Research development on electrolytes for magnesium-ion batteries

Conductivity and Diffusivity of Ions in Aqueous MgCl2 from Equilibrium and Nonequilibrium Simulations

Advanced electrochemical energy storage technologies require new electrolytes to be considered, so efficient computational characterization of ionic conductivity in a range of systems is of importance. In this manuscript we compare different equilibrium (EMD) and nonequilibrium molecular dynamics (NEMD) simulation algorithms to determine ionic conductivities. Aqueous magnesium ion batteries utilizing magnesium chloride as the electrolyte are a promising alternative to conventional lithium-ion batteries, so we focus on magnesium chloride electrolytes to demonstrate our results. We show the importance of accounting for ionic correlations and find that NEMD algorithms can provide more efficient calculations of ionic conductivity than EMD algorithms when ionic correlations need to be accounted for. In contrast, diffusivities and Nernst-Einstein conductivities can be determined more efficiently with EMD algorithms in the highly conductive systems considered here. We also demonstrate that the alignment of the water molecules due to the applied field in NEMD simulations is small at typical field strengths and has no impact on the calculated conductivities. Comparison of the results for the conductivity of different ions and their coupling provides insight into how force fields might be improved.

Research Progress of Electrolytes and Electrodes for Lithium- and Sodium-Ion Batteries at Extreme Temperatures

Lithium-ion batteries (LIBs) and sodium-ion batteries (SIBs) have recently received considerable attention in electrical energy storage (EES) systems due to their sustainability, high energy density, and superior energy conversion efficiency. However, with the expansion of energy storage application scenarios, the ability of batteries to operate under extreme conditions, especially low and high temperatures, is becoming increasingly important. Therefore, extending the operating temperature of electrochemically stable and safe LIBs and SIBs has become a critical research topic. In this review, the failure mechanism of batteries under extreme conditions and at the same time the problems faced by LIBs and SIBs in electrolyte and electrode materials are discussed, and various targeted optimization strategies are proposed. Additionally, the performance of LIBs and SIBs in such environments is compared, drawing an instructive understanding. Finally, a summary and perspective are presented for improving the battery electrochemical performance at low and high temperatures, respectively. Overall, this review aims to provide design guidelines for future LIBs and SIBs with high performance under extreme conditions.

Low-Concentration Electrolyte Engineering for Rechargeable Batteries

Low-concentration electrolytes (LCEs) present significant potential for actual applications because of their cost-effectiveness, low viscosity, reduced side reactions, and wide-temperature electrochemical stability. However, current electrolyte research predominantly focuses on regulation strategies for conventional 1 m electrolytes, high-concentration electrolytes, and localized high-concentration electrolytes, leaving design principles, optimization methods, and prospects of LCEs inadequately summarized. LCEs face unique challenges that cannot be addressed by the existing theories and approaches applicable to the three common electrolytes mentioned above; thus, tailored strategies to provide development guidance are urgently needed. Herein, a systematic overview of recent progress in LCEs is provided and subsequent development directions are suggested. This review proposes the core challenge of the high solvent ratio in LCEs, which triggers unstable organic-enriched electrolyte/electrode interface formation and anion depletion near the anode. On the basis of these issues, modification strategies for LCEs, including passivation interface construction and solvent‒anion interaction optimization, are used in various rechargeable battery systems. Finally, the role of advanced simulations and cutting-edge characterization techniques in revealing LCE failure mechanisms is further highlighted, offering new perspectives for their future development and practical application in next-generation rechargeable batteries.

Interplay between organic solvent geometry and divalent cation dynamics in divalent metal batteries

This study investigates the interplay between organic solvent geometry and divalent cation dynamics in liquid electrolytes, emphasizing their relevance for energy storage systems. Using classical molecular dynamics simulations, the structural and transport properties of Mg2+ and Ca2+ were evaluated in cyclic (ethylene carbonate, EC; propylene carbonate, PC) and linear (ethyl methyl carbonate, EMC) solvents in the presence of TFSI- anions across a range of temperatures. The results reveal that Mg2+ exhibits superior diffusion compared to Ca2+ due to its smaller ionic radius and weaker ion-pair interactions. Diffusion increases with temperature, following the solvent trend EC > EMC > PC. Coordination analysis showed compact solvation shells for both cations, with Ca2+ forming denser structures and demonstrating higher residence times compared to Mg2+. Solvent geometry significantly influenced solvation dynamics, with cyclic solvents enhancing ion coordination and linear solvents reducing solvation due to steric hindrance. These findings underscore the critical role of solvent structure and ion dynamics in optimizing divalent-ion battery performance, positioning Mg2+ as a promising candidate for sustainable energy storage solutions.

