A Rechargeable Al/S Battery with an Ionic‐Liquid Electrolyte

Aluminum metal is a promising anode material for next generation rechargeable batteries owing to its abundance, potentially dendrite‐free deposition, and high capacity. The rechargeable aluminum/sulfur (Al/S) battery is of great interest owing to its high energy density (1340 Wh kg^?1) and low cost. However, Al/S chemistry suffers poor reversibility owing to the difficulty of oxidizing AlS_x. Herein, we demonstrate the first reversible Al/S battery in ionic‐liquid electrolyte with an activated carbon cloth/sulfur composite cathode. Electrochemical, spectroscopic, and microscopic results suggest that sulfur undergoes a solid‐state conversion reaction in the electrolyte. Kinetics analysis identifies that the slow solid‐state sulfur conversion reaction causes large voltage hysteresis and limits the energy efficiency of the system.     

Multi‐Electron Reactions Enabled by Anion‐Based Redox Chemistry for High‐Energy Multivalent Rechargeable Batteries

The development of multivalent metal (such as Mg and Ca) based battery systems is hindered by lack of suitable cathode chemistry that shows reversible multi‐electron redox reactions. Cationic redox centres in the classical cathodes can only afford stepwise single‐electron transfer, which are not ideal for multivalent‐ion storage. The charge imbalance during multivalent ion insertion might lead to an additional kinetic barrier for ion mobility. Therefore, multivalent battery cathodes only exhibit slope‐like voltage profiles with insertion/extraction redox of less than one electron. Taking VS₄ as a model material, reversible two‐electron redox with cationic–anionic contributions is verified in both rechargeable Mg batteries (RMBs) and rechargeable Ca batteries (RCBs). The corresponding cells exhibit high capacities of >300 mAh g^?1 at a current density of 100 mA g^?1 in both RMBs and RCBs, resulting in a high energy density of >300 Wh kg^?1 for RMBs and >500 Wh kg^?1 for RCBs. Mechanistic studies reveal a unique redox activity mainly at anionic sulfides moieties and fast Mg²⁺ ion diffusion kinetics enabled by the soft structure and flexible electron configuration of VS₄.     

Multi-Electron Reactions Enabled by Anion-Based Redox Chemistry for High-Energy Multivalent Rechargeable Batteries

The development of multivalent metal (such as Mg and Ca) based battery systems is hindered by lack of suitable cathode chemistry that shows reversible multi-electron redox reactions. Cationic redox centres in the classical cathodes can only afford stepwise single-electron transfer, which are not ideal for multivalent-ion storage. The charge imbalance during multivalent ion insertion might lead to an additional kinetic barrier for ion mobility. Therefore, multivalent battery cathodes only exhibit slope-like voltage profiles with insertion/extraction redox of less than one electron. Taking VS₄ as a model material, reversible two-electron redox with cationic–anionic contributions is verified in both rechargeable Mg batteries (RMBs) and rechargeable Ca batteries (RCBs). The corresponding cells exhibit high capacities of >300 mAh g⁻¹ at a current density of 100 mA g⁻¹ in both RMBs and RCBs, resulting in a high energy density of >300 Wh kg⁻¹ for RMBs and >500 Wh kg⁻¹ for RCBs. Mechanistic studies reveal a unique redox activity mainly at anionic sulfides moieties and fast Mg²⁺ ion diffusion kinetics enabled by the soft structure and flexible electron configuration of VS₄.     

The Long‐Term Stability of KO2 in K‐O2 Batteries

The rechargeable K‐O₂ battery is recognized as a promising energy storage solution owing to its large energy density, low overpotential, and high coulombic efficiency based on the single‐electron redox chemistry of potassium superoxide. However, the reactivity and long‐term stability of potassium superoxide remains ambiguous in K‐O₂ batteries. Parasitic reactions are explored and the use of ion chromatography to quantify trace amounts of side products is demonstrated. Both quantitative titrations and differential electrochemical mass spectrometry confirm the highly reversible single‐electron transfer process, with 98 % capacity attributed to the formation and decomposition of KO₂. In contrast to the Na‐O₂ counterparts, remarkable shelf‐life is demonstrated for K‐O₂ batteries owing to the thermodynamic and kinetic stability of KO₂, which prevents the spontaneous disproportionation to peroxide. This work sheds light on the reversible electrochemical process of K⁺+e^?+O₂?KO₂.     

