Iodine Vapor Transport-Triggered Preferential Growth of Chevrel Mo6S8 Nanosheets for Advanced Multivalent Batteries

Unveiling potential of cellulose gel electrolyte: Molecular engineering for enhanced electrostatic interactions with Mg adatoms in Mg-ion battery

The Mg-ion battery faces significant limitations due to its liquid electrolyte, which suffers from inherent issues such as leakage and the growth of Mg dendrites. In contrast, gel polymer electrolytes (GPEs) offer heightened safety, a wide voltage window, and excellent flexibility, making them a promising alternative with outstanding electrochemical performance. In this study, a cyano-modified cellulose (CEC) GPE was engineered to aim at enhancing ion transportation and promoting uniform ion-flux through interactions between N and Mg2+ ions. The resulting CEC-based GPE demonstrated a high ionic conductivity of 1.73 mS cm-1 at room temperature. Furthermore, it exhibited remarkable Mg plating/stripping performance (coulombic efficiency ~96.7 %) and compatibility with electrodes. Importantly, when employed in a Mo6S8//Mg battery configuration, the CEC GPE displayed exceptional cycle stability, with virtually no degradation observed even after 650 cycles at 1C, thereby significantly advancing Mg-ion battery technology due to its excellent electrochemical properties. This study provides valuable insights into the molecular engineering of cellulose-based GPEs.

Nanosized Chevrel phases for dendrite-free zinc-ion based energy storage: unraveling the phase transformations

The nanoscale form of the Chevrel phase, Mo6S8, is demonstrated to be a highly efficient zinc-free anode in aqueous zinc ion hybrid supercapacitors (ZIHSCs). The unique morphological characteristics of the material when its dimensions approach the nanoscale result in fast zinc intercalation kinetics that surpass the ion transport rate reported for some of the most promising materials, such as TiS2 and TiSe2. In situ Raman spectroscopy, post-mortem X-ray diffraction, Hard X-ray photoelectron spectroscopy, and density functional theory (DFT) calculations were combined to understand the overall mechanism of the zinc ion (de)intercalation process. The previously unknown formation of the sulfur-deficient Zn2.9Mo15S19 (Zn1.6Mo6S7.6) phase is identified, leading to a re-evaluation of the mechanism of the (de)intercalation process. A full cell comprised of an activated carbon (YEC-8A) positive electrode delivers a cell capacity of 38 mA h g-1 and an energy density of 43.8 W h kg-1 at a specific current density of 0.2 A g-1. The excellent cycling stability of the device is demonstrated for up to 8000 cycles at 3 A g-1 with a coulombic efficiency close to 100%. Post-mortem microscopic studies reveal the absence of dendrite formation at the nanosized Mo6S8 anode, in stark contrast to the state-of-the-art zinc electrode.

Enhancing Reversibility and Stability of Mg Metal Anodes: High-Exposure (002) Facets and Nanosheet Arrays for Superior Mg Plating/Stripping

Magnesium metal batteries (MMBs), recognized as promising contenders for post-lithium battery technologies, face challenges such as uneven magnesium (Mg) plating and stripping behaviors, leading to uncontrollable dendrite growth and irreversible structural damage. Herein, we have developed a Mg foil featuring prominently exposed (002) facets and an architecture of nanosheet arrays (termed (002)-Mg), created through a one-step acid etching method. Specifically, the prominent exposure of Mg (002) facets, known for their inherently low surface and adsorption energies with Mg atoms, not only facilitates smooth nucleation and dense deposition but also significantly mitigates side reactions on the Mg anode. Moreover, the nanosheet arrays on the surface evenly distribute the electric field and Mg ion flux, enhancing Mg ion transfer kinetics. As a result, the fabricated (002)-Mg electrodes exhibit unprecedented long-cycle performance, lasting over 6000 h (>8 months) at a current density of 3 mA cm-2 for a capacity of 3 mAh cm-2. Furthermore, the corresponding pouch cells equipped with various electrolytes and cathodes demonstrate remarkable capacity and cycling stability, highlighting the superior electrochemical compatibility of the (002)-Mg electrode. This study provides new insights into the advancement of durable MMBs by modifying the crystal structure and morphology of Mg.