Critical Ingredients Revitalize Magnesium-Metal Batteries: Rationality and Challenges

Multivalent-metal batteries hold tremendous promise in solving safety and sustainability problems encountered by common lithium-ion batteries, but the lack of ideal electrolyte solutions restricts their large-scale adoption. Tuning electrolyte structures with functional ingredients, especially amines/methoxy-based amines and phosphates, can revitalize multivalent-metal anodes and high-voltage cathodes in conventional electrolytes, unlocking their full potential. However, a rational and clear understanding of the implications of these ingredients, notwithstanding critically important to commercially available electrolyte design, has not been widely accepted. This concise perspective aims to provide timely analysis and discussion on ingredients' functionalities of solvation shell speciation, interphase evolution, and consequently metal plating/stripping kinetics acceleration. In addition to prevailing coordination interactions, fresh understandings of intermolecular ionization/association and unique interphase formation are underscored by the close relationship between electrolyte chemistries and weakly passivated interphase properties. The existing understandings and proposed outlooks are expected to promote the next breakthroughs for rechargeable multivalent-metal batteries.

Recent advances in potassium metal batteries: electrodes, interfaces and electrolytes

The exceptional theoretical capacity of potassium metal anodes (687 mA h g-1), along with their low electrochemical potential, makes potassium metal batteries (PMBs) highly attractive for achieving high energy density. This review first provides an overview of potassium metal anodes, including their origin, current development status, and distinctive advantages compared to other metal anodes. Then, it discusses the composition and characteristics of emerging breakthrough PMBs, such as K-S, K-O2, K-CO2 batteries, and anode-free metal batteries. Subsequently, we delve into the pivotal challenges and theoretical research pertaining to PMBs, such as potassium metal nucleation/stripping, dendritic growth in PMBs, and unstable interfaces. Furthermore, we comprehensively examine the latest strategies in electrode design (including alloy, host, and current collector design), interface engineering (such as artificial solid electrolyte interphase layers, barrier layer design, and separator modification), and electrolyte optimization concerning nucleation, cycling stability, coulombic efficiency, and the development of PMBs. Finally, we introduce key characterization techniques, including in situ liquid phase secondary ion mass spectrometry, titration gas chromatography, neutron-based characterization, and computational simulation. This review will propel advancements in electrodes, separators, and electrolytes for innovative PMBs and other similar alkali metal batteries.

Constructing Three-Dimensional Porous SnS2/RGO as Superior-Rate and Long-Life Anodes for Lithium-Ion Batteries

Tin-based sulfides, possessing a unique layered structure and a high theoretical capacity, stand as highly prospective contenders for anode materials in lithium-ion batteries (LIBs). Nevertheless, the pronounced volume expansion that occurs during lithium storage and poor capacity retention have limited its progress toward commercialization. Herein, we designed and prepared a SnS2/RGO composite with a three-dimensional porous structure by sulfurizing the Sn6O4(OH)4/GO precursor. Through the integration of the structural architecture during the solvent reaction process and the nanomodification during the vulcanization process, the prepared SnS2/RGO composite has a porous structure, and the particle size is optimized at 2-5 nm. This structure is conducive to improving the conductivity of electrode materials, increasing reaction active sites, and enhancing the structural stability of electrode materials. Consequently, the synthesized SnS2/RGO composite is capable of retaining reversible capacities of 975 and 592 mA h g-1 after 250 cycles at 1.0 and 2.0 A g-1, respectively. Moreover, it exhibits a capacity of 349 mA h g-1 after 1100 cycles at 5.0 A g-1. This efficient and convenient preparation method provides guidance for enhancing the lithium storage properties of tin-based sulfides.

