Cyclic Instability Research Articles

Enabling Separator Modification with Sulfiphilic CoTe2 Sites on Electrospun Carbon Nanofibers for High-Performance Lithium-Sulfur Batteries

Lithium-sulfur batteries (LSBs) have been recognized as a promising candidate for next generation electrochemical energy-storage technologies owing to their unparalleled theoretical capacity and energy density compared to conventional lithium-ion batteries. However, the sluggish redox kinetics of the electrochemistry and the formidable dissolution of polysulfides during cycling lead to poor sulfur utilization, serious polarization, cyclic instability, and hazardous Li corrosion/dendrites issues. Herein, cobalt tellurides and carbon nanofibers composites (CoTe2@CNFs) were designed, synthesized by facial electrospinning, and applied to modify the separator of Li–S batteries, providing a viable solution for these challenges. The composites feature polar CoTe2 nanoparticles embedded in each carbon nanofiber, and the carbon nanofibers intertwine with each other to form an interconnected 3D nanofiber network. The sulfiphilic CoTe2 nanoparticles exhibit dual functionality, as they both strongly interact with soluble polysulfides and dynamically facilitate polysulfide redox reactions. Moreover, the 3D nanofiber network not only provides an additional physical barrier to lithium polysulfides (LiPSs) but also enables uniform sulfur distribution, thereby significantly inhibiting LiPSs shuttling and accelerating sulfur conversion reactions. In summary, the functionally modified separator synergistically works as both redox mediators, catalyzing the sulfur conversion, and a buffer layer, regulating Li ions stripping/deposition behaviors. This work has provided a new avenue for designing nanomaterials with synergistic effect of catalytic conversion and chemisorption of polysulfides to promote high-performance Li-S batteries. Furthermore, it is expected to inspire the engineering of novel material architectures with enhanced properties for various energy-storage devices.

Ultrafast microwave synthesis of MoSSe@ graphene composites via dual anion design for long-cyclable Li-S batteries

Lithium-sulfur batteries (LSBs) have been increasingly recognized as a promising candidate for the next-generation energy-storage systems. This is primarily because LSBs demonstrate an unparalleled theoretical capacity and energy density far exceeding conventional lithium-ion batteries. However, the sluggish redox kinetics and formidable dissolution of polysulfides lead to poor sulfur utilization, serious polarization issues, and cyclic instability. Herein, sulfiphilic few-layer MoSSe nanoflake decorated on graphene (MoSSe@graphene), a two-dimensional and catalytically active hetero-structure composite, was prepared through a facile microwave method, which was used as a conceptually new sulfur host and served as an interfacial kinetic accelerator for LSBs. Specifically, this sulfiphilic MoSSe nanoflake not only strongly interacts with soluble polysulfides but also dynamically promotes polysulfide redox reactions. In addition, the 2D graphene nanosheets can provide an extra physical barrier to mitigate the diffusion of lithium polysulfides and enable much more uniform sulfur distribution, thus dramatically inhibiting polysulfides shuttling meanwhile accelerating sulfur conversion reactions. As a result, the cells with MoSSe@graphene nanohybrid achieved a superior rate performance (1091 mAh/g at 1C) and an ultralow decaying rate of 0.040 % per cycle after 1000 cycles at 1C.

