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

High-Performance Rechargeable Aluminum-Selenium Battery with a New Deep Eutectic Solvent Electrolyte: Thiourea-AlCl3

Aluminum-sulfur batteries (ASBs) have attracted substantial interest due to their high theoretical specific energy density, low cost, and environmental friendliness, while the traditional sulfur cathode and ionic liquid have very fast capacity decay, limiting cycling performance because of the sluggishly electrochemical reaction and side reactions with the electrolyte. Herein, we demonstrate, for the first time, excellent rechargeable aluminum-selenium batteries (ASeBs) using a new deep eutectic solvent, thiourea-AlCl₃, as an electrolyte and Se nanowires grown directly on a flexible carbon cloth substrate (Se NWs@CC) by a low-temperature selenization process as a cathode. Selenium (Se) is a chemical analogue of sulfur with higher electronic conductivity and lower ionization potential that can improve the battery kinetics on the sluggishly electrochemical reaction and the reduction of the polarization where the thiourea-AlCl₃ electrolyte can stabilize the side reaction during the reversible conversion reaction of Al-Se alloying processes during the charge-discharge process, yielding a high specific capacity of 260 mAh g^-1 at 50 mA g^-1 and a long cycling life of 100 times with a high Coulombic efficiency of nearly 93% at 100 mA g^-1. The working mechanism based on the reversible conversion reaction of the Al-Se alloying processes, confirmed by the ex situ Raman, XRD, and XPS measurements, was proposed. This work provides new insights into the development of rechargeable aluminum-chalcogenide (S, Se, and Te) batteries.

Approaching the voltage and energy density limits of potassium-selenium battery chemistry in a concentrated ether-based electrolyte

Potassium–selenium (K–Se) batteries offer fairly high theoretical voltage (∼1.88 V) and energy density (∼1275 W h kg_Se⁻¹). However, in practice, their operation voltage is so far limited to ∼1.4 V, resulting in insufficient energy utilization and mechanistic understanding. Here, it is demonstrated for the first time that K–Se batteries operating in concentrated ether-based electrolytes follow distinctive reaction pathways involving reversible stepwise conversion reactions from Se to K₂Se_x (x = 5, 3, 2, 1). The presence of redox intermediates K₂Se₅ at ∼2.3 V and K₂Se₃ at ∼2.1 V, in contrast with previous reports, enables record-high average discharge plateau voltage (1.85 V) and energy density (998 W h kg_Se⁻¹ or 502 W h kg_K2Se⁻¹), both approaching the theoretical limits and surpassing those of previously reported Na/K/Al–Se batteries. Moreover, experimental analysis and first-principles calculations reveal that the effective suppression of detrimental polyselenide dissolution/shuttling in concentrated electrolytes, together with high electron conductibility of Se/K₂Se_x, enables fast reaction kinetics, efficient utilization of Se, and long-term cyclability of up to 350 cycles, which are impracticable in either K–S counterparts or K–Se batteries with low/moderate-concentration electrolytes. This work may pave the way for mechanistic understanding and full energy utilization of K–Se battery chemistry.

K–Se batteries follow distinctive reaction pathways in concentrated ether electrolytes, and deliver record-high discharge plateau voltage of 1.85 V on average and energy density of 998 W h kg_Se⁻¹, both approaching the theoretical limits.

Organoboron Ionic Liquids as Extractants for Distillation Process of Binary Ethanol + Water Mixtures

Aminoethers of boric acid, which are organoboron ionic liquids, were synthesized by using boric acid, triethanolamine, and triethylene glycol/diethylene glycol. Due to the formation of intermolecular complexes of borates, the structure of aminoethers of boric acid contains ion pairs separated in space, giving these compounds the properties inherent to ionic liquids. It is established that the thermal stability of aminoethers under normal atmospheric conditions increases with an increase in the size of the glycol. According to measurements of fast scanning calorimetry, density, dynamic viscosity, and electrical conductivity, water is involved in the structural organization of aminoethers of boric acid. The impact of the most thermostable organoboron ionic liquids on the phase equilibrium conditions of the vapor–liquid azeotropic ethanol–water mixture is studied. It is shown that the presence of these substances leads to increase in the relative volatility of ethanol. In general, the magnitude of this effect is at the level shown by imidazole ionic liquids, which provide high selectivity in the separation of aqueous alcohol solutions. A large separation factor, high resistance to thermal oxidative degradation processes, accompanied by low cost start reagents, make aminoethers of boric acid on the basis of triethylene glycol a potentially effective extractant for the extractive distillation of water–alcohol mixtures.