Unlocking Four-electron Conversion in Tellurium Cathodes for Advanced Magnesium-based Dual-ion Batteries

Magnesium (Mg) batteries hold promise as a large-scale energy storage solution, but their progress has been hindered by the lack of high-performance cathodes. Here, we address this challenge by unlocking the reversible four-electron Te0/Te4+ conversion in elemental Te, enabling the demonstration of superior Mg//Te dual-ion batteries. Specifically, the classic magnesium aluminum chloride complex (MACC) electrolyte is tailored by introducing Mg bis(trifluoromethanesulfonyl)imide (Mg(TFSI)2), which initiates the Te0/Te4+ conversion with two distinct charge-storage steps. Te cathode undergoes Te/TeCl4 conversion involving Cl- as charge carriers, during which a tellurium subchloride phase is presented as an intermediate. Significantly, the Te cathode achieves a high specific capacity of 543 mAh gTe -1 and an outstanding energy density of 850 Wh kgTe -1, outperforming most of the previously reported cathodes. Our electrolyte analysis indicates that the addition of Mg(TFSI)2 reduces the overall ion-molecule interaction and mitigates the strength of ion-solvent aggregation within the MACC electrolyte, which implies the facilized Cl- dissociation from the electrolyte. Besides, Mg(TFSI)2 is verified as an essential buffer to mitigate the corrosion and passivation of Mg anodes caused by the consumption of the electrolyte MgCl2 in Mg//Te dual-ion cells. These findings provide crucial insights into the development of advanced Mg-based dual-ion batteries.

Cost-Effective Rechargeable Magnesium Battery Based on a Fluorinated Alkoxyaluminate Electrolyte and a Carbonyl Polymer Cathode

Rechargeable magnesium batteries (RMBs) are one of the most promising "post-lithium" battery technologies, but the electrochemical performance is still far from expectation due to the sluggish reaction kinetics of divalent Mg2+ ions. Herein, we report a low-cost, high-performance Mg-organic battery based on the combination of a fluorinated alkoxyaluminate electrolyte and a carbonyl polymer cathode material. First, the one-pot synthesized Mg[Al(HFIP)4]2 (HFIP = hexafluoro-2-propanol) is proved superior to the Mg[B(HFIP)4]2 analogue in both Mg anode compatibility and electrochemical window, as the electrolyte salt in the G2-DME (G2 = diethylene glycol dimethyl ether; DME = 1,2-dimethoxyethane) mixture solvent. Second, a simple wet grinding method is proposed to effectively improve the dispersion uniformity of the poly(benzoquinone-pyrrole) (PBQPy) active material in the cathode. Third, the elaborate Mg-PBQPy battery exhibits superior electrochemical performance within 0.4-3.0 V, including a high reversible capacity of 197 mA h g-1, a high average discharge voltage of 1.6 V, and a high capacity retention of 71% after 500 cycles. Finally, based on various electrochemical analysis and ex situ characterization results, we propose a general microscopic structure evolution model to reveal the electrochemical behaviors of carbonyl polymer cathode in RMBs, including the swelling of polymer active material, trapping of Mg2+ ions, and reversible redox reaction.

Bottom-Up Magnesium Deposition Induced by Paper-Based Triple-Gradient Scaffolds toward Flexible Magnesium Metal Batteries

The development of advanced magnesium metal batteries (MMBs) has been hindered by longstanding challenges, such as the inability to induce uniform magnesium (Mg) nucleation and the inefficient utilization of Mg foil. This study introduces a novel solution in the form of a flexible, lightweight, paper-based scaffold that incorporates gradient conductivity, magnesiophilicity, and pore size. This design is achieved through an industrially adaptable papermaking process in which the ratio of carboxylated multi-walled carbon nanotubes to softwood cellulose fibers is meticulously adjusted. The triple-gradient structure of the scaffold enables the regulation of Mg ion flux, promoting bottom-up Mg deposition. Owing to its high flexibility, low thickness, and reduced density, the scaffold has potential applications in flexible and wearable electronics. Accordingly, the triple-gradient electrodes exhibit stable operation for over 1200 h at 3 mA cm-2 /3 mAh cm-2 in symmetrical cells, markedly outperforming the non-gradient and metallic Mg alternatives. Notably, this study marks the first successful fabrication of a flexible MMB pouch full cell, achieving an impressive volumetric energy density of 244 Wh L-1 . The simplicity and scalability of the triple-gradient design, which uses readily available materials through an industrially compatible papermaking process, open new doors for the production of flexible, high-energy-density metal batteries.

Mo3S13 Cluster-Based Cathodes for Rechargeable Magnesium Batteries: Reversible Magnesium Association/Dissociation at the Bridging Disulfur along with Sulfur-Sulfur Bond Break/Formation

