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[Display omitted] Rechargeable magnesium battery is regarded as the promising candidate for the next generation of high-specific-energy storage systems. Nevertheless, issues related to severe Mg-Cl dissociation at the electrolyte–electrode interface impede the insertion of Mg2+ into most materials, leading to severe polarization and low utilization of Mg-storage electrodes. In this study, a metal–organic polymer (MOP) Ni-TABQ (Ni-coordinated tetramino-benzoquinone) with superior surface catalytic activity is proposed to achieve the high-capacity Mg-MOP battery. The layered Ni-TABQ cathode, featuring a unique 2D π-d linear conjugated structure, effectively reduces the dissociation energy of Mg x Cl y clusters at the Janus interface, thereby facilitating Mg2+ insertion. Due to the high utilization of active sites, Ni-TABQ achieves high capacities of 410 mAh/g at 200 mA g−1, attributable to a four-electron redox process involving two redox centers, benzoid carbonyls, and imines. This research highlights the importance of surface electrochemical processes in rechargeable magnesium batteries and paves the way for future development in multivalent metal-ion batteries. [ABSTRACT FROM AUTHOR]

Rechargeable magnesium batteries (RMBs) have the potentials in terms of high energy density, resource abundancy and safety beyond current lithium‐ion batteries. However, the bare Mg metal electrode is prone to be passivated by solvents, suffering from the extremely high overpotential and short life during cycling. Herein, a facile chloride‐free solution pretreatment method for Mg anode is developed to construct the fluoride‐rich artificial interphase. Driven by the strong‐Lewis‐acidity trifluoromethanesulfonate anion, the interphase consisting of magnesiophilic and fluoride‐rich components are constructed by the substitution reaction of Mg metal with antimony trifluoride. The formed porous Sb‐based skeletons can uniform the electric‐field distribution and Mg ions flux at anode side, inducing the self‐adapting dendrite‐free Mg deposition even under large current density. The generated alloyable metal fluoride enables to lower the desolvation energy barrier for Mg ions and sustainedly release metallic antimony to compensate for the potentially invalid magnesiophilic sites during cycling. Therefore the symmetric cells with modified Mg anodes achieve the excellent cycling over 2000 h at 1 mA cm−2 and under a high areal capacity of 5 mAh cm−2. The full cells with CuS cathodes exhibit a superior high voltage stability (2.6 V vs Mg/Mg2+) and high coulombic efficiency close to 100%. [ABSTRACT FROM AUTHOR]

Rechargeable Mg batteries are an advantageous energy‐storage technology with low cost and high safety, but the design of high‐performance cathode materials is currently the major difficulty. Herein, a new cathode material of Cu3VSe4 is fabricated with a comprehensive consideration of the chemical and electronic structures. The intermediate band semiconductor Cu3VSe4 has a cubic crystal structure containing interlaced 3D tunnels. The V and Se atoms form chemical bonds with high covalent proportions and facilitate the charge delocalization via the V‒Se bonds. Because of these features, Cu3VSe4 provides a high capacity of 251 mAh g‒1 with co‐redox of Cu, V, and Se elements and an outstanding rate performance of 44 mAh g‒1 at 15 A g‒1. Prominently, a high mass load of 3.0 mg cm‒2 is achieved without obvious rate capability decay, which is quite favorable to pair with the high‐capacity Mg metal anode in practical application. The mechanism investigation and theoretical computation demonstrate that Cu3VSe4 undergoes first a Mg‐intercalation and then a displacement reaction, during which the crystal structure is maintained, assisting the reaction reversibility and cycling stability. These findings reveal a rational design principle of rechargeable Mg battery cathodes based on a comprehensive consideration of chemical and electronic structures. [ABSTRACT FROM AUTHOR]