Unlocking Reversible Silicon Redox for High-Performing Chlorine Batteries

Chlorine (Cl)-based batteries such as Li/Cl₂ batteries are recognized as promising candidates for energy storage with low cost and high performance. However, the current use of Li metal anodes in Cl-based batteries has raised serious concerns regarding safety, cost, and production complexity. More importantly, the well-documented parasitic reactions between Li metal and Cl-based electrolytes require a large excess of Li metal, which inevitably sacrifices the electrochemical performance of the full cell. Therefore, it is crucial but challenging to establish new anode chemistry, particularly with electrochemical reversibility, for Cl-based batteries. Here we show, for the first time, reversible Si redox in Cl-based batteries through efficient electrolyte dilution and anode/electrolyte interface passivation using 1,2-dichloroethane and cyclized polyacrylonitrile as key mediators. Our Si anode chemistry enables significantly increased cycling stability and shelf lives compared with conventional Li metal anodes. It also avoids the use of a large excess of anode materials, thus enabling the first rechargeable Cl₂ full battery with remarkable energy and power densities of 809 Wh kg⁻¹ and 4,277 W kg⁻¹, respectively. The Si anode chemistry affords fast kinetics with remarkable rate capability and low-temperature electrochemical performance, indicating its great potential in practical applications.     

Full Dissolution of the Whole Lithium Sulfide Family (Li2S8 to Li2S) in a Safe Eutectic Solvent for Rechargeable Lithium–Sulfur Batteries

The lithium–sulfur battery is an attractive option for next‐generation energy storage owing to its much higher theoretical energy density than state‐of‐the‐art lithium‐ion batteries. However, the massive volume changes of the sulfur cathode and the uncontrollable deposition of Li₂S₂/Li₂S significantly deteriorate cycling life and increase voltage polarization. To address these challenges, we develop an ?‐caprolactam/acetamide based eutectic‐solvent electrolyte, which can dissolve all lithium polysulfides and lithium sulfide (Li₂S₈–Li₂S). With this new electrolyte, high specific capacity (1360 mAh g^?1) and reasonable cycling stability are achieved. Moreover, in contrast to conventional ether electrolyte with a low flash point (ca. 2 °C), such low‐cost eutectic‐solvent‐based electrolyte is difficult to ignite, and thus can dramatically enhance battery safety. This research provides a new approach to improving lithium–sulfur batteries in aspects of both safety and performance.     

Proton-Reservoir Hydrogel Electrolyte for Long-Term Cycling Zn/PANI Batteries in Wide Temperature Range

Advanced aqueous batteries are promising for next generation flexible devices owing to the high safety, yet still requiring better cycling stability and high capacities in wide temperature range. Herein, a polymeric acid hydrogel electrolyte (PAGE) with 3 M Zn(ClO₄)₂ was fabricated for high performance Zn/polyaniline (PANI) batteries. With PAGE, even at −35 °C the Zn/Zn symmetrical battery can keep stable for more than 1 500 h under 2 mA cm⁻², and the Zn/PANI battery can provide ultra-high stable specific capacity of 79.6 mAh g⁻¹ for more than 70 000 cycles at 15 A g⁻¹. This can be mainly ascribed to the −SO₃⁻H⁺ function group in PAGE. It can generate constant protons and guide the (002) plane formation to accelerate the PANI redox reaction kinetics, increase the specific capacity, and suppress the side reaction and dendrites. This proton-supplying strategy by polymeric acid hydrogel may further propel the development of high performance aqueous batteries.     

An Efficient Halogen‐Free Electrolyte for Use in Rechargeable Magnesium Batteries

Unlocking the full potential of rechargeable magnesium batteries has been partially hindered by the reliance on chloride‐based complex systems. Despite the high anodic stability of these electrolytes, they are corrosive toward metallic battery components, which reduce their practical electrochemical window. Following on our new design concept involving boron cluster anions, monocarborane CB₁₁H₁₂^? produced the first halogen‐free, simple‐type Mg salt that is compatible with Mg metal and displays an oxidative stability surpassing that of ether solvents. Owing to its inertness and non‐corrosive nature, the Mg(CB₁₁H₁₂)₂/tetraglyme (MMC/G4) electrolyte system permits standardized methods of high‐voltage cathode testing that uses a typical coin cell. This achievement is a turning point in the research and development of Mg electrolytes that has deep implications on realizing practical rechargeable Mg batteries.     