Experimental study on overtopping failure of concrete face rockfill dam

With the frequent occurrence of natural disasters, the problem of dam failure with low probability and high risk has gradually attracted people's attention. This paper uses flume model tests to systematically analyze the overtopping failure mechanisms of concrete face rockfill dam (CFRD) and identify its failure modes. The tests reveal that the longitudinal erosion of the CFRD breach progress through stages of soil erosion, panel failures, and water flow stabilization. Meanwhile, the cross-section breach process involves the evolution of breach size in rockfill materials, including traceable erosion, lateral broadening, and breach morphology stabilization. The fracture characteristics of the water-blocking panel are primarily evident in the flow-time curve. By analyzing the breach morphology evolution processes in longitudinal and cross sections, the flow-time curve can be subdivided into stages of burst flow formation, breach expansion with flow increase, rapid increase of breach flow discharge due to panel failures, and stabilization of breach flow and size. The primary damage process of the CFRD occurs in a cyclical stage of breach expansion, flow increase, panel failure, and rapid discharge. The rigid face plate and granular body structure contribute to partial dam failure, showing a tendency for gradual expansion of the breach. The longitudinal section illustrates dam failure resulting from panel fracture and rockfill erosion interaction, while downstream slopes exhibit failure due to lateral intrusion of rockfill and cyclic instability. These research results can serve as a reference for constructing a concrete CFRD failure prediction model and conducting disaster risk assessments.

Recoverable and plastic strains generated by forward and reverse martensitic transformations under external stress in NiTi SMA wires

Although superelastic NiTi shape memory alloy wire displays very high resistance to plastic deformation in austenite and martensite phases, incremental plastic strains are recorded whenever the cubic to monoclinic martensitic transformation (MT) proceeds under external stress leading to functional fatigue degradation. Therefore, special closed-loop thermomechanical loading tests were performed to shed light on the mechanism by which the incremental plastic strain are generated. These tests revealed that both forward and reverse MTs occurring above certain stress thresholds generate plastic strains specific for the [temperature, stress] conditions under which the MTs occurred. While the forward MT upon cooling does not produce plastic strain or permanent lattice defects up to 500 MPa stress, the reverse MT upon heating starts to generate them from 100 MPa. While plastic strain generated by the forward MT merely elongates the wire, plastic strain generated by the reverse MT also reduces the recoverable strain. Since the reverse MT upon heating generates plastic strains at lower external stresses than the forward MT upon cooling, it is largely responsible for cyclic instability of NiTi actuators. The characteristic thresholds and magnitudes of plastic strains generated by the forward and reverse MTs define the functional fatigue limits for specific NiTi wires.

Mesoporous copper-doped δ-MnO2 superstructures to enable high-performance aqueous zinc-ion batteries

Aqueous zinc-ion batteries (AZIBs) are competitive alternatives for large-scale energy-storage devices owing to the abundance of zinc and low cost, high theoretical specific capacity, and high safety of these batteries. High-performance and stable cathode materials in AZIBs are the key to storing Zn2+. Manganese-based cathode materials have attracted considerable attention because of their abundance, low toxicity, low cost, and abundant valence states (Mn2+, Mn3+, Mn4+, and Mn7+). However, as a typical cathode material, birnessite-MnO2 (δ-MnO2) has low conductivity and structural instability. The crystal structure may undergo severe distortion, disorder, and structural damage, leading to severe cyclic instability. In addition, its energy-storage mechanism is still unclear, and most of the reported manganese oxide-based materials do not have excellent electrochemical performance. Herein, we propose a copper-doped Cu0.05K0.11Mn0.84O2·0.54H2O (Cu2-KMO) cathode, which exhibits a large interlayer spacing, a stable structure, and accelerated reaction kinetics. This cathode was prepared using a simple hydrothermal method. The AZIB assembled using Cu2-KMO showed high specific capacity (600 mA h g−1 at 0.1 A g−1 after 75 cycles). The dissolution-deposition energy storage mechanism of Cu-KMO in AZIBs with double electron transfer was revealed using ex situ tests. The good electrochemical performance of the Cu2-KMO cathode fabricated by the doping strategy in this study provides ideas for the subsequent preparation of manganese dioxide using other strategies.