A strategy for massively suppressing the shuttle effect in rechargeable Al–Te batteries

Due to the chemical and electrochemical dissolution of active materials in Lewis acid electrolytes, an AB–PVDF-MS has been constructed to promote the utilization of active materials and rechargeability at both positive and negative electrodes.

Novel One-Dimensional Hollow Carbon Nanotubes/Selenium Composite for High-Performance Al-Se Batteries

Herein, we successfully prepared one-dimensional nanowire with carbon-coated selenium (Se@CW) by using a simple wet chemical method and obtained a one-dimensional hollow Se@C nanotube (Se@CT) after the subsequent calcination treatment. We have formed a new Al-Se secondary battery by using Se@CT as the cathode and metal aluminum as the anode in the AlCl₃/[EMIm]Cl electrolyte. It is believed that the oxidation intermediate of Se in Al-Se batteries may not only have Se₂²⁺, but there may be other oxidation intermediates, such as Se⁴⁺, Se²⁺, and Se₈²⁺. Therefore, Se@CT exhibits excellent charge-discharge performance in Al-Se batteries. Its initial discharge capacity reaches 447.2 mA h g^-1 at 200 mA g^-1, and the operating voltage is above 1.6 V. Its energy density approaches 708.8 W h k g^-1, the capacity is still 162.9 mA h g^-1 after 200 cycles at 500 mA g^-1, and the corresponding capacity retention rate is up to 83.5%. In addition, its electrochemical performance is far superior to that of Se@CMK-3 in Al-Se batteries and the electrochemical properties of carbon materials, oxides, and sulfide electrode materials in some aluminum-ion batteries, which will open up a new direction for the development of new secondary aluminum-based batteries.

Two-dimensional boron nitride as a sulfur fixer for high performance rechargeable aluminum-sulfur batteries

Aluminum-ion batteries (AIBs) are regarded as promising candidates for post-lithium-ion batteries due to their lack of flammability and electrochemical performance comparable to other metal-ion batteries. The lack of suitable cathode materials, however, has hindered the development of high-performing AIBs. Sulfur is a cost-efficient material, having distinguished electrochemical properties, and is considered an attractive cathode material for AIBs. Several pioneering reports have shown that aluminum-sulfur batteries (ASBs) exhibit superior electrochemical capacity over other cathode materials for AIBs. However, a rapid decay in the capacity is a huge barrier for their practical applications. Here, we have demonstrated systematically for the first time that the two-dimensional layered materials (e.g. MoS2, WS2, and BN) can serve as fixers of S and sulfide compounds during repeated charge/discharge processes; BN/S/C displays the highest capacity of 532 mAh g-1 (at a current density of 100 mA g-1) compared with the current state-of-the-art cathode material for AIBs. Further, we could improve the life-span of ASBs to an unprecedented 300 cycles with a high Coulombic efficiency of 94.3%; discharge plateaus at ~1.15 V vs. AlCl4-/Al was clearly observed during repeated charge/discharge cycling. We believe that this work opens up a new method for achieving high-performing ASBs.

A Four-Electron Sulfur Electrode Hosting a Cu2+ /Cu+ Redox Charge Carrier

The elemental sulfur electrode with Cu²⁺ as the charge carrier gives a four-electron sulfur electrode reaction through the sequential conversion of S↔CuS↔Cu₂ S. The Cu-S redox-ion electrode delivers a high specific capacity of 3044 mAh g^-1 based on the sulfur mass or 609 mAh g^-1 based on the mass of Cu₂ S, the completely discharged product, and displays an unprecedently high potential of sulfur/metal sulfide reduction at 0.5 V vs. SHE. The Cu-S electrode also exhibits an extremely low extent of polarization of 0.05 V and an outstanding cycle number of 1200 cycles retaining 72 % of the initial capacity at 12.5 A g^-1 . The remarkable utility of this Cu-S cathode is further demonstrated in a hybrid cell that employs an Zn metal anode and an anion-exchange membrane as the separator, which yields an average cell discharge voltage of 1.15 V, the half-cell specific energy of 547 Wh kg^-1 based on the mass of the Cu₂ S/carbon composite cathode, and stable cycling over 110 cycles.