Coupling Manipulation of Interfacial Chemistry and Coordination Structure in Vanadium Oxides Enables Rapid Magnesium Ion Diffusion Kinetics

Rechargeable magnesium batteries (RMBs) are a highly promising energy storage system due to their high volumetric capacity and intrinsic safety. However, the practical development of RMBs is hindered by the sluggish Mg2+ diffusion kinetics, including at the cathode-electrolyte interface (CEI) and within the cathode bulk. Herein, we propose an efficient strategy to manipulate the interfacial chemistry and coordination structure in oligolayered V2O5 (L-V2O5) for achieving rapid Mg2+ diffusion kinetics. In terms of the interfacial chemistry, the specific exposed crystal planes in L-V2O5 possess strong electron donating ability, which helps to promote the degradation dynamics of C-F/C-S bonds in the electrolyte, thereby establishing the inorganic-organic interlocking CEI layer for rapid Mg2+ diffusion. In terms of the coordination structure, the straightened V-O structure in L-V2O5 provides efficient ions diffusion path for accelerating Mg2+ diffusion in the cathode. As a result, the L-V2O5 delivers a high reversible capacity (355.3 mA h g-1 at 0.1 A g-1) and an excellent rate capability (161 mAh g-1 at 1 A g-1). Impressively, the interdigital micro-RMBs is firstly assembled, exhibiting excellent flexibility and practicability. This work gives deeper insights into the interface and interior ions diffusion for developing high-kinetics RMBs.

Succinonitrile Electrolyte Additive for Stabilizing Aqueous Zinc Metal Batteries

The utilization of water electrolytes in zinc-ion batteries offers the advantages of enhanced safety, reduced cost, and improved environmental friendliness, rendering them an optimal choice for replacing lithium-ion batteries. Nevertheless, the conventional zinc sulfate electrolyte fails to meet stringent requirements. Therefore, developing electrolytes is crucial for addressing the low cycle life of zinc ions and suppressing the growth of zinc dendrites. So we proposed a strategy for engineering dilution of aqueous Zn(OTf)2 solution with succinonitrile (SN) network electrolytes. The introduction of SN also disrupts the original hydrogen bonding network within the system and mitigates issues related to side reactions. Additionally, the inclusion of SN additives significantly diminishes the reactivity of water molecules and smoothing zinc deposition to form favorable two-component Zn3N2/ZnF2 SEI. The results indicate that symmetric cells exhibit a remarkable cycling performance (877 h at current density and capacity of 1 mA cm-2 and 1 mAh cm-2, respectively). Furthermore, after 2000 cycles at a current density of 5 A g-1, the full battery demonstrates an impressive capacity of 151.2 mAh g-1. These results show that the electrolyte structure project provides a promising direction for the design of aqueous zinc-metal batteries, aiming to achieve high reversibility and long cycle life.

Influence of Chloride and Electrolyte Stability on Passivation Layer Evolution at the Negative Electrode of Mg Batteries Revealed by operando EQCM-D

Rechargeable magnesium batteries are promising for future energy storage. However, among other challenges, their practical application is hindered by low coulombic efficiencies of magnesium plating and stripping. Fundamental processes such as the formation, structure, and stability of passivation layers and the influence of different electrolyte components on them are still not fully understood. In this work, we gain unique insights into the initial Mg plating and stripping cycles by comparing magnesium bis(trifluoromethanesulfonyl)imide (Mg(TFSI)2)- and magnesium tetrakis(hexafluoroisopropyloxy)borate (Mg[B(hfip)4]2)-based electrolytes, each with and without MgCl2, on gold electrodes by highly sensitive operando electrochemical quartz crystal microbalance with dissipation monitoring (EQCM-D) applying hydrodynamic spectroscopy. With the stable Mg[B(hfip)4]2-based electrolytes, highly efficient and interphase-free cycling is possible and passivation layers are attributed to electrolyte contaminants. These are forming and degrading during the so-called initial conditioning process. With the more reactive Mg(TFSI)2-based electrolyte, thick passivation layers with small pores are growing during cycling. We demonstrate that the addition of chloride lowers the amount of passivated Mg deposits in these electrolytes and accelerates the currentless dissolution of the passivation layer. This has a positive effect since we observe the most efficient cycling and uniform deposition when no interphase is present on the electrode.