Highly Rechargeable Lithium-CO2 Batteries with a Boron- and Nitrogen-Codoped Holey-Graphene Cathode

Metal-air batteries, especially Li-air batteries, have attracted significant research attention in the past decade. However, the electrochemical reactions between CO₂ (0.04 % in ambient air) with Li anode may lead to the irreversible formation of insulating Li₂CO₃, making the battery less rechargeable. To make the Li-CO₂ batteries usable under ambient conditions, it is critical to develop highly efficient catalysts for the CO₂ reduction and evolution reactions and investigate the electrochemical behavior of Li-CO₂ batteries. Here, we demonstrate a rechargeable Li-CO₂ battery with a high reversibility by using B,N-codoped holey graphene as a highly efficient catalyst for CO₂ reduction and evolution reactions. Benefiting from the unique porous holey nanostructure and high catalytic activity of the cathode, the as-prepared Li-CO₂ batteries exhibit high reversibility, low polarization, excellent rate performance, and superior long-term cycling stability over 200 cycles at a high current density of 1.0 A g⁻¹. Our results open up new possibilities for the development of long-term Li-air batteries reusable under ambient conditions, and the utilization and storage of CO₂.     

A Full Li–S Battery with Ultralow Excessive Li Enabled via Lithiophilic and Sulfilic W2C Modulation

The practical application of Li–S batteries demands low cell balance (Li_capacity/S_capacity), which involves uniform Li growth, restrained shuttle effect, and fast redox reaction kinetics of S species simultaneously. Herein, with the aid of W₂C nanocrystals, a freestanding 3D current collector is applied as both Li and S hosts owing to its lithiophilic and sulfilic property. On the one hand, the highly conductive W₂C can reduce Li nucleation overpotentials, thus guiding uniform Li nucleation and deposition to suppress Li dendrite growth. On the other hand, the polar W₂C with catalytic effect can enhance the chemisorption affinity to lithium polysulfides (LiPSs) and guarantee fast redox kinetics to restrain S species in cathode region and promote the utilization of S. Surprisingly, a full Li–S battery with ultralow cell balance of 1.5:1 and high sulfur loading of 6.06 mg cm⁻² shows obvious redox plateaus of S and maintains high reversible specific capacity of 1020 mAh g⁻¹ (6.2 mAh cm⁻²) after 200 cycles. This work may shed new sights on the facile design of full Li–S battery with low excessive Li supply.     

Highly Rechargeable Lithium‐CO2 Batteries with a Boron‐ and Nitrogen‐Codoped Holey‐Graphene Cathode

Metal‐air batteries, especially Li‐air batteries, have attracted significant research attention in the past decade. However, the electrochemical reactions between CO₂ (0.04 % in ambient air) with Li anode may lead to the irreversible formation of insulating Li₂CO₃, making the battery less rechargeable. To make the Li‐CO₂ batteries usable under ambient conditions, it is critical to develop highly efficient catalysts for the CO₂ reduction and evolution reactions and investigate the electrochemical behavior of Li‐CO₂ batteries. Here, we demonstrate a rechargeable Li‐CO₂ battery with a high reversibility by using B,N‐codoped holey graphene as a highly efficient catalyst for CO₂ reduction and evolution reactions. Benefiting from the unique porous holey nanostructure and high catalytic activity of the cathode, the as‐prepared Li‐CO₂ batteries exhibit high reversibility, low polarization, excellent rate performance, and superior long‐term cycling stability over 200 cycles at a high current density of 1.0 A g⁻¹. Our results open up new possibilities for the development of long‐term Li‐air batteries reusable under ambient conditions, and the utilization and storage of CO₂.     