Experimental study on the influence of cyclic loading frequency on liquefaction characteristics of saturated sand

A series of undrained cyclic torsional shear tests was conducted to investigate the effect of cyclic loading frequency on the liquefaction characteristics of saturated sand using a hollow cylinder apparatus. The test results show that the dilative and contractive tendencies of various saturated sands are not only related to the physical properties of the sand, but are also affected by loading frequency. Under low-frequency loading, the saturated sand has a dilative behaviour, excess pore water pressure fluctuates after initial liquefaction and the soil maintains the ability to resist liquefaction to some extent after the initial liquefaction. The liquefaction mode in terms of the stress–strain relationship generally performs as the ‘cyclic mobility’. However, under high-frequency loading, the saturated sand has a contractive behaviour, and excess pore water pressure generally remains stable after the initial liquefaction. The liquefaction mode in terms of stress–strain relationship generally exhibits as ‘cyclic instability’. The deformation caused by low-frequency loading is significantly larger compared with that caused by high-frequency loading. At higher loading frequencies, the phase transformation stress ratio increases with the increase of loading frequency, and gradually approaches the failure stress ratio.

Failure mechanisms of saturated sand under different loading frequencies: Experimental observation and constitutive modelling

In this paper, we report on cyclic hollow cylinder tests on Fujian sand and Nanjing sand subjected to different loading frequencies. Depending on the loading frequencies we observed two distinct failure modes, i.e. cyclic mobility and cyclic instability. We proceed to develop a plasticity model to capture the features of our observations. The model employed a new flow rule for the effect of loading frequency on shear dilation and contraction characteristics to better reflect the changes in excess pore water pressure, deformation and strength of the saturated sand under cyclic loading. The model was validated by comparing numerical simulations with experimental results.

Achieving High Initial Coulombic Efficiency and Capacity in a Surface Chemical Grafting Layer of Plateau-type Sodium Titanate.

The plateau-type sodium titanate with suitable sodiation potential is a promising anode candidate for high safe and high energy density of sodium-ion batteries (SIBs). However, the poor initial Coulombic efficiency (ICE) and cyclic instability of sodium titanate are attributed to the unstable interfacial structure along with the decomposition of electrolytes, resulting in the continuous formation of solid electrolyte interface (SEI) film. To address this issue, a chemical grafting method is developed to fabricate a highly stable interface layer of inert Al2 O3 on the sodium titanate anode, rendering the high ICE and excellent cycling stability. Based on theoretical calculations, NaPF6 are more likely adsorption on the Al2 O3 surface and produce sodium fluoride. The formation of a thin and dense SEI film with rich sodium fluoride achieves the low interfacial resistances and charge-transfer resistances. Benefitting from our design, the obtained sodium titanate exhibits a high ICE from 67.7 % to 79.4 % and an enhanced reversible capacity from 151 mAh g-1 to 181 mAh g-1 at 20 mA g-1 , along with an increase in capacity retention from 56.5 % to 80.6 % after 500 cycles. This work heralds a promising paradigm for rational regulation of interfacial stability to achieve high-performance anodes for SIBs.

Effect of cobalt substitution for nickel on microstructural evolution and hydrogen storage properties of La0.66Mg0.34Ni3.5–xCox alloys

Superlattice hydrogen storage alloys offer a compelling advantage with rapid hydriding rate and high storage capacity. However, its practical applications face challenges including complex structure, low dehydriding capacity, and cyclic instability. In this work, we successfully prepared La0.66Mg0.34Ni3.5–xCox superlattice hydrogen storage alloys with enhanced dehydriding capacity and stability by partially substituting Co for Ni. X-ray diffraction (XRD) refinements analysis reveals the presence of (La,Mg)3Ni9, (La,Mg)5Ni19, and LaNi5 phases within the alloy. Following Co substitution in the La0.66Mg0.34Ni3.4Co0.1 alloy, there is a significant increase in content of the (La, Mg)3Ni9 phase and a reduction in the hysteresis factor, resulting in an improved reversible hydrogen storage capacity from 1.45 wt% to 1.60 wt%. The dehydriding kinetics of the alloy is controlled by diffusion model with an activation energy of 8.40 kJ/mol. Furthermore, the dehydriding enthalpy value of the Co-substituted alloy decreases from 30.84 to 29.85 kJ/mol. Impressively, the cycling performance of the alloy after Co substitution exhibits excellent stability, with a capacity retention rate of 92.3% after 100 cycles. These findings provide valuable insights for the development of cost-effective hydrogen storage materials.