3D Tunnel Copper Tetrathiovanadate Nanocube Cathode Achieving Ultrafast Magnesium Storage Reactions through a Charge Delocalization and Displacement Mechanism

Rechargeable magnesium batteries are attractive candidates for large-scale energy storage applications because of the low cost and high safety, but the scarcity and inferior performance of the cathode materials are hindering the development. In the present study, a kind of copper tetrathiovanadate (Cu3VS4) cathode is designed and developed with a comprehensive consideration of the chemical and electronic structures. The vanadium and sulfur atoms form chemical bonds with high covalent proportion, facilitating electron delocalization via the vanadium-sulfur bonds. This reduces the interaction with the bivalent magnesium cation and induces the coredox of vanadium and sulfur. The crystal structure of Cu3VS4 has interlaced 3D tunnels for solid-state magnesium cation transport. The Cu3VS4 cathode shows a high capacity of 350 mA h g-1 at 100 mA g-1, an outstanding rate performance of 67 mA h g-1 at 10 A g-1, and stable cycling for 1000 cycles at 5 A g-1 without obvious capacity fading. Prominently, a high areal mass load of 3.5 mg cm-2 could be achieved without obvious rate capability decay, which is quite favorable to pair with the high-capacity magnesium metal anode in practical application. The mechanism investigation and theoretical computation demonstrate that Cu3VS4 undergoes first a magnesium intercalation and then a displacement reaction, during which the crystal structure is maintained, assisting the reaction reversibility and cycling stability. All the copper, vanadium, and sulfur elements experience redox and contribute to the high capacity. Moreover, the weakened interaction with magnesium cations, well-kept 3D cation transport tunnels, and high electronic conductivity result in the superior rate performance and high areal active material loading. The present study develops a high-performance cathode for rechargeable magnesium batteries and reveal the design principle based on both of chemical and electronic structures.

Enhancement of zinc-ion storage capability by synergistic effects on dual-ion adsorption in hierarchical porous carbon for high-performance aqueous zinc-ion hybrid capacitors

Aqueous zinc-ion capacitors (AZICs) are considered potential energy storage devices thanks to their ultrahigh power density, high safety, and extended cycling life. Carbon-based materials widely used as cathodes in AZICs face challenges, such as inappropriate pore sizes, poor electrolyte-electrode wettability, and insufficient vacancy defects and active sites. These limitations hinder efficient energy storage capacity and long-term stability. To address these issues, the B and F co-doped hierarchical porous carbon cathode materials (BFPC) are constructed through a facile annealing treatment process. The BFPC-2//Zn device exhibited high capacities of 222.4 and 118.3 mAh g-1 at current densities of 0.2 and 10 A g-1, respectively. Notably, the BFPC-2//Zn device demonstrated long-term cycling stability with a high capacity retention of 96.9 % after 20,000 cycles at 10 A g-1. Additionally, the assembled BFPC-2 based AZICs displayed a maximum energy density of 175.8 Wh kg-1 and an ultrahigh power density of 17.3 kW kg-1. Mechanism studies revealed that the exceptional energy storage ability and charge-transfer process of the BFPC cathode are attributed to the synergistic effect of B and F heteroatoms and the coupling effect between vacancy defects and pore size. This work presents a novel design strategy by incorporating B and F active sites into hierarchical porous carbon materials, providing enhanced energy storage capabilities for practical application in AZICs.

Recent Progress in Using Covalent Organic Frameworks to Stabilize Metal Anodes for Highly-Efficient Rechargeable Batteries

Alkali metals (e.g. Li, Na, and K) and multivalent metals (e.g. Zn, Mg, Ca, and Al) have become star anodes for developing high-energy-density rechargeable batteries due to their high theoretical capacity and excellent conductivity. However, the inevitable dendrites and unstable interfaces of metal anodes pose challenges to the safety and stability of batteries. To address these issues, covalent organic frameworks (COFs), as emerging materials, have been widely investigated due to their regular porous structure, flexible molecular design, and high specific surface area. In this minireview, we summarize the research progress of COFs in stabilizing metal anodes. First, we present the research origins of metal anodes and delve into their advantages and challenges as anodes based on the physical/chemical properties of alkali and multivalent metals. Then, special attention has been paid to the application of COFs in the host design of metal anodes, artificial solid electrolyte interfaces, electrolyte additives, solid-state electrolytes, and separator modifications. Finally, a new perspective is provided for the research of metal anodes from the molecular design, pore modulation, and synthesis of COFs.