Multivalent cation batteries are attracting increasing attention in energy-storage applications, but reversible storage of highly polarizing multivalent cations is a major difficulty for the electrode materials. In the present study, charge-delocalizing Mo3S13 cluster-based materials (crystalline (NH4)2Mo3S13 and amorphous MoSx) are designed and investigated as cathodes for rechargeable magnesium batteries. Both of the cathodes show high magnesium storage capacities (296 and 302 mAh g-1 at 100 mA g-1) and superior rate performances (76 and 80 mAh g-1 at 15 A g-1). A high area loading of 3.0 mg cm-2 could be achieved. These performances are of the highest level compared with those of reported magnesium storage materials. Further mechanism study and theoretical computation demonstrate the magnesium storage active sites are the bridging disulfur groups of the Mo3S13 cluster. The valence state of bridging disulfur decreases/increases largely during magnesiation/demagnesiation along with breaking/formation of the sulfur-sulfur bond, which makes the Mg-association/dissociation highly reversible. The sulfur-sulfur bond breaking and formation provides high reversible capacities. Prominently, the valence state increase and sulfur-sulfur bond formation of the bridging disulfur during charge weakens the bonding with Mg2+, significantly assisting the magnesium dissociation. The present study not only develops high-performance magnesium storage cathode materials but also demonstrates the importance of constructing favorable magnesium storage active sites in the high-performance cathode materials design. The findings presented herein are of great significance for the development of electrode materials for the storage of multivalent cations.

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.

Accumulative Delocalized Mo 4d Electrons to Bound the Volume Expansion and Accelerate Kinetics in Mo6S8 Cathode for High-Performance Aqueous Cu2+ Storage

Electronic structure defines the conductivity and ion absorption characteristics of a functional electrode, significantly affecting the charge transfer capability in batteries, while it is rarely thought to be involved in mesoscopic volume and diffusion kinetics of the host lattice for promoting ion storage. Here, we first correlate the evolution in electronic structure of the Mo6S8 cathode with the ability to bound volume expansion and accelerate diffusion kinetics for high-performance aqueous Cu2+ storage. Operando synchrotron energy-dispersive X-ray absorption spectroscopy reveals that accumulative delocalized Mo 4d electrons enhance the Mo-Mo interaction with distinctly contracting and uniformizing Mo6 clusters during the reduction of Mo6S8, which potently restrain lattice expansion and release space to promote Cu2+ diffusion kinetics. Operando synchrotron X-ray diffraction and comprehensive characterizations further validate the structural and electrochemical properties induced by the Cu2+ intercalation electronic structure, endowing the Mo6S8 cathode a high specific capacity with small volume expansion, fast ions diffusion, and long-term cycling stability.

Cellulose acetate network via ion pre-anchored strategy for simultaneous regulation of uniform Mg2+ flux and ion conductivity

Hybrid LiMg batteries stand out by combining the rapid lithium diffusion kinetics and the advantages of magnesium. However, the uneven Mg deposits may result in continuous parasitic reactions and penetrate the separator. Herein, cellulose acetate (CA), with functional groups, was applied to engineer coordination with MOFs and construct the evenly-distributed and ample nucleation sites. Moreover, the hierarchical MOFs@CA network was fabricated via the metal ion pre-anchored strategy to regulate the uniform Mg²⁺ flux and improve ion-conductivity simultaneously. Furthermore, the hierarchical CA networks with well-ordered MOFs provided efficient MOF-to-MOF ion-transportation channels and served as ion sieves to inhibit anion transportation, thereby mitigating polarization. The super dendrite-inhibition and interfacial compatibility was confirmed and the assembled Mo₆S₈//Mg batteries exhibited high capacity about 105 mAh g^-1 and capacity decay of 4 % after 600 cycles at 30 C, which surpassed the state-of-the-art LMBs system employing Mo₆S₈ electrode. The fabricated GPE sheds fresh strategy for the design of CA-based GPEs and bright light on the promise of high-performance LMBs.

A solution-to-solid conversion chemistry enables ultrafast-charging and long-lived molten salt aluminium batteries

Conventional solid-to-solid conversion-type cathodes in batteries suffer from poor diffusion/reaction kinetics, large volume changes and aggressive structural degradation, particularly for rechargeable aluminium batteries (RABs). Here we report a class of high-capacity redox couples featuring a solution-to-solid conversion chemistry with well-manipulated solubility as cathodes-uniquely allowed by using molten salt electrolytes-that enable fast-charging and long-lived RABs. As a proof-of-concept, we demonstrate a highly reversible redox couple-the highly soluble InCl and the sparingly soluble InCl₃-that exhibits a high capacity of about 327 mAh g^-1 with negligible cell overpotential of only 35 mV at 1 C rate and 150 °C. The cells show almost no capacity fade over 500 cycles at a 20 C charging rate and can sustain 100 mAh g^-1 at 50 C. The fast oxidation kinetics of the solution phase upon initiating the charge enables the cell with ultrafast charging capability, whereas the structure self-healing via re-forming the solution phase at the end of discharge endows the long-term cycling stability. This solution-to-solid mechanism will unlock more multivalent battery cathodes that are attractive in cost but plagued by poor reaction kinetics and short cycle life.