4D Printable liquid crystal elastomers with restricted nanointerfacial slippage for long-term-cyclic-stability photothermal actuation.

Liquid crystal elastomers (LCEs) blended with photothermal nanofillers can reversibly and rapidly deform their shapes under external optical stimuli. However, nanointerfacial slipping inevitably occurs between the LCE molecules and the nanofillers due to their weak physical interactions, eventually resulting in cyclic instability. This work presents a versatile strategy to fabricate nanointerfacial-slipping-restricted photoactuation elastomers by chemically bonding the nanofillers into a thermally actuatable liquid crystal network. We experimentally and theoretically investigated three types of metal-based nanofillers, including zero-dimensional (0D) nanoparticles, one-dimensional (1D) nanowires, and two-dimensional (2D) nanosheets. The toughly crosslinked nanointerface allows for remarkably promoted interfacial thermal conductivity and stress transfer. Therefore, the resultant actuators enable the realization of long-term-cyclic-stability 4D-printed flexible intelligent systems such as the optical gripper, crawling robot, light-powered self-sustained windmill, butterflies with fluttering wings, and intelligent solar energy collection system.

In-Situ Convertible Amorphous Silicon Nitride (SiNx) Anode: Resolving the Long-Term Cyclic Instability of Silicon

Silicon (Si) has shown its promises as anode material for next-generation high-energy lithium-ion batteries (LIBs) due to its high theoretical capacity1. However, its practical application has been impeded by the severe cyclic instability caused by a large volume change during (de) lithiation. Recently, a new family of silicon-based anode materials called “in-situ convertible-type anode materials” has emerged to resolve the cyclic instability of silicon.2,3 This family includes sub-stoichiometric oxides, nitrides, and carbides of silicon (SiAx, where A = N, C, O). The working principle of these materials follow two mechanisms: (1) irreversible conversion and (2) reversible alloying/dealloying. During initial lithiation, the conversion reaction occurs, forming Si-Li nanodomains inside a stable Li-conductive matrix denoted as LiySixA (A=N, C, O). In the subsequent cycles, the Si-Li nanodomains reversibly alloying/dealloying with Li, while the Li-conductive matrix ensures stable cycling and good rate capability. Such composition mitigates the challenges associated with Si’s large volume change ensuring long-term cyclic stability.In this study, we demonstrate our approach on the development of silicon-rich, sub-stochiometric, amorphous silicon nitride (SiNx) nanoparticles, as an in-situ convertible-type anode material and its long-term cyclic performance for LIBs. In this approach, the SiNx nanoparticles are produced via the decomposition of silane gas in the presence of ammonia using an industrially scalable, free space reactor (FSR), which is developed and customized in our research institute (IFE) (Fig. 1a). Proper proportions of silane and ammonia gases are introduced into the reactor, leading to the nucleation and growth of SiNx nanoparticles. The synthesized SiNx nanoparticles exhibited Si-rich domain and amorphous structure with particle size between 100 nm - 200 nm (Fig. 1b), as confirmed by SEM, TEM and XRD characterizations. The presence of nitrogen in silicon dominated composition is revealed by energy dispersive electron spectroscopy (EDS) and Fourier-transform infrared spectroscopy (FTIR). The scalability and reproducibility of the FSR synthesis method makes it a promising approach for the industrial production of SiNx for advance anode materials for LIBs.The electrochemical performance of the synthesized SiNx anode is evaluated by galvanostatic cycling and electrochemical impedance spectroscopy. The electrochemical performance of the SiNx performed on the electrodes with the active mass loading of 0.987 mg/cm2 and cycled at C/5 rate has preserved its capacity about 852 mAh/g after around 600 cycles. As seen from Fig. 1c, the improved cyclic stability of the SiNx compared with pure silicon indicates that the Li-conductive matrix plays crucial role in stabilizing the anode. The authors emphasize the need for further investigation and collaboration, particularly in advance characterization, to better understand the composition and mechanisms of the Li-conductive matrix in the SiNx anode. Such detailed understanding can significantly benefit the conversion-type anode materials for their widespread use in future LIB technologies.References Zuo, X., Zhu, J., Müller-Buschbaum, P. & Cheng, Y.-J. Silicon based lithium-ion battery anodes: A chronicle perspective review. Nano Energy 31, 113–143 (2017).Ulvestad, A. et al. Stoichiometry-Controlled Reversible Lithiation Capacity in Nanostructured Silicon Nitrides Enabled by in Situ Conversion Reaction. ACS Nano 15, 16777–16787 (2021).Kilian, S. O. et al. Active Buffer Matrix in Nanoparticle-Based Silicon-Rich Silicon Nitride Anodes Enables High Stability and Fast Charging of Lithium-Ion Batteries. Advanced Materials Interfaces 9, 2201389 (2022). Figure 1