Rechargeable magnesium batteries (RMBs) become a highly promising candidate for the large‐scale energy storage system by right of the high volumetric capacity, intrinsic safety and abundant resources of Mg anode. However, the uneven Mg stripping and large overpotential will cause a severe pitting perforation and the followed failure of Mg anode. Herein, we proposed a high‐performance binary Mg‐1 at% Gd alloy anode prepared by the melting and hot extrusion. The introduction of 1 at% Gd element can effectively reduce the Mg2+ diffusion energy barrier (0.34 eV) on alloy surface and induces the formation of a robust and low‐resistance electrolyte/anode interphase, thus enabling a uniform and fast Mg plating/stripping. As a result, the Mg‐1 at.% Gd anode displays a largely enhanced life of 220 h and a low overpotential of 213 mV at a high current density of 5.0 mA cm−2 with 2.5 mAh cm−2. Moreover, the assembled Mg‐1 at.% Gd//Mo6S8 full cell delivers a high rate performance (73.5 mAh g−1 at 5 C) and ultralong cycling stability of 8000 cycles at 5 C. This work brings new insights to design the new‐type and practical Mg alloy anodes for commercial RMBs. [ABSTRACT FROM AUTHOR]

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 Mg2Mo6S8‐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 Mg2Mo6S8 and MgS acts as the active material to reversibly provide high capacities. Besides, Mg2Mo6S8 shows superior catalytic activity on the decomposition of MgS and provides the strong affinity to polysulfides to restrain their dissolution. Consequently, the anode‐free Mg2Mo6S8‐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. [ABSTRACT FROM AUTHOR]

Abstract 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 Mg2Mo6S8‐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 Mg2Mo6S8 and MgS acts as the active material to reversibly provide high capacities. Besides, Mg2Mo6S8 shows superior catalytic activity on the decomposition of MgS and provides the strong affinity to polysulfides to restrain their dissolution. Consequently, the anode‐free Mg2Mo6S8‐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.

There is an increasing demand for rechargeable batteries in high-performance energy storage systems. The current dominating Li-ion batteries are limited by price, resource availability, as well as their theoretical capacities. So that the community has started to explore alternative battery chemistries. As a promising multivalent battery type, rechargeable magnesium batteries (RMBs) have attracted increasing attention because of high safety, high volumetric energy density, and low cost thanks to abundant resource of Mg. However, the development of high-performance anodes is still hampered by formation of passivating layers on the Mg surface. Additionally, dendrites can also grow under certain conditions with pure Mg anodes, which requires further studies for reliable operation window and substitutes. Therefore, this review specifically aims to provide an overview on the often overlooked yet very important anode materials of RMBs, with the hope to inspire more attention and research efforts for the achievement of over-all better performance of future RMBs.

In recent decades, rechargeable Mg batteries (RMBs) technologies have attracted much attention because the use of thin Mg foil anodes may enable development of high‐energy‐density batteries. One of the most critical challenges for RMBs is finding suitable electrolyte solutions that enable efficient and reversible Mg cells operation. Most RMB studies concentrate on the development of novel electrolyte systems, while only few studies have focused on the practical feasibility of using pure metallic Mg as the anode material. Pure Mg metal anodes have been demonstrated to be useful in studying the fundamentals of nonaqueous Mg electrochemistry. However, pure Mg metal may not be suitable for mass production of ultrathin foils (<100 microns) due to its limited ductility. The metals industry overcomes this problem by using ductile Mg alloys. Herein, the feasibility of processing ultrathin Mg anodes in electrochemical cells was demonstrated by using AZ31 Mg alloys (3 % Al; 1 % Zn). Thin‐film Mg AZ31 anodes presented reversible Mg dissolution and deposition behavior in complex ethereal Mg electrolytes solutions that was comparable to that of pure Mg foils. Moreover, it was demonstrated that secondary Mg battery prototypes comprising ultrathin AZ31 Mg alloy anodes (≈25 μm thick) and MgxMo6S8 Chevrel‐phase cathodes exhibited cycling performance equal to that of similar cells containing thicker pure Mg foil anodes. The possibility of using ultrathin processable Mg metal anodes is an important step in the realization of rechargeable Mg batteries. [ABSTRACT FROM AUTHOR]