Electrocatalysis in deep eutectic solvents: from fundamental properties to applications

Electrocatalysis stands out as a promising avenue for synthesizing high-value products with minimal environmental footprint, aligning with the imperative for sustainable energy solutions. Deep eutectic solvents (DESs), renowned for their eco-friendly, safe, and cost-effective nature, present myriad advantages, including extensive opportunities for material innovation and utilization as reaction media in electrocatalysis. This review initiates with an exposition on the distinctive features of DESs, progressing to explore their applications as solvents in electrocatalyst synthesis and electrocatalysis. Additionally, it offers an insightful analysis of the challenges and prospects inherent in electrocatalysis within DESs. By delving into these aspects comprehensively, this review aims to furnish a nuanced understanding of DESs, thus broadening their horizons in the realm of electrocatalysis and facilitating their expanded application.

Fine nanostructure design of metal chalcogenide conversion-based cathode materials for rechargeable magnesium batteries

Magnesium-ion batteries (MIBs) a strong candidate to set off the second-generation energy storage boom due to their double charge transfer and dendrite-free advantages. However, the strong coulombic force and the huge diffusion energy barrier between Mg2+ and the electrode material have led to need for a cathode material that can enable the rapid and reversible de-insertion of Mg2+. So far, researchers have found that the sulfur-converted cathode materials have a greater application prospect due to the advantages of low price and high specific capacity, etc. Based on these advantages, it is possible to achieve the goal of increasing the magnesium storage capacity and cycling stability by reasonable modification of crystal or morphology. In this review, we focus on the application of a variety of sulfur-converted cathode materials in MIBs in recent years from the perspective of microstructural design, and provide an outlook on current challenges and future development.

Superlong cycle-life sodium-ion batteries supported by electrode/active material interaction and heteroatom doping: Mechanism and application

To achieve both the capacity and stability of metal sulfides simultaneously remains a significant challenge. In this study, we have synthesized the manganese-doped copper sulfide three-dimensional (3D) hollow flower-like sphere (M/CuS-NSC), encapsulated in a nitrogen and sulfur co-doped carbon. The hollow lamellae structure allows the rational self-aggregation process of numerous active surface area enlarged nanosheets, thereby enhancing electrochemical activity. The subsurface framework characterized by CSC bonds enhances the pseudo-capacitive properties. Furthermore, the transformation of sulfur and the isomerization of carbon contribute to the enhancement of sodium ion storage. The incorporation of Mn into CuS lattice increases the interplanar distance, providing additional space for the accommodation of sodium ions. Mn doping facilitates the localization of electrons near the Fermi level, thereby improving conductivity. Additionally, Cu foils coated with M/CuS-NSC-2 engage with the electrolyte and sulfur, initiating the reaction sequence through the formation of Cu9S8. Consequently, M/CuS-NSC-2 exhibits highly reversible capacities of 676.24 mAh g-1 after 100 cycles at 0.1 A g-1 and 511.52 mAh g-1 after 10000 cycles at 10 A g-1, with an average attenuation ratio of only 0.009 %. In this study, we propose an effective strategy that combines structural design with heteroatom doping, providing a novel approach to enhance the electrochemical performance of monometallic sulfide.

Unveiling Organic Electrode Materials in Aqueous Zinc-Ion Batteries: From Structural Design to Electrochemical Performance

Aqueous zinc-ion batteries (AZIBs) are one of the most compelling alternatives of lithium-ion batteries due to their inherent safety and economics viability. In response to the growing demand for green and sustainable energy storage solutions, organic electrodes with the scalability from inexpensive starting materials and potential for biodegradation after use have become a prominent choice for AZIBs. Despite gratifying progresses of organic molecules with electrochemical performance in AZIBs, the research is still in infancy and hampered by certain issues due to the underlying complex electrochemistry. Strategies for designing organic electrode materials for AZIBs with high specific capacity and long cycling life are discussed in detail in this review. Specifically, we put emphasis on the unique electrochemistry of different redox-active structures to provide in-depth understanding of their working mechanisms. In addition, we highlight the importance of molecular size/dimension regarding their profound impact on electrochemical performances. Finally, challenges and perspectives are discussed from the developing point of view for future AZIBs. We hope to provide a valuable evaluation on organic electrode materials for AZIBs in our context and give inspiration for the rational design of high-performance AZIBs.

