Optimizing interplanar spacing, oxygen vacancies and micromorphology via lithium-ion pre-insertion into ammonium vanadate nanosheets for advanced cathodes in aqueous zinc-ion batteries

Ammonium vanadates, featuring an N─H···O hydrogen bond network structure between NH4+ and V─O layers, have become popular cathode materials for aqueous zinc-ion batteries (AZIBs). Their appeal lies in their multi-electron transfer, high specific capacity, and facile synthesis. However, a major drawback arises as Zn2+ ions tend to form bonds with electronegative oxygen atoms between V─O layers during cycling, leading to irreversible structural collapse. Herein, Li+ pre-insertion into the intermediate layer of NH4V4O10 is proposed to enhance the electrochemical activity of ammonium vanadate cathodes for AZIBs, which extends the interlayer distance of NH4V4O10 to 9.8 Å and offers large interlaminar channels for Zn2+ (de)intercalation. Moreover, Li+ intercalation weakens the crystallinity, transforms the micromorphology from non-nanostructured strips to ultrathin nanosheets, and increases the level of oxygen defects, thus exposing more active sites for ion and electron transport, facilitating electrolyte penetration, and improving electrochemical kinetics of electrode. In addition, the introduction of Li+ significantly reduces the bandgap by 0.18 eV, enhancing electron transfer in redox reactions. Leveraging these unique advantages, the Li+ pre-intercalated NH4V4O10 cathode exhibits a high reversible capacity of 486.1 mAh g−1 at 0.5 A g−1 and an impressive capacity retention rate of 72% after 5,000 cycles at 5 A g−1

Influence of Symmetry from Crystal Structure and Chemical Environments of Magnetic Ions on the Fully Compensated Ferrimagnetism of Full Heusler Cr₂<i>YZ</i> and Mn₂<i>YZ</i> Alloys

Fully compensated ferrimagnets do not create any magnetic stray field and allow for a completely polarized current of charges. As a result, these alloys show promising prospects for applications as spintronic devices. In this paper, we investigated the phase stability, the site preference, the tetragonal distortion and the influence of symmetry from the crystal structure and chemical environments of magnetic ions on the magnetic properties of Cr2YZ and Mn2YZ (Y = void, Ni, Cu, and Zn; Z = Ga, Ge, and As) full Heusler alloys by first-principles calculations. We found that the selected Cr2-based alloys, except for Cr2NiGa and Cr2NiGe, prefer to crystallize in the centrosymmetric L21-type structure, while the selected Mn2-based alloys, except for Mn2CuAs, Mn2ZnGe and Mn2ZnAs, tend to crystallize in the non-centrosymmetric XA-type structure. Due to the symmetry, the antiferromagnetism of the selected L21-type alloys is very stable, and no spin-polarized density of states could be generated. In contrast, the magnetic moment of the selected XA-type alloys depends heavily on the number of valence electrons and tetragonal distortion, and spin-polarized density of states is generated. Therefore, the selected alloys with L21-type structures and their tetragonal-distorted structure are potential candidates for conventional antiferromagnets, while those with XA-type structure and their tetragonal-distorted structure are promising candidates for (fully) compensated ferrimagnets

Influence of Symmetry from Crystal Structure and Chemical Environments of Magnetic Ions on the Fully Compensated Ferrimagnetism of Full Heusler Cr2YZ and Mn2YZ Alloys

Fully compensated ferrimagnets do not create any magnetic stray field and allow for a completely polarized current of charges. As a result, these alloys show promising prospects for applications as spintronic devices. In this paper, we investigated the phase stability, the site preference, the tetragonal distortion and the influence of symmetry from the crystal structure and chemical environments of magnetic ions on the magnetic properties of Cr2YZ and Mn2YZ (Y = void, Ni, Cu, and Zn; Z = Ga, Ge, and As) full Heusler alloys by first-principles calculations. We found that the selected Cr2-based alloys, except for Cr2NiGa and Cr2NiGe, prefer to crystallize in the centrosymmetric L21-type structure, while the selected Mn2-based alloys, except for Mn2CuAs, Mn2ZnGe and Mn2ZnAs, tend to crystallize in the non-centrosymmetric XA-type structure. Due to the symmetry, the antiferromagnetism of the selected L21-type alloys is very stable, and no spin-polarized density of states could be generated. In contrast, the magnetic moment of the selected XA-type alloys depends heavily on the number of valence electrons and tetragonal distortion, and spin-polarized density of states is generated. Therefore, the selected alloys with L21-type structures and their tetragonal-distorted structure are potential candidates for conventional antiferromagnets, while those with XA-type structure and their tetragonal-distorted structure are promising candidates for (fully) compensated ferrimagnets