Effects of Conjugated Structure on the Magnesium Storage Performance of Dianhydrides

Inorganic cathodes of rechargeable Mg batteries suffer from limited selections, while organic materials provide more options. Herein, three conjugated dianhydrides, pyromellitic dianhydride, 1,4,5,8-naphthalenetetracarboxylic dianhydride and 3,4,9,10-perylenetetracarboxylic dianhydride are comparatively investigated to elucidate the effects of conjugated structure on the Mg²⁺ storage performances. It is observed that the reversible Mg²⁺ storage capacity is more dependent on the conjugated structure than carbonyl numbers. Ex-situ mechanism study illustrates that the extended conjugated structure delocalizes the electron density, hence enhancing carbonyl enolization and increasing the Mg²⁺ storage capacity. Furthermore, the largely conjugated structure buffers the charge density change during repeated magnesiation/demagnesiation resulting in better cyclability. Prominently, 3,4,9,10-perylenetetracarboxylic dianhydride shows a high Mg²⁺ storage capacity (160 mAh g⁻¹) and a good cycling stability (80 % capacity retention after 100 cycles) with the largest conjugated structure. This work provides a low-cost cathode for rechargeable Mg batteries that can be utilized for designing high-performance organic Mg battery cathodes.     

Electron Redistribution Enables Redox-Resistible Li6PS5Cl towards High-Performance All-Solid-State Lithium Batteries

Sulfide electrolytes with high ionic conductivity hold great promise for all-solid-state lithium batteries. However, the parasitic redox reactions between sulfide electrolyte and Li metal result in interfacial instability and rapid decline of the battery performance. Herein, a redox-resistible Li₆PS₅Cl (LPSC) electrolyte is created by regulating the electron distribution in LPSC with Mg and F incorporation. The introduction of Mg triggers the electron agglomeration around S atom, inhibiting the electron acceptance from Li, and F generates the self-limiting interface, which hinders the redox reactions between LPSC and Li metal. This redox-resistible Li₆PS₅Cl-MgF₂ electrolyte therefore presents a high critical current density (2.3 times that of pristine electrolyte). The LiCoO₂/Li₆PS₅Cl-MgF₂/Li cell shows an outstanding cycling stability (93.3 %@100 cycles at 0.2 C). This study highlights the electronic structure modulation to address redox issues on sulfide-based lithium batteries.     

The Stabilization Effect of CO2 in Lithium–Oxygen/CO2 Batteries

The lithium (Li)–air battery has an ultrahigh theoretical specific energy, however, even in pure oxygen (O₂), the vulnerability of conventional organic electrolytes and carbon cathodes towards reaction intermediates, especially O₂^?, and corrosive oxidation and crack/pulverization of Li metal anode lead to poor cycling stability of the Li‐air battery. Even worse, the water and/or CO₂ in air bring parasitic reactions and safety issues. Therefore, applying such systems in open‐air environment is challenging. Herein, contrary to previous assertions, we have found that CO₂ can improve the stability of both anode and electrolyte, and a high‐performance rechargeable Li–O₂/CO₂ battery is developed. The CO₂ not only facilitates the in situ formation of a passivated protective Li₂CO₃ film on the Li anode, but also restrains side reactions involving electrolyte and cathode by capturing O₂^?. Moreover, the Pd/CNT catalyst in the cathode can extend the battery lifespan by effectively tuning the product morphology and catalyzing the decomposition of Li₂CO₃. The Li–O₂/CO₂ battery achieves a full discharge capacity of 6628 mAh g^?1 and a long life of 715 cycles, which is even better than those of pure Li–O₂ batteries.     

Revealing the Interfacial Chemistry of Fluoride Alkyl Magnesium Salts in Magnesium Metal Batteries

Exploring promising electrolyte-system with high reversible Mg plating/stripping and excellent stability is essential for rechargeable magnesium batteries (RMBs). Fluoride alkyl magnesium salts (Mg(OR^F)₂) not only possess high solubility in ether solvents but also compatible with Mg metal anode, thus holding a vast application prospect. Herein, a series of diverse Mg(OR^F)₂ were synthesized, among them, perfluoro-tert-butanol magnesium (Mg(PFTB)₂)/AlCl₃/MgCl₂ based electrolyte demonstrates highest oxidation stability, and promotes the in situ formation of robust solid electrolyte interface. Consequently, the fabricated symmetric cell sustains a long-term cycling over 2000 h, and the asymmetric cell exhibits a stable Coulombic efficiency of 99.5 % over 3000 cycles. Furthermore, the Mg||Mo₆S₈ full cell maintains a stable cycling over 500 cycles. This work presents guidance for understanding structure–property relationships and electrolyte applications of fluoride alkyl magnesium salts.     