Reversible Magnesium Metal Cycling in Additive-Free Simple Salt Electrolytes Enabled by Spontaneous Chemical Activation

Rechargeable magnesium (Mg) batteries can offer higher volumetric energy densities and be safer than their conventional counterparts, lithium-ion batteries. However, their practical implementation is impeded due to the passivation of the Mg metal anode or the severe corrosion of the cell parts in conventional electrolyte systems. Here, we present a chemical activation strategy to facilitate the Mg deposition/stripping process in additive-free simple salt electrolytes. By exploiting the simple immersion-triggered spontaneous chemical reaction between reactive organic halides and Mg metal, the activated Mg anode exhibited an overpotential below 0.2 V and a Coulombic efficiency as high as 99.5% in a Mg(TFSI)₂ electrolyte. Comprehensive analyses reveal simultaneous evolution of morphology and interphasial chemistry during the activation process, through which stable Mg cycling over 990 cycles was attained. Our activation strategy enabled the efficient cycling of Mg full-cell candidates using commercially available electrolytes, thereby offering possibilities of building practical Mg batteries.

The Proof-of-Concept of Anode-Free Rechargeable Mg Batteries

The desperate pursuit of high gravimetric specific energy leads to the ignorance of volumetric energy density that is one of the basic requirements for batteries. Due to the high volumetric capacity, less-prone formation of dendrite, and low reduction potential of Mg metal, rechargeable Mg batteries are considered with innately high volumetric energy density. Nevertheless, the substantial elevation in energy density is compromised by extremely excessive Mg metal anode. Herein, the proof-of-concept of anode-free Mg₂ Mo₆ S₈ -MgS/Cu batteries is proposed, in which MgS as the premagnesiation additive constantly decomposes to replenish Mg loss by electrolyte corrosion over cycling, while both Mg₂ Mo₆ S₈ and MgS acts as the active material to reversibly provide high capacities. Besides, Mg₂ Mo₆ S₈ shows superior catalytic activity on the decomposition of MgS and provides the strong affinity to polysulfides to restrain their dissolution. Consequently, the anode-free Mg₂ Mo₆ S₈ -MgS/Cu batteries deliver a high reversible capacity of 190 mAh g^-1 with the capacity retention of 92% after 100 cycles, corresponding to the highly competitive energy density of 420 Wh L^-1 . The proposed anode-free Mg battery here spotlights the great promise of Mg batteries in achieving high volumetric energy densities, which will significantly expedite the advances of Mg batteries in practice.

Chevrel Phase Mo6 S8 Nanosheets Featuring Reversible Electrochemical Li-Ion Intercalation as Effective Dynamic-Phase Promoter for Advanced Lithium-Sulfur Batteries

Modifying sulfur cathodes with lithium polysulfides (LiPSs) adsorptive and electrocatalytic host materials is regarded as one of the most effective approaches to address the challenging problems in lithium-sulfur (Li-S) batteries. However, because of the high operating voltage window of Li-S batteries from 1.7 to 2.8 V, most of the host materials cannot participate in the sulfur redox reactions within the same potential region, which exhibit fixed or single functional property, hardly fulfilling the requirement of the complex and multiphase process. Herein, Chevrel phase Mo₆ S₈ nanosheets with high electronic conductivity, fast ion transport capability, and strong polysulfide affinity are introduced to sulfur cathode. Unlike most previous inactive hosts with a fixed affinity or catalytic ability toward LiPSs, the reaction involving Mo₆ S₈ is intercalative and the adsorbability for LiPSs as well as the ionic conductivity can be dynamically enhanced via reversible electrochemical lithiation of Mo₆ S₈ to Li-ion intercalated Li_x Mo₆ S₈ , thereby suppressing the shuttling effect and accelerating the conversion kinetics. Consequently, the Mo₆ S₈ nanosheets act as an effective dynamic-phase promoter in Li-S batteries and exhibit superior cycling stability, high-rate capability, and low-temperature performance. This study opens a new avenue for the development of advanced hosts with dynamic regulation activity for high performance Li-S batteries.

Cathode Electrolyte Interphase (CEI) Endows Mo6 S8 with Fast Interfacial Magnesium-Ion Transfer Kinetics

Magnesium (Mg) metal secondary batteries have attracted much attention for their high safety and high energy density characteristics. However, the significant issues of the cathode/electrolyte interphase (CEI) in Mg batteries are still being ignored. In this work, a significant CEI layer on the typical Mo₆ S₈ cathode surface has been unprecedentedly constructed through the oxidation of the chloride-free magnesium tetrakis(hexafluoroisopropyloxy)borate (Mg[B(hfip)₄ ]₂ ) salt under a proper charge cut-off voltage condition. The CEI has been identified to contain B_x O_y effective species originating from the oxidation of [B(hfip)₄ ]^- anion. It is confirmed that the B_x O_y species is beneficial to the desolvation of solvated Mg²⁺ , speeding up the interfacial Mg²⁺ transfer kinetics, thereby improving the Mg²⁺ -storage capability of Mo₆ S₈ host. The firstly reported CEI in Mg batteries will give deeper insights into the interface issues in multivalent electrochemical systems.