Dual‐ion batteries (DIBs) offer a great alternative to state‐of‐the‐art lithium‐ion batteries, based on their high promises due to the absence of transition metals and the use of low‐cost materials, which could make them economically favorable targeting stationary energy storage applications. In addition, they are not limited by certain metal cations, and DIBs with a broad variety of utilized ions could be demonstrated over the last years. Herein, a systematic study of different electrolyte approaches for Mg‐ion‐based DIBs was conducted. A side‐by‐side comparison of Li‐ and Mg‐ion‐based electrolytes using activated carbon as negative electrode revealed the opportunities but also limitations of Mg‐ion‐based DIBs. Ethylene sulfite was successfully introduced as electrolyte additive and increased the specific discharge capacity significantly up to 93±2 mAh g−1 with coulombic efficiencies over 99 % and an excellent capacity retention of 88 % after 400 cycles. In addition, and for the first time, highly concentrated carbonate‐based electrolytes were employed for Mg‐ion‐based DIBs, showing adequate discharge capacities and high coulombic efficiencies. [ABSTRACT FROM AUTHOR]

Rechargeable batteries based on Mg metal anodes may be a promising alternative to current Li‐ion battery systems. However, the development of practical rechargeable Mg batteries (RMBs) is hindered by the absence of cathode materials that can reversibly intercalate Mg ions with a reasonably fast kinetic, while still exhibiting high capacity and high working voltages. In this minireview we summarize our recent progress in understanding cathodes/electrolyte solutions interfaces in non‐aqueous Mg systems. While most studies in the field of cathode materials for RMBs focus on the solid‐state diffusion phenomena of the bare Mg ion within the solid hosts, this minireview summarizes several important findings that demonstrate how the electrochemical response of the cathode material is also significantly influenced by the solution chemistry and structure. We provide a comprehensive description of the sequential steps taking place in the electrochemical intercalation reactions, with an emphasis on the charge transfer process across the solution/electrode interfaces. We discuss the different manner in which the electrolyte solutions′ chemical characteristics can impact each step of the intercalation process and why this information is important for the development of new cathode materials for rechargeable Mg batteries. We believe that these types of fundamental investigations are crucial steps for the realization of this interesting battery technology. [ABSTRACT FROM AUTHOR]

There is an increasing demand for rechargeable batteries in high-performance energy storage systems. The current dominating Li-ion batteries are limited by price, resource availability, as well as their theoretical capacities. So that the community has started to explore alternative battery chemistries. As a promising multivalent battery type, rechargeable magnesium batteries (RMBs) have attracted increasing attention because of high safety, high volumetric energy density, and low cost thanks to abundant resource of Mg. However, the development of high-performance anodes is still hampered by formation of passivating layers on the Mg surface. Additionally, dendrites can also grow under certain conditions with pure Mg anodes, which requires further studies for reliable operation window and substitutes. Therefore, this review specifically aims to provide an overview on the often overlooked yet very important anode materials of RMBs, with the hope to inspire more attention and research efforts for the achievement of over-all better performance of future RMBs. [ABSTRACT FROM AUTHOR]

The pursuit of novel cathode materials with excellent performance is the key to promoting the application of rechargeable magnesium batteries (RMBs). Herein, bimetallic copper-cobalt selenide (CuCo 2 Se 4) as a cathode material for RMBs, synthesized via a microwave-assisted method. In contrast to the monometallic selenide (Co 0.85 Se), CuCo 2 Se 4 exhibits a high reversible capacity of 108 mAh g−1 at 50 mA g−1 after 80 cycles, and a superior rate capability (90 mAh g−1 at 200 mA g−1). The crystal phase transition of the conversion electrode material during the cycles is analyzed using ex-situ XRD technology. The enhanced stability of bimetallic selenide provides a good experimental support for the preparation of high-performance rechargeable magnesium batteries based on bimetallic strategy. • Spinel CuCo 2 Se 4 nanosheets are synthesized by a microwave-anion-exchange route. • The bimetallic Co-Cu selenide with hierarchical structure has good cycling stability. • The magnesium storage mechanism of spinel CuCo 2 Se 4 is studied via ex-situ XRD. [ABSTRACT FROM AUTHOR]

