO/TiO 2 /Ti 3 C 2 F 2 as well, these of which enable to boost the specific capacitance. As a result, the specific capacity of rGO/TiO 2 /Ti 3 C 2 F 2 anode reaches to 175.9 mAh g −1 after 100 cycles at 0.1 A g −1 , which is almost twice higher than that of pure Ti 3 C 2 F 2 (94.6 mAh g −1 ). Further, the rGO/TiO 2 /Ti 3 C 2 F 2 electrode demonstrates superior cyclic stability after 200 cycles at 1 A g −1 . The kinetics analysis features that the capacitive contribution increases to 78.6%. Beyond that, the Na + diffusion coefficient of rGO/TiO 2 /Ti 3 C 2 F 2 is 4.47 × 10 −11 ∼ 6.87 × 10 −10 cm 2 s −1 , which is higher than that of TiO 2 /Ti 3 C 2 F 2 (2.12 × 10 −12 ∼ 4.16 × 10 −11 cm 2 s −1 ).

First-principles comparative study of Cr migration in O3 and O/P hybrid-phased NaCrO2

In layered Na transition-metal (TM) oxides, TM migration usually occurs at highly charged states and severely deteriorates the capacity and reversibility. Meanwhile, the formation of hybrid phases with the intergrowth of octahedral (O-type) and prismatic (P-type) Na layers also takes place at highly charged states. These hybrid phases are often more stable than simple O3 or P3 stackings. However, little is known about the mechanism and impact of TM migration in these hybrid phases. In this work, a comparative first-principles study is performed to understand the connections between structural changes and Cr migration in layered O3 and hybrid-phased ${\mathrm{NaCrO}}_{2}$. After Cr migration, the hybrid-phased ${\mathrm{NaCrO}}_{2}$ suffers from greater layer shrinkage than the O3 phase. Three factors affect the Cr migration energy ${E}_{\mathrm{mig}}$: the Na concentration, local 3D configurations, and 2D in-plane geometries. Low Na concentrations and certain local 3D configurations facilitate the Cr migration. The Cr migration barriers in both O3 and hybrid-phased ${\mathrm{NaCrO}}_{2}$ are positively correlated with the $\mathrm{Cr}\phantom{\rule{0.28em}{0ex}}{E}_{\mathrm{mig}}$. The Cr migration in 17 doped O3 and hybrid-phased ${\mathrm{NaCrO}}_{2}$ is surveyed. In these doped ${\mathrm{NaCrO}}_{2}$, a more uniform distribution of the Cr--O bond lengths usually suggests suppressed Cr migration. Optimal dopants for suppressing Cr migration are identified by considering ${E}_{\mathrm{mig}}$ for both Cr and the dopant. Our comparative study on Cr migration in O3 and hybrid-phased ${\mathrm{NaCrO}}_{2}$ reveals the significant role of hybrid-phased structures in the development of layered cathode materials.

Insights into LiMXO4F (M-X = Al-P and Mg-S) as Cathode Coatings for High-Performance Lithium-Ion Batteries.

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 LiMXO4F (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 LiMXO4F (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 LiMXO4F (M-X = Al-P and Mg-S) are promising cathode coatings, among which LiAlPO4F has been experimentally confirmed. The theoretical cathode coating computational methods presented here can be extended to the solid-state battery system.

Vertically oriented 2D layered perovskite-based resistive random access memory (ReRAM) crossbar arrays

Resistive random-access memory (ReRAM) based on 2D layered perovskites have recently emerged as a new class of data storage devices, and the switching materials used in these devices have attracted extensive attention in recent years. There is a certain amount of variability in ReRAM owing to the stochastic nature of the formation and rupture of the conductive path, causing failure of the switching operation in the memory array. In this work, we fabricated both randomly and vertically oriented PEA2MA4Pb5I16-based ReRAM devices and conducted comparative studies of their switching variability. We demonstrated the formation of vertical alignment in PEA2MA4Pb5I16 films using methylammonium chloride (MACl) additives. Thereafter, the fabrication of 8×8 ReRAM crossbar arrays by patterning perovskites (∼600μm) and electrodes (line width ∼ 5 μm) using photolithography and e-beam lithography is demonstrated, and the resistive switching characteristics of both samples are discussed. Both cycle-to-cycle and device-to-device switching uniformity were improved in the vertically oriented film-based ReRAM devices, which can be explained by the narrow distribution of the energy barriers for VI migration owing to the vertically aligned charge transport path. These results suggest that vertically oriented 2D layered perovskites have great potential in ReRAM devices with improved switching uniformity.