Metal-Organic Framework Flowers as a Naked-Eye Colorimetric Indicator of Trace Water

Convenient and sensitive trace water indication is of great significance in various industrial processes. Here, a flower-like metal-organic framework Cu-FMM is assembled from ultrathin nanosheets that change its coordination structure reversibly with the capture and loss of water molecules, enabling sensitive trace water naked-eye colorimetric indication ability. A recognizable black/yellow color change can be observed when the dried Cu-FMM is exposed to the atmosphere or solvent with trace water as low as RH 3% and a water content of 0.25‰ (v/v) and further enables potential trace water imaging applications. The excellent accessibility of the multi-scale pore structure of Cu-FMM contributes to a fast response time of 3.8 s with good reversibility (>100 cycles), outperforming traditional coordination polymer humidity sensors. The present study provides new inspirations for the design of sensitive and applicable naked-eye water indicator materials that are applicable to in situ and continuous monitoring in industrial processes.

Halogen-Doped Chevrel Phase Janus Monolayers for Photocatalytic Water Splitting

Chevrel non-van der Waals crystals are promising candidates for the fabrication of novel 2D materials due to their versatile crystal structure formed by covalently bonded (Mo₆X₈) clusters (X-chalcogen atom). Here, we present a comprehensive theoretical study of the stability and properties of Mo-based Janus 2D structures with Chevrel structures consisting of chalcogen and halogen atoms via density functional theory calculations. Based on the analysis performed, we determined that the S₂Mo₃I₂ monolayer is the most promising structure for overall photocatalytic water-splitting application due to its appropriate band alignment and its ability to absorb visible light. The modulated Raman spectra for the representative structures can serve as a blueprint for future experimental verification of the proposed structures.

A Molybdenum Polysulfide In-Situ Generated from Ammonium Tetrathiomolybdate for High-Capacity and High-Power Rechargeable Magnesium Battery Cathodes

Rechargeable magnesium batteries (RMBs) are a promising large-scale energy-storage technology with low cost and high reliability. However, developing high-performance cathode materials remains the most prominent obstacle because of the insufficient magnesium-storage active sites and unfavorable magnesium cation transport paths, as well as the strong interaction between the cathode material and the bivalent magnesium cation. Herein, ammonium tetrathiomolybdate is demonstrated to be a high-performance RMB cathode material. Ammonium tetrathiomolybdate exhibits a high capacity of 333 mAh g^-1 at 50 mA g^-1 and a good rate performance of 129 mAh g^-1 at 5.0 A g^-1 (∼15 C). An amorphous structure with plenty of efficient magnesium-storage active sites and open magnesium transport paths is in situ formed during the first cycle via ammonium extraction. The covalent-like bond between the molybdenum and sulfur delocalizes the negative charge, weakening the interaction with the bivalent magnesium cation and accelerating the kinetics. The covalent-like molybdenum-sulfur bond also promotes the simultaneous redox of molybdenum and sulfur, leading to a high specific capacity. The present work introduces a high-capacity and high-power RMB cathode material, elucidates the origin of the high performance, and provides insights for the design and optimization of RMB cathode materials.

High Utilization of Composite Magnesium Metal Anodes Enabled by a Magnesiophilic Coating

Metallic magnesium is a promising high-capacity anode material for energy storage technologies beyond lithium-ion batteries. However, most reported Mg metal anodes are only cyclable under shallow cycling (≤1 mAh cm^-2) and thus poor Mg utilization (<3%) conditions, significantly compromising their energy-dense characteristic. Herein, composite Mg metal anodes with high capacity utilization of 75% are achieved by coating magnesiophilic gold nanoparticles on copper foils for the first time. Benefiting from homogeneous ionic flux and uniform deposition morphology, the Mg-plated Au-Cu electrode exhibits high average Coulombic efficiency of 99.16% over 170 h cycling at 75% Mg utilization. Moreover, the full cell based on Mg-plated Au-Cu anode and Mo₆S₈ cathode achieves superior capacity retention of 80% after 300 cycles at a low negative/positive ratio of 1.33. This work provides a simple yet effective general strategy to enhance Mg utilization and reversibility, which can be extended to other metal anodes as well.