Viromimetic STING Agonist-Loaded Hollow Polymeric Nanoparticles for Safe and Effective Vaccination against Middle East Respiratory Syndrome Coronavirus

The continued threat of emerging, highly lethal infectious pathogens such as Middle East respiratory syndrome coronavirus (MERS-CoV) calls for the development of novel vaccine technology that offers safe and effective prophylactic measures. Here, a novel nanoparticle vaccine is developed to deliver subunit viral antigens and STING agonists in a virus-like fashion. STING agonists are first encapsulated into capsid-like hollow polymeric nanoparticles, which show multiple favorable attributes, including a pH-responsive release profile, prominent local immune activation, and reduced systemic reactogenicity. Upon subsequent antigen conjugation, the nanoparticles carry morphological semblance to native virions and facilitate codelivery of antigens and STING agonists to draining lymph nodes and immune cells for immune potentiation. Nanoparticle vaccine effectiveness is supported by the elicitation of potent neutralization antibody and antigen-specific T cell responses in mice immunized with a MERS-CoV nanoparticle vaccine candidate. Using a MERS-CoV-permissive transgenic mouse model, it is shown that mice immunized with this nanoparticle-based MERS-CoV vaccine are protected against a lethal challenge of MERS-CoV without triggering undesirable eosinophilic immunopathology. Together, the biocompatible hollow nanoparticle described herein provides an excellent strategy for delivering both subunit vaccine candidates and novel adjuvants, enabling accelerated development of effective and safe vaccines against emerging viral pathogens.

Current Status and Future Prospects of Metal-Sulfur Batteries

Lithium-sulfur batteries are a major focus of academic and industrial energy-storage research due to their high theoretical energy density and the use of low-cost materials. The high energy density results from the conversion mechanism that lithium-sulfur cells utilize. The sulfur cathode, being naturally abundant and environmentally friendly, makes lithium-sulfur batteries a potential next-generation energy-storage technology. The current state of the research indicates that lithium-sulfur cells are now at the point of transitioning from laboratory-scale devices to a more practical energy-storage application. Based on similar electrochemical conversion reactions, the low-cost sulfur cathode can be coupled with a wide range of metallic anodes, such as sodium, potassium, magnesium, calcium, and aluminum. These new "metal-sulfur" systems exhibit great potential in either lowering the production cost or producing high energy density. Inspired by the rapid development of lithium-sulfur batteries and the prospect of metal-sulfur cells, here, over 450 research articles are summarized to analyze the research progress and explore the electrochemical characteristics, cell-assembly parameters, cell-testing conditions, and materials design. In addition to highlighting the current research progress, the possible future areas of research which are needed to bring conversion-type lithium-sulfur and other metal-sulfur batteries into the market are also discussed.

The Rechargeable Aluminum Battery: Opportunities and Challenges

Aluminum battery systems are considered as a system that could supplement current lithium batteries due to the low cost and high volumetric capacity of aluminum metal, and the high safety of the whole battery system. However, first the use of ionic liquid electrolytes leading to AlCl₄ ^- instead of Al³⁺ , the different intercalation reagents, the sluggish solid diffusion process and the fast capacity fading during cycling in aluminum batteries all need to be thoroughly explored. To provide a good understanding of the opportunities and challenges of the newly emerging aluminum batteries, this Review discusses the reaction mechanisms and the difficulties caused by the trivalent reaction medium in electrolytes, electrodes, and electrode-electrolyte interfaces. It is hoped that the Review will stimulate scientists and engineers to develop more reliable aluminum batteries.