Multiaxial Strength Criterion Model of Concrete Based on Random Forest

The concrete strength criterion is the basis of strength analysis and evaluation under a complex stress state. In this paper, a large number of multiaxial strength tests were carried out, and many mathematical expressions of strength criteria were proposed based on the geometric characteristics and the assumption of a convex function. However, the rationality of the assumption of a convex function limits the use of these strength criteria. In particular, misjudgment will occur near the failure curve surface. Therefore, this paper does not assume the shape function of the criterion in advance. By collecting experimental data and using a machine learning method, it proposes a method of hidden function of failure curve surface. Based on 777 groups of experimental data, the random forest (RF), the back propagation neural network (BP) and the radial basis neural network (RBF) models were used to analyze and verify the feasibility and effectiveness of the method. Subsequently, the results were compared with the Ottosen strength criterion, the Guo Wang strength criterion and the Drucker&ndash;Prager (DP) strength criterion. The results show that the consistency between the strength criterion model established by the machine learning algorithm (especially random forest) and the experimental data is higher than the convex function multiaxis strength criterion of the preset failure surface shape. Moreover, the physical significance is clearer, the deficiency of the convex function failure surface hypothesis is avoided and the established multiaxial strength criterion of concrete is more universal

Stress Estimation of Concrete Dams in Service Based on Deformation Data Using SIE–APSO–CNN–LSTM

The stress behavior of key parts of concrete dams is related to the safe operation of the dam. However, the stress sensors in concrete are susceptible to aging and failure with increasing service life. Estimating the structural stress under sensor failure or data loss scenarios for concrete dams in service is essential and complex. This study presents a stress estimation method driven by the observation data. Firstly, a one-to-one correspondence exists between dam deformation reflecting the load effect and structural stress. Estimating the structural stress by simulating load effects with dam deformation is more convenient when it is hard to simulate complex load effects directly. Therefore, based on the observed data before stress sensor failure, the spatial–temporal relationship between structure stress and multi-point deformations of a concrete dam is developed using convolutional neural networks (CNN) and long short-term memory (LSTM). An improved particle swarm optimization algorithm combined with swarm information entropy (SIE–APSO) is proposed simultaneously for tuning the network’s hyperparameter and accelerating the convergence. Finally, the stress estimation of the target part of the concrete dam in service is obtained. The case shows that it is valid and feasible. The RMSE decreased by approximately 21–58%, MAPE decreased by 19–58%, and ARV decreased by 22–94% compared with the load-stress relationship model

Boosting the Development of Hard Carbon for Sodium-Ion Batteries: Strategies to Optimize the Initial Coulombic Efficiency

Given the merits of affordable cost, superior low-temperature performance, and advanced safe properties, sodium-ion batteries (SIBs) have exhibited great development potential in large scale energy storage applications. Among various emerging carbonaceous anode materials applied for SIBs, hard carbon (HC) has recently gained significant attention regarding their relatively low cost, wide availability, and optimal overall performance. However, the insufficient initial Coulombic efficiency (ICE) of HC is the main bottlenecks, which is inevitably hindering their further commercial applications. Herein, an in-depth holistic exposition about the reasons causing the unsatisfied ICE and the recent advances on effective improvement strategies are comprehensively summarized in this review, which have been divided into two aspects including the intrinsic property (degree of graphitization, pore structure, defect, et al.) and the extrinsic factor (electrolyte, electrode materials, et al.). In addition, future prospects and perspectives on HC to enable practical application in SIBs are also briefly outlined

Challenges and Strategies toward Manganese Hexacyanoferrate for High-Performance Sodium-Ion Batteries