Surface Transformation Enables a Dendrite-Free Zinc-Metal Anode in Nonaqueous Electrolyte

Significant challenges remain in developing rechargeable zinc batteries mainly because of reversibility problems on zinc-metal anodes. The dendritic growth and hydrogen evolution on zinc electrodes are major obstacles to overcome in developing practical and safe zinc batteries. Here, a dendrite-free and hydrogen-free Zn-metal anode with high Coulombic efficiency up to 99.6% over 300 cycles is realized in a newly designed nonaqueous electrolyte, which comprises an inexpensive zinc salt, zinc acetate, and a green low-cost solvent, dimethyl sulfoxide. Surface transformation on Cu substrate plays a critical role in facilitating the dendrite-free deposition process, which lowers the diffusion energy barrier of the Zn atoms, leading to a uniform and compact thin film for zinc plating. Furthermore, in situ electrochemical atomic force microscopy reveals the plating process via a layer-by-layer growth mechanism and the stripping process through an edge-dissolution mechanism. In addition, Zn||Mo₆ S₈ full cells exhibit excellent electrochemical performance in terms of cycling stability and rate capability. This work presents a new opportunity to develop nonaqueous rechargeable zinc batteries.

Nanocubes of Mo6S8 Chevrel phase as active electrode material for aqueous lithium-ion batteries

The development of intrinsically safe and environmentally sustainable energy storage devices is a significant challenge. Recent advances in aqueous rechargeable lithium-ion batteries (ARLIBs) have made considerable steps in this direction. In parallel to the ongoing progress in the design of aqueous electrolytes that expand the electrochemically stable potential window, the design of negative electrode materials exhibiting large capacity and low intercalation potential attracts great research interest. Herein, we report the synthesis of high purity nanoscale Chevrel Phase (CP) Mo₆S₈via a simple, efficient and controllable molecular precursor approach with significantly decreased energy consumption compared to the conventional approaches. Physical characterization of the obtained product confirms the successful formation of CP-Mo₆S₈ and reveals that it is crystalline nanostructured in nature. Due to their unique structural characteristics, the Mo₆S₈ nanocubes exhibit fast kinetics in a 21 m lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) electrolyte as a result of the shorter Li⁺ ion diffusion distance. Full battery cells comprised of Mo₆S₈ and LiMn₂O₄ as negative and positive electrode materials, respectively, operate at 2.23 V delivering a high energy density of 85 W h kg^-1 (calculated on the total mass of active materials) under 0.2 C-rate. At 4 C, the coulombic efficiency (CE) is determined to be 99% increasing to near 100% at certain cycles. Post-mortem physical characterization demonstrates that the Mo₆S₈ anode maintained its crystallinity, thereby exhibiting outstanding cycling stability. The cell outperforms the commonly used vanadium-based (VO₂ (B), V₂O₅) or (NASICON)-type LiTi₂(PO₄)₃ anodes, highlighting the promising character of the nanoscale CP-Mo₆S₈ as a highly efficient anode material. In summary, the proposed synthetic strategy is expected to stimulate novel research towards the widespread application of CP-based materials in various aqueous and non-aqueous energy storage systems.

Storing Mg Ions in Polymers: A Perspective

The electrochemical performance of rechargeable Mg batteries (RMBs) is primarily determined by the cathodes. However, the strong interaction between highly polarized Mg²⁺ and the host lattice is a big challenge for inorganic cathode materials. While endowed with weak interaction with Mg²⁺ , organic polymers are capable of fast reaction kinetics. Besides, with the advantages of light weight, abundance, low cost, and recyclability, polymers are deemed as ideal cathode materials for RMBs. Although polymer cathodes have remarkably progressed in recent years, there are still significant challenges to overcome before reaching practical application. In this perspective, the challenges faced by polymer cathodes are critically focused, followed by the retrospection of efforts devoted to design polymers. Some feasible strategies are proposed to explore new structures and chemistries for the practical application of polymer cathodes in RMBs.

Construction of stable MoxSy/CeO2 heterostructures for the electrocatalytic hydrogen evolution reaction

The unique structures of polynuclear Mo_xS_y clusters make it possible to maximize the number of their active sites and for them to be good candidates for HER catalysts. An appropriate support is highly necessary not only to avoid the desorption of Mo_xS_y clusters in a working environment, but also to improve their HER activity. Our work here shows that the CeO₂ support could provide strong support for interaction with various Mo_xS_y clusters and the formed Mo_xS_y/CeO₂ hetero-structures also have modest ΔG_H* for the HER. The electronic features of Mo_xS_y clusters are regulated by the CeO₂ support, which leads to charge redistribution on edge atoms and plays a key role in H adsorption. Our studies provide instructive predictions on efficient candidates of molybdenum-sulfur based catalysts for the HER.