Optimizing supercooling and phase stability by additives in calcium chloride hexahydrate for cyclical latent heat storage

Calcium chloride hexahydrate (CaCl2·6H2O) based phase change material (PCM) is promising for latent heat storage due to its favorable thermal properties, but supercooling and thermal cyclic instability limits its wider application. We examine the role of nucleation agents, in particular strontium chloride hexahydrate (SrCl2·6H2O), as an additive to the PCM, on the degree of supercooling and the latent heat. Utilizing a water bath and a cooling chamber, we systematically evaluate the degree of supercooling in various PCM samples, while X-Ray diffraction and microscopic analysis are employed to characterize the role of the additive. The results suggest that particle shapes of the additives and their crystallographic phase contribute significantly to supercooling suppression. Optimizing a tradeoff between supercooling and latent heat reduction for long-term nucleation performance, we identify designer PCM composition with an optimal 3 wt% of SrCl2·6H2O for an automated thermal cycling system by differential scanning as well as drop calorimetry. Incorporating 2 wt% potassium chloride (KCl) shifts the composition at the peritectic point away from the unfavorable CaCl2·4H2O phase, enhancing the freeze-thaw cycle stability of CaCl2·6H2O. Notably, the latent heat variation is ∼0.08% over 1000 freeze-thaw cycles.

Low hysteresis and high cyclic stability in a Ti50Ni45.2Cu1Fe3.8 shape memory alloy

Shape memory alloys, exhibiting shape memory effect and superelasticity, are the key components of actuators and sensors. However, the hysteresis and cyclic instability associated with the martensitic phase transformation, limit their use in the long-duration precise control. We report a quaternary TiNiCuFe shape memory alloy with ultra-low hysteresis and high cyclic stability. The discovery of this alloy is guided by investigating the synergistic effect of Fe and Cu on the martensitic phase transformation. The optimized alloy Ti50Ni45.2Cu1Fe3.8, shows a hysteresis measured by electric resistance, as low as 0.3 K (the hysteresis by differential scanning calorimetry is about 3.5 K), and a shift of phase transformation temperature about 0.05 K (after 60 cycles). Compared to the state-of-the-art TiNiCuPd alloy with a Cu content higher than 10 at %, the Cu content in our alloy is reduced to only 1 at %, thereby suppress the brittleness and improve the workability. In addition, the precious metal, Pd is replaced by the low-cost Fe, which may facilitate the wide applications of shape memory alloys. The origin of the optimized hysteresis and cyclic stability, is ascribed to the possible phase coexistence of B19 and R that is realized by manipulating the phase transformation paths with Fe and Cu. This singular microstructure may accommodate more phase transformation strain and consequently mitigate the incompatibility of the austenite/martensite interfaces.