Sodium-ion batteries (SIBs) are considered as a beneficial complement to lithium-ion batteries for large-scale energy storage systems because of the abundant sodium resources. However, the relatively large ionic radius of Na+ inevitably results in a huge volume change and sluggish electrochemical reaction kinetics, which put forward higher requirements for electrode materials. Among the reported cathode materials for SIBs, the manganese hexacyanoferrate (MnHCF) with the merits of large channels for fast sodium ion transport, high theoretical capacity and low cost has attracted extensive attention. In this review, the recent achievements of MnHCF for SIBs are focused. The key challenges of MnHCF limiting the practical application include the interstitial water, vacancies, low electronic conductivity, and the Jahn-Teller effect. Subsequently, the mainstream strategies to boost the sodium storage performance of MnHCF are summarized (such as structure regulation, surface coating, hybridization with carbon materials, and element substitution). Finally, the potential research directions are also proposed to promote the practical application of MnHCF for SIBs. This review is expected to provide a whole insight into exploring MnHCF cathode materials for SIBs

Recent Progress on Electrolyte Boosting Initial Coulombic Efficiency in Lithium-Ion Batteries

The initial Coulombic efficiency (ICE) of electrode materials is closely related to the energy density of lithium-ion batteries (LIBs). However, some promising electrode materials for next generation LIBs suffer from low ICE, which inevitably hinders their practical application. Among the discovered modified strategies for LIBs, electrolyte optimization has attracted extensive attention due to its facile operation process. Herein, the role of ICE in LIBs is first analyzed. Subsequently, the recent progress on effective electrolyte optimization strategies for boosting ICE in LIB is summarized (including the optimization of lithium salt, salt concentration, solvent, and electrolyte additive). Finally, future research directions of electrolyte optimization for boosting ICE are proposed. This review provides valuable guidance for developing advanced electrolyte for LIBs

Reappraisal of hard carbon anodes for practical lithium/sodium-ion batteries from the perspective of full-cell matters

Hard carbon (HC) has the potential to be a viable commercial anode material in both lithium-ion batteries (LIBs) and sodium-ion batteries (SIBs). However, current battery performance evaluation methods based on half-cells are insufficient for accurately assessing the performance of HC anodes due to their ultra-low discharge voltage windows. To develop the next-generation of large-scale rechargeable batteries, it is necessary to examine reported HC materials from a full-cell perspective. This review emphasizes the importance of full-cell validation and provides a comprehensive overview of HC anodes - including their history, fundamentals, carbon chemistry induced by temperature, microstructure correlation with electrochemical performance, and debates surrounding lithium/sodium-ion storage mechanisms. Additionally, this review highlights various optimization strategies and suggests potential areas for future application of HC-based lithium-ion batteries (HC-LIBs) and HC-based sodium-ion batteries (HC-SIBs). Furthermore, different challenges and strategies that need to be addressed are presented in the hope of providing inspiration and guidance for the commercialization of HC anodes

Catalytic Defect-Repairing Using Manganese Ions for Hard Carbon Anode with High-Capacity and High-Initial-Coulombic-Efficiency in Sodium-Ion Batteries

Hard carbon (HC) anodes have shown extraordinary promise for sodium-ion batteries, but are limited to their poor initial coulombic efficiency (ICE) and low practical specific capacity due to the large amount of defects. These defects with oxygen containing groups cause irreversible sites for Na+ ions. Highly graphited carbon decreases defects, while potentially blocking diffusion paths of Na+ ions. Therefore, molecular-level control of graphitization of hard carbon with open accessible channels for Na+ ions is key to achieve high-performance hard carbon. Moreover, it is challenging to design a conventional method to obtain HCs with both high ICE and capacity. Herein, a universal strategy is developed as manganese ions-assisted catalytic carbonization to precisely tune graphitization degree, eliminate defects, and maintain effective Na+ ions paths. The as-prepared hard carbon has a high ICE of 92.05% and excellent cycling performance. Simultaneously, a sodium storage mechanism of “adsorption-intercalation-pore filling-sodium cluster formation” is proposed, and a clear description given of the boundaries of the pore structure and the specific dynamic process of pore filling