Amorphous Redox-Rich Polysulfides for Mg Cathodes

The lack of appropriate cathodes is restraining the advances of Mg batteries. Crystalline cathode materials suffer from sluggish reaction kinetics and low-capacity delivery. The finite type of crystalline structure further confines the rational design of cathode materials. Herein, we proposed amorphization and anion enrichment as a brand-new strategy to not only enhance the solid-state ion diffusion and provide more ion-storage sites in amorphous structure but also contribute to the local transfer of multiple electrons through the additional anionic redox centers. Accordingly, a series of amorphous titanium polysulfides (a-TiS x , x = 2, 3, and 4) were designed, which significantly outperformed their crystalline counterparts and achieved a highly competitive energy density of ∼260 Wh/kg. The unique Mg2+ storage mechanism involves the dissociation/formation of S-S bonds and changes in the coordination number of Ti, namely, a mixture of conversion and intercalation reaction, accompanied by the joint cationic (Ti) and anionic (S) redox-rich chemistry. Our proposed amorphous and redox-rich design philosophy might provide an innovative direction for developing high-performance cathode materials for multivalent-ion batteries.

Amorphous anion-rich titanium polysulfides for aluminum-ion batteries

The strong electrostatic interaction between Al³⁺ and close-packed crystalline structures, and the single-electron transfer ability of traditional cationic redox cathodes, pose challenged for the development of high-performance rechargeable aluminum batteries. Here, to break the confinement of fixed lattice spacing on the diffusion and storage of Al-ion, we developed a previously unexplored family of amorphous anion-rich titanium polysulfides (a-TiS _x , x = 2, 3, and 4) (AATPs) with a high concentration of defects and a large number of anionic redox centers. The AATP cathodes, especially a-TiS₄, achieved a high reversible capacity of 206 mAh/g with a long duration of 1000 cycles. Further, the spectroscopy and molecular dynamics simulations revealed that sulfur anions in the AATP cathodes act as the main redox centers to reach local electroneutrality. Simultaneously, titanium cations serve as the supporting frameworks, undergoing the evolution of coordination numbers in the local structure.

A Chlorine-Free Electrolyte Based on Non-nucleophilic Magnesium Bis(diisopropyl)amide and Ionic Liquid for Rechargeable Magnesium Batteries

The electrolyte based on magnesium bis(diisopropyl)amide (MBA), a low-cost and non-nucleophilic organic magnesium salt, is proposed to be an admirable alternative for rechargeable magnesium batteries but suffers from limited ionic conductivity and an inferior electrochemical window in the commonly used ether solvents. In this work, the 1-butyl-1-methylpiperidinium bis(trifluoromethyl sulfonyl)imide (PP₁₄TFSI) ionic liquid as the cosolvent of tetrahydrofuran (THF) in chlorine-free MBA-based electrolytes has been first demonstrated to remarkably improve the ionic conductivity and broaden the oxidative stable potential (2.2 V vs Mg/Mg²⁺) on stainless steel. Reversible Mg electrochemical plating/stripping with a low overpotential below 200 mV and ca. 90% Coulombic efficiency are obtained. The current density of Mg plating/stripping is increased 238 times after the addition of PP₁₄TFSI, where the mechanism of competitive coordination of TFSI^- making an easier Mg plating/stripping is proposed theoretically. The MBA-2AlF₃ electrolyte with a ratio-optimized THF/PP₁₄TFSI cosolvent exhibits good compatibility with the Mo₆S₈ cathode. Furthermore, the Se@pPAN|Mg full cell exhibits an initial capacity of 447.8 mAh g^-1 and as low as ∼0.66% capacity decay per cycle for more than 70 cycles at 0.2 C with the synergy of LiTFSI additives. The facile modification strategy of ionic liquid in the MBA-based electrolyte sheds inspiring light on exploring non-nucleophilic and chlorine-free electrolytes for practical rechargeable magnesium batteries.

Dense All-Electrochem-Active Electrodes for All-Solid-State Lithium Batteries

The energy density presents the core competitiveness of lithium (Li)-ion batteries. In conventional Li-ion batteries, the utilization of the gravimetric/volumetric energy density at the electrode level is unsatisfactory (<84 wt% and <62 vol%, respectively) due to the existence of non-electrochemical active parts among the 3D porous electrodes, including electrolytes, binders, and carbon additives. These are regarded as indispensable and irreducible components of the electronic and ionic transport network. Here, a dense "all-electrochem-active" (AEA) electrode for all-solid-state Li batteries is proposed, which is entirely constructed from a family of superior mixed electronic-ionic-conducting cathodes, to minimize the energy density gap between the accessible and theoretical energy density at the electrode level. Furthermore, with the ionic-electronic-conductive network self-supported from the AEA cathode, the dense hybrid sulfur (S)-based AEA electrode exhibits a high compacted filling rate of 91.8%, which indicates a high energy density of 777 W h kg^-1 and 1945 W h L^-1 at the electrode level based on the total cathodes and anodes when at 70 °C.