The lack of high‐power and stable cathodes prohibits the development of rechargeable metal (Na, Mg, Al) batteries. Herein, poly(hexaazatrinaphthalene) (PHATN), an environmentally benign, abundant and sustainable polymer, is employed as a universal cathode material for these batteries. In Na‐ion batteries (NIBs), PHATN delivers a reversible capacity of 220 mAh g−1 at 50 mA g−1, corresponding to the energy density of 440 Wh kg−1, and still retains 100 mAh g−1 at 10 Ag−1 after 50 000 cycles, which is among the best performances in NIBs. Such an exceptional performance is also observed in more challenging Mg and Al batteries. PHATN retains reversible capacities of 110 mAh g−1 after 200 cycles in Mg batteries and 92 mAh g−1 after 100 cycles in Al batteries. DFT calculations, X‐ray photoelectron spectroscopy, Raman, and FTIR show that the electron‐deficient pyrazine sites in PHATN are the redox centers to reversibly react with metal ions. [ABSTRACT FROM AUTHOR]

• First ever synthesis and isolation of MgCl+ cations containing Mg electrolytes. • Novel MgCl(THF) 5 PhAlCl 3 /THF electrolyte show reversible Mg deposition/dissolution. • Electrochemical "conditioning" increases the cycling efficiency to around 95%. • Investigation of electrolyte solution with Mg prototype full cell configuration. Synthesis of complex magnesium cations in ethereal solutions, is receiving a lot of attention due to their potential utilization in rechargeable magnesium batteries (RMB). The simplest complex cation, namely, solvated MgCl+, was hypothesized and reported as the most important cation in nonaqueous magnesium electrolyte solutions chemistry. However, such ions have never been isolated as the only cationic species in ethereal solutions developed for RMB. In this study, we report on successful isolation of the pure electrolyte MgCl(THF) 5 +- PhAlCl 3 , and on the electrochemical behavior of it in ethereal solutions. The structure of this compound was proved by single-crystal X-ray diffraction, Raman, and NMR spectroscopies. The novel MgCl(THF) 5 PhAlCl 3 /THF electrolyte solutions exhibit reversible Mg deposition/dissolution processes with anodic stability up to 2.7 V. The application of electrochemical cleaning pre-treatment for these solutions enabled to profoundly increase the coulombic efficiency of their Mg deposition/dissolution processes. Examining Mg prototype batteries with Mg foil anodes, composite Mo 6 S 8 Chevrel phase (CP) cathodes containing these solutions exhibited a viable battery performance, indicating that upon a further optimization, electrolyte solutions based on the complex MgCl(THF) 5 +- PhAlCl 3 −electrolyte may be suitable for practical RMB. [Display omitted] [ABSTRACT FROM AUTHOR]

In this paper, we report the synthesis of graphene-like MoS 2 /graphene hybrid by a facile lithium-assisted sonication method and its cathode application for rechargeable Mg batteries. Instrumental analyses elucidate that the composite displays a three-dimensional (3D) porous architecture constructed by exfoliated single or few MoS 2 layers, and some graphene is intercalated in the MoS 2 gallery with an enlarged interlayer spacing from 0.62 to 0.98 nm. The obtained MoS 2 /graphene hybrid exhibits high electrochemical performance with a remarkable capacity (115.9 mA h g −1 ) and good cyclic stability (82.5 mA h g −1 after 50 cycles). This is owing to the synergistic effect between the graphene-like MoS 2 and the highly conductive graphene, which can effectively facilitate the Mg 2+ ions diffusion and electrons transfer, provide abundant active sites for Mg 2+ intercalation, and prevent structural collapse upon prolonged cycling. [ABSTRACT FROM AUTHOR]

Exploring high-performance cathode materials is of great significance for development of rechargeable magnesium batteries. Herein, two-dimensional ultrathin spinel CuCo 2 S 4 nanosheets synthesized via microwave-assisted liquid-phase growth and anion-exchange post-sulfuration method. As a magnesium storage material, the electrochemical behavior of the CuCo 2 S 4 nanosheets is investigated in different voltage ranges. After activated for several cycles in 0.1–2.1 V, the CuCo 2 S 4 nanosheet material can show good electrochemical reversibility between 0.1 and 2.0 V with capacity of 191.4 mAh g−1 (50 mA g−1) and 114.5 mAh g−1 (500 mA g−1). The excellent Mg-storage properties are attributed to the fast kinetics of Mg2+ by the 2D morphology and ternary structure. A conversion reaction of the magnesium ion storage mechanism is confirmed by ex situ X-ray diffraction characterization. The excellent performance of spinel CuCo 2 S 4 nanosheets validates the viability of the multinary strategy and sheds light on the application of 2D material design for cathode research. • Spinel CuCo 2 S 4 nanosheets are synthesized by a microwave-anion-exchange route. • CuCo 2 S 4 with multinary structure and 2D morphology has good rate performance. • The Mg2+ storage performance can be enhanced by altering upper cut-off voltage. • The magnesium storage mechanism of spinel CuCo 2 S 4 is studied by ex-situ XRD. [ABSTRACT FROM AUTHOR]