Enhancing Kinetics in Sodium Super Ion Conductor Na3MnTi(PO4)3 through Microbe-Assisted and Structural Optimization

Sodium (Na) super ion conductor (NASICON) structure Na3MnTi(PO4)3 (NMTP) is considered a promising cathode for sodium-ion batteries due to its reversible three-electron reaction. However, the inferior electronic conductivity and sluggish reaction kinetics limit its practical applications. Herein, we successfully constructed a three-dimensional cross-linked porous architecture NMTP material (AsN@NMTP/C) by a natural microbe of Aspergillus niger (AsN), and the structure of different NMTP cathodes was optimized by adjusting different transition metal Mn/Ti ratios. Both approaches effectively altered the three-dimensional NMTP structure, not only improving electronic conductivity and controlling Na+ diffusion pathways but also enhancing the electrochemical kinetics of the material. The resultant AsN@NMTP/C-650, sintered at 650 °C, exhibits better electrochemical performance with higher reversible three-electron reactions corresponding to the voltage platforms of Ti4+/3+, Mn3+/2+, and Mn4+/3+ around 2.1, 3.6, and 4.1 V (vs Na+/Na), respectively. The capacity retention rate is up to 89.3% after 1000 cycles at a 2C rate. Moreover, a series of results confirms that the Na3.4Mn1.2Ti0.8(PO4)3 cathode has the most excellent electrochemical performance when the Mn/Ti ratio is 1.2/0.8, with a high capacity of 96.59 mAh g-1 and 97.1% capacity retention after 500 cycles.

Rational Design of Nanosheet Array-Like Layered-Double-Hydroxide-Derived NiCo2O4 In Situ Grown on Reduced-Graphene-Oxide-Coated Nickel Foam for High-Performance Solid-State Supercapacitors

The investigation of high-performance supercapacitors is essential for accelerating the development of energy storage devices. In this work, a 3D hierarchical nanosheet array-like nickel cobaltite/reduced graphene oxide/nickel foam composite (NiCo2O4/rGO/NF) was assembled via an aqueous coprecipitation-hydrothermal strategy assisted by citric acid. Benefiting from a NiCo layered-double-hydroxide precursor with an atomic-level lattice confinement effect of metal ions and effective hybridization with rGO, the NiCo2O4/rGO/NF composite is featured as thin NiCo2O4 nanosheets (∼113.6 nm × 11.2 nm) composed of NiCo2O4 nanoparticles (∼10.9 nm) vertically staggered on the surface of a rGO-modified NF skeleton, leading to high surface area, abundant mesoporous structure, and active site exposure. The as-obtained NiCo2O4/rGO/NF was directly used as a binder-free integrated electrode for supercapacitors, achieving an excellent specific capacitance of 2863.4 F g-1 (1503.3 C g-1) at 1 A g-1, a superior rate performance of 2335.2 F g-1 at 20 A g-1, and a stability retention of 91.7% after 5000 cycles. More impressively, a solid-state asymmetric supercapacitor assembled by the present NiCo2O4/rGO/NF integrated electrode as the positive electrode and commercial activated carbon as the negative electrode achieved a high energy density of 69.2 Wh kg-1 at a power density of 800 W kg-1, and the energy density at a peak power density of 20004 W kg-1 still remained at 48.9 Wh kg-1, also showing a good cycling stability of 87.2% retention over 10000 cycles. The present facile synthesis strategy of the as-obtained NiCo2O4/rGO/NF nanosheet array composite can be used for the design and construction of many other transition-metal oxide/graphene/NF composite materials with excellent structural stability and performance in energy storage and other related areas.