Designing Nanostructured Metal Chalcogenides as Cathode Materials for Rechargeable Magnesium Batteries

Rechargeable magnesium batteries (RMBs) are regarded as promising candidates for beyond-lithium-ion batteries owing to their high energy density. Moreover, as Mg metal is earth-abundant and has low propensity for dendritic growth, RMBs have the advantages of being more affordable and safer than the currently used lithium-ion batteries. However, the commercial viability of RMBs has been negatively impacted by slow diffusion kinetics in most cathode materials due to the high charge density and strongly polarizing nature of the Mg²⁺ ion. Nanostructuring of potential cathode materials such as metal chalcogenides offers an effective means of addressing these challenges by providing larger surface area and shorter migration routes. In this article, a review of recent research on the design of metal chalcogenide nanostructures for RMBs' cathode materials is provided. The different types and structures of metal chalcogenide cathodes are discussed, and the synthetic strategies through which nanostructuring of these materials can be achieved are described. An organized summary of their electrochemical performance is also presented, along with an analysis of the current challenges and future directions. Although particular focus is placed on RMBs, many of the nanostructuring concepts that are discussed here can be carried forward to other next-generation energy storage systems.

Electronic Conductive Inorganic Cathodes Promising High-Energy Organic Batteries

The electrochemical utilization of organic electrode materials (OEMs) is highly dependent on an excess amount of inactive carbon at the expense of low packing density and energy density. In this work, the challenges by substituting inactive carbon with electronic conductive inorganic cathode (ECIC) materials, which are endowed with high electronic conductivity to transport electrons for redox reactions of the whole electrodes, high ion-storage capacity to act as secondary active materials, and strong affinity with OEMs to inhibit their dissolution, are addressed. Combining representative ECICs (TiS₂ and Mo₆ S₈ ) with organic electrode materials (perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA) and hexaazatrinaphthalene (HATN)) simultaneously achieves high capacity, low porosity, lean electrolyte, and thus high energy density. High gravimetric and volumetric energy densities of 153 Wh kg^-1 and 200 Wh L^-1 are delivered with superior cycling stability in a 30 mA h-level Li/PTCDA-TiS₂ pouch cell. The proof-of-concept of organic-ECIC electrodes is also successfully demonstrated in monovalent Na, divalent Mg, and trivalent Al batteries, indicating their feasibility and generalizability. With the discovery of more ECIC materials and OEMs, it is anticipated that the proposed organic-ECIC system can result in further improvements at cell level to compete with transition metal-based Li-ion batteries.

Recent Progress and Challenges in the Optimization of Electrode Materials for Rechargeable Magnesium Batteries

Rechargeable magnesium batteries (RMBs) have been regarded as one of the promising electrochemical energy storage systems to complement Li-ion batteries owing to the low-cost and high safety characteristics. However, the various challenges including the sluggish solid-state diffusion of highly polarizing Mg²⁺ ions in hosts, and the formation of blocking layers on Mg metal surface have seriously impeded the development of high-performance RMBs. In order to solve these problems toward practical applications of RMBs, a tremendous amount of work on electrodes and electrolytes has been conducted in the last few decades. Creative optimization strategies including the modification of cathodes and anodes such as shielding the charges of divalent Mg²⁺ , expanding the layers of host materials, and optimizing the interface of electrode-electrolyte are raised to promote the technology. In this review, the detailed description of innovative approaches, representative examples, and facing challenges for developing high-performance electrodes are presented. Based on the review of these strategies, guidelines are provided for future research directions on improving the overall battery performance, especially on the electrodes.

Joint Cationic and Anionic Redox Chemistry for Advanced Mg Batteries

Lack of appropriate cathodes severely restrains the development of high-energy Mg batteries. In this work, we proposed joint cationic and anionic redox chemistry of transition-metal (TM) sulfides as the most promising way out. A series of solid-solution pyrite Fe_xCo_1-xS₂ (0 ≤ x ≤ 1) was specially designed, in which S 3p electrons pour into the d bands of Fe and Co, generating redox-active dimerized (S₂)^2-. The Fe_0.5Co_0.5S₂ sample is highlighted to deliver a high specific energy of 240 Wh/kg at room temperature involving both cationic (Fe and Co) and anionic (S) redox. The highly delocalized electronic clouds in pyrite structures comfortably accommodate the charge of Mg²⁺, contributing to the fast kinetics and the superior cycling stability of the Fe_0.5Co_0.5S₂. It is anticipated that the joint cationic and anionic redox chemistry proposed in this work would be the ultimate answer for designing high-energy cathodes for advanced Mg batteries.