The nature of dendrite-free magnesium (Mg) metal anodes is an important advantage in rechargeable magnesium batteries (RMBs). However, this traditional cognition needs to be reconsidered due to inhomogeneous Mg deposits under extreme electrochemical conditions. Herein, we report a three-dimensional (3D) Cu-based host with magnesiophilic Ag sites (denoted as "Ag@3D Cu mesh") to regulate Mg deposition behaviors and achieve uniform Mg electrodeposition. Mg deposition/stripping behaviors are obviously improved under the cooperative effect of nanowire structures and Ag sites. The test results indicate that nucleation overpotentials are reduced distinctly and cycling performances are prolonged, suggesting that the general rules of 3D structures and affinity sites improve the durability and reversibility of Mg deposition/stripping. Besides, a unique concave surface structure can induce Mg to deposit into the interior of the interspace, which utilizes Mg more efficiently and leads to improved electrochemical performances with limited Mg content. Furthermore, in situ optical microscopic images show that the Ag@3D Cu mesh can attain a smooth surface, nearly without Mg protrusions, under 8.0 mA cm -2 , which prevents premature short circuits. This report is a pioneering work to demonstrate the feasibility of modification of Cu-based current collectors and the necessity of functional current collectors to improve the possibility of practical applications for RMBs.

• Metallic 2D V 6 O 13 nanosheets are synthesized via an ultra-rapid and low-cost microwave-assisted method. • The high magnesium reversible capacity of metallic 2D V 6 O 13 nanosheet positive electrode has been realized. • The magnesium ion storage mechanism of metallic 2D V 6 O 13 was preliminarily confirmed by ex-situ XRD. To explore and design cathode with high capacity is the key and challenge to promote the development of rechargeable Mg batteries (rMBs). Herein, metallic 2D V 6 O 13 nanosheet is synthesized via a facile microwave-assisted method. As cathode for rMBs, metallic 2D V 6 O 13 nanosheet delivers a high specific capacity of 324 mAh g−1 and exhibits moral cycling stability. This research shows the superiority of metallic V 6 O 13 nanosheet and its potential application in rechargeable Mg batteries. [ABSTRACT FROM AUTHOR]

Keywords: batteries; electrochemistry; energy storage; Mg electrodes; rechargeable Mg batteries EN batteries electrochemistry energy storage Mg electrodes rechargeable Mg batteries 4611 4611 1 11/09/21 20211104 NES 211104 B The Cover Feature b shows the electrochemical performance of 25 m AZ31 alloy as anode, in a full magnesium cell with Chevrel phase as cathode, in 0.25 m APC as electrolyte. Batteries, electrochemistry, energy storage, Mg electrodes, rechargeable Mg batteries. [Extracted from the article]

• Cu 2 MoS 4 hollow nanocages are used as advanced Mg-intercalation cathodes. • A high capacity of 180 mAh g−1 is provided as well as good rate performance. • A superior long-term cycleability over 2500 cycles is achieved. • Layered structure and hollow morphology favors Mg2+ diffusion kinetics. Rechargeable Mg batteries attract an increasing interest for grid energy storage because of the high safety and low cost; however, lack of Mg-intercalation cathodes is seriously hindering their development. In the present study, hollow polyhedral Cu 2 MoS 4 nanocages (CMS-H) are synthesized and investigated as a novel cathode for rechargeable Mg batteries. The layered structure of I-phase Cu 2 MoS 4 acts as ideal host for reversible Mg2+ intercalation/deintercalation, during which the interlayer spacing changes along with valence state change of Cu and Mo elements. CMS-H provides a high reversible capacity (180 mAh g−1 at 50 mA g−1) and an excellent rate performance beyond simple Cu 2 MoS 4 nanosheets, demonstrating the privilege of hollow architecture in Mg-storage via accommodating the strain and constructing short-range electron/ion transport pathways. CMS-H exhibits a superior cycleability over 2500 cycles, indicating the stability of I-phase Cu 2 MoS 4 during long-term Mg-intercalation cycling. The present results highlight a new type of hollow Cu 2 MoS 4 material for fast and stable Mg-storage, which is of great significance and provides scientific insights for the development of high-performance cathodes for rechargeable Mg batteries. [ABSTRACT FROM AUTHOR]