Separator designs for aqueous zinc-ion batteries

Aqueous zinc-ion batteries (AZIBs) are attracting worldwide attention due to their multiple merits such as extreme safety, low cost, feasible assembly, and environmentally friendly enabled by water-based electrolytes. At present, AZIBs have experienced systematic advances in battery components including cathode, anode, and electrolyte, whereas research involving separators is insufficient. The separator is the crucial component of AZIBs through providing ion transport, forming contact with electrodes, serving as a container for electrolyte, and ensuring the efficient battery operation. Considering this great yet ignored significance, it is timely to present the latest advances in design strategies, the systematic classification and summary of separators. We summarize the separator optimization strategies mainly along two approaches including the modification of the frequently used glass fiber and the exploitation of new separators. The advantages and disadvantages of the two strategies are analyzed from the material types and the characteristics of different strategies. The effects and mechanisms of various materials on regulating the uniform migration and deposition of Zn2+, balancing the excessively concentrated nucleation points, inhibiting the growth of dendrites, and the occurrence of side reactions were discussed using confinement, electric field regulation, ion interaction force, desolvation, etc. Finally, potential directions for further improvement and development of AZIBs separators are proposed, aiming at providing helpful guidance for this booming field.

A Perspective on Uniform Plating Behavior of Mg Metal Anode: Diffusion Limited Theory versus Nucleation Theory

Utilizing metal anode is the most attractive way to meet the urgent demand for rechargeable batteries with high energy density. Unfortunately, the formation of dendrites, which is caused by uneven plating behavior, always threaten the safety of the batteries. To explore the origin of different plating behavior and predict the plating morphology of anode under a variety of operating conditions, multifarious models have been developed. However, abuse of models has led to conflictive views. In this perspective, to clarify the controversial reports on magnesium (Mg) metal plating behavior, the previously proposed models are elaborated that govern the plating process. Through linking various models and clarifying their boundary conditions, a scheme is drawn to illustrate the strategy for achieving the most dense and uniform plating morphology, which also explains the seemingly contradictory of diffusion limited theory and nucleation theory on uniform plating. This perspective will undoubtedly enhance the understanding on the metal anode plating process and provide meaningful guidance for the development of metal anode batteries.

Enhancing Sodium-Ion Transport by Hollow Nanotube Structure Design of a V5S8@C Anode for Sodium-Ion Batteries

V5S8 has received extensive attention in the field of sodium-ion batteries (SIBs) due to its two-dimensional (2D) layered structure, and weak van der Waals forces between V-S accelerate the transport of sodium ions. However, the long-term cycling of V5S8 still suffers from volume expansion and low conductivity. Herein, a hollow nanotube V5S8@C (H-V5S8@C) with improved conductivity was synthesized by a solvothermal method to alleviate cracking caused by volume expansion. Benefiting from the large specific surface area of the hollow nanotube structure and uniform carbon coating, H-V5S8@C exhibits a more active site and enhanced conductivity. Meanwhile, the heterojunction formed by a few residual MoS2 and the outer layer of V5S8 stabilizes the structure and reduces the ion migration barrier with fast Na+ transport. Specifically, the H-V5S8@C anode provides an enhanced rate performance of 270.1 mAh g-1 at 15 A g-1 and high cycling stability of 291.7 mAh g-1 with a retention rate of 90.98% after 300 cycles at 5 A g-1. This work provides a feasible approach for the structural design of 2D layered materials, which can promote the practical application of fast-charging sodium-ion batteries.

MOF-Derived Bimetallic Selenide CoNiSe2 Nanododecahedrons Encapsulated in Porous Carbon Matrix as Advanced Anodes for Lithium-Ion Batteries

Transition metal selenides have received considerable attention as promising candidates for lithium-ion battery (LIB) anode materials due to their high theoretical capacity and safety characteristics. However, their commercial viability is hampered by insufficient conductivity and volumetric fluctuations during cycling. To address these issues, we have utilized bimetallic metal-organic frameworks to fabricate CoNiSe2/C nanodecahedral composites with a high specific surface area, abundant pore structures, and a surface-coated layer of the carbon-based matrix. The optimized material, CoNiSe2/C-700, exhibited impressive Li+ storage performance with an initial discharge specific capacity of 2125.5 mA h g-1 at 0.1 A g-1 and a Coulombic efficiency of 98% over cycles. Even after 1000 cycles at 1.0 A g-1, a reversible discharge specific capacity of 549.9 mA h g-1 was achieved. The research highlights the synergistic effect of bimetallic selenides, well-defined nanodecahedral structures, stable carbon networks, and the formation of smaller particles during initial cycling, all of which contribute to improved electronic performance, reduced volume change, increased Li+ storage active sites, and shorter Li+ diffusion paths. In addition, the pseudocapacitance behavior contributes significantly to the high energy storage of Li+. These features facilitate rapid charge transfer and help maintain a stable solid-electrolyte interphase layer, which ultimately leads to an excellent electrochemical performance. This work provides a viable approach for fabricating bimetallic selenides as anode materials for high-performance LIBs through architectural engineering and compositional tailoring.