Anomalous fatigue crack propagation behavior in near-threshold region of L-PBF prepared austenitic stainless steel

Laser powder bed fusion (L-PBF) process produces a specific non-equilibrium microstructure with properties significantly different from those of conventionally processed materials. In the present study, the near-threshold fatigue crack propagation in austenitic stainless steel 304L processed by L-PBF was investigated. Three series of specimens with different orientation of initial notch with respect to build direction were manufactured in order to evaluate the effect of specimen orientation on the near-threshold fatigue crack propagation behavior. The results showed absence of the orientation dependence of the fatigue crack propagation behavior. In addition, abnormally low threshold stress intensity factor values were recorded, which were attributed to the absence of crack closure even at low load ratio (R = 0.1). In order to explain observed behavior, the specimens of selected orientation were heat treated to relieve build-in residual stresses (HT1) and to create recrystallized microstructure (HT2) comparable to conventionally processed (wrought) stainless steels. It was found that the characteristic microstructure produced by L-PBF is the main reason for the absence of crack closure and the low threshold values at low load ratios. As-built microstructure containing sub-micron dislocation cell-substructure is prone to cyclic instability. In the crack tip region, cyclic plasticity results in strain-induced phase transformation and continuous thin martensitic layer is formed in the crack vicinity. The induced martensite phase is softer compared to the austenite matrix strengthened by cell-substructure. Together with cyclic instability of the matrix, the macroscopic cyclic softening occurs as the result within the crack tip region. Under such conditions, the formation of the plasticity-induced and roughness-induced crack closure is significantly reduced and macroscopic resistance to the fatigue crack propagation is low.

Recent advances of structural/interfacial engineering for Na metal anode protection in liquid/solid-state electrolytes.

Na metal anode is one of most promising anode materials for next-generation secondary batteries. However, the practical application of Na anode is limited by dendritic growth, rapid volume change, and serious interface problems in the process of Na electroplating/stripping, resulting in low coulombic efficiency, short life, and safety issues of sodium metal batteries (SMBs). Herein, the cyclic instability mechanisms of the Na anode and the corresponding advanced protection strategies including in situ solid-electrolyte-interphase (SEI), artificial SEI, and three-dimensional conductive frame, are systematically reviewed. Notably, this review summarizes the latest research progress on interface modification and electrode modification of all-solid-state SMBs. Finally, the outlooks of anode interphase in SMBs are summarized and prospected, providing a promising way for high-energy and safe SMBs.

Linking inherent anisotropy with liquefaction phenomena of granular materials by means of DEM analysis

The liquefaction phenomena of sands have been studied by many researchers to date. Laboratory element tests have revealed key factors that govern liquefaction phenomena, such as relative density, particle size distribution, and grain shape. However, challenges remain in quantifying inherent anisotropy and in evaluating its impact on liquefaction phenomena. This contribution explores the effect of inherent anisotropy on the mechanical response of granular materials using the discrete element method. Samples composed of spherical particles are prepared which have approximately the same void ratio and mean coordination number (CN), but varying degrees of inherent anisotropy in terms of contact normals. Their mechanical responses are compared under drained and undrained triaxial monotonic loading as well as under undrained cyclic loading. The simulation results reveal that cyclic instability followed by liquefaction can be observed for loose samples having a large degree of inherent anisotropy. Since a sample having initial anisotropy tends to deform more in its weaker direction, leading to lower liquefaction resistance, a sample having an isotropic fabric potentially exhibits the greatest liquefaction resistance. Moreover, the effective stress path during undrained cyclic loading is found to follow the instability and failure lines observed for static liquefaction under undrained monotonic loading. From a micromechanical perspective, the recovery of effective stress during liquefaction can be observed when a threshold CN develops along with the evolving induced anisotropy. Realising that the conventional index of the anisotropic degree (a) is not effective when the CN drops to almost zero during cyclic liquefaction, this contribution proposes an alternative index, effective anisotropy (a×CN), with which the evolution of induced anisotropy can be tracked effectively, and common upper and lower bounds can be defined for both undrained monotonic and cyclic loading tests.