• Hierarchical starfish-like Cu 2−x Se of nanosheets is used for Mg batteries. • The cathode delivers a high capacity of 210 mAh g−1 at 100 mA g−1. • A superior long-term cycleability over 300 cycles is obtained. • The thin nanosheets enhance solid-state Mg2+ diffusion kinetics. Rechargeable Mg battery is a low-cost and highly safe energy storage technique suitable for large-scale application; however, searching for high-performance cathodes remains a large challenge blocking their development. Non-stoichiometric Cu 2−x Se has extraordinarily high conductivity and its unique crystal structure could better accommodate Mg2+ cations. In this work, Cu 2−x Se with nanosheets assembling starfish-like hierarchical structure (S-Cu 2−x Se) and nanocrystal (C-Cu 2−x Se) are synthesized by facile one-step hydrothermal methods and used as cathode for rechargeable Mg batteries. It is observed that S-Cu 2−x Se exhibits a high specific capacity of 210 mAh g−1 at 100 mA g−1, an excellent rate capability of 100 mA h g−1 at 1000 mA g−1, and a long-term cycling stability over 300 cycles. Mechanism investigation demonstrates that the Cu 2−x Se cathodes experience a two-step magnesiation/demagnesiation process during cycling, in which phase transformation is involved. The high-performance of S-Cu 2−x Se is owing to the fast solid-state Mg2+ diffusion in the thin nanosheets and the material integrity of the hierarchical structure. This work not only delivers facile approaches for the construction of high-performance Cu 2−x Se Mg cathodes, but also highlights scientific insights for the exploration of conversion-type Mg-storage materials. [ABSTRACT FROM AUTHOR]

Rechargeable Mg batteries are attractive candidates for large‐scale energy storage batteries with high safety due to the low‐cost and non‐dendritic metallic Mg anode. However, exploring high‐performance cathode materials is blocking their development. Herein, a high‐rate rechargeable Mg battery is established with a AgCl cathode, delivering a high reversible capacity of 70.3 mAh g−1 at 100 mA g−1, an outstanding rate capability of 32.6 mAh g−1 at 1000 mA g−1, and a superior long‐term cyclability over 500 cycles. Further investigation of the mechanism demonstrates that a conversion reaction takes place between AgCl and metallic Ag0 for the cathode. The solid‐state Mg2+ diffusion coefficient is as high as 8.1 × 10−11 cm2 s−1, which would be the reason for the high rate capability. The current study reveals significant insights to select promising Mg‐storage conversion cathodes by a combination of soft anions and soft transition‐metal cations. [ABSTRACT FROM AUTHOR]

Because of its high theoretical volumetric capacity and dendrite-free stripping/plating of Mg, rechargeable magnesium batteries (RMBs) hold great promise for high energy density in consumer electronics. However, the lack of high-energy-density cathodes severely constrains their practical applications. Herein, for the first time, we report that a CuS cathode can fully reversibly work through a displacement reaction in CuS/Mg pouch cells at room temperature and provide a high capacity of ∼400 mA h/g in a MACC electrolyte, corresponding to the gravimetric and volumetric energy density of 608 W h/kg and1042 W h/L, respectively. Even after 80 cycles, CuS/Mg pouch cells can maintain a high capacity of 335 mA h/g. Detailed mechanistic studies reveal that CuS undergoes a displacement reaction route rather than a typical conversion mechanism. This work will provide a guide for more discovery of high-performance cathode candidates for RMBs.