Encapsulation of SeS2 into Nitrogen-Doped Free-Standing Carbon Nanofiber Film Enabling Long Cycle Life and High Energy Density K-SeS2 Battery

K-SeS₂ batteries could provide a low-cost and high energy density energy storage system, because the earth-abundant element potassium (K) shows a low reduction potential and a high gravimetric capacity. But the K-SeS₂ battery has never been reported because of the lack of high-performance electrode materials. Herein, we design an advanced K-SeS₂ battery by encapsulation of SeS₂ in the nitrogen-doped free-standing porous carbon matrix (SeS₂@NCNFs). The self-supported SeS₂@NCNFs electrode achieves a high reversible capacity of 417 mAh g^-1 after 1000 cycles with 85% capacity retention at 0.5 Ag^1- with nearly 100% Coulombic efficiency. The nanosized SeS₂ nanoparticles are encapsulated in the carbon matrix, which minimizes the volume expansion during cycling and shortens the ion transport pathways, thus enhancing the rate capability. The interconnected porous carbon nanofiber structure could improve the flexibility and offer a continuous pathway for rapid ionic/electronic transport. The DFT calculations confirm that high content N-doping (11.2 at. %) can enhance the chemical affinity between the discharge product and the N-doped carbon. The pyrrolic and pyridinic N-doping lead to stronger adsorption than that of the graphitic N-doping. This proposed design holds great promise for practical application of high energy density K-SeS₂ batteries.

Paving the Path toward Reliable Cathode Materials for Aluminum-Ion Batteries

Aluminum metal is a high-energy-density carrier with low cost, and thus endows rechargeable aluminum batteries (RABs) with the potential to act as an inexpensive and efficient electrochemical device, so as to supplement the increasing demand for energy storage and conversion. Despite the enticing aspects regarding cost and energy density, the poor reversibility of electrodes has limited the pursuit of RABs for a long time. Fortunately, ionic-liquid electrolytes enable reversible aluminum plating/stripping at room temperature, and they lay the very foundation of RABs. In order to integrate with the aluminum-metal anode, the selection of the cathode is pivotal, but is limited at present. The scant option of a reliable cathode can be accounted for by the intrinsic high charge density of Al³⁺ ions, which results in sluggish diffusion. Hence, reliable cathode materials are a key challenge of burgeoning RABs. Herein, the main focus is on the insertion cathodes for RABs also termed aluminum-ion batteries, and the recent progress and optimization methods are summarized. Finally, an outlook is presented to navigate the possible future work.

Nonlithium Metal-Sulfur Batteries: Steps Toward a Leap

Present mobile devices, transportation tools, and renewable energy technologies are more dependent on newly developed battery chemistries than ever before. Intrinsic properties, such as safety, high energy density, and cheapness, are the main objectives of rechargeable batteries that have driven their overall technological progress over the past several decades. Unfortunately, it is extremely hard to achieve all these merits simultaneously at present. Alternatively, exploration of the most suitable batteries to meet the specific requirements of an individual application tends to be a more reasonable and easier choice now and in the near future. Based on this concept, here, a range of promising alternatives to lithium-sulfur batteries that are constructed with non-Li metal anodes (e.g., Na, K, Mg, Ca, and Al) and sulfur cathodes are discussed. The systems governed by these new chemistries offer high versatility in meeting the specific requirements of various applications, which is directly linked with the broad choice in battery chemistries, materials, and systems. Herein, the operating principles, materials, and remaining issues for each targeted battery characteristics are comprehensively reviewed. By doing so, it is hoped that their design strategies are illustrated and light is shed on the future exploration of new metal-sulfur batteries and advanced materials.

Beyond Intercalation Chemistry for Rechargeable Mg Batteries: A Short Review and Perspective

Rechargeable magnesium (Mg) batteries are an attractive candidate for next-generation battery technology because of their potential to offer high energy density, low cost, and safe use. Despite recent substantial progress achieved in the development of efficient electrolytes, identifying high-performance cathode materials remains a bottleneck for the realization of practical Mg batteries. Due to the strong interaction between the doubly charged Mg²⁺ ions and the host matrix, most of the conventional intercalation cathodes suffer from low capacity, high voltage hysteresis, and low energy density in Mg based battery systems. Alternatively, the thermodynamically favorable conversion reaction may circumvent the sluggish Mg²⁺ diffusion kinetics. In this review, the focus will be laid on promising cathodes beyond the typical intercalation-type materials. We will give an overview of the recent emerging Mg systems with conversion-type and organic cathodes.