Scalable synthesis of N/S co-doped hard carbon microspheres as a high-performance anode material for sodium-ion batteries

Hard carbon is a promising anode material for sodium-ion batteries (SIBs) due to its abundance. However, it exhibits low reversible capacity and slow kinetics if inappropriate microstructural features are developed during synthesis. Herein, N/S co-doped phenolic resin-based hard carbon microspheres are prepared by a scalable strategy, and the electrochemical performance is assessed both in half cells and full cells. We demonstrate that the expanded interlayer spacing, the increased active sites, and the enhanced capacitive behavior result in the enhanced reversible capacity and promoted kinetics for Na+storage. The sample with appropriate doping amount exhibits an initial charge capacity of 536.8 mAh g-1at 50 mA g-1and maintains 445.9 mAh g-1after 1000 cycles at a current density of 1 A g-1in a Na-metal half cell. Coupled with a carbon-coated Na4Fe3(PO4)2P2O7(NFPP) cathode, the full cell exhibits a capacity of 92.5 mAh g-1after 90 cycles, with a capacity retention of 91.6%. This work provides a facile and scalable method for synthesizing high-performance hard carbon anode materials for SIBs.

Interlayer Engineering of VS2 Nanosheets via In Situ Aniline Intercalative Polymerization toward Long-Cycling Magnesium-Ion Batteries

Rechargeable magnesium batteries (RMBs) show great potential in large-scale energy storage systems, due to Mg2+ with high polarity leading to strong interactions within the cathode lattice, and the limited discovery of functional cathode materials with rapid kinetics of Mg2+ diffusion and desirable cyclability retards their development. Herein, we innovatively report the confined synthesis of VS2/polyaniline (VS2/PANI) hybrid nanosheets. The VS2/PANI hybrids with expanded interlayer spacing are successfully prepared through the exfoliation of VS2 and in situ polymerization between VS2 nanosheets and aniline. The intercalated PANI increases the interlayer spacing of VS2 from 0.57 to 0.95 nm and improves its electronic conductivity, leading to rapid Mg-ion diffusivity of 10-10-10-12 cm2 s-1. Besides, the PANI sandwiched between layers of VS2 is conducive to maintaining the structural integrity of electrode materials. Benefiting from the above advantages, the VS2/PANI-1 hybrids present remarkable performance for Mg2+ storage, showing high reversible discharge capacity (245 mA h g-1 at 100 mA g-1) and impressive long lifespan (91 mA h g-1 after 2000 cycles at 500 mA g-1). This work provides new perspectives for designing high-performance cathode materials based on layered materials for RMBs.

Fabrication of Nitrogen-Doped Carbon-Coated NiS1.97 Quantum Dots for Advanced Magnesium-Ion Batteries

Magnesium (Mg) batteries have garnered considerable interest because of their safety characteristics and low costs. However, the practical application of Mg batteries is hindered by the slow diffusion of Mg ions in the cathode materials. In this study, we prepared NiS1.97 quantum dot composites with nitrogen doping and carbon coating (NiS1.97 QDs@NC) using a one-step sulfurization process with NiO QDs/Ni@NC as the precursor. We applied the prepared NiS1.97 QDs/Ni@NC-based cathodes to Mg batteries because of the large surface area of the quantum dot composite, which provided abundant intercalation sites. This design ensured efficient deintercalation of magnesium ions during charge-discharge processes. The fabricated NiS1.97 QDs@NC displayed a high reversible Mg storage capacity of 259.1 mAh g-1 at 100 mA g-1 and a good rate performance of 96.0 mAh g-1 at 1000 mA g-1. Quantum dot composites with large surface areas provide numerous embedded sites, which ensure effective deintercalation of Mg ions during cycling. Thus, the proposed cathode synthesis strategy is promising for Mg-ion-based energy storage systems.