Multi‐decadal coastline dynamics in Suriname controlled by migrating subtidal mudbanks

AbstractFor the development of climate‐resilient coastal management strategies, which focus on challenges in the decades to come, it is critical to incorporate spatial and temporal variability of coastline changes. This is particularly true for the mud‐dominated coastline of Suriname, part of the Guianas, where migrating subtidal mudbanks cause a cyclic instability of erosion and accretion of the coast that can be directly related to interbank and bank phases. The coastline hosts extensive mangrove forests, providing valuable ecosystem services to local communities. Recent studies on mudbank dynamics in Suriname predominantly focused on large‐scale trends without accounting for local variability, or on local changes considering the dynamics of a single mudbank over relatively short time scales. Here we use a remote sensing approach, with sufficient spatial and temporal resolution and full spatial and temporal coverage, to quantify the influence of mudbank migration on spatiotemporal coastline dynamics along the entire coast of Suriname.We show that migration of six to eight subtidal mudbanks in front of the Suriname coast has a strong imprint on local coastline dynamics between 1986 and 2020, with an average 32 m/yr accretion during mudbank presence and 4 m/yr retreat of the coastline during mudbank absence. Yet, coastal erosion can still occur when mudbanks are present and coastal aggregation may happen in the absence of mudbanks, exemplifying local variability and thus suggesting the importance of other drivers of coastline changes.The novel remote sensing workflow allowed us to analyse local spatial and temporal variations in the magnitude and timing of expanding and retreating trajectories. Our results demonstrate that it is essential that all coastal behaviours, including changes that cannot be explained by the migration of mudbanks, are included in multi‐decadal management frameworks that try to explain current variability, and predict future coastline changes in Suriname.

Tuning Transition Metal Oxides Towards Achieving Water-Stability and Electrochemical Stability As Electrode Materials for Sodium-Ion Batteries

Transition metal (TM) oxides are a fascinating class of materials, whose properties can be suitably tuned in a variety of ways; such as by selecting TM-ions/dopants having preferred electronic configurations, engineering the crystallographic site occupancy by dopants, controlling/modifying the degree of covalence of TM-O bonds, modifying lattice spacing(s), tuning phase assemblage etc. Such modifications done from the fundamental perspectives influence the performances of TM-oxides for a variety of applications, including their widespread usage as electrode-active materials in alkali metal-ion batteries.In the context of the upcoming Na-ion battery system, O3-type ‘layered’ Na-TM-oxides are promising as cathode-active materials due to their inherently high initial Na-content (as compared to the P2 counterparts). However, they suffer from instabilities caused due to multiple phase transformations during Na-removal/insertion and sensitivity to air/moisture. Against this backdrop, with the help of a dopant, having d 0 electronic configuration (viz., no octahedral site preference energy), we have been able to tune the composition and structural features to suppress the phase transitions upon Na-removal/insertion and also improve the air/water-stability in significant terms; so much so that long-term cyclic stability has been achieved with health/environment-friendly ‘aqueous processed’ electrodes (sans, usage of toxic/hazardous/expensive chemicals like NMP and PVDF) [1]. As will be explained in more elaborate terms during the talk, the changes in structural features, which have led to such outstanding water-stability, include differential contraction/dilation of the Na-‘inter-slab’/TM-‘slab’ spacing and partial occupancy of the dopant at tetrahedral sites of the structure.On the anode front, successful development of Na-ion battery system necessitates looking beyond hard carbon based anodes, which possess safety hazards due to the Na-insertion potential being a bit too close to the Na-plating potential. In this context, Na-titanates promise to be ‘safe’ anode materials; but suffer from cyclic instability [2]. Against this backdrop, we have developed carefully tuned bi-phase Na-titanate based electrodes, having Na2Ti3O7 and Na2Ti6O13 as the primary and secondary phases, respectively. The as-developed phase assemblage has been able to address the cyclic instability of single-phase Na-titanate, leading to long-term cyclic stability even at high current densities (up to 50C!) [3]. These are important steps towards the development of health/environment-friendly, cost-effective, safe and high-performance Na-ion batteries.Acknowledgement to RRCAT, Indore, India, for enabling the usage of Synchrotron facility.Parts of the concerned works have been published as (i.e., the associated publications); B. S. Kumar, A. Pradeep, A. Dutta, and A. Mukhopadhyay; J. Mater. Chem. A 8 (2020) 18064H. S. Bhardwaj, T. Ramireddy, A. Pradeep, M. K. Jangid, V. Srihari, H. K. Poswal, and A. Mukhopadhyay; ChemElectroChem 5[8] (2018) 1219A. Pradeep, B. S. Kumar, A. Kumar, V. Srihari, H. K. Poswal, and A. Mukhopadhyay; Electrochim. Acta 362 (2020) 137122