Electrochemically activated spinel manganese oxide for rechargeable aqueous aluminum battery

Aluminum is a naturally abundant, trivalent charge carrier with high theoretical specific capacity and volumetric energy density, rendering aluminum-ion batteries a technology of choice for future large-scale energy storage. However, the frequent collapse of the host structure of the cathode materials and sluggish kinetics of aluminum ion diffusion have thus far hampered the realization of practical battery devices. Here, we synthesize Al_xMnO₂·nH₂O by an in-situ electrochemical transformation reaction to be used as a cathode material for an aluminum-ion battery with a configuration of Al/Al(OTF)₃-H₂O/Al_xMnO₂·nH₂O. This cell is not only based on aqueous electrolyte chemistry but also delivers a high specific capacity of 467 mAh g^-1 and a record high energy density of 481 Wh kg^-1. The high safety of aqueous electrolyte, facile cell assembly and the low cost of materials suggest that this aqueous aluminum-ion battery holds promise for large-scale energy applications.

A sub-100 °C aluminum ion battery based on a ternary inorganic molten salt

Using a ternary inorganic molten salt electrolyte, a sub-100 °C aluminum ion battery is presented with improved operational feasibility simply by water heating.

Solid electrolyte interphases for high-energy aqueous aluminum electrochemical cells

Electrochemical cells based on aluminum (Al) are of long-standing interest because Al is earth abundant, low cost, and chemically inert. The trivalent Al³⁺ ions also offer among the highest volume-specific charge storage capacities (8040 mAh cm^-3), approximately four times larger than achievable for Li metal anodes. Rapid and irreversible formation of a high-electrical bandgap passivating Al₂O₃ oxide film on Al have, to date, frustrated all efforts to create aqueous Al-based electrochemical cells with high reversibility. Here, we investigate the interphases formed on metallic Al in contact with ionic liquid (IL)-eutectic electrolytes and find that artificial solid electrolyte interphases (ASEIs) formed spontaneously on the metal permanently transform its interfacial chemistry. The resultant IL-ASEIs are further shown to enable aqueous Al electrochemical cells with unprecedented reversibility. As an illustration of the potential benefits of these interphases, we create simple Al||MnO₂ aqueous cells and report that they provide high specific energy (approximately 500 Wh/kg, based on MnO₂ mass in the cathode) and intrinsic safety features required for applications.

Emerging Nonaqueous Aluminum-Ion Batteries: Challenges, Status, and Perspectives

Aluminum-ion batteries (AIBs) are regarded as viable alternatives to lithium-ion technology because of their high volumetric capacity, their low cost, and the rich abundance of aluminum. However, several serious drawbacks of aqueous systems (passive film formation, hydrogen evolution, anode corrosion, etc.) hinder the large-scale application of these systems. Thus, nonaqueous AIBs show incomparable advantages for progress in large-scale electrical energy storage. However, nonaqueous aluminum battery systems are still nascent, and various technical and scientific obstacles to designing AIBs with high capacity and long cycling life have not been resolved until now. Moreover, the aluminum cell is a complex device whose energy density is determined by various parameters, most of which are often ignored, resulting in failure to achieve the maximum performance of the cell. The purpose here is to discuss how to further develop reliable nonaqueous AIBs. First, the current status of nonaqueous AIBs is reviewed based on statistical data from the literature. The influence of parameters on energy density is analyzed, and the current situation and existing problems are summarized. Furthermore, possible solutions and concerns regarding the construction of reliable nonaqueous AIBs are comprehensively discussed. Finally, future research directions and prospects in the aluminum battery field are proposed.

Environmental Screening of Electrode Materials for a Rechargeable Aluminum Battery with an AlCl₃/EMIMCl Electrolyte

Recently, rechargeable aluminum batteries have received much attention due to their low cost, easy operation, and high safety. As the research into rechargeable aluminum batteries with a room-temperature ionic liquid electrolyte is relatively new, research efforts have focused on finding suitable electrode materials. An understanding of the environmental aspects of electrode materials is essential to make informed and conscious decisions in aluminum battery development. The purpose of this study was to evaluate and compare the relative environmental performance of electrode material candidates for rechargeable aluminum batteries with an AlCl₃/EMIMCl (1-ethyl-3-methylimidazolium chloride) room-temperature ionic liquid electrolyte. To this end, we used a lifecycle environmental screening framework to evaluate 12 candidate electrode materials. We found that all of the studied materials are associated with one or more drawbacks and therefore do not represent a “silver bullet” for the aluminum battery. Even so, some materials appeared more promising than others did. We also found that aluminum battery technology is likely to face some of the same environmental challenges as Li-ion technology but also offers an opportunity to avoid others. The insights provided here can aid aluminum battery development in an environmentally sustainable direction.

Rechargeable aluminum-selenium batteries with high capacity

Rechargeable aluminum (Al) batteries are emerging as a promising post lithium-ion battery technology. Herein, we demonstrate a conceptually new design of rechargeable aluminum-selenium (Al-Se) batteries by understanding the selenium chemistry and controlling the electrode reaction. The Al-Se battery consists of a composite cathode including selenium nanowires and mesoporous carbon (CMK-3) nanorods, an Al metal anode and chloroaluminate ionic liquid electrolyte. The working mechanism of the Al-Se battery is the reversible redox reaction of the Se₂Cl₂/Se pair confined in the mesopores of CMK-3 nanorods. Al-Se batteries deliver a high reversible capacity of 178 mA h g^-1 (by Se mass), high discharge voltages (mainly above 1.5 V), and good cycling/rate performances.

Rechargeable aluminum batteries utilizing a chloroaluminate inorganic ionic liquid electrolyte

Rechargeable aluminum batteries composed of an aluminum anode, an expanded graphite cathode, and an inorganic chloroaluminate ionic liquid electrolyte show remarkably improved capacity, reversibility, and rate capability at 393 K compared to cells based on a common organic salt based ionic liquid, AlCl3-1-ethyl-3-methylimidazolium chloride.

Electrochemical Synthesis of Battery Electrode Materials from Ionic Liquids

Electrode materials as well as the electrolytes play a decisive role in batteries determining their performance, safety, and lifetime. In the last two decades, different types of batteries have evolved. A lot of work has been done on lithium ion batteries due to their technical importance in consumer electronics, however, the development of post-lithium systems has become a focus in recent years. This chapter gives an overview of various battery materials, primarily focusing on development of electrode materials in ionic liquids via electrochemical route and using ionic liquids as battery electrolyte components.

A Binder-Free and Free-Standing Cobalt Sulfide@Carbon Nanotube Cathode Material for Aluminum-Ion Batteries

Rechargeable aluminum-ion batteries (AIBs) are considered as a new generation of large-scale energy-storage devices due to their attractive features of abundant aluminum source, high specific capacity, and high energy density. However, AIBs suffer from a lack of suitable cathode materials with desirable capacity and long-term stability, which severely restricts the practical application of AIBs. Herein, a binder-free and self-standing cobalt sulfide encapsulated in carbon nanotubes is reported as a novel cathode material for AIBs. The resultant new electrode material exhibits not only high discharge capacity (315 mA h g^-1 at 100 mA g^-1 ) and enhanced rate performance (154 mA h g^-1 at 1 A g^-1 ), but also extraordinary cycling stability (maintains 87 mA h g^-1 after 6000 cycles at 1 A g^-1 ). The free-standing feature of the electrode also effectively suppresses the side reactions and material disintegrations in AIBs. The new findings reported here highlight the possibility for designing high-performance cathode materials for scalable and flexible AIBs.

Thermodynamics and Kinetics of Sulfur Cathode during Discharge in MgTFSI2 -DME Electrolyte

Rechargeable magnesium/sulfur battery is of significant interest because its energy density (1700 Wh kg^-1 and 3200 Wh L^-1 ) is among the highest of all battery chemistries (lower than Li/O₂ and Mg/O₂ but comparable to Li/S), and Mg metal allows reversible operation (100% Coulombic efficiency) with no dendrite formation. This great promise is already justified in some early reports. However, lack of mechanistic study of sulfur reaction in the Mg cation environment has severely hindered our understanding and prevents effective measures for performance improvement. In this work, the very first systematic fundamental study on Mg/S system is conducted by combining experimental methods with computational approach. The thermodynamics and reaction pathway of sulfur cathode in MgTFSI₂ -DME electrolyte, as well as the associated kinetics are thoroughly investigated. The results here reveal that sulfur undergoes a consecutive staging pathway in which the formation and chain-shortening of polysulfide occur at early stage accompanied by the dissolution of long-chain polysulfide, and solid-state transition from short-chain polysulfide to magnesium sulfide occurs at late stage. The former process is much faster than the latter due to the synergetic effect of the mediating effect of dissolved polysulfide and the fast diffusion of Mg ion in the amorphous intermediate.

Two-Dimensional Vanadium Carbide (MXene) as a High-Capacity Cathode Material for Rechargeable Aluminum Batteries

Rechargeable aluminum batteries (Al batteries) can potentially be safer, cheaper, and deliver higher energy densities than those of commercial Li-ion batteries (LIBs). However, due to the very high charge density of Al³⁺ cations and their strong interactions with the host lattice, very few cathode materials are known to be able to reversibly intercalate these ions. Herein, a rechargeable Al battery based on a two-dimensional (2D) vanadium carbide (V₂CT_x) MXene cathode is reported. The reversible intercalation of Al³⁺ cations between the MXene layers is suggested to be the mechanism for charge storage. It was found that the electrochemical performance could be significantly improved by converting multilayered V₂CT_x particles to few-layer sheets. With specific capacities of more than 300 mAh g^-1 at high discharge rates and relatively high discharge potentials, V₂CT_x MXene electrodes show one of the best performances among the reported cathode materials for Al batteries. This study can lead to foundations for the development of high-capacity and high energy density rechargeable Al batteries by showcasing the potential of a large family of intercalation-type cathode materials based on MXenes.

Oxide Film Efficiently Suppresses Dendrite Growth in Aluminum-Ion Battery

Aluminum metal foil is the optimal choice as an anode material for aluminum-ion batteries for its key advantages such as high theoretical capacity, safety, and low cost. However, the metallic nature of aluminum foil is very likely to induce severe dendrite growth with further electrode disintegration and cell failure, which is inconsistent with previous reports. Here, we discover that it is aluminum oxide film that efficiently restricts the growth of crystalline Al dendrite and thus improves the cycling stability of Al anode. The key role of surficial aluminum oxide film in protecting Al metal anode lies in decreasing the nucleation sites, controlling the metallic dendrite growth, and preventing the electrode disintegration. The defect sites in aluminum oxide film provide channels for electrolyte infiltration and further stripping/depositing. Attributed to such a protective aluminum oxide film, the Al-graphene full cells can attain up to 45 000 stable cycles.

Titanium Sulfides as Intercalation-Type Cathode Materials for Rechargeable Aluminum Batteries

We report the electrochemical intercalation-extraction of aluminum (Al) in the layered TiS₂ and spinel-based cubic Cu_0.31Ti₂S₄ as the potential cathode materials for rechargeable Al-ion batteries. The electrochemical characterizations demonstrate the feasibility of reversible Al intercalation in both titanium sulfides with layered TiS₂ showing better properties. The crystallographic study sheds light on the possible Al intercalation sites in the titanium sulfides, while the results from galvanostatic intermittent titration indicate that the low Al³⁺ diffusion coefficients in the sulfide crystal structures are the primary obstacle to facile Al intercalation-extraction.

Progress of rechargeable lithium metal batteries based on conversion reactions

In this review, we focus on the conversion reaction in newly raised rechargeable lithium batteries instanced by lithium–sulfur and lithium–oxygen batteries. A comprehensive discussion is made on the fundamental electrochemistry and recent advancements in key components of both types of the batteries. The critical problems in the Li–S and Li–O2 conversion electrochemistry are addressed along with the corresponding improvement strategies, for the purpose of shedding light on the rational design of batteries to reach optimal performance.