A Stable,Non‐Corrosive Perfluorinated Pinacolatoborate Mg Electrolyte for Rechargeable Mg Batteries

Mg batteries are a promising energy storage system because of the physicochemical merits of Mg as an anode material. However, the lack of electrochemically and chemically stable Mg electrolytes impedes the development of Mg batteries. In this study, a newly designed chloride‐free Mg perfluorinated pinacolatoborate, Mg[B(O₂C₂(CF₃)₄)₂]₂ (abbreviated as Mg‐FPB ), was synthesized by a convenient method from commercially available reagents and fully characterized. The Mg‐FPB electrolyte delivered outstanding electrochemical performance, specifically, 95 % Coulombic efficiency and 197 mV overpotential, enabling reversible Mg deposition, and an anodic stability of up to 4.0 V vs. Mg. The Mg‐FPB electrolyte was applied to assemble a high voltage, rechargeable Mg/MnO₂ battery with a discharge capacity of 150 mAh g^?1.     

A Stable,Non‐Corrosive Perfluorinated Pinacolatoborate Mg Electrolyte for Rechargeable Mg Batteries

Mg batteries are a promising energy storage system because of the physicochemical merits of Mg as an anode material. However, the lack of electrochemically and chemically stable Mg electrolytes impedes the development of Mg batteries. In this study, a newly designed chloride‐free Mg perfluorinated pinacolatoborate, Mg[B(O₂C₂(CF₃)₄)₂]₂ (abbreviated as Mg‐FPB ), was synthesized by a convenient method from commercially available reagents and fully characterized. The Mg‐FPB electrolyte delivered outstanding electrochemical performance, specifically, 95 % Coulombic efficiency and 197 mV overpotential, enabling reversible Mg deposition, and an anodic stability of up to 4.0 V vs. Mg. The Mg‐FPB electrolyte was applied to assemble a high voltage, rechargeable Mg/MnO₂ battery with a discharge capacity of 150 mAh g^?1.     

A New Perspective on Li–SO2 Batteries for Rechargeable Systems

Primary Li–SO₂ batteries offer a high energy density in a wide operating temperature range with exceptionally long shelf life and have thus been frequently used in military and aerospace applications. Although these batteries have never been demonstrated as a rechargeable system, herein, we show that the reversible formation of Li₂S₂O₄, the major discharge product of Li–SO₂ battery, is possible with a remarkably smaller charging polarization than that of a Li–O₂ battery without the use of catalysts. The rechargeable Li–SO₂ battery can deliver approximately 5400 mAh g^?1 at 3.1 V, which is slightly higher than the performance of a Li–O₂ battery. In addition, the Li–SO₂ battery can be operated with the aid of a redox mediator, exhibiting an overall polarization of less than 0.3 V, which results in one of the highest energy efficiencies achieved for Li–gas battery systems.     

Synthesis,Crystal Structure,and Electrochemical Properties of a Simple Magnesium Electrolyte for Magnesium/Sulfur Batteries

Most simple magnesium salts tend to passivate the Mg metal surface too quickly to function as electrolytes for Mg batteries. In the present work, an electroactive salt [Mg(THF)₆][AlCl₄]₂ was synthesized and structurally characterized. The Mg electrolyte based on this simple mononuclear salt showed a high Mg cycling efficiency, good anodic stability (2.5 V vs. Mg), and high ionic conductivity (8.5 mS cm^?1). Magnesium/sulfur cells employing the as‐prepared electrolyte exhibited good cycling performance over 20 cycles in the range of 0.3–2.6 V, thus indicating an electrochemically reversible conversion of S to MgS without severe passivation of the Mg metal electrode surface.     

Synthesis,Crystal Structure,and Electrochemical Properties of a Simple Magnesium Electrolyte for Magnesium/Sulfur Batteries

Most simple magnesium salts tend to passivate the Mg metal surface too quickly to function as electrolytes for Mg batteries. In the present work, an electroactive salt [Mg(THF)₆][AlCl₄]₂ was synthesized and structurally characterized. The Mg electrolyte based on this simple mononuclear salt showed a high Mg cycling efficiency, good anodic stability (2.5 V vs. Mg), and high ionic conductivity (8.5 mS cm⁻¹). Magnesium/sulfur cells employing the as‐prepared electrolyte exhibited good cycling performance over 20 cycles in the range of 0.3–2.6 V, thus indicating an electrochemically reversible conversion of S to MgS without severe passivation of the Mg metal electrode surface.