Low Cycle Fatigue of Structural Alloys

Metallurgy, mechanical engineering, energy, agriculture, food industry, energy, electronics, rocket and space technology – this is a far from complete list of areas of the national economy in which liquid cryogenic products (cryoproducts). The production volumes of such products and the scale of their use are constantly increasing. This is due to the fact that cryogenic temperatures (below 120 K) provide unique opportunities for the implementation of such physical phenomena and processes that do not manifest themselves under normal conditions, but are used very effectively in science and technology. The solution of fundamental scientific problems and applied problems of both promising and current importance is determined by the level of development of cryogenic technology and the degree of its practical application. The continuous expansion of the scale of production of liquid cryogenic products has led in recent years to a significant increase in the volume of production of systems for their storage and transportation. These systems, as a rule, are welded shell structures in execution, they are operated in difficult conditions of temperature and force effects. The share of their production in the total output of cryogenic engineering products is very significant, and the operating conditions are the most stressful in comparison with other types of cryogenic structures. For the manufacture of cryogenic shell structures, expensive non-ferrous alloys and special steels are used, the degree of consumption of which, taking into account the sufficient material consumption of such structures and the expanding scale of their production, is constantly increasing. Therefore, one of the most urgent for cryogenic mechanical engineering at present is the problem of reducing the material consumption of shell structures and increasing their reliability and durability. It is obvious that a solution to this problem for cryogenic engineering products can be achieved by improving the methods of their strength calculations based on taking into account the specific hardening effect of low temperature on structural alloys. The phenomenon of low-cycle fatigue of metals is associated with elastoplastic deformation of their macrovolumes. The kinetics of elastoplastic deformation processes under cyclic loading depends on the loading conditions and material properties, and the nature of these processes and their intensity have a decisive influence on the features of material destruction. If the accumulation of deformation is small, then the destruction, as a rule, is of a fatigue nature; quasi-static fracture (similar in appearance to fracture during static tests for short-term strength) occurs after the realization of the ultimate plasticity of the material. The task of assessing the bearing capacity and durability under cyclic loading conditions is extremely important. Under cyclic loading, a number of specific phenomena and factors that are difficult to take into account analytically arise, which are primarily associated with the development of fatigue damage, with the need to assess the cyclic and structural instability of materials [1]. Since such studies are very laborious and expensive, the problem of minimizing such experiments is currently urgent. In this paper, we investigate the possibility of using mathematical planning methods for experimental studies at cryogenic temperatures. Experiment planning is usually understood as the procedure for choosing the volume and conditions of testing necessary and sufficient to solve the problem with the required accuracy.

MACLOCYCLE FATIGUE OF STRUCTURAL ELEMENT UNDER SOFT LOADING.

In the article the method of calculation of capacity for work construction element of low – cycle deformation diagrams with considering of cyclic instability and unilateral accommodation of